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Digitally Signed by: Content manager’s Name
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O = University of Nigeria, Nsukka
OU = Innovation Centre
Ugwoke Oluchi C.
Faculty of Biological Sciences
Department of Biochemistry
CHARACTERIZATION OF COCONUT OIL AND ITS
TRANS STERIFICATION REACTION RATE WITH ETHANOL
OTAMIRI, FAITH OLUCHI
PG/M.Sc/11/ 58646
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TITLE PAGE
CHARACTERIZATION OF COCONUT OIL AND ITS TRANS-ESTERIFICATION
REACTION RATE WITH ETHANOL
A DISSERTATION SUBMITTED IN PARTIAL FULFILMENT OF THE
REQUIREMENT FOR THE AWARD OF DEGREE OF MASTER OF SCIENCE
(M.Sc) IN INDUSTRIAL BIOCHEMISTRY AND BIOTECHNOLOGY
UNIVERSITY OF NIGERIA
NSUKKA
BY
OTAMIRI, FAITH OLUCHI
PG/M.Sc/11/ 58646
DEPARTMENT OF BIOCHEMISTRY
UNIVERSITY OF NIGERIA
NSUKKA
SUPERVISOR: DR. V. N. OGUGUA
SEPTEMBER, 2013.
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CERTIFICATION
This is to certify that Otamiri, Faith Oluchi, a postgraduate student with Registration
Number PG/M.Sc/11/58646 in the Department of Biochemistry has satisfactorily completed
the requirement for the course work and research for the degree of Master of Science (M.Sc)
in Industrial Biochemistry and Biotechnology. The work embodied in this report is original
and has not been submitted in part or full for any other diploma or degree of this or any
other University.
----------------------- ---------------------------
Dr. V. N. Ogugua Prof. O. F. C. Nwodo (Supervisor) (Head of Department)
-------------------------
External Examiner
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DEDICATION
This work is dedicated to God Almighty who in his infinite mercy led to the success of this
work.
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ABSTRACT
Biodiesel is a renewable alternate fuel that could partially/fully replace or reduce the use of
petroleum diesel fuel. This research project evaluates the viability of coconut oil for
biodiesel production and the effect of varied oil-to-ethanol ratios on its transesterification
reaction rate with ethanol. Thus, the moisture content of the coconut kernel was determined
and coconut oil was extracted from coconut copra using cold extraction. The percentage
moisture content of the kernel and the yield of the coconut oil extracted were 14.99% and
44.13% respectively. The physicochemical properties of the coconut oil were determined
and the result revealed that the oil is pale yellow, with a specific gravity of 0.88, viscosity of
35.04 mm2/s at 40
oC, flash point of 220
oC, cloud point of 24
oC, pour point of 23
oC, volatile
matter of 99.72%, refractive index of 1.46, heat of combustion of 35.60 MJ/kg, acid value of
2.24 mgKOH/g, saponification value of 273.38 mgKOH/g, peroxide value of 3.02 meq/kg,
iodine value of 9.11 mI2/g and free fatty acid content of 5.64%. The transesterification of the
coconut oil (50ml) with ethanol (150 ml) using sodium hydroxide (0.1g) as catalyst gave
93.90% yield of ethyl ester. The physicochemical properties of the ethyl ester produced were
also determined and the result obtained were as follows: colour (colourless), specific gravity
(0.86), viscosity (6.00mm2/s at 40
oC), cetane number (71), flash point (132
oC), cloud point
(-5oC), pour point (-10
oC), ash content (0.02%), refractive index (1.43), conductivity (0.00
µS/cm), heat of combustion (36.786 MJ/kg), acid value (0.25 mgKOH/g), saponification
value (218.076 mgKOH/g), peroxide value (0.15 meq/kg) and iodine value (1.91 mI2/g). The
transesterification rate constant at varied oil to ethanol ratio of 1:6, 1:3, 1:2, 1:1.5 and 1:1
were 0.4150, 0.3616, 0.2135, 0.1833 and 0.1006 respectively. The result showed that as the
oil to ethanol ratios increased from 1:1 to 1:6, the reaction rate constant increased with the
highest reaction rate constant of 0.4150 at 1:6 oil to ethanol ratio.
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ACKNOWLEDGEMENT
Above all, I thank the Almighty God for His blessings, protection and assistance throughout
my project research. Also, my heartfelt gratitude goes to my parents, Mr. and Mrs. Otamiri
Alexander, for their parental guidance and financial support throughout this research.
This research would not have been a reality without the assistance, encouragement and
support of numerous individual to whom I owe my gratitude. First and foremore, I want to
appreciate my supervisors, Prof. I. N. E. Onwurah and Dr. V. N. Ogugua for their time and
effort put into this work. My profound gratitude goes to Prof. O. F. C. Nwodo, the Head, and
the entire staffs of the Department of Biochemistry among whom are Prof. L. U. S.
Ezeanyika, the immediate past Head, Prof. F. C. Chilaka, Prof. O. U. Njoku, Prof. P. N.
Uzoegwu, Prof. E. A. Alumanah, Prof. M. O. Eze, Prof. O. Obidoa, Dr. H. A. Onwubiko,
Dr. B. C. Nwanguma, Dr. S. O. O. Eze, Dr. Parker. E. Joshua, Dr. (Mrs). C. A. Anosike,
Dr. (Mrs). C. I. Ezekwe, Dr. O. C. Enechi, Dr. C. S. Ubani, Mr. P. A. C. Egbuna, Mr. O. E.
Ikwuagwu, Mrs M. N. Awachie, Mr. V. E. O. Ozougwu, Mrs. U. O. Njoku and a host of
others, for their assistance and the knowledge they imparted to me.
I also thank Mr. Obinna Ojeh, Obiora, Atamah Jane, Akudo, Rex, Emeka, Darlington,
Joseph, Ejike, Blessing, Chibueze, Onyinyechi, Chinenye, chioma Eze, Ozioma Nwabor,
Dickson I. Dickson, Nsikak and all my colleagues I worked with in the laboratory for their
friendly relationship and support.
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TABLE OF CONTENTS
Title Page - - - - - - - - - - i
Certification - - - - - - - - - - ii
Dedication - - - - - - - - - - iii
Abstract - - - - - - - - - - iv
Acknowledgement - - - - - - - - - v
Table of Content - - - - - - - - - vi
List of Figures - - - - - - - - - - xi
List of Tables - - - - - - - - - - xii
List of Abbreviations - - - - - - - - -
xiii
CHAPTER ONE: INTRODUCTION
1.1 Background of study - - - - - - - - 1
1.2 History of biodiesel - - - - - - - - 2
1.3 Sources of biodiesel - - - - - - - - 4
1.3.1 The coconut - - - - - - - - - 4
1.3.1.1 Botanical description of coconut - - - - - - 6
1.3.1.2 Scientific classification of coconut - - - - - - 7
1.3.1.3 Geographical distribution and propagation - - - - - 7
1.3.1.4 Coconut oil - - - - - - - - - 8
1.3.1.5 Uses of coconut oil - - - - - - - - 9
1.4 Methods of modification of vegetable oils to fuel - - - - 9
1.4.1 Dilution - - - - - - - - - - 10
1.4.2 Microemulsion - - - - - - - - - 10
1.4.3 Pyrolysis - - - - - - - - - - 10
1.4.4 Catalytic cracking - - - - - - - - 10
1.4.5 Transesterification - - - - - - - - 11
1.5 Methods of transesterification - - - - - - - 12
1.5.1 Non-Catalytic transesterification - - - - - - 12
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1.5.2 Catalytic transesterification - - - - - - - 12
1.5.2.1 Heterogenous catalytic transesterification - - - - - 12
1.5.2.2 Homogenous catalytic transesterification - - - - - 13
1.5.2.2.1 Acid catalyzed transesterification - - - - - - 13
1.5.2.2.2 Base catalyzed transesterification - - - - - - 15
1.5.2.2.3 Enzyme catalyzed transesterification - - - - - 17
1.6 Factors effecting transesterification reaction - - - - - 18
1.6.1 Effect of molar ratio of oil to alcohol - - - - - 18
1.6.2 Type and amount of catalyst - - - - - - - 18
1.6.3 Effect of water and free fatty acid content - - - - - 19
1.6.4 Effect of temperature - - - - - - - - 20
1.6.5 Effect of stirring intensity - - - - - - - 20
1.6.6 Effect of reaction time - - - - - - - 21
1.7 Influence of biodiesel composition on fuel properties - - - - 21
1.7.1 Viscosity - - - - - - - - - 21
1.7.2 Low temperature operability - - - - - - - 22
1.7.3 Oxidative stability - - - - - - - - 23
1.7.4 Heat of combustion - - - - - - - - 23
1.7.5 Cetane number - - - - - - - - - 24
1.7.6 Exhaust emissions - - - - - - - - 25
1.7.7 Lubricity - - - - - - - - - - 26
1.7.8 Contaminants - - - - - - - - - 26
1.7.9 Biodiesel standard specifications and test methods - - - - 27
1.8 Advantages of biodiesel - - - - - - - - 29
1.9 Disadvantages of biodiesel - - - - - - - 30
1.10 Uses of biodiesel - - - - - - - - - 30
1.11 Aim and objectives - - - - - - - - 31
1.11.1 Aim of the study - - - - - - - - 31
1.11.2 Specific objectives of the study - - - - - - 31
CHAPTER TWO: MATERIALS AND METHODS
2.1 Materials - - - - - - - - - - 32
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2.1.1 Plant material - - - - - - - - - 32
2.1.2 Instruments / Equipment - - - - - - - 32
2.1.3 Reagents/Chemicals - - - - - - - - 32
2.2 Methods - - - - - - - - - - 33
2.2.1 Preparation of reagents - - - - - - - - 33
2.2.2 Moisture content determination of the kernel - - - - - 36
2.2.3 Extraction of coconut oil - - - - - - - 36
2.2.4 Purification of crude coconut oil - - - - - - 37
2.2.4.1 Water degumming - - - - - - - - 37
2.2.4.2 Acid pretreatment - - - - - - - - 38
2.2.5 Physicochemical characterization of coconut oil - - - - 38
2.2.5.1 Physical characterization of coconut oil - - - - - 38
2.2.5.1.1 Determination of the colour of the oil - - - - - 38
2.2.5.1.2 Determination of the specific gravity of the oil - - - - 38
2.2.5.1.3 Determination of the viscosity of the oil - - - - - 38
2.2.5.1.4 Determination of the flash point of the oil - - - - - 39
2.2.5.1.5 Determination of the cloud point of the oil - - - - - 39
2.2.5.1.6 Determination of the pour point of the oil - - - - - 40
2.2.5.1.7 Determination of the volatile matter of the oil - - - - 40
2.2.5.1.8 Determination of the refractive index of the oil - - - - 40
2.2.5.1.9 Determination of heat of combustion of the oil - - - - 41
2.2.5.2 Chemical characterization of coconut oil - - - - - 41
2.2.5.2.1 Determination of acid value of the oil - - - - - 41
2.2.5.2.2 Determination of saponification value of the oil - - - - 42
2.2.5.2.3 Determination of peroxide value of the oil - - - - - 42
2.2.5.2.4 Determination of iodine value of the oil - - - - - 43
2.2.5.2.5 Determination of percentage free fatty acids of the oil - - - 43
2.2.6 Transesterification of coconut oil with ethanol using NaOH as catalyst - 44
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2.2.7 Physicochemical characterization of the ethyl esters produced - - - 45
2.2.7.1 Physical characterization of ethyl ester produced - - - - 45
2.2.7.1.1 Determination of the colour of the ethyl ester - - - - 45
2.2.7.1.2 Determination of the specific gravity of the ethyl ester - - - 45
2.2.7.1.3 Determination of the viscosity of the ethyl ester - - - - 45
2.2.7.1.4 Determination of the cetane number of the ethyl ester - - - 46
2.2.7.1.5 Determination of the flash point of the ethyl ester - - - - 46
2.2.7.1.6 Determination of the cloud point of the ethyl ester - - - - 46
2.2.7.1.7 Determination of the pour point of the ethyl ester - - - - 47
2.2.7.1.8 Determination of the ash content of the ethyl ester - - - - 47
2.2.7.1.9 Determination of the refractive index of the ethyl ester - - - 47
2.2.7.1.10 Determination of conductivity of the ethyl ester - - - - 48
2.2.7.1.11 Determination of heat of combustion of the ethyl ester - - - 48
2.2.7.2 Chemical characterization of coconut oil - - - - - 49
2.2.7.2.1 Determination of acid value of the ethyl ester - - - - 49
2.2.7.2.2 Determination of saponification value of the ethyl ester - - - 49
2.2.7.2.3 Determination of peroxide value of the ethyl ester - - - - 50
2.2.7.2.4 Determination of iodine value of the ethyl ester - - - - 50
2.2.8 Investigation of the transesterification reaction rate - - - - 51
2.2.8.1 Experimental design - - - - - - - - 51
2.2.8.2 Analysis of ethyl esters using UV-visible spectrophotometer - - 51
CHAPTER THREE: RESULTS
3.1 Result of Percentage moisture content, oil yield and ethyl ester yield - - 53
3.2 Physicochemical properties of the coconut oil - - - - - 54
3.2.1 Physical properties of the coconut oil - - - - - - 54
3.2.2 Chemical properties of the coconut oil - - - - - - 55
3.3 Physicochemical properties of the coconut oil ethyl ester - - - 56
3.3.1 Physical properties of the coconut oil ethyl ester - - - - 56
3.3.2 Chemical properties of the coconut oil ethyl ester - - - - 57
3.4 Investigation of the transesterification reaction rate - - - - 58
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3.4.1 Progress curve for 1:6 oil/ethanol volumetric ratio transesterification - - 59
3.4.2 Progress curve for 1:3 oil/ethanol volumetric ratio transesterification - - 60
3.4.3 Progress curve for 1:2 oil/ethanol volumetric ratio transesterification - - 61
3.4.4 Progress curve for 1:1.5 oil/ethanol volumetric ratio transesterification - 62
3.4.5 Progress curve for 1:1 oil/ethanol volumetric ratio transesterification - - 63
3.5 Reaction rate constant against oil to ethanol volumetric ratio - - - 64
3.6 Determination of kinetic parameters (Km and Vmax) of the transesterification
Reaction - - - - - - - - - - 65
CHAPTER FOUR: DISCUSSION
4.1 Discussion - - - - - - - - - - 66
4.2 Conclusion - - - - - - - - - 75
4.3 Suggestions for Further Studies - - - - - - - 75
References - - - - - - - - - - 76
Appendices - - - - - - - - - - 89
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LIST OF FIGURES
Fig. 1: Bunch of coconuts on a coconut tree - - - - - - 5
Fig. 2: The transesterification reaction - - - - - - 11
Fig. 3: Mechanism of acid catalyzed transesterification - - - - 14
Fig. 4: Mechanism of base catalyzed transesterification - - - - 16
Fig. 5: Saponification reaction of free fatty acids during base catalyzed transesterification 20
Fig. 6: Dehusked coconuts and extracted coconut oil- - - - - 36
Fig. 7: Pictures of coconut oil after degumming and standing in a separating funnel to form
two distinct layers; the upper layer (of oil) and the lower layer (of phosphatides and
other impurities) - - - - - - - - 37
Fig. 8: Experimental set-up during transesterification and separation of the mixture
into biodiesel (upper layer) and glycerol (lower layer) in a separating funnel 44
Fig. 9: Appearance of the yellow colour in the standard and test samples - - 52
Fig. 10: Progress curve for 1:6 oil/ethanol volumetric ratio transesterification - 59
Fig. 11: Progress curve for 1:3 oil/ethanol volumetric ratio transesterification - 60
Fig. 12: Progress curve for 1:2 oil/ethanol volumetric ratio transesterification - 61
Fig. 13: Progress curve for 1:1.5 oil/ethanol volumetric ratio transesterification - 62
Fig. 14: Progress curve for 1:1 oil/ethanol volumetric ratio transesterification - 63
Fig. 15: Reaction rate constant against oil to ethanol volumetric ratio - - 64
Fig.16: Lineweaver-Burk plot of NaOH-catalysed transesterification reaction - 65
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LIST OF TABLES
Table 1: World production of coconuts, area and productivity in 2005 - - 6
Table 2: Scientific classification of coconut - - - - - - 7
Table 3: The chemical composition of coconut oil - - - - - 8
Table 4: Specifications and test methods of ASTM d6751 and EN 14214 standards for
Biodiesel - - - - - - - - - 28
Table 5: Glycerol standard preparation and absorbance results - - - 52
Table 6: Result of percentage moisture content, oil yield and ethyl ester - - 53
Table 7: Physical properties of the coconut oil - - - - - 54
Table 8: Chemical properties of the coconut oil - - - - - 55
Table 9: Physical properties of the coconut oil ethyl ester - - - - 56
Table 10: Chemical properties of the coconut oil ethyl ester - - - - 67
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LIST OF ABBREVIATIONS
AOAC Association of Official Analytical Chemists
APCC Asian and Pacific Coconut Community
ASTM American Society for Testing Material
CFPP Cold Filter Plugging Point
CN Cetane Number
CO Carbon Monoxide
CP Cloud Point
EN European Standards
EPA Environmental Protection Agency
FAAE Fatty Acids Alkyl Esters
FFA Free Fatty Acid
NMCE National Multi-Commodity Exchange
NOx Nitrogen Oxide Species
PM Particulate Matter
PP Pour Point
SME Soyabean Methyl Ester
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CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
The search for environmentally-friendly materials that have potential to substitute mineral
oil in various industrial applications is currently being considered a top priority research area
in the fuel and energy sector (Jha et al., 2007). With, the scarcity of conventional fossil
fuels, growing emissions of combustion-generated pollutants, and their increasing costs will
make biomass or renewable sources more attractive (Sensoz et al., 2000). An alternative fuel
to petrodiesel must be technically feasible, economically competitive, environmentally-
friendly, and easily available. Biodiesel is the best alternative for diesel fuels in diesel
engine (Demirbas, 2009).
Biodiesel is defined as the mono alkyl esters of long fatty acids derived from renewable lipid
feedstock such as vegetable oils or animal fats, for use in compression ignition (diesel)
engines (National Biodiesel Board, 1996). The advantages of biodiesel are availability,
lower exhaust emissions, renewability, biodegradability, higher lubricity and higher
combustion efficiency (Demirbas, 2009). It can be used in its pure state or blended with
petroleum-based diesel fuel (B20 is assigned for 20 vol. % biodiesel and 80 vol. %
petroleum-based fuel blend) (Issariyakul et al., 2007). Biodiesel can offer other benefits,
including reduction of greenhouse gas emissions, regional development and social structure,
especially to developing countries (Dermirbas and Dermirbas, 2007). On the other hand, the
major disadvantages of biodiesel are its high viscosity, low energy content, high cloud point
and pour point, high nitrogen oxide (NOx) emissions, low engine speed and power, injector
coking, engine compatibility, and high price (Demirbas, 2008a). Nevertheless, the
advantages of biodiesel supersede the disadvantages generally on the environmental aspects,
making it a very popular alternative to petroleum derived-diesel oil (Dermirbas, 2009).
Biodiesel can be processed from any type of vegetable oil, animal fats (Vicente et al., 2004)
and algal oil (Hossain et al., 2008). Alamu et al. (2010) investigated the biodiesel
production potential of coconut oil and the biodiesel produced was subsequently blended
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with petroleum diesel and characterized as alternative diesel fuel through the American
Society for Testing and Materials standard fuel tests (Alamu et al., 2010).
The conventional method for vegetable oil conversion into biodiesel is called
transesterification (Srivastava and Prasad, 2000). Transesterification is a chemical reaction
involving oil or fat, and an alcohol to yield fatty acid alkyl esters and glycerol
(Thiruvengadaravi et al., 2009). In the reaction, each mole of triglyceride reacts
stoichiometrically with 3 moles of a primary alcohol and yields 3 moles of alkyl esters and 1
mole of glycerol (Singh et al., 2006). The actual mechanism of the reaction consists of a
sequence of three consecutive and reversible reactions (Darnoko and Cheryan, 2000), in
which di- and monoglycerides are formed as intermediates (Knothe et al., 2005).
Furthermore, this process can be performed with or without catalyst (Gerpen, 2005), with
the catalytic process being mostly used due to its simpler operation and shorter reaction
period to produce biodiesel (Marchetti et al., 2007). Under catalytic process,
transesterification is carried out using homogeneous or heterogeneous catalysts which may
be bases, acids or enzymes (Krishnan and Dass, 2012). Homogeneous alkaline catalysts are
widely used due to the fact that the reaction is completed in a short time under mild
temperature and pressure conditions (Pilar et al., 2004). Usually uses catalysts such as
sodium hydroxide (NaOH), potassium hydroxide (KOH) (Meher et al., 2006b).
There are number of factors which could affect the transesterification process, these factors
include moisture content, free fatty acid contents, molar ratio of oil to alcohol, type and
amount of catalyst, reaction time, reaction temperature, mixing intensity, and co-solvent
(Sharma and Singh, 2009). Evidentally, for optimization of the transesterification reaction
the effect of these factors should be examined (Thiruvengadaravi et al., 2009).
1.2 History of Biodiesel
The term “biodiesel” was first coined in 1988, but the history of using vegetable oil in place
of diesel as a fuel dates back to 1900 (Songstad et al., 2009). The roots of what eventually
became known as “biodiesel” extend back to the discovery of the diesel engine by Rudolf
Diesel. When first demonstrating the engine bearing his name, Rudolf Diesel ran it on
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peanut oil at the World’s Fair in Paris in1900. The diesel engine was built by the French
Otto Company and it was tested at this event using peanut oil (Knothe, 2001). Knothe
(2001) also relates that the French Government was interested in vegetable oil fuels for
diesel engines because of its availability in their colonies in Africa, thereby eliminating the
need to import liquid fuels or coal. Knowledge that vegetable oils could be used to fuel the
diesel engine gave a sense of energy self-sufficiency to those countries producing oil crops,
especially for those countries in Africa in the 1940s (Songstad et al., 2009). In China, tung
oil and other vegetable oils were used to produce a version of gasoline and kerosene
(Songstad et al., 2009).
Furthermore, prompted by fuel shortages during World War II, India conducted research on
conversion of a variety of vegetable oils to diesel. This interest in biodiesel was also evident
in the USA where research was performed to evaluate cottonseed oil as a diesel fuel
(Songstad et al., 2009). However, related to this are the efforts of automobile entrepreneur
Henry Ford and the development of the “soybean car” in 1941. Mr. Ford was a true
visionary and was motivated by combining the strength of the automobile industry with
agriculture (Songstad et al., 2009). According to the Benson Ford Research Center, there
was a single experimental soybean car built, made in part with soybean and propelled by
ethanol derived from corn (Young, 2003).
Since the 1950s, interest in converting vegetable oils into biodiesel has been driven more by
geographical and economic factors than by fuel shortages. For instance, the USA is a top
producer of soybean oil, whereas Europe produces large amounts of canola oil, and this
essentially determines which oil is used for biodiesel within these geographies (Songstad et
al., 2009). Also, for those remote geographic locations to which fossil fuel refining and
distribution are problematic, vegetable oil-based biodiesel is a sustainable and practical
means to meet the fuel energy demands. Furthermore, sources for biodiesel have been
expanded to include spent vegetable oil from the food service industry as well as animal fats
from slaughterhouses (Knothe, 2001). However, additional research is required to identify
new oil crops to meet the increasing demand for biodiesel. A variety of tools including plant
breeding, molecular breeding, and biotechnology are needed to increase oil production from
18
conventional crops such as soybean and to develop new oil crops for specific regions
(Songstad et al., 2009).
1.3 Sources of Biodiesel
A variety of biolipids can be used to produce biodiesel. These are (a) virgin vegetable oil
feedstock; rapeseed and soybean oils are most commonly used; though other crops such as
mustard, palm oil, sunflower, hemp, (Dermirbas, 2006) and even algae can also be used; (b)
waste vegetable oil; (c) animal fats including tallow, lard, and yellow grease (Ramadhas et
al., 2004); and (d) non-edible oils such as jatropha, neem oil, castor oil, and tall oil
(Dermirbas, 2008a).
Various oils have been in use in different countries as raw materials for biodiesel production
owing to their availability. Soybean oil is commonly used in United States and rapeseed oil
is used in many European countries for biodiesel production, whereas, coconut oil and palm
oils are used in Malaysia and Indonesia for biodiesel production (Dermirbas, 2009). In India
and Southeast Asia, the Jatropha tree (Jatropha curcas) (Tiwari et al., 2007), Karanja
(Pongamia pinnata) (Srivastava and Verma, 2008; Sharma and Singh, 2008) and Mahua (M.
indica) (Ghadge and Raheman, 2005) is used as a significant fuel source. Commonly
accepted biodiesel raw materials include the oils from soy, canola, corn, rapeseed, and palm.
New plant oils that are under consideration include mustard seed, peanut, coconut,
sunflower, and cotton seed (Dermirbas, 2009). The most commonly considered animal fats
include those derived from poultry, beef and pork (Usta et al., 2005). Also, it may be
possible to produce enough oil by farming microbes, such as algae, whose oil yields per unit
land area could be two orders of magnitude higher than with conventional oil crops (Hossain
et al., 2008).
1.3.1 The Coconut
The coconut (Cocos nucifera L.) (Fig. 1) is an important fruit tree in the world, providing
food for millions of people, especially in the trophical and subtropical regions and with its
many use it is called the tree of life (Chan and Elevitch, 2006). India is the third largest
coconut-producing country, after Indonesia and the Philippines, having an area of about 1.94
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million hectares under the crop. Annual production is about 7562 million nuts with an
average of 5295 nuts/hectare (APCC Coconut Statistical Yearbook 2005) (Table 1).
.
Fig. 1: Bunch of coconuts on a coconut tree
Source: (Chan and Elevitch, 2006).
20
Table 1: World production of coconuts, area and productivity in 2005
COUNTRY Production
Nut
Equivalent
(billion nuts
Production
Copra
Equivalent
(million
tones)
% of Total
World
Production
Area
under
Coconuts
(million
ha)
Productivity
(tonnes
copra
equiv /ha)
Indonesia 16.49 3.30 27.7% 3.89 0.85
Philippines 14.06 2.81 23.6% 3.24 0.87
India 12.83 2.57 21.5% 1.94 1.33
Brazil 3.79 0.76 6.4% 0.28 2.70
Sri Lanka 2.22 0.44 3.7% 0.40 1.12
Thailand 1.20 0.24 2.0% 0.34 0.70
Mexico 1.19 0.24 2.0% 0.15 1.58
Papua New Guinea 0.81 0.16 1.4% 0.26 0.63
Vietnam 0.68 0.14 1.1% 0.13 1.03
Malaysia 0.39 0.08 0.7% 0.13 0.60
80 Other Countries 5.91 1.18 9.9% 1.40 0.84
TOTAL / AVERAGE 59.57 11.91 100% 12.17 0.98
Source: (APCC Coconut Statistical Yearbook 2005).
1.3.1.1 Botanical Description of Coconut
Coconut (Cocos nucifera L.) is a monocotyledon belonging to the Arecaceae family (Order
Arecales). There are mainly two distinct varieties of coconut i.e. tall and the dwarf; the tall
varieties grow slow and bear fruits 6 to 10 years after planting (NMCE, 2007). Its copra, oil
and fiber are of good quality and this type is comparatively hardy, and lives up to a ripe age
of 80 to 120 years (Ohler, 1999). As the male flowers mature earlier than the female flowers,
this type is highly cross- pollinated. The nuts mature within a period of 12 months after
pollination (Mandal and Mandal, 2011).
The dwarf varieties are fast-growing and bear early i.e. takes 4 to 5 years (NMCE, 2007).
Due to overlapping of the male and female phases, the dwarf varieties are self pollinated; the
nuts are yellow, red, green and orange coloured (Ohler, 1999). These are less hardy and
require favourable climatic conditions and soil type for better yield (Mandal and Mandal,
2011).
21
1.3.1.2 Scientific Classification of Coconut
Table 2: Scientific classification of coconut
Kingdom Plantae – Plants
Subkingdom Tracheobionta – Vascular plants
Superdivision Spermatophyta – Seed plants
Division Magnoliophyta – Flowering plants
Class Liliopsida – Monocotyledons
Subclass Arecidae
Order Arecales
Family Arecaceae – Palm family
Genus Cocos L. – coconut palm P
Species Cocos nucifera L. – coconut palm
Source: (Chan and Elevitch, 2006).
1.3.1.2 Geographical Distribution and Propagation
Within 20 North and South latitudes, the coconut palm is productive, especially along
coastal areas. Palms grown beyond the limits of the Torrid Zone are generally non-
productive (Mandal and Mandal, 2011). The major coconut-growing areas are located in
Asia, islands of the Pacific Ocean, Africa, and Central and South America. In 1991 the
world coconut hectarage was 10.9 million (Arranza, 1994).
Cultivation of coconut depends on type, slope of land, and rainfall distribution. It grows well
on well-drained loamy and clay soil. A year-round warm and humid climate favours the
growth of coconut (Ohler, 1999). A mean annual temperature of 27oC, an evenly distributed
rainfall of 1500-2500 mm per annum and relative humidity of above 60% provide the ideal
climatic conditions for the vigorous growth and yield of the palm (Chan and Elevitch, 2006).
For cultivation of coconut, usually 7-8 month old seedlings, raised from fully mature fruits
are used for transplants (Ohler, 1999). Nuts are planted in nursery after about 16 weeks,
usually 70-150 trees/ hectare; with triangular spacing of 10 meters (Mandal and Mandal,
2011). It is desirable to transplant in rainy season. During first three years seedlings are
watered during drought, with an application of 16 L/tree of water, twice a week (Ohler,
22
1999). Female flowers set in 12 months and fruits set to mature with a yield 60-100 nuts /
tree. A coconut tree in its life time can produce up 10,000 nuts (Mandal and Mandal, 2011).
1.3.1.3 Coconut Oil
The kernel is the origin of the products which are mainly coconut oil and desiccated coconut
or dried kernel (copra). The copra which is mainly used for oil extraction contains about 65
to 75% oil (Mandal and Mandal, 2011). The different fatty acids present in coconut oil
(Table 3) range from C6 to C18 (Russell and Williams, 1995) and approximately 50% of the
fatty acid is lauric acid (Mandal and Mandal, 2011).
Table 3: Chemical composition of coconut oil
Component Fraction
%
Chemical Formula Systematic name Acronym
Lauric acid 51.0 CH3(CH2)10COOH Dodecanoic acid 12:0
Myristic acid 18.5 CH3(CH2)12COOH Tetradecanoic
acid
14:0
Caprilic acid 9.5 CH3(CH2)6COOH Octanoic acid 8:0
Palmitic acid 7.5 CH3(CH2)14COOH Hexadecanoic
acid
16:0
Oleic acid 5.0 CH3(CH2)7CH=CH
3(CH2)7COOH 9Z‐Octadecenoic
acid
18:1
Capric acid 4.5 CH3(CH2)8COOH Decanoic acid 10:0
Stearic acid 3.0 CH3(CH2)16COOH Octadecanoic
acid
18:0
Linoleic acid 1.0 CH3(CH2)4CH=CH
CH2CH=CH(CH2)7
COOH
9Z,12Z‐
Octadecadienoic
acid
18:2
Source: (Mandal and Mandal, 2011). Note: ( a) Z denotes cis configuration; (b) The numbers
denote the number of carbon atoms and double bonds in one molecule.
1.3.1.4 Uses of Coconut Oil
The Spectrum of Coconut Products states that in food preparation and in diet, coconut oil
performs the following functions (Enig, 1998).
• It serves as an important source of energy in the diet.
• It supplies specific nutritional requirements.
• It provides a lubricating action in dressings or leavening effect in baked items.
23
• It acts as carrier and protective agent for fat-soluble vitamins.
• It enhances the flavour of food.
One of the major non-edible applications of coconut oil is in the soap industries. Coconut oil
has many other industrial uses in the pharmaceuticals, cosmetics, plastics, synthetic resins
(Krishna et al., 2010). In Thailand, coconut oil is mixed with 10 to 20% kerosene, settle to
remove free fats, filtered and used as a diesel fuel substitute. In Vanuatu and other Pacific
Islands, coconut oil is used directly as a substitute for diesel (Bawalan, 2005). The
Philippines has discovered that coconut methyl ester (CME) or coco-biodiesel derived from
coconut oil is better than conventional diesel fuel (Mandal and Mandal, 2011). The higher
cetane number of CME (70) relative to diesel (56) implies that CME burns more completely,
resulting in more mileage and lower emissions (Robeerto, 2001). Methyl esters of coconut
oil fatty acids are also being used as lubricants and biodiesel in aviation industry (Krishna et
al., 2010).
1.4 Methods of Modification of Vegetable Oils to Fuel
Vegetable oils can be used as fuels for diesel engines, but their viscosities are much higher
than that of common diesel fuel and so require modifications of the engines (Kerschbaum
and Rinke, 2004). To overcome this problem, different methods have been considered to
reduce the viscosity of vegetable oils such as dilution, micro-emulsification, pyrolysis,
catalytic cracking and trans-esterification (Dermirbas, 2009). Among these, trans-
esterification has been considered as the most suitable modification because technical
properties of esters are nearly similar to diesel.
1.4.1 Dilution
Dilution of vegetable oils with solvents lowers their viscosities. For instance, the viscosity of
oil can be lowered by blending with pure ethanol or diesel (Bilgin et al., 2002). When
twenty-five parts of sunflower oil and seventy-five parts of diesel were blended as diesel
fuel; the viscosity obtained was 4.88 centistoke at 313 K (Dermirbas, 2009).
24
1.4.2 Microemulsion
A microemulsion is defined as a colloidal equilibrium dispersion of optically isotropic fluid
microstructure with dimensions generally into 1–150 range formed spontaneously from two
normally immiscible liquids and one and more ionic or more ionic amphiphiles (Singh and
Singh, 2010). Short-chain alcohols such as ethanol or methanol are used for microemulsions,
to reduce of the high viscosity of vegetable oils, microemulsions with immiscible liquids
such as methanol and ethanol and ionic or non-ionic amphiphiles have been studied (Billaud
et al., 1995).
1.4.3 Pyrolysis
Pyrolysis or thermal cracking is the conversion of one substance into another by means of
heating; it involves heating in the absence of air or oxygen and cleavage of chemical bonds
to yield small molecules (Mohan et al., 2006). Pyrolysis of oils and fats result in production
of alkanes, alkenes, alkadienes, cycloalkanes, alkylbenzenes, carboxylic acids, aromatics
and small amounts of gaseous products (Dermirbas, 2008b). The pyrolyzed material can be
vegetable oils, animal fats, natural fatty acids and methyl esters of fatty acids (Dermirbas,
2009).
1.4.4 Catalytic Cracking
This refers to pyrolytic treatment in the presence of a catalyst, which directs the process
mainly towards lower molecular weight aliphatic and aromatic hydrocarbons with lower
oxygen content (Sang et al., 2003).
1.4.5 Trans-esterification
The conventional method for vegetable oil conversion into biodiesel is trans-esterification
(Srivastava and Prasad, 2000). Trans-esterification refers to a chemical reaction involving
oil or fat, and an alcohol to yield fatty acid alkyl esters and glycerol (Thiruvengadaravi et
al., 2009).
25
Fig. 2: The trans-esterification reaction
Source: (Schuchardta et al., 1998)
The overall process consists of a sequence of three consecutive reversible reactions where
triglycerides are converted to diglycerides and then diglycerides are converted to
monoglycerides followed by the conversion of monoglycerides to glycerol (Dermirbas,
2009). In each step an ester is produced and thus three ester molecules are produced from
one molecule of triglycerides; these esters are commonly referred to as biodiesel (Sharma
and Singh, 2008).
The alcohols that can be used in the trans-esterification reaction are methanol, ethanol,
propanol, butanol and amyl alcohol; with methanol and ethanol being most frequently used
(Dermirbas, 2009). Ethanol is a preferred alcohol in the trans-esterification process
compared to methanol because it is derived from agricultural products and is renewable and
biologically less objectionable in the environment (Dermirbas, 2005). However methanol
has the merit of low cost as well as physical and chemical advantages (polar and shortest
chain alcohol) which make the trans-esterification process faster (Dermirbas, 2009).
1.5 Methods of Trans-esterification
The trans-esterification process can be performed with or without a catalyst (Gerpen, 2005;
Meher et al., 2006b). However, conventional trans-esterification process has been using
catalytic process to produce biodiesel due to its simpler operation and shorter reaction period
(Marchetti et al., 2007).
26
1.5.1 Non-Catalytic Trans-esterification
Non-catalytic trans-esterification process requires no catalyst. However, it is also less
favorable due to its high energy demand as non-catalytic process usually operates at
supercritical temperature and pressure of the alcohol (Marchetti et al., 2007). This process
usually uses supercritical alcohol such as supercritical methanol and supercritical ethanol to
produce fatty acid alkyl esters (biodiesel) (Dermirbas, 2005). Furthermore, at supercritical
conditions, non-catalytic trans-esterification process tends to become very difficult to
handle. Due to these factors, alternative methods, which have lower operational costs and
simpler operational processes, have been considered (Marchetti et al., 2007).
1.5.2 Catalytic Trans-esterification
Under catalytic process, trans-esterification of vegetable oils can be carried out using
homogeneous or heterogeneous catalysts that are base, acid or enzymes (Krishnan and Dass,
2012).
1.5.2.1 Heterogenous Catalytic Trans-esterification
Heterogeneous trans-esterification process uses solid catalyst such as metal oxides (Liu et
al., 2008), active metals supported on various medium, zeolites, resins, membranes and
enzymes (Miertus et al., 2009) to catalyze the trans-esterification process (Serio et al.,
2008). The benefits of heterogeneous trans-esterification process include easier and simpler
separation process (as the catalyst is in a different phase from the products/reactants),
elimination of soap formation and corrosion problems associated with their use (Miertus et
al., 2009). One of the main problems with heterogeneous catalysts is their deactivation with
time owing to many possible phenomena, such as poisoning, coking, sintering, and leaching
(Miertus et al., 2009). However, the performance of heterogeneous catalysts is generally
lower than that of the commonly used homogeneous catalysts. Notably, diffusional
limitations might sometimes drastically reduce the surface of the solid that is available for
promoting the trans-esterification reaction. Therefore, a careful design of the pore structure
of these materials is important. In this respect, zeolites are ideal systems (Miertus et al.,
2009).
27
1.5.2.2 Homogenous Catalytic Trans-esterification
Homogenous trans-esterification process usually uses catalysts which are in the same phase
the reactant such as sodium hydroxide, potassium hydroxide, sulfuric acid and hydrochloric
acid to catalyze the trans-esterification process (Dermirbas, 2009). Homogeneous trans-
esterification method has been long regarded as the easiest method to produce biodiesel
(Miertus et al., 2009). Unfortunately, the problems associated with the homogeneous
catalysts are high consumption of energy, formation of unwanted soap byproduct by reaction
of the free fatty acids (FFA), high cost of separation of the homogeneous catalyst from the
reaction mixture, and generation of large amount of wastewater during separation and
cleaning of the catalyst and the products. These could contribute to the loss of triglycerides.
All these downsides eventually lead to a very high production cost (Vyas et al., 2010).
1.5.2.2.1 Acid-Catalyzed Trans-esterification
Acid catalyzed trans-esterification process is catalyzed by Bronsted acids, preferably
sulfonic, sulfuric and hydrochloric acids, these catalysts are dissolved in alcohol by vigorous
stirring in a small reactor (Issariyakul et al., 2007). The oil is transferred into the biodiesel
reactor and then the catalyst/alcohol mixture is pumped into the oil (Dermirbas, 2009). Acid-
catalyzed trans-esterification can be used in a two-stage process, in which the first stage
involves the esterification of FFAs into biodiesel in the presence of the acid catalyst
followed by base-catalyzed trans-esterification (Miertus et al., 2009). Acid catalysts give
very high yields of alkyl esters and are insensitive to free fatty acids and moisture resulting
in the absence of soap formation, but there are a number of serious problems associated with
acid catalyzed trans-esterification such as requirement of high operating temperature and
pressure conditions (Miertus et al., 2009), slow reaction rate, requirement of an anti-
corrosion reactor and high alcohol-to-oil molar ratio (Dermirbas, 2009).
Zhang et al. (2003a) showed that, in a large excess of methanol, the acid-catalyzed trans-
esterification reaction of waste cooking oils is essentially a pseudo-first-order reaction. The
oil/methanol, acid molar ratio and temperature are the most significant factors affecting the
yield of fatty acid methyl esters (FAMEs) (Zhang et al., 2003a). Zullaikah et al. (2005)
28
investigated the acid-catalyzed methanolysis of dewaxed/degummed rice bran oil with
varying FFA contents at atmospheric pressure and 60oC using 1:10 molar ratio of oil:
methanol and 2 wt% sulfuric acid as catalyst. The initial FFA content appreciably influences
the rate of methanolysis and the final methyl ester content in the product. A methyl ester
content of about 96% in the product could be obtained in 8 h for rice bran oil with an initial
FFA content of 76 % (Miertus et al., 2009).
In the mechanism of acid-catalyzed trans-esterification of fatty acids (Fig. 3), the initial step
is protonation of the acid to give an oxonium ion, which can undergo an exchange reaction
with an alcohol to give the intermediate, and this in turn can lose a proton to become an
ester. Each step in the process is reversible, but in the presence of a large excess of the
alcohol, the equilibrium point of the reaction is displaced so that esterification proceeds
virtually to completion (Dermirbas, 2009).
Fig. 3: Mechanism of acid catalyzed trans-esterification
Source: (Schuchardta et al., 1998)
1.5.2.2.2 Base-Catalyzed Trans-esterification
The base-catalyzed trans-esterification of vegetable oils proceeds faster than the acid-
catalyzed reaction (Dermirbas, 2009). Due to this reason, and the fact that the alkaline
catalysts are less corrosive than acidic compounds, industrial processes usually favour base
catalysts, such as alkaline metal alkoxides and hydroxides as well as sodium or potassium
carbonates (Miertus et al., 2009). In the base-catalyzed trans-esterification method, the
29
catalyst (KOH or NaOH) is dissolved into alcohol by vigorous stirring in a small reactor.
The oil is transferred into a biodiesel reactor and then the catalyst/alcohol mixture is pumped
into the oil (Dermirbas, 2009).
Base-catalyzed trans-esterification is most often used industrially today (Meher et al.,
2006b). The most commonly-used alkaline catalysts in the biodiesel industry are potassium
hydroxide (KOH) and sodium hydroxide (NaOH) flakes which are inexpensive, easy to
handle in transportation and storage, and are preferred by small producers (Singh et al.,
2006). However, where the raw material has a high water or free fatty acid (FFA) content
pretreatment with an acidic catalyst is needed in order to esterify FFA (Zhang et al., 2003a).
Pretreatment is necessary to reduce soap formation during the reaction and ease the
extensive handling for separation of biodiesel and glycerol together with removal of catalyst
and alkaline wastewater (Meher et al., 2006b). On the other hand, the water problem can be
avoided if sodium and potassium methoxide (NaOMe and KOMe) solutions, which can be
prepared water-free, are applied (Issariyakul et al., 2007). Additionally, although the use of
methoxides cannot avoid soap formation if the feedstock contains free fatty acids, which is
also true for use of KOH or NaOH, very little saponification of esters or triglycerides occurs
because methoxides behave as weak Lewis bases (Singh et al., 2006).
Singh et al. (2006) studied the reaction of methanol with canola oil at different
concentrations of alkaline catalyst (NaOH, KOH, NaOMe, and KOMe), reaction
temperatures, and methanol-to-oil molar ratios. The result showed that potassium- based
catalysts gave better yields than the sodium-based catalysts, and methoxide catalysts gave
higher yields than the corresponding hydroxide catalysts. On the other hand, potassium-
based catalysts resulted in a larger extent of soap formation than the corresponding sodium-
based catalysts. Potassium and sodium hydroxides and methoxides were also investigated as
catalysts by Vicente et al. (2004) in the trans-esterification of sunflower oil using a
methanol-to-oil molar ratio of 6:1 and 1% catalyst. The yields of esters were reported to be
higher than 98% for the methoxide catalysts, and 85.9 and 91.67 wt% for the sodium and
potassium hydroxides, respectively, because the saponification resulted in more substantial
decreases in yield (Miertus et al., 2009).
30
The mechanism of alkali-catalyzed trans-esterification reaction (Fig. 4) shows that the first
step is the reaction of the base with the alcohol, producing an alkoxide and a protonated
catalyst. The nucleophilic attack of the alkoxide at the carbonyl group of the triglyceride
generates a tetrahedral intermediate, from which the alkyl ester and the corresponding anion
of the diglyceride are formed. Diglycerides and monoglycerides are converted by the same
mechanism into a mixture of alkyl esters and glycerol (Dermirbas, 2009).
Fig. 4: Mechanism of base catalyzed trans-esterification
Source: (Schuchardta et al., 1998)
1.5.2.3 Enzyme-Catalyzed Trans-esterification
Biodiesel can be obtained from enzyme or biocatalytic trans-esterification methods (Hama et
al., 2004). However, with the problems associated with conventional homogeneous catalytic
processes, such as removal of glycerol and the catalyst, high energy requirements, and the
need to pretreat feedstocks containing FFAs or to post-treat large amounts of waste water
enzyme-catalysed trans-esterification is preferred to other methods (Vyas et al., 2010).
31
These problems can be overcome by using enzymes catalysts (such as lipases) which are
able to effectively catalyze the trans-esterification of triglycerides with high selectivity to
yield FAMEs either in aqueous or in non-aqueous systems (Fukuda et al., 2001). Several
examples of the lipase-catalyzed production of biodiesel have been reported using different
feedstocks namely soybean oil, sunflower oil, palm oil, coconut oil, rice bran oil, mixtures
of vegetable oils, grease, and tallow (Dermirbas, 2006). It has been shown that the
enzymatic production of biodiesel is possible by using either extracellular or intracellular
lipases. The choice of the method is based on the balance between simplified upstream
operations (intracellular) and high conversions (extracellular). Both types can be
immobilized for use without a need for downstream operations (Fukuda et al., 2001).
However, some disadvantages of enzyme catalysis include the ease of inactivation of
enzymes in these systems, generally low reaction rates, and low conversions. For example,
the immobilized enzymes are easily inactivated in the absence of polar compounds such as
water and methanol. Moreover, immobilized enzymes are generally more expensive than
chemical catalysts (Miertus et al., 2009).
Noureddini et al. (2005) studied the enzymatic trans-esterification of soybean oil with
methanol and ethanol. Among nine lipases tested, lipase PS from Pseudomonas cepacia
resulted in the highest yield of alkyl esters.
1.6 Factors Effecting Trans-esterification Reactions
There are a number of factors which could affect the trans-esterification process. These
factors include moisture content, free fatty acid contents, molar ratio of oil-to-alcohol, type
and amount of catalyst, reaction time, reaction temperature and mixing intensity (Demirbas
and Dermirbas, 2007).
1.6.1 Effect of Molar Ratio of Oil-to-Alcohol
Based on the stoichiometry of trans-esterification reaction, every mole of triglyceride
requires three moles of alcohol to produce three moles of fatty acid alkyl esters and one
mole of glycerol (Dermirbas, 2009). However, trans-esterification is an equilibrium-
32
controlled reaction in which excess of alcohol is required to drive the reaction in the forward
direction, to achieve maximum conversions (Meher et al., 2006b). A molar ratio of 1:6 9 (oil
to alcohol) is considered the standard ratio (Fukuda et al., 2001; Gerpen, 2005). Ramadhas
et al. (2004) and Sahoo et al. (2007) have reported a molar ratio of 6:1 during acid
esterification and a molar ratio of 9:1 vegetable oil-alcohol during alkaline esterification, as
the optimum values for biodiesel production from high FFA rubber seed oil and polanga
seed oil. Veljkovic et al. (2006) used 18:1 molar ratio during acid esterification and 6:1
molar ratio during alkaline esterification. Meher et al. (2006a) used 6:1 molar ratio during
acid esterification and 12:1 molar ratio during alkaline esterification. Tiwari et al. (2007)
and Ghadge and Raheman (2005) used volume as a measure of ratio instead of taking molar
ratio. However, in all, higher molar ratios resulted in greater ester conversions in a shorter
time (Dermirbas, 2009).
1.6.2 Type and Amount of Catalyst
The type and amount of catalyst required in the trans-esterification process usually depend
on the quality of the feedstock and method applied for the trans-esterification process
(Miertus et al., 2009). However, for feedstock with high moisture and free fatty acid
contents, homogenous trans-esterification process is unsuitable due to high possibility of
occurrence of saponification process instead of trans-esterification process to occur, rather,
an acid catalyzed trans-esterification is suitable (Gerpen, 2005). For a purified feedstock,
any type of catalyst could be used for the trans-esterification process (Edger et al., 2005). In
addition, biodiesel formation is also affected by the amount or concentration of catalyst:
with increasing concentration of catalyst and oil, the conversion of triglycerides into
biodiesel also increases. On the other hand insufficient amount of catalyst leads to the
incomplete conversion of triglycerides to fatty acid esters (Guo, 2005; Leung and Guo,
2006). However, optimal product yield (biodiesel) has been achieved when the
concentration of NaOH reaches 1.5 wt. % at the same time further increase of catalyst
concentration proved to have negative impact on end product yield, but addition of excess
amount of alkali catalyst react with triglycerides to form more soap (Leung and Guo, 2006).
33
1.6.3 Effect of Water and Free Fatty Acid Content
The water and free fatty acid (FFA) contents are critical factors for trans-esterification
reaction. Generally, in the conventional trans-esterification of fats and vegetable oils for
biodiesel production, free fatty acids and water always produce negative effects since the
presence of free fatty acids and water causes soap formation, consumes catalyst, and reduces
catalyst effectiveness (Demirbas, 2009). Water content is an important factor in the
conventional catalytic trans-esterification of vegetable oil as the base-catalyzed trans-
esterification reaction requires water-free and low acid value (< 1) raw materials for
biodiesel production (Demirbas, 2009). Also, if the oil samples have high FFA content
(more than 1%) then the reaction requires more alkali catalyst to neutralize the FFA or
pretreatment with an acid catalyst (Zhang et al., 2003a).
Kusdiana and Saka (2004) are of the opinion that water can pose a greater negative effect
than the presence of free fatty acids and hence the feedstock should be water-free. Canakci
and Gerpen (1999) insist that even a small amount of water (0.1%) in the trans-esterification
reaction will decrease the ester conversion from vegetable oil.
Fig. 5: Saponification reaction of free fatty acids during base catalyzed trans-esterification
source: (Moser, 2009).
1.6.4 Effect of Temperature
The reaction temperature influences the reaction in a positive manner (Ojolo et al., 2011).
The trans-esterification reaction temperature should be below the boiling point of alcohol in
order to prevent evaporation of the alcohol (Dermirbas, 2009). The range of optimal reaction
temperature may vary from 50°C to 70°C depending on the type of oils or fats used (Leung
and Guo, 2006). It has been observed that increasing the reaction temperature, especially to
supercritical conditions, has a favourable influence on the yield of ester (Dermirbas, 2009).
For example higher reaction temperature increases the reaction rate and shortens the reaction
time due to the reduction in viscosity of oils (Mathiyazhagan and Ganapathi, 2011).
34
However, Leung and Guo (2006) and Eevera et al. (2009) found that increase in reaction
temperature beyond the optimal level leads to decrease of biodiesel yield, because higher
reaction temperature accelerates the saponification of triglycerides.
1.6.5 Effect of Stirring Intensity
Agitation speed plays an important role in the formation of end-product (biodiesel)
(Mathiyazhagan and Ganapathi, 2011). Generally, low reaction rates are observed in trans-
esterification as a result of a poor dispersion of the alcohol and oil phases, and an induction
period can be often seen on the kinetic curves (slow initial reaction before steady-state
concentrations are reached) (Miertus et al., 2009). On the other hand higher stirring speed
favors formation of soap. This is due to the reverse behavior of trans-esterification reaction
(Eevera et al., 2009). Therefore, intense mixing is very important for the trans-esterification
process with the optimum stirring rates in the range of 1000 rpm using both motionless and
high-shear mixers (Miertus et al., 2009).
1.6.6 Effect of Reaction Time
The reaction time of trans-esterification depends on the choice of method or catalyst,
notably further increase in reaction time does not increase the product yield (i.e.
biodiesel/mono alkyl ester) (Leung and Guo, 2006; Alamu et al., 2007). Besides, longer
reaction time leads to the reduction of end product (biodiesel) due to the reversibility of the
trans-esterification reaction, thus resulting in loss of esters as well as soap formation (Eevera
et al., 2009). The effect of reaction time has been studied from 45 minutes to 120 minutes on
methyl ester (biodiesel) yield (Ojolo et al., 2011). It was found that ester yield increased as
the reaction time increased. However, if the reaction time is increased beyond 1 hour, the
increase in the yield of ester is small (Krishnakumar et al., 2008).
1.7 Influence of Biodiesel Composition on Fuel Properties
The fatty ester composition, along with the presence of contaminants and minor components
dictate the fuel properties of biodiesel fuel; these properties include low-temperature
35
operability, oxidative and storage stability, viscosity, exhaust emissions, cetane number, and
energy content (Moser, 2009).
1.7.1 Viscosity
Viscosity is defined as the resistance to shear or flow; it is highly dependent on temperature
and it describes the behavior of a liquid in motion near a solid boundary like the walls of a
pipe (Sanford et al., 2009). Viscosity is the primary reason why biodiesel is used as an
alternative fuel instead of the pure vegetable oils or animal fats (Moser, 2009). The high
kinematic viscosities of vegetable oils and animal fats ultimately lead to operational
problems such as deposits in engines when used directly as fuels (Knothe and Steidley,
2005a): this is as a result of poorer atomization of the fuel spray and less accurate operation
of the fuel injectors (Dermirbas, 2009). The lower the viscosity of the biodiesel, the easier it
is to pump, atomize and achieve finer droplets (Islam and Beg, 2004). The conversion of
triglycerides to methyl or ethyl esters through the trans-esterification process reduces the
molecular weight of the triglyceride to one-third of its value, and reduces the viscosity by a
factor of about eight (Dermirbas, 2009).
Several structural features influence the kinematic viscosities of fatty acids alkyl esters
(FAAE), such as chain length, degree of unsaturation, double bond orientation, and type of
ester head group (Moser, 2009). Factors such as longer chain length and larger ester head
group result in increase in the viscosity (Kulkarni et al., 2007). Viscosity increases with the
molecular weight and decreases with increasing level of unsaturation and high temperature
(Moser, 2009).
1.7.2 Low Temperature Operability
Low temperature operability of biodiesel fuel is an important aspect from the engine
performance standpoint in cold weather conditions (Knothe et al., 2005). Low temperature
operability of biodiesel is normally determined by three common parameters: cloud point
(CP), pour point (PP) and cold filter plugging point (CFPP) (Moser, 2009). The PP is the
temperature at which the amount of wax from a solution is sufficient to gel the fuel; thus it is
the lowest temperature at which the fuel can flow (Dermirbas, 2009). The cloud point is the
36
temperature at which crystals first appear in the fuel when cooled. Biodiesel has a higher CP
and PP compared to conventional diesel (Prakash, 1998). The CFPP is defined as the lowest
temperature at which a given volume of biodiesel completely flows under vacuum through a
wire mesh filter screen within 60s (Moser, 2009). The CFPP is generally considered to be a
more reliable indicator of low-temperature operability than CP or PP, since the fuel will
contain solids of sufficient size to render the engine inoperable due to fuel filter plugging
once the CFPP is reached (Park et al., 2008).
The low-temperature behaviour of chemical compounds is dictated by molecular structure
(Moser, 2009). Structural features such as chain length, degree of unsaturation, orientation
of double bonds and type of ester head group strongly influence the low temperature
operability of biodiesel (Moser, 2009). The larger the ester head group, the lower the cloud
point (Foglia et al., 1997). A higher degree of unsaturation results in lower cloud point
(Moser, 2008).
1.7.3 Oxidative Stability
Oxidative stability is determined by parameters such as iodine value and peroxide value.
Iodine value is a measure of the unsaturation of fats and oil and high iodine value shows
high unsaturation of the oil (Belewu et al., 2010). The peroxide value measures the
miliequivalent of peroxide oxygen per kilogram weight. The higher the peroxide value of
biodiesel the greater the development of rancidity due do the products that are formed
through oxidation of lipids, such as aldehydes, shorter-chain fatty acids, other oxygenated
species (such as ketones), and polymers (Moser, 2009).
Stability of fatty compounds is influenced by factors such as presence of air, heat, traces of
metal, peroxides, light and structural features of the compounds themselves, mainly the
presence of double bonds (Bajpai and Tyagi, 2006). Oxidative stability decreases with the
increase of polyunsaturated fatty acid methyl esters content (McCormick et al., 2007; Park
et al., 2008). Autoxidation of unsaturated fatty compounds proceeds at different rates
depending on the number and position of double bonds. The bis-allylic positions in common
polyunsaturated fatty acids such as linoleic acid (one bis-allylic position at C-11) and
37
linolenic acid (two bisallylic positions at C-11 and C-14) are more susceptible to
autoxidation than allylic positions (Sokoto et al., 2011). Therefore, vegetable oils rich in
linoleic and linolenic acids, tend to impart poor oxidation stability to fuels (Sokoto et al.,
2011).
1.7.4 Heat of Combustion
Heat of combustion is the thermal energy that is liberated upon combustion, so it is
commonly referred to as energy content (Moser, 2009). The heat of combustion is an
important parameter for estimating fuel consumption, the greater the heat of combustion, the
lower the fuel consumption (Knothe, 2008). The heat of combustion or heating value is not
specified in the biodiesel standards ASTM D6751 and EN14214. However, a European
standard for using biodiesel as heating oil, EN 14213, specifies a minimum heating value of
35 MJ/kg (Sokoto et al., 2011).
Factors that influence the energy content of biodiesel include the oxygen content and
carbon-to-hydrogen ratio (Moser, 2009). Generally, lower carbon-to-hydrogen ratios (i.e.,
more hydrogen) exhibit greater energy content (Moser, 2009). The oxygen content of
biodiesel (contains 11% oxygen by weight and no sulfur) improves the combustion process
and decreases its oxidation potential, thus higher oxygen content of fatty acids alkyl esters
increase the energy content (Dermirbas, 2009). The structural oxygen content of a fuel
improves its combustion efficiency due to an increase in the homogeneity of oxygen with
the fuel during combustion due to this the combustion efficiency of biodiesel is higher than
that of petrodiesel (Dermirbas, 2009).
Heat of combustion increases with increasing chain length; thus, the energy content of
FAAE is directly proportional to chain length (Knothe, 2008). Therefore, energy content can
be predicted by saponification value, which is defined as the amount of potassium hydroxide
(KOH) in milligrams required to saponify one gram of fat or oil under the specified
conditions (AOAC, 1998). Based on the length of the fatty acids present in the
triacylglycerol molecule, the weight of the triacylglycerol molecule changes which in turn
affects the amount of KOH required to saponify the molecule (Sanford et al., 2009). Hence,
saponification value is a measure of the average molecular weight or the chain length of the
38
fatty acids present. As most of the mass of a triglyceride is due to the three fatty acid
moeities, it allows for comparison of the average fatty acid chain length (Sanford et al.,
2009). Saponification values is inversely related to the average molecular weight or chain
length of the fatty acids in the oil fractions. Thus, oil fractions with saponification values of
200 mg KOH/g and above possess low molecular weight fatty acids (Abayeh et al., 1998).
1.7.5 Cetane Number
Cetane number (CN) is widely used as diesel fuel quality parameter related to the ignition
delay time and combustion quality. An appropriate cetane number is required for good
engine performance (Dermirbas, 2009). The higher the cetane number, the better the ignition
property as it ensures good cold start properties and minimize the formation of white smoke
(Meher et al., 2006b). Cetane number (CN) is based on two compounds, hexadecane also
known as cetane (trivial name) as a high-quality reference standard with a short ignition
delay time and an arbitrarily assigned CN of 100; and 2,2,4,4,6,8,8-heptamethylnonane as
low-quality reference standard with a long ignition delay time and an arbitrarily-assigned
CN of 15 (Knothe et al., 1997). The CN of biodiesel is influenced by the fatty acid chain
length and degree of unsaturation, the longer the fatty acid chain length and the more
saturated the molecules, the higher the CN (Moser, 2009). The CN of biodiesel is generally
higher than that of conventional diesel, and the CN of biodiesel from animal fats is higher
than those of vegetable oils (Bala, 2005).
1.7.6 Exhaust Emissions
The combustion of biodiesel (B100) in diesel engines results in an average increase in NOx
exhaust emissions of 12% and decreases in PM and CO emissions of 48% and 48%,
respectively, in comparison to petrodiesel (Hess et al., 2007). For B20 blends of SME in
petrodiesel, NOx emissions are increased by 0–4% when neat petrodiesel is used, but PM,
THC, and CO emissions are reduced by 10%, 20%, and 11%, respectively (Hess et al.,
2007; EPA, 2002).
The increase in NOx emissions with combustion of biodiesel and in some cases of
biodiesel–petrodiesel blends is of concern in environmentally-sensitive areas such as
39
national parks and urban centers (Moser, 2009). Reduction of smog forming NOx exhaust
emissions to levels equal to or lower than those observed for petrodiesel is essential for
universal acceptance of biodiesel (Moser, 2009). NOx exhaust emissions of biodiesel and
blends with petrodiesel NOx emission may be reduced by several engine or after-treatment
technologies, such as exhaust gas re-circulation, selective catalytic reduction, diesel
oxidation catalysts, and NOx or particulate traps (McGeehan, 2004).
NOx emissions are influenced by the chemical nature of FAAE that constitute biodiesel.
Specifically, decreasing the chain length and/or increasing the number of double bonds (i.e.,
higher iodine value) of FAAE results in an increase in NOx emissions (Szybist et al. 2005;
Knothe et al., 2006). The chemical composition of biodiesel varies according to the
feedstock from which it is prepared. As a result, biodiesel obtained from feedstocks of
significantly different compositions will exhibit different NOx exhaust emission behavior
(Moser, 2009).
1.7.7 Lubricity
This is the property of the fuel that gives it the capacity to reduce friction. Biodiesel
possesses inherently good lubricity, especially when compared to petrodiesel (Knothe and
Steidley 2005b; Moser et al., 2008). Lubricity is determined at 60°C in accordance with
ASTM D6079 using a high-frequency reciprocating rig instrument. Lubricity is not
prescribed in ASTM D6751 or EN 14214. However, the petrodiesel standards, ASTM D975
and EN 590, contain maximum allowable wear scar limits of 520 and 460 µm respectively
(Moser, 2009).
Various structural features such as the presence of heteroatoms, chain length, and
unsaturation influence the lubricity of biodiesel (Moser, 2009). Biodiesel fuels possess at
least two oxygen atoms that in large part explain their enhanced lubricities over typical
hydrocarbon-containing petrodiesel fuels (Knothe and Steidley, 2005b). Generally,
increasing fatty acid chain length and increasing levels of unsaturation impart superior
lubricity to biodiesel (Moser, 2009).
40
1.7.8 Contaminants
Contaminants in biodiesel may include alcohol, water, FFA, soaps, metals, catalyst, glycerol
and its intermediates. Alcohol contamination in biodiesel is indirectly measured through
flash point determination following ASTM D93. If methanol, with its flash point of 12°C is
present in the biodiesel the flash point can be lowered considerably (Sanford et al., 2009).
The flash point is the lowest temperature at which fuel emits enough vapors to ignite
(ASTM, 2008). Biodiesel has a high flash point; usually more than 150°C, while
conventional diesel fuel has a flash point of 55-66°C (Knothe et al., 2005). However, the
flash point values of vegetable oil methyl esters are much lower than those of vegetable oils
(Dermirbas, 2009).
Water is a major source of fuel contamination. Its presence in biodiesel causes four serious
problems: corrosion of engine fuel system components, promotion of microbial growth,
hydrolysis of the biodiesel (Moser, 2009). Water also reduces the heat of combustion which
leads to more smoke, harder starting and less power (Dermirbas, 2009).
The acid value and conductivity test of the biodiesel can be used to determine the presence
of water; the acid value determination is an important test to assess the quality of a particular
biodiesel (Sanford et al., 2009). Acid value can indicate the extent or degree of hydrolysis of
the methyl ester, a particularly important aspect when considering storage and transportation
as large quantities of free fatty acids can cause corrosion in tanks (Wang et al., 2008). High
acid value and high conductivity of biodiesel indicate the presence of water (Moser, 2009).
Free fatty acids may be present in biodiesel that was prepared from a feedstock with high
FFA content or may be formed during hydrolysis of biodiesel in the presence of water and
catalyst (Moser, 2009). The presence of FFA in biodiesel may impact other important fuel
properties such as low temperature performance, oxidative stability, kinematic viscosity, and
lubricity (Moser, 2009). In addition to soap formation, FFAs are known to act as pro-
oxidants (Knothe and Steidley, 2005a), so the presence of FFA in biodiesel may have
negative impact to the oxidative stability. FFA increases the lubricity which is beneficial but
41
negatively increases the viscosity and low temperature operability properties of the biodiesel
(Moser, 2009).
Other contaminants such as soaps, metals, catalyst, glycerol and its intermediates may be
present in insufficiently purified biodiesel and their presence can be detected by simple
chemical test of the individual compounds (Moser, 2009). The primary problem associated
with metal contamination is elevated ash production during combustion (Knothe et al.,
2005). Thus, high percentage ash content is indicative of the presence of metals.
1.7.9 Biodiesel Standard Specifications and Test Methods
The standard specifications and test methods for biodiesel are summarized in Table 4.
42
Table 4: Specifications and test methods of ASTM D6751 and EN 14214 standards for
biodiesel
United States Standards
ASTM D6751
European Standards EN
14214
Property Units Test Methods Limits Test Methods limits
Density at 15 °C (Kg/m3) EN ISO 3675,
EN ISO 12185
860–900
Kinematic
viscosity, 40oc
mm2/s ASTM D445 1.9–6.0 EN ISO 3104,
ISO 3105
3.5–5.0
Cetane number ASTM D613 47 min EN ISO 5165 51 min.
Flash point oC ASTM D93 130.0 min EN ISO 3679 120 min.
Cloud point oC ASTM
D2500-05
–3 - +12 - -
Pour point ASTM D 97-
96a
–15- +10 -
Oxidation
stability
h EN 14112 3.0 min.
Cold filter
plugging point
ASTMD 6371 –4 to –9
Acid value
mg
KOH/g
ASTM D664 0.50 max EN 14104 0.50 max
Total glycerin % mass ASTM D6584 0.240 EN 14105 0.25 max %
(mol/mol)
Free glycerin % mass ASTM D6584
0.020 EN 14105 EN
14106
0.020 max %
(mol/mol)
Water content mg/kg ASTM D2709 500ppm EN ISO
12937
500 max
Iodine value I2/100 g EN 14111 120 max
Ash content % ASTM D 482 0.01 0.02
metals (group 1
&2)
mg/kg EN 14108,
14109
EN 14538
5 max
Carbon residue % mass ASTM D4530 0.050
max
EN ISO 10370 0.30 max %
(mol/mol)
Source: (Moser, 2009)
1.8 Advantages of Biodiesel
The biggest advantage of biodiesel is environmental friendliness that it has over gasoline
and petroleum diesel (Dermirbas, 2009). The advantages of biodiesel as a diesel fuel are its
portability, ready availability, renewability, higher combustion efficiency, lower sulfur and
43
aromatic content (Ma and Hanna 1999; Knothe et al., 2006), higher cetane number, and
higher biodegradability (Zhang et al., 2003b; Knothe et al., 2005).
A number of technical advantages of biodiesel fuel are (i) it prolongs engine life and reduces
the need for maintenance (biodiesel has better lubricating qualities than fossil diesel); (ii) it
is safer to handle, being less toxic, more biodegradable, and having a higher flash point; and
(iii) it reduces some exhaust emissions (Wardle, 2003). Among the many advantages of
biodiesel fuel, it is safe for use in all conventional diesel engines, offers the same
performance and engine durability as petroleum diesel fuel, it is non-flammable and non-
toxic, and reduces tailpipe emissions, visible smoke, and noxious fumes and odours (Chand,
2002). Biodiesel is better than diesel fuel in terms of sulfur content and aromatic content
(Martini and Schell, 1997).
The economic advantages of biodiesel are that it reduces greenhouse gas emissions, helps to
reduce reliance on crude oil imports, and supports agriculture by providing new labour and
market opportunities for domestic crops. In addition, it enhances lubrication and is widely
accepted by vehicle manufacturers (Palz et al., 2002; Clarke et al., 2003). Biodiesel is non-
toxic and degrades about four times faster than petrodiesel (Dermirbas, 2009). Biodiesel
provides significant lubricity improvement over petroleum diesel fuel; the lubricity
properties of fuel are important for reducing friction wear in engine components normally
lubricated by the fuel rather than crankcase oil (Ma and Hanna 1999; Dermirbas, 2003).
Even biodiesel levels below 1% can provide up to a 30% increase in lubricity (Dermirbas,
2008a). The sulfur content of petrodiesel is 20–50 times that of biodiesels (Dermirbas,
2009). Biodiesel has demonstrated a number of promising characteristics, including
reduction of exhaust emissions (Dunn, 2001). The risks of handling, transporting, and
storing biodiesel are much lower than those associated with petrodiesel (Dermirbas, 2009).
1.9 Disadvantages of Biodiesel
The major disadvantages of biodiesel are its higher viscosity, lower energy content, higher
cloud point and pour point, higher nitrogen oxide (NOx) emissions, lower engine speed/
power, injector coking and high price (Dermirbas, 2008a). Important operating
44
disadvantages of biodiesel in comparison with petrodiesel are cold start problems, the lower
energy content, higher copper strip corrosion and fuel pumping difficulty from higher
viscosity (Dermirbas, 2007).
1.10 Uses of Biodiesel
Apart from its use as an alternative fuel to petrodiesel in diesel engines, biodiesel may be
used as a replacement for petroleum as heating oil (Mushrush et al. 2001). As such, a
European standard (EN 14213) was established to cover the use of biodiesel for this
purpose. In the United States, blends of up to 5% biodiesel in heating oils (B5 Bioheat) have
recently been approved for inclusion in the ASTM heating oil standard, D396 (ASTM,
2008). The less harmful exhaust emissions from biodiesel to that of petrodiesel, have
encouraged the use of biodiesel to power underground mining equipment (Moser, 2009).
Another combustion-related application of biodiesel is as an aviation fuel, although the
relatively poor low-temperature properties of biodiesel restrict its use to low-altitude aircraft
(Dunn, 2001).
The use of biodiesel in diesel-fueled marine engines to reduce environmental impact is
another important application of this biodegradable and non-toxic fuel (Nine et al., 2000).
Biodiesel may also be used as a fuel for generators and turbines for the generation of
electricity (Hashimoto et al., 2008; Kalbande et al., 2008; Lin et al., 2008) or as a substitute
for hydrogen in fuel cells (Kram, 2008).
An important non-fuel application of FAAE is as an industrial environmentally friendly
solvent, since they are biodegradable, have high flash points, and have very low volatilities
(Wildes, 2002). The high solvent strength of biodiesel makes it attractive as a substitute for a
number of conventional and harmful organic solvents (Hu et al., 2004) in applications such
as industrial cleaning and degreasing, resin cleaning and removal (Wildes, 2002), as
plasticizers in the production of plastics (Wehlmann, 1999); in liquid–liquid extractions
(Spear et al., 2007); as polymerization solvent (Salehpour and Dube, 2008), and as a
medium in site bioremediation of crude petroleum spills (Pereira and Mudge, 2004;
Fernandezalvarez et al., 2006).
45
Fatty acid alkyl esters can also serve as valuable starting materials or intermediates in the
synthesis of fatty alcohols (Peters, 1996), lubricants (Moser et al., 2007; Sharma et al.,
2007; Dailey et al., 2008), cold flow improver additives (Moser et al., 2007; Dailey et al.,
2008), cetane improving additives (Poirier et al., 1995), and multifunctional lubricity and
combustion additives (Suppes et al., 2001; Suppes and Dasari, 2003). Moreover, biodiesel in
conjunction with certain surfactants can act as a contact herbicide to kill broadleaf weeds in
turfgrass (Vaughn and Holser, 2007).
1.11 Aim and Objectives
1.11.1 Aim of the Study
This study is aimed at characterizing coconut oil and evaluating its trans-esterification
reaction rate with ethanol.
1.11.2 Specific Objectives of the Study
This research is designed to achieve the following objectives:
• Extraction of oil from coconut copra (dry flesh) using cold extraction.
• Physicochemical characterization of the coconut oil.
• Trans-esterification of coconut oil with ethanol (ethanolysis) using NaOH as catalyst.
• Physicochemical characterization of the ethyl esters produced.
• Investigation of the trans-esterification reaction rate of the varied oil/ethanol
volumetric ratios of 1:6, 1:3, 1:2, 1:1.5 and 1:1.
46
CHAPTER TWO
MATERIALS AND METHODS
2.1 Materials
2.1.1 Plant Material
The coconut (Cocos nucifera) was obtained from Nnihi in Etche Local Government Area of
Rivers State, Nigeria. The nuts were dehusked and the shell split open in order to remove the
kernel (flesh). The kernel was ground into fine particles with a blender and sun-dried for 2
days.
2.1.2 Instruments/Equipment
The following instruments/equipment were used during the investigation:
Instruments/Equipments Manufacturers
Oswald viscometer B. Brain, made in England
Oxygen bomb calorimeter Model XRY-1A, Shanghai Changji, China
Blender Panasonic, made in Japan
Water bath Model SM801A, made by uniscope England
Oven Gellenkamp Hotbox, made in England
Abbe refractometer Model WYA-2S, Made by Searchtech Instruments
WTW conductivity meter Model LF. 90, made in Germany
UV/visible spectrophotometer: Jenway 6405, made in U.S.A.
Glass wares Pyrex, made in England
Heating magnetic stirrer Pyro-magnestir, made in USA, cat no.1266
Weighing balance: B2404-5 mettler Toledo, made in Switzerland.
Electric Muffle Furnace Model LF 3, made by Vecstar Limited.
2.1.3 Reagents/Chemicals
All chemicals used in this study were of analytical grade. Absolute ethanol, chloroform, n-
hexane and phenolphthalein were products of Riedel-de Haen, Germany. Iodine trichloride,
47
potassium chloride, sodium thiosulphate and starch powder were products of British Drug
House (BDH) Chemical, England. Potassium hydroxide (pellets), potassium iodide and
sodium hydroxide (pellets) were products of Avondale laboratories, England. Iodine crystals
and sodium sulphate were products of Burgoyne, India. Glacial acetic acid and sulphuric
acid were products of Cartivalues, India. Hydrochloric acid, diethylether, glycerol, acetyl
acetone, sodium carbonate and sodium periodate were products of Sigma Chemical
Company Limited (U.S.A.).
2.2 Methods
2.2.1 Preparation of reagents
Preparation of 0.5M Alcoholic Potassium Hydroxide (KOH) Solution
In preparing this, KOH pellets (28g) were transferred into a 1000ml conical flask, 300ml of
absolute ethanol was added to dissolve the pellets. Thereafter, the solution was made up to
1000ml mark using the same solvent.
Preparation of 0.1M Alcoholic Potassium Hydroxide (KOH) Solution
This was prepared by putting 5.6 g KOH into a 1000ml conical flask; 100ml of absolute
ethanol was added to dissolve the solute and then, the solution was made up to 1000ml mark
using the same solvent. The solution was filtered and stored in brown bottle for five days.
Preparation of Ethanol:Diethyl Ether Solution (1:1 v/v)
This solution was prepared by mixing 50ml of 95% ethanol and 50ml of diethyl ether in a
500ml conical flask.
Preparation of Phenolphthalein Indicator
Phenolphthalein indicator was prepared by putting 1g of phenolphthalein into a 100ml
conical flask, 66ml of ethanol was added to dissolve solute, after which the solution was
made up to 100 ml mark using distilled water.
48
Preparation of 20% Potassium Iodide (KI) Solution
This was prepared by putting 100g of KI into a 500ml conical flask and then 200ml of
distilled water was added to dissolve the KI. After that, the solution was made up to 500 ml
mark with distilled water.
Preparation of 0.1M Sodium Thiosulphate (Na2S2O3)
Sodium thiosulphate pentahydrate (24.8g) was put into a 1000ml conical flask, 300ml of
distilled was added to dissolve the solute, after which the solution was made up to 1000 ml
using distilled water.
Preparation of Starch Indicator
In preparing this, 1g of soluble starch powder was dissolved in little water and the
suspension was poured into 100ml of boiling water with constant stirring. The mixture was
boiled for one minute, allowed to cool and 3g of potassium iodide was added for
preservation.
Preparation of Wijs Reagent (Iodine monochloride) Solution
Wijs reagent was prepared by putting 2g of iodine trichloride into an amber bottle and 50ml
of glacial acetic acid was added. Iodine (2.25g) was dissolved in 100ml of glacial acetic acid
in another bottle and both solutions mixed together. The resulting mixture was then made up
to 250ml with glacial acetic, stored in the amber bottle at room temperature and kept out of
light its use.
Preparation of Glacial acetic acid:Chloroform Solution (3:2 v/v)
This solution was prepared by mixing 300ml of glacial acetic acid and 200ml of chloroform
in a 1000ml conical flask.
Preparation of 0.5M Hydrochloric acid (HCl) Solution
This was prepared with 37% HCl; 41.5 ml of HCl was pipetted into a 1000ml conical flask
containing 300ml of distilled water with thorough mixing, after which the solution was
made up to 1000ml with distilled water.
49
Preparation of 0.1M Sodium Hydroxide (NaOH) Solution
In preparing this solution, 4g of NaOH was put into a 1000ml conical flask, 100ml of
distilled water was added to dissolve the solute and then the solution was made up to 1000
ml with distilled water.
Preparation of 0.01M Potassium Chloride (KCl) Solution
Potassium chloride (0.75g) was put into a 1000ml conical flask, the solute was dissolved in
100ml of distilled water and then the solution was made up to 1000ml with distilled water.
Preparation of 0.2M Acetyl Acetone Solution
This was prepared by pipetting 21ml of acetyl acetone into a 1000ml conical flask, 300ml of
distilled water was added and the solution was thoroughly stirred. Then, the solution was
made up to 1000ml with distilled water.
Preparation of 10mM Sodium Periodate Solution
Sodium periodate (2.1g) was put into a 1000ml conical flask, 100ml of distilled was added
to dissolve the solute, after which the solution was made up to 1000ml with distilled water.
Preparation of 95% Ethanol:Deionized Water Solvent Solution (1:1)
This solution was prepared by mixing 500ml of 95% ethanol and 500ml of deionized water
in a 2000ml conical flask.
Preparation of 0.036mg/ml Glycerol Standard Solution
This was prepared with 98% glycerol; 29 µl of glycerol was pipetted into a 1000ml conical
flask, 200ml of 95% ethanol:deionized water was added with thorough mixing, after which
the solution was made up to 1000ml with the same solvent solution.
Preparation of 0.7M Sodium Carbonate Solution
In preparing this solution, 74.2g of sodium carbonate was put into a 1000ml conical flask,
100ml of distilled water was added to dissolve the solute and then the solution was made up
to 1000 ml with distilled water.
50
2.2.2 Determination of the Moisture Content of Kernel
The empty dish was weighed without and with the amount of kernel. This was placed in an
oven and dried at 105oC for 7 hr, weighing was repeated every 2 hr till a constant weight
was obtained and the weight was taken and compared with the initially recorded weight. The
percentage moisture content was calculated using the formula (Appendix 1);
% Moisture Content of the kernel =
Where W1 = Original weight of the sample before drying
W2 = Weight of the sample after drying.
2.2.3 Extraction of Coconut Oil
Extraction was done using cold extraction. Oil was extracted from the powdered sample
with n- hexane. The solvent mixture was poured into the powdered sample, covered, shaken
vigorously for 5 mins and left for 72 hrs. The mixture was filtered with Whatman no. 1 filter
paper and the solvent evaporated using a distillation apparatus and an oven. The liquid that
left after evaporation is the oil (Fig. 6B). The percentage yield was calculated using the
formula (Appendix 2):
% yield of oil =
Fig. 6: Dehusked coconuts (A) and extracted coconut oil (B)
A B
51
2.2.4 Purification of Crude Coconut Oil
2.2.4.1 Water De-gumming
The extracted crude coconut oil contains phosphatides, gums and other complex compounds
which can promote hydrolysis (increase in free fatty acid) of vegetable oil during storage.
During trans-esterification process, these compounds can also interfere. Therefore these
compounds are removed by water de-gumming process.
This was carried out by measuring 100ml of the extracted oil with a measuring cylinder into
a beaker. The oil and water was heated to 70oC on a water bath separately. As the oil was
stirred gently, the water was poured into the oil. Then, the mixture was stirred for 30 mins
and poured into a separating funnel. The mixture was allowed to stand for 60 mins, two
layers were formed. The lower layer (of phosphatides and other impurities) was run-off,
while the upper layer (of oil) was then run into a steel bowl and oven dried at 105oC for 5 hr
to remove moisture (Fig. 7).
Fig. 7: Coconut oil after degumming and standing in a separating funnel to form two distinct
layers; the upper layer of oil (A) and the lower layer of phosphatides and other impurities
(B)
A B
52
2.2.4.2 Acid Pretreatment
The oil (100ml) was introduced into a 500ml three-necked round-bottomed flask (reaction
flask) attached with a reflux condenser and thermometer; this was then placed in a beaker
containing water. The overall set-up was mounted on a heating magnetic stirrer and the oil
in the reaction flask was heated to 60oC. Concentrated sulfuric acid (0.1ml) was added to
40ml of ethanol in another flask; this was heated to 60°C and added to the reaction flask
containing the pre-heated oil (Zullaikah et al., 2005). This mixture was stirred on heating for
1 hr and without heating for 1 hr. The resulting mixture was then poured into a separating
funnel and allowed to settle for 2 hours. The top layer comprised unreacted methanol,
whereas the middle layer was oil and fatty acid ethyl ester (FAME) (small amount obtained
by conversion of free fatty acids to esters), and water at the bottom layer.
2.2.5 Physicochemical Characterization of the Coconut Oil
2.2.5.1 Physical Characterization of the Coconut Oil
2.2.5.1.1 Determination of the Colour of the Oil
This was determined visually.
2.2.5.1.2 Determination of the Specific Gravity of the Oil
A 4ml aliquot of the oil was weighed and its density calculated using the relationship
Then, the specific gravity of the oil was calculated using the formular (Appendix 3.1):
Specific Gravity =
2.2.5.1.3 Determination of the Viscosity of the Oil
Determination of the viscosity of the oil was done using the method of AOAC (1998). The
oil was gradually poured into the viscometer until its lobe was almost filled and then it was
placed in a water bath and allowed to heat up to an equilibrium temperature of 40oC. The oil
53
on the broad arm was sucked through the narrow arm until it reached the upper mark above
the lower lobe of this narrow arm. The oil was then allowed to flow back to the lower mark
just below the lower lobe. The time taken for the flow (flow time, t) was recorded. Then, the
viscosity was calculated using the formular (Appendix 3.2):
Where n = Viscosity of the oil, mm2/s
v = Viscosity of water, mm2/s
ρ1 = Density of the oil, kg/m3
ρ2 = Density of water, kg/m3
t1 = Time taken for the oil to flow back
t2 = Time taken for water to flow back
2.2.5.1.4 Determination of the Flash Point of the Oil
The flash point of the oil was determined according to the ASTM D 93 open cup method.
The cup was filled with a sample of the oil up to the mark (75ml) and the cup was heated
with a bunsen burner maintaining a small open flame from an external supply of natural gas.
Periodically, the flame was passed over the surface of the oil. When the flash temperature
was reached the surface of the oil caught fire. The temperature (at the moment) was noted
and recorded as the flash point temperature.
2.2.5.1.5 Determination of the Cloud Point of the Oil
The cloud point of the oil was determined according to the ASTM D 5773 method. The
cloud point is a measure of the temperature at which components in the oil begin to solidify
out of the solution.
A test tube with a thermometer inserted in it, was filled with a sample of the oil. The oil was
cooled at 2oC/min rate and continuously monitored until a white cloud appeared on the bulb
of thermometer. The temperature that corresponds to the first formation of a cloud in the oil
was recorded.
54
2.2.5.1.6 Determination of the Pour Point of the Oil
The pour point of the oil was determined according to the ASTM D 97-96a method. A
sample of the oil in a capillary tube was solidified; thereafter, it was attached to a
thermometer and inserted into a gradually heating beaker of water. The temperature at which
the sample started moving in the capillary tube was recorded.
2.2.5.1.7 Determination of the Volatile Matter of the Oil
Determination of the volatile matter of the oil was done using the method of AOAC (1998).
A porcelain crucible which was washed, dried in an oven at 100oC, cooled in a desiccators
and weighed. An aliquot of the oil was transferred into the porcelain crucible, weighed and
then placed in an oven at 105oC for 5 hr to evaporate water. The resulting dry oil was
weighed and heated in a muffle furnace at 600oC for 10 mins. The residue left after heating
was cooled in a dessicator and weighed. The percentage volatile matter was calculated using
the formular (Appendix 3.3):
Volatile Matter =
Where x = Weight of dried oil after oven drying at 105oc
y = Weight of residue after further heating at 600oC
w = Weight of sample (g)
2.2.5.1.8 Determination of the Refractive Index of the Oil
The refractive index of the oil was determined with a refractometer. The power switch was
turned on; the illuminating lamp came up and the display showed 0000. A drop of the oil
was introduced on the working surface of the lower refracting prism. The rotating arm and
the collecting lens cone of the light gathering illuminating units were rotated so as to make
the light-intake surface of the upper light-intake prism to be illuminated evenly. The field of
view was observed through the eye piece and the adjustable hand wheel was rotated so as to
make the line dividing the dark and light areas fall in the cross line. The dispersion
correction hand wheel was rotated so as to get a good contrast between the light and dark
area and minimum dispersion. The read button was pressed and the refractive index was
displayed on the screen.
55
2.2.5.1.9 Determination of the Heat of Combustion of the Oil
The heat of combustion was determined according to the method of AOAC (1998) using a
bomb calorimeter. Benzoic acid was used to standardize the calorimeter. A weighed amount
of a sample of the oil (1.11g) was put in the crucible of the calorimeter and the fuse wire
was attached between the electrodes. Thereafter, it was placed in the bomb, which was
pressurized to 18atm of oxygen. The bomb was placed in a vessel containing a measured
quantity of water (2000g). The ignition circuit was connected and the water temperature was
noted. After ignition, the temperature rise was monitored every minute till a constant
temperature was reached and recorded. The pressure was released, the length of unburned
fuse wire was measured and the residue titrated with 0.7M sodium carbonate solution using
phenolphthalein as indicator. The heat of combustion was calculated using the formular
(Appendix 3.4):
Heat of Combustion = g
VLTE −−∆ 3.2 (KJ/Kg)
Where E = Energy equivalent of the calorimeter using benzoic acid
∆T = Temperature rise
L = Length of burnt wire
V = Titration volume
g = Weight of sample
2.2.5.2 Chemical Characterization of Coconut Oil
2.2.5.2.1 Determination of Acid Value of the Oil
The acid value of the oil was determined according to the ASTM D 664 method. To
determine the acid value of the oil, a 2g aliquot of it was dissolved in 25 ml of 1:1 mixture
of ethanol and diethyl ether. The solution was titrated with 0.1M ethanolic KOH solution in
the presence of 5 drops of phenolphthalein as indicator until the end point (colourless to
pink) was recognized. The volume of 0.1M ethanolic KOH (V) for the sample titration was
noted. The total acidity (acid number) in mg KOH/g was calculated using the following
formular (Appendix 3.5):
56
Acid value =
Where V = Volume of 0.1N solution of ethanolic KOH in milliliter (ml)
m = Weight of the sample in gram
N = Normality of ethanolic KOH
2.2.5.2.2 Determination of Saponification Value of the Oil
The saponification value of the oil was determined using the method of AOAC (1998). The
oil (2.206g) was added to 25ml of 0.5N ethanolic potassium hydroxide solution in a flask to
which a reflux condenser was attached. The mixture was heated, and as soon as the ethanol
boiled, the flask was occasionally shaken using magnetic stirrer until the oil was completely
dissolved, and the solution was boiled for half an hour. After completely dissolving the oil, 5
drops of phenolphthalein indicator was added and the hot soap solution obtained was slowly
titrated with 0.5N hydrochloric acid and volume was recorded.
Then a blank determination was carried out upon the same quantity of potassium hydroxide
solution at the same time and under the same conditions and volume was recorded. The final
result was calculated using the formular (Appendix 3.6):
Saponification value =
Where W= Weight of oil taken in gram.
S = Sample titre value in ml
B = Blank titre value in ml
N = Normality of hydrochloric acid
2.2.5.2.3 Determination of Peroxide Value of the Oil
The Peroxide value of the oil was determined using the method of AOAC (1998). To
determine the peroxide value, 2.206g of the oil was dissolved in 30 ml of a mixture of
glacial acetic acid and chloroform (3:2, v/v). Then, 20% of potassium iodide (0.5 ml) was
added and the solution swirled in the dark for one minute after which 75ml of distilled water
was added. The mixture was titrated with 0.1M sodium thiosulphate with vigorous shaking
until the yellow colour of the iodine had disappeared. Starch indicator (0.5ml) was added
57
then to obtain a blue colour and titration continued until all the blue colour had disappeared.
The peroxide value was calculated from the formular (Appendix 3.7):
Peroxide value =
Where S = Sample titre value in ml
B = Blank titre value in ml
M = Molarity of sodium thiosulphate
2.2.5.2.4 Determination of Iodine Value of the Oil
The iodine value of the oil was determined using the method of AOAC (1998). An aliquot of
the oil (0.8825g) was weighed into a conical flask, tetrachloromethane (15ml) and 25 ml of
Wij’s solution was added. This mixture was placed in a stoppered conical flask, swirled
gently and placed in a dark cupboard for one hour after which 20 ml of 20% potassium
iodide solution and 100ml of distilled water were added. After gentle shaking, liberated
iodine was titrated with 0.1M sodium thiosulphate solution until the yellow colour of the
iodine had appeared. Starch indicator (1ml) was added then to obtain a blue colour and
titration continued until all the blue colour had disappeared. The iodine value was calculated
from the formular (Appendix 3.8):
Iodine value =
Where B = blank titre value in ml
S = sample titre value in ml
M = Molarity of sodium thiosulphate
2.2.5.2.5 Determination of Percentage Free Fatty Acid of the Oil
The percentage free fatty acid of the oil was determined using the method of AOAC (1998).
Two grams of the oil was weighed into a conical flask and 10 ml of 95% ethanol was added.
This was then titrated with 0.1 M sodium hydroxide using phenolphthalein as an indicator.
The conical flask was shaken constantly until a pink colour that persisted for 30 seconds was
obtained. The percentage free fatty acid was calculated from the formular (Appendix 3.9):
58
%Free Fatty Acid =
Where V=Volume of 0.1M sodium hydroxide used in ml
M=Molarity of sodium hydroxide
2.2.6 Trans-esterification of Coconut Oil with Ethanol Using NaOH as Catalyst
This was done using the methods of Ojolo et al. (2011) and Rahayu and Mindaryani (2009).
Ethanolysis reaction was carried out in a 500 ml three-necked round-bottomed flask attached
with a reflux condenser and thermometer and placed in a beaker containing water. The
overall set-up was mounted on a heating magnetic stirrer as shown in Fig. 8A.
Fig. 8: Experimental set-up during trans-esterification and separation of the mixture into
biodiesel (upper layer) (A) and glycerol (lower layer) in a separating funnel (B)
Initially, 50 ml of coconut oil was introduced into the three necked flask which was heated
to the temperature of 65oC. At the same time, but in another flask, 0.2g of NaOH was
dissolved in 150 ml of ethanol and the mixture was heated. When the selected oil
temperature was achieved, the mixture was added to the hot oil under stirring and heating.
The attainment of the selected temperature of the mixture determined the start of the
reaction time. The system was maintained under these conditions during the reaction. At the
end of the process, the mixture was poured into a separating funnel (Fig. 8B), allowing the
A B
59
glycerol and the catalyst to separate from the biodiesel. The glycerol layer and the biodiesel
layer were drained separately. The biodiesel was washed with hot distilled water and dried
with an oven prior to characterization. The percentage yield of the ethyl ester was calculated
from the formular (Appendix 4):
% yield of ethyl ester =
2.2.7 Physicochemical Characterization of the Ethyl Esters Produced
2.2.7.1 Physical Characterization of Ethyl Ester (Biodiesel) Produced
2.2.7.1.1 Determination of the Colour of the Ethyl Ester
This was determined visually.
2.2.7.1.2 Determination of the Specific Gravity of the Ethyl Ester
A 3ml aliquot of the ethyl ester was weighed and its density calculated using the relationship
Then, the specific gravity of the ethyl ester was calculated using the formular (Appendix
5.1):
Specific Gravity =
2.2.7.1.3 Determination of the Viscosity of the Ethyl Ester
Determination of the viscosity of the ethyl ester was done using the method of AOAC
(1998). The ethyl ester was gradually poured into the viscometer until its lobe was almost
filled and then it was placed in a water bath and allowed to heat up to an equilibrium
temperature of 40oC. The ethyl ester on the broad arm was sucked through the narrow arm
until it reached the upper mark above the lower lobe of this narrow arm. The ethyl ester was
then allowed to flow back to the lower mark just below the lower lobe. The time taken for
60
the flow (flow time, t) was recorded. Then, the viscosity was determined using the formular
(Appendix 5.2);
Where n = Viscosity of the ethyl ester, mm2/s
v = Viscosity of water, mm2/s
ρ1 = Density of the ethyl ester, kg/m3
ρ2 = Density of water, kg/m3
t1 = Time taken for the ethyl ester to flow back
t2 = Time taken for water to flow back
2.2.7.1.4 Determination of the Cetane Number of the Ethyl Ester
The cetane number of the ethyl ester was determined according to the ASTM D 613 method.
The cetane number of the ethyl ester was calculated from the empirical formula suggested
by Mohibbe et al. (2005), using the result of saponification value (SV) and the iodine value
(IV) of the ethyl ester (Appendix 5.3):
CN = 46.3+ (5458/SV) - 0.225(IV)
2.2.7.1.5 Determination of the Flash Point of the Ethyl Ester
The flash point of the ethyl ester was determined according to the ASTM D 93 open cup
method. The cup was filled with a sample of the ethyl ester up to the mark (75ml) and the
cup was heated with a bunsen burner maintaining a small open flame from an external
supply of natural gas. Periodically, the flame was passed over the surface of the ethyl ester.
When the flash temperature was reached the surface of the ethyl ester caught fire. The
temperature (at the moment) was noted and recorded as the flash point temperature.
2.2.5.6. Determination of the Cloud Point of the Ethyl Ester
The cloud point of the ethyl ester was determined according to the ASTM D 5773 method.
The cloud point is a measure of the temperature at which components in the ethyl ester
begin to solidify out of the solution.
61
A test tube with a thermometer inserted in it, was filled with a sample of the ethyl ester. The
ethyl ester was cooled at 2oC/min rate and continuously monitored until a white cloud
appeared on the bulb of thermometer. The temperature that corresponds to the first
formation of a cloud in the ethyl ester was recorded.
2.2.7.1.7 Determination of the Pour Point of the Ethyl Ester
The pour point of the ethyl ester was determined according to the ASTM D 97-96a method.
A sample of the ethyl ester in a capillary tube was solidified; thereafter, it was attached to a
thermometer and inserted into a gradually heating beaker of water. The temperature at which
the sample started moving in the capillary tube was recorded.
2.2.7.1.8 Determination of the Ash Content of the Ethyl Ester
Determination of the ash content of the ethyl ester was done using the method of AOAC
(1998). A porcelain crucible which was washed, dried in an oven at 100oC, cooled in a
desiccators and weighed. An aliquot of the ethyl ester was transferred into the porcelain
crucible, weighed and then heated in a muffle furnace at 600oC for 4 hr. The residue left
after heating was cooled in a dessicator and weighed. The percentage ash content was
calculated using the formular (Appendix 5.4):
% Ash Content =
x = Weight of ash
w = Weight of sample
2.2.7.1.9 Determination of Refractive Index of the Ethyl Ester
The refractive index of the ethyl ester was determined with a refractometer. The power
switch was turned on; the illuminating lamp came up and the display showed 0000. A drop
of the oil was introduced on the working surface of the lower refracting prism. The rotating
arm and the collecting lens cone of the light gathering illuminating units were rotated so as
to make the light-intake surface of the upper light-intake prism to be illuminated evenly. The
field of view was observed through the eye piece and the adjustable hand wheel was rotated
62
so as to make the line dividing the dark and light areas fall in the cross line. The dispersion
correction hand wheel was rotated so as to get a good contrast between the light and dark
area and minimum dispersion. The read button was pressed and the refractive index was
displayed on the screen.
2.2.7.1.10 Determination of Conductivity of the Ethyl Ester
The conductivity of the ethyl ester was determined using a conductivity meter. The
conductivity meter was standardized with 0.01M KCl solution. The electrode was rinsed
with deionized water, wiped and dipped into a sample of the ethyl ester and left for some
time to stabilize the reading. The reading was displayed on the screen and then recorded in
micro Siemens per centimeter (µS/cm).
2.2.7.1.11 Determination of Heat of Combustion of the Ethyl Ester
The heat of combustion was determined according to the method of AOAC (1998) using a
bomb calorimeter. Benzoic acid was used to standardize the calorimeter. A weighed amount
of a sample of the ethyl ester (1.058g) was put in the crucible of the calorimeter and the fuse
wire was attached between the electrodes. Thereafter, it was placed in the bomb, which was
pressurized to 18atm of oxygen. The bomb was placed in a vessel containing a measured
quantity of water (2000g). The ignition circuit was connected and the water temperature was
noted. After ignition, the temperature rise was monitored every minute till a constant
temperature was reached and recorded. The pressure was released, the length of unburned
fuse wire was measured and the residue titrated with 0.7M of sodium carbonate solution
using phenolphthalein as indicator. The heat of combustion was calculated using the
formular (Appendix 5.5):
.
Heat of Combustion = g
VLTE −−∆ 3.2 (KJ/Kg)
Where E = Energy equivalent of the calorimeter using benzoic acid
∆T = Temperature rise
L = Length of burnt wire
V = Titration volume
g = Weight of sample
63
2.2.7.2 Chemical Characterization of Coconut Oil
2.2.7.2.1 Determination of Acid Value of the Ethyl Ester
The acid value of the ethyl ester was determined according to the ASTM D 664 method. To
determine the acid value of the ethyl ester, a 3g aliquot of it was dissolved in 25 ml of 1:1
mixture of ethanol and diethyl ether. The solution was titrated with 0.1N ethanolic KOH
solution in the presence of 5 drops of phenolphthalein as indicator until the end point
(colourless to pink) was recognized. The volume of 0.1 N ethanolic KOH (V) for the sample
titration was noted. The total acidity (acid number) in mg KOH/g was calculated using the
following formular (Appendix 5.6):
Acid value =
Where V = Volume of 0.1N solution of ethanolic KOH in milliliter (ml)
m = Weight of the sample in gram
N = Normality of ethanolic KOH
2.2.7.2.2 Determination of Saponification Value of the Ethyl Ester
The saponification value of the ethyl ester was determined using the method of AOAC
(1998). The ethyl ester (2.054g) was added to 25ml of 0.5N ethanolic potassium hydroxide
solution in a flask to which a reflux condenser was attached. The mixture was heated, and as
soon as the ethanol boiled, the flask was occasionally shaken using magnetic stirrer until the
ethyl ester was completely dissolved, and the solution was boiled for half an hour. After
completely dissolving the ethyl ester, 5 drops of phenolphthalein indicator was added and
the hot soap solution obtained was slowly titrated with 0.5N hydrochloric acid and volume
was recorded.
Then a blank determination was carried out upon the same quantity of potassium hydroxide
solution at the same time and under the same conditions and volume was recorded. The final
result was calculated using the formular (Appendix 5.7):
Saponification value =
64
Where W = Weight of oil taken in gram.
S = Sample titre value in ml
B = Blank titre value in ml
N = Normality of hydrochloric acid
2.2.7.2.3 Determination of Peroxide Value of the Ethyl Ester
The Peroxide value of the ethyl ester was determined using the method of AOAC (1998). To
determine the peroxide value, 2.16g of the ethyl ester was dissolved in 30 ml of a mixture of
glacial acetic acid and chloroform (3:2, v/v). Then, 20% of potassium iodide (0.5 ml) was
added and the solution swirled in the dark for one minute after which 75ml of distilled water
was added. The mixture was titrated with 0.1M sodium thiosulphate with vigorous shaking
until the yellow colour of the iodine had disappeared. Starch indicator (0.5ml) was added
then to obtain a blue colour and titration continued until all the blue colour had disappeared.
The peroxide value (PV) was determined from the formular (Appendix 5.8):
Peroxide value =
Where S = Sample titre value in ml
B = Blank titre value in ml
M = Molarity of sodium thiosulphate
2.2.7.2.4 Determination of Iodine Value of the Ethyl Ester
The iodine value of the ethyl ester was determined using the method of AOAC (1998). An
aliquot of the ethyl ester (0.8633g) was weighed into a conical flask, tetrachloromethane
(15ml) and 25 ml of Wij’s solution was added. This mixture was placed in a stoppered
conical flask, swirled gently and placed in a dark cupboard for one hour after which 20 ml of
20% potassium iodide solution and 100ml of distilled water were added. After gentle
shaking, liberated iodine was titrated with 0.1M sodium thiosulphate solution until the
yellow colour of the iodine had appeared. Starch indicator (1ml) was added then to obtain a
blue colour and titration continued until all the blue colour had disappeared. The iodine
value was determined from the formular (Appendix 5.9):
65
Iodine value =
Where B = Blank titre value in ml.
S = Bample titre value in ml
M = Molarity of sodium thiosulphate
2.2.8 Investigation of the Trans-esterification Reaction Rate
2.2.8.1 Experimental Design
The experiment was designed to determine the reaction rate constants for the
transesterification of the following varied oil/ethanol volumetric ratio of 1:6, 1:3, 1:2, 1:1.5
and 1:1. The ethanolysis was conducted at fixed reaction temperature (65oC), catalyst
concentration (0.1g), stirring rate (maximum level of the equipment) and the reaction time of
90 minutes. These conditions were chosen based on the recommendation of Rahayu and
Mindaryani (2009). For each ethanolysis or transesterification, samples of 10mls were
withdrawn at 10, 20, 40, 60 and 90 mins reaction time. The reaction in the sample was
stopped by immersing it in cold water before the glycerol content was analyzed using UV-
visible spectrophotometer.
2.2.8.2 Analysis of Ethyl Ester Using UV-Visible Spectrophotometer
Principle
The amount of free glycerol in biodiesel can be measured with a UV-visible
spectrophotometer using a two-step reaction process according to the method of Bondioli
and Bella (2005). This results in the formation of a yellow complex proportional to the
amount of free glycerol in the sample. The sample is first treated with sodium periodate.
Sodium periodate reacts with free glycerol in the sample to generate formaldehyde. Reaction
between this formaldehyde and acetyl acetone produces the yellow complex, 3,5-diacetyl-
1,4-dihydrolutidine. This yellow compound exhibits a maximum absorbance at 410 nm,
where its concentration in the sample is measured.
66
Procedure
A solvent solution containing a 1:1 ratio of deionized water and 95% ethanol, and a
reference solution of 0.036 mg/ml glycerol in solvent was prepared. A series of six glycerol
reference standards was then prepared from these solutions as shown in Table 5, to obtain a
glycerol standard curve (Appendix 6). A pretreated biodiesel sample was mixed 1:4 with
solvent to get 2 ml of working sample solution.
Table 5: Glycerol standard preparation and absorbance results
standards Glycerol Reference Solution (ml) Solvent Solution (ml) Final Concentration
of Glycerol (mg/kg)
1 0.0 2.00 0.00
2 0.25 1.75 3.75
3 0.50 1.50 7.50
4 0.75 1.25 11.25
5 1.0 1.00 15.00
6 1.25 0.75 18.75
Each working standard and the sample were treated with 1.2 ml of a 10 mM sodium
periodate solution and shaken for 30 secs. Each solution was then treated with 1.2 ml of 0.2
M acetylacetone solution, placed in a water bath at 70 °C for 1 min and stirred manually.
The solutions turned yellow (Fig. 9) and were immediately placed in cold water to stop the
reaction. Absorbance of standards and samples were measured at 410 nm using a UV–
visible spectrophotometer. Standard 1 is a control sample and also used as the blank.
St Fig. 9: Appearance of the yellow colour in the standard and test samples
67
CHAPTER THREE
RESULTS
3.1 Result of Percentage Moisture Content, Oil Yield and Ethyl Ester Yield
Table 6 shows the percentage moisture content of the kernel, the percentage yield of the oil
after extraction and the percentage ethyl ester yield after transesterification of the coconut
oil with ethanol using sodium hydroxide as catalyst. The result revealed the moisture content
of 14.99% while the oil yield and ethyl ester yield were 14.13 and 89.55% respectively.
Table 6: Result of percentage moisture content, oil yield and ethyl ester
Parameter % value
Moisture content of kernel 14.99
Oil yield 44.13
Ethyl ester yield 93.90
68
3.2 Physicochemical Properties of the Coconut Oil
3.2.1 Physical Properties of the Coconut Oil
The physical characterization of the coconut oil extracted gave the physical properties as
summarized in Table 7. The result showed that the coconut oil has a specific gravity of
0.8825 and viscosity of 35.04 mm2/s at 40
oC. The flash point, cloud point and pour point of
oil are 220oC, 24
oC and 23
oC respectively.
Table 7: Physical properties of the coconut oil
Parameter Result
Colour
Specific gravity
Viscosity (mm2/s) at 40
oC
Flash point (oC)
Cloud point (oC)
Pour point (oC)
Volatile matter (%)
Refractive index
Heat of combustion (MJ/kg)
Pale yellow
0.88
35.04
220
24
23
99.72
1.46
35.60
69
3.2.2 Chemical Properties of the Coconut Oil
The chemical properties of the coconut oil in table 8 revealed an acid value of 2.24
mgKOH/g, saponification value of 273.38 mgKOH/g, peroxide value of 3.02 meq/kg, iodine
value of 9.11 mgI2/g and free fatty acid content of 5.64%.
Table 8: Chemical properties of the coconut oil
Parameter
Acid value (mgKOH/g)
Saponification value (mgKOH/g)
Peroxide value (meq/kg)
Iodine value (mgI2/g)
Free Fatty Acid (%)
value
2.24
273.38
3.02
9.11
5.64
70
3.3. Physicochemical Properties of the Coconut Oil Ethyl Ester
3.4.1 Physical Properties of the Coconut Oil Ethyl Ester
Table 9 shows the physical properties of the coconut oil ethyl ester, the result revealed a
specific gravity (0.86), viscosity (6.00 mm2/s), cetane number (71), flash point (132
oC),
cloud point (-5oC), pour point (-10
oC), ash content (0.02%), refractive index (1.43)
conductivity (0.00 µS/cm) and heat of combustion (36.79 MJ/kg).
Table 9: Physical properties of the coconut oil ethyl ester
Parameter Result
Colour
Specific Gravity
Viscosity (mm2/s) at 40
oc
Cetane Number
Flash Point (oC)
Cloud Point (oC)
Pour Point (oC)
Ash Content (%)
Refractive Index
Conductivity (µS/cm)
Heat of Combustion (MJ/kg)
colourless
0.86
6.00
71
132
-5
-10
0.02
1.43
0.00
36.79
71
3.3.2 Chemical Properties of the Coconut Oil Ethyl Ester
Table 10 shows the chemical properties of the coconut oil ethyl ester. The result revealed an
acid value of 0.25 mgKOH/g, saponification value of 218.08 mgKOH/g, peroxide value of
1.50 meq/kg and iodine value of 1.91 mgI2/g.
Table 10: Chemical properties of the coconut oil ethyl ester
Parameter
Acid value (mgKOH/g)
Saponification value (mgKOH/g)
Peroxide value (meq/kg)
Iodine value (mgI2/g)
value
0.25
218.08
1.50
1.91
72
3.4 Investigation of the Trans-esterification Reaction Rate
The progress curve for the trans-esterification of varied oil/ethanol volumetric ratio of 1:6,
1:3, 1:2, 1:1.5 and 1:1, showed that as the reaction time increased the concentration of
glycerol produced during the reaction increased (indicating progress of the reaction) until it
came to a point at which the curve became horizontal (indicating the end point/ completion
of the reaction or depletion of the oil) as presented in Fig.10 to 14. The determinations of the
rate constant are shown in Appendix 7.1 to 7.5.
The 1:6 oil/ethanol volumetric ratio trans-esterification showed that increase in the reaction
time was accompanied by increase in glycerol concentration at the rate of 0.415 mg/kg/min
for 40 mins, after which subsequent increase in the reaction time gave little or no increase in
the concentration of glycerol.
It was observed in the 1:3 oil/ethanol volumetric ratio trans-esterification that as the reaction
time increased, the concentration of glycerol increased at the rate of 0.3616 mg/kg/min for
60 mins. Thereafter, little increase was observed as the reaction time increased to 90 mins.
The progress curve for 1:2 oil/ethanol volumetric ratio trans-esterification showed that
increase in the reaction time gave increase in the concentration of glycerol at the rate of
0.2135 mg/kg/min for 60 mins reaction time, after which the glycerol concentration showed
no increase on further increase if the reaction time. A slight decrease was observed at 40
mins reaction time.
The 1:1.5 oil/ethanol volumetric ratio trans-esterification showed that increase in the
reaction time was accompanied by increased glycerol concentration at the rate of 0.1833
mg/kg/min 60 mins, after which subsequent increase in the reaction time gave little or no
increase in the concentration of glycerol.
It was observed that the 1:1 oil/ethanol volumetric ratio trans-esterification proceeded at the
rate of 0.1006 mg/kg/ min for 60 mins. Thereafter, the concentration of glycerol remained
fairly constant on further increase of the reaction time.
73
3.4.1. Progress Curves for the Trans-esterification of Varied Oil/Ethanol Volumetric
Ratio
Fig. 10: Progress curves for the trans-esterification of the varied oil/ethanol volumetric ratio
1:6
1:3
1:2
1:1.5
1:1
74
3.5 Reaction Rate Constant for varying Oil-to-Ethanol Volumetric Ratios
Fig. 15 shows the oil to ethanol ratio-dependent increase in the specific rate constant. The
highest reaction rate constant (0.415) was observed in 1:6 oil to ethanol volumetric ratio
while the lowest (0.1006) was observed in 1:1 oil to ethanol volumetric ratio.
Fig. 15: Reaction rate constant for varying oil-to-ethanol volumetric ratios
75
3.6 Determination of Kinetic Parameters (km and vmax) of the Trans-esterification
Reaction
The result obtained from the effect of varied oil to ethanol ratio on NaOH catalysed trans-
esterification was used for the Lineweaver-Burk plot. The kinetic parameter (km and vmax)
of the NaOH catalysed trans-esterification were calculated from the Lineweaver-Burk plot.
Fig. 16 revealed that the km and vmax of the reaction are 6.25 ml/ml ratio and 0.94
mg/kg/min respectively. [S] Represent ethanol volumetric ratio.
Fig. 16: Lineweaver-Burk plot of NaOH catalysed trans-esterification reaction
76
CHAPTER FOUR
DISCUSSION
The moisture content is an important parameter as it affects the percentage yield of the oil
during extraction. High moisture content could lead to reduction of oil yield (Mansor, et al.,
2012). The percentage moisture content of the coconut kernel was found to be 14.99%; the
high moisture content of the coconut kernel lead to the sun-drying of the kernel before
extraction in order to obtain optimum yield. Afolabi (2008) observed that the moisture
content of the coconut oil was found to be lower than that of fresh groundnut (37.002%) but
higher to those of almond nut (5.006%), castor seed (3.500%) and palm kernel seed
(4.870%). Oil was extracted from coconut (Cocos nucifera) copra using n-hexane. The yield
of the oil extracted from the coconut was 44.13%. The oil yield of the seeds as suggested by
the result, showed that coconut (Cocos nucifera) seeds have higher oil yield than fluted
pumpkin seed (33.732%), soybean (36%). This result is consistent with the findings of Eze
(2012) who observed that the value was almost the same to that of palm kernel (45.60 %)
and may be considered economical for commercial production of oil in Nigeria.
The physical characterization of the coconut oil showed a pale yellow colour. The colour
was the same with that reported by Akubugwo et al. (2008) and Eze (2012) for coconut oil.
The specific gravity of the oil was 0.88. This value was found to be slightly lower than that
reported by Alamu et al. (2010) for coconut oil (0.91), Lang, et al. (2001) for canola oil
(0.912) and sunflower oil (0.914); this could be due to location and variation in speices. The
result was almost the same with that of jatropha oil (0.8813) as reported by Belewu et al.
(2010). Viscosity of oil is the measure of the resistance of the oil to flow (Sanford et al.,
2009). The viscosity of the coconut oil at 40oC was found to be 35.04 mm
2/s; this high
viscosity of vegetable oils and animal fats ultimately lead to operational problems such as
engine deposits when used directly as fuels (Knothe and Steidley, 2005a). The viscosity of
the coconut oil was found to be lower to those of rapeseed oil (45.01 mm2/s) as reported by
Lang et al. (2001) and coconut oil at room temperature (43.30 mm2/s) as observed by Alamu
et al., (2010), but was higher than that reported by Kumar, et al., (2010) for coconut oil
(27.23mm2/s), Jatropha curcas oil (20.49 mm
2/s) and linseed oil (22.4 mm
2/s) as reported
by Belewu et al. (2010) and Lang, et al. (2001) respectively. The flash point is the lowest
77
temperature at which the oil emits enough vapour to ignite and it is a measure of the
volatility and flammability of the oil (Bello et al., 2011). The flash point of the oil was
220oC; the high flash point of the oil was as a result of its high viscosity. The flash point was
found to be low when compared to that reported by Kumar, et al. (2010) for coconut oil
(266oC) and sunflower oil (274
oC) as observed by Shereena and Thangaraj (2009), but was
higher than that of Babassu (150oC) as reported by Shereena and Thangaraj (2009). The
volatile matter is the measure of the true organic matter in the oil and gives information on
the volatility of the oil. This was found to be 99.72% for the coconut oil and implies that the
oil contains high amount of volatile organic matter which is an advantage for its use for
biodiesel production. The volatile matter of the coconut oil was found to be higher than that
observed by Ozioko (2012) for soya bean oil (72.27%) and Danish pine as reported by
Jahirul et al. (2012).
The cloud point is the temperature at which crystals first appear in the oil when cooled
(Dermirbas, 2009). This was found to be 24oC for the coconut oil and this implies that the
oil cannot be used in low temperature regions. The cloud point was high when compared to
that of peanut oil (12.8oC) and safflower oil (18.3
oC) as reported by Shereena and Thangaraj
(2009) but lower to that of palm (31oC) as observed by Shereena and Thangaraj (2009). The
pour point of oil is the lowest temperature at which the oil can flow (Dermirbas, 2009). This
was found to be 23oC for the coconut oil which also implies that the oil cannot be used
directly as fuel in regions where the temperature is below 23oC. The pour point was much
higher than that reported by Kumar, et al. (2010) for coconut (-6oC) soya bean (12.2
oC) by
the findings of Shereena and Thangaraj (2009) and most of other vegetable oils. The high
cloud and pour point of coconut oil indicates that the oil contains high proportion of
saturated fatty acids.
The heat of combustion measures the energy content in a fuel. It is an important property of
the biodiesel that determines the suitability of the fuel as an alternative diesel fuel (Sokoto et
al., 2011). The heat of combustion of the coconut oil was found to be 35.60MJ/kg. This
result is supported by the findings of Lang et al. (2001) which observed that this value was
found to be lower than those of canola oil (39.78 MJ/kg), sunflower oil (39.46 MJ/kg),
rapeseed oil (40.27 MJ/kg) and linseed oil (39.51 MJ/kg). The refractive index is the ratio
78
of the velocity of light in vacuum to the velocity of light in a medium which is an indication
of the level of saturation of the oil and also gives information on the purity of the oil
(Oderinde et al., 2009). The refractive index of the coconut oil found to be was 1.46, this
value was high when compared to that reported by opoku-Boahen et al. (2012) for coconut
oil (1.4450) and the recommended range for coconut oil by the Codex Standards (1.448-
1.450). The slight increase above the Codex Standard could be as a result of some impurities
and other components of the oil mixture.
This low value may be due to little or absence of water and low level of free fatty acids.
Thus, acid value is a measure of free fatty acid content due to hydrolytic activity and it
assesses the quality of the oil (Afolabi, 2008). The acid value was lower than that of coconut
oil (9.537 mgKOH/g) and groundnut oil (3.82 mgKOH/g) as reported by Opoku-Boahen et
al. (2012), but higher than those of castor seed oil (0.279 mgKOH/g), palm kernel seed oil
(0.834 mgKOH/g) and almond oil (0.770 mgKOH/g) as reported by Afolabi (2008).
Similarly, the value was almost the same to that reported by Kumar, et al. (2010) for
coconut oil (2.1 mgKOH/g). The percentage free fatty content was found to be 5.64%. The
value is higher than that reported by Akubugwo et al. (2008) for coconut oil (4.80%) and
other edible oils such as pumpkin (1.98%), breadfruit seed oil (4.22%) and oil bean seed oil
(1.40%), but was lower than that of Jatropha oil (14.8%) based on the search findings of
Mohammed-Dabo et al. (2012) and almost the same to that of avocado seed oil (5.77%) as
observed by Akubugwo et al. (2008). However, if the oil samples have high Free Fatty Acid
content (more than 1%) then the reaction requires more alkali catalyst to neutralize the Free
Fatty Acid or pretreatment with an acid catalyst (Zhang et al., 2003a). This suggests that
there should be acid pretreatment of the oil prior to base catalysed trans-esterification.
Saponification value is a measure of the average molecular weight or the chain length of the
fatty acids present in the oil (Sanford et al., 2009). It had been reported to be inversely
related to the average molecular weight of the fatty acids in the oil fractions (Abayeh et al.,
1998). The saponification of the coconut oil was found to be 273.38 mgKOH/g; this high
value implies a low average molecular weight. Akubugwo et al. (2008) had observed lower
saponification value (246 mgKOH/g) compared with value reported in this study. In the
same vien, similar trend was reported for jatropha seed oil (202.34 mgKOH/g) (Mohammed-
79
Dabo et al., 2012), palm kernel oil (191.97 mgKOH/g) (Afolabi, 2012) and bread fruit oil
(221.59mgKOH/g) (Eze, 2012).
Iodine value is a measure of the degree of unsaturation of the oil (Belewu et al., 2010). The
iodine value of the coconut oil was found to be 9.11 mgI2/g. This value was found to be
within the recommended range for coconut oil by the Codex Standards (6.3-10.6 mgI2/g)
and almost the same to that reported by Akubugwo et al. (2008) for coconut oil (9.60
mgI2/g) but lower than that of fluted pumpkin seed oil (49.4 mgI2/g) as observed by
Akubugwo et al. (2008). The low iodine value is indicative of low content of unsaturated
fatty acids. Peroxide value is an indicator of deterioration and oxidative stability/rancity
(Eze, 2012) of the oil. Fresh oils have peroxide values less than 10 meq/kg but peroxide
values between 20 and 40 result to rancid taste (having a disagreeable odour) (Akubugwo et
al., 2008). The peroxide value of the coconut oil was found to be 3.02 meq/kg; this low
value could have resulted from low content of unsaturated fatty acids in the oil, proper
storage and handling of the oil during and after extraction to avoid contaminants and factors
that enhance autoxidation of the oil. The peroxide value was lower when compared to that
reported for coconut seed oil (10.562 meq/kg), soya bean oil (16.32meq/kg), melon oil
(8.386 meq/kg) and palm kernel oil (7.96meq/kg) (Eze, 2012), but higher than those of
breadfruit (1.75meq/kg), oil bean (2.35meq/kg) (Akubugwo et al., 2008) and groundnut seed
oil (1.03meq/kg) (Eze, 2012).
Anastopoulos et al. (2009) revealed that the coconut oil ethyl ester yield was higher than
those of rapeseed ethyl esters yield (81.4%), olive oil ethyl esters (82.6%) while Alamu et
al. (2012) showed that coconut oil methyl esters yield was (10.4%). However, Rashid et al.
(2010) showed lower value compared to that of jatropha oil methyl esters (96.8%).
The physical characterization of the coconut oil ethyl esters showed a colourless colour. The
specific gravity of the coconut ethyl ester was 0.86; this value was lower than that of the oil.
The specific gravity obtained was found to be within the limits of EN 14214 (0.86 – 0.90)
biodiesel fuel standard. The specific gravity was found to be lower than those of palm kernel
oil ethyl esters (0.883), rapeseed oil ethyl esters (0.876) (Alamu et al., 2008), and sunflower
oil ethyl esters (0.876) (Lang et al., 2001), but was higher than that of petrol diesel (0.853)
80
(Alamu et al., 2008) and almost the same with that of canola oil ethyl esters (0.869) (Lang et
al., 2001). The viscosity of the coconut oil ethyl esters at 40 °C was 6.00 mm2/s; this value
is far lower than that of the oil, but was found to be within the limits of ASTM D6751 (1.9 –
6.0 mm2/s) biodiesel fuel standard. The viscosity of the coconut oil ethyl ester was found to
be higher than those of Jatropha oil biodiesel (4.80 mm2/s) as report by Rashid et al. (2012),
canola oil ethyl esters (4.892 mm2/s) (Alamu et al., 2008), olive oil ethyl esters (4.00
mm2/s), (Anastopoulos et al., 2009), but slightly higher than that of rapeseed ethyl esters
(6.170 mm2/s) (Alamu et al., 2008). The flash point of the coconut oil ethyl ester was 132
oC;
this value was lower than that of the oil due to the low viscosity of ethyl ester. The value
was also found to be above the minimum value (120 °C) of the EN 14214 and (130oc) of the
ASTM D6751 biodiesel fuel standard. The flash point of the coconut oil ethyl ester was
reported by Alamu et al. (2008) to be lower than that of palm kernel oil biodiesel (167°C)
but was higher than those of canola ethyl esters (177oC), sunflower ethyl esters (178
oC),
olive ethyl ester (182oC), and rapeseed ethyl ester (181
oC) as observed by Anastopoulos et
al. (2009). In the same vein, Alamu et al. (2008) found out that the flash point was
extremely higher than that of petrol diesel with a value of 74°C. These relatively higher
flash point values of coconut oil ethyl ester is indicative of the presence of little or no
residual alcohol and is of prime importance for prevention of fire outbreak in the compressor
engine when used as fuel, also important for storage and transportation of the fuel (Moser,
2009).
The cloud point of the coconut oil ethyl ester was -5oC and this was far lower than that of
the oil, but was within the limits of ASTM D6751 (-3 to 12oC) biodiesel fuel standard.
Alamu et al. (2008) reported that the cloud point was higher compared to that of canola
ethyl esters (-6oC), rapeseed ethyl esters (-10
oC) and extremely higher than that of petrol
diesel (-12oC) but lower to those of palm kernel oil biodiesel (6
oC), kumar et al. (2010)
reported -3oC for coconut methyl esters and Lang et al. (2001) reported -1
oC for sunflower
ethyl ester. The pour point of the coconut oil ethyl ester was found to be -10oC; this was also
far lower than that of the oil. The lowered pour point and cloud point implies that the
coconut oil ethyl ester can be used as fuel in regions where the temperature is within the
range of -5 to -10oC. The pour point of the coconut oil ethyl ester was found to be within the
81
limits of ASTM D 6751 (-15 to 10oC) biodiesel fuel standard. The value was lower
compared to those of sunflower ethyl esters (-6oC), rapeseed ethyl esters (-8
oC) and olive
ethyl esters (-5oC) as reported by Anastopoulos et al. (2009), but higher than that of petrol
diesel which is -12oC as shown by Alamu et al. (2008) and coconut methyl esters (12
oC)
being reported by Kumar et al. (2010).
Bello et al. (2011) pointed out that cetane number is one of the primary indicators of a good
diesel fuel quality and is related to the ignition delay time a fuel experiences once injected
into a diesel engine combustion chamber. The coconut oil biodiesel had empirically
calculated cetane number of 71 which is above the minimum value of the ASTM D6751 (40
minimum) and EN 14214 (51 minimum) international biodiesel fuel standards. The cetane
number of the coconut oil biodiesel (ethyl ester) was found to be higher than some
conventional biodiesels such as jatropha oil biodiesel (55) (Reddy and Ramesh, 2005), waste
cooking oil biodiesel (10.96) (Owolabi et al., 2011) and that reported for coconut biodiesel
(51) (Kumar, et al., 2001). Thus, the higher cetane number of coconut oil ethyl ester
indicates a shorter ignition delay time.
The ash content is a measure of the amount of residue left when the fuel is heated to 600oC
(Sanford et al., 2009); this was found to be 0.02% for the coconut oil ethyl ester. The ash
content of the coconut oil ethyl ester was found to be above the limit of ASTM D 6751
(0.01%), but was within the limit of EN 14214 (0.02%) biodiesel fuel standard. The ash
content of the coconut oil ethyl ester was also comparable to that of jatropha (0.016%) as
reported by Rashid et al. (2010). The slight increase of the ash content of the coconut oil
ethyl ester above the biodiesel fuel standard could be as a result of the presences of little
amount of metal contaminants. The heat of combustion of the coconut oil ethyl ester was
36.79 MJ/kg. Although, this value was lower than that of petrol diesel (45MJ/kg) as reported
by Lang et al. (2001), the heat of combustion of the coconut oil ethyl ester was comparable
to those of sunflower (38.6 MJ/kg), olive oil ethyl ester (39.2 MJ/kg) (Anastopoulos et al.,
2009) rapeseed oil ethyl ester (40.97 MJ/kg) and linseed oil ethyl ester (39.65 MJ/kg) as
reported by Lang et al. (2001).
82
This value was almost the same to that of palm oil methyl ester (1.430) and ghee methyl
ester (1.431) (Deshpande and Kulkarni, 2012), but lower than that of groundnut oil methyl
ester (1.463; Ibeto et al., 2011).The refractive index of petrodiesel was found to be 1.425
and from observations, biodiesel has refractive index of 1.430 to 1.431; these values indicate
that heavier molecules get converted into lighter one during transesterification process
(Deshpande and kulkarni, 2012). The slight increase above the normal range could be as a
result of the presence of some impurities. Conductivity is a measure of the ability of water to
pass an electrical current, it is indicative of the presence of water in the biodiesel (Sanford et
al., 2009). The conductivity of the ethyl ester was 0.00 µS/cm, this could be due to proper
drying and short storage time before the test was carried out.
The acid values of the coconut oil ethyl ester was found to be within the limits of the ASTM
D6751 (0.5 mgKOH/g maximum) and EN 14214 (0.5 mgKOH/g maximum) biodiesel fuel
standards and almost the same to that of canola oil ethyl ester (0.265 mgKOH/g) (Lang et
al., 2001). The acid value of the coconut oil ethyl ester was lower to those of sunflower oil
ethyl ester (0.610 mgKOH/g), linseed oil ethyl ester (0.324 mgKOH/g) as observed by Lang
et al. (2001) and rapeseed oil ethyl ester (1.02 mgKOH/g) as reported by Anastopoulos et al.
(2009). The acid value of the coconut oil ethyl ester was also lower to that of its oil but
higher than that reported for coconut oil methyl ester (0.18 mgKOH/g) as observed by
Kumar et al. (2010). The low acid value of the coconut oil ethyl ester indicates that the fuel
contains relatively little or no water which could hydrolyse the biodiesel to free fatty acids.
It could also indicate that the acid pretreatment done reduced the free fatty to the minimal.
This high value, though, lower than that of the coconut oil, indicates a low average
molecular weight. The saponification value of the coconut oil ethyl ester was found to be
higher than that of sunflower oil ethyl ester (192.1 mgKOH/g), rapeseed oil ethyl ester
(170.4 mgKOH/g), olive oil ethyl ester (196.2 mgKOH/g) and used frying oil ethyl ester
(193.2 mgKOH/g) (Anastopoulos et al., 2009).
The iodine value of the coconut oil ethyl ester was found to be 1.91 mgI2/g; this implies
lower degree of unsaturation and better oxidative stability of the coconut oil ethyl ester. The
iodine value of the coconut oil ethyl ester was found to be within the limits of EN 14214
83
(120 mgI2/g maximum) biodiesel fuel standard, but was lower than that of Jatropha methyl
ester (104 mgI2/g) (Singh and Padhi, 2009). The peroxide value of the coconut oil ethyl
ester was 1.50 meq/Kg. This value was lower when compared to that of the coconut oil and
groundnut oil methyl ester (3.23 meq/kg) as reported by Ibeto et al. (2011). The low
peroxide value of the coconut oil ethyl ester could be as a result of low level of unsaturated
fatty acids (as indicated by the iodine value of the ethyl ester). Also, proper storage and
handling of the coconut oil ethyl ester to avoid contaminants and factors that enhance
autoxidation could have contributed to the low peroxide value.
The investigation of the reaction rate constant of the trans-esterification of the varied oil to
ethanol volumetric ratio of 1:6, 1:3, 1:2, 1:1.5 and 1:1 showed that as the oil-to-ethanol
volumetric ratio increases from 1:1 to 1:6 the rate of trans-esterification increases with the
highest reaction rate constant of 0.415 at a ratio of 1:6 oil to ethanol. This could be due to
the fact that in a reversible reaction such as that of trans-esterification, at equilibrium, there
is a balance between the concentration of the reactants and products. If the volume of
ethanol is increased or more reactants are introduced into the equilibrium system, the
balance is disturbed. In order to relieve this restriction, the equilibrium position will shift to
the right, favouring the forward reaction or production of more esters as proposed product
(Dorado et al., 2004). This gives trans-esterification reaction an upper hand over
saponification (a side reaction of the process). However, a greater portion of the oil becomes
trans-esterified thereby resulting in higher concentration of glycerol/ high reaction rate
constant as seen as the oil to ethanol ratio increases from 1:1 to 1:6 (Figs 10 to 14). This
finding is in agreement with the work of Hossain and Al-saif (2010) where the effect of
volumetric ratio of oil to methanol and ethanol was investigated using percentage yield of
biodiesel. The results showed that the highest biodiesel yield was nearly 99.5% at 1:6
oil/methanol and 98.0% at 1:6 oil/ethanol. The work of Ehiri (2012) indicates that the yield
increases with increase in reactant ratio from 1:1 to 8:1 and decsreases thereafter from 9:1 to
10:1; with an optimal methyl ester yield of 95% occurred at 8:1 methanol: oil volume ratio.
The trans-esterification of coconut oil with ethanol using NaOH as catalyst also showed that
the reaction was almost completed after 1 hr, beyond this gave a small ethyl ester yield with
exception of the 1:6 volumetric ratio trans-esterification that was almost completed before 1
84
hr reaction time. This is in agreement with the work of Krishnakumar et al. (2008) where the
effect of reaction time was studied from 45 minutes to 120 minutes on the methyl ester
(biodiesel) yield. It was found that ester yield increased as the reaction time increases.
However if the reaction time is increased beyond 1 hour, the increase in the yield of ester is
small.
The catalysis of NaOH in the trans-esterification reaction was described using enzyme
kinetics (Lineweaver-Burk plot) owing to the fact that both are catalyst. Thus, it increases
the rate of a reaction without itself being consumed by the process. The kinetic parameters
from the Lineweaver-Burk plot were found to be 0.94 mg/kg/min and 6.25 ml/ml ratio (oil
to ethanol ratio) for Vmax and Km respectively. The Vmax (maximum velocity/rate) is the
maximum attainable rate of the reaction. The Vmax gives information on the rate at which
the product is formed (turnover number) (Anosike, 2001). It also gives information on how
efficient a catalyst is, in catalyzing a particular reaction. The Km or Michealis constant is the
substrate concentration at half the maximum velocity/rate (Vmax). It establishes the
relationship between the catalyst and its affinity for its substrate. A small Km value indicates
that the catalyst requires only a small amount of the substrate to become saturated; hence,
the maximum velocity is reached at relatively low substrate concentration while a large Km
indicates the need for high substrate concentration to achieve the maximum velocity
(Anosike, 2001).
4.2 Conclusion
The results obtained suggest that the coconut oil could be considered a viable raw material
for biodiesel production; this is due to the fact that its ethyl ester (biodiesel) meets the
standard specification of the American Society for Testing and Material (ASTM). The base
catalyzed transesterification reaction of coconut oil with ethanol gave higher yield of
biodiesel at higher oil to ethanol volume ratios. HoweverS, it is advised to increase the
concentration/volume of the alcohol than that of the oil because increase in the oil
concentration/volume favours saponification reaction which is a side reaction to the overall
process. This side reaction depletes the oil in the reaction; thereby, reducing the yield of
biodiesel.
85
4.3 Suggestions for Further Studies
Based on the findings of this work, the following suggestions are made for further studies:
• Process optimization study of ethanolysis of coconut oil using 1:6 oil/ethanol ratio,
such as the best amount of catalyst, temperature, reaction time, and/or agitation
intensity for the transesterification reaction.
• Further research on the use of variety of tools such as plant breeding, molecular
breeding, genetic modification and biotechnology as potential strategy for the
improvement of oil yield of coconut and fuel properties of coconut oil biodiesel, to
meet the increasing demand of biodiesel and food needs (since it an edible oil).
86
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APPENDICES
Appendix 1: Percentage Moisture Content of the Kernel
Original weight of the sample before drying (W1) = 10.2
Weight of the sample after drying (W2) = 8.87
% Moisture Content = = = 14. 994%
Appendix 2: Percentage Yield of Oil
% yield of oil =
= =44.125%
Appendix 3: Calculations for physicochemical characterization of oil
3.1 Specific Gravity of Oil
Density of oil =
= =0.8825g/ml
Specific Gravity of oil =
= = 0.8825
3.2 Viscosity of Oil
Viscosity of the oil at 40oc =
100
ν= viscosity of water = 1.005
ρ1=density of sample = 0.8825g/ml
ρ2= density of water = 1.00g/ml
t1=time taken for sample to flow back = 1987 sec
t2=time taken for water to flow back = 50.3 sec
=
= 35.04cst = 35.04mm2/s
3.3 Percentage Volatile Matter of Oil
Weight of empty crucible = 10.014g
Weight of empty crucible + sample = 13.204g
Weight of sample (w) = 3.190g
Weight of crucible + dry matter after oven drying for 5hrs at 105oc = 13.199
Weight of dried oil after oven drying at 105oc (x) = 3.185g
Weight of crucible + residue after drying in the furnace for 10mins at 600oc = 10.018
Weight of residue after further heating at 600oC (y) = 0.004
% volatile matter =
= = 99.72%
3.4 Heat of Combustion of Oil
Initial temperature = 30.218
Final temperature = 32.978
Energy equivalent of the calorimeter (E) = 13039.308
Temperature rise (∆T) = 32.978-30.218 = 2.760
101
Length of unburnt wire = 3.9+3.5 =7.4cm
Length of burnt wire (L) = 10-7.4 = 2.6cm
Titration volume (V) = 4.3
Weight of sample (g) = 1.011
Heat of Combustion = g
VLTE −−∆ 3.2 = =
35595.312kJ/kg
= 35.595MJ/kg
3.5 Acid Value of Oil
Volume of KOH 1st 2nd 3rd
Initial reading 32.00 33.00 40.00
Final reading 32.90 33.80 40.70
difference 0.90 0.80 0.70
Average titre = = 0.8
Acid Value = = = 2.244
3.6 Saponification Value of Oil
Volume of HCl (ml) Sample blank
1st 2nd 3rd 1st 2nd 3rd
Initial reading 22.50 23.40 24.10 17.50 10.00 16.50
Final reading 23.40 24.10 24.70 40.00 32.20 38.50
difference 0.90 0.70 0.60 22.50 22.20 22.00
Average titre for sample = = 0.7333ml
Average titre for sample = = 22.233ml
102
Saponification value = =
=273.38
3.7 Peroxide Value of Oil
Volume of sodium
thiosulfate (ml)
Sample blank
1st 2nd 3rd 1st 2nd 3rd
Initial reading 18.20 17.90 18.60 14.30 14.10 15.50
Final reading 18.60 18.20 18.80 14.70 14.30 15.60
difference 0.40 0.30 0.20 0.40 0.20 0.10
Average titre for sample = = 0.3ml
Average titre for blank = = 0.2333ml
Peroxide value = = = 3.024meq/kg
3.8 Iodine Value of the Oil
Volume of
sodium
thiosulfate (ml)
Sample blank
1st 2nd
3rd 1st 2nd 3rd
Initial reading 0.00 0.00 0.00 0.00 0.00 0.00
Final reading 39.50 40.10 40.90 45.00 48.20 46.30
difference 39.50 40.10 40.90 45.00 48.20 46.30
Average titre for sample = = 40.167ml
Average titre for blank = = 46.5ml
Iodine value = = = 9.107
103
3.9 Percentage Free Fatty Acid of Oil
Volume of KOH 1st 2nd 3rd
Initial reading 34.00 35.00 36.00
Final reading 34.50 35.40 36.30
difference 0.50 0.40 0.30
Average titre = = 0.4
% Free Fatty = = = 5.64%
Appendix 4: Percentage Yield of Ethyl Ester
% yield of ethyl ester =
= =93.90%
Appendix 5: Calculations for the physicochemical characterization of the Ethyl Ester
(biodiesel)
5.1 Specific Gravity of the Ethyl Ester
Density of ethyl ester =
= =0.8633g/ml
Specific Gravity Ethyl Ester =
= = 0.8633
104
5.2 Viscosity of the Ethyl Ester
Viscosity of the Ethyl Ester at 40oc =
=
ν= viscosity of water = 1.005
ρ1=density of sample = 0.8825g/ml
ρ2= density of water = 1.00g/ml
t1=time taken for sample to flow back = 1987 sec
t2=time taken for water to flow back = 50.3 sec
=
= 6.00cst = 6.00mm2/s
5.3 Cetane Number of the Ethyl Ester
CN = 46.3+ (5458/SV) - 0.225(IV)
= 46.3+ (5458/218.076) - 0.225(1.911)
= 71.7972-0.429975 = 70.897997 = approximately 71
5.4 Percentage Ash Content of Ethyl Ester
Weight of empty crucible = 9.535g
Weight of empty crucible + sample = 13.659g
Weight of sample (w) = 4.124g
Weight of crucible + ash after drying in the furnace for 5hrs at 600oc = 9.536
Weight of ash (x) = 0.001
% ash content =
= = 0.02%
105
5.5 Heat of Combustion of Ethyl Ester
Initial temperature = 30.865
Final temperature = 33.851
Energy equivalent of the calorimeter (E) = 13039.308
Temperature rise (∆T) = 2.986
Length of unburnt wire = 2.7+3.2 =5.9cm
Length of burnt wire (L) = 10-5.9 = 4.1cm
Titration volume (V) = 5.4
Weight of sample (g) = 1.058
Heat of Combustion = g
VLTE −−∆ 3.2 = = 36,786.90kJ/kg
= 36.786MJ/kg
5.6 Acid Value of Ethyl Ester
Volume of KOH 1st 2nd 3rd
Initial reading 20.00 21.00 22.00
Final reading 20.20 21.10 22.10
difference 0.20 0.10 0.10
Average titre = = 0.133
Acid Value = = = 0.25mgKOH/g
106
5.7 Saponification Value of Ethyl Ester
Volume of HCl (ml) Sample blank
1st 2nd 3rd 1st 2nd 3rd
Initial reading 17.9 24.40 30.6 17.50 10.00 16.50
Final reading 24.4 30.60 36.00 40.00 32.20 38.50
difference 6.50 6.20 6.00 22.50 22.20 22.00
Average titre for sample = = 6.2333ml
Average titre for sample = = 22.233ml
Saponification value = =
=218.076mgKOH/kg
5.8 Peroxide Value of Ethyl Ester
Volume of sodium
thiosulfate (ml)
Sample blank
1st 2nd 3rd 1st 2nd 3rd
Initial reading 18.20 17.90 18.60 14.30 14.10 15.50
Final reading 18.60 18.20 18.80 14.70 14.30 15.60
difference 0.30 0.30 0.20 0.40 0.20 0.10
Average titre for sample = = 0.2667ml
Average titre for blank = = 0.2333ml
Peroxide Value = = =1.5meq/kg
107
5.9 Iodine Value of the Ethyl Ester
Volume of sodium
thiosulfate (ml)
Sample blank
1st 2nd 3rd 1st 2nd 3rd
Initial reading 0.00 0.00 0.00 0.00 0.00 0.00
Final reading 44.70 45.40 45.50 45.00 48.20 46.30
difference 44.70 45.40 45.50 45.00 48.20 46.30
Average titre for sample = = 45.2ml
Average titre for blank = = 46.5ml
Iodine Value = = = 1.911mgI2/g
Appendix 6: Glycerol Standard Curve
108
Appendix 7: Determination of Rate of Constant of the Progress Curves
7.1 Determination of Rate Constant for 1:6 Oil/Ethanol Volumetric Ratio
Transesterification
7.2 Determination of Rate Constant for 1:3 Oil/Ethanol Volumetric Ratio
Transesterification
109
7.3 Determination of Rate Constant for 1:2 Oil/Ethanol Volumetric Ratio
Transesterification
7.4 Determination of Rate Constant for 1:1.5 Oil/Ethanol Volumetric Ratio
Transesterification
110
7.5 Determination of Rate Constant for 1:1 Oil/Ethanol Volumetric Ratio
Transesterification