Energy Fuels 2010, 24, 2652–2656 Published on Web 03/19/2010
: DOI:10.1021/ef901172t
Oxidation Stability of Palm Methyl Ester: Effect of Metal Contaminants and Antioxidants Amit Sarin,*,† Rajneesh Arora,‡ N.P. Singh,‡ Rakesh Sarin,§ and R.K. Malhotra§ †
Department of Applied Sciences, Amritsar College of Engineering and Technology, Amritsar-143001, India, ‡Punjab Technical University, Jalandhar-144011, India, and §Indian oil Corporation Ltd., R&D Centre, Sector-13, Faridabad-121007, India Received October 14, 2009. Revised Manuscript Received March 10, 2010
The European biodiesel standard EN-14214 calls for determining the oxidation stability (OS) at 110 °C with a minimum induction time of 6 h by the Rancimat method (EN-14112). The ASTM standard D-6751 has recently introduced a minimum induction period of 3 h. Palm methyl ester (PME) has been successfully evaluated as a diesel substitute in summer and with an additive in winter due to its poor cold-flow properties. Neat PME exhibited an OS of 9.24 h; thus, it was highly stable. Research was conducted to investigate the effect of the presence of transition metals, likely to be present in the metallurgy of storage tanks and barrels, on the highly stable PME. It was found that the influence of metal was detrimental and catalytic even for stable PME. Small concentrations of metal contaminants showed nearly the same influence on OS as large amounts. Copper showed the strongest detrimental and catalytic effect. Antioxidants, namely, tert-butylated hydroxytoluene (TBHT), tert-butylated phenol derivative (TBP), octylated butylated diphenyl amine (OBPA), and tert-butylhydroxquinone (TBHQ) were doped to improve the OS of metal-contaminated PME. It was found that the antioxidant TBHQ was most effective among all of the antioxidants used.
method.7-9 Indian specification IS-15607 also requires a minimum induction time of 6 h.10,11 The oxidation process is reported in the literature. Relative rates of oxidation are 1 for oleates, 41 for linoleats, and 98 for linolenates.12,13 The oxidation chain reaction is usually initiated at the allylic to double bonds. Therefore, fatty acids with methylene-interrupted 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 methylene groups, for example, linolenic acid [(9Z,12Z,15Z)-octadecatrienoic acid], are even more susceptible to degradation. There are several publications on the storage, OS of biodiesel, and effect of antioxidants on the stability of biodiesel. Dunn has studied the oxidative stability of soybean oil fatty acid methyl esters by oil stability index (OSI).14 Polavka et al. studied the OS of methyl esters derived from rapeseed oil and waste frying oil, both distilled and undistilled, by differential thermal analysis and Rancimat.15 Ferrari et al. compared the oxidative stability of neutralized, refined, and frying oil waste soybean oil fatty acid ethyl ester.16 Mittelbach et al. investigated the influence of different synthetic and natural antioxidants on the OS of biodiesel produced from rapeseed oil, sunflower oil, used frying oil, and beef tallow, both distilled and undistilled.17 Dunn has also studied the effect of different
1. Introduction A number of researchers have investigated alternate renewable fuel sources and concluded that vegetable oil-based fuels can be used as alternative fuels.1-6 Biodiesel is commercially produced through the transesterification of vegetable oils, residual frying oils, or animal fats with alcohol and alkaline catalysts. Soybean oil and rapeseed are common feedstocks used for biodiesel production in USA and Europe. However, Southeast Asian countries such as Indonesia have surplus palm crops. The quality of biodiesel is designated by several standards such as EN-14214 and ASTM D-6751, and oxidation stability (OS) is among the monitored parameters as the 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 the ASTM standard D-6751 has recently introduced a minimum IP of 3 h by the same *To whom correspondence should be addressed. E-mail: amit.sarin@ yahoo.com. (1) Ali, Y.; Hanna, M. A. Bioresour. Technol. 1994, 50, 153–163. (2) Chien, Y.-C.; Lu, M.; Chai, M.; Boreo, F. J. Energy Fuels 2009, 23, 202–206. (3) Qian, J.; Yun, Z. Energy Fuels 2009, 23, 507–512. (4) Ma, F.; Hanna, M. A. Bioresour. Technol. 1999, 70, 1–15. (5) Yuan, H.; Yang, B. L.; Zhu, G. L. Energy Fuels 2009, 23, 548–552. (6) May, C. Y.; Liang, Y. C.; Foon, C. S.; Ngan, M. A.; Hook, C. C.; Basiron, Y. Fuel 2005, 84, 1717–1720. (7) Dunn, R. O. J. Am. Oil Chem. Soc. 2002, 79, 915–920. (8) Knothe, G. Energy Fuels 2008, 22, 1358–1364. (9) Sarin, A.; Arora, R.; Singh, N. P.; Sarin, R.; Sharma, M.; Malhotra, R. K. J. Am. Oil Chem. Soc. [Online early access]. DOI: 10.1007/s11746-009-1530-0. Published Online: Dec 29, 2009. (10) Sarin, A.; Arora, R.; Singh, N. P.; Sarin, R.; Malhotra, R. K.; Kundu, K. Energy 2009, 34, 2016–2021. (11) Sarin, A.; Arora, R.; Singh, N. P.; Sarin, R.; Malhotra, R. K.; Sarin, S. Energy Fuels [Online early access]. DOI: 10.1021/ef901131m. Published Online: Feb 16, 2010. r 2010 American Chemical Society
(12) Frankel, E. N. Lipid Oxidation; The Oily Press: Dundee, Scotland, 1998; p 19. (13) Hui, Y. H., Ed. Bailey’s Industrial Oil and Fat Products, 5th ed.; John Wiley & Sons, Inc.: New York, 1996; Vol. 4, pp 411-415. (14) Dunn, R. O. J. Am. Oil Chem. Soc. 2005, 82, 381–387. (15) Polavka, J.; Paligova, J.; Cvengros, J.; Simon, P. J. Am. Oil Chem. Soc. 2005, 82, 519–524. (16) Ferrari, R. A.; Oliveira, V. D.; Scabio, A. Sci. Agric. 2005, 62, 291–295. (17) Mittelbach, M.; Schober, S. J. Am. Oil Chem. Soc. 2003, 80, 817–823.
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: DOI:10.1021/ef901172t
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Table 1. Physico-Chemical Properties of Palm Methyl Ester in Accordance with ASTM D-6751, EN-14214, and IS-15607 Standards10,11
property (units)
ASTM D 6751 ASTM D 6751 test method limits
EN 14214 test method
EN 14214 limits
IS 15607 test method
IS 15607 limits
mean PME
standard deviation
EN ISO 3679 EN ISO 3104 EN ISO 3987 EN ISO 20846/20884
min. 120 3.5-5.0 Max. 0.02 max. 0.0010
IS 1448 P:21 IS 1448 P:25 IS 1448 P:4 ASTM D 5453
min. 120 2.5-6.0 Max. 0.02 max. 0.005
138 4.50 0.002 0.003
1.51 0.014 0.0 0.0012
EN ISO 2160 EN ISO 5165
max. 1 min. 51
IS 1448 P:15 IS 1448 P:9 D-2709
max. 1 min. 51 max. 0.05
1 55.3 0.01
0.0 0.10 0.0056
flash point (°C) viscosity at 40 °C (cSt) sulfated ash (% mass) sulfur (% mass)
D-93 D-445 D-874 D-5453/ D-4294
copper corrosion cetane number water and sediment (vol. %) conradson carbon residue (CCR) 100% (% mass) neutralization value (mg, KOH/g) free glycerin (% mass)
D-130 D-613 D-2709
min.130 1.9-6.0 max. 0.02 max. 0.0015 (S 15) max. 0.05 (S 500) max. 3 min. 47 max. 0.05
D-4530
max. 0.05
EN ISO 10370
max. 0.3
D-4530
max. 0.05
0.032
0.0055
D-664
max. 0.50
EN ISO 14104
max. 0.5
max. 0.50
0.26
0.025
D-6584
max. 0.02
max. 0.02
max. 0.02
0.01
0.0
total glycerin (% mass) phosphorus (% mass) distillation temperature oxidation stability at 110 °C (h) CFPP (°C)
D-6584 D-4951 D-1160 EN 14112
max. 0.24 max. 0.001 90% at 360 °C min. 3 h
EN ISO 14105/14106 EN ISO 14105 EN 14107
IS 1448 P:1/ Sec.1 D-6584
max. 0.25 max. 0.001 min 90% min. 6 h
0.015 90% 9.24
0.0057 0.013
14
0.57
D 6371
EN ISO 14112
max. 0.25 D-6584 max. 0.0010 D-4951 not under spec. min. 6 h EN 14112
EN 116
variable
antioxidants on the OS of biodiesel from soybean oil.18 Thermal and oxidative degradation of castor oil biodiesel was also investigated.19 Researchers also studied the effects of oxidation during long-term storage on the fuel properties of palm oil-based biodiesel.20 Recently, surrogate molecules, i.e., methyl, ethyl, isopropyl, and butyl esters of β-branched fatty acid, were synthesized and had substantially better OS, low temperature flow properties, and cetane number.21 From these literature reports and quality survey reports,22-24 it can be concluded that it will not be possible to use biodiesel without antioxidants. Recently, Sarin et al. studied the influence of the presence of five metals, iron, nickel, manganese, cobalt, and copper, commonly found in the metallurgy of storage tanks and barrels, on the OS of biodiesel synthesized from nonedible oil seeds from Jatropha curcas and Pongamia pinnata with the Rancimat test method.9,25 Loh et al. investigated the oxidative stability and storage behavior of fatty acid methyl esters derived from used palm oil,26 and Liang et al. studied the effect of natural and synthetic antioxidants on the oxidative stability of palm diesel.27 However, no paper is
IS 1448 P:10
Table 2. Fatty Acid Methyl Ester Composition of Palm Methyl Ester10,11 fatty acid methyl ester
palm methyl ester (wt %)
palmitic (C16:0) stearic (C18:0) oleic (C18:1) linoleic (C18:2) saturated unsaturated
40.3 4.1 43.4 12.2 44.4 55.6
available on the influence of the presence of metals on the OS of biodiesel from palm. In the present study, we have undertaken studies on the stability of biodiesel synthesized from palm. The first objective of this study is to investigate the influence of the presence of metals on the OS of palm methyl ester (PME) and then to compare the effects of various metals on OS with results reported in the literature.25 The second objective is to improve the OS of PME by doping with various antioxidants and to compare their effectiveness with results reported in the literature.25 Several transition metals, iron, nickel, manganese, cobalt, and copper, commonly found in the metallurgy of storage tanks and barrels, were blended with varying concentrations in PME samples.
(18) Dunn, R. O. Fuel Process. Technol. 2005, 86, 1071–1085. (19) Conceicao, M. M.; Fernandes, V. J., Jr.; Aranjo, A. S.; Farias, M. F.; Santos, L. M. G.; Souza, A. G. Energy Fuels 2007, 21, 1522–1527. (20) Lin, C.-Y.; Chiu, C.-C. Energy Fuels 2009, 23, 3285–3289. (21) Sarin, R.; Kumar, R.; Srivastav, B.; Puri, S. K.; Tuli, D. K.; Malhotra, R. K.; Kumar, A. Bioresour. Technol. 2009, 100, 3022–3028. (22) McCormick, R. L.; Alleman, T. L.; Ratcliff, M.; Moens, L. Survey of Quality and Stability of Biodiesel and Biodiesel Blends in the United States in 2004. In National Renewable Energy Laboratory Technical Report No. NREL/TP-540-38836, 2005. (23) Alleman, T. L.; McCormick, R. L. Results of the 2007 B100 Quality Survey. In National Renewable Energy Laboratory Technical Report No. NREL/TP-540-42787, 2008. (24) Tang, H.; Abunasser, N.; Wang, A.; Clark, B. R.; Wadumesthrige, K.; Zeng, S.; Kim, M.; Salley, S. O.; Hirschlieb, G.; Wilson, J.; Ng, K. Y. S. Fuel 2008, 87, 2951–2955. (25) Sarin, A.; Arora, R.; Singh, N. P.; Sharma, M.; Malhotra, R. K. Energy 2009, 34, 1271–1275. (26) Loh, S.-K.; Chew, S. M.; Choo, Y.-M. J. Am. Oil Chem. Soc. 2006, 83, 947–952. (27) Liang, Y. C.; May, C. Y.; Foon, C. S.; Ngan, M. A.; Hock, C. C.; Basiron, Y. Fuel 2006, 85, 867–870.
2. Experimental Section 2.1. Materials. Methanol used in the synthesis of PME was of 99.8% purity and was purchased from Ranbaxy Fine Chemicals Ltd. (New Delhi, India). N-Hexane and MeOH/KOH were of analytical grade and were procured from Merck Specialties Pvt. Ltd. (New Delhi, India) and Sigma-Aldrich Chemical Co. (New Delhi, India), respectively. Antioxidants, namely, tertbutylated hydroxytoluene (TBHT), tert-butylated phenol derivative (TBP), octylated butylated diphenyl amine (OBPA), and tert-butylhydroxquinone (TBHQ), were of analytical grade and were purchased from Sigma-Aldrich Chemical Co. (New Delhi, India). Cobalt, manganese, iron, copper, and nickel naphthenates were procured from M/s Notional Chemicals & Dyes Co. (Varanasi, India). 2.2. Methods. PME was synthesized from refined palm oil in the laboratory according to the methodology described in the 2653
Energy Fuels 2010, 24, 2652–2656
: DOI:10.1021/ef901172t
Sarin et al.
Figure 1. Effect of metal contamination (ppm) on the oxidation stability (h) of PME.
literature.28,29 Biodiesel from palm oil was prepared by a transesterification process, involving the reaction of oil with methanol under reflux conditions. A series of experiments were designed to determine the optimal reaction conditions to maximum conversion. Methanol (8:1 molar ratio, alcohol/oil) was added to the reactor followed by the slow addition of catalyst (0.6 wt % of oil) with stirring. The stirring was continued until the complete dissolution of catalyst (15 min). Thus, palm oil was added, and the reaction temperature was set at 65 °C for the experiment. After the completion of the reaction, the material was transferred to a separating funnel, and both phases were separated. The upper phase was methyl ester (biodiesel), and the lower part was glycerin. Alcohol from both phases was distilled off under vacuum. The glycerin phase was neutralized with acid and stored as crude glycerin. The methyl ester was washed with water twice to remove the traces of glycerin, unreacted catalyst, and soap formed during transesterification. The residual product was kept under vacuum to get rid of residual moisture. The product obtained (>98%) was sufficiently pure for testing. The synthesized PME was tested for physicochemical properties according to ASTM D-6751, EN14214, and Indian IS-15607 specifications (Table 1).10,11 It is clear from the data that PME met all of the specifications but had poor flow properties. The fatty acid methyl ester composition of PME was 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 a di(ethylene glycol) succinate column (DEGS) by preparing the corresponding fatty acid esters and comparing them with standard fatty acid ester samples. The GC was equipped with a flame ionization detector (FID) and a glass column 3.1 m 2.1 mm i.d. with a temperature program of 150-250 °C (6 °C/min, hold for 20 min). The oven temperature was kept at 200 °C; the injector temperatures were 230 and 250 °C. Detailed fatty acid methyl ester composition (wt %) is given in Table 2.10,11 Metal naphthenates were selected, being highly soluble in biodiesel. The metal concentration in metal naphthenates was checked by the ASTM D4951 test method, using inductively coupled plasma atomic emission spectroscopy. The concentrations of cobalt, manganese, iron, copper, and nickel in their naphthenates were 5.21, 5.20, 3.91, 6.80, and 4.99%, respectively. The samples were further diluted in PME to the desired concentration. The concentration of carboxylic acid in metal naphthenates was practically none (
