Biodiesel Production-reaction and Process Parameters of Alkali-catalyzed Transesterification of...

8/3/2019 Biodiesel Production-reaction and Process Parameters of Alkali-catalyzed Transesterification of Waste Frying Oils

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Biodiesel Production: Reaction and Process Parameters of

Alkali-Catalyzed Transesterification of Waste Frying Oils

K. G. Georgogianni, M. G. Kontominas,*, E. Tegou, D. Avlonitis, and V. Gergis|

Section of Industrial and Food Chemistry, Department of Chemistry, UniVersity of Ioannina,45110-Ioannina, Greece, General Chemical State Laboratory, DChemical SerVices of Pireaus, Akti

Kondyli 32, 18510 Pireaus, Greece, Department of Petroleum Technology, Technological EducationalInstitute of KaVala, 65404-KaVala, Greece, and Department of Food Technology, Technological

Educational Institute of Athens, Ag. Spyridonos Str., 12210 Egaleo, Athens, Greece

ReceiVed February 26, 2007. ReVised Manuscript ReceiVed May 9, 2007

The transesterification of two different frying oils (soybean oil and a mixture of soybean and cotton seedoil) with methanol, in the presence of an alkali catalyst (NaOH), by means of low-frequency ultrasonication(24 kHz, 200 W) and mechanical stirring (600 rpm) for the production of biodiesel fuel was studied. The twodifferent frying oils gave similar yields of isolated methyl esters both under mechanical stirring andultrasonication. Also the physical and chemical properties of the two biodiesel fuels produced were investigated.The fuels produced were characterized by determining their density, viscosity, flash point, boiling point, cetanenumber, sulfur content, cloud point, pour point, cold filter plugging point, acid value, iodine value, and

saponification value. From the physical and chemical properties of the two biodiesel fuels, it is concluded thatthese fuels have very similar properties to those of conventional diesel, except for the cetane number, whichis higher, and the sulfur content of the biodiesel, which is negligible. Thus, experimental biodiesel fuels areenvironmentally friendly and attractive alternatives to conventional diesel.

1. Introduction

Alternative fuels for diesel engines are becoming increasinglyimportant because of diminishing petroleum reserves and theenvironmental consequences of exhaust gases from petroleum-fueled engines. Air pollution is one of the most seriousenvironmental problems all over the world. Because dieselengines of vehicles such as buses and trucks exhaust a huge

amount of NOx and particulates, a clean alternative fuel isincreasingly in demand. Among many possible sources, biodie-sel fuel derived from vegetable oil attracts attention as apromising substitute for conventional diesel fuel.1,2

According to the Official Journal of the European Union,biodiesel is composed of methyl or ethyl esters produced fromvegetable oil or animal oil, of diesel quality, to be used asbiofuel.3 In this context, biodiesel shows the following generaladvantages: (a) an alternative to petroleum-derived fuel, whichimplies a lower dependence on crude oil foreign imports; (b)renewable fuel, helping to achieve the European Union (EU)renewable energy target (12% of the total energy output toconsist of renewable energy by 2010);4 (c) a favorable energy

return on energy invested; (d) a reduction on greenhouseemissions in line with the Kyoto Protocol agreement; (e) lowerharmful emissions, which is very advantageous in environmen-tally sensitive areas such as large cities and mines; (f)biodegradable and nontoxic fuel, being beneficial for reservoirs,lakes, marine life, and other environmentally sensitive areas;and (g) the use of an agricultural surplus, as a raw material forits production in agreement with the European Agricultural

Policy regulations, which can also help to improve ruraleconomies. When the above advantages are taken into consid-eration, there is a growing interest in expanding the biodieselindustry. Along this line, research is focused on improving thebiodiesel quality and yield and increasing the number of rawmaterials available for its production.

Fatty acid alkyl esters are products of the transesterification(also called alcoholysis) of vegetable oils and fats with methanolor ethanol in the presence of a suitable catalyst 5 (Figure 1).

The stoichiometry of the transesterification reaction requires3 mol of methanol (or ethanol) and 1 mol of triglyceride togive 3 mol of fatty acid methyl (or ethyl) ester and 1 mol ofglycerol. After the reaction, the glycerol is separated by settling

or centrifuging and purified to be used in its traditionalapplications (pharmaceutical, cosmetics, and food industries).In addition, glycerol can be used in recently developed applica-tions in the field of animal feed, polymers, surfactants,intermediates, and lubricants.6 The alkyl ester phase is alsopurified before being used as a diesel fuel.

The chemical and physical properties of biodiesel closelyresemble those of conventional diesel fuel. This has been

* To whom correspondence should be addressed. Telephone:+302651098342. Fax: +302651098795. E-mail: [email protected]. University of Ioannina. DChemical Services of Pireaus. Technological Educational Institute of Kavala.| Technological Educational Institute of Athens.(1) Laforgia, D.; Ardito, V. Bioresour. Technol. 1995, 51, 53.(2) Schumacher, L. G.; Borgelt, S. C.; Fosseen, D.; Goets, W.; Hires,

W. G. Bioresour. Technol. 1996, 57, 31.(3) Directive 2003/30/EC of the European Parliament and of the Council

of 8 May 2003 on the promotion of use of biofuels or other renewablefuels for transport OJ L123 17.5.2003, p 42.

(4) European Commission. Energy for the future: Renewable sourcesof energy. White paper for a Community Strategy and Action Plan, COM1997, 599 final of 26/11/1997.

(5) Harrington, K. J.; Arcy-Evans, C. D. J. Am. Oil Chem. Soc. 1985,62, 1009.

(6) Claude, S. Fett/Lipid1999, 3, 101.

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documented by many workers.7-9 The cetane number, energycontent, viscosity, and phase changes of biodiesel are similarto those of diesel fuel. Moreover, biodiesel is essentially sulfur-free. Engines fueled with biodiesel emit significantly fewerparticulates, hydrocarbons, and less carbon monoxide than thoseoperating with conventional diesel fuel.8 Biodiesel has a highercloud point and a flash point comparable to conventional dieselfuel.10

Although short-term tests using vegetable oils showedpromising results, longer tests led to injector coking, moreengine deposits, ring sticking, thickening of the engine lubricant,etc.11

Low-frequency ultrasonication is a useful tool for emulsifica-tion of immiscible liquids. Ultrasonic processing technology canbe used, for example, for the reduction of the particle size inminerals, powders, and emulsions or for water treatment.12

Ultrasonic technology is unique for the activation and accelera-tion of chemical, petrochemical, and polymerization processes.13

Ultrasonication also has a general accelerating effect onheterogeneous reactions.

In the present work, a comparative study on the preparationof biodiesel from two different used cooking oils (a soybeanfrying oil and a mixture of soybean and cotton seed oil) by twodifferent processes was investigated. The process of conventionalalkali-catalyzed transesterification, in which the reacting mixturewas stirred using mechanical stirring (600 rpm), was comparedto that using ultrasonication. Evaluation of waste cooking-oil-based biodiesels was carried out by the determination of their

physical and chemical properties.

2. Experimental Section

2.1. Materials and Reagents. The soybean frying oil wasprovided from the student cafeteria of the University of Ioannina,and the mixture of frying oils (cotton oil and soybean oil, 1:1) wasprovided from the student cafeteria of the Technological EducationalInstitute (TEI) in Kavala, Greece.

Sodium hydroxide (>96%) was purchased from Merck (Darm-stadt, Germany) and used after milling, to facilitate the dilution inmethanol. Methanol of purity >95%, sulfuric acid of purity 95-97%, and petroleum ether (pro-analysis) employed were purchasedfrom Fluka (Sigma-Aldrich, Germany).

2.2. Transesterification Reaction. Frying oils (80 g, 0.102 mol)

(for molecular weight determination of oils, see section 2.3),methanol (30 mL/0.15 mol), and NaOH in various concentrations[1.0, 1.5, and 2.0% (w/w)] were refluxed in a 500 mL round-bottomflask equipped with a glass anchor-shaped mechanical stirrer, awater condenser, and funnel. Heating was achieved by means of a

heating mantle controlled by a proportional integral derivative (PID)temperature controller including a type K-thermocouple. Thetemperature was raised to 60 C, and the mixture was stirred eitherusing the mechanical stirrer (600 rpm) or the low-frequencyultrasonicator (24 kHz, 200 W, UP 200S, IKA, U.K.).

Samples (10 mL) were taken from the reaction mixture atpredetermined time intervals, neutralized with a 4% methanol

solution of citric acid, and analyzed by thin-layer chromatography(TLC). TLC analysis was performed on glass plates coated withSilica Cel G (Merck) and developed in a solvent system ofpetroleum ether/diethyl ether/hydrochloric acid (8:2:0.1). Spots weredetermined by an iodine vapor stain.14

After the complete conversion of the vegetable oil, the reactionwas stopped and the mixture was allowed to stand for phaseseparation: the ester mixture formed the upper layer, and glycerinformed the lower layer.15 The residual catalyst and nonreactedalcohol were distributed between the two phases. After phaseseparation, using a separatory funnel, the ester mixture was driedover anhydrous sodium sulfate and analyzed by gas chromatogra-phy.

2.3. Sampling and Analysis. The fatty acid composition ofsoybean frying oil and the mixture of soybean and cotton seed oils

(1:1), shown in Table 1, was determined by the well-establishedgas chromatographic (GC) procedure of Alcantara et al.:12 A 0.1mL sample of the mixture of the fatty acid methyl esters (FAMEs)was dissolved in 5 mL of petroleum ether, and 3 L of this solutionwere injected into a Varian 3700 GC equipped with a flameionization detector (FID; Varian Associates, Palo Alto, CA). Forseparation and quantification purposes, a DEGS 15% on Chro-mosorb, WAW 80/100 mesh, 2 m 1/8 in. packed column wasused. The analyses were carried out isothermally under thefollowing conditions: the carrier gas was nitrogen (30 mL/min);the temperature of the detector and injection port was 250 C; and

(7) Clark, S. J.; Wagner, L.; Schrock, M. D.; Piennaar, P. G. J. Am. OilChem. Soc. 1984, 61, 1632.

(8) Mittelbach, M.; Tritthart, P. J. Am. Oil Chem. Soc. 1988, 65, 1185.(9) Al-Widnyan, M. I.; Al-Shyoukh, A. O. Bioresour. Technol. 2002,

85, 253.(10) Muniyappa, P. R.; Brammer, S. C.; Noureddini, H. Bioresour.

Technol. 1996, 56, 19.(11) Demirbas, A. Energy ConVers. Manage. 2003, 44, 2093.(12) Alcantara, R.; Amores, J.; Canoira, L.; Fidalgo, E.; Franco, M. J.;

Navarro, A. Biomass Bioenergy 2000, 18, 515.(13) Telsonic Ultrasonics. www.telsonic.com.

(14) Kildiran, G. S.; Yucel, O.; Turkay, S. J. Am. Oil Chem. Soc. 1996,73, 225.

(15) Stravarache, C.; Vinatoru, M.; Nishimura, R.; Maeda, Y. Ultrason.Sonochem. 2005, 12, 367.

Figure 1. General equation for the transesterification of triglycerides.

Table 1. Principal Fatty Acid Composition and Molecular Weight

(MW) for Soybean Frying Oil and the Mixture of Soybean andCotton Seed Oil (1:1)

fattyacid

molecularweight

fatty acid contentin soybean

frying oil (%)

fatty acid contentin the mixture of

frying oil (%)

palmitic (16:0) 256 11.5 18.0stearic (18:0) 284 4.0 3.0oleic (18:1) 282 24.5 16.0linoleic (18:2) 280 53.0 57.5

linolenic (18:3) 292 7.0 5.5

Table 2. Yields of Isolated Methyl Esters of Soybean Frying Oil(B1) and the Mixture of Soybean and Cotton Seed Frying Oil (B2)Using Mechanical Stirring (600 rpm) and Ultrasonication (24 kHz)

yields (%)

1.0% (w/w)NaOH

1.5% (w/w)NaOH

2.0% (w/w)NaOH

time(min) B1 B2 B1 B2 B1 B2

mechanical stirring

5 42 42 53 55 64 5810 51 49 61 64 86 8815 57 53 68 88 97 9320 68 64 94 94 95 9530 79 82 96 97 94 9440 82 94 94 98 96 96

60 96 95 95 95 95 95

ultrasonication

5 36 49 51 53 71 8010 45 58 77 67 88 9315 57 63 88 71 93 9520 68 72 97 74 94 9430 82 81 96 95 94 9440 93 83 98 97 93 9360 94 91 96 96 95 95

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the column temperature was 170 C. The standard mixture of theFAMEs used was purchased from Sigma (stock number 189-3).

The analysis of biodiesel by GC was carried out by dissolving

0.050 g of the biodiesel sample in 5 mL of petroleum ether andinjecting 3 L of this solution into the GC, under the sameconditions as above.

The concentration of biodiesel for each sample was quantifiedby comparing the FID response for each methyl ester of the GCsample of biodiesel with the FID response of the methyl esterstandard mixture of FAMEs, respectively.

The conversion of oil in each experiment was calculated fromthe content in methyl esters of biodiesel as analyzed by GC, andthe material balance of the reaction

where MW is the mean molecular weight of biodiesel/oil. The meanmolecular weight of biodiesel was calculated averaging theindividual molecular weights (MWi) of each constituent methylester, according to the biodiesel FAME analysis (i). The meanmolecular weight of the oil was calculated averaging the individualmolecular weights (MWi) of each constituent triglyceride accordingto the fatty acid oil analysis (i). The factor 3 appears in the formulabecause each triglyceride molecule yields three methyl estermolecules.

2.4. Physical and Chemical Properties of Biodiesel. Physicaland chemical properties of the biodiesel sample produced from thefrying oils were determined in the General Chemical State Labora-tory, according to the International Organization for Standardization(ISO) norms and standard test methods given in Table 3.

3. Results and Discussion

3.1. Transesterification Reaction: Effect of the Catalyst

Concentration and Stirring Method. Yields of methyl estersisolated from both frying oils by conventional transesterificationusing mechanical stirring and ultrasoncation as a function ofthe time and NaOH concentration are given in Table 2.

3.1.1. Effect of the Catalyst Concentration. Results in Table2 show that, for both biodiesels produced, the highest yieldswere obtained when the catalyst was used at the highestconcentration [2.0% (w/w) NaOH]. To be more specific, using

mechanical stirring and 2.0% (w/w) NaOH oil, the transesteri-fication reaction was completed in 15 min (conversion of 97%for soybean frying oil and 93% for mixed soybean and cotton

seed frying oil). On the other hand, employing a lower catalystconcentration [1.0 or 1.5% (w/w)] resulted in a 60 and 20 minreaction time, respectively (conversion of 96 and 94% forsoybean frying oil, respectively, and 95 and 94% for mixedsoybean and cotton seed frying oil, respectively). Similar resultswere obtained when ultrasonication was employed; i.e., highestyields were obtained when the catalyst was used at the highestconcentration. However, a further increase of the catalystconcentration [e.g., 2.5% (w/w) NaOH] led to soap formationand a decrease in the yields of FAMEs (data not shown).

In addition, when the amount of alkaline catalyst is increasedto 2.0% (w/w) NaOH, the yields of methyl esters also increaseusing both mechanical stirring and ultrasonication. These resultscontradict those of Stavarache et al.15 according to which, whenthe catalyst concentration is increased [to 0.5% (w/w) alcoholsolution of NaOH], the yields of isolated methyl esters decreasebecause of soap formation. According to these authors, whenthe catalyst concentration is increased, emulsions are formedin the washing step, thus, hindering purification. Duringwashing, the soap present in the ester phase has the tendencyto accumulate at the surface of the two liquids. The soapmolecules, which are trapped inside esters, form emulsions withthe water molecules present in the solution. Thus, the yields ofisolated esters are very low. In the present study, this phenom-enon did not occur and the increase of the catalyst concentrationcaused a yield increase of the isolated FAMEs to the thresholdof 2.0% (w/w) NaOH for both processes, involving ultrasoni-cation and mechanical stirring.

3.1.2. Effect of Ultrasonication Versus Mechanical Stirring.

In comparison to mechanical stirring, the effect of ultrasonica-tion is not clear. Table 2 shows that, for soybean frying oil, thereaction time is the same for catalyst concentrations of 1.5 and2.0% (w/w), while it decreases for ultrasonication and thecatalyst concentration of 1.0% (w/w) as the reaction is completedin 40 min instead of 60 min.

Unlike soybean frying oil, for the mixture of soybean andcotton seed frying oil, for 1.0 and 1.5% (w/w) catalystconcentrations, the reaction rate is significantly enhanced whenmechanical stirring is employed, i.e., completion of the trans-esterification reaction in 40 versus 60 min (for 1.0% NaOH)and 20 versus 30 min (for 1.5% NaOH). In the presence of

Table 3. Physical and Chemical Properties of (a) Conventional Diesel, (b) Biodiesel from Soybean Frying Oil, and (c) Biodiesel from Mixed

Soybean and Cotton Seed Frying Oil

fuel propertyconventional

dieselspecifications

of diesel

biodiesel ofsoybean

frying oil

biodiesel ofmixture

frying oilstandardmethoda

density (kg/m3, 15 C) 825-835 820-845 857 826 EN-ISO 3675/98viscosity (mm2/s, 40 C) 2-4.5 4.76 4.45 EN-ISO 3704/96flash point (C) 60-70 55 min 67 83 ISO 2719/02boiling point (C) 180-360 305-355 302-354 Pr EN-ISO3405/98cetane number 51-53 51 min 53.7 52.8 EN-ISO 5165/98

sulfur content (wt %) 10-

40 50 max 0.03 0.01 EN-ISO 14596/98AOCS CD3a-63CFPP (C) -15 to -7 -5 max (October-April)

+5 (April-October)-4 -5 EN 116:1997

pour point (C) -12 to -18 -3 -4 D 97-87cloud point (C) -10 to -15 -6 -7 ISO 3015:1992acid value (mg of KOH/g of oil) 0.80 0.50iodine value (cg of I/g of oil) 95 71 AOCS CD1-25 1993saponification value

(mg of KOH/g of oil)215 220 AOCS CD3 1993

a Methods used to determine physical and chemical properties of oils.

conversion (%) )

weight of biodiesel

MW of biodiesel

weight of oil 3

MW of oil

biodiesel concentration (%)

(1)

MW )MWii

Biodiesel Production Energy & Fuels, Vol. 21, No. 5, 2007 3025


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2.0% NaOH, the reverse is true; i.e., the reaction is completedin 10 min under ultrasonication versus 15 min under mechanicalstirring. Thus, ultrasonication is an efficient, time-saving, andeconomical process compared to mechanical stirring only in thecase of biodiesel produced from mixture frying oils and whenthe reaction occurs under the most favorable conditions, i.e.,appropriate catalyst concentration (2.0% NaOH).

Lifka and Ondruscka16 studied the effect of ultrasonicationversus mechanical stirring on the alkaline transesterification of

rapeseed oil using NaOH at a concentration of 0.5% (w/w) at45 C. A conversion of 80-85% was obtained for bothultrasonicated and mechanically stirred reactions after 30 min.

Ji et al.17 studied the effect of mechanical stirring, ultrasoni-cation, and hydrodynamic cavitation on methyl ester yields inthe alkaline (KOH) transesterification of soybean oil usingmethanol (alcohol/oil molar ratio of 6:1) at a temperature of45 C and reported that ultrasonication gave the shortest reactiontime and highest yield, while mechanical stirring gave theshortest reaction time and the lowest yield.

Stavarache et al.18 studied the alkaline (KOH and NaOH)transesterification of a series of vegetable oils using bothmechanical stirring and ultrasonication and concluded that yieldsin both cases were identical but a significantly shorter reaction

time was observed in the case of ultrasonication.Finally, Stavarache et al.19 studied the effect of ultrasonication

versus mechanical stirring in the transesterification of palm oiland commercial edible oil in a bench-scale continuous process.Additional parameters investigated included the reaction volumeand residence time. The highest conversion was achieved whenthe short residence time was employed. The advantage of anultrasonic continuous manufacture of biodiesel was a small sizereactor (2.6 L) and shorter reaction time (20 min).

3.2. Evaluation of Biodiesel Properties. Physical andchemical quality parameters of the two biodiesel samples weredetermined. Samples were produced using 2% (w/w) NaOH andultrasonication as described in section 3.1. Data are presentedin Table 3. For comparison purposes, properties of conventional

diesel (typical values of commercial diesel fuels for year 2006based on unpublished data of the General Chemical StateLaboratory) are also presented.

3.2.1. Density. The densities of biodiesels produced fromsoybean oil and the mixture of soybean and cotton seed fryingoil were 857 and 826 kg/m3, respectively (Table 3). Alcantaraet al.,12 Strivastava et al.,20 and Varese et al.21 reported that thedensity of soybean oil ranged between 880 and 890 kg/m3.

The density of conventional diesel ranges between 825 and835 kg/m3. The higher density of experimental biodiesels mayresult in the delivery of a slightly greater mass of fuel in theengine as the fuel injection equipment operates on a volume-metering principle. Of course, there are additional factors to beconsidered to the volume metering, including the respective

calorific values.3.2.2. Viscosity. Viscosity is the most important property of

biodiesel because it affects the fluidity of the fuel. High viscosityleads to poorer atomization of the fuel spray and less accurateoperation of the fuel injectors.22 As shown in Table 3, the

kinematic viscosities of the soybean frying oil and the mixtureof soybean and cotton seed frying oil were 4.76 and 4.45 mm 2/sat 40 C, respectively. Meher et al.23 reported that the kinematicviscosity of biodiesel ranges between 3.5 and 6.0 cSt, asmeasured in Austria, Czech Republic, France, Germany, Italy,and the U.S.A. Moreover, Alcantara et al.,12 Strivastava et al.,20

and Varese et al.21 reported that the viscosity of soybean oilranges between 4.0 and 4.5 mm2/s.

Thus, the viscosities of both biodiesels evaluated in the

present study are within these limits. Besides, the kinematicviscosity of the conventional diesel ranges between 2 and 4.5mm2/s at 40 C. Thus, it can be concluded that the biodiesels,produced from the above frying oils, are within the viscosityrange of conventional diesel.

3.2.3. Cetane Number (CN). Cetane is a hydrocarbonmolecule that ignites very easily under compression, beingassigned a score of 100. All of the hydrocarbons in diesel fuelare compared to cetane as to how well they ignite undercompression. The higher the cetane number, the more ignitablethe fuel is. Biodiesel generally has a higher cetane number thanmineral diesel.11 The cetane number decreases with a decreasingchain length and increasing branching.24

As shown in Table 3, the cetane number of the biodiesel

produced from the soybean frying oil was 53.7 and therespective number of the biodiesel produced from the mixtureof soybean and cotton seed oil was 52.8. Meher et al.23

mentioned that the cetane number of biodiesel is g48, asmeasured in Austria, Czech Republic, France, Germany, Italy,and the U.S.A. Alcantara et al.,12 Strivastava et al.,20 and Vareseet al.21 reported that the cetane number of soybean oil rangesbetween 45 and 56.

Thus, the cetane numbers of both biodiesels evaluated in thepresent study are within these limits. In addition, the cetanenumber of these biodiesels is within the specifications ofconventional diesel (cetane number of 51).

3.2.4. Sulfur Content. The purpose for limiting the sulfurcontent in diesel and other liquid fuels is both to reduce theformation of sulfur oxides and particulates during combustionand to enable the use of add-on control devices for diesel-fueledinternal combustion engines. From data in Table 3, it is obviousthat, in contrast to conventional diesel fuels (sulfur content of50 ppm), the biodiesel from soybean frying oil had a negligiblesulfur content (0.03 ppm), while that from the mixture ofsoybean and cotton seed oil had a sulfur content of 0.01 ppm.

It is important to mention that, when the biodiesels wereneutralized with a 4% methanol solution of sulfuric acid, insteadof a 4% methanol solution of citric acid, the sulfur content was70.5 ppm for the soybean frying oil and 72.8 ppm for themixture of frying oil. In other words, the sulfur content ofbiodiesels was greater than that of conventional diesel fuels.Thus, sulfuric acid should not be used in the production ofbiodiesel at all.

3.2.5. Flash Point. The flash point of a fuel is the temperatureat which vapor given off will ignite when an external flame isapplied under specified test conditions. Even when fuels are ata temperature below their measured flash point, they are capableof producing light hydrocarbons in the tank headspace, suchthat the vapor composition may be close to or within theflammable range. Hence, all fuel oil headspaces should beconsidered to be potentially flammable.23

(16) Lifka, J.; Ondruschka, B. Chem. Eng. Technol. 2004, 27, 1156.(17) Ji, J.; Wang, J.; Li, Y.; Yu, Y.; Xu, Z. Ultrasonics 2006, 44, e411.(18) Stravarache, C.; Vinatoru, M.; Maeda, Y. Ultrason. Sonochem. 2006,

13, 401.(19) Stravarache, C.; Vinatoru, M.; Maeda, Y.; Bandow, H. Ultrason.

Sonochem. 2007, 14, 413.(20) Srivastava, A.; Prassad, R. Renewable Sustainable Energy ReV. 2000,

4, 111.(21) Varese, R.; Varese, M. INFORM 1996, 7, 816.(22) Demirbas, A. Energy ConVers. Manage. 2006, in press.

(23) Meher, L. C.; Vidya Sagar, D.; Naik, S. N. Renewable Sustainable Energy ReV. 2006, 10, 248.

(24) Prakash, C. B. Global Changes Strategies International, Inc. (GCSI),Canada, 1998.

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Table 3 shows that biodiesel produced from soybean fryingoil had a flash point similar to conventional diesel (67 C), whilethe mixture of soybean and cotton seed frying oil had asomewhat higher flash point (83 C). Thus, there is negligiblefire risk during normal storage and handling of such biodieselproducts. Meher et al.23 reported that the flash point of biodieselranges between 65 and 110 C, as measured in Austria, CzechRepublic, France, Germany, Italy, and the U.S.A. Thus, the flashpoint of both biodiesels, evaluated in the present study, is within

these limits.3.2.6. Cloud and Pour Points. Biodiesel is less suitable for

use at low temperatures than petrodiesel. The cloud point isthe temperature at which a sample of the fuel starts to becomecloudy, indicating that wax crystals have begun to form. At evenlower temperatures, the fuel becomes a gel that cannot bepumped. The pour point is the temperature below which thefuel will not flow. As the cloud and pour points for biodieselare higher than those for petroleum diesel, the performance ofbiodiesel under cold conditions is markedly worse than that ofpetroleum diesel.

Table 3 shows that biodiesels produced from vegetable fryingoils have higher cloud (-3 and -4 C) and pour (-6 and -7C) points than those of conventional diesel (from -10 to -15

C for the cloud point and from -12 to -18 C for the pourpoint). Alcantara et al.,12 Strivastava et al.,20 and Varese et al.21

reported that the cloud points of biodiesels produced fromdifferent waste vegetable oils range between 1 and 13 C.Antolin et al.25 stated that the limits of the cloud point ofbiodiesel are 4 C for summer months and -1 C for wintermonths. Joshi et al.26 reported that the cloud point of biodieselranges between -3 and 12 C and the pour point ranges between-15 and 10 C. Finally, Nestor et al.27 state that the cloud andpour points of biodiesel range between -4 and 18 C and -13and 12 C, respectively. Thus, the cloud and pour points of bothbiodiesels in the present study are between these limits.

3.2.7. Cold Filter Plugging Point (CFPP). The CFPP of afuel reflects its cold-weather performance. At low operating

temperatures, fuel may thicken and might not flow properly,affecting the performance of fuel lines, fuel pumps, and injectors.The CFPP defines the fuel limit of filterability. The CFPP is amore useful index of both biodiesel and conventional diesel thanthe cloud point.24

Table 3 shows that biodiesels produced from vegetable fryingoil have higher CFPPs (-4 and -5 C) than those ofconventional diesel (from -15 to -7 C). Gomez et al.28 andFabbri et al.29 reported that the CFPP of biodiesels ranges

between -5 and 1 C. Thus, the CFPP point of both biodieselsin the present study are within these limits.

4. Conclusions

Two waste frying oils (a soybean oil and a 50% mixture ofsoybean and cotton seed oil) were converted into biodiesel bythe transesterification reaction with methanol. The operatingconditions for this chemical conversion were studied, and keyproperties of these biodiesels were determined.

Transesterification was carried out at different catalystconcentrations using mechanical stirring and ultrasonication. Itwas found that the optimum catalyst concentration was 2.0%NaOH. Ultrasonication was shown to be an efficient, time-saving

procedure, offering a number of advantages as compared tomechanical stirring.

On the basis of values of physical and chemical propertiesdetermined, it can be concluded that biodiesel can be used asan alternative fuel in conventional diesel engines.

Acknowledgment. This work was funded by the ArchimedesEuropean Program through the Greek Ministry of Education. Workwas conducted at the University of Ioannina.

Note Added after ASAP Publication. There were numerouscorrections made by the author to the original version of thepaper published ASAP August 16, 2007; the corrected versionwas published ASAP September 4, 2007.

EF070102B(25) Antolin, G.; Tinaut, F. V.; Briceno, Y.; Castano, V.; Perez, C.;

Ramirez, A. I. Bioresour. Technol. 2002, 83, 111.(26) Joshi, R. M.; Pegg, M. J. Fuel 2007, 86, 143.(27) Nestor, J. R.; Soriano, N. U.; Migo, V. P.; Matsumura, M. Fuel

2006, 85, 25.

(28) Gonzalez Gomez, M. E.; Howard-Hildige, R.; Leahy, J. J.; Rice,B. Fuel 2002, 81, 33.

(29) Fabbri, D.; Bevoni, V.; Notari, M.; Rivetti, F. Fuel 2007, 86, 690.

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