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Advanced supercritical Methyl acetate method for biodiesel production from Pongamia pinnata oil
Renewable Energy 83 (2015) 1245e1249
Contents lists available at ScienceDirect
Renewable Energy journal homepage: www.elsevier.com/locate/renene
Advanced supercritical Methyl acetate method for biodiesel production from Pongamia pinnata oil Fadjar Goembira a, *, Shiro Saka b a b
Department of Environmental Engineering, Faculty of Engineering, Andalas University, Kampus Unand Limau Manis, Padang 25163, Indonesia Department of Socio-Environmental Energy Science, Graduate School of Energy Science, Kyoto University, Yoshida-honmachi, Kyoto 606-8501, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 6 September 2014 Received in revised form 3 April 2015 Accepted 9 June 2015 Available online xxx
At present, alkali-catalyzed transesterification process is widely used in biodiesel production. However, in this process up to 88% of total production cost is for the feedstock, due to the requirement of using low free fatty acid (FFA) content feedstocks that are commonly attributed to refined edible plant-oils. This work was, therefore, carried out to know the potential use of non-edible Pongamia pinnata oil in biodiesel production. Instead of using a transesterification, this work applied an interesterification process called one-step supercritical methyl acetate method under reaction condition of 300 C/20 MPa/45 min/42 M ratio in methyl acetate to oil. In this glycerol-free method, 10wt% aqueous acetic acid was added as an additive to proceed the interesterification process under such reaction condition. It was found out that high FFA content in Pongamia pinnata oil did not give any adverse effect on the process as the highest yield of 96.6wt% FAME and 11.5wt% triacetin (total 108.1wt%) was achievable. Both products were miscible and their evaluation on biodiesel properties showed the compliance towards biodiesel standards. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Biodiesel Fatty acid methyl ester Triacetin Supercritical methyl acetate Pongamia pinnata oil
1. Introduction Presently, the most common method in biodiesel production is transesterification by alkali-catalyzed method [1]. However, this method is very sensitive to the presence of free fatty acids (FFA) in biodiesel feedstocks, as it will consume the alkali catalyst, reduce the reaction rate and complicate the separation of fatty acid methyl esters (FAME) with glycerol [2]. Ma et al. [3] suggested that the FFA content of feedstocks must be lower than 0.5wt% for an effective alkali-catalyzed transesterification reaction. Due to this requirement, edible feedstocks with low FFA contents such as rapeseed/canola and soybean oils are used for biodiesel production in European and North American countries, respectively. Since the edible plant oils are also consumed as food, the raise in biodiesel production has been considered as the reason behind the increase of the plant oil prices. As the worldwide biodiesel production increased from 2 million tons in 2004 to around 15 million tons in 2009 [4], the prices of rapeseed/canola and soybean oils increased from 650 to 550USD/ton, respectively, to
* Corresponding author. E-mail address: [email protected] (F. Goembira). http://dx.doi.org/10.1016/j.renene.2015.06.022 0960-1481/© 2015 Elsevier Ltd. All rights reserved.
900USD/ton [5]. Due to the inevitable use of the high-price edible plant oils in biodiesel production, up to 88% of total biodiesel production cost comes from the cost of feedstock [6]. Since biodiesel can also be produced from non-edible plant and waste cooking oils [7e11], it is very important to prioritize their use for preventing food and energy competitions and for reducing biodiesel production cost. Yet, the presence of relatively high FFA contents in those alternative feedstocks inhibits their current applications in biodiesel production [12e14]. It is, therefore, very important to develop unconventional biodiesel production methods that are applicable for broader range of feedstocks, regardless their FFA contents. In 2005, Saka [15] pioneered the development of a non-catalytic supercritical methyl acetate method to produce FAME and triacetin, as a by-product, which was followed by further works [16e20]. Methyl acetate is one of carboxylate esters, which shows the highest yield in biodiesel production by supercritical process [16]. Since triacetin is also considered as a fuel additive [21] and its mixture with FAME exhibits no detrimental effects on biodiesel properties [22], this process has the potential in maximizing the use of biodiesel feedstocks, due to the potential use of product and by-product as an alternative fuel. This work was, therefore, carried out to find possible application
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of the supercritical method on non-edible oil from the seeds of Pongamia pinnata. 2. Experimental 2.1. Materials Pongamia seeds were collected from Bogor, Indonesia. They were kept in an ordinary room condition for 6 months before being processed to extract its oil, hereinafter named Pongamia oil. Hexane for oil extraction and chemicals for producing biodiesel by supercritical interestrification, i.e., methyl acetate, acetic acid and distilled water (purity higher than 99%) were purchased from Nacalai Tesque Inc., Kyoto, Japan. In addition, analytical grade standards of various individual FAME compounds and triacetin were used for analytical purposes. All standard chemicals were also obtained from the same chemical supplier. 2.2. Methods Pongamia oil was extracted from Pongamia seeds by a hexaneextraction process for 10 h in a Soxhlet apparatus. Prior to the extraction process, the seeds were ground by a biomass blender and the crushed seeds were oven dried for 1 h under 105 C. The oil property measurement was carried out by using I-type floating density test method specified in JIS K2249, automatic kinematic viscosity test apparatus for kinematic viscosity, titration by potassium hydroxide for acid value and FFA content, Karl Fischer moisture content test instrument for water content, high performance liquid chromatography (HPLC) analysis for tocopherol content and gas chromatography with flame ionization detector for fatty acid profile. Supercritical methyl acetate process with the addition of CH3COOH(aq) in 26wt% aqueous concentration, hereinafter mentioned as CH3COOH(aq) (26wt% conc.), is a continuation from previous research by Goembira and Saka [20]. In this research, the amount of CH3COOH(aq) (26wt% conc.) was 10wt% to the amount of Pongamia oil. In addition, the amount of methyl acetate used in this experiment was 42 M ratio to the amount of oil. The supercritical process was conducted in a flow-type reaction system, in order to obtain sufficient amount of FAME and triacetin for biodiesel property evaluation. Fig. 1 shows the flow diagram of the process. After removing unreacted methyl acetate and additives by vacuum rotary evaporation instrument, obtained products were analyzed by using HPLC with a refractive index detector (RID). A Cadenza CD-C18 was used as the column with methanol as the mobile phase at 1 mL/min flow rate. The oven temperature was set 40 C and 10 mL of methanol-diluted sample (0.1 g per 3 mL methanol) was injected into the HPLC. Identification of products was carried out by comparing their retention times with the ones obtained from the standard
Table 1 Physico-chemical properties of Pongamia oil. Property
Measured value
Density at 15 C (kg/m3) Viscosity at 40 C (mm2/s) Acid value (mg KOH/g) Water content (wt%) Tocopherol content (ppm) Free fatty acid content (wt%) Fatty acid profile (wt%) Palmitic acid Stearic acid Oleic acid Linoleic acid Linolenic acid Others
0.93 38.5 4.40 0.07 385 2.20 7.4 3.8 65.6 15.4 4.4 3.4
compounds. Moreover, calibration curves of standard compounds were used for product quantification based on the peak areas from HPLC chromatograms. The yield of FAME was calculated from the peak in HPLC chromatograms with a value of 100 for the assumed theoretical maximum concentration. As for the yield of triacetin, it was also calculated from the peak area in the HPLC chromatogram, with its maximum theoretical value of 25wt%. Therefore, the total maximum theoretical value of FAME and triacetin is 125wt%. Moreover, evaluation of biodiesel properties was conducted to measure pour point, cloud point, cold filter plugging point, flash point, carbon residue and oxidation stability by using automatic pour and point test instrument MPC-102, cold filter plugging point test apparatus AFP-102, Pensky-Martens closed cup lash point measurement apparatus APM-7, micro residue carbon fraction measurement apparatus ACR-M3 and Rancimat oxidation stability testing instrument, respectively. 3. Results and discussion 3.1. Properties of Pongamia oil The results of evaluation on oil properties for Pongamia oil used in this work are presented in Table 1. We can see from the table that as crude oil, Pongamia has high viscosity that must be reduced for its application in diesel engines [23]. Furthermore, the high FFA and water contents are an indication for the inapplicability of this oil to the alkali-catalyzed transesterification and acid-catalyzed esterification, respectively. 3.2. Interesterification of Pongamia oil Fig. 2 shows the yield of FAME and triacetin from the interesterification of Pongamia oil by supercritical methyl acetate at 300 C/20 MPa/45 min/42:1 M ratio in methyl acetate to oil, with
Fig. 1. Supercritical methyl acetate method with the addition of 10wt% CH3COOH(aq) (26wt% conc.).
F. Goembira, S. Saka / Renewable Energy 83 (2015) 1245e1249
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biodiesel yield in total 1 h reaction time. A higher biodiesel yield of 90.4wt% in the same two-step acid-catalyzed esterification and alkali-catalyzed transesterification was reported by De and Bhattacharyya [27], but under a much longer reaction time of 11 h. 3.3. Fuel properties of Pongamia biodiesel
Fig. 2. Yield from supercritical methyl acetate method of Pongamia oil at 300 C/ 20 MPa/42 M ratio with and without 10wt% additions of CH3COOH(aq) (26wt% conc.).
and without the addition of 10wt% CH3COOH(aq) (26wt% conc.). As reported earlier by Goembira and Saka [18], the optimum reaction condition of one-step supercritical methyl acetate treatment of triglycerides is 350 C/20 MPa/45 min/42 M ratio. Triglycerides have lower reactivity than FFA towards supercritical methyl acetate [16,22], therefore, such a reaction condition is necessary if the one-step supercritical process is carried out without any additive additions [20]. On the other hand, as 10wt% CH3COOH(aq) (26wt% conc.) was added in the reaction system, significant yield increase was evident. Under 15 min reaction time, the total yield was already more than 50wt%, while the highest yield of 96.6wt% FAME and 11.5wt% triacetin (total 108.1wt%) was acquired in 45 min of reaction. The successful interesterification reaction at 300 C and 20 MPa with the addition of CH3COOH(aq) (26wt% conc.) was most likely due to the formation of FFA from triglycerides in the reaction system. The FFA, which has higher reactivity than triglycerides towards supercritical methyl acetate, further reacts with supercritical methyl acetate to form FAME. This phenomenon has been well explained earlier by Saka et al. [24]. However, a longer reaction time of 60 min reduced the yield to 104.9wt%, due most likely to the occurrence of thermal decomposition of some products. From experimental data shown in Fig. 2, it is obvious that FAME yield was reduced from 96.6wt% under 45 min reaction time to around 92.3wt% after 60 min reaction time. In contrast, triacetin yield was increased from 11.5 to 14.6wt% under 45 and 60 min reaction times, respectively. As we can see from Table 1, there are around 20wt% poly-unsaturated fatty acids in the oil that can be converted into their corresponding FAME by the interesterification reaction. As reported by Imahara et al. [25], polyunsaturated FAME is vulnerable to thermal decomposition even under relatively lower reaction temperatures in supercritical process. In comparison, Karmee and Chadha [26] utilized alkalicatalyzed transesterification with methanol and 1wt% KOH to obtain 92wt% biodiesel from Pongamia oil in 90 min. While the utilization of Hb-zeolite as a solid acid catalyst by the same research group shows lower yield of 83wt% at higher reaction temperature of 120 C after 24 h reaction time. Moreover, Sharma and Singh [13] observed that the use of H2SO4 for acid esterification followed by a transesterification reaction with KOH catalyst can achieve 89.5wt%
The results of evaluation on fuel properties are presented in Table 2. The density of FAME and triacetin mixture was higher than the value required by the Japan and EU standards. This property is not regulated by the US standard, therefore, it can still be considered as acceptable. The same condition also happened for oxidation stability that was lower than that required by the European biodiesel standard, but not regulated by the Japan and US standards. A more concerning issue regarding the fuel property is on the acid value parameter. Although the acid value of Pongamia oil was considerably reduced after it was converted into biodiesel by the interesterification reaction, i.e., from 4.40 to 1.05mgKOH/g, the value was still not in accordance with any of the biodiesel standards referred in this work. The high acid value can be due to the remaining CH3COOH(aq) that was used as an additive in the supercritical process. Therefore, an additional washing step of products with water was developed to remove the remaining additive from the products. The schematic drawing of the supercritical methyl acetate method with the additional product washing step is shown in Fig. 3. As we can see from Fig. 3, after finishing the supercritical treatment, evaporation was done to separate unreacted methyl acetate from the products. Afterwards, water was mixed with the products followed by a vigorous shaking of the mixture. Phase separation of the oil and water portions was further done before separating triacetin from water and acetic acid in the water portion by using vacuum rotary evaporator. Finally, FAME and triacetin can be mixed to be used as biodiesel. Evaluation of biodiesel properties was done for individual FAME and triacetin obtained from the washing and separation steps. Furthermore, the fuel property evaluation was also carried out for the mixture of FAME and triacetin, and the results are presented in Table 3. Based on the measurements, acid value that was the main concern can be reduced to fulfill the requirement of all biodiesel standards. At this point, only oxidation stability parameter that was still not in compliance with the European biodiesel standard. However, this biodiesel property can be improved by the addition of commercially-available anti-oxidants, such as propyl gallate, diphenyl phenylene-diamine and butylated hydroxytoluene [28,29]. According to Xin et al. [29], the addition of 400 ppm propyl gallate could ensure the fulfillment of oxidation stability
Table 2 Fuel properties of biodiesel produced by supercritical methyl acetate method of Pongamia oil at 300 C/20 MPa/45 min/42 M ratio with 10wt% addition of CH3COOH(aq) (26wt% conc.). Property
3
Density at 15 C (kg/m ) Viscosity at 40 C (mm2/s) Acid value (mg KOH/g) Pour point ( C) Cloud point ( C) Cold filter plugging point ( C) Flash point ( C) Carbon residue (wt%) Oxidation stability (h) a
Measured value
Biodiesel standard Japan
EU
US
0.94 4.9 1.05 10.0 10.0 16.0 163.0 0.04 4.0
0.86e0.90 3.5e5.0 0.5 e e e 100 0.3(10%)a e
0.86e0.90 3.5e5.0 0.5 e e e 101 0.3(10%)a 6
e 1.9e6.0 0.5 e e e 130 0.03 e
Calculated from 10wt% sample.
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Fig. 3. Supercritical methyl acetate method with 10wt% addition of CH3COOH(aq) (26wt% conc.) and additional washing step of products.
Table 3 Fuel properties of biodiesel produced by supercritical methyl acetate method of Pongamia oil at 300 C/20 MPa/45 min/42 M ratio with 10wt% addition of CH3COOH(aq) (26wt% conc.) and an additional washing step. Property
FAME
Triacetin
FAME þ triacetin
Biodiesel standard Japan
EU
US
Density at 15 C (kg/m3) Viscosity at 40 C (mm2/s) Ester content (wt%) Acid value (mgKOH/g) Pour point ( C) Cloud point C Cold filter plug. Point ( C) Flash point ( C) Water content (mg/kg) Carbon residue (wt%) Oxidation stability (h)
0.88 4.5 97.6 0.30 15.0 15.0 16.0 160 300 0.01 1.5
1.20 6.4 N/Aa 0.05 30.0 25.0 30.0 146 345 0.02 10.0
0.92 4.9 87.0 0.23 17.0 17.0 20.0 155 315 0.03 3.5
0.86e0.90 3.5e5.0 96.5 0.5 e e e 100 500 0.3(10%)b e
0.86e0.90 3.5e5.0 96.5 0.5 e e e 101 500 0.3(10%)b 6
e 1.9e6.0 e 0.5 e e e 130 500 0.05 e
a b
N/A ¼ not applicable. Calculated from 10wt% sample.
parameter for biodiesel as regulated by the European biodiesel standard. From the results of this work, we can see that supercritical methyl acetate method with the addition of 10wt% CH3COOH(aq) (26wt% conc.) and a simple washing step, successfully converted Pongamia oil into FAME and triacetin. The mixture of FAME and triacetin obtained from the supercritical process hardly showed any incompliance with most biodiesel standards. Therefore, it can be concluded that this process has the potential for the utilization of most biodiesel feedstocks. Furthermore, the use of the supercritical process will maximize the utilization of the feedstock as a limited resource, because both product and by-product can be mixed to be used as biodiesel.
[3] [4] [5] [6] [7] [8]
[9]
4. Concluding remarks [10]
Supercritical methyl acetate method for biodiesel production from Pongamia oil at 300 C/20 MPa/45 min/42 M ratio with the addition of 10wt% CH3COOH(aq) (26wt% conc.) and a washing step of products, resulted in 96.6wt% FAME and 11.5wt% triacetin yields (total 108.1wt%). Furthermore, the quality of biodiesel produced in this work complies with the requirements of biodiesel standards. This process is, therefore, very potential to reduce the dependency on using edible oils in biodiesel production, due to its possible application on broader range of feedstocks.
[11] [12]
[13] [14]
[15]
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production by supercritical methyl acetate method, in: T. Yao (Ed.), Zerocarbon Energy Kyoto 2012, Green Energy and Technology, Springer, Japan, 2012, pp. 91e96. F. Ma, L.D. Clements, M. Hanna, The effects of catalyst, free fatty acids and water on transesterification of beef tallow, Trans. ASAE 41 (1998) 1261e1264. REN21, Renewables, Global Status Report in, 2011. http://www.ren21.net/ Portals/97/documents/GSR/REN21_GSR2011.pdf (accessed on April 26, 2012). L. Lin, Z. Cunshan, S. Vittayapadung, S. Xiangqian, D. Mingdong, Opportunities and challenges for biodiesel fuel, Appl. Energ. 88 (2011) 1020e1031. M.J. Haas, A.J. McAloon, W.C. Yee, T.A. Foglia, A process model to estimate biodiesel production cost, Bioresour. Technol. 97 (2006) 671e678. T.P. Durrett, C. Benning, J. Ohlrogge, Plant triacylglycerols as feedstocks for the production of biofuels, Plant J. 54 (2008) 593e607. F. Goembira, S. Saka, Pongamia pinnata as potential biodiesel feedstock, in: T. Yao (Ed.), Zero-carbon Energy Kyoto 2010. Green Energy and Technology, Springer, Japan, 2011, pp. 111e116. Z.W.M.M. Phoo, Z. Ilham, F. Goembira, L.F. Razon, S. Saka, Physico-chemical properties of biodiesel from various feedstocks, in: T. Yao (Ed.), Zero-carbon Energy Kyoto 2012, Green Energy and Technology, Springer, Japan, 2013, pp. 113e121. Z.W.M.M. Phoo, L. Razon, G. Knothe, Z. Ilham, F. Goembira, C. Madrazo, S. Roces, S. Saka, Evaluation of Indian milkweed (Calotropis gigantea) seed oil as alternative feedstock for biodiesel, Ind. Crops Prod. 54 (2014) 226e232. M.G. Kulkarni, A.K. Dalai, Waste cooking oil-an economical source for biodiesel: a review, Ind. Eng. Chem. Res. 45 (2006) 2901e2913. H.J. Berchmans, S. Hirata, Biodiesel production from crude Jatropha curcas L. seed oil with a high content of free fatty acids, Bioresour. Technol. 99 (2008) 1716e1721. Y.C. Sharma, B. Singh, Development of biodiesel from karanja: a tree found in rural India, Fuel 87 (2008) 1740e1742. M. Satyanarayana, C. Muraleedharan, Comparative studies of biodiesel production from rubber seed oil, coconut oil and palm oil including thermogravimetric analysis, Energy Sources Part A 33 (2011) 925e937. S. Saka, Manufacturing method for fatty acid methyl esters, Japan Patent no. 4378534 (application: 19 Dec 2005; granted: 2 Oct 2009). F. Goembira, K. Matsuura, S. Saka, Biodiesel production by various supercritical carboxylate esters, Fuel 97 (2012) 373e378. F. Goembira, S. Saka, Factors affecting biodiesel yield in interesterification of rapeseed oil by supercritical methyl acetate, in: T. Yao (Ed.), Zero-carbon Energy Kyoto 2011, Green Energy and Technology, Springer, Japan, 2012, pp.
F. Goembira, S. Saka / Renewable Energy 83 (2015) 1245e1249 147e152. [18] F. Goembira, S. Saka, Optimization of biodiesel production by supercritical methyl acetate, Bioresour. Technol. 131 (2013) 47e52. [19] F. Goembira, S. Saka, Effect of water and free fatty acids in oil on biodiesel production by supercritical methyl acetate, in: T. Yao (Ed.), Zero-carbon Energy Kyoto 2012, Green Energy and Technology, Springer, 2013, pp. 91e96. [20] F. Goembira, S. Saka, Effect of additives to supercritical methyl acetate on biodiesel production, Fuel Process. Technol. 125 (2014) 114e118. [21] J.A. Malero, R. van Grieken, G. Morales, J. Paniagna, Acidic mesoporous silica for the acetylation of glycerol: synthesis of bioadditives for petrol fuels, Energy Fuels 21 (2007) 1782e1791. [22] S. Saka, Y. Isayama, A new process for catalyst-free production of biodiesel using supercritical methyl acetate, Fuel 88 (2009) 1307e1313. [23] M. Mittelbach, Diesel fuel derived from vegetable oils, VI: specifications and
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quality control of biodiesel, Bioresour. Technol. 56 (1996) 7e11. [24] S. Saka, Y. Isayama, Z. Ilham, X. Jiayu, New process for catalyst-free biodiesel production using subcritical acetic acid and supercritical methanol, Fuel 89 (2010) 1442e1446. [25] H. Imahara, E. Minami, S. Hari, S. Saka, Thermal stability of biodiesel in supercritical methanol, Fuel 87 (2008) 1e6. [26] S.K. Karmee, A. Chadha, Preparation of biodiesel from crude oil of Pongamia pinnata, Bioresour. Technol. 96 (2005) 1425e1429. [27] B.K. De, D.K. Bhattacharyya, Biodiesel from minor vegetable oils like karanja oil and nahor oil, Fett/Lipid 101 (1999) 404e406. [28] J. Xin, H. Imahara, S. Saka, Oxidation stability of biodiesel fuel as prepared by supercritical methanol, Fuel 87 (2008) 1807e1813. [29] J. Xin, H. Imahara, S. Saka, Kinetics on the oxidation of biodiesel stabilized with antioxidant, Fuel 88 (2009) 282e286.
Contents lists available at ScienceDirect
Renewable Energy journal homepage: www.elsevier.com/locate/renene
Advanced supercritical Methyl acetate method for biodiesel production from Pongamia pinnata oil Fadjar Goembira a, *, Shiro Saka b a b
Department of Environmental Engineering, Faculty of Engineering, Andalas University, Kampus Unand Limau Manis, Padang 25163, Indonesia Department of Socio-Environmental Energy Science, Graduate School of Energy Science, Kyoto University, Yoshida-honmachi, Kyoto 606-8501, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 6 September 2014 Received in revised form 3 April 2015 Accepted 9 June 2015 Available online xxx
At present, alkali-catalyzed transesterification process is widely used in biodiesel production. However, in this process up to 88% of total production cost is for the feedstock, due to the requirement of using low free fatty acid (FFA) content feedstocks that are commonly attributed to refined edible plant-oils. This work was, therefore, carried out to know the potential use of non-edible Pongamia pinnata oil in biodiesel production. Instead of using a transesterification, this work applied an interesterification process called one-step supercritical methyl acetate method under reaction condition of 300 C/20 MPa/45 min/42 M ratio in methyl acetate to oil. In this glycerol-free method, 10wt% aqueous acetic acid was added as an additive to proceed the interesterification process under such reaction condition. It was found out that high FFA content in Pongamia pinnata oil did not give any adverse effect on the process as the highest yield of 96.6wt% FAME and 11.5wt% triacetin (total 108.1wt%) was achievable. Both products were miscible and their evaluation on biodiesel properties showed the compliance towards biodiesel standards. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Biodiesel Fatty acid methyl ester Triacetin Supercritical methyl acetate Pongamia pinnata oil
1. Introduction Presently, the most common method in biodiesel production is transesterification by alkali-catalyzed method [1]. However, this method is very sensitive to the presence of free fatty acids (FFA) in biodiesel feedstocks, as it will consume the alkali catalyst, reduce the reaction rate and complicate the separation of fatty acid methyl esters (FAME) with glycerol [2]. Ma et al. [3] suggested that the FFA content of feedstocks must be lower than 0.5wt% for an effective alkali-catalyzed transesterification reaction. Due to this requirement, edible feedstocks with low FFA contents such as rapeseed/canola and soybean oils are used for biodiesel production in European and North American countries, respectively. Since the edible plant oils are also consumed as food, the raise in biodiesel production has been considered as the reason behind the increase of the plant oil prices. As the worldwide biodiesel production increased from 2 million tons in 2004 to around 15 million tons in 2009 [4], the prices of rapeseed/canola and soybean oils increased from 650 to 550USD/ton, respectively, to
* Corresponding author. E-mail address: [email protected] (F. Goembira). http://dx.doi.org/10.1016/j.renene.2015.06.022 0960-1481/© 2015 Elsevier Ltd. All rights reserved.
900USD/ton [5]. Due to the inevitable use of the high-price edible plant oils in biodiesel production, up to 88% of total biodiesel production cost comes from the cost of feedstock [6]. Since biodiesel can also be produced from non-edible plant and waste cooking oils [7e11], it is very important to prioritize their use for preventing food and energy competitions and for reducing biodiesel production cost. Yet, the presence of relatively high FFA contents in those alternative feedstocks inhibits their current applications in biodiesel production [12e14]. It is, therefore, very important to develop unconventional biodiesel production methods that are applicable for broader range of feedstocks, regardless their FFA contents. In 2005, Saka [15] pioneered the development of a non-catalytic supercritical methyl acetate method to produce FAME and triacetin, as a by-product, which was followed by further works [16e20]. Methyl acetate is one of carboxylate esters, which shows the highest yield in biodiesel production by supercritical process [16]. Since triacetin is also considered as a fuel additive [21] and its mixture with FAME exhibits no detrimental effects on biodiesel properties [22], this process has the potential in maximizing the use of biodiesel feedstocks, due to the potential use of product and by-product as an alternative fuel. This work was, therefore, carried out to find possible application
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F. Goembira, S. Saka / Renewable Energy 83 (2015) 1245e1249
of the supercritical method on non-edible oil from the seeds of Pongamia pinnata. 2. Experimental 2.1. Materials Pongamia seeds were collected from Bogor, Indonesia. They were kept in an ordinary room condition for 6 months before being processed to extract its oil, hereinafter named Pongamia oil. Hexane for oil extraction and chemicals for producing biodiesel by supercritical interestrification, i.e., methyl acetate, acetic acid and distilled water (purity higher than 99%) were purchased from Nacalai Tesque Inc., Kyoto, Japan. In addition, analytical grade standards of various individual FAME compounds and triacetin were used for analytical purposes. All standard chemicals were also obtained from the same chemical supplier. 2.2. Methods Pongamia oil was extracted from Pongamia seeds by a hexaneextraction process for 10 h in a Soxhlet apparatus. Prior to the extraction process, the seeds were ground by a biomass blender and the crushed seeds were oven dried for 1 h under 105 C. The oil property measurement was carried out by using I-type floating density test method specified in JIS K2249, automatic kinematic viscosity test apparatus for kinematic viscosity, titration by potassium hydroxide for acid value and FFA content, Karl Fischer moisture content test instrument for water content, high performance liquid chromatography (HPLC) analysis for tocopherol content and gas chromatography with flame ionization detector for fatty acid profile. Supercritical methyl acetate process with the addition of CH3COOH(aq) in 26wt% aqueous concentration, hereinafter mentioned as CH3COOH(aq) (26wt% conc.), is a continuation from previous research by Goembira and Saka [20]. In this research, the amount of CH3COOH(aq) (26wt% conc.) was 10wt% to the amount of Pongamia oil. In addition, the amount of methyl acetate used in this experiment was 42 M ratio to the amount of oil. The supercritical process was conducted in a flow-type reaction system, in order to obtain sufficient amount of FAME and triacetin for biodiesel property evaluation. Fig. 1 shows the flow diagram of the process. After removing unreacted methyl acetate and additives by vacuum rotary evaporation instrument, obtained products were analyzed by using HPLC with a refractive index detector (RID). A Cadenza CD-C18 was used as the column with methanol as the mobile phase at 1 mL/min flow rate. The oven temperature was set 40 C and 10 mL of methanol-diluted sample (0.1 g per 3 mL methanol) was injected into the HPLC. Identification of products was carried out by comparing their retention times with the ones obtained from the standard
Table 1 Physico-chemical properties of Pongamia oil. Property
Measured value
Density at 15 C (kg/m3) Viscosity at 40 C (mm2/s) Acid value (mg KOH/g) Water content (wt%) Tocopherol content (ppm) Free fatty acid content (wt%) Fatty acid profile (wt%) Palmitic acid Stearic acid Oleic acid Linoleic acid Linolenic acid Others
0.93 38.5 4.40 0.07 385 2.20 7.4 3.8 65.6 15.4 4.4 3.4
compounds. Moreover, calibration curves of standard compounds were used for product quantification based on the peak areas from HPLC chromatograms. The yield of FAME was calculated from the peak in HPLC chromatograms with a value of 100 for the assumed theoretical maximum concentration. As for the yield of triacetin, it was also calculated from the peak area in the HPLC chromatogram, with its maximum theoretical value of 25wt%. Therefore, the total maximum theoretical value of FAME and triacetin is 125wt%. Moreover, evaluation of biodiesel properties was conducted to measure pour point, cloud point, cold filter plugging point, flash point, carbon residue and oxidation stability by using automatic pour and point test instrument MPC-102, cold filter plugging point test apparatus AFP-102, Pensky-Martens closed cup lash point measurement apparatus APM-7, micro residue carbon fraction measurement apparatus ACR-M3 and Rancimat oxidation stability testing instrument, respectively. 3. Results and discussion 3.1. Properties of Pongamia oil The results of evaluation on oil properties for Pongamia oil used in this work are presented in Table 1. We can see from the table that as crude oil, Pongamia has high viscosity that must be reduced for its application in diesel engines [23]. Furthermore, the high FFA and water contents are an indication for the inapplicability of this oil to the alkali-catalyzed transesterification and acid-catalyzed esterification, respectively. 3.2. Interesterification of Pongamia oil Fig. 2 shows the yield of FAME and triacetin from the interesterification of Pongamia oil by supercritical methyl acetate at 300 C/20 MPa/45 min/42:1 M ratio in methyl acetate to oil, with
Fig. 1. Supercritical methyl acetate method with the addition of 10wt% CH3COOH(aq) (26wt% conc.).
F. Goembira, S. Saka / Renewable Energy 83 (2015) 1245e1249
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biodiesel yield in total 1 h reaction time. A higher biodiesel yield of 90.4wt% in the same two-step acid-catalyzed esterification and alkali-catalyzed transesterification was reported by De and Bhattacharyya [27], but under a much longer reaction time of 11 h. 3.3. Fuel properties of Pongamia biodiesel
Fig. 2. Yield from supercritical methyl acetate method of Pongamia oil at 300 C/ 20 MPa/42 M ratio with and without 10wt% additions of CH3COOH(aq) (26wt% conc.).
and without the addition of 10wt% CH3COOH(aq) (26wt% conc.). As reported earlier by Goembira and Saka [18], the optimum reaction condition of one-step supercritical methyl acetate treatment of triglycerides is 350 C/20 MPa/45 min/42 M ratio. Triglycerides have lower reactivity than FFA towards supercritical methyl acetate [16,22], therefore, such a reaction condition is necessary if the one-step supercritical process is carried out without any additive additions [20]. On the other hand, as 10wt% CH3COOH(aq) (26wt% conc.) was added in the reaction system, significant yield increase was evident. Under 15 min reaction time, the total yield was already more than 50wt%, while the highest yield of 96.6wt% FAME and 11.5wt% triacetin (total 108.1wt%) was acquired in 45 min of reaction. The successful interesterification reaction at 300 C and 20 MPa with the addition of CH3COOH(aq) (26wt% conc.) was most likely due to the formation of FFA from triglycerides in the reaction system. The FFA, which has higher reactivity than triglycerides towards supercritical methyl acetate, further reacts with supercritical methyl acetate to form FAME. This phenomenon has been well explained earlier by Saka et al. [24]. However, a longer reaction time of 60 min reduced the yield to 104.9wt%, due most likely to the occurrence of thermal decomposition of some products. From experimental data shown in Fig. 2, it is obvious that FAME yield was reduced from 96.6wt% under 45 min reaction time to around 92.3wt% after 60 min reaction time. In contrast, triacetin yield was increased from 11.5 to 14.6wt% under 45 and 60 min reaction times, respectively. As we can see from Table 1, there are around 20wt% poly-unsaturated fatty acids in the oil that can be converted into their corresponding FAME by the interesterification reaction. As reported by Imahara et al. [25], polyunsaturated FAME is vulnerable to thermal decomposition even under relatively lower reaction temperatures in supercritical process. In comparison, Karmee and Chadha [26] utilized alkalicatalyzed transesterification with methanol and 1wt% KOH to obtain 92wt% biodiesel from Pongamia oil in 90 min. While the utilization of Hb-zeolite as a solid acid catalyst by the same research group shows lower yield of 83wt% at higher reaction temperature of 120 C after 24 h reaction time. Moreover, Sharma and Singh [13] observed that the use of H2SO4 for acid esterification followed by a transesterification reaction with KOH catalyst can achieve 89.5wt%
The results of evaluation on fuel properties are presented in Table 2. The density of FAME and triacetin mixture was higher than the value required by the Japan and EU standards. This property is not regulated by the US standard, therefore, it can still be considered as acceptable. The same condition also happened for oxidation stability that was lower than that required by the European biodiesel standard, but not regulated by the Japan and US standards. A more concerning issue regarding the fuel property is on the acid value parameter. Although the acid value of Pongamia oil was considerably reduced after it was converted into biodiesel by the interesterification reaction, i.e., from 4.40 to 1.05mgKOH/g, the value was still not in accordance with any of the biodiesel standards referred in this work. The high acid value can be due to the remaining CH3COOH(aq) that was used as an additive in the supercritical process. Therefore, an additional washing step of products with water was developed to remove the remaining additive from the products. The schematic drawing of the supercritical methyl acetate method with the additional product washing step is shown in Fig. 3. As we can see from Fig. 3, after finishing the supercritical treatment, evaporation was done to separate unreacted methyl acetate from the products. Afterwards, water was mixed with the products followed by a vigorous shaking of the mixture. Phase separation of the oil and water portions was further done before separating triacetin from water and acetic acid in the water portion by using vacuum rotary evaporator. Finally, FAME and triacetin can be mixed to be used as biodiesel. Evaluation of biodiesel properties was done for individual FAME and triacetin obtained from the washing and separation steps. Furthermore, the fuel property evaluation was also carried out for the mixture of FAME and triacetin, and the results are presented in Table 3. Based on the measurements, acid value that was the main concern can be reduced to fulfill the requirement of all biodiesel standards. At this point, only oxidation stability parameter that was still not in compliance with the European biodiesel standard. However, this biodiesel property can be improved by the addition of commercially-available anti-oxidants, such as propyl gallate, diphenyl phenylene-diamine and butylated hydroxytoluene [28,29]. According to Xin et al. [29], the addition of 400 ppm propyl gallate could ensure the fulfillment of oxidation stability
Table 2 Fuel properties of biodiesel produced by supercritical methyl acetate method of Pongamia oil at 300 C/20 MPa/45 min/42 M ratio with 10wt% addition of CH3COOH(aq) (26wt% conc.). Property
3
Density at 15 C (kg/m ) Viscosity at 40 C (mm2/s) Acid value (mg KOH/g) Pour point ( C) Cloud point ( C) Cold filter plugging point ( C) Flash point ( C) Carbon residue (wt%) Oxidation stability (h) a
Measured value
Biodiesel standard Japan
EU
US
0.94 4.9 1.05 10.0 10.0 16.0 163.0 0.04 4.0
0.86e0.90 3.5e5.0 0.5 e e e 100 0.3(10%)a e
0.86e0.90 3.5e5.0 0.5 e e e 101 0.3(10%)a 6
e 1.9e6.0 0.5 e e e 130 0.03 e
Calculated from 10wt% sample.
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Fig. 3. Supercritical methyl acetate method with 10wt% addition of CH3COOH(aq) (26wt% conc.) and additional washing step of products.
Table 3 Fuel properties of biodiesel produced by supercritical methyl acetate method of Pongamia oil at 300 C/20 MPa/45 min/42 M ratio with 10wt% addition of CH3COOH(aq) (26wt% conc.) and an additional washing step. Property
FAME
Triacetin
FAME þ triacetin
Biodiesel standard Japan
EU
US
Density at 15 C (kg/m3) Viscosity at 40 C (mm2/s) Ester content (wt%) Acid value (mgKOH/g) Pour point ( C) Cloud point C Cold filter plug. Point ( C) Flash point ( C) Water content (mg/kg) Carbon residue (wt%) Oxidation stability (h)
0.88 4.5 97.6 0.30 15.0 15.0 16.0 160 300 0.01 1.5
1.20 6.4 N/Aa 0.05 30.0 25.0 30.0 146 345 0.02 10.0
0.92 4.9 87.0 0.23 17.0 17.0 20.0 155 315 0.03 3.5
0.86e0.90 3.5e5.0 96.5 0.5 e e e 100 500 0.3(10%)b e
0.86e0.90 3.5e5.0 96.5 0.5 e e e 101 500 0.3(10%)b 6
e 1.9e6.0 e 0.5 e e e 130 500 0.05 e
a b
N/A ¼ not applicable. Calculated from 10wt% sample.
parameter for biodiesel as regulated by the European biodiesel standard. From the results of this work, we can see that supercritical methyl acetate method with the addition of 10wt% CH3COOH(aq) (26wt% conc.) and a simple washing step, successfully converted Pongamia oil into FAME and triacetin. The mixture of FAME and triacetin obtained from the supercritical process hardly showed any incompliance with most biodiesel standards. Therefore, it can be concluded that this process has the potential for the utilization of most biodiesel feedstocks. Furthermore, the use of the supercritical process will maximize the utilization of the feedstock as a limited resource, because both product and by-product can be mixed to be used as biodiesel.
[3] [4] [5] [6] [7] [8]
[9]
4. Concluding remarks [10]
Supercritical methyl acetate method for biodiesel production from Pongamia oil at 300 C/20 MPa/45 min/42 M ratio with the addition of 10wt% CH3COOH(aq) (26wt% conc.) and a washing step of products, resulted in 96.6wt% FAME and 11.5wt% triacetin yields (total 108.1wt%). Furthermore, the quality of biodiesel produced in this work complies with the requirements of biodiesel standards. This process is, therefore, very potential to reduce the dependency on using edible oils in biodiesel production, due to its possible application on broader range of feedstocks.
[11] [12]
[13] [14]
[15]
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