Synergistic effect of metal deactivator and antioxidant on oxidation stability of metal contaminated Jatropha biodiesel

Synergistic effect of metal deactivator and antioxidant on oxidation stability of metal contaminated Jatropha biodiesel

Energy 35 (2010) 2333e2337 Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy Synergistic effect of ...

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Energy 35 (2010) 2333e2337

Contents lists available at ScienceDirect

Energy journal homepage: www.elsevier.com/locate/energy

Synergistic effect of metal deactivator and antioxidant on oxidation stability of metal contaminated Jatropha biodiesel Amit Sarin a, *, Rajneesh Arora b, N.P. Singh b, Rakesh Sarin c, R.K. Malhotra c, Meeta Sharma c, d, Arif Ali Khan d a

Department of Applied Sciences, Amritsar College of Engineering & Technology, Amritsar 143001, India Punjab Technical University, Jalandhar, India Indian Oil Corporation Ltd., R&D Centre, Sector-13, Faridabad 121007, India d University School of Basic and Applied Sciences, Guru Gobind Singh Indraprastha University, Kashmere Gate, Delhi 110403, India b c

a r t i c l e i n f o

a b s t r a c t

Article history: Received 2 July 2009 Received in revised form 22 December 2009 Accepted 21 February 2010 Available online 19 March 2010

Biodiesel is relatively unstable on storage and European biodiesel standard EN-14214 calls for determining oxidation stability at 110  C with a minimum induction time of 6 h by the Rancimat method (EN14112). According to proposed National Mission on biodiesel in India, we have undertaken studies on stability of biodiesel from tree borne non-edible oil seeds Jatropha. Neat Jatropha biodiesel exhibited oxidation stability of 3.95 h. It is found possible to meet the desired EN specification for neat Jatropha biodiesel and metal contaminated Jatropha biodiesel by using antioxidants; it will have a cost implication, as antioxidants are costly chemicals. Research was conducted to increase the oxidation stability of metal contaminated Jatropha biodiesel by doping metal deactivator with antioxidant, with varying concentrations in order to meet the aforementioned standard required for oxidation stability. It was found that usage of antioxidant can be reduced by 30e50%, therefore the cost, even if very small amount of metal deactivator is doped in Jatropha biodiesel to meet EN-14112 specification. Ó 2010 Elsevier Ltd. All rights reserved.

Keywords: Oxidation stability Rancimat Antioxidants Metal contaminants Metal deactivators Jatropha curcas

1. Introduction Biodiesel, defined as the mono-alkyl esters of vegetable oils or animal fats, is becoming more readily available for use in blends with conventional diesel fuel for transportation applications. In South Asian countries like India, biodiesel can be harvested and sourced from non-edible seed oils like Jatropha. Jatropha curcas is such a tree which can grow on any type of soil, needs minimum input and management, has low moisture demand, starts giving seeds after third year of plantation, has 25e30% oil content and productive life is more than 40 years [1]. The quality of biodiesel is designated by several standards; like EN-14214 and ASTM D-6751 and the oxidation stability (OS) is among the monitored parameters as EN-14214 calls for determining oxidative stability at 110  C with a minimum induction period (IP) of 6 h by the Rancimat method (EN-14112) and ASTM standard D-6751 has recently introduced a minimum IP of 3 h by same method [2e4]. Indian specification IS-15607 also requires minimum induction time of 6 h [5]. * Corresponding author. Tel.: þ91 183 5069538; fax: þ91 183 5069535. E-mail address: [email protected] (A. Sarin). 0360-5442/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2010.02.032

Oxidation process is reported in literature and relative rates of oxidation are 1 for oleates, 41 for linoleats, and 98 for linolenates [6,7]. The oxidation chain reaction is usually initiated at the positions allylic to double bonds. Therefore, fatty acids with methyleneinterrupted double bonds, for example, linoleic acid [(9Z, 12Z)octadecadienoic acid], are more susceptible to oxidation because they contain methylene groups that are allylic to two double bonds. Fatty acids with two such methylene groups, for example, linolenic acid [(9Z, 12Z, 15Z)-octadecatrienoic acid], are even more susceptible to oxidation. All these make biodiesel relatively unstable on storage and residual products of biodiesel such as insoluble gums, total acids, and aldehydes formed from degradation may cause engine problems like filter clogging, injector coking, and corrosion of metal parts. This is why OS is an important criterion for biodiesel. Although there are numerous publications on storage, OS of biodiesel, and effect of antioxidants on the stability of biodiesel synthesized from edible oils, little is available on OS of biodiesel from tree borne non-edible oil seeds and influence of presence of metal on OS of biodiesel from non-edible oil seeds. Dunn has studied oxidative stability of soybean oil fatty acid methyl esters by oil stability index (OSI) [8]. Polavka et al. studied the OS of methyl esters derived from rapeseed oil and waste frying oil, both distilled

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and undistilled, by differential thermal analysis and Rancimat [9]. Ferrari et al. compared the oxidative stability of neutralized, refined and frying oil waste soybean oil fatty acid ethyl ester [10]. Mittelbach and Schober investigated the influence of different synthetic and natural antioxidants on OS of biodiesel produced from rapeseed oil, sunflower oil, used frying oil, and beef tallow, both distilled and undistilled [11]. Dunn has also studied the effect of different antioxidants on OS of biodiesel from soybean oil [12]. Liang et al. have reported that synthetic antioxidants are more effective than natural antioxidants [13]. Long storage stability studies were also carried out on biodiesels synthesized from rapeseed oil, used frying oil, high oleic sunflower oil, high and low erucic Brassica carinata oil [14e16]. Park et al. have studied the blending effects of biodiesels on OS [17]. Recently, Sarin et al. synthesized the surrogate molecules i.e. methyl, ethyl, isopropyl and butyl esters of b-branched fatty acid having substantially better OS, low temperature flow properties and cetane number [18]. Sarin et al. have studied the influence of metal contaminants on OS of Jatropha biodiesel (JBD) [19]. Different transition metals e iron, nickel, manganese, cobalt, and copper, commonly found in metallurgy of storage tanks and barrels, were blended with varying concentrations (parts per million (ppm)) in JBD samples. It was found that influence of metal was detrimental to OS and catalytic. Copper showed strongest detrimental and catalytic effect. They also concluded that the OS of metal contaminated JBD can be increased with increase in dosage of antioxidants. Dosage of 1000 ppm of phenolic 2,6-ditertiarybutyl hydroxytoluene antioxidant was required for copper contaminated JBD to meet EN-14112 specifications. Recently, Sarin et al. investigated the effect of metal contaminants and antioxidants on the OS of methyl ester of Pongamia [20]. From these literature reports and quality survey reports [21e23], it can be concluded that it will not be possible to use biodiesel without antioxidants. Precautions have been taken to decrease metal contamination to a minimum. When it is considered however that only trace metallic contamination noticeably increase the rate of oxidation, it seems probable that such trace contamination could occur despite precautions [19,20]. Therefore, further treatment to inactivate these trace quantities of metals would be of considerable importance. Morris et al. evaluated the combined effect of antioxidants and metal deactivators as deactivators for copper, iron, nickel and tin in lard [24]. Krishnamoorthy et al. have investigated on effect of antioxidants and metal deactivators on oxidation of transformer oil [25]. Golubeva et al. reported on stabilization of blended diesel fuels by combinations of antioxidants and metal deactivators [26,27]. Effect of antioxidants and metal deactivators for gasoline is also reported in literature [28]. There is no publication of synergistic effect of metal deactivator (MD) and antioxidant on the OS of metal contaminated biodiesel synthesized from tree borne non-edible oil seeds. According to proposed National Mission on biodiesel in India, we have undertaken studies on stability of biodiesel from tree borne non-edible oil seeds Jatropha. As discussed earlier, it is found possible to meet the desired EN specification by using antioxidant in metal contaminated biodiesel, but it will have a cost implication, as antioxidants are costly chemicals. Therefore, objective of this study is to reduce the cost of antioxidants by adding very small amounts of MD. Then synergistic effect of both was studied on OS of metal contaminated JBD. 2. Experimental 2.1. JBD synthesis and testing Jatropha methyl ester (biodiesel) was synthesized by reaction of methanol (200 ml) with Jatropha oil (1000 ml), in the presence of

KOH (1 wt% of oil) under reflux conditions. The reaction mixture was refluxed for 3 h and the progress of the reaction was monitored by thin layer chromatography (TLC). After completion of the reaction, material was transferred to separating funnel and both the phases were separated. Upper phase was biodiesel and lower part was glycerin. Alcohol from both the phases was distilled off under vacuum. The glycerin phase was neutralized with acid and stored as crude glycerin. Upper phase i.e. methyl ester (biodiesel) was washed with the water twice to remove the traces of glycerin, unreacted catalyst and soap formed during the transesterification. The residual product was kept under vacuum to get rid of residual moisture. The fatty acid methyl ester (FAME) composition of JBD were determined by gas chromatography on a gas chromatograph (GC) (PerkinElmer, Clarus 500, New Delhi, India, located at IOC, R & D Centre, Faridabad), using nitrogen as a carrier gas and di(ethylene glycol) succinate column (DEGS) by preparing the corresponding fatty acid esters and comparing them with standard fatty acid ester samples. GC was equipped with a flame ionization detector (FID) and a glass column 3.1 m  2.1 mm i.d. with temperature program of 150e250  C (6  C/min, hold 20 min). The oven temperature was kept at 200  C; the injector temperatures were 230 and 250  C, respectively. Detailed fatty acid methyl ester composition (wt%) is given in Table 1 [19]. The synthesized JBD was tested for physico-chemical properties as per ASTM D-6751 and Indian IS-15607 specifications (Table 2) [19]. It is clear from the data that JBD meets all the specifications, except IP of 6 h. Various metal naphthenates were procured from M/s Notional Chemicals & Dyes Co., Varanasi, India. The metal concentration was checked by ASTM D4951 test method, using inductively coupled plasma atomic emission spectroscopy. The concentration of cobalt, manganese, iron, copper and nickel in their naphthenates is 5.21%, 5.20%, 3.91%, 6.80% and 4.99% respectively. The samples were further diluted in JBD, as per desired concentration. 2.2. Determination of OS OS of JBD in presence of metal contaminants and their blends with different dosages of antioxidant and metal deactivator was studied in Rancimat equipment model 743 as per EN-14112 and Indian IS-15607 specifications (Fig. 1). In Rancimat method, the oxidation is induced by passing a stream of air at the rate of 10 L/h through the biodiesel sample, kept at constant temperature 110  C. The vapors released during the oxidation process, together with the air, are passed into the flask containing 50 mL of demineralized water, and contain an electrode for measuring the conductivity. The electrode is connected to a measuring and recording device. It indicates the end of IP when the conductivity begins to increase rapidly. This accelerated increase is caused by the dissociation of Table 1 Fatty acid methyl ester composition of Jatropha biodiesel. Fatty acid methyl ester

Jatropha BD (wt%)

Caprylic (C8/0) Capric (C10/0) Lauric (C12/0) Myristic (C14/0) Palmitic (C16/0) Palmitoleic (C16/1) Stearic (C18/0) Oleic (C18/1) Linoleic (C18/2) Linolenic (C18/3) Arachidic (C20/0) Behenic (C22/0) Saturated Unsaturated

e e e e 14.2 1.4 6.9 43.1 34.4 e e e 21.1 78.9

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Table 2 Physico-chemical properties of Jatropha biodiesel. Property(units)

ASTM D 6751-08 test method

ASTM D 6751-08 limits

IS-15607 test method

IS-15607 limits

Jatropha methyl ester

Mean

Standard Deviation

Flash point( C) Viscosity at 40  C (cSt) Sulphated ash (% mass) Sulphur (% mass) Copper corrosion Cetane number Water and sediment (vol. %) Conradson Carbon Residue (CCR) 100% (%mass) Neutralization value (mg, KOH/gm) Free glycerin (%mass) Total glycerin (%mass) Phosphorus (%mass) Distillation temperature Oxidation stability at 110  C, hrs

D-93 D-445 D-874 D-5453 D-130 D-613 D-2709 D-4530

Min.130 1.9e6.0 Max. 0.02 Max. 0.05 Max. 3 Min. 47 Max. 0.05 Max. 0.05

IS 1448 P:21 IS 1448 P:25 IS 1448 P:4 ASTM D 5453 IS 1448 P:15 IS 1448 P:9 D-2709 D-4530

Min. 120 2.5e6.0 Max. 0.02 Max. 0.005 Max. 1 Min. 51 Max. 0.05 Max. 0.05

164,162,163 4.2,4.4,4.3 0.002,0.002,0.002 0.004,0.004,0.004 1,1,1 57.6,57.3,57.3 0.05,0.05,0.05 0.03,0.04,0.04

163 4.3 0.002 0.004 1 57.4 0.05 0.037

1 0.1 0.0 0.0 0.0 0.17 0.0 0.0058

D-664 D-6584 D-6584 D-4951 D-1160 EN-14112

Max. 0.80 Max. 0.02 Max. 0.24 Max. 0.001 90% at 360  C Min. 3 h

IS 1448 P:1/Sec.1 D-6584 D-6584 D-4951 Not under spec. EN-14112

Max. 0.50 Max. 0.02 Max. 0.25 Max. 0.001 Min 90% Min. 6 h

0.49,0.47,0.48 0.01,0.01,0.01 0.017,0.022,0.021 <0.001 90% 3.85,4.1,3.9

0.48 0.01 0.02 e e 3.95

0.01 0.0 0.0026 e e 0.13

volatile carboxylic acids produced during the oxidation process and absorbed in the water. When conductivity of this measuring solution is recorded continuously, an oxidation curve is obtained whose point of inflection is known as the IP. Data for all analytical measurements are means of triplicate. Subsequent analysis showed no statistically significant difference among the measurements. Repeatability of EN-14112 test method is as follows: Repeatability is difference between two single results carried out using same method on identical test material in a same laboratory by the same operator using same machine within short span of time and it should not exceed 0.09  0.16 h. The precision calculated by this method also hold about 95 % probability. 3. Results and discussion 3.1. Analyses of biodiesel samples FAME composition of Jatropha biodiesel samples given in Table 1 showed that JBD mainly consisted of oleic and linoleic fatty acid methyl esters. Saturated fatty acid methyl esters in JBD were 21.1%, and unsaturated fatty acid methyl esters were 78.9%. According to EN-14112/IS-15607 test method, JBD did not meet the given limit of a 6 h IP due to high content of unsaturated fatty acid methyl esters. The results were very much in line with the previous work done on biodiesel properties and biodiesel quality survey reports, which indicated that majority of samples, failed in EN-14112 test [19e24].

3.2. Improvement of OS of neat JBD and metal contaminated JBD As discussed earlier, biodiesel OS is one of the major issues as it cannot be stored beyond a period. Rancimat test is the specified standard method for OS testing for biodiesel sample in accordance to EN-14112/IS-15607. A minimum IP of 6 h is defined for biodiesel samples. It is already discussed in various literature reports mentioned above that it is very difficult to meet this limit for biodiesel fuels derived from various vegetable oils, unless antioxidants are added to the biodiesel. Neat Jatropha methyl ester showed an IP of 3.95 h and so meets the limit of 3 h IP in accordance with recent ASTM D-6751 but did not achieve the minimum limit of 6 h IP as required by EN-14112/IS15607. Thus, an antioxidant must be doped to enhance the IP of Jatropha methyl ester. Sarin et al. doped, two phenolic antioxidants namely 2,6-ditertiarybutyl hydroxytoluene (AO-1), bis-2,6ditertiarybutyl phenol derivative (AO-2), and aminic antioxidant octylated butylated diphenyl amine (AO-3) with varying concentrations (ppm) in JBD and noted the corresponding IPs with the Rancimat test method to observe the effectiveness of different antioxidants [19]. They found that antioxidant AO-1 is the most effective among all the antioxidants used and minimum dose of 200 ppm of AO-1 was needed to improve the IP of neat JBD from 3.95 h to above 6 h as required by EN-14112 specification for biodiesel OS. Different transition metals e iron, nickel, manganese, cobalt, and copper, commonly found in metal containers were blended, as metal naphthenates, with varying concentrations (ppm) in JBD

7

Induction Period (h)

6 5

Fe

4

Ni

3

Co

Mn Cu

2 1 0 200

300

400

500

600

700

Antioxidant, AO-1 (ppm)

Fig. 1. Principles of measurement of the Rancimat test method (EN-14112/IS-15607).

Fig. 2. Synergistic effect of antioxidant concentration and metal deactivator (5 ppm) on the oxidation stability of metal contaminated (2 ppm) Jatropha methyl ester.

A. Sarin et al. / Energy 35 (2010) 2333e2337

7

7

6

6

5

Fe

4

Ni

3

Co

Mn Cu

2 1

Induction Period (h)

Induction Period (h)

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5

Fe

4

Ni

3

Co

Mn Cu

2 1

0 200

250

300

350

400

450

500

0

550

200

Antioxidant, AO-1 (ppm)

250

300

350

400

450

500

550

Antioxidant, AO-1 (ppm) Fig. 3. Synergistic effect of antioxidant concentration and metal deactivator (10 ppm) on the oxidation stability of metal contaminated (2 ppm) Jatropha methyl ester.

samples. Sarin et al. also observed that the presence of these metals depressed the OS of biodiesel, as measured by the IP [19]. The presence of metals in biodiesel resulted in acceleration of free radical oxidation due to a metal-mediated initiation reaction. They concluded that copper had strongest catalytic effect and other metals e iron, nickel, manganese, and cobalt also had strong negative influence on OS.

3.3. Synergistic effect of MD and antioxidant on the OS of metal contaminated JBD As discussed earlier, Sarin et al. already observed that antioxidant AO-1 is the most effective among all the antioxidants used and minimum dose of 200 ppm of AO-1 was needed to improve the IP of neat JBD from 3.95 h to above 6 h as required by EN-14112 specifications for biodiesel OS [19]. They also concluded that minimum 500 ppm dosage of AO-1 was needed to improve the IP of iron and nickel contaminated JBD and minimum dosing of 700 ppm of AO-1 in manganese contaminated JBD was needed to meet EN-14112 specification for biodiesel OS. Further, they concluded that for cobalt and copper contaminated JBD, minimum dosing of 900 ppm and 1000 ppm respectively were required to meet EN-14112 specifications.

Fig. 4. Synergistic effect of antioxidant concentration and metal deactivator (15 ppm) on the oxidation stability of metal contaminated (2 ppm) Jatropha methyl ester.

Although it is found possible to meet the desired EN specification by using antioxidant, it will have a cost implication, as antioxidants are costly chemicals. Therefore, experiments were undertaken to blend very small amounts of MD with antioxidant. Then influence of both was studied on OS of metal contaminated JBD and the corresponding IPs were measured with the Rancimat test method. MD chosen for the study was N, N0 -disalicylidene-1,2diaminopropane. As metallic impurities have catalytic effect, 2 ppm metal concentration was selected for antioxidant dose optimization [19]. Fig. 2 shows the variation of IP of 2 ppm metal contaminated JBD with varying concentrations of AO-1. Blend of 5 ppm of MD concentration in AO-1 is chosen for initial study. OS of metal contaminated JBD has been found to increase with increase in dosage of antioxidant AO-1 with 5 ppm of MD. It is found that minimum 300 ppm dosage of AO-1 was needed to improve the IP of iron and nickel contaminated JBD and minimum dosage of 500 ppm of AO-1 in manganese contaminated JBD was needed to meet EN-14112 specification for biodiesel OS. Fig. 2 also shows that for cobalt and copper contaminated JBD, minimum dosages of 600 ppm and 700 ppm respectively were required to meet EN-14112 specifications. Hence, it is observed that, when 5 ppm of MD was blended with AO-1 to enhance the IP of JBD to

7

Induction Period (h)

6 5

Fe

4

Ni

3

Co

Mn Cu

2 1 0 200

250

300

350

400

450

500

550

Antioxidant, AO-1 Fig. 5. Synergistic effect of antioxidant concentration and metal deactivator (20 ppm) on the oxidation stability of metal contaminated (2 ppm) Jatropha methyl ester.

A. Sarin et al. / Energy 35 (2010) 2333e2337

meet EN-14112 specification, there was reduction of usage of minimum of 200 ppm of AO-1 for iron, nickel and manganese contaminated JBD, and 300 ppm of AO-1 for cobalt and copper contaminated JBD. 10 ppm MD is blended with AO-1 for second set-up of experiments. It is observed that minimum 250 ppm dosage of AO-1 was needed to improve the IP of iron and nickel contaminated JBD and minimum dosage of 450 ppm of AO-1 in manganese contaminated JBD was needed to meet EN-14112 specification for biodiesel OS (Fig. 3). Minimum dosage of 550 ppm of AO-1 was required for cobalt and copper contaminated JBD were required to meet EN14112 specifications. Hence, it is observed that, when 10 ppm of MD was blended with AO-1 to enhance the IP of JBD to meet EN14112 specification for biodiesel OS, there was reduction of usage of minimum of 250 ppm of AO-1 for iron, nickel and manganese contaminated JBD, and 350 ppm of AO-1 for cobalt and 450 ppm for copper contaminated JBD respectively. Reduction of minimum of 300e450 ppm of usage of antioxidant AO-1 is noted, when 15 ppm of MD is blended with AO-1 (Fig. 4). Reduction of minimum 300e450 ppm of usage of AO-1 is again noted when 20 ppm of MD is blended with AO-1 (Fig. 5). Further increase in concentration of MD in antioxidant AO-1 showed approximately same results (Figures not shown). Experiments are also performed and verified with bigger amounts of metal contaminated FAME and results matched with the behavior and effectiveness of AO-1 and MD studied with smaller amounts of metal contaminated FAME. Results are comparable with the previous work done on stabilization of metal contaminated fats and oils by combinations of metal deactivators and antioxidants [24e28]. Morris et al. concluded that antioxidants become relative ineffective in presence of traces of metallic contaminants unless metal deactivators are also added [24]. Krishnamoorthy et al. have reported that oxidation of transformer oil improved with antioxidants and metal deactivators [25]. Golubeva et al. concluded that antioxidants with metal deactivators in weight ratio 15:1, are highly effective in stabilizing blended diesel fuels [26,27].

4. Conclusion The stability of biodiesel is very critical and biodiesel requires antioxidant to meet storage requirements and to ensure fuel quality at all points along the distribution chain. Although it is found possible to meet the desired EN specification for metal contaminated JBD by using antioxidant, it will have a cost implication, as antioxidants are costly chemicals. Therefore, a very small amount of MD was blended with antioxidant AO-1. It is observed that, when 5 ppm of MD was blended with AO-1 to enhance the IP of JBD to meet EN-14112 specification, there was reduction of usage of minimum of 200 ppm of AO-1 for iron, nickel and manganese contaminated JBD, and 300 ppm of AO-1 for cobalt and copper contaminated JBD. Further, it is observed that, when 10 ppm of MD was blended with AO-1 to enhance the IP of JBD to meet EN-14112 specification for biodiesel OS, there was reduction of usage of minimum of 250 ppm of AO-1 for iron, nickel and manganese contaminated JBD, and 350 ppm of AO-1 for cobalt and 450 ppm for copper contaminated JBD respectively. Reduction of minimum of 300e450 ppm of usage of antioxidant AO-1 is noted, when 15 ppm of MD is blended with AO-1. Reduction of minimum of 300e450 ppm of usage of AO-1 is again noted when 20 ppm of MD is blended with AO-1.

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It can be concluded that usage of antioxidant can be reduced by 30e50%, therefore the cost, even if very small amount of MD is doped in JBD to meet EN-14112 specification. References [1] Kumar R, Sharma M, Ray SS, Sarpal AS, Gupta AA, Tuli DK, et al. Biodiesel from Jatropha curcas and Pongamia Pinnata, SAE Publication No. 2004-28-0087. [2] Dunn RO. Effect of oxidation under accelerated conditions on fuel properties of methyl soyate (biodiesel). Journal of the American Oil Chemists' Society 2002;79(9):915e20. [3] Knothe G. “Designer” biodiesel: optimizing fatty ester composition to improve fuel properties. Energy & Fuels 2008;22(2):1358e64. [4] Burton R. An overview of ASTM D6751: biodiesel standards and testing methods. Alternative Fuels Consortium; 2008. [5] Sarin R, Sharma M, Sinharay S, Malhotra RK. Jatrohaepalm biodiesel blends: an optimum mix for Asia. Fuel 2007;86(10e11):1365e71. [6] Frankel EN. Lipid oxidation. Dundee, Scotland: The Oily Press; 1998. p. 19. [7] Hui YH, editor. Bailey's industrial oil and fat products. 5th ed, vol. 4. New York: John Wiley & Sons, Inc.; 1996. p. 411e5. [8] Dunn RO. Oxidative stability of soybean oil fatty acid methyl esters by oil stability index (OSI). Journal of the American Oil Chemists' Society 2005;82 (5):381e7. [9] Polavka J, Paligova J, Cvengros J, Simon P. Oxidation stability of methyl esters studied by differential thermal analysis and Rancimat. Journal of the American Oil Chemists' Society 2005;82(7):519e24. [10] Ferrari RA, Oliveira VD, Scabio A. Oxidative stability of biodiesel from soybean oil fatty acid ethyl esters. Scientia Agricola 2005;62(3):291e5. [11] Mittelbach M, Schober S. The influence of antioxidants on the oxidation stability of biodiesel. Journal of the American Oil Chemists' Society 2003;80 (8):817e23. [12] Dunn RO. Effect of antioxidants on oxidative stability of methyl soyate. Fuel Process Technology 2005;86(10):1071e85. [13] Liang YC, May CY, Foon CS, Ngan MA, Hock CC, Basiron Y. The effect of natural and synthetic antioxidants on the oxidative stability of palm diesel. Fuel 2006;85(5e6):867e70. [14] Mittelbach M, Gangl S. Long storage stability of biodiesel made from rapeseed and used frying oil. Journal of the American Oil Chemists' Society 2001;78 (6):573e7. [15] Bondioli P, Gasparoli A, Bella LD. Biodiesel stability under commercial storage conditions over one year. European Journal of Lipid Science and Technology 2003;105(12):735e41. [16] Bouaid A, Mercedes M, Aracil J. Long storage stability of biodiesel from vegetable and used frying oils. Fuel 2007;86(16):2596e602. [17] Park JY, Kim DK, Lee JP, Park SC, Kim YJ, Lee JS. Blending effects of biodiesels on oxidation stability and low temperature flow properties. Bioresource Technology 2008;99(5):1196e203. [18] Sarin R, Kumar R, Srivastav B, Puri SK, Tuli DK, Malhotra RK, et al. Biodiesel surrogates: achieving performance demands. Bioresource Technology 2009;100:3022e8. [19] Sarin A, Arora R, Singh NP, Sharma M, Malhotra RK. Influence of metal contaminants on oxidation stability of Jatropha biodiesel. Energy 2009;34 (9):1271e5. [20] Sarin A, Arora R, Singh NP, Sarin R, Sharma M, Malhotra RK. Effect of metal contaminants and antioxidants on oxidation stability of methyl ester of Pongamia. doi: JAOCS 10.1007/s11746-009-1530-0. [21] McCormick RL, Alleman TL, Ratcliff M, Moens L. Survey of quality and stability of biodiesel and biodiesel blends in the United States in 2004. National Renewable Energy Laboratory, http://www.nrel.gov/docs/fy06osti/38836.pdf; 2005. Technical report No. NREL/TP-540-38836. [22] Alleman TL, McCormick RL. Results of the 2007 B100 quality survey. National Renewable Energy Laboratory, http://www.biodiesel.org/resources/ reportsdatabase/reports/gen/20080301-gen383.pdf; 2008. Technical report No. NREL/TP-540-42787. [23] Tang H, Abunasser N, Wang A, Clark BR, Wadumesthrige K, Zeng S, et al. Quality survey of biodiesel blends sold at retail stations. Fuel 2008;87 (13e14):2951e5. [24] Morris SG, Myers Jr JS, Kip ML, Riemenschneider RW. Metal deactivation in lard. Journal of the American Oil Chemists' Society 1950;27(3):105e7. [25] Krishnamoorthy PR, Vijayakumari S, Sankaralingam S. Effect of antioxidants and metal deactivators on the oxidation of transformer oil. Electrical Insulation, IEEE Transaction on 1992;27(2):271e7. [26] Golubeva IA, Klinaeva EV, Yakovlev VS. Stabilization of blended diesel fuels by combination of antioxidants and metal deactivators. Chemistry and Technology of Fuels and Oils 1994;30(3e4):119e22. [27] Golubeva IA, Klinaeva EV, Koshelev VN, Kelarev VI, Gol'dsher IA. Stabilization of blended diesel fuel with additive combinations. Chemistry and Technology of Fuels and Oils 1997;33(1):23e6. [28] Akinori K. Fuel oil additives (No. 2). Antioxidants and metal deactivators for gasoline. Petrotech 2007;30(1):63e4.