Acid Esterification-Alkaline Transesterification Process For
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Journal of Oleo Science Copyright ©2012 by Japan Oil Chemists’ Society J. Oleo Sci. 61, (2) 81-88 (2012) Acid Esterifi cation-Alkaline Transesterifi cation Process for Methyl Ester Production from Crude Rubber Seed Oil Prachasanti Thaiyasuit, Kulachate Pianthong* and Ittipon Worapun Department of Mechanical Engineering, Faculty of Engineering, Ubon Ratchathani University (Ubonratchathani, 34190, THAILAND) Abstract: This study aims to examine methods and the most suitable conditions for producing methyl ester from crude rubber seed oil. An acid esterifi cation-alkaline transesterifi cation process is proposed. In the experiment, the 20% FFA of crude rubber seed oil could be reduced to 3% FFA by acid esterifi cation. The product after esterifi ed was then tranesterifi ed by alkaline transesterifi cation process. By this method, the maximum yield of methyl ester was 90% by mass. The overall consumption of methanol was 10.5:1 by molar ratio. The yielded methyl ester was tested for its fuel properties and met required standards. The major fatty acid methyl ester compositions were analyzed and constituted of methyl linoleate 41.57%, methyl oleate 24.87%, and methyl lonolenate 15.16%. Therefore, the cetane number of methyl ester could be estimated as 47.85, while the tested result of motor cetane number was 51.20. Key words: methyl ester, crude rubber seed oil, esterifi cation, transesterifi cation 1 INTRODUCTION madhas et al.5)had found that the FFA content in the crude Nowadays, the shortage or crisis of fossil fuel lately rubber seed oil was about 17% and 19% of FFA in mahua becomes one of the most concerns in automotive industry oil was found by Ghadge and Raheman6). This FFA value is and world energy sector. This infl uences researchers and significantly high and obstructs the transesterification industries to search for a renewable energy to compensate process in the methyl ester production. It has been con- the fossil fuel. Methyl ester fuel is one of the possible firmed that the ester yield decreases with increasing in choices, because it is renewable and free of sulfur. Methyl FFA significantly. Usually, the alkaline-catalyzed trans- ester contains about 10-11% oxygen by weight. This char- esterifi cation takes place well only with refi ned oil having acteristic reduces the emissions of CO, HC, and particulate FFA value of less than 2%5-7). Canakci and Van Gerpen8) matter in the exhaust gas compared with diesel fuel. As it had found that transesterification would not occur if the is obtained mainly from plantation resources, it is able to FFA content in the oil were above 3%. Usually, free car- reduce the lifecycle of carbon dioxide by almost 78% com- boxylic acids form soaps with alkaline-catalyzed trans- pared to conventional diesel fuel1), while its fuel properties esterification, hence they impede the separation of the are very closed to diesel. Also, methyl ester can be used in glycerol phase due to the emulsifying effects of soaps and diesel engines with few or no engine modifi cations2). lower their catalytic activity9, 10). In extreme cases, of more Usually, methyl ester has been produced from the edible than 5% FFA oil, Canakci and Van Gerpen11)reported that plant oils such as soybean oil3)and palm oil4). However, it is the reacted mixture might completely gel after the addition always controversial on using edible oil or food resource as of KOH or NaOH, so that the charge has to be discarded. fuels. Therefore, in recent years, considerable research Therefore, the single step alkaline-catalyzed tranesterifi ca- effort has been directed towards replacing food oils with tion process is not suitable to produce methyl esters from various non-edible, wasted, or low-cost oils. The unrefi ned high FFA crude oil. In order to reduce the FFA, the crude non-edible oils have been considered, however they have oil should be refi ned, but the overall production cost of the high impurities such as free fatty acid(FFA)and phospha- methyl ester will be increased. The single step acid trans- tide. These impurities impede the transesterification esterifi cation is a typical method of producing methyl ester process in the methyl ester production. For instance, Ra- from high FFA oil, however, it requires more methanol, *Correspondence to: Kulachate Pianthong, Department of Mechanical Engineering, Faculty of Engineering, Ubon Ratchathani University, Warinchamrab, Ubonratchathani, 34190, THAILAND. E-mail: [email protected] Accepted September 26, 2011 (received for review August 19, 2011) Journal of Oleo Science ISSN 1345-8957 print / ISSN 1347-3352 online http://www.jstage.jst.go.jp/browse/jos/ http://mc.manusriptcentral.com/jjocs 81 P. Thaiyasuit, K. Pianthong and I. Worapun high temperature, and is also time consuming. 600 which is widely growth in Thailand. The rubber seeds Recently, researchers searched for means to produce were cracked and the kernels(52.5% of seed weight)were methyl ester from high FFA oil such as non-edible crude dried in the oven at 100℃ for 20 h. The CRSO was extract- plant oils, animal oils, and fi sh oils. The reduction of FFA in ed from kernels by hydraulic press machine and was about crude oil before tranesterifi cation process has been exam- 10% of seed weight as shown in Fig. 1. The extracted ined. This method is also effi cient to produce methyl ester crude rubber seed oil usually contains sediment of kernel from high FFA oils. However, it consumes more methanol, and moisture. The CRSO should be cleared from adulter- as Ghadge and Raheman6)studied the production of methyl ants before the acid esterifi cation process in order to avoid ester from mahua oil having 19% FFA by pretreatment the imperfection of the process. The dregs of the kernel process and transesterifi cation process. The pretreatment can be removed by the filter fabric. The moisture in the process comprised of double acid-esterifi cation. The 19% CRSO is in water form. It is found that existence the addi- high FFA level of mahua oil was reduced to less than 1% tion of 0.5% water to a mixture of oil, methanol, and sulfu- by this pretreatment process. This process consumed 0.7 ric acid could reduce ester conversion from 95% to below v/v(16.8:1 molar ratio)methanol-to-oil ratio. Then, the 90%. Also at a water content of 5%, ester conversion de- product of pretreatment process was proceed to trans- creased to only 5.6%11). Thereby, the fi ltered oil is heated esterifi cation process and consumed methanol 0.25 v/v(6:1 at 120℃ for 5 min to remove the moisture. Then, the free molar ratio), thus the overall of methanol consumption was fatty acid(FFA)content of CRSO was determined. It was 22.8:1 in molar ratio. Ramadhas et al.5)investigated on the found that the FFA content was increased associate with production of methyl ester from 17% FFA rubber seed oil the times keeping the rubber seed before extracting crude by two steps transesterifi cation process. The fi rst step was oil as shown in Fig. 2. The CRSO using in this study has acid-esterification and consumed methanol 6:1 in molar FFA content of 20%(Oleic). The physical properties of ratio. The second step consumed methanol 9:1, thus the CRSO tested by the Research and Technology Institute of overall of methanol consumption was 15:1 in molar ratio. the Petroleum Authority of Thailand(PTT Public Company By this method, over usage of methanol, compare to theo- Limited)are shown in Table 1. The fatty acid compositions retical requirement, is unavoidable. Ei-Mashad et al.12) analysis carried out by the Thailand Institute of Scientifi c found the two steps transesterification was effective and Technological Research(TISTR)with gas chromato- method for producing methyl ester from the acidified graphic method are shown in Table 2. Knowing the fatty salmon oil having 6% FFA. The 6% FFA salmon oil was acid composition, the molecular mass of the CRSO can be reduce to 1.5% by esterifi cation and consumed methanol then estimated. In this research, the molecular mass of about 9:1 in molar ratio. In the second step, the methanol CRSO was determined as 872.4 g/mole. This molecular was used at molar ratio about 5:1 for transesterification. mass is very useful for the calculation of the amount of the The overall methanol consumption of this studied was 14:1. catalyst and methyl alcohol in the esterifi cation and tranes- Even thought the two steps transesterifi cation can be suit- able for produce methyl ester from high FFA crude oils, however it consume too much methanol. Therefore, the aim of this study is to examine the method to reduce the consumption of methanol in methyl ester production from non-edible high FFA crude oil. The non-edible high FFA crude oil in this study was crude rubber seed oil(CRSO). It was extracted from the rubber seed kernels and then carried out to produce methyl ester by the acid esterification-alkaline transesterification process. The acid esterification process was for reducing FFA content of the CRSO. Then the product of acid esteri- fi cation is transesterifi ed using alkaline catalyst in the alka- line transesterification process. Then fuel properties of methyl ester from rubber seed oil were examined and com- pared with diesel and methyl ester standards. 2 MATERIALS AND METHODS Fresh rubber seeds were collected from the local area called Ubonratchathani, Thailand. The rubber tree is RRIM Fig. 1 Rubber seed and crude rubber seed oil. 82 J. Oleo Sci. 61, (2) 81-88 (2012) Acid Esterifi cation-Alkaline Transesterifi cation Process by the acid esterification-alkaline transesterification process.