The Influence of Storing Time to Biodiesel Degradation Rate.pdf

International Seminar on Chemical Engineering Soehadi Reksowardojo 2011

ISBN 978-979-98300-1-2

The Influence of Storing Time to Biodiesel Degradation Rate

Agus Raksodewanto, Bina Restituta Barus, Oni Fariza

Balai Rekayasa Desain dan Sistem Teknologi BPPT

Telp. (021) 7563213/7563217 Fax. (021) 7563273

Email : [email protected]

Abstract. The most complaint from biodiesel consumers lately is about oxidation stability

of biodiesel itself. Due to their chemical composition, fatty acid methyl esters are more

sensitive to oxidative degradation than fossil diesel. Biodiesel produce from vegetable oils

and other feedstocks can be more prone to oxidation than a typical petroleum diesel unless

it is modified or treated with additives. Exposure to air, heat, light, water and some metals

are contributing factors that will cause it to degrade. Besides that, the fatty acid

composition of feedstock, and such as impurities that catalyze the formation of radical

compound in oil such as free fatty acid remains, acid catalyst remain from esterification

process, metal element, peroxide and hydroperoxide compounds, short-chain of organic

acid, etc. Consequently of the presence of those compounds is degradation of biodiesel

quality, signed by the increasing of Total Acid Number and viscosity. The samples of

biodiesel were made from palm oil and jatropha oil feedstocks with total acid number and

viscosity fulfilled the standard of SNI 04-7182-2006. Both of testing biodiesel were stored

in stainless steel and carbon steel tanks during six months. The results showed that jatropha

biodiesel just survived for four months, while palm biodiesel can be survived for six

months.

Keywords: biodiesel, oxidation stability, quality degradation

1 Introduction

Biodiesel, a fuel derived from vegetable oil or animal fats [1,2], is well-positioned to replace

some petrodiesel. Compatibility with the existing fuel infrastructure, renewability, domestic

origin, biodegradability, inherent lubricity in the neat form, and competitiveness with

petrodiesel in terms of many fuel properties are significant attributes of biodiesel. Technical

issues remaining when using biodiesel include low-temperatures properties and reduction of

NOx exhaust emissions although the interaction with new emissions control technologies still

needs to be fully evaluated, along oxidative stability [3].

Transesterifying oil or fat with alcohol (methanol/ethanol), leads to produce methyl ester

(biodiesel) as main product and glycerine as by-product. Biodiesel has the same fatty acid

profile as the parent oil or fat. Due to the fact that many vegetable oils posses a significant

amount of fatty acids with double bonds, oxidative stability is being concerned, espesially

when storing biodiesel over an extended period of time. The storage problem is exacerbated

by storage conditions which may include exposure to air, light, moisture, higher of ambient

temperature, and storage materials.

Oxidative stability is not recognized as a parameter in the Indonesia National Standard (SNI

04-7182-2006) that refers to the American Society for Testing and Materials (ASTM D

6751) provisional fuel standard guideline for biodiesel, PS 121 [4] because cummulative

effects of autoxidation on engine performance and emissions are difficult to quantify.

Autoxidation is known to affect kinematic viscosity (ϑ), acid value (AV), and peroxide value

(PV) [5-8]. Two of these parameters, ϑ and AV, are among the specifications listed within

Raksodewanto et al. / Int. Sem. Chem. Eng. Soehadi Reksowardojo 2011

ISBN 978-979-98300-1-2

PS 121, and extensive oxidation may increase either of these parameters beyond their

maximal limits. Although PV itself is not listed as a parameter in the biodiesel fuel

spesification, formation of hydroperoxides caused by oxidative degradation during storage is

known to influence cetane number [9-10]. In addition to effects on ϑ, AV, and PV, extensive

degradation may produce insoluble high-MW polymers that clog fuel lines and filters or lead

to injector coking, incomplete combustion, and engine deposit.

Table 1 Biodiesel specification negatively impacted by autoxidation

Parameter Test Method Units ASTM D 6751 EN 14214 **

Oxidative

stability, 110oC

EN 14112 h 3.0 min 6.0 min

Acid Value ASTM D 664

EN 14104

mg KOH/g 0.8 max 0.5 max

Kinematic

Viscosity, 40oC

ASTM D 445

EN ISO 310

cSt 2.3-6.0 3.5-5.0

** Oxidative stability (EN 14214) is accelerated measurement by Rancimat

Bondioli and co-workers stored several drum-quantity samples of biodiesel at ambient

conditions for 1 year. One sample was “shaken” once per week to promote intimate contact

with air. Over this period the quiescent samples exhibited little or no change in properties,

including only minor reductions in EN 14112 induction time. This contrasts strongly with

the results of studies conducted at higher temperatures (for example, 43oC, as in ASTM D

4625), which have shown large changes in acid value and other parameters for some

biodiesel samples [11,12]. The agitated sample exhibited significant increases in peroxide

and acid values, however, and a large reduction in induction time because of the increased

exposure to dissolved oxygen. Mittelbach and Gangl also stored biodiesel produced from

rapeseed oil and used frying oil under different conditions for up to 200 days [13].

Degradation caused by oxidation began immediately, as shown by the formation of

peroxides and reduction in induction time.

The objectives of this research were to determine the stability of biodiesel and blends of

biodiesel with straight run petrodiesel over an extended storage period, to evaluate the

storage life of biodiesel and and biodiesel/petrodiesel blends without addition of antioxidant

and to determine the effect of typical metals present in diesel fuel storage systems on the

long-term stability of these fuels and fuel blends.

2 Experimental Procedures

Materials. Biodiesel Palm and Biodiesel Jatropha were produced in Balai Rekayasa Disain

dan Sistem Teknologi (BRDST)-BPPT plant facility. Then, analyzed to know the initial

value of each product based on SNI 04-7182-2006. As storage tank, the mechanical team

designed and manufactured several tanks from two kind of materials stainless steel and

carbon steel. Those tanks were conditioned similar to the Pertamina storage. Espesially to

Biodiesel Palm, is blended to petrodiesel (B5, B10, B20, and B-50).

Table 2 Properties of Biodiesel Jatropha and Palm

No. Parameter Standard Testing Method Biodiesel

Jatropha

Biodiesel

Palm

1 Acid Value max. 0,8 mg

KOH/gr ASTM D974 0,2473 0,2589


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2 Free Glycerol max. 0,02% (w/w) FBI- A01- 03 0,0091 0,014

3 Total Glycerol max. 0,24% (w/w) FBI-A01-03 0,2014 0,1914

4 Density 850-890 kg/m3 ASTM D1298 862 873

5 Soap Content - FBI-A03-03 181,61

6 Ester Content Min 96,5% (w/w) FBI-A03-03 99,36 99,58

7 Iodine Value max. 115 gI2/100gr FBI-A04-03 38,79 58,98

8 Helphen Test Negative AOCS Cb 1-25 Negative Negative

9 Water and Sediment

Content max. 0,05% ASTM D2709-96 < 0,05 < 0,05

10 Cloud Point max. 180C ASTM D2500 3 15

11 Kinematic

Viscosity, 400C 2,3 – 6,0 cSt ASTM D445 2.88 4,02

Methods. Storing biodiesel were conducted in tanks that placed inside and outside building

without limitation of storing time. Biodiesel was stored in tanks without limitation of storing

time. This method is adopted from ASTM D 4625, “Standard Test Method for Distillate

Fuel Storage Stability at 43oC, for a specified period time [14], but in this method, biodiesel

sample is stored in bottle, completed with venting as a pathway to contact with the air. 100

ml sample was taken once per day, week, and month from each tanks to analyze the

changing of biodiesel fuel properties (ϑ and AV) until the propeties out of specification.

Along the storing process, the ambient temperature and humidity were measured by

hygrometer. Before taken for analyzing, the biodiesel were mixing to make homogenity of

all parts. Kinematic viscosities were determined at 40oC according to ASTM (American

Society for Testing and Materials) standard D 445. And acid values were determined with

ASTM D 664.

3 Result and Discussion

The issue of oxidative stability affects biodiesel primarily during extended storage. The

influence of parameter such as presence of air, heat, traces of metal, peroxides as well as

nature of the storage container was investigated in the studies cited here. Generally, factors

such as presence of air, elevated temperatures of presence of metals facilitate oxidation.

Studies performed that the biodiesel feedstock influenced the resistancy of biodiesel during

storage period. It proved that compound structure of fatty esters, especially unsaturation was

even greater.

3.1 Oxidation mechanisms, autoxidation and photoxidation

The rates of oxidation of unsaturated fatty acids or esters can vary considerably. The

understanding of oxidation is complicated by the fact that fatty acid occur in complex

mixtures, with minor component in this mixtures catalyzing or inhibiting oxidation. This

observation affects biodiesel because usually significant amounts of esters of oleic, linoleic

and linolenic acids as well as minor components which may affect oxidation are present.


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Table 3 Fatty Acid Composition of Biodiesel Palm and Jatropha

No. Compound CPO

(Patzaris)

CJO

(Gubitz)

1 Lauric Acid C12:0 0 – 0.4 -

2 Myristic Acid C14:0 0.6 – 1.7 0 – 0.1

3 Palmitic Acid C16:0 41.1 – 47 14.1 – 15.3

4 Palmitoleic Acid C16:1 0 – 0.6 0 – 1.3

5 Stearic Acid C18:0 3.7 – 5.6 3.7 – 9.8

6 Oleic Acid C18:1 38.2 – 43.5 34.3 – 45.8

7 Linoleic Acid C18:2 6.6 – 11.9 29.0 – 44.2

8 Linolenic Acid C18:3 0 – 0.5 0 – 0.3

9 Aradic Acid C20:0 0 – 0.8 0 – 0.3

10 Erucate Acid C22:1 - -

Oxidation of fatty materials promoted by factors such as elevated temperature, presence of

light or extraneous materials such as metals or initiators. The nature of the radicals also

influences the product observed and double bond geometry can also play a role.

Antioxidants function by delaying oxidation but not preventing it.

Oxidation mechanism in oil and fat is as follow:

Initiation

RH + I → R* + IH

Propagation

R* + O2 → ROO*

ROO* + RH → ROOH + R*

Termination

R* + R* → R-R

ROO* + ROO* → stable product

Photo-oxidation is more rapid than autoxidation by several orders of magnitude. For oleat,

photo-oxidation is about 30,000 times more rapid and for linoleat and linolenate this value

1500 and 900 [15]. Literature values for relative autoxidation rates of oleate, linoleat, and

linolenate are 1, 27, and 77, respectively [15] and 1, 41, and 98 respectively [16] with that of

20:4 being 195. The relative oxidation rate of triaglycerols is lower, that trilinolein being 50.

Thus the relative rates of photo-oxidation between oleate, linoleate, and linolenate are

considerably smaller compared to autoxidation.

The autoxidation process usually exhibits an induction time during which overall reaction is

slow, followed by a more rapid stage. The purpose of antioxidants is to either prolong the

onset of the initiation reaction or to enhance the termination, reducing the length of

propagation. However, the rates of oxidation in natural mixtures such as vegetable oils can

differ from those in studies on pure compounds due to the presence of pro- and antioxidants.


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3.2 Oxidation of Biodiesel

The oxidation reactions mentioned above utimately affect the fuel quality of biodiesel,

primarily during extended storage. Beside oxidation caused by exposure to air (oxygen),

biodiesel is also potentially subject to hydrolitic degradation due to the presence of water.

This is largely a housekeeping issue although the presence of, for example, mono- and

diglycerides (intermediates in the transesterification reaction) or glycerol which can emulsify

water can play a major role [17]. \

As mentioned above, double bonds may also be prone to polymerization-type reactions so

that molecular weight products, leading to an increase in viscosity, can occur. This may lead

to formation of insoluble species which can clog fuel lines and pumps. One study [18]

reports that polymers formed during storage under controlled conditions are soluble in

biodiesel due to its polar nature and are insoluble only when mixing the biodiesel with

petrodiesel. The formation of higher molecular weight species, which posses higher

viscosity, is a reason why the viscosity specification in biodiesel standards can be used to

assess the fuel quality status of stored biodiesel. Long term storage tests on biodiesel have

been conducted. Viscosity and acid value increased in biodiesel stored for six months.

3.2.1 Effect of Storing Period to Kinematic Viscosity at 40oC

Viscosity increases with chain length (number of carbon atoms) and with increasing degree

of sturation. Free fatty acids have greater viscosity than the corresponding methyl or ethyl

esters. Bouble bond configuration influences viscosity (cis double bond configuration giving

a lower viscosity than trans) while double bond position affects viscosity less. Since

oxidation processes lead to the formation of free fatty acids, double bond isomerization,

usually cis to trans, saturation and products of higher molecular weight, viscosity increases

with increasing oxidation.

Biodiesel from Palm and Blended Biodiesel Palm-Petrodiesel stored for 180 days, while

Biodiesel from Jatropha stored for 120 days at temperature 25-31oC and humidity 57-98%

did not exceed the range of viscosity (2,3-6,0 cSt). On the other hand, following the test

results, increasing of viscosity just represented the indication that oxidation occur during the

storing period.


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Figure 1 Increasing of Kinematic Viscosity on Biodiesel Palm

Figure 2 Increasing of Kinematic Viscosity on Biodiesel Jatropha


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3.2.2 Effect of Storing Period to Acid Value

Acid Number is a good indicator of the level of Free Fatty Acids (FFA) in Biodiesel. High

teste values for Acid Number can be correlated to manufacturing a FAME fuel from

unrefined feedstock (i.e. high in Free Fatty Acids) and/or poor process control in the

conversion of the feedstock oils or fats to a FAME fuel (i.e. methanol carryover). High acid

levels in Biodiesel can cause fuel system deposits and is another indicator that the fuel will

act as a solvent resulting in the deterioration of rubber components of a fuel system.

Furthermore, moisture be present in transport or storage tanks, the methyl esters in the

Biodiesel will degrade quicker resulting in further increases in Acid Number. Moisture

causes the methyl esters in Biodiesel to undergo hydrolysis forming Free Fatty Acids.

Moisture is very common in diesel storage tanks and should be minimized or eliminated

when storing Biodiesel. Users of Biodiesel should monitor the Acid Number when the fuel

is received and during storage to see if the Biodiesel is susceptible to degradation or if

degradation is occurring. Normally moisture would not present a problem with diesel fuel or

diesel equipment, however, moisture is detrimental when combined with any Biodiesel

product and would ultimately affect both equipment performance and equipment

maintenance. Another concern with moisture presence in diesel fuel storage is the

possibility of the formation of bacteria. If algae appear in Biodiesel storage tanks, it is

recommended that periodic testing be done to ensure microorganisms are not present in

diesel fuel storage tanks. The testing have found that when moisture is present in Biodiesel

degradation fuel by hydrolysis to Free Fatty Acids is more of a problem to the user than

bacteria growth and pushed the degradation of biodiesel signed by the increasing of acid

value.

Figure 3 Increasing of Acid Value on Biodiesel Palm


ISBN 978-979-98300-1-2

Figure 4 Increasing of Acid Value on Biodiesel Palm

Refers to SNI 04-7182-2006, the maximum value of acid value is 0,8 mg KOH/g sample.

The testing shown that biodiesel palm without antioxidant were starting to decrease after six

months (180 days) stored period both of inside and outside, whereas biodiesel jatropha

started to exceed the maximum limit after four months (120 days) stored period.

The different stored environment (light, air, moisture) had influenced the characteristic of

biodiesel itself. Biodiesel that placed outside were prone to decompose faster than inside the

building. It was indicated that the air, light, and heat play big role in degradation process of

biodiesel.

3.2.3 Oxidation Stability by Rancimat

OSI (hour) was measured following EN 14112 at 110oC utilizing a Metrohm 743 instrument.

Measurement of oxidative stability can be accomplished with accelerated method whereby

various experimental parameters are influenced to yield results in a reasonable period of

time. Such parameters may include elevated temperature, presssure, and/or flowrate of air

(oxygen) through the sample, among others.


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Figure 5 Rancimat Result of Storage Testing on Biodiesel Palm and Jatropha

The degradation of biodiesel palm and jatropha were measured according to stored period

bytwo method manually (ϑ and AV) and accelerated method (Rancimat). Both of method

had described the degradation of biodiesel during the stored period. The additional of

antioxidants could be delayed but not completely prevented.

4 Summary and Conclusion

Biodiesel oxidation is a very complex process that is affected by a variesty of factors,

including the composition of the fuel itself and conditions of storage. The different

unsaturated components of biodiesel can generate different degradation products. Periodic

monitoring of biodiesel during storage may be necessary to ensure effects of autoxidation do

not compromise fuel quality. Both of ϑ and AV showed the greatest potential in terms of

timely and relative ease of measurement. Either of these parameters should provide insight to

determine whether storage conditions are need to be upgrade. Either parameter should also

provide quantitative information on status of the fuel before its oxidation induction period

has expired.

According this testing result, biodiesel palm could be survive until six months without any

addition of antioxidant, while biodiesel jatropha will survive for only four months without

antioxidant.

5 References

[1] G. Knothe, J. Krahl, J. Van Gerpen (Eds), The Biodiesel Handbook, AOCS Press,

Champaign, IL, 2005.

[2] M. Mittelbach, C. Remschmidt, Biodiesel – The Comprehensive Handbook, M.

Mittelbach Karl-Franzens University Graz, Austria, 2004.

[3] American Oil Chemist’ Society Official Method Cd 12b-92, Oil Stability Index

(OSI), AOCS, Champaign, IL, 2005.

[4] ASTM PS121, Provinsial Specification for Biodiesel Fuel (B100) Blend Stock for

Distillate Fuel, in Annual Book of ASTM Standards, American Society for Testing

and Materials,. West Conshohocken, PA, 2000.

[5] Thompson, J.C., C.L. Peterson, D.L. Reece, and S.M. Beck, Two-Year Storage Study

with Methyl and Ethyl Esters of Rapeseed, Trans. ASAE 41:931-939 (1998).

[6] Bondioli, P., A. Gasparoli, A. Lanzani, E. Fedeli, S. Veronese, and M. Sala, Storage

Stability of Biodiesel, J. Am. Oil Chem. Soc. 72:699-702 (1995).


ISBN 978-979-98300-1-2

[7] Du Plessis, L.M, J.B.M. de Villiers, and W.H. Van der Walt, Stability Studies on

Methyl and Ethyl Fatty Acid Esters of Sunflower Seed Oil, Ibid. 62:748-752 (1985).

[8] Du Plessis, L.M, and J.B.M. de Villiers, Stability Studies on Methyl and Ethyl Esters

of Sunflower Seed Oil, in Vegetable Oil as Diesel Fuel Seminar III, edited by M.O.

Bagby and E.H. Pryde, USDA Northern Regional Research Center, Peoria, 1983, pp.

57-62.

[9] Van Gerpen, J.H., Cetane Number Testing of Biodiesel, in Proceedings, Third Liquid

Fuel Conference: Liquid Fuel and Industrial Products from Renewable Resources,

edited by J.S. Cundiff and E.E. Gavett, American Society of Agricultural Engineers,

St. Joseph, MI 1996, pp 197-206.

[10] Clothier, P.Q.E., B.D. Aguda, A. Moise, and H. Pitchard, How do Diesel Fuel

Ignition Improvers Work? Chem. Soc. Rev. 22:101-108 (1993).

[11] Westbrook, S. R. An Evaluation and Comparison of Test Methods to Measure the

Oxidation Stability of Neat Biodiesel, NREL/SR-540-38983; National Renewable

Energy Laboratory: Golden, Colorado,USA, 2005.

[12] Bondioli, P.; Gasparoli, A.; Della Bella, L.; Tagliabue, S. Eur. J.Lipid Sci. Technol.

2002, 104, 777–784.

[13] Mittelbach, M.; Gangl, S. J. Am. Oil Chem. Soc. 2001, 78, 573–577.

[14] P. Bondioli, A. Gasparoli, L. Della Bella, S. Tagliabue, G. Toso, Biodiesel stability

under commerical storage conditions over one year, Eur. J. Lipid Sci. Tech, 105

(2003), pp. 735-741.

[15] F.D. Gunstone, Oxidation through reaction with oxygen, in The Chemistry of Fats

and Oils by Gunstone, F.D., Blackwell Publishing, CRC Press, Oxford, UK, 2004,

pp. 150-168.

[16] E.N. Frankel, Lipid Oxidation, second edition, The Oily Press, PJ Barnes &

Associates, Bridgwater, England, 2005.

[17] J.M. Weiksner Sr., P.E., S. Crump, and Thomas L. White, Understanding Biodiesel

Fuel Quality and Performance, available electronically at

http://www.osti.gov/bridge.

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