The Effect of Acid Catalyst Concentration on The Purity and Yield of Biodiesel Produced from in-situ Esterification of Rice Bran Setiyo Gunawan *, Syahrizal Maulana, Khairiel Anwar, Mulyanto, Arief Widjaja, and Tri Widjaja Department Sepuluh Nopember Institute of Technology, Surabaya 60111 Indonesia * Corresponding Author s E-mail: gunawan@chem-eng.its.ac.id Abstract Biodiesel is biodegradable, renewable, non-toxic and environmentally friendly energy. The cost of the raw materials comprises 60-88% of the production cost in commercial biodiesel (fatty acid methyl esters, FAMEs) production. Therefore, due to the economic reasons, the use of low cost raw materials as substrats for biodiesel production is being preferred. In this case, rice bran, which contents 13.5% oil, is an interesting substrat. In-situ esterification of high-acidity rice bran with methanol and sulfuric acid catalyst was investigated.the effects of sulfuric acid catalyst concentration and reaction time on purity and yield of biodiesel were discussed. The compositions of produced methyl esters due to the conditions were also determined. Increasing the sulfuric acid catalyst concentration from 1.5 to 5% decreased the FAMEs yield by about 84%. Using larger sulfuric acid catalyst concentration resulted in bran darkening and an increase in bran stickiness that interfered with separation operations. This was probably due to bran cell wall disruption by the acid. It was found that the ratio between saturated and unsaturated fatty acids of the isolated FAMEs was 1.08. Keywords: in-situesterification; sulfuric acid catalyst concentration; rice bran. 1. Introduction The energy crisis is an irony to Indonesia, one of the world s fossil fuel producers. Yet, it is a logical consequence of heavily export-oriented policy and behavior in the sector. The high production of coal and gas, both with huge reserves, is prioritized for export, instead of domestic consumption. Daily national oil consumption reaches 1.3 million barrel and is predicted to increase by 1.5% annually, a trend that will not easily be coped with due to difficulties in finding substitute to oil. Therefore, finding alternative renewable energies becomes an important topic. Biodiesel is biodegradable, renewable, non-toxic and environmentally friendly. It can be mixed with petroleum diesel in any proportion or directly be used in diesel engine without modification. Recently, most commercial biodiesels are produced from edible vegetable oils (Murugesan et. al., 2008). Due to the economic reasons, the use of low cost raw materials (Bozbas, 2008; Dorado et al., 2006; Hass et al., 2004,2006), such as rice bran oil, as substrats for biodiesel production is being preferred. Indonesia is currently the fourth-largest producer of rice in the world. Indonesian rice production increased to 38.3 MMT from 37.3 MMT in 2009. Moreover, rice bran, a by-product of rice milling, is a brown layer present between rice and the outer husk of the paddy. It represents about 5-10% of the G014-1
paddy depending on the variety of paddy. At present, it is mostly used as livestock feed and as boiler fuel in most rice producing countries (Ju and Vali, 2005). The economic competitiveness of biodiesel process can be improved by applying in-situ process, such as in-situ acid esterification (Özgül-Yücel and Türkay, 2002; Yustianingsih, 2007), insitu supercritical tranesterification of rice bran (Kasim et al., 2009), and two-steps in-situ process (Shiu et al., 2010). This method didn t include extraction time from seeds, and actually extraction oil from oilseed is not a short step. However, the excess alcohol and acid were needed. In esterification, the sulfuric acid attacks free fatty acids in the oil and allows methanol to attach to them to form biodiesel. However, sulfuric acid is not easy to handle, it is quite corrosive and dangerous. Therefore, the objective of this work was to produce biodiesel from rice bran by in-situ esterification in high yield and reasonable short time. The effects of reaction conditions, such as acid to methanol ratio, and time on the yield and purity of biodiesel production were studied systematically. 2. Experimental 2.1. Materials Rice bran was donated by a local mill in Surabaya (Indonesia) and was put into a 60 o C oven for a month to increase their free fatty acids (FFAs) contents and to reduce its water content. Afterwards, the rice bran sample was stored at -60 o C to prevent the formation of free fatty acid caused by the hydrolysis of acylglycerols catalyzed by lipase contained in rice bran. Thin-layer chromatograph (TLC) aluminum plates (20cm x 20cm x 250μm) were purchased from Merck (Darmstadt, Germany). Triacylglycerols were obtained from commercial sources. Standard fatty acids were obtained from Brataco Chemika Company (Jakarta, Indonesia). All solvents and reagents were either of highperformance liquid chromatography (HPLC) grade or analytical reagent grade and were obtained from commercial sources. 2.2. Syntheses of FAMEs standards The fatty acids were converted into their corresponding fatty acid methyl esters (FAMEs) by heating with sulfuric acid in methanol at 60 o C and the reaction was completed in about 1 day. FAMEs were separated by extraction using n-hexane-water. The hexane extract, which contains FAMEs, was collected and the hexane was removed.the products were analyzed by gas chromatography (GC) and TLC. 2.3. Total FAMEs in Rice Bran Rice bran (10 g) was wrapped with filter paper and was placed inside soxhlet extractor. Neutral lipids, such as fatty acids and acylglycerols, were extracted from the rice bran with hexane (350 ml) as the solvent, which was put in a 500 ml round-bottom flask and was heated. After predetermined time, the extraction process was stopped; the flask that contained the desired extract was removed and replaced immediately by another flask that contained 350 ml fresh hexane so that the total amount of solvent remained the same as in the beginning of the run. The first fraction, which was designated as the crude rice bran oil, CRBO (1.35 g), was obtained by extracting with hexane for 4 h. Neutral lipids were not detected in the next fraction, which was obtained after extracting with solvent for another 4 h. The lipids contents in rice bran was calculated by the equation Lipids contents = {[weight of hexane extract, g] / [weight of rice bran, g]} 100 % (1) CRBO was added to a 50 ml tube with a Teflon-lined screw cap. Potassium hydroxide solution (10 ml; 2 N) was added under nitrogen, and the tube was closed with screw cap. The tube was then heated at 60 o C until the saponification reaction was completed (overnight), as verified by analytical TLC (silica gel; eluted with a mixture solvent, hexane/ethyl-acetate/acetic-acid = 90:10:1, v/v/v). The mixture containing saponified matter was acidified to ph2 by using sulfuric acid and the reaction was completed in about 1 day. Water was then added to the mixture to stop the reaction, and unsaponifiable matter was separated by extraction using n-hexane-water. The hexane extract, which contains fatty acids, was collected and the hexane was removed. The fatty acids were then converted into their corresponding fatty acid methyl esters (FAMEs) by heating with sulfuric acid in methanol at 60 o C and the reaction was completed in about 1 day. FAMEs were separated by extraction using n- hexane-water. The hexane extract, which contains FAMEs, was collected and the hexane was removed.the products were analyzed by gas chromatography (GC) and TLC. G014-2
2.4. In-Situ Esterification and Biodiesel Purification A batch reactor, equipped with a magnetic stirrer, a water bath and connected to a condenser system was employed in this study. Ten grams of rice bran was mixed with a solution that was prepared from methanol and sulfuric acid with different concentration, the mixture was then put into a 250 ml batch reactor at 60 o C and atmospheric pressure. The condenser was inserted into the top of reactor and tap water was used as the refrigerant. The condenser ensures that methanol vapor condenses and drips back into the reactor. The mixture was magnetically stirred at 600 rpm and the reaction was carried out for a predetermined time. The mixture was then filtered by using replaceable filter. The solid phase was washed with 50 ml methanol and dried overnight at room temperature. Methanol was removed from the collected liquid phase by rotary evaporator. After that, FAMEs was extracted by hexane (3 50 ml) from the liquid phase. The mixture was washed with water until neutral ph. The mixture was separated into an upper organic layer and a lower aqueous layer. The lower layer was removed and discarded. This liquid-liquid extraction was repeated three times. Residual water was removed from the pooled organic phase by using anhydrous magnesium sulfate. After hexane was removed from the pooled organic layers by using rotary evaporator, the substance left was referred to as the reaction product. The product was analyzed by gas chromatography and TLC. 2.5. Determination of FFAs Contents FFAs contents as oleic acid were determined by the American Oil Chemists Society (AOCS) official method using phenolphtalein as an indicator (AOCS, 1997). Sample was dissolved in ethyl alcohol at 60 oc and FFAs contained in the sample were neutralized with sodium hydroxide solution. The sample mass and the volume of sodium hydroxide used were used to calculate the contents of FFAs. 2.6. TLC and GC Analyses Individual components in each sample were identified by using authentic standards as described by Gunawan et al. (2008). Spots on each plate were visualized by exposing the chromatogram to iodine vapor (Fried, 1996). The sample was dissolved in n-hexane and 0.5 µl of this sample was injected into the gas chromatography. External standard calibration curves were obtained by using 0.2-20 mg pure standard. stearic methyl ester was selected for the determination of FAMEs calibration factor and was used for all FAMEs. Chromatographic analysis was performed in a HP 6890 (Hewlett-Packard Inc., Avondale, Pennsylvania, USA) gas chromatograph equipped with a flame ionization detector. The column used was HP-1 crosslinked methyl siloxane column (60m 0.25mm i.d. 1 μm film thickness, Hewlett-Packard Inc., Avondale, Pennsylvania, USA). The operating conditions were: the injector and detector temperatures were set at 250 o C, the column temperature was held at 200 o C for 2 min, and then was raised to 300 o C at 15 o C/min and was held for 10 min. Helium was used as the carrier gas with a linear velocity of 40 cm/s at 200 o C. The yield of FAMEs was calculated by the equation (Shiuet al., 2010). Yield = {[(weight of the product, g) (content of the compounds in the product, %)] / [weight of potential FAMEs in rice bran]} 100 %. (2) 3. Results and Discussion In this study, production of biodiesel from rice bran by in-situ esterification was investigated. Rice bran obtained from local milling was put into a 60 o C oven for a month to increase their FFAs contents and to reduce its water content. The FFAs contents was increased from 5% to 23.73% and the moiture content was decreased from 14% to 4%. The total lipids (hexane extract) on dry weight basis was 13.54%. This agrees with previuos observations that depending on variety of rice and degree of milling, the bran contains 12-25 wt% of lipids (Gupta, 1989). Another, Saunders (1986) reported that rice bran contains 6.7-17.2% protein, 4.7-22.6% lipids; 6.2-26.9% fibre; 8.0-22.2% ash; and 33.5-53.5% nitrogen free extract. Six fatty acids were identified: myristic acid (2.61%), palmitic acid (47.11%), stearic acid (4.10%), oleic acid (38%), linoleic acid (6.02%) and arachidic acid (1.48%). Palmitate acid was the G014-3
predominat fatty acid followed by oleic, linoleic, stearic, and myristic acids. The ratio of saturated to polyunsaturated fatty acids was 1.26. An in-situ esterification reaction of rice bran with different sulfuric acid concentration in methanol and reaction time were studied at methanol to rice bran ratio of 5 and reaction temperature of 60 o C. The results are shown in Figure 1-3. The excess methanol was used in this study (methanol to rice bran ratios of 5). This was because methanol played the role of both reactant and solvent for extraction. Moreover, the esterification is a reversible reaction so excess methanol favors the formation of FAMEs. The excess methanol was also used in the previous observations (Özgül-Yücel and Türkay, 2002; Yustianingsih et al., 2009; Shiu et al., 2010). Figure 1 shows that the product obtained after purification increased with increasing reaction time. At 1.5% (v/v) sulfuric acid in methanol, rapid conversion of FFAs into FAMEs was observed within 60 min. After that the conversion rate was slower. Previous study, Shiu (2010) reported that the reaction between methanol and FFAs catalyzed by acid is very fast in the first 30 min. It can be also seen that the product obtained at 1.5% (v/v) sulfuric acid in methanol was significantly higher than that of obtained at 5% (v/v) sulfuric acid in methanol after 40 min. Moreover, using larger sulfuric acid catalyst concentration (5% (v/v) sulfuric acid in methanol) resulted in bran darkening and an increase in bran stickiness. This was probably due to bran cell wall disruption by the acid. Therefore, when excess methanol was used, compounds more polar than neutral lipids, such as protein and carbohydrate, were preferentially extracted from rice bran. 0,18 0,16 1.5% (v/v) sulfuric acid in methanol 5% (v/v) sulfuric acid in methanol Product (g) 0,14 0,12 0,10 0,08 0 10 20 30 40 50 60 70 80 90 100 Reaction time (min) Figure 1 Effects of sulfuric acid concentration and reaction time on the product obtained. The purity of FAMEs remains stable about 100% with increasing sulfuric acid concentration and reaction time as shown in Figure 2. This was because the purification process can remove significant the unwanted compounds, such as polar compounds. As the results, the yield of FAMEs increased with increasing reaction time and decreased with increasing sulfuric acid concentration as shown in Figure 3. G014-4
100% Product purity 90% 80% 70% 1,5% (v/v) sulfuric acid in methanol 5% (v/v) sulfuric acid in methanol 0 10 20 30 40 50 60 70 80 90 100 Reaction time (min) Figure 2 Effects of sulfuric acid concentration and reaction time on the purity of FAMEs 60% FAMEs yield 50% 40% 30% 20% 1,5% (v/v) sulfuric acid in methanol 5% (v/) sulfuric acid in methanol 0 10 20 30 40 50 60 70 80 90 100 Reaction time (min) Figure 3 Effects of sulfuric acid concentration and reaction time on the yield of FAMEs 4. Conclusions Biodiesel production from Indonesia rice bran by in-situ esterification was carried out in this work with objective of studying the effect of methanol amount and reaction time on the purity and yield of FAMEs. The product obtained at 1.5% (v/v) sulfuric acid in methanol was significantly higher than that of obtained at 5% (v/v) sulfuric acid in methanol after 40 min. Using larger sulfuric acid catalyst concentration (5% (v/v) sulfuric acid in methanol) resulted in bran darkening and an increase in bran stickiness. This was probably due to bran cell wall disruption by the acid. Therefore, when excess methanol was used, compounds more polar than neutral lipids, such as protein and carbohydrate, were preferentially extracted from rice bran. Acknowledment This work was supported by a grant (I-MHERE 04248/I2.36/RG/2010) provided by the INDONESIA - Managing Higher Education for Relevance & Efficiency. G014-5
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