Effect of Antioxidants and Additives on the Oxidation Stability of Jatropha Biodiesel

Transcription

1 Kasetsart J. (Nat. Sci.) 44 : (2010) Effect of Antioxidants and Additives on the Oxidation Stability of Jatropha Biodiesel Duanpen Chaithongdee 1, Jarun Chutmanop 1, 2 and Penjit Srinophakun 1, 2 * ABSTRACT Jatropha biodiesel was produced by a transesterification reaction, using potassium hydroxide at 1.5% by weight of Jatropha oil as a catalyst. The mole ratio of methanol and Jatropha oil was 7:1. The temperature, speed of mixing and reaction time used were 45 C, 600 rpm and 1.5 h, respectively. Antioxidants and additives were added to Jatropha biodiesel. The range of antioxidant and additive concentrations was and 0-1,000 ppm, respectively. The three antioxidants used were PG (3,4,5- trihydroxybenzoic acid propyl ester, propyl gallate), TBHQ (t-butyl hydroquinone) and BHA (butylated hydroxyanisole). The three commercial additives used were ZEP additive, NITROX and L-power. The induction time of biodiesel with either antioxidant or additive was measured according to EN14112, using a Rancimat instrument. The results showed that PG was the best antioxidant for the production of Jatropha biodiesel at concentrations of 50, 150, 250, 350, 500, 650 and 750 ppm, which improved the induction time from 4.21 with no additive to 18.93, 26.35, , 34.04, and h respectively. Regarding the effect on storage for 20 weeks, Jatropha biodiesel with PG added at a concentration of 150 ppm, resulted in an induction time from the first week storage of h and this reduced to h in the final week (10.47% reduction from the first week). The Jatropha biodiesel properties that resulted from the addition of PG at a concentration of 150 ppm were within the acceptable range, according to ASTM and EN Standards. Key words: oxidation stability, biodiesel, Jatropha oil, induction time INTRODUCTION With the increasing price of petroleum fuel as supplies are depleted, the need for alternative fuel sources has steadily increased. Biodiesel is an alternative fuel, derived from vegetable oil, animal fat or waste cooking oil that can be used directly or blended with petroleum diesel at any percentage without engine modification (Faupel and Kurki, 2002). The advantages of biodiesel are a reduction in vehicle emissions and engine wear, and it is non-toxic and biodegradable (Faupel and Kurki, 2002; Hancsok et al., 2008; Kalam and Masjuki, 2008). The use of edible vegetable oil for biodiesel production has not been successful because of its unstable price (Chhetri et al., 2008). As the demand for vegetable oils for food has increased substantially in recent years, it would be better to use non-edible oils for biodiesel production. Therefore, non-edible oils, such as Jatropha oil, will become significant sources for 1 Department of Chemical Engineering, Faculty of Engineering, Kasetsart University, Bangkok 10900, Thailand. 2 Center for Petroleum, Petrochemicals and Advanced Materials, Chulalongkorn University, Bangkok 10330, Thailand. * Corresponding author, fengpjs@ku.ac.th Received date : 31/07/09 Accepted date : 09/10/09

2 244 Kasetsart J. (Nat. Sci.) 44(2) biodiesel production now or in the future (Chhetri et al., 2008; Kywe and Oo, 2009). Jatropha is a fast growing plant, which requires little water or fertilizer; it can survive in infertile soils (Sarin et al., 2007). Generally, the oil content of the Jatropha seed is 30 40% (Augustus et al., 2002; Sarin et al., 2007). Oil from the Jatropha seed has excellent properties, including low acidity, low viscosity compared to castor oil and a better cloud point and pour point when compared to palm oil (Tapanes et al., 2008). Biodiesel is an ester of a fatty acid. The properties of biodiesel depend on the feedstock. If the feedstock is composed of high unsaturated fatty acids, the oxidation stability of biodiesel is low (Domingos et al., 2007; McCormick et al., 2007; Sarin et al., 2007). The oxidation stability affects fuel qualities. In fact, esters have low stability (Sarin et al., 2007). If biodiesel is exposed to air or oxygen, it is oxidized to alcohol and acids (Knothe, 2007; Sarin et al., 2007). The presence of alcohol will lead to a reduction in the flash point and the presence of acid will increase the total acid number (Sarin et al., 2007). The sensitivity of the oxidation stability is due to the unsaturated fatty acid content in the oil (McCormick et al., 2007; Sarin et al., 2007). Other factors, which also have an influence on the oxidation stability of biodiesel are light, high temperature, metals, peroxides and antioxidants (Knothe, 2007; McCormick et al., 2007; Sarin et al., 2007). The mechanism of the biodiesel oxidation process can be divided into three steps, which are shown in Figure 1, where RH is the fatty acid methyl ester, R is a free radical, O 2 is the oxygen in the air, ROO is a peroxide radical and R-R and ROOR are the products of the oxidation process. During the oxidation process, the fatty acid methyl ester is likely to form a free radical at the position next to the double bond (Equation 1) (McCormick et al., 2007; Sarin et al., 2007). The radical quickly reacts with the oxygen in the air and becomes a peroxide radical (Equation 2), which immediately creates a new free radical from the fatty acid methyl ester (Equation 3) (McCormick et al., 2007; Sarin et al., 2007). The reaction will continue until two free radicals react with each other (Equation 4) or the peroxide radical reacts with a free radical in the terminal step (Equation 5) (Sarin et al., 2007). This process results in the formation of acids, esters, aldehydes, ketones etc. (McCormick et al., 2007; Sarin et al., 2007). This leads to changes in the biodiesel properties, such as viscosity, acid number and oxidation stability (Bondioli et al., 2003). The European standard for biodiesel (EN14112) evaluates the oxidation stability using a Rancimat instrument. The standard oxidation stability is 6 h at 110 C. The oxidation stability of biodiesel can be improved by adding an appropriate antioxidant (McCormick et al., 2007). Two common types of antioxidants are either a phenolic-type and an aminic-type (Sarin et al., 2007) (Figure 2). Generally, the antioxidant, which can hinder the combination oxidation reaction in Figure 1, contains highly labile hydrogen that is Initiation RH R (1) Propagation R + O 2 ROO (2) ROO + RH ROOH + R (3) Termination R + R R-R (4) ROO + R ROOR (5) Figure 1 Mechanism of the biodiesel oxidation process.

3 Kasetsart J. (Nat. Sci.) 44(2) 245 more easily abstracted by the peroxy radical than the fatty oil or ester hydrogen (Sarin et al., 2007). Mittelbatch and Schober (2003) found that the efficiency of a given antioxidant depends on the raw material of the biodiesel. Therefore, while any type of antioxidant may be suitable for a particular feedstock of biodiesel, some antioxidants can improve oxidation stability slightly, while others can produce a substantial improvement in oxidation stability. Consequently, this research was conducted to determine the type of antioxidant appropriate for use with Jatropha biodiesel. MATERIALS AND METHODS Jatropha oil, which was a feedstock for biodiesel production, was extracted from the expeller. Three antioxidant and three commercial additives were used in this experiment. The antioxidants, which were PG (Propyl gallate), TBHQ (t-butyl hydroquinone) and BHA (butylated hydroxyanisole), were analytical grade (Fluka, Switzerland). The three additives were ZEP additive, NITROX and L-power. The ZEP additive (ZEP diesel fuel additive) was obtained from the Zep Manufacturing Company of Canada. NITROX (NITROX injector cleaner) was obtained from Tetrosyl Limited (United Kingdom). L-power was obtained from Loxley Public Company Limited (Thailand). Jatropha biodiesel was produced by transesterification reaction. Potassium hydroxide was used as a catalyst at 1.5% by weight of Jatropha oil. The mole ratio of methanol and Jatropha oil was 7:1. The temperature, speed of mixing and reaction time were 45 C, 600 rpm and 1.5 h respectively, after which the various antioxidants and additives were added to the Jatropha biodiesel. The range in the antioxidant and additive concentrations was and 0-1,000 ppm, respectively. The oxidation stability of the samples was measured by the induction time according to EN14112 (standard method) using a Rancimat instrument (Domingos et al., 2007; Knothe, 2007; Sarin et al., 2007). The best antioxidant or additive was then added to Jatropha biodiesel, which was kept for long-term stability testing. The Jatropha biodiesel sample was stored in a brown bottle, which was closed by parafilm and kept at room temperature for 20 weeks. Every two weeks, a sample was taken to determine the induction time. RESULTS AND DISCUSSION Figure 2 Mechanism of the anti-oxidation process of antioxidants (Sarin et al., 2007). Effect of antioxidants on the oxidation stability of Jatropha biodiesel In this experiment, the induction time was measured as an indication of the oxidation stability of biodiesel. Three antioxidants, PG, TBHQ and BHA, were added to Jatropha biodiesel in a concentration range of ppm. Figure 3 shows the effect of the concentration of antioxidants on the oxidation stability. The induction time of Jatropha biodiesel

4 246 Kasetsart J. (Nat. Sci.) 44(2) without antioxidant was 4.21 h, which is below the standard value of the oxidation stability of 6 h (Domingos et al., 2007; Knothe, 2007; Sarin et al., 2007). The induction time increased with incremental increases in the antioxidant concentration. Dunn (2005) and McCormick et al. (2007) also reported similar results. Dunn (2005) studied the effect of five antioxidants (BHA, BHT, TBHQ, α-tocopherol and PG) on the oxidation stability of biodiesel produced from soybean oil by transesterification. It was reported that the oxidation stability increased with increases in the antioxidant concentration. McCormick et al. (2007) also studied the oxidation stability of biodiesel produced from soybean oil, waste oil and tallow, reporting that the oxidation stability increased when the concentration of antioxidant increased. An increment in the antioxidant concentration results in an increase in the number of hydrogen atoms that then can react with the peroxide radical in the oxidation reaction (Ramos et al., 2007), The comparison among PG, BHA and TBHQ at the same concentration is shown in Figure 3. It was found that PG was the most effective antioxidant for Jatropha biodiesel at the minimum concentration of 50 ppm leading to an induction time of h. TBHQ and BHA were the second and the third most effective antioxidants, respectively, being able to produce an induction time in excess of 6 h at a concentration higher than 150 ppm. A similar result was also found by Xin et al. (2008), who studied the effect of two antioxidants (diphenyl-pphenylenediamine and PG) on the oxidation stability of biodiesel produced from palm oil, sunflower oil and rapeseed oil. They reported that PG was the best suitable antioxidant for biodiesel produced from palm oil, sunflower oil and rapeseed oil. Effect of additives on the oxidation stability of Jatropha biodiesel Three commercial additives, ZEP, NITROX and L-power, were added to Jatropha biodiesel in a concentration range of 0-1,000 ppm. The oxidation stability of Jatropha biodiesel with the additive is shown in Figure 4. None of the additives increased the induction time to longer than the standard oxidation stability of 6 h. The Figure 3 Influence of antioxidant concentration on the oxidation stability of Jatropha biodiesel.

5 Kasetsart J. (Nat. Sci.) 44(2) 247 oxidation stability of Jatropha biodiesel with ZEP added increased slightly when the ZEP concentration was increased, with a concentration of ZEP at 1,000 ppm causing an increase in the induction time to 5.30 h. The induction time of Jatropha biodiesel with NITROX added increased slightly with a NITROX concentration of ppm. However, the induction time decreased when the concentration of NITROX was higher than 1,000 ppm. The concentration of NITROX at 750 ppm extended an induction time to 5.29 h. However, the induction time decreased slightly as the concentration of L-power increased. Accordingly, ZEP, NITROX and L-power, did not improve the oxidation stability of Jatropha biodiesel. Changes in the oxidation stability during 20 weeks of storage PG, TBHQ, BHA, ZEP, NITROX and L- power were studied in order to find the best antioxidant or additive to improve the oxidation stability of Jatropha biodiesel. The results showed that PG was the best antioxidant that resulted in an induction time longer than the other products. Consequently, PG was selected for addition to Jatropha biodiesel for further study. PG was added to Jatropha biodiesel at a concentration of 150 ppm and stored for 20 weeks. The concentration level of 150 ppm was selected to ensure that the induction time remained higher than 6 h during storage. A concentration of 50 ppm produced an induction time lower than 6 h within the 20 weeks of storage. After storage, the induction time of the sample was more than 6 h when PG was added at a concentration of 250 ppm. However, the lowest concentration of antioxidant was preferred as it meant a cost saving by requiring less antioxidant concentration. Consequently, a concentration of 150 ppm was used. The sample was stored in a brown bottle at room temperature (about 30 C) for 20 weeks. Every two weeks, the induction time of the sample was measured and the results are shown in Figure 5. The aim of this experiment was to predict the behavior of Jatropha biodiesel when it was maintained under steady environmental conditions for a reasonable period. During storage, the Figure 4 Influence of additive concentration on the oxidation stability of Jatropha biodiesel.

6 248 Kasetsart J. (Nat. Sci.) 44(2) Figure 5 Changes in the oxidation stability during storage. induction time steadily decreased. The induction time after one week of storage was h and this reduced to h in the final weeks (a reduction of 10.47% from the first week). The oxidation reaction of biodiesel during storage caused the acid number to increase, as was suggested by Bouaid et al. (2007). The acid number increased with the increase in peroxide because the ester (biodiesel) was oxidized to form peroxide, which underwent a complex reaction, including the formation of a reactive aldehyde, which could be oxidized into acid. In addition, acid could be formed also from hydrolysis of the ester into alcohol and acid (Bouaid et al., 2007). Consequently, the increment of acid, alcohol and aldehyde resulted in a reduction in the induction time during storage (Bouaid et al., 2007). Prankl and Schindlbauer (1998) and Bondioli et al. (2003) studied the long-term stability of biodiesel produced from rapeseed oil kept at room temperature. They reported that the induction time decreased during storage. Properties of Jatropha biodiesel The objective of this experiment was to study the effect of PG antioxidant on the major properties of Jatropha biodiesel. The major properties studied were: viscosity at 40 C, cloud point, pour point, flash point, density at 15 C, neutralization value (acid number, acid value) and the induction time. Table 1 compares the properties of Jatropha biodiesel without antioxidant with those when PG is added at a concentration of 150 ppm. According to Table 1, the properties of Jatropha biodiesel, with PG added at a concentration of 150 ppm, changed slightly within the range of the standard properties of biodiesel defined by ASTM D6751 (Knothe, 2007; McCormick et al., 2007; Dunn, 2005). Consequently, PG was considered an interesting option to improve the oxidation stability of Jatropha biodiesel with no effect on the principal properties. CONCLUSION The study compared the effects of various types of antioxidants and additives on the oxidation stability of Jatropha biodiesel. PG was identified as the most suitable antioxidant to improve the oxidation stability of Jatropha

7 Kasetsart J. (Nat. Sci.) 44(2) 249 Table 1 Physico-chemical properties of Jatropha biodiesel. Property (units) Test method Limits Jatropha Jatropha biodiesel with biodiesel PG added at 150 ppm Viscosity at 40 C (cst) ASTM D Cloud point ( C) ASTM D Pour point ( C) ASTM D Flash point ( C) ASTM D 93 Min Density at 15 C ASTM D (kg/m 3 ) Neutralization value ASTM D 664 Max (mg KOH/gm) Oxidation stability (h) EN Min biodiesel. ZEP, NITROX and L-power were not appropriate additives to improve the oxidation stability of Jatropha biodiesel. From this study, the minimum concentration of 50 ppm of PG was the best antioxidant for Jatropha biodiesel according to the standard for the oxidation stability of biodiesel (EN14112). When Jatropha biodiesel with PG added at a concentration of 150 ppm was stored for 20 weeks, the induction time after the first week of storage was and reduced to in the final week (a 10.47% reduction). All the properties of Jatropha biodiesel with PG added at a concentration of 150 ppm were within the acceptable range for the standard properties of biodiesel. Therefore, PG was considered a suitable antioxidant to improve the oxidation stability of Jatropha biodiesel with long-term oxidation stability retention. ACKNOWLEDGEMENTS The authors thank the Center of Excellence for Petroleum, Petrochemicals and Advanced Materials, the Graduate School, Kasetsart University and the KU Biodiesel Project for financial support. LITERATURE CITED Augustus, G.S., M. Jayabalan and G.J. Seiler Evaluation and bioinduction of energy components of Jatropha curcas. Biomass Bioenerg. 23: Bondioli, P., A. Gasparoli, L.D. Bella, S. Tagliabue, G. Toso, J. Fischer and A. Frohlich Work Package 2 Storage Tests, pp In H. Prankl (ed.). Stability of Biodiesel. Druckerei Queiser GmbH, Amstetten, Austria. Bouaid, A., M. Martinez and J. Aracil Long storage stability of biodiesel from vegetable and used frying oils. Fuel 86: Chhetri, A.B., M.S. Tango, S.M. Budge, K.C. Watts and M.R. Islam Non-edible plant oils as new sources for biodiesel production. Int. J. Mol. Sci. 9: Domingos, A.K., E.B. Saad, W.D. Vechiatto, H.M. Wilhelm and L.P. Ramos The Influence of BHA, BHT and TBHQ on the Oxidation Stability of Soybean Oil Ethyl Ester (Biodiesel). J. Braz. Chem. Soc. 18: Dunn, R.O Effect of antioxidants on the oxidative stability of methyl soyate (biodiesel). Fuel Process. Technol. 86: Faupel, K. and A. Kurki Biodiesel: a Brief Overview. Available source: June 10, Hancsok, J., M. Bubalik, A. Beck and J. Baladincz Development of multifunctional

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