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Bioresource Technology 99 (2008) 1716–1721
Biodiesel production from crude Jatropha curcas L. seed oil with a high content of free fatty acids Hanny Johanes Berchmans a, Shizuko Hirata b
b,*
a Energy Technology Center, Agency for Assessment and Application of Technology, Kawasan Puspiptek, Serpong, Tangerang 15314, Indonesia Biomass Technology Research Center, Advanced Industrial Science and Technology, Chugoku, 2-2-2 Hirosuehiro, Kure, Hiroshima 737-0197, Japan
Received 27 January 2007; received in revised form 30 March 2007; accepted 30 March 2007 Available online 24 May 2007
Abstract A technique to produce biodiesel from crude Jatropha curcas seed oil (CJCO) having high free fatty acids (15%FFA) has been developed. The high FFA level of JCJO was reduced to less than 1% by a two-step pretreatment process. The first step was carried out with 0.60 w/w methanol-to-oil ratio in the presence of 1% w/w H2SO4 as an acid catalyst in 1-h reaction at 50 C. After the reaction, the mixture was allowed to settle for 2 h and the methanol–water mixture separated at the top layer was removed. The second step was transesterified using 0.24 w/w methanol to oil and 1.4% w/w NaOH to oil as alkaline catalyst to produce biodiesel at 65 C. The final yield for methyl esters of fatty acids was achieved ca. 90% in 2 h. 2007 Elsevier Ltd. All rights reserved. Keywords: Biodiesel; Jatropha curcas; Transesterification; Free fatty acids
1. Introduction Biodiesel as an alternative fuel for diesel engines is becoming increasingly important due to diminishing petroleum reserves and the environmental consequences of exhaust gases from petroleum-fuelled engines. Biodiesel, which is made from renewable sources, consists of the simple alkyl esters of fatty acids. As a future prospective fuel, biodiesel has to compete economically with petroleum diesel fuels. One way of reducing the biodiesel production costs is to use the less expensive feedstock containing fatty acids such as inedible oils, animal fats, waste food oil and byproducts of the refining vegetables oils (Veljkovic´ et al., 2006). The availability and sustainability of sufficient supplies of less expensive feedstock will be a crucial determinant delivering a competitive biodiesel to the commercials filling stations. Fortunately, inedible vegetable oils, mostly produced by seed-bearing trees and shrubs can provide an alternative. With no competing food uses, this *
Corresponding author. Tel.: +81 823 72 1931; fax: +81 823 72 1990. E-mail address:
[email protected] (S. Hirata).
0960-8524/$ - see front matter 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2007.03.051
characteristic turns attention to Jatropha curcas, which grows in tropical and subtropical climates across the developing world (Openshaw, 2000). Oil contents, physicochemical properties, fatty acid composition and energy values of Jatropha species were investigated (Banerji et al., 1985; Kandpal and Madan, 1995; Kumar et al., 2003; Pramanik, 2003; Akintayo, 2004; Shah et al., 2004). While, it is considered that Jatropha has toxic substance (Hirota et al., 1988; Gandhi et al., 1995; Makkar et al., 1998; Haas and Mittelbach, 2000; Abdel Gadir et al., 2003). In many cases CJCO quality deteriorate gradually due to improper handling and inappropriate storage condition. It was known that improper handling of CJCO would cause the water content increase. In addition, exposing the oil to open air and sunlight for long time would affect the concentration of FFA increase significantly to high level of FFA above 1%. The FFA amount of CJCO will vary and depend on the quality of feedstock. The FFA and moisture contents have significant effects on the transesterification of glycerides with alcohol using catalyst (Goodrum, 2002). The high FFA content (>1%
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w/w) will happen soap formation and the separation of products will be exceedingly difficult, and as a result, it has low yield of biodiesel product. The acid-catalyzed esterification of the oil is an alternative (Crabbe et al., 2001), but it is much slower than the base-catalyzed transesterification reaction. Therefore, an alternative process such as a two-step process was investigated for feedstock having the high FFA content (Ghadge and Raheman, 2005; Veljkovic´ et al., 2006). This paper presents the development of two-step process for the production of biodiesel from the CJCO having the high FFA. The special attention was focused to optimize the first step of the process for reducing the FFA content of CJCO to below 2%. The second attention was focused to optimize the reaction condition for weight ratio of catalyst to oil and weight ratio of methanol to oil at 65 C. 2. Methods 2.1. Materials The CJCO used in this study was supplied by Chemical Engineering Department Laboratory, Bandung Institute of Technology, Bandung, Indonesia. Fatty acid composition of CJCO is given in Table 1. While the Crude Palm oil (CPO) and Net Coconut oil (NCO) used in this study were supplied by Lion Oleo Chemical Company, Japan. Certified methanol of 99.8% purity was obtained from Sigma– Aldrich, Tokyo, Japan. The catalyst was pure sodium hydroxide from Wako Chemicals, Tokyo, Japan. Concentric sulphuric acid of 98% purity was purchased from Wako Chemicals, Tokyo Japan. 2.2. Equipments Experiments were conducted in a 15 cm3 special reaction glass tube, of which thickness was 2 mm and was sealed tightly with a silicon rubber cap that retained any vaporized mixture. The reaction glass tube was immersed in a glass water bath placed on the plate of magnetic stirrer Table 1 Fatty acid composition of crude Jatropha curcas oila Fatty acid
Formula
Systemic name
Structureb
wt%
Myristic Palmitic
C14H28O2 C16H32O2
Tetradecanoic Hexadecanoic
14:0 16:0
Palmitoleic Stearic Oleic
C16H30O2 C18H36O2 C18H34O2
cis-9-Hexadecenoic Octadecanoic cis-9-Octadecenoic
16:1 18:0 18:1
Linoleic
C18H32O2
18:2
Linolenic
C18H30O2
18:3
Arachidic Behenic
C20H40O2 C22H44O2
cis-9,cis-12Octadecedianoic cis-6,cis-9,cis-12Octadecatrienoic Eicosanoic Docosanoic
0–0.1 14.1– 15.3 0–1.3 3.7–9.8 34.3– 45.8 29.0– 44.2 0–0.3
20:0 22:0
0–0.3 0–0.2
a b
Adapted from Gubitz et al. (1999). xx:y indicates xx carbons in the fatty acid chain with y double bonds.
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of 400 rpm. Inside the glass water bath, there was a 100 V, 500 W electric water heater and a shielded K type thermocouple probe. A voltage regulator controls temperature level and heat supply. 2.3. Experimental procedure 2.3.1. One-step alkali base catalyzed transesterification One-step alkali base catalyzed transesterification was carried out for methyl ester production process from CPO, NCO, and CJCO. It was established that transesterification depends on several basic variables, namely, catalyst type, alcohol type, catalyst-to-oil ratio, alcohol-to-oil ratio, reaction temperature, reaction time, agitation rate, FFA, and water content of oils (Ma and Hanna, 1999). In this work, extensive preliminary experimentation with vegetable oils samples indicated that it was most efficient to fix reaction temperature at 65 C, agitation rate 400 rpm, and reaction time for 2 h. Firstly, in the transesterification process, different catalyst NaOH-to-oil ratios (0.5%, 1.0%, 1.5%, 2.0%, 2.5% and 3.0% w/w) and different methanol-to-oil ratios (10%, 15%, 20%, 25%, 30% and 40% w/w) were used to investigate their influence on the methyl ester yields of the oils. All the reactions were carried out in the reaction glass tubes, which were immersed in a glass water bath placed on the plate of magnetic stirrer of 400 rpm. The temperature and the reaction time for all process were maintained at 65.0 ± 0.5 C and for 2 h, respectively. After the reaction, the mixture was allowed to settle for 2 h to overnight before separating the glycerol layer and the top layer including methyl ester fraction was removed in a separated bottles, weight and analyzed by GC. In practically, the separated methyl esters must be conducted to remove impurities by washing with hot water until washing water was neutral. However, due to small amount of the oil samples used in the glass reaction tubes, the refinement stage on this experiment was omitted. 2.3.2. A two-step acid–base catalyzed transesterification Therefore, a two step process, acid-catalyzed esterification process and followed by base-catalyzed transesterification process, were selected for converting CJCO to methyl esters of fatty acids. The first step was acid esterification and pretreatment for removing FFA in the oil, which is mainly a pretreatment process, which could reduce the FFA. It was reported that to get complete FFA esterification in some vegetable oils, could be done in the reaction temperature 50 C. The process was intended to convert FFA to esters using an acid catalyst (H2SO4 1% w/w) to reduce the FFA concentration of CJCO below 2%. Second step was alkali base catalyzed transesterification. 2.3.2.1. Acid pretreatment. On this step, the CJCO was poured into the reaction glass tubes and heated. The solution of concentration H2SO4 acid (1.0% based on the oil weight) in methanol was heated at 50 C and then added
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into the reaction glass tubes. Different methanol to oil ratios by weight were used, namely at 0.10, 0.15, 0.20, 0.25, 0.30, 0.40, 0.50, 0.60 and 0.70 to investigate their influence on the acid value of CJCO. The acid values of the reaction mixtures were measured, while the compositions of the reaction mixtures were investigated by high performance liquid chromatography (HPLC) and by gas chromatography (GC). After one hour of reaction, the mixture was allowed to settle for 2 h and the methanol– water fraction at the top layer was removed. The optimum condition having the lowest acid value was used for the main transesterification reaction. 2.3.2.2. Base catalyzed transesterification. In the second step, optimum condition for NaOH to oil ratio and methanol to oil ratio were investigated. Firstly, the oil product that has been pretreated from the first step was poured into the reaction glass tubes and heated at 50 C. The solution of NaOH in methanol at 0.5%, 1.0%, 1.5%, 2.0% and 3.0% w/w of the oil were heated to 50 C prior to addition and then added to the heated oil. The reaction mixture was heated and stirred again at 65.0 ± 0.5 C and 400 rpm for 2 h. The mixture was allowed to settle 2 h or overnight before separate the glycerol layer to get the methyl ester layer of fatty acids on the top. Then the produced methyl esters were determined by GC. The same procedure was conducted for the investigation of optimum methanol to oil ratio. The investigation was carried out by using optimum NaOH amount in various methanols to oil ratio by weight at 0.1, 0.2, 0.35, 0.5, and 0.6.
6890 series that equipped with a flame ionization detector and a capillary column of acidified polyethylene glycol (HP-624, 30 m · 25 lm · 0.25 lm). The GC oven was kept at 80 C for 5 min, heated at 10 C/min up to 310 C, where it was kept for 1 min, and a total analytical time was 29 min. The carrier gas was helium (0.7 ml/min). The analysis of a sample by GC was carried out by injecting 1 ll of the sample solution into the GC. The formed methyl ester was identified by comparing its retention time to the retention time of standard methyl ester of fatty acid. Quantitative analysis of the weight percentage of the produced methyl esters/biodiesel was determined by decane internal standard method (Nguyen et al., 2005). Free fatty acids in the oils were transesterificated using boron trifluoride methanol solution and measured by GC (Yamaoka, 1978). 2.4.3. LC method Fatty acids in the methanol extracts from the oils were then analyzed by using high performance liquid chromatography (HPLC) (Shimadzu, LC-10AT) which consisted of the column (Capcell Pak C18, 25 cm in length · 4.6 mm in inner diameter, 5 lm, Shiseido Finechemicals. Co.) and ultraviolet detector at 220 nm (Tosoh, UV-8024) operated at 30 C with 0.7 ml/min flow rate of 80% acetonitrile solution containing 20% of 0.1% H3PO4 as a carrier solvent. The sample volume was 20 ll and a peak identification was made by comparing the reaction time between the sample and the standard compound. 3. Result and discussion
2.4. Analytical methods
3.1. One-step alkali base catalyzed transesterification
2.4.1. Acid value The acid value of the reaction mixture in the first stage was determined by the acid base titration technique (ASTM, 2003). A standard solution of one mol potassium hydroxide solution was used.
Alkali base catalyzed transesterification result of CPO, NCO, and CJCO were investigated by changing catalyst NaOH to oil ratios (% w/w) and catalyst to oil ratios (% w/w) as shown in Fig. 1a and b. The high conversion was obtained with 1.0% of catalyst NaOH to oil ratio and 28% of methanol to oil ratio, and under these condition, the FAME yield was 80% for CPO and 85% for NCO. The results of CJCO were shown in Fig. 2. Fig. 2 indicated that the optimum condition of alkali base cata-
2.4.2. GC method The composition of biodiesel products were analyzed using a Gas Chromatography of Hewlett Packard Plus
Fig. 1. FAME yields of alkali base catalyzed transesterification of CPO and NCO: (a) effect of NaOH-to-oil-ratio and (b) effect of methanol-to-oil-ratio.
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Table 2 The analytical result of FFA for CJCO, CPO and NCO by GC
Fig. 2. FAME yields of alkali base catalyzed transesterification of CJCO.
lyzed transesterification for CJCO required more catalyst and methanol. The optimum NaOH to oil ratio and the optimum methanol to oil ratio were 3.3% w/w and 70% w/w for CJCO. The reason of higher consumption catalyst NaOH and methanol in the transesterification process of CJCO is considered to be FFA. A high FFA in the oil deactivates the catalyst NaOH, and the addition of excess amount of NaOH as compensation gave rise to the formation of emulsion, which increased viscosity, lead to the formation of gels and the problem associated with glycerin separation and loss in ester yield. Although it is shown that the maximum FAME yields of CPO and NCO were 85% and 87%, respectively as shown in Fig. 1b, the methyl ester yield of CJCO was only 55% as shown in Fig. 2. Since one of reasons for low yield of base catalyst transesterification of CJCO is considered to be due to coexistence of FFA in the oil, FFA in the oil were investigated by HPLC, GC and acid titration method. 3.2. Contents of FFA in CJCO In Jatropha curcas seed oil extraction, CJCO is stored at long time prior to utilization. Without proper handling and storage, the process causes various chemical reactions such as hydrolysis, polymerization, and oxidation. Therefore, the physical and chemical properties of the CJCO changes during handling and storage. Many researches have been conducted to characterize these physical and chemical changes in the other vegetable oils (Monyem and Van Gerpen, 2001; Leung et al., 2006; Oversen et al., 1998). The percentage of FFA has been found to increase due to the hydrolysis of triglycerides in the presence of moisture and oxidations. Degradation of the CJCO results higher concentration of FFA. Comparing to CPO and NCO, CJCO contains higher concentration of unsaturated fatty acids, which are mainly linoleic acid (18:2) and oleic acid (18:1), as shown Table 1. The oxidation of the unsaturated fatty acids component in the CJCO might occur easily and it
Oil
FFA (%)
Myristic (%)
Palmitic (%)
Linoleic (%)
Oleic (%)
Stearic (%)
Crude Jatropha curcas oil (CJCO) Crude palm oil (CPO) Net coconut oil (NCO)
14.9
0.0
2.4
6.9
5.4
0.2
6.1
0.2
2.6
2.5
0.5
0.3
1.2
0.3
0.2
0.2
0.3
0.2
could lead to degradation of the oil (Canakci, 2007). The reason for auto oxidation is due to the presence of double bounds in the chains of unsaturated fatty acids compounds. The free fatty acids in the extracts with methanol from the oils were analyzed by HPLC. Oleic acid and linoleic acid were detected in the FFA extract from CJCO, and their concentrations were much higher than FFA in the methanol extracts from CPO and NCO. The precise contents of FFA in the oils were analyzed by GC, and the total concentrations of FFA in the oils were 14.9% w/w for JCJO, 7.2% w/w for CPO and 1.8% w/w for NCO, respectively (see Table 2). 3.3. A two-step acid–base transesterification of CJCO The problem with processing of CJCO that had high content FFA was that FFA could not be converted to FAME using an alkaline catalyst due to formation of fatty acid salts (soap). The soap could prevent separation of the methyl ester layer from the glycerin fraction. An alternative method is to use acid catalysis, which are able to esterify FFA. While, the esterification reaction stop in many cases due to the effect of the water produced when the FFA react with methanol to form esters (Canakci and Van Greppen, 1999). Therefore, the two steps process, acid-catalyzed esterification process and followed by base-catalyzed transesterification process, were selected for converting CJCO to methyl esters of fatty acids. 3.3.1. Acid pretreatment The objective of this stage was to reduce the acid value or FFA contents of CJCO. Important variable affecting the acid value in the esterification process was the methanol to oil ratio, the acid to oil ratio, reaction temperature, and reaction time. It was reported that to get completely FFA esterification in some vegetable oils, could be done in the reaction temperature 50 C, the reaction time one hour, and the acid H2SO4 to oil ratio 1% w/w (Ghadge and Raheman, 2005; Veljkovic´ et al., 2006). Therefore, these conditions were selected to investigate the effect of methanol to oil ratios in the acid values of CJCO. The effect of methanol amount on acid values and FFA of the mixtures after one hour reaction is shown in Fig. 3. The figure indicates that the acid value or FFA concentration was
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Fig. 3. Influence of methanol quantity on acid value and FFA of crude Jatropha curcas oil in the acid catalyst esterification stage.
influenced by the quantity of methanol. The FFA concentration reduced sharply to 3% at 10% w/w of methanol to oil ratio and then decreased gradually to 1% at 70% w/w of methanol to oil ratio. Increasing the methanol amount was no significant effect to acid value or FFA concentration reduction. It was due to the effect of water produced during the esterification of FFA. In practically, the esterification process might be improved by water removal in the mixture continuously. Therefore, there was an optimum quantity of methanol required to complete the esterification process of all FFA in CJCO. The optimum methanol to oil ratio was selected 60% w/w at the FFA concentration less than 1%, acid value of 2 mg KOH/g-oil. The first stage process was pretreatment process for removing FFA in the oil and the second stage process. 3.3.2. Base catalyzed transesterification Successful alkali base catalyzed transesterification process requires lower FFA content in CJCO, which is less than 2%. However, Table 2 indicates higher FFA content in CJCO sample, which is about 15%. Although Fig. 2 shows the result of direct transesterification of CJCO using basic catalyst, by direct transesterification, methyl ester yield of CJCO was only 55%, which was very low yield comparing to methyl ester yield of CPO and NCO. Thus, it is clear that high FFA content in the oil affected the methyl ester yield. The two-stage transesterification process of CJCO showed higher methyl ester yield than single stage or direct transesterification process. After acid pretreatment/acid catalyst esterification, FFA in the oil moved into methanol phase. The cleaned oil was brought to the second stage, base catalyzed transesterification with only NaOH to oil ratio at 1% w/w. In the second stage, the low level of remained FFA from the first stage clearly affected the transesterification process. Therefore, investigation of optimum catalyst to oil ratio and optimum methanol to oil ratio was required. Fig. 4 shows that the optimum catalyst to oil ratio was 1.4% w/w and optimum methanol to oil ratio was 24% w/w. At this optimum condition, the methyl ester yield was 90%, which was higher than the methyl ester yield of direct transesterification.
Fig. 4. FAME yields of CJCO after a two step acid/base transesterification process.
Table 3 The analytical result of components of FAME for CPO, NCO and CJCO Methyl ester
CPO (%)
NCO (%)
CJCO (%)
Methyl Methyl Methyl Methyl Methyl Methyl Methyl
0.41 1.24 42.42 0.28 3.30 47.04 5.32
54.39 21.40 10.58 0.24 1.69 6.41 5.29
0.06 0.10 14.96 1.10 3.85 32.49 47.43
laurate myristate palmitate palmitoleate stearate oleate linoleate
Qualitative and quantitative analysis result of methyl ester components in CJCO, CPO, and NCO transesterification product are presented in Table 3. The table indicates that the FAME from CJCO contained mainly methyl linoleate (47.4%) and methyl oleate (32.4%), which are comparable to fatty acid composition in CJCO feedstock. The other hand, the methyl esters from CPO contained mainly methyl palmitate (42.4%) and methyl oleate (47.0%), and the methyl esters from NCO contained mainly methyl laurate (54.4%), methyl myristate (21.4%), and methyl Palmitate (10.6%). 4. Conclusion Biodiesel production from CJCO with a high content of FFA has been investigated. In alkali base catalyzed transesterification process, the presence of high concentration of FFA reduced the yield of methyl esters of fatty acids significantly. A two-stage transesterification process was selected to improve the methyl ester yield. The first stage was acid pretreatment process, which could reduced the FFA level of CJCO to less than 1%. The second stage, alkali base catalyzed transesterification process gave 90% methyl ester yield. Acknowledgements This work was done in Biomass Technology Research Center AIST Chugoku, Kure-Hiroshima and was supported by Japanese International Centre Agency (JICA), Japan under the project ‘‘Research on Standard, Material
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