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Biodiesel production from rice bran by a two-step in-situ process
Bioresource Technology 101 (2010) 984–989
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Biodiesel production from rice bran by a two-step in-situ process Pei-Jing Shiu a, Setiyo Gunawan a,b, Wen-Hao Hsieh a, Novy S. Kasim a, Yi-Hsu Ju a,* a b
Department of Chemical Engineering, National Taiwan University of Science and Technology, 43 Sec. 4, Keelung Road, Taipei 106-07, Taiwan Department of Chemical Engineering, Institut Teknologi Sepuluh Nopember, Kampus ITS Keputih Sukolilo, Surabaya 60111, Indonesia
a r t i c l e
i n f o
Article history: Received 24 July 2009 Received in revised form 2 September 2009 Accepted 3 September 2009 Available online 29 September 2009 Keywords: Rice bran Two-step in-situ transesterification
a b s t r a c t The production of fatty acid methyl esters (FAMEs) by a two-step in-situ transesterification from two kinds of rice bran was investigated in this study. The method included an in-situ acid-catalyzed esterification followed by an in-situ base-catalyzed transesterification. Free fatty acids (FFAs) level was reduced to less than 1% for both rice bran A (initial FFAs content = 3%) and rice bran B (initial FFAs content = 30%) in the first step under the following conditions: 10 g rice bran, methanol to rice bran ratio 15 mL/g, H2SO4 to rice bran mass ratio 0.18, 60 °C reaction temperature, 600 rpm stirring rate, 15 min reaction time. The organic phase of the first step product was collected and subjected to a second step reaction by adding 8 mL of 5 N NaOH solution and allowing to react for 60 and 30 min for rice bran A and rice bran B, respectively. FAMEs yields of 96.8% and 97.4% were obtained for rice bran A and rice bran B, respectively, after this two-step in-situ reaction. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction Fuel plays an important role in the economy of every country. More than 98% of the energy needs of Taiwan are imported. Therefore, improving energy efficiency, developing alternative energy, and securing a stable energy supply are the framework of Taiwan’s sustainable energy policies. Biodiesel is a biodegradable, renewable, non-toxic and environmental friendly alternative fuel. It can be mixed with petroleum diesel in any proportion or used directly in diesel engines without modification. It can be produced from various raw materials such as animal fat (Lin and Li, 2009; Öner and Altun, 2009), refined vegetable oils (Bunyakiat et al., 2006; Estela and Otero, 2008; Liu et al., 2008; Rashid and Anwar, 2008), crude oils (Ghadge and Rahemen, 2005; Jitputti et al., 2006; Veljkovic et al., 2006), and waste edible oils (Tsai et al., 2007). Most commercial biodiesels are produced from edible vegetable oils, such as soybean oil in US, rapeseed and sunflower seed oils in Europe, palm oil in Southeast Asia, and coconut oil in the Philippines (Murugesan et al., 2008). However, the cost of the raw materials comprises 60–70% (Haas et al., 2004) or 75–88% (Bozbas, 2008; Dorado et al., 2006; Haas et al., 2006) of the production cost in commercial biodiesel production. One way of reducing biodiesel production costs is to use low cost raw material, such as rice bran which basically is treated as agricultural waste in most rice producing countries. * Corresponding author. Tel.: +886 2 27376612; fax: +886 2 27376644. E-mail address: [email protected] (Y.-H. Ju). 0960-8524/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2009.09.011
In 2007, the amount of rice bran produced as the by-product of rice milling in Taiwan was about 100,000 tons with a potential of yielding 20,000 tons of crude rice bran oil (CRBO). CRBO is non-edible due to its high free fatty acids (FFAs) contents. Up to 16,000 tons of biodiesel can be produced per year from rice bran which can account for up to 10% of the biodiesel demand in Taiwan when the mandatory B2 is adopted in 2010. A two-step chemical catalyzed methanolysis (Zullaikah et al., 2005) and a two-step lipase catalyzed methanolysis (Lai et al., 2005) have been developed using crude rice bran oil for the production of biodiesel. CRBO can be converted effectively into fatty acid methyl esters (FAMEs) in a reasonably short time (<8 h) with high conversion (>95%). The economic competitiveness of biodiesel can be improved by applying an ‘‘in-situ process”, such as in-situ acid esterification (Özgül-Yücel and Türkay, 2002; Yustianingsih et al., 2009). Kasim et al. (2009) studied biodiesel production from rice bran by in-situ transesterification under supercritical conditions. However, the maximum yield achieved was only 51.3%. When dewaxed–degummed rice bran oil was used under the same conditions, the final yield achieved was 94.8%. In-situ production of biodiesel from seed/bran spares the need of oil extraction. However, additional alcohol and catalyst are usually required. The objective of this work was to produce biodiesel from rice bran by a two-step in-situ reaction (acid-catalyzed followed by base-catalyzed) with high yield in a reasonably short time. The effects of reaction conditions, such as methanol to rice bran ratio, catalyst amount, and reaction time on the yield of biodiesel production were investigated systematically.
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2. Methods 2.1. Materials Rice bran A and B were donated by a local mill in Kaohsiung and Taoyuan (Taiwan), respectively. Both rice bran samples were stored at 60 °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 (20 cm 20 cm 250lm) were purchased from Merck (Darmstadt, Germany). Standard nonacosane, farnesene, cholesta-3,5diene, squalene, fatty acids, a-,d-,c-tocopherol, monooleylglycerol, diolein, triolein, and tripalmitin were obtained from Sigma Chemicals Company (St. Louis, MO). Various methyl esters such as palmitic, stearic, oleic, linoleic, and linolenic acids were obtained from Supelco (Bellefonte, PA) as standards. Standard b-sitosterol (practical grade) was obtained from MP Biomedicals, LLC (Aurora, OH). Derivatization reagent boron trifluoride in methanol (14%) was purchased from Sigma Chemicals Company (St. Louis, MO). All solvents and reagents were either of HPLC grade or analytical reagent grade and were obtained from commercial sources. 2.2. Total FAMEs in rice bran Rice bran (10 g) was packed into an extraction thimble (9.4 cm 3.3 cm i.d.), and the top surface was covered with cotton to prevent natural contaminations. Neutral lipids were extracted from the rice bran by soxhlet extraction with hexane (350 mL) as the solvent, which was put in a 500 mL round-bottom flask and heated. After a 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 of 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 CRBO, was obtained by extracting with hexane for 4–5 h. Neutral lipids were not detected in the next fraction, which was obtained after extracting with solvent for another 4 h. CRBO (1 g) was added to a 10 mL tube with a Teflon-lined screw cap. Potassium hydroxide solution (5 mL; 9 N) was added under nitrogen, and the tube was closed with screw cap. The tube was then heated at 60 °C in an oil bath until the saponification reaction was complete (overnight), as verified by analytical TLC (silica gel; eluted with a mixture solvent, hexane/ethyl acetate/acetic acid = 90:10:1, v/v/v) and high temperature gas chromatography (HT-GC). The mixture containing the saponified matter was acidified to pH2 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 contained the fatty acids, was collected and removed. The fatty acids were then converted into their corresponding FAMEs by heating with boron trifluoride (BF3) in methanol and analyzed by gas chromatography and TLC. 2.3. Two-step in-situ process (acid-catalyzed followed by base catalyzed) A batch reactor, equipped with a magnetic stirrer, a water bath and a condenser system was employed in this study. Rice bran was put into a 55 °C oven for 2 h to reduce its water content from 12% to 4%. Ten grams of this rice bran was mixed with a solution that was prepared from methanol and sulfuric acid, the mixture was then put into a 250 mL batch reactor at 60 °C and atmospheric pressure. The condenser was inserted into the top of reac-
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tor and tap water was used as the refrigerant. The condenser ensured that methanol vapor condensed and dripped back into the reactor. The mixture was stirred magnetically at 600 rpm and the reaction was carried out for a predetermined time. Afterwards, 5 N NaOH in methanol was added directly into the mixture and the reaction was continued for a predetermined time. The mixture was put in a refrigerator at 20 °C for 10 min to stop the reaction. The mixture was then filtered using a replaceable filter and vacuum pump. The solid phase was washed with 50 mL methanol and dried overnight at room temperature. Soxhlet extraction was applied to extract residual lipids in the solid phase with 350 mL hexane for 4 h. Methanol was removed from the collected liquid phase with a rotary evaporator. After that, FAMEs was extracted with 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 using anhydrous magnesium sulfate. After the hexane was removed from the pooled organic layers using rotary evaporator, the remaining substance was referred to as the reaction product. The product was analyzed by gas chromatography and TLC. The flowchart of the two-step in-situ process is shown in Fig. 1. 2.4. TLC analysis Individual components in each sample were identified using authentic standards as described by Gunawan et al. (2008b). Spots on each plate were visualized by exposing the chromatogram to iodine vapor, and by spraying with specific reagents, such as a fresh solution of ferric chloride, and 2,4-dinitrophenylhydrazine (Fried, 1996). 2.5. HT-GC analysis Qualitative and quantitative analyses of the FFAs, squalene, free phytosterols, and acylglycerols in each sample were performed on a Shimadzu GC-17A (Kyoto, Japan) gas chromatograph equipped with a flame ionization detector as described by Gunawan et al. (2008a). Separations were carried out on a DB-5HT (5% phenyl)methylpolysiloxane nonpolar column (15 m 0.32 mm i.d.; Agilent Technologies, Palo Alto, CA). The temperatures of the inject and the detector were both set at 370 °C. The temperature of the column was started at 80 °C, increased to 365 °C at 15 °C/min, and maintained at 365 °C for 8 min. The split ratio was 1:50 using nitrogen as the carrier gas with a linear velocity of 30 cm/s at 80 °C. 2.6. Determination of FAMEs contents The samples were dissolved in n-hexane and 0.5 ll of each sample was injected into the gas chromatography. External standard calibration curves were obtained by using 0.2–20 mg pure standard. Nonadecanoic methyl ester was selected for the determination of FAMEs calibration factor and was used for all FAMEs. Chromatographic analysis was performed in a China 8700F (Taiwan) gas chromatograph equipped with a flame ionization detector. The column used was a Rtx-2330 10% cyanopropylphenyl– 90% biscyanopropyl polysiloxane column (30 m 0.25 mm i.d., Supelco, Bellefonte, PA). The operating conditions were: the injector and detector temperatures were set at 250 °C, the column temperature was held at 150 °C for 2 min, and then raised to 245 °C at 5 °C/min and held for 14 min. Capillary head pressure, purge velocity, and vent velocity were 1.5 kg/cm2, 2–3 mL/min and 100 mL/ min, respectively. The make up hydrogen and air pressures were
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Rice Bran
In-situ esterification (Acid catalzed) In-situ Transesterification (Base catalzed)
Solid phase
Liquid phase
Extraction by hexane (50 ml 3)
Glycerol phase
Organic phase
Water washing (50 ml)
Waste water
FAMEs
Fig. 1. Flowchart of the two-step in-situ process.
0.5, 0.5, and 1.0 bar, respectively. Total yield of FAMEs was calculated by the equation
followed by Fisher’s LSD (Least Significant Difference) method. Differences associated with p < 0.05 were considered significant (Montgomery, 2005).
Total yield ¼ f½ðweight of the product; gÞ ðcontent of the compounds
3. Results and discussion
in the product; %Þ =½weight of potential FAMEs in rice brang 100%: 2.7. Statistical analysis Reliability of the results was checked by a statistical analysis. Standard deviation of the measures (S) was calculated considering the difference between the value of individual experiment, x, and the mean value of three independent experiments, x using the formula
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Rðx xÞ2 S¼ ; n1 here n represents the total number of experiments. The differences in mean values were evaluated by analysis of variance (ANOVA)
Rice bran, a by-product of rice milling, is a brown layer present between rice and the outer husk of the paddy. It is used mostly as livestock feed and as boiler fuel in most rice producing countries (Ju and Vali, 2005). Rice bran and its oil can be used as a low cost raw material for biodiesel production. In this study, production of biodiesel from rice bran by a twostep in-situ process was investigated. Two samples of rice bran with different initial free fatty acid contents were used. The oil content of rice bran A and B are 16.9 ± 0.6% and 17.1 ± 0.1%, respectively. This agrees with previous observations that depending on variety of rice and degree of milling, the bran contains 16–32 wt.% of oil (Houston, 1972). The compositions of CRBO extracted from rice bran A and B are shown in Table 1. Since CRBO contains a significant amount of water and/or FFAs, pretreatment of the starting material to remove excess water and/or FFAs is required if base-catalyzed methanolysis is to be employed for producing biodiesel.
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P.-J. Shiu et al. / Bioresource Technology 101 (2010) 984–989 Table 1 The composition of CRBO extracted from rice bran A and B (wt.%).a
a b
Table 3 Effect of reaction time on residual FFAs dan yield of FAMEs.a,b
Compounds
Rice bran A
Rice bran B
Reaction time (t1), min
Total residual FFAs
FAMEs
FFAs Squalene Free phytosterols Monoacylglycerols (MAGs) Diacylglycerols (DAGs) Triacylglycerols (TAGs) Othersb
3.32 0.15 0.67 0.02 2.69 87.70 5.46
30.12 0.14 0.53 0.01 3.48 54.88 10.84
15 30 60 120 240
1.00 ± 0.27 0.81 ± 0.11 0.98 ± 0.27 0.95 ± 0.13 0.21 ± 0.17
48.86 ± 2.55 71.62 ± 4.81 73.34 ± 4.86 87.72 ± 7.20 89.54 ± 6.86
Averages of three independent measurements. Waxes, glycolipis, and phospholipids.
3.1. First-step in-situ esterification of rice bran 3.1.1. Effect of methanol to rice bran ratio An in-situ esterification reaction of rice bran A (10 g) with different methanol to rice bran ratios were studied in the presence of 1.5 mL sulfuric acid (27.6 wt.% of rice bran mass) at 60 °C for 1 h. The results are shown in Table 2. Excess methanol was used in this study. This was because methanol played the role of both reactant and solvent for extraction. This agrees with previous observations (Özgül-Yücel and Türkay, 2002; Yustianingsih et al., 2009). Methanol to rice bran ratio of 4 mL/g (Özgül-Yücel and Türkay, 2002) and 10 mL/g (Yustianingsih et al., 2009) were employed in the in-situ esterification of rice bran. The yield of FAMEs increased with increasing methanol to rice bran ratio. The stoichiometry of the esterification reaction requires 1 mol of methanol per mole of FFAs to yield 1 mol of fatty acid methyl ester. However, esterification is a reversible reaction so excess methanol favors the formation of FAMEs. The yield of FAMEs at a methanol to rice bran ratio of 15 mL/g was significantly higher (p < 0.05) than those obtained at methanol to rice bran ratios of 2.5, 5, and 10 mL/g. However, at a methanol to rice bran ratio of 15 mL/ g, the FAMEs yield was not significantly different (p > 0.05) from that obtained at a methanol to rice bran ratio of 20 mL/g. On the other hand, the content of FAMEs decreased with increasing methanol amount. This may be because, when excess methanol was used, compounds more polar than neutral lipid, such as protein and carbohydrate, were preferentially extracted from rice bran. Significant amounts of FFAs (>0.5%) were observed in the reaction products. The term ‘‘total residual FFAs” refers to total FFAs contained in the organic phase and in the rice bran. Table 2 shows that total residual FFAs content was not significantly different (p > 0.05) among all methanol to rice bran ratios studied. 3.1.2. Effect of reaction time (t1) Table 3 shows the effect of reaction time on FAMEs content, yield and total residual FFAs content in the presence of 1.5 mL sulfuric acid (27.6% of rice bran mass) at a methanol to rice bran ratio of 15 mL/g, and a reaction temperature of 60 °C. Rapid conversion
(23.44 ± 1.78) (47.13 ± 1.41) (50.48 ± 0.77) (60.58 ± 2.99) (75.09 ± 2.34)
Reaction conditions: rice bran A = 10 g, T = 60 °C, H2SO4 to rice bran mass ratio = 27.6%, 600 rpm, and methanol to rice bran = 15 mL/g. a Averages of three independent measurements. b Values reported as content (wt.%), with recoveries (%) in parenthesis.
of FFAs into FAMEs was observed within the first 30 min. After that the conversion rate was slower. FAMEs yield of 75% can be obtained by extending reaction time up to 4 h. Freedman et al. (1984) investigated acid-catalyzed transesterification of refined soybean oil with methanol to obtain more than 90% oil conversion in 69 h. Yustianingsih et al. (2009) reported that FAMEs yield of 73% was obtained by in-situ esterification from rice bran with an initial FFAs content of 13% after 4 h. It was found that total residual FFAs (1%) is not significantly different (p > 0.05) within 120 min as can be seen in Table 3. However, at a reaction time of 240 min, the content of total residual FFAs (<0.5%) was significantly lower (p < 0.05) than those obtained at reaction times of 15, 30, 60, and 120 min. Acylglycerols and FFAs must be extracted from rice bran before they can react with methanol. The extraction of lipids by methanol is a slow process, needs 2–3 h to extract most lipids (data not shown). The reaction between FFA and methanol catalyzed by acid is very fast, resulting in the low FFA contents (1%) in the first 2 h. After 2–3 h, there were very little FFAs remained in the bran, resulting in a lower (0.2%) FFA content in the reaction mixture at 4 h. 3.1.3. Effect of acid amount The appropriate amount of acid catalyst required was 18.4 wt.% of rice bran as it gave an optimum yield of FAMEs and a low total residual FFAs (<1%) as shown in Table 4. Our results suggest that in-situ esterification of rice bran A could produce FAMEs (23% yield and 42% content) with a total residual FFAs contents of 0.17% under the following operation conditions: methanol to rice bran ratio 15 mL/g; H2SO4 to rice bran mass ratio 18.4%; reaction temperature 60 °C; and reaction time 15 min. The effectiveness of this reaction was confirmed in subsequent experiments carried out under the same conditions using rice bran B which has an initial FFA content of 30%. Using rice bran B as the starting material, FAMEs (48.42% yield and 62.99% content) were obtained with a total residual FFAs content of 0.38%. The first step was capable of reducing FFAs contents in rice bran by 95–98% and obtaining FAMEs with yield depending on the initial contents of FFAs in rice bran. The results were comparable with previous observations of Ghadge and Rahemen (2005). They
Table 2 Effect of methanol to rice bran ratio on residual FFAs dan yield of FAMEs.a,b Methanol to rice bran ratio (v/w, mL/g)
Total residual FFAs
Reaction product (FAMEs)
2.5 5 10 15 20
1.07 ± 0.83 0.99 ± 0.48 1.51 ± 0.42 0.98 ± 0.27 2.48 ± 1.46
91.66 ± 0.90 90.28 ± 4.11 82.01 ± 0.57 73.34 ± 4.86 54.03 ± 4.19
(23.15 ± 3.05) (29.13 ± 3.56) (40.18 ± 5.68) (50.48 ± 0.77) (47.70 ± 5.40)
Reaction conditions: rice bran A = 10 g, T = 60 °C, H2SO4 to rice bran mass ratio = 27.6%, 600 rpm and t1 = 60 min. a Averages of three independent measurements. b Values reported as content (wt.%), with recoveries (%) in parenthesis.
Table 4 Effect of acid catalyst amount on in-situ esterification of rice bran.a,b H2SO4 to rice bran mass ratio (%)
Total residual FFAs
FAMEs
9.2 18.4 27.6
2.61 ± 0.48 0.17 ± 0.12 1.00 ± 0.27
30.30 ± 1.82 (13.79 ± 0.56) 41.95 ± 4.30 (23.17 ± 2.93) 48.86 ± 2.55 (23.44 ± 1.78)
Reaction conditions: rice bran A = 10 g, methanol to rice bran = 15 mL/g, T = 60 °C, 600 rpm, and t1 = 15 min. a Averages of three independent measurements. b Values reported as content (wt.%), with recoveries (%) in parenthesis.
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employed mahua oil (Madhuca indica) as the starting material with initial FFAs level from 19% to 2.5%. FFAs content in the oil was reduced to less than 1% after the first and second acid pretreatments of esterification. Pretreatment steps proposed by Chongkhong et al. (2007) and Veljkovic et al. (2006) reduced FFAs content of oil to 2%.
2nd step
1st step
100 80
3.2. Second-step in-situ transterification
3.2.2. Effect of reaction time (t2) A two-step in-situ process was employed on rice bran A and B under the same reaction conditions. The effects of reaction time on FAMEs yield and content for rice bran A and B are shown in Figs. 2 and 3, respectively. FAMEs yield increased rapidly with increasing reaction time in the first 20 min. For rice bran A, a maximal FAMEs yield of 96.8% was obtained in the second step reaction time of 60 min; while a maximal FAMEs yield of 97.4% can be obtained in the second step reaction time of 30 min for rice bran B.
Rice bran A
Yield % Y
60
Rice bran B 40 20 -
0
Total residual FFAs
FAMEs
NDc ND ND ND
50.18 ± 6.22 91.27 ± 2.30 94.57 ± 1.21 87.69 ± 4.98
120
150
100 80 Rice bran A
60
Rice bran B 40 20 -
30
60
90
120
150
Total reaction time (min.) Fig. 3. Effect of total reaction time on FAMEs content profile. First step operation conditions: rice bran = 10 g, methanol to rice bran = 15 mL/g, H2SO4 to rice bran mass ratio = 27.6%, T = 60 °C, t1 = 15 min, and 600 rpm. Second step operation conditions: starting material = the mixture obtained from first step in-situ esterification of rice bran, NaOH (5 N) in methanol = 8 mL, T = 60 °C, and 600 rpm.
Table 6 Comparison of the yield of FAMEs from rice bran A and B using one-step and twosteps in-situ process.a
Table 5 Effect of base catalyst amount on in-situ transesterification.a,b
7 8 9 10
90
2nd step
1st step
3.3. Comparison of one-step and two-step in-situ processes
NaOH amount, mL
60
Fig. 2. Effect of total reaction time on FAMEs yield profile. First step operation conditions: rice bran = 10 g, methanol to rice bran ratio = 15 mL/g, H2SO4 to rice bran mass ratio = 27.6%, T = 60 °C, t1 = 15 min, and 600 rpm. Second step operation conditions: starting material = mixture obtained from first step in-situ esterification of rice bran, NaOH (5 N) in methanol = 8 mL, T = 60 °C, and 600 rpm.
0
The effects of initial FFAs content in rice bran on the products of one-step and two-step in-situ process are shown in Table 6. It can be seen that the acid-catalyzed esterification was much slower than the base transesterification. The yield of acid-catalyzed esterification increased from 47% to 55%, while the yield of base-catalyzed transesterification decreased from 85% to 65% as FFAs
30
Total reaction time (min.)
Purity %
3.2.1. Effect of base amount In most studies reported in the literature about biodiesel production using a two-step in-situ process, a separation step (water washing) was necessary for recovering the esterification product. After that, the resulting organic phase from the first step was used as the starting material for the next step (transesterification). This study is the first investigation reporting on the production of biodiesel from rice bran using an in-situ process in which esterification was followed directly by transesterification without employing a separation step in between. NaOH in methanol (5 N) was used as the base catalyst in this study. It was observed that 6 mL NaOH in methanol was necessary to neutralize the acid left from the first step. Therefore, the base catalyst amounts investigated in this study were 7, 8, 9, and 10 mL. Table 5 shows that the yield of FAMEs at 8 mL NaOH was significantly higher (p < 0.05) than those obtained at 7 and 10 mL NaOH. However, at 9 mL NaOH, the FAMEs yield was not significantly different (p > 0.05) from that of obtained at 8 mL NaOH. Therefore, 8 mL NaOH was chosen in this study as it gave an optimum yield of FAMEs (84%). Although this process still requires a large amount of methanol and catalysts (H2SO4 and NaOH), methanol can be recovered easily and Na2SO4 as a by-product of this process can be used for the manufacture of detergents and in the Kraft process of paper pulping.
(25.04 ± 5.90) (83.85 ± 0.10) (81.71 ± 4.87) (66.16 ± 2.08)
Reaction conditions: starting material = the mixture obtained from first step in-situ esterification of rice bran A, T = 60 °C, 600 rpm, and t2 = 240 min. a Averages of three independent measurements. b Values reported as content (wt.%), with recoveries (%) in parenthesis. c Not detected.
Process
The average FAMEs yield in rice bran (wt.%) Rice bran A (FFAs = 3%)
Rice bran B (FFAs = 30%)
Acidb Baseb Acid + basec
47.13 ± 1.41 85.23 ± 1.74 92.33 ± 2.68
55.29 ± 2.09 65.54 ± 1.24 92.10 ± 2.13
a The reaction conditions: rice bran = 10 g, methanol = 150 ml, T = 60 °C, and 600 rpm. b Reaction time = 30 min. c 15 min acid-catalyzed reaction followed by 15 min base-catalyzed reaction.
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content of rice bran increased from 3% to 30%. High final yield (92%) was obtained for rice bran with low (3%) and high (30%) FFAs content by employing a two-step in-situ process without employing a separation step between the two steps.
4. Conclusions A study of biodiesel production from rice bran by a two-step insitu transesterification process was carried out in this work with the objective of obtaining high FAMEs yield from rice bran with high initial FFAs content. In the first step, most FFAs in rice bran were converted to FAMEs with FAMEs yield depending on the initial FFAs content. By employing the two-step in-situ process, high FAMEs yield was obtained in a reasonably short time. Acknowledgement This work was supported by a Grant (97-ET-7-011-001-ET) provided by the National Science Council of Taiwan. References Bozbas, K., 2008. Biodiesel as an alternative motor fuel: production and policies in the European Union. Renew. Sust. Energ. Rev. 12, 542–552. Bunyakiat, K., Makmee, S., Sawangkeaw, R., Ngampresertsith, S., 2006. Continuous production of biodiesel via transesterification from vegetable oils in supercritical methanol. Energ. Fuel. 20, 812–817. Chongkhong, S., Tongurai, C., Chetpattananondh, P., Bunyakan, C., 2007. Biodiesel production by esterification of palm fatty acid distillate. Biomass Bioenerg. 31, 563–568. Dorado, M.P., Cruz, F., Palomar, J.M., Lopez, F.J., 2006. An approach to economics of two vegetable oil-based biofuels in Spain. Renew. Energ. 31, 1231–1237. Estela, H.M., Otero, C., 2008. Different enzyme requirement for the synthesis of biodiesel: Novozym 435 and Lipozyme TL IM. Bioresour. Technol. 99, 277–286. Freedman, B., Pryde, E.H., Mounts, T.L., 1984. Variables affecting the yield of fatty esters from transesterified vegetable oils. J. Am. Oil Chem. Soc. 61, 1638–1643. Fried, B., 1996. Lipids. In: Sherma, J., Fried, B. (Eds.), Handbook of Thin-Layer Chromatography. Marcel Dekker Press, New York, p. 704. Ghadge, S.V., Rahemen, H., 2005. Biodiesel production from mahua (Madhuca indica) oil having high free fatty acids. Biomass Bioenerg. 28, 601–605.
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Gunawan, S., Fabian, C., Ju, Y.H., 2008b. Isolation and purification of fatty acid steryl esters from soybean oil deodorizer distillate. Ind. Eng. Chem. Res. 47, 7013– 7018. Gunawan, S., Kasim, N.S., Ju, Y.H., 2008a. Separation and purification of squalene from soybean oil deodorizer distillate. Sep. Purif. Technol. 60, 128–135. Haas, M.J., Scott, K.M., Marmer, W.N., Foglia, T.A., 2004. In situ alkaline transesterification: an effective method for the production of fatty acid esters from vegetable oils. J. Am. Oil Chem. Soc. 81, 83–89. Haas, M.J., Mc Aloon, A.J., Winnie, C.Y., Foglia, T.A., 2006. A process model to estimate biodiesel production costs. Bioresour. Technol. 97, 671–678. Houston, D.F., 1972. Rice bran and polish. In: Houston, D.F. (Ed.), Rice Chemistry and Technology. American Association of Cereal Chemists, St. Paul, MN, pp. 1–56. Jitputti, J., Kitiyanan, B., Rangsunvigit, P., Bunyakiat, K., Attanaho, L., Jenvanitpanjakul, P., 2006. Transesterification of crude palm kernel oil and crude coconut oil by different solid catalysts. Chem. Eng. J. 116, 61–66. Ju, Y.H., Vali, S.R., 2005. Rice bran oil as a potential resource for biodiesel: a review. J. Sci. Ind. Res. 64, 866–882. Kasim, N.S., Tsai, T.H., Gunawan, S., Ju, Y.H., 2009. Biodiesel production from rice bran oil and supercritical methanol. Bioresour. Technol. 100, 2007–2011. Lai, C.C., Zullaikah, S., Vali, S.R., Ju, Y.H., 2005. Lipase-catalyzed production of biodiesel from rice bran oil. J. Chem. Technol. Biotechnol. 80, 331–337. Lin, C.Y., Li, R.J., 2009. Fuel properties of biodiesel produced from the crude fish oil from the soapstock of marine fish. Fuel Process Technol. 90, 30–136. Liu, X., He, H., Wang, Y., Zhu, S., Piao, X., 2008. Transesterification of soybean oil to biodiesel using CaO as a solid base catalyst. Fuel 87, 216–221. Montgomery, D.C., 2005. Design and Analysis of Experiments, sixth ed. Jhon Wiley and Sons, Inc., New York. p. 96. Murugesan, A., Umarani, C., Chinnusamy, T.R., Krishnan, M., Subramanian, R., Neduzchezhain, N., 2008. Production and analysis of bio-diesel from non-edible oils – a review. Renew. Sust. Energ. Rev. 13, 825–834. Öner, C., Altun, Sß ., 2009. Biodiesel production from inedible animal tallow and an experimental investigation of its use as alternative fuel in a direct injection diesel engine. Appl. Energ. 86, 2114–2120. Özgül-Yücel, S., Türkay, S., 2002. Variables affecting the yields of methyl esters derived from in-situ esterification of rice bran oil. J. Am. Oil Chem. Soc. 79, 611– 614. Rashid, U., Anwar, F., 2008. Production of biodiesel through base-catalyzed transesterification of sunflower oil using an optimized protocol. Energ. Fuel. 22, 1306–1312. Tsai, W.T., Lin, C.C., Yeh, C.W., 2007. An analysis of biodiesel fuel from waste edible oil in Taiwan. Renew. Sust. Energ. Rev. 11, 838–857. Veljkovic, V.B., Lakic´evic´, S.H., Stamenkovic´, O.S., Todorovic´, Z.B., Lazic´, M.L., 2006. Biodiesel production from tobacco (Nicotiana tabacum L.) seed oil with a high content of free fatty acids. Fuel 85, 2671–2675. Yustianingsih, L., Zullaikah, S., Ju, Y.H., 2009. Ultrasound-assisted in-situ production of biodiesel from Rice Bran. J. Energ. Inst. 82 (3), 133–137. Zullaikah, S., Lai, C.C., Vali, S.R., Ju, Y.H., 2005. A two-step acid-catalyzed process for the production of biodiesel from rice bran oil. Bioresour. Technol. 96, 1889– 1896.
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Biodiesel production from rice bran by a two-step in-situ process Pei-Jing Shiu a, Setiyo Gunawan a,b, Wen-Hao Hsieh a, Novy S. Kasim a, Yi-Hsu Ju a,* a b
Department of Chemical Engineering, National Taiwan University of Science and Technology, 43 Sec. 4, Keelung Road, Taipei 106-07, Taiwan Department of Chemical Engineering, Institut Teknologi Sepuluh Nopember, Kampus ITS Keputih Sukolilo, Surabaya 60111, Indonesia
a r t i c l e
i n f o
Article history: Received 24 July 2009 Received in revised form 2 September 2009 Accepted 3 September 2009 Available online 29 September 2009 Keywords: Rice bran Two-step in-situ transesterification
a b s t r a c t The production of fatty acid methyl esters (FAMEs) by a two-step in-situ transesterification from two kinds of rice bran was investigated in this study. The method included an in-situ acid-catalyzed esterification followed by an in-situ base-catalyzed transesterification. Free fatty acids (FFAs) level was reduced to less than 1% for both rice bran A (initial FFAs content = 3%) and rice bran B (initial FFAs content = 30%) in the first step under the following conditions: 10 g rice bran, methanol to rice bran ratio 15 mL/g, H2SO4 to rice bran mass ratio 0.18, 60 °C reaction temperature, 600 rpm stirring rate, 15 min reaction time. The organic phase of the first step product was collected and subjected to a second step reaction by adding 8 mL of 5 N NaOH solution and allowing to react for 60 and 30 min for rice bran A and rice bran B, respectively. FAMEs yields of 96.8% and 97.4% were obtained for rice bran A and rice bran B, respectively, after this two-step in-situ reaction. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction Fuel plays an important role in the economy of every country. More than 98% of the energy needs of Taiwan are imported. Therefore, improving energy efficiency, developing alternative energy, and securing a stable energy supply are the framework of Taiwan’s sustainable energy policies. Biodiesel is a biodegradable, renewable, non-toxic and environmental friendly alternative fuel. It can be mixed with petroleum diesel in any proportion or used directly in diesel engines without modification. It can be produced from various raw materials such as animal fat (Lin and Li, 2009; Öner and Altun, 2009), refined vegetable oils (Bunyakiat et al., 2006; Estela and Otero, 2008; Liu et al., 2008; Rashid and Anwar, 2008), crude oils (Ghadge and Rahemen, 2005; Jitputti et al., 2006; Veljkovic et al., 2006), and waste edible oils (Tsai et al., 2007). Most commercial biodiesels are produced from edible vegetable oils, such as soybean oil in US, rapeseed and sunflower seed oils in Europe, palm oil in Southeast Asia, and coconut oil in the Philippines (Murugesan et al., 2008). However, the cost of the raw materials comprises 60–70% (Haas et al., 2004) or 75–88% (Bozbas, 2008; Dorado et al., 2006; Haas et al., 2006) of the production cost in commercial biodiesel production. One way of reducing biodiesel production costs is to use low cost raw material, such as rice bran which basically is treated as agricultural waste in most rice producing countries. * Corresponding author. Tel.: +886 2 27376612; fax: +886 2 27376644. E-mail address: [email protected] (Y.-H. Ju). 0960-8524/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2009.09.011
In 2007, the amount of rice bran produced as the by-product of rice milling in Taiwan was about 100,000 tons with a potential of yielding 20,000 tons of crude rice bran oil (CRBO). CRBO is non-edible due to its high free fatty acids (FFAs) contents. Up to 16,000 tons of biodiesel can be produced per year from rice bran which can account for up to 10% of the biodiesel demand in Taiwan when the mandatory B2 is adopted in 2010. A two-step chemical catalyzed methanolysis (Zullaikah et al., 2005) and a two-step lipase catalyzed methanolysis (Lai et al., 2005) have been developed using crude rice bran oil for the production of biodiesel. CRBO can be converted effectively into fatty acid methyl esters (FAMEs) in a reasonably short time (<8 h) with high conversion (>95%). The economic competitiveness of biodiesel can be improved by applying an ‘‘in-situ process”, such as in-situ acid esterification (Özgül-Yücel and Türkay, 2002; Yustianingsih et al., 2009). Kasim et al. (2009) studied biodiesel production from rice bran by in-situ transesterification under supercritical conditions. However, the maximum yield achieved was only 51.3%. When dewaxed–degummed rice bran oil was used under the same conditions, the final yield achieved was 94.8%. In-situ production of biodiesel from seed/bran spares the need of oil extraction. However, additional alcohol and catalyst are usually required. The objective of this work was to produce biodiesel from rice bran by a two-step in-situ reaction (acid-catalyzed followed by base-catalyzed) with high yield in a reasonably short time. The effects of reaction conditions, such as methanol to rice bran ratio, catalyst amount, and reaction time on the yield of biodiesel production were investigated systematically.
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2. Methods 2.1. Materials Rice bran A and B were donated by a local mill in Kaohsiung and Taoyuan (Taiwan), respectively. Both rice bran samples were stored at 60 °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 (20 cm 20 cm 250lm) were purchased from Merck (Darmstadt, Germany). Standard nonacosane, farnesene, cholesta-3,5diene, squalene, fatty acids, a-,d-,c-tocopherol, monooleylglycerol, diolein, triolein, and tripalmitin were obtained from Sigma Chemicals Company (St. Louis, MO). Various methyl esters such as palmitic, stearic, oleic, linoleic, and linolenic acids were obtained from Supelco (Bellefonte, PA) as standards. Standard b-sitosterol (practical grade) was obtained from MP Biomedicals, LLC (Aurora, OH). Derivatization reagent boron trifluoride in methanol (14%) was purchased from Sigma Chemicals Company (St. Louis, MO). All solvents and reagents were either of HPLC grade or analytical reagent grade and were obtained from commercial sources. 2.2. Total FAMEs in rice bran Rice bran (10 g) was packed into an extraction thimble (9.4 cm 3.3 cm i.d.), and the top surface was covered with cotton to prevent natural contaminations. Neutral lipids were extracted from the rice bran by soxhlet extraction with hexane (350 mL) as the solvent, which was put in a 500 mL round-bottom flask and heated. After a 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 of 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 CRBO, was obtained by extracting with hexane for 4–5 h. Neutral lipids were not detected in the next fraction, which was obtained after extracting with solvent for another 4 h. CRBO (1 g) was added to a 10 mL tube with a Teflon-lined screw cap. Potassium hydroxide solution (5 mL; 9 N) was added under nitrogen, and the tube was closed with screw cap. The tube was then heated at 60 °C in an oil bath until the saponification reaction was complete (overnight), as verified by analytical TLC (silica gel; eluted with a mixture solvent, hexane/ethyl acetate/acetic acid = 90:10:1, v/v/v) and high temperature gas chromatography (HT-GC). The mixture containing the saponified matter was acidified to pH2 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 contained the fatty acids, was collected and removed. The fatty acids were then converted into their corresponding FAMEs by heating with boron trifluoride (BF3) in methanol and analyzed by gas chromatography and TLC. 2.3. Two-step in-situ process (acid-catalyzed followed by base catalyzed) A batch reactor, equipped with a magnetic stirrer, a water bath and a condenser system was employed in this study. Rice bran was put into a 55 °C oven for 2 h to reduce its water content from 12% to 4%. Ten grams of this rice bran was mixed with a solution that was prepared from methanol and sulfuric acid, the mixture was then put into a 250 mL batch reactor at 60 °C and atmospheric pressure. The condenser was inserted into the top of reac-
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tor and tap water was used as the refrigerant. The condenser ensured that methanol vapor condensed and dripped back into the reactor. The mixture was stirred magnetically at 600 rpm and the reaction was carried out for a predetermined time. Afterwards, 5 N NaOH in methanol was added directly into the mixture and the reaction was continued for a predetermined time. The mixture was put in a refrigerator at 20 °C for 10 min to stop the reaction. The mixture was then filtered using a replaceable filter and vacuum pump. The solid phase was washed with 50 mL methanol and dried overnight at room temperature. Soxhlet extraction was applied to extract residual lipids in the solid phase with 350 mL hexane for 4 h. Methanol was removed from the collected liquid phase with a rotary evaporator. After that, FAMEs was extracted with 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 using anhydrous magnesium sulfate. After the hexane was removed from the pooled organic layers using rotary evaporator, the remaining substance was referred to as the reaction product. The product was analyzed by gas chromatography and TLC. The flowchart of the two-step in-situ process is shown in Fig. 1. 2.4. TLC analysis Individual components in each sample were identified using authentic standards as described by Gunawan et al. (2008b). Spots on each plate were visualized by exposing the chromatogram to iodine vapor, and by spraying with specific reagents, such as a fresh solution of ferric chloride, and 2,4-dinitrophenylhydrazine (Fried, 1996). 2.5. HT-GC analysis Qualitative and quantitative analyses of the FFAs, squalene, free phytosterols, and acylglycerols in each sample were performed on a Shimadzu GC-17A (Kyoto, Japan) gas chromatograph equipped with a flame ionization detector as described by Gunawan et al. (2008a). Separations were carried out on a DB-5HT (5% phenyl)methylpolysiloxane nonpolar column (15 m 0.32 mm i.d.; Agilent Technologies, Palo Alto, CA). The temperatures of the inject and the detector were both set at 370 °C. The temperature of the column was started at 80 °C, increased to 365 °C at 15 °C/min, and maintained at 365 °C for 8 min. The split ratio was 1:50 using nitrogen as the carrier gas with a linear velocity of 30 cm/s at 80 °C. 2.6. Determination of FAMEs contents The samples were dissolved in n-hexane and 0.5 ll of each sample was injected into the gas chromatography. External standard calibration curves were obtained by using 0.2–20 mg pure standard. Nonadecanoic methyl ester was selected for the determination of FAMEs calibration factor and was used for all FAMEs. Chromatographic analysis was performed in a China 8700F (Taiwan) gas chromatograph equipped with a flame ionization detector. The column used was a Rtx-2330 10% cyanopropylphenyl– 90% biscyanopropyl polysiloxane column (30 m 0.25 mm i.d., Supelco, Bellefonte, PA). The operating conditions were: the injector and detector temperatures were set at 250 °C, the column temperature was held at 150 °C for 2 min, and then raised to 245 °C at 5 °C/min and held for 14 min. Capillary head pressure, purge velocity, and vent velocity were 1.5 kg/cm2, 2–3 mL/min and 100 mL/ min, respectively. The make up hydrogen and air pressures were
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Rice Bran
In-situ esterification (Acid catalzed) In-situ Transesterification (Base catalzed)
Solid phase
Liquid phase
Extraction by hexane (50 ml 3)
Glycerol phase
Organic phase
Water washing (50 ml)
Waste water
FAMEs
Fig. 1. Flowchart of the two-step in-situ process.
0.5, 0.5, and 1.0 bar, respectively. Total yield of FAMEs was calculated by the equation
followed by Fisher’s LSD (Least Significant Difference) method. Differences associated with p < 0.05 were considered significant (Montgomery, 2005).
Total yield ¼ f½ðweight of the product; gÞ ðcontent of the compounds
3. Results and discussion
in the product; %Þ =½weight of potential FAMEs in rice brang 100%: 2.7. Statistical analysis Reliability of the results was checked by a statistical analysis. Standard deviation of the measures (S) was calculated considering the difference between the value of individual experiment, x, and the mean value of three independent experiments, x using the formula
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Rðx xÞ2 S¼ ; n1 here n represents the total number of experiments. The differences in mean values were evaluated by analysis of variance (ANOVA)
Rice bran, a by-product of rice milling, is a brown layer present between rice and the outer husk of the paddy. It is used mostly as livestock feed and as boiler fuel in most rice producing countries (Ju and Vali, 2005). Rice bran and its oil can be used as a low cost raw material for biodiesel production. In this study, production of biodiesel from rice bran by a twostep in-situ process was investigated. Two samples of rice bran with different initial free fatty acid contents were used. The oil content of rice bran A and B are 16.9 ± 0.6% and 17.1 ± 0.1%, respectively. This agrees with previous observations that depending on variety of rice and degree of milling, the bran contains 16–32 wt.% of oil (Houston, 1972). The compositions of CRBO extracted from rice bran A and B are shown in Table 1. Since CRBO contains a significant amount of water and/or FFAs, pretreatment of the starting material to remove excess water and/or FFAs is required if base-catalyzed methanolysis is to be employed for producing biodiesel.
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P.-J. Shiu et al. / Bioresource Technology 101 (2010) 984–989 Table 1 The composition of CRBO extracted from rice bran A and B (wt.%).a
a b
Table 3 Effect of reaction time on residual FFAs dan yield of FAMEs.a,b
Compounds
Rice bran A
Rice bran B
Reaction time (t1), min
Total residual FFAs
FAMEs
FFAs Squalene Free phytosterols Monoacylglycerols (MAGs) Diacylglycerols (DAGs) Triacylglycerols (TAGs) Othersb
3.32 0.15 0.67 0.02 2.69 87.70 5.46
30.12 0.14 0.53 0.01 3.48 54.88 10.84
15 30 60 120 240
1.00 ± 0.27 0.81 ± 0.11 0.98 ± 0.27 0.95 ± 0.13 0.21 ± 0.17
48.86 ± 2.55 71.62 ± 4.81 73.34 ± 4.86 87.72 ± 7.20 89.54 ± 6.86
Averages of three independent measurements. Waxes, glycolipis, and phospholipids.
3.1. First-step in-situ esterification of rice bran 3.1.1. Effect of methanol to rice bran ratio An in-situ esterification reaction of rice bran A (10 g) with different methanol to rice bran ratios were studied in the presence of 1.5 mL sulfuric acid (27.6 wt.% of rice bran mass) at 60 °C for 1 h. The results are shown in Table 2. Excess methanol was used in this study. This was because methanol played the role of both reactant and solvent for extraction. This agrees with previous observations (Özgül-Yücel and Türkay, 2002; Yustianingsih et al., 2009). Methanol to rice bran ratio of 4 mL/g (Özgül-Yücel and Türkay, 2002) and 10 mL/g (Yustianingsih et al., 2009) were employed in the in-situ esterification of rice bran. The yield of FAMEs increased with increasing methanol to rice bran ratio. The stoichiometry of the esterification reaction requires 1 mol of methanol per mole of FFAs to yield 1 mol of fatty acid methyl ester. However, esterification is a reversible reaction so excess methanol favors the formation of FAMEs. The yield of FAMEs at a methanol to rice bran ratio of 15 mL/g was significantly higher (p < 0.05) than those obtained at methanol to rice bran ratios of 2.5, 5, and 10 mL/g. However, at a methanol to rice bran ratio of 15 mL/ g, the FAMEs yield was not significantly different (p > 0.05) from that obtained at a methanol to rice bran ratio of 20 mL/g. On the other hand, the content of FAMEs decreased with increasing methanol amount. This may be because, when excess methanol was used, compounds more polar than neutral lipid, such as protein and carbohydrate, were preferentially extracted from rice bran. Significant amounts of FFAs (>0.5%) were observed in the reaction products. The term ‘‘total residual FFAs” refers to total FFAs contained in the organic phase and in the rice bran. Table 2 shows that total residual FFAs content was not significantly different (p > 0.05) among all methanol to rice bran ratios studied. 3.1.2. Effect of reaction time (t1) Table 3 shows the effect of reaction time on FAMEs content, yield and total residual FFAs content in the presence of 1.5 mL sulfuric acid (27.6% of rice bran mass) at a methanol to rice bran ratio of 15 mL/g, and a reaction temperature of 60 °C. Rapid conversion
(23.44 ± 1.78) (47.13 ± 1.41) (50.48 ± 0.77) (60.58 ± 2.99) (75.09 ± 2.34)
Reaction conditions: rice bran A = 10 g, T = 60 °C, H2SO4 to rice bran mass ratio = 27.6%, 600 rpm, and methanol to rice bran = 15 mL/g. a Averages of three independent measurements. b Values reported as content (wt.%), with recoveries (%) in parenthesis.
of FFAs into FAMEs was observed within the first 30 min. After that the conversion rate was slower. FAMEs yield of 75% can be obtained by extending reaction time up to 4 h. Freedman et al. (1984) investigated acid-catalyzed transesterification of refined soybean oil with methanol to obtain more than 90% oil conversion in 69 h. Yustianingsih et al. (2009) reported that FAMEs yield of 73% was obtained by in-situ esterification from rice bran with an initial FFAs content of 13% after 4 h. It was found that total residual FFAs (1%) is not significantly different (p > 0.05) within 120 min as can be seen in Table 3. However, at a reaction time of 240 min, the content of total residual FFAs (<0.5%) was significantly lower (p < 0.05) than those obtained at reaction times of 15, 30, 60, and 120 min. Acylglycerols and FFAs must be extracted from rice bran before they can react with methanol. The extraction of lipids by methanol is a slow process, needs 2–3 h to extract most lipids (data not shown). The reaction between FFA and methanol catalyzed by acid is very fast, resulting in the low FFA contents (1%) in the first 2 h. After 2–3 h, there were very little FFAs remained in the bran, resulting in a lower (0.2%) FFA content in the reaction mixture at 4 h. 3.1.3. Effect of acid amount The appropriate amount of acid catalyst required was 18.4 wt.% of rice bran as it gave an optimum yield of FAMEs and a low total residual FFAs (<1%) as shown in Table 4. Our results suggest that in-situ esterification of rice bran A could produce FAMEs (23% yield and 42% content) with a total residual FFAs contents of 0.17% under the following operation conditions: methanol to rice bran ratio 15 mL/g; H2SO4 to rice bran mass ratio 18.4%; reaction temperature 60 °C; and reaction time 15 min. The effectiveness of this reaction was confirmed in subsequent experiments carried out under the same conditions using rice bran B which has an initial FFA content of 30%. Using rice bran B as the starting material, FAMEs (48.42% yield and 62.99% content) were obtained with a total residual FFAs content of 0.38%. The first step was capable of reducing FFAs contents in rice bran by 95–98% and obtaining FAMEs with yield depending on the initial contents of FFAs in rice bran. The results were comparable with previous observations of Ghadge and Rahemen (2005). They
Table 2 Effect of methanol to rice bran ratio on residual FFAs dan yield of FAMEs.a,b Methanol to rice bran ratio (v/w, mL/g)
Total residual FFAs
Reaction product (FAMEs)
2.5 5 10 15 20
1.07 ± 0.83 0.99 ± 0.48 1.51 ± 0.42 0.98 ± 0.27 2.48 ± 1.46
91.66 ± 0.90 90.28 ± 4.11 82.01 ± 0.57 73.34 ± 4.86 54.03 ± 4.19
(23.15 ± 3.05) (29.13 ± 3.56) (40.18 ± 5.68) (50.48 ± 0.77) (47.70 ± 5.40)
Reaction conditions: rice bran A = 10 g, T = 60 °C, H2SO4 to rice bran mass ratio = 27.6%, 600 rpm and t1 = 60 min. a Averages of three independent measurements. b Values reported as content (wt.%), with recoveries (%) in parenthesis.
Table 4 Effect of acid catalyst amount on in-situ esterification of rice bran.a,b H2SO4 to rice bran mass ratio (%)
Total residual FFAs
FAMEs
9.2 18.4 27.6
2.61 ± 0.48 0.17 ± 0.12 1.00 ± 0.27
30.30 ± 1.82 (13.79 ± 0.56) 41.95 ± 4.30 (23.17 ± 2.93) 48.86 ± 2.55 (23.44 ± 1.78)
Reaction conditions: rice bran A = 10 g, methanol to rice bran = 15 mL/g, T = 60 °C, 600 rpm, and t1 = 15 min. a Averages of three independent measurements. b Values reported as content (wt.%), with recoveries (%) in parenthesis.
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employed mahua oil (Madhuca indica) as the starting material with initial FFAs level from 19% to 2.5%. FFAs content in the oil was reduced to less than 1% after the first and second acid pretreatments of esterification. Pretreatment steps proposed by Chongkhong et al. (2007) and Veljkovic et al. (2006) reduced FFAs content of oil to 2%.
2nd step
1st step
100 80
3.2. Second-step in-situ transterification
3.2.2. Effect of reaction time (t2) A two-step in-situ process was employed on rice bran A and B under the same reaction conditions. The effects of reaction time on FAMEs yield and content for rice bran A and B are shown in Figs. 2 and 3, respectively. FAMEs yield increased rapidly with increasing reaction time in the first 20 min. For rice bran A, a maximal FAMEs yield of 96.8% was obtained in the second step reaction time of 60 min; while a maximal FAMEs yield of 97.4% can be obtained in the second step reaction time of 30 min for rice bran B.
Rice bran A
Yield % Y
60
Rice bran B 40 20 -
0
Total residual FFAs
FAMEs
NDc ND ND ND
50.18 ± 6.22 91.27 ± 2.30 94.57 ± 1.21 87.69 ± 4.98
120
150
100 80 Rice bran A
60
Rice bran B 40 20 -
30
60
90
120
150
Total reaction time (min.) Fig. 3. Effect of total reaction time on FAMEs content profile. First step operation conditions: rice bran = 10 g, methanol to rice bran = 15 mL/g, H2SO4 to rice bran mass ratio = 27.6%, T = 60 °C, t1 = 15 min, and 600 rpm. Second step operation conditions: starting material = the mixture obtained from first step in-situ esterification of rice bran, NaOH (5 N) in methanol = 8 mL, T = 60 °C, and 600 rpm.
Table 6 Comparison of the yield of FAMEs from rice bran A and B using one-step and twosteps in-situ process.a
Table 5 Effect of base catalyst amount on in-situ transesterification.a,b
7 8 9 10
90
2nd step
1st step
3.3. Comparison of one-step and two-step in-situ processes
NaOH amount, mL
60
Fig. 2. Effect of total reaction time on FAMEs yield profile. First step operation conditions: rice bran = 10 g, methanol to rice bran ratio = 15 mL/g, H2SO4 to rice bran mass ratio = 27.6%, T = 60 °C, t1 = 15 min, and 600 rpm. Second step operation conditions: starting material = mixture obtained from first step in-situ esterification of rice bran, NaOH (5 N) in methanol = 8 mL, T = 60 °C, and 600 rpm.
0
The effects of initial FFAs content in rice bran on the products of one-step and two-step in-situ process are shown in Table 6. It can be seen that the acid-catalyzed esterification was much slower than the base transesterification. The yield of acid-catalyzed esterification increased from 47% to 55%, while the yield of base-catalyzed transesterification decreased from 85% to 65% as FFAs
30
Total reaction time (min.)
Purity %
3.2.1. Effect of base amount In most studies reported in the literature about biodiesel production using a two-step in-situ process, a separation step (water washing) was necessary for recovering the esterification product. After that, the resulting organic phase from the first step was used as the starting material for the next step (transesterification). This study is the first investigation reporting on the production of biodiesel from rice bran using an in-situ process in which esterification was followed directly by transesterification without employing a separation step in between. NaOH in methanol (5 N) was used as the base catalyst in this study. It was observed that 6 mL NaOH in methanol was necessary to neutralize the acid left from the first step. Therefore, the base catalyst amounts investigated in this study were 7, 8, 9, and 10 mL. Table 5 shows that the yield of FAMEs at 8 mL NaOH was significantly higher (p < 0.05) than those obtained at 7 and 10 mL NaOH. However, at 9 mL NaOH, the FAMEs yield was not significantly different (p > 0.05) from that of obtained at 8 mL NaOH. Therefore, 8 mL NaOH was chosen in this study as it gave an optimum yield of FAMEs (84%). Although this process still requires a large amount of methanol and catalysts (H2SO4 and NaOH), methanol can be recovered easily and Na2SO4 as a by-product of this process can be used for the manufacture of detergents and in the Kraft process of paper pulping.
(25.04 ± 5.90) (83.85 ± 0.10) (81.71 ± 4.87) (66.16 ± 2.08)
Reaction conditions: starting material = the mixture obtained from first step in-situ esterification of rice bran A, T = 60 °C, 600 rpm, and t2 = 240 min. a Averages of three independent measurements. b Values reported as content (wt.%), with recoveries (%) in parenthesis. c Not detected.
Process
The average FAMEs yield in rice bran (wt.%) Rice bran A (FFAs = 3%)
Rice bran B (FFAs = 30%)
Acidb Baseb Acid + basec
47.13 ± 1.41 85.23 ± 1.74 92.33 ± 2.68
55.29 ± 2.09 65.54 ± 1.24 92.10 ± 2.13
a The reaction conditions: rice bran = 10 g, methanol = 150 ml, T = 60 °C, and 600 rpm. b Reaction time = 30 min. c 15 min acid-catalyzed reaction followed by 15 min base-catalyzed reaction.
P.-J. Shiu et al. / Bioresource Technology 101 (2010) 984–989
content of rice bran increased from 3% to 30%. High final yield (92%) was obtained for rice bran with low (3%) and high (30%) FFAs content by employing a two-step in-situ process without employing a separation step between the two steps.
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