CHAPTER II CURRENT STATUS OF BIODIESEL PRODUCTION PROCESS

Transcription

1 5 CHAPTER II CURRENT STATUS OF BIODIESEL PRODUCTION PROCESS Introduction As energy demands increase and fossil fuel reserves are limited, many research efforts are directed towards alternative renewable fuels. Biomass is considered as one of the potential renewable energy resources for the future owing to its large potential, economic viability and various social and environmental benefits. Oils and fats, both being biomass resources, are considered as the best candidate for diesel fuel substitute in diesel engines. More than 100 years ago, a brilliant inventor named Rudolph Diesel designed the original diesel engine to run on vegetable oil. Rudolph Diesel used peanut oil to fuel one of his engines at the Paris Exhibition in 1900 [15]. However, several obstacles had to be overcome. Vegetable oils typically have viscosities ten to twenty times higher than the viscosity of fossil diesel fuel. This quality leads to poor fuel atomization and results incomplete combustion, which was already attested in the 1920s [15]. The high flash point attributes to its lower volatility characteristics. This leads to more deposit formation, carbonization of injector tips, ring sticking and, a gradual dilution and degradation of the lubricating oil. The combination of high viscosity and low volatility of vegetable oils causes poor cold engine start up, misfire and ignition delay. Oxidative and thermal polymerisation of vegetable oil cause a deposition on the injectors forming a film that will continue to trap fuel and interfere with combustion. As a consequence, long-term operation on neat vegetable oils or on mixtures of vegetable oils and fossil diesel fuel inevitably results in engine breakdown [16]. These problems can be solved by either adapting the engine to the fuel or by adapting the fuel to the engine. The first strategy led to the development of vegetable oil engines, but this strategy is hard to realize because such engines would be more difficult to be built since it would be larger, heavier and more expensive. The latter strategy aimed at modifying plant oils by various technologies to produce fuels which approximate the properties and performance

2 6 of fossil diesel. The four most widely used technologies in this context are pyrolysis, microemulsification, dilution, and transesterification [16], but only transesterification reaction can lead to the products commonly known as biodiesel, i.e., alkyl esters of oil and fats [17]. Vegetable Oils as Alternative Diesel Fuels Nowadays, various of vegetable oils, such as palm, soybean, sunflower, peanut and olive oils have been used as alternative fuels for diesel engines. Due to the rapid decline in crude oil reserves, the use of vegetable oils as diesel fuels is again promoted in many countries. Depending upon climate and soil conditions, different nations or regions have different vegetable oil sources. For example, soybeans oil in the United States, rapeseed and sunflower oils in Europe, palm oil in South East Asia (mainly Malaysia and Indonesia), and coconut oil in the Philippines. Composition of Vegetable Oils The basic constituent of vegetable oils is TG. Figure 1 shows a typical TG molecule, where R 1, R 2, R 3 are long chains of carbons and hydrogen atoms, sometimes called fatty acid chains. Vegetable oils comprise 90 to 98% TG and O H 2 C O C - R 1 O HC O C - R 2 O H 2 C O C - R 3 Fig.1 Structure of a typical TG molecule. small amounts of MG and DG. TG are esters of fatty acids and one GL. These contain substantial amounts of oxygen in its structure. Fatty acids vary in their

3 7 carbon chain length and in the number of double bonds. The structures of common fatty acids are given in Table 1 [18]. Table 1 Chemical structure of common fatty acids Fatty acid Systematic name Structure a Formula Lauric Dodecanoic 12:0 C 12 H 24 O 2 Myristic Tetradecanoic 14:0 C 14 H 28 O 2 Palmitic Hexadekanoic 16:0 C 16 H 32 O 2 Stearic Octadekanoic 18:0 C 18 H 36 O 2 Arachidic Eicosanoic 20:0 C 20 H 40 O 2 Behenic Docosanoic 22:0 C 22 H 44 O 2 Lignoceric Tetracosanoic 24:0 C 24 H 48 O 2 Oleic cis-9-octadecenoic 18:1 C 18 H 34 O 2 Linoleic cis-9, cis-12-octadecadienoic 18:2 C 18 H 32 O 2 Linolenic cis-9, cis-12,cis-15-18:3 C 18 H 30 O 2 Octadecatrienoic Erucic cis-13-docosenoic 22:1 C 22 H 42 O 2 a xx:y indicates xx carbon in the fatty acid chain with y double bonds The fatty acid composition of some vegetable oils is summarized in Table 2 [19]. The fatty acids which are commonly found in vegetable oils are stearic, palmitic, oleic, linoleic and linolenic. Vegetable oils contain FFA (generally 1 to 5%), phospholipids, phosphatides, carotenes, tocopherols, sulfur compounds and traces of water [18].

4 8 Table 2 Fatty acid compositions of vegetable oil samples Sample Fatty acid composition in wt. % 16:0 16:1 18:0 18:1 18:2 18:3 Others Cotton seed 28,7 0 0, ,4 0 0 Poppy seed 12,6 0,1 4,0 22,3 60,2 0,5 0 Rapeseed 3,5 0 0,9 64,1 22,3 8,2 0 Safflower 7,3 0 1,9 13,6 77,2 0 0 seed Sunflower 6,4 0,1 2,9 17,7 72,9 0 0 seed Sesame seed 13,1 0 3,9 52,8 30,2 0 0 Linseed 5,1 0,3 2,5 18,9 18,1 55,1 0 Wheat grain 20,6 1,0 1,1 16,6 56,0 2,9 1,8 Palm 42,6 0,3 4,4 40,5 10,1 0,2 1,1 Corn 11,8 0 2,0 24,8 61,3 0 0,3 marrow Castor a 1,1 0 3,1 4,9 1,3 0 89,6 Soybean 13,9 0,3 2,1 23,2 56,2 4,3 0 Peanut 11,4 0 2,4 48,3 32,0 0,9 4,0 kernel Hazelnut 4,9 0,2 2,6 83,6 8,5 0,2 0 kernel Walnut 7,2 0,2 1,9 18,5 56,0 16,2 0 kernel Almond 6,5 0,5 1,4 70,7 20,0 0 0,9 kernel Olive kernel 5,0 0,3 1,6 74,7 17,6 0 0,8 a Castor oil contains 89.6% ricinoleic acid.

5 Fuel-Related Properties of Vegetable Oils 19].. The fuel-related properties of vegetable oils are presented in Table 3 [16, Table 3 Fuel-related properties of vegetable oils Oils KV CN HV CP PP FP DT CR SC Corn a 34,9 37,6 39,5-1,1-40, ,9095 0,24 0,01 Cotton 33,5 41,8 39,5 1,7-15, ,9148 0,24 0,01 seed a Crambe a 53,6 44,6 40,5 10,0-12, ,9044 0,23 0,01 Linseed a 27,2 34,6 39,3 1,7-15, ,9236 0,22 0,01 Peanut a 39,6 41,8 39,8 12,8-6, ,9026 0,24 0,01 Rapeseed a 37 37,6 39,7-3,9-31, ,9115 0,30 0,01 Safflower a 31,3 41,3 39,5 18, ,9144 0,25 0,01 Sesame a 35,5 40,2 39,3-3,9-9, ,9133 0,25 0,01 Soybean a 32,6 37,9 39,6-3,9-12, ,9138 0,27 0,01 Sunflower a 33,9 37,1 39,6 7, ,9161 0,23 0,01 Palm a 39,6 42,0-31, ,9180-0,01 Babasu a 30,3 38,0-20, ,9460-0,01 Castor b ,3 37, ,21 0,01 Poppyseed b 42,4 36,7 39, ,25 0,01 Wheat 32,6 35,2 39, ,23 0,02 grain b Hazelnut b 24,0 52,9 39, ,21 0,02 Walnut b 36,8 33,6 39, ,24 0,02 Almond b 34,2 34,5 39, ,22 0,02 Olive b 29,4 49,3 39, ,23 0,02 a Source: [16] b Source: [19] KV = Kinematics Viscosity at 38 o C ( mm 2 / s), CN = Cetane Number, HV = Heating Value (MJ/kg), CP = Cloud Point ( o C), PP = Pour Point ( o C), FP = Flash Point ( o C), DT = Density (kg/l), CR = Carbon Residue (% w/w), SC = Sulphur Content (% w/w) 9

6 10 Biodiesel Production by Catalytic Process Biodiesel has been defined as the monoalkyl esters of long-chain fatty acids derived from renewable feedstocks, such as vegetable oils and animal fats, for use in compression-ignition (diesel) engines [20]. Biodiesel, consisting of FAME can be produced by transesterification of triglycerides and/or esterification of fatty acids with short-chain alcohol, mainly MeOH. Chemistry of Transesterification Process Transesterification [21], also called alcoholysis, is the displacement of alcohol from an ester by another alcohol in a process similar to hydrolysis, except than an alcohol is used in instead of water. This process has been widely used to reduce the viscosity of TG. The transesterification reaction is represented by general equation: RCOOR 1 + R 2 OH RCOOR 2 + R 1 OH (1) Ester Alcohol Ester Alcohol If MeOH is used in the above reaction ( Eq.(1)), it is termed methanolysis. The overall transesterification reaction is given by Eq. (2). However, three consecutive and reversible reactions are believed to occur. These reactions are given by Eq. (3), (4) and (5). O O H 2 C - O-C-R 1 CH 3 -O- C-R 1 O O CH 2 -OH HC - O-C-R CH 3 OH CH 3 - O-C-R 2 + CH - OH O O CH 2 -OH H 2 C - O-C-R 3 CH 3 O-C-R 3 TG 3 MeOH 3 FAME (ME) GL (2)

7 11 TG + MeOH DG + ME (3) DG + MeOH MG + ME (4) MG + MeOH GL + ME (5) The first step is the conversion of TG to DG, followed by the conversion of DG to MG, and of MG to GL, yielding one FAME molecule from each glyceride at each step [6, 7, 8]. Alkaline-Catalyzed Transesterification Alkaline catalysis is far the most commonly used in transesterification reaction for biodiesel production. The main advantage of this form of catalysis over acid-catalyzed transesterification is about 4000 times faster under the same temperature condition and amount of catalyst. Moreover, alkaline catalysts are less corrosive to industrial equipment, so that they enable the use of less expensive carbon-steel reactor material. Finally, alkaline-catalyzed transesterification make do with far smaller alcohol volumes than are required for acid-catalyzed reaction, so that reactor sizes can be reduced [15]. Different technologies are currently available and used in the industrial production of biodiesel fuel, which is sold under different trademarks. For example, there are the Italian processes Novemont, the French IFP, the German Henkel and ATT. Generally, the process is batchwise in the presence of alkaline catalyst such as potassium hydroxide (KOH) or sodium hydroxide (NaOH) under atmospheric pressure and at temperature of approximately 60 to 70 o C (close to the boiling point of MeOH) with an excess of MeOH. The FFA is neutralized with alkali to form soap during the reaction. After the reaction is finished, an acid is added to neutralize the catalyst. The mixture at the end of reaction is allowed to settle. The lower GL layer is drawn off, while the upper methyl esters layer is washed and processed further for purification. Unreacted MeOH in the ester layer is removed and recovered by distillation or evaporation. Purification is made by washing two or three times with water to remove the soap and catalyst. Under the

8 12 same condition, 67 to 84% conversion of crude vegetable oils into methyl esters can be obtained, compared with 94 to 97% when using refined oils [22]. There are several variables affecting the yield of FAME (biodiesel) by transesterification of vegetable oil. It would be related with the quality of feedstock (free fatty acids and water content), reaction parameters (temperature, pressure, molar ratio of MeOH to oil, mixing intensity), the length of alkyl chain of alcohol (a number of simple alcohols up to n-hexanol), and catalyst (type and concentration). Some types of catalyst have been used for the transestrification that can be categorized as homogeneous alkaline catalysis and heterogeneous alkaline catalysis. The reaction mechanism of alkaline-catalyzed transesterification is given in Fig. 2 [23]. Fig. 2 The reaction mechanism of alkaline-catalyzed transesterification. The main drawback of the alkaline-catalysis is the sensitivity of alkaline catalysts to FFA contained in the feedstock material. When an alkaline catalyst is added to these feedstocks, the FFA reacts with the catalyst to form soap and water as shown in Eq. (6 ).

9 13 R-COOH + KOH R-COOK + H 2 O (6) FFA Potassium hydroxide Soap Water This means that alkaline-catalyzed transesterification optimally works with high-quality and low-acidic vegetable oils, which are however more expensive than waste oils. If low-cost materials, such as waste fats/cooking oils or unrefined vegetable oils with a high amount of FFA, are to be processed by alkaline catalysis, costly deacidification or pre-esterification steps are required. Acid-Catalyzed Transesterification Acid catalysis transesterification offers the advantage of also esterifying FFA contained in the fats and oils as presented in Eq.(7), and is therefore especially suited for the transesterification of highly acidic fatty materials, such as palm oil or waste edible oil. R-COOH + CH 3 OH R-COOCH 3 + H 2 O (7) FFA MeOH FAME Water Figure 3 shows the reaction mechanism with H 2 SO 4 as a catalyst. The catalyst (H 2 SO 4 ) dissociates to 2H + and SO 2-4. In the first step, H + attaches to the oxygen of the carbonyl group, and thus renders carbonyl carbon even more susceptible to nucleophilic attack. In this reaction, the nucleophile is alcohol. As in the alkalicatalyzed reaction, the intermediate molecule reacts with alcohol to form mostly tetrahedral molecule, which further rearranges to a fatty acid methyl ester and diglyceride [24].

10 14 Fig. 3 The reaction mechanism of transesterification with H 2 SO 4 as a catalyst. However, acid-catalyzed tranesterification are usually far slower than alkalicatalyzed reaction and require higher temperatures and pressures as well as higher amounts of alcohol. The typical reaction conditions for homogeneous acidcatalyzed methanolysis are temperatures of up to 100 o C and pressures of up to 5 bars in order keep the alcohol liquid. A further disadvantage of acid catalysis - probably prompted by the higher reaction temperatures is an increased formation of unwanted secondary products, such as dialkylethers or glycerol ethers [17]. Finally, in contrast to alkaline reactions, the presence of water in the reaction mixture proves absolutely detrimental for acid catalysis. Canakci and Van Gerpen [25] reported that the addition of 0.5% water to a mixture comprising soybean oil, methanol and sulfuric acid reduced ester conversion from 95% to below 90%. At a water content of 5%, ester conversion decreased to only 5.6%. It should be noted that also water released during esterification of FFA might inhibit further reaction, so that very acidic raw materials might give moderate conversion even in acid-catalyzed alkoholysis reactions.

11 15 Enzymatic Catalysis Although biodiesel is at present successfully produced chemically, alkalinecatalyzed and acid-catalyzed methods are both sensitive to the presence of water and free fatty acids. In addition, the reaction has several drawbacks: it is energy intensive, recovery of glycerol is difficult, the catalyst should be removed from the product and alkaline waste-water required treatment. The disadvantages of using chemical catalysts can be overcome by using lipases (enzymes) as the catalysts for ester synthesis [26]. As compared to other catalyst types, biocatalysts have several advantages. They enable conversion under mild temperature-, pressure- and ph-conditions. Neither the ester product nor the glycerol phase has to be purified from alkaline catalyst residues or soap. That means that phase separation is easier, high-quality glycerol can be sold as a byproduct, and environmental problems due to alkaline wastewater are eliminated [27]. Moreover, both the transesterification of triglycerides and the esterification of FFA occur in one step. As a consequence, also highly acidic fatty materials, such as palm oil or waste oil, can be used without pretreatment [28]. Finally, many lipases show considerable activity in catalyzing transesterification with long or branched-chain alcohol, which can hardly be converted to fatty acid ester in the presence of conventional alkaline catalysts and catalysts can be reused. Bottlenecks to use of enzymatic catalysts include the high cost of lipases compared with inorganic catalysts (in the absence effective schemes for multiple enzyme use), the reaction is slowly (8-70 h), inactivation of the lipase by contaminants in the feedstocks (phospholipids and water), and inactivation by polar short-chain alcohols. An effort to reduce the production cost made by utilizing an immobilized enzyme was reported by Shimada et al. [29]. They researched the factors affecting methanolysis of vegetable oils by Candida antartica lipase for the continuous production of biodiesel. An important finding was that by a novel stepwise addition of methanol, serious degradation of lipase in the presence of a high concentration of MeOH could be avoided. A significant conversion was achieved for the reaction time of 70 h. The series of drawbacks make this process is still far for industrialization.

12 16 Development of the Catalytic Process for Biodiesel Production Alkaline-catalyzed traneseterification of TG in vegetable oils, with the addition of an acid-catalyzed reaction to esterify FFA are the technologies presently in use for industrial-scale biodiesel production. However, the desire to reduce or remove catalyst cost, waste output and to obtain the simpler process has stimulated the investigation of alternate methods of biodiesel synthesis. These methods, described here, are largely in the developmental stage, with little or no actual application in the biodiesel industry to date. In-situ Transesterification The term in-situ transesterification refers to process, in which the oil contained in vegetable seeds is extracted and transesterified in one step. That means that the lower alcohol serves both as an extracting agent for the oils and the reagent for alcoholysis. This method may serve essentially to reduce substrate costs in biodiesel production. In-situ transesterification offers a series of advantages. First, hexane is no longer necessary as a solvent in oil recovery. Second, the whole oil seed is subjected to the transesterification process, so that losses due to incomplete oil production are minimized. Finally, the esterified oils tend to be easier to recover from the solid residue than native oils due to their decreased viscosities [30]. Both alkaline catalysis [31, 32] and acid catalysis [30, 33, 34] have been applied. Unlike conventional alcoholysis reactions, ethanol and higher alcohols, such as 1-propanol or 1-butanol, are favored over MeOH for in-situ processes. This is due to the fact that MeOH is a very poor solvent for oils, so that the yields of in-situ methanolysis tend to be low [34]. One exception is the acid-catalyzed in-situ methanolysis of high-acidity rice-bran oil, which was found to give higher conversion than the respective processes conducted with other alcohols [35]. The main limitation of in-situ ethanolysis reactions is the water content of the alcohol. It is suggested that only anhydrous ethanol will give satisfactory results, as otherwise the esters will be contaminated with sulphurous and phosphorous compounds. Because of the high prices of absolute ethanol and the alternative

13 17 longer-chain alcohols, in-situ transesterification is generally considered as uneconomic at the moment. Monophasic Transesterification One major problem in alkaline-catalyzed transesterification of TG is the fact that the oil substrate is not miscible with the alcohol-catalyst phase. Reaction occurs at the interface between the two phases, resulting in a much lower rate than if the reaction mixture was a single phase. That means that transesterification does not proceed properly, unless the reaction mixture is homogenized in some way. Vigorous stirring/mixing of components is one method of homogenization, which has been found successful for both batch processes [8] and continuous operation [36]. Also the application of low frequency ultrasonic irradiation to form emulsions of oil and alcohol has been reported [37]. Alternatively a common solvent for both alcohol and oil may be added, including toluene [38], and tetrahydrofuran (THF) [39]. In addition to the use of solvent to promote the miscibility of methanol and oil, a high-meoh:oil molar ratio (27:1) is employed, raising the polarity of the medium sufficiently to allow a one-phase system, thereby increasing the transesterification rate. The advantages of this approach are the use of a one-step transesterification process, methyl ester yields >98%, reaction times of <10 min, and lower reaction temperatures. The disadvantages are necessity of recovering the THF and the large molar excess of unreacted MeOH, and inherent hazards associated with flammable solvent. Nonetheless, adoption of this technology for commercial biodiesel production was reported recently [40]. Using Reactive Distillation (RD) Technique In reactive distillation both chemical conversion and the distillative separation of the product mixture are carried out simultaneously. Through this integrative strategy, chemical equilibrium limitations can be overcome, higher selectivities can be achieved and heat of reaction can be directly used for the process. Increased process efficiency and reduction of investments and operational costs are the direct results of this approach. The idea of RD is old but it is used for some outstanding applications in the recent years and hence the

14 18 various aspects of it are being investigated worldwide at a tremendous pace. Some works exits in which the production of biodiesel by RD is reported, as the one developed by Omata et al [41, 42], He et al [43, 44]. A continuous-flow reactor using RD has been found feasible for biodiesel production from canola oil with potassium hydroxide as the catalyst [44]. The operating parameters of 65 C column temperature and 4:1 MeOH:oil molar ratio with a pre-reactor have yielded promising results. Preliminary results showed that the RD reactor was very effective in transesterifying canola oil to biodiesel. The use of excess alcohol in the feed was reduced by 66%. This implies that the downstream alcohol recovery effort would also be reduced by 66%. The short reaction time, which was 10 to 15 times shorter than those used in batch and existing continuous-flow reactors, led to a 6 to 10 times higher productivity. In summary, this RD reactor bears three major advantages over batch and traditional continuous-flow processes: (1) shorter reaction time and higher unit productivity, which is highly desirable in commercial production units; (2) much lower excess alcohol requirement, which greatly reduces the effort of downstream alcohol recovery and operating costs; and (3) lower capital costs due to its smaller size and the reduced need for alcohol recovery equipment. Generally speaking, the operation of an RD reactor is complicated because its performance is affected by several parameters, including the reaction kinetics, size of the reaction and separation zones, reflux ratio, feed rate, and feeding tray location, etc. The optimum operating conditions are determined as the result of systematic investigations of all operating parameters. Since it is the combination of reaction, distillation and mixing, the design and control of such processes is extremely difficult and at least with the present knowledge and experience, one cannot just rely on thumb rules and gut feelings. Systematic design methods and simulation strategies are being worked out to design a commercial reactive distillation unit for the given application. Complex interaction of reaction and phase equilibria may lead to non-linear dynamic effects such as multiple steady states, oscillation etc., which are important considerations while operating a reactive distillation column and proper control strategies are required to be devised.

15 19 Biodiesel Production by Non-Catalytic Process At present, as mentioned above, most of the methods on transesterification reaction are in the employing an alkali catalyst. This method has, however, drawbacks such as difficulties recovery of GL, the need for removal of the residual catalyst and the saponified product (soaps) to obtain biodiesel product by neutralization, washing and drying. Furthermore, oils containing free fatty acids and/or water are incompletely transesterified using alkaline catalyst. It prevents a maximum utilization of low-quality feed stocks such waste frying oil and waste industrial oil. In fact, the use of acid catalyst results in long reaction time and this process is also sensitive to water and free fatty acids content. As a result, it may then affect the success of biodiesel application because of high-energy production cost. Nowadays, the high cost of biodiesel is the major obstacle to its commercialization. The high cost of biodiesel is mainly due to the cost of virgin vegetable oil. Exploring ways to reduce the high cost of biodiesel is of much interest in recent biodiesel research, especially for those methods concentrating on minimizing the raw material cost and production cost as well. The disadvantages resulted from the use of a catalyst and its removal from the products can be eliminated if the non-catalytic transesterification reaction of vegetable oils with alcohol can be realized. Non-Catalytic Transesterification in Supercritical MeOH A key advantage of chemistry in supercritical fluid including MeOH is the possibility of varying the properties of the reaction medium over a wide range solely by changing the pressure and temperature and thus optimizing the reaction without changing the solvent. Saka and Kusdiana [9], Dermibas [12] and Han et al [13] have proposed that biodiesel may be prepared from vegetable oil via noncatalytic transesterification with supercritical MeOH. Critical state of MeOH is 239 o C and 8.1 MPa, the condition which is much milder than that of water. Hydrogen-bonded liquids such as water and MeOH in the supercritical state have unique properties not available under ambient conditions. Under the supercritical state, hydrogen bonding could be reduced making MeOH just like a free

16 20 monomer. This condition also contributes to the change in ionic product in which methanol can be expected to act as acid catalyst. Or in another word, supercritical state is possible to substitute the function of catalysts usually used in the reaction. By applying such a high pressure, the solubility of MeOH can be improved. Therefore, many non-polar organic substances including vegetable oil could be highly soluble in supercritical methanol so that restrictions in mass transfer due to the phase boundaries do not apply. As a result, a vigorous stirring which is normally applied for heterogeneous reaction such as those in the biodiesel fuel production can be eliminated and the reaction was found to be complete in a very short time (4-10 min).the disadvantages of the non-catalytic process in supercritical MeOH are the necessity of the large molar excess of MeOH (the molar ratio of MeOH/oil was 24 42) and high operating temperature and Pressure ( o C, 9-65 MPa), which are not viable in practice in industry. Therefore, non-catalytic process for biodiesel production need to be developed so that a feasible process and simpler can be realized. Non-Catalytic Transesterification in a BCR As mentioned above, using RD technique for biodiesel production is a newest catalyzed process that has many advantages as compared to conventional catalyzed process. If the advantages of the RD can be applied in the non-catalytic process so a process that more and more advantage can be obtained. Thus, the advantages of non catalytic process are combined with the advantages of RD technique. In the catalytic process, reactants (oil and MeOH) react in the liquid phase so the reaction temperature is close to the boiling point of MeOH (± 65 o C at atmospheric pressure). In the non-catalytic process reaction temperature must be increased to obtain the feasible reaction rate. Therefore, if the reaction temperature is increased to be > 65 o C at atmospheric pressure, MeOH changes to be vapor and the transesterification is conducted in the heterogeneous (gas-liquid) reaction. Bubble columns are widely used for conducting gas-liquid reactions in variety of practical applications in industry such as absorption, fermentations, bioreactions, coal liquefaction and waste water treatment, but it has not yet been used

17 21 for biodiesel production. Due to their simple construction, low operating cost, high energy efficiency and good mass and heat transfer, bubble columns offer many advantages when used as gas-liquid contactors [45]. For the first time, research about biodiesel production in BCR by non-catalytic process was conducted by Yamazaki et al [14] that studied the effects of reaction temperature, MeOH feed flow rate, operating pressure, stirring rate and initial oil (sunflower oil) volume on out flow rate of FAME. Based on the maximum out flow rate of FAME in the gas phase, the optimum condition is 290 o C and 0.1 MPa. This condition is same with normal boiling point of GL but is below normal boiling point of TG and FAME. This research need to be continued to discuss about kinetics study of the transesterification and esterification reaction, the effect of FFA in the vegetable oil, etc. Conclusion Efforts are underway in many countries, including Indonesia, to search for suitable alternative diesel fuels that are environment friendly. Among the different possible sources, diesel fuels derived from TG (vegetable oils/animal fats) present a promising alternative to substitute diesel fuels. Although TG can fuel diesel engines, their high viscosities, low volatilities and poor cold flow properties have led to the investigation of various derivatives. Fatty acid methyl esters, known as biodiesel derived from TG by transesterification with MeOH received the most attention. At present, the high cost of biodiesel is the major obstacle to its commercialization. The various process and research for biodiesel production have been developed to reduce the high cost of biodiesel, especially for those methods concentrating on minimizing the raw materials cost and production cost as well. Research using bubble column in now underway as our effort to reduce the raw materials and production cost.