Biodiesel Production from Rubber Seed Oil using SCM

Transcription

1 3 rd World Conference on Applied Sciences, Engineering & Technology September 2014, Kathmandu, Nepal Biodiesel Production from Rubber Seed Oil using SCM HA TRAM HUY, TRAN TAN VIET, LE THI KIM PHUNG Faculty of Chemical Engineering, Ho Chi Minh City University of Technology, Ho Chi Minh City, Vietnam Abstract: In this work, the objective was biodiesel production from rubber seed oil using SCM in a batch reactor. A non-edible rubber seed oil with high viscosity than diesel contains high FFA and water contents, was used as the feedstock in this study. SCM treatment method is appropriate for this feedstock than the conventional catalyst method. Effects of reaction temperature ( o C), reaction pressure (78 96 bar), reaction time (2 50 min), and the solvent to feed ratio (10:1 50:1) on methyl esters in the transesterification reaction were examined. As a result, the highest content of methyl esters was 92.7% in 20 min reaction, the reaction temperature of 280 o C, the molar ratio methanol to oil of 42:1. In addition, Fourier transform infrared spectroscopy was used as an analytical method to determine methyl esters content of biodiesel in the reaction mixture to monitor the transesterification reaction with a high accuracy. This study demonstrates that SCM treatment method is a feasible process in producing biodiesel from rubber seed oil and the by-product of this reaction (glycerol) is high purity and valuable. Keywords: Supercritical, Biodiesel, Rubber Seed Oil, Methanol 1. Introduction: The dramatic increase in the price of petroleum, the finite nature of fossil fuels, increasing concerns regarding environmental impact, especially related to greenhouse gas emissions, and health and safety considerations are forcing the search for new energy sources and alternative ways to power the world s motor vehicles. In recent years, many studies have investigated the economic and environmental impacts of the biofuels, especially bioethanol, biodiesel, biogas, and biohydrogen. In developed countries there is a growing trend towards employing modern technologies and efficient bioenergy conversion using a range of biofuels, which are becoming cost-wise competitive with fossil fuels [1]. Along with bioethanol, solar and wind power, biodiesel is a type of alternative fuel, which is stepping up research and production in many countries around the world.now the research on biodiesel has been implemented in more than 28 countries with Germany and France as pioneer countries. Reserve Federal Energy has estimated that nearly 50% of conventional diesel fuel can be replaced entirely by biodiesel in the future. The feedstock accounts for 70% to 80% of the cost of biodiesel production, and clearly is the key factor to evaluate when considering the competitiveness of biodiesel with petroleum-based diesel fuel [2]. The raw materials for the production of biodiesel are from edible and non-edible oils all over the world. Currently, more than 95% of the world biodiesel is produced from edible oils which are easily available on large scale from the agricultural industry. However, the use of edible oils with a large amount to produce biodiesel will cause certain obstacles for causing competition with materials for the food industry [3]. There are concerns that biodiesel feedstock may compete with food supply in the longterm. Non-edible plant oils have been found to be promising crude oils for the production of biodiesel. The use of non-edible oils when compared with edible oils is very significant in developing countries because of the tremendous demand for edible oils as food, and they are far too expensive to be used as fuel at present. Throughout the world, large amounts of non-edible oil plants are available in nature. The production of biodiesel from different non-edible oilseed crops has been extensively investigated over the last few years. Some of these non-edible oilseed crops include jatropha tree (Jatropha curcas), karanja (Pongamiapinnata), tobacco seed (Nicotianatabacum L.), rice bran, mahua (Madhucaindica), neem (Azadirachtaindica), rubber plant (Heveabrasiliensis), castor, linseed, and microalgae [1], etc. Typically, rubber seed oil (RSO), which is non-edible, is considered as a prospective feedstock for biodiesel production.rso with high viscosity is pressed from the rubber seed kernels. It consists of 18.9% saturation comprising of palmitic and stearic acids and 80.5% unsaturation comprising mainly of oleic, linoleic and linolenic acids. Saturated fatty acid methyl esters increase the cloud point, cetane number and improve stability more whereas polyunsaturated ones reduce the cloud point and cetane number and stability. The free fatty acid (FFA) content of unrefined RSO was about 17%, i.e. acid value of 34. Rubber seed kernels (5060% of seed) contain 40 50% of brown color oil. The estimated availability of rubber seeds in India is about30,000 tons per annum, which can yield RSO to the tune of about 5,000 tons. In 2005, a two-step transesterification process is developed to convert the high FFA RSO to its monoesters by Ramadhas. The first step, acid catalyzed esterification reduces the FFA content of the oil to less than 2%. The second step, alkaline catalyzed transesterification process converts the products of the first step to its mono-esters and glycerol. The WCSET BASHA RESEARCH CENTRE. All rights reserved.

2 HA TRAM HUY, TRAN TAN VIET, LE THI KIM PHUNG viscosity of biodiesel fuel is nearer to that of diesel fuel and the calorific value is about 14% less than that of diesel. The important properties of biodiesel such as specific gravity, flash point, cloud point and pour point are found out and compared with that of diesel [4]. Feedstock quality in large part dictates what type of catalyst or process is needed to produce biodiesel that satisfies relevant biodiesel fuel standards such as ASTM D6751 or EN If the feedstock contains a significant percentage of FFA (> 3 wt.%), typical homogenous base catalysts such as sodium or potassium hydroxide or methoxide will not be effective as a result of an unwanted side reaction. In fact, the base-catalyzed transesterification reaction will not occur or will be significantly retarded if the FFA content of the feedstock is 3 wt. % or greater [5]. With the material properties of RSO and other oilscontain FFAs and water contents high, the conventional process has some disadvantages, especially from environmental, production efficiency and feedstock flexibility points of view. Firstly, the conventional process produces a large volume of waste water and some saponified components that need to be treated before discharging to the environment or recycling to the process. Chemicals that are used as a catalyst and neutralizers are difficult to recover. Secondly, as the conventional production process for pretreated or refined triglyceride consists of four separate steps, namely, reacting, separating, washing and drying, the overall production time takes over 4 hour. The washing step that removes the saponified components in the crude biodiesel is the longest of these steps, since the saponified components interfere with and retard phase separation. Thirdly, the conventional process requires refined and expensive vegetable oils as feedstock, i.e. lower than 0.06% (v/v) moisture and 0.50% (w/w) FFAs. As a consequence, this increases the price of the biodiesel and reduces its sustainability, since the requirement of such virgin oils, rather than spent waste oils, is indirect competitive conflict with human or animal food grade feedstock [6]. Biodiesel production with supercritical methanol (SCM) offers an optimistic alternative to the catalytic method since it does not have inherent disadvantages such as saponifiedproducts or catalyst deactivation. Biodiesel production process with SCM has advantages over other processes in its low use of auxiliary chemicals, and chemicals associated with waste water treatment and feedstock pretreatment. The overall process is simple since many discrete operations such as catalyst preparation, product neutralization and purification are not required. Although biodiesel price depends greatly on feedstock price, feed stock flexibility becomes a remarkably strong advantage of the biodiesel production with SCM [6]. As the result of K.T. Tan et al, the yield of biodiesel in SCM treatment is not affected by the presence of water in oil. Instead, the yield increased steadily with increasing amount of water content. Apart from water, FFA content in triglycerides sources is also one of the major nuisances in biodiesel production. However, FFA contained in oil does not affect negatively the yield of biodiesel. On the other hand, for SCM treatment, the yield is not sensitive to the presence of FFA as well since the FFA can be simultaneously esterified with methanol to produce methyl esters. Compared to homogeneous reaction involving established catalysts such as sodium hydroxide, the reported yield of biodiesel is very low due to the side formation of soap from FFA and sodium [7]. According to Saka and Kusdiana, the SCM transesterification treatment on rapeseed oil to biodiesel achieved95% yield for just 240 second at a temperature of 350 o C, pressure of 450 bar[8].their further kinetic study in free catalyst transesterification of rapeseed oil was made in subcritical and SCM and as a result, the conversion rate increased dramatically in the supercritical state [9].Madras et al investigated transesterification of sunflower oil in supercritical fluids at various temperatures ( o C) at 200 bar [10].Hawash and El Diwani obtained 100% yield of esters when they carried out synthesisof biodiesel fuel from a non-edible Jatropha oil using SCM within 4 min only, at a temperature of 320 o C and under a pressure of 84 bar and the molar ratio of methanol to oil was 43:1 [11].RSO was used as the main feedstock for biodiesel production by SCM method in the research of Shokib et al. The highest yield of biodiesel produced was achieved under the reaction temperature of 350 o C at about 430 bar, reaction time of 9 min and 42:1 methanol to oil ratio [12]. In Vietnam, the annual rubber seed production is about 200 kg per hectare. By 2020, there is about 1 million hectare of rubber trees, the estimated availability of rubber seeds can reach 200 thousand tons, which can yield to the tune of about 20 thousand tons of RSO, and can be obtained thousand tons if improving technology [13]. Currently, RSO has been studied in many applications of industrial sector and using it as the main raw material for the production of biodiesel has great potential. In recent years, there are many experiments which used RSO as raw material for biodiesel production with different methods. Nguyen et al. with the two-step transesterification process using the catalyst H 2 SO 4 KOH to produce biodiesel from RSO [14], Tran et al. with the transesterification of RSO into biodiesel using solid base catalyst and K 3 PO 4 solid acid catalyst (GF101 ion exchange resin) [15].However, there is no research on supercritical alcohol technology for biodiesel production from RSO. This study produces biodiesel from RSO using SCM treatment and examines effects of the factors on this process.

3 Biodiesel Production from Rubber Seed Oil using SCM 2. Materials and methods: 2.1. Materials: RSO is pressed from the seeds in BinhPhuoc Province, Vietnam on December Oil is dark yellow color, not impurities and used as a feedstock directly for reaction. Oil sample was analyzed to determine composition of fatty acids by gas chromatography GC-MS analysis (Table 1) and characterization of RSO (Table 2). Methanol (99.5%) was purchased from China; the critical point of methanol is 240 o C, 78.6 bar. Methyl palmitate (> 99%) obtained from Fluka, was used as a standard to determine biodiesel content in the reaction mixture by FTIR method. Table 1. Composition of fatty acids in RSO Fatty acid Formula Composition (wt. %) Palmitic Acid (C 16:0 ) C 16 H 32 O Stearic Acid (C 18:0 ) C 18 H 36 O Oleic Acid (C 18:1 ) C 18 H 34 O Octadecenoic Acid, (Z) (C 18:1 ) C 18 H 34 O Linoleic Acid (C 18:2 ) C 18 H 32 O Linolenic Acid (C 18:3 ) C 18 H 30 O Table 2.Physicochemical properties of RSO Property (units) Value Specific gravity Viscosity (mm 2 /s) at 40 o C 37.0 Water content (wt. %) Acid value(mgkoh/g) 42.7 Calorific value (MJ/kg) a 37.5 Approximate molecular weight of RSO (g/mole) b 873 a Reported by Ramadhas et al. [4] b Calculated from the composition in Table SCM transesterification method: A Parr Instruments 4546 series, high pressure 1.2-L reactor, made of tempered 316-stainless steel and rated at 350 o C and 2,000 psi (138 bar), was employed in this study and shown in Fig. 1. For each trial, the vessel was charged with a given amount of RSO and liquid methanol with different molar ratios (1:10, 1:20, 1:30, 1:40, 1:42 and 1:50). The stirring speed was set at a fixed level for all runs, 300 rpm. The range of temperature and pressure studied was between o C and bar, respectively. After a fixed reaction period (from 2 to 50 min), the vessel was removed from the heater and cooling water was supplied in the spiral cooling-coil to quickly cool the reactor contents, thus quenching the reaction and depressurizing to ambient pressure. Figure 1.Schematic batch reactor of SCM transesterification reaction Reactor (1), Heater (2), Type-J thermocouple (3), Thermo well (4), Thermocouple reader (5), Pressure gauge (6), Twin blade impellers (7), Magnetic drive shaft (8), Cooling-coil (9), In out cooling water (10), Dip tube (11), Valve for liquid sampling (12), Gas inlet angle valve (13), Burst disc (rated at 2,000 psi, 350 C) (14), Bottom valve (15) The mixture of product was evaporated at 50 o C for 20 min by the vacuum equipment to remove and recover the remaining methanol. This mixture was then allowed to settle for about 30 min to have the two phases separated: the top phase consists of the biodiesel (fatty acid methyl esters) and the lower phase consists of the glycerol and other minor components. According to the diagram (Fig. 2),experiments were carried out repeated three times for each variable point in order to confirmthe resulted data.the chemical reaction of the transesterification process is described below: The effect of pressure on fatty acid methyl esters production with SCM is limited since these reactions have principally been conducted in batch reactor. The pressure in a batch reactor cannot be controlled independently from density since it varies with the presence of both the reactants and products. In practice, the reaction pressure can be adjusted by altering the initial amounts of oil and methanol, calculated by the use of appropriate equations of state and mixing rule for triglyceride and methanol, but the final pressure will deviate from its calculated value due to the composition changes during the reaction [6]. In this study, with a type-batch reactor, the pressure inside the reaction vessel changes from 78 to 96 bar, it was dependent on the reaction temperature and the amounts of methanol and methanol used for each run. The methyl esters content and the yield of

4 HA TRAM HUY, TRAN TAN VIET, LE THI KIM PHUNG esters were examined through the influence of these factors: the reaction temperature, the reaction time and the molar ratio of methanol to RSO. RSO Figure 2.Diagram of biodiesel preparation from RSO using SCM 2.3. Analytical methods: Transesterification in SCM Vacuum evaporation (50 o C, 20 min) Standing separation (30 min) Methyl esters phase Vacuum filtering Biodiesel Methanol Methanol Glycerin Residue Mid-range infrared (MIR), cm -1 spectra of RSO and its methyl ester are shown in Fig. 3. It is evident from Fig. 3 that there is not much difference in the MIR spectra of RSO and its methyl ester. Still there are some regions, such as region I, cm -1, and region II, cm -1, where there is a slight difference in the spectra of oil and biodiesel. These peaks are present in the biodiesel spectra but not in the oil spectra. There are other regions, such as region III, cm -1, and region IV, cm -1, that are present in oil spectra but absent in its biodiesel spectra. There are also other regions, such as cm -1 corresponding to the C=O bond and cm -1 corresponding to the CH stretching mode of olefins. However, these regions are present in both oil and biodiesel and so were not considered for quantification [16]. Table 3shows these regions and their corresponding chemical bonds. The mixtures of RSO and methyl palmitate were prepared standard mixtures for quantifying methyl ester content in biodiesel and monitoring the conversion of the transesterification reaction. The region I ( cm -1 ) of spectra selected for quantification of biodiesel in the biodiesel oil mixture, the peak height increased as the biodiesel composition increased. The calibration curve of peak height and the quantity of methyl ester in biodiesel was linear. The yield of the reaction is the ability to transesterify RSO into biodiesel (methyl esters). Yield is calculated by the following equation (1): (1) Where: m 1 weight of the oil sample (g); m weight of the biodiesel sample (g); C methyl ester content of the biodiesel sample (wt. %). High performance liquid chromatography (HPLC) was also used to determine the conversion of RSO to methyl esters, as well as for comparison with FTIR. Biodiesel fuel properties such as specific gravity, kinematic viscosity, sulfur content, copper strip corrosion, cetane number, cloud point, carbon residue, acid value and phosphorus content were determined by following American Society for Testing and Materials (ASTM) standard methods: ASTM D4052, ASTM D445, ASTM D5453, ASTM D130, ASTM D613, ASTM D2500, ASTM D4530, ASTM D664 and ASTM D4951, respectively. The iodine value was determined according to Vietnam Standards: TCVN 7869:2008. The ash content and heating value of biodiesel samples were measured by ASTM D482 and ASTM D Results and discussion: 3.1. Effect of the methanol to RSO molar ratio: With the transesterification of RSO, the stoichiometric ratio requires three molecules of methanol to react with one molecule of RSO. Since the transesterification is an equilibrium reaction, the amount of methanol reactant in fact is higher than in theory in order to shift the reaction to the product side, i.e. methyl ester.

5 Methyl ester content (wt. %) Biodiesel Production from Rubber Seed Oil using SCM Figure 3. MIR spectra of RSO and its methyl ester Table 3. Characteristic regions of oil and biodiesel spectra used for quantification [16] Region (cm -1 ) Assignment Oil Biodiesel CH 3 asymmetric bending absent present O-CH 3 stretching absent present O-CH 2 groups in glycerol moiety of TG, present absent DG, and MG O-CH 2 -C asymmetric axial stretching present absent symmetric CH 2 stretching and the present present asymmetric CH 3 and CH 2 stretching C=O stretch present present According to the research results, the molar ratio of methanol to oil was from 6:1 to 9:1 to achieve the high conversion in the conventional catalytic transesterification [3, 4, 14, 15], while this operating ratio can be increased to 50:1 in the SCM condition [6, 8, 9, 10].The effect of the molar ratio of methanol to RSO on methyl esters content was examined from 10:1 to 50:1. The ratio of 42:1 was also investigated because the maximum conversion was obtained for rapeseed oil at this one by Saka and Kusdiana [8]. All the experiments were conducted at the temperature of 280 o C, for 20 min. Fig. 4 shows the effect of the methanol to RSO ratio on methyl ester content using SCM. The experimental result indicated that the methyl ester content was low 51.6% when a 10:1 of methanol to oil ratio was used and increased with increasing methanol to RSO ratio. The conversion of methyl ester increased, the methyl ester content obtained from 51.6% to 92.7% at the 10:1 to 42:1 ratio of methanol to oil, with 92.7% maximum content at 42:1. Methanol is not only the reactant but also the solvent more. When methanol to oil ratio in the reaction increase, it causes the amount of oil which dissolves in the methanol increase, increases the contact area between methanol and triglycerides and reduces the mass transfer restraints between the reactants. Saka and Kusdiana showed that under the molar ratio of methanol to rapeseed oil of 21:1 and 42:1, the yield was 80 and 90 %, respectively [8] :1 20:1 30:1 40:1 42:1 50:1 Methanol to RSO molar ratio Figure 4.Effect of the methanol to RSOmolar ratio on methyl ester content (temperature 280 o C, 20 min) Furthermore, the higher molar ratio not only increases methanol molecules of methanol around the oil molecules but also because it contributes to the lower critical temperature of the mixture, which helps the transition from two heterogeneous phases to one homogeneous phase mixture easily at lower temperatures. For example, the reaction mixture of soybean oil and methanol are partially miscible up to temperatures close to 350ºC at a methanol to oil molar ratio of 24:1, while the two liquid phases of soybean oil and methanol become completely miscible at 180ºC and 157ºC with a higher molar ratio of 40:1 and 65:1, respectively [17]. However, the ratio was beyond 42, the methyl ester content did not increase significantly because the transesterification reaction reached the state of

6 Methyl ester content (wt. %) HA TRAM HUY, TRAN TAN VIET, LE THI KIM PHUNG equilibrium (see Fig. 4). The addition of a large amount of methanol is not necessary due to the disadvantages such as increasing in the device size, difficulties in the separation of product and glycerin, and recovery of excess methanol. Clearly, the use of high amount of methanol to oil would increase the conversion yield, i.e. increased the methyl ester content of biodiesel and the achieved result shows good agreement with previous work Effect of the reaction temperature: According to the research results, the reaction temperature is a key parameter, which affects significantly the rate of transesterification reaction of triglycerides in SCM conditions. The effect of reaction temperature were examined from 240 o C (critical temperature point of methanol) to 320 o C with the reaction time of 20 min. The methanol to RSO molar ratio was fixed at 42:1 based on the maximized condition of methyl ester content from the previous experiment. In SCM treatment, feedstock and methanol are charged to a reactor in which they are subjected to temperatures and pressures beyond the critical point of methanol (T c = 240 o C, P c = 78.6 bar). The basic concept of SCM treatment is based on the effect of temperature and pressure on the thermo physical properties of methanol, such as viscosity, diffusivity, density, and polarity. When treated beyond its critical point, methanol no longer has a distinct liquid or vapor phase, but rather a single fluid phase. With this phase change, methanol possesses an increased mass diffusivity, decreased viscosity, and a density that can be manipulated over a large range through relatively small changes in temperature and pressure. These fluid properties allow SCM to be used as a tunable solvent with superior mass transfer characteristics [18]. Therefore, methanol could interact better with triglycerides or FFAs without the use of an alkali or acidic catalyst anymore. Fig. 5 shows the effect of the reaction temperature on the methyl ester content in SCM transesterification reaction. At 240 o C, which is the point critical temperature of methanol, the methyl ester content obtained only 62.2%, increased slightly to 66.1% when the reaction was carried out at 260 o C. And the sharp increase of methyl ester content was from 66.1% to 92.7% at a temperature of 280 o C with a reaction time of 20 min Reaction temperature ( o C) Figure 5.Effect of the reaction temperature on methyl ester content (molar ratio 42:1, 20 min) Liquid methanol is a polar solvent and has hydrogen bondings to form methanol clusters. Because the degree of hydrogen bonding decreases with increasing temperature, the polarity of methanol would decrease in supercritical state. This means that SCM has a hydrophobic nature with the lower dielectric constant [9,19]. And it can explain why the reaction of RSO to biodiesel occurred at 240 o C without catalyst. As a result, RSO with non-polar triglycerides and FFAs can be well solvated with SCM to form a single phase of oil/methanol mixture and it promoted the transesterification reaction occurs easily. Moreover, the study of Ma represented the solubility of triglycerides in methanol increased at a rate of 2 ± 3% (w/w) per 10 o C as the reaction temperature increased [8].In addition, a kinetic research of the transesterification reaction clearly indicated that the rate constant of the reaction greatly increased in the supercritical state [9]. All those are suitable for the obtained data; the conversion of oil to methyl ester increased significantly, i.e. the methyl ester content increased from 66.1% to 92.7% as the reaction temperature rose to 280 o C. After reaching a maximum value of 92.7% at temperature of 280 o C, the percent of methyl ester in product decreased slightly from 92.7% to 92.2% and 90.1% as the experimental temperature was 300 o C and 320 o C, respectively. Although the factor of temperature was a positive effect on yield of methyl ester, increasing the reaction temperatures higher than 300 o C can cause the thermal decomposition reactions of unsaturated methyl esters and unreacted triglycerides, which reduced the yield of methyl ester [20, 21]. This effect will become significantly if the original feedstock contains high amount of unsaturated fatty acid in its composition. RSO with high polyunsaturated fatty acid so when the reaction temperature was above 300 o C, yields on oil to methyl ester obtained lower by the side reactions.

7 Methyl ester content (wt. %) Biodiesel Production from Rubber Seed Oil using SCM 3.3. Effect of the reaction time: In general, the effect of the reaction time in a batch reactor can be studied and obtained simply by first heating the reactor to initiate the reaction, holding at this temperature for various times to allow the reaction to go to completion and then quenching the reactor to terminate the reaction [6]. In this work, the reaction time was examined from 2 min to 50 min to assess the influence of the reaction time on the methyl ester content. The fixed parameters were the reaction temperature of 280 o C and the solvent to feed molar ratio of 42:1, which were the best experimental data above. The pressure of the reaction system was about 85 bar. The effect of the reaction time on the conversion efficiency in biodiesel production with SCM follows the general rate law. For instance, the methyl ester content increases gradually with reaction time and then levels off when the maximum methyl ester content or optimal point is achieved. The optimal reaction time varied between 4 and 30 min [6]. The advantage of reaction in supercritical conditions compared with common catalytic methods is that a reaction time is short, may be just a few minutes, and because the reaction rate of transesterification is great at high temperature and pressure, the reaction quickly reaches the equilibrium state. According to Saka and Kusdiana, the SCM transesterification treatment on rapeseed oil to biodiesel achieved the 95% yield for just 240 second at a temperature of 350 o C, pressure of 450 bar [8] Reaction time (min) Figure 6.Effect of the reaction time on methyl ester content (molar ratio 42:1, temperature 280 o C) With the condition of operating temperature and pressure in this study, the result indicated that the percent of methyl ester content obtained at temperature of 280 o C, pressure of 85 bar, ratio of 42:1 and reaction time of 2 50 min was in the range of % (see Fig. 6). Themethyl ester content washighest at 20 min. The temperature and pressure of the reaction system have a strong influence on the reaction rate, when the reaction conditions are less hardly than the reaction rate is lower. Therefore, it needs more time to reach the equilibrium reaction. The methyl ester content was 56.5% in weight for 2 min, increased to 92.7% when the reaction time increased from 2to 20 min. Fig. 6 shows that an extension of the reaction time from 20 to 50 min led to a decrease in the methyl ester content (88.1%).It can be interpreted in two reasons: firstly, the reaction reached the equilibrium, as increasing the reaction time could shift the reaction to the opposite direction, i.e. the reverse reaction of transesterification because product and glycerin were not separated from each other; secondly, in the composition of RSO contains a large amount of unsaturated fatty acids, which was low in oxidized durability, the side reactions may occur to degrade the obtained yield of methyl ester with extended time. In this study, the obtained optimum conditions of SCM transesterification RSO into biodiesel have several differences with the result of the study reported by Shokib et al. The highest yield of biodiesel in their study achieved was 90.86%, which obtained under the molar ratio of methanol to oil of 42:1, the reaction time of 9 minute, the temperature of 350 o C and the pressure of about 430 bar [12]. The maximum yield of biodiesel obtained 92.7% by using unrefined RSO in this study is higher than their result. In addition, reaction parameters of pressure and temperature utilized was 85 bar and 280 o C, respectively, are milder compared to their ones but the parameter of optimal time is longer. These differences could be explained based on the kinetics of transesterification made in SCM by Kusdiana and Saka [9]. When operating temperature and pressure increase, a rate constant of transesterification reactionalso increases. As a result, a speed of transesterification reaction is fast and yield of biodiesel achieved high with a short duration. However, a thermal stability of fatty acid methyl esters decreases at high temperature and high pressure conditions, especially poly-unsaturated fatty acids, which be decomposed and reduced in yield [17, 20, 21].The composition of unsaturated fatty acids in RSO is high, 79.19%in weight (see Table 1). And this leads to yield of biodiesel reported by Shokib et al. is lower than in this study because of the decomposition of unsaturated methyl esters Biodiesel fuel properties: The overall yield of the transesterification reaction of RSO to biodiesel was about 90.85% (calculated by (1)) and the 92.7% conversion to methyl esters was achieved after 20 min duration, under milder conditions compared with previous reports: reaction temperature of 280 o C, reaction pressure of only 85 bar with the molar ratio methanol to RSO of 42:1. From comparing results of methyl ester content in biodiesel product determined by FTIR and HPLC methods (Table 4) shows the reliability of the FTIR method is very high. The difference between the two methods of measurement is within ± 2% wt. ME. The HPLC analysis indicated that the methyl ester content of biodiesel product was the same with in FTIR. This result confirms FTIR could use as a highly accurate analytical method to determine methyl esters content

8 HA TRAM HUY, TRAN TAN VIET, LE THI KIM PHUNG of biodiesel in the reaction mixture to monitor the transesterification reaction. Table 4. ME content of the samples as FTIR and HPLC methods Sample ME content (wt. %) FTIR HPLC Difference 01 89,40 90,97 1,57 % 02 90,10 88,03 + 1,87 % 03 92,70 92,05 + 0,65 % The properties of biodiesel produced from RSO in this study were comparable with ASTM D6751 biodiesel fuel standard (Table 5). The SCM process substantially reduced the viscosity and acid value of RSO. The viscosity of the methyl esters obtained from RSO was reduced from 37.0 mm 2 /s to 5.0 mm 2 /s at 40 o C. The acid value of biodiesel after the reaction was only 0.5 mg KOH/g compared with 42.7 mg KOH/g original. Most of the physic-chemical properties of RSO methyl ester are in the range of biodiesel standard ASTM D6751. Besides, the important fuel properties of RSO methyl esters also were compared with those of other esters and diesel fuel. Results obtained were presented in Table 6. Specific gravity and viscosity of RSO methyl ester obtained was slightly higher than that of diesel fuel. Heating value of RSO methyl ester (39.56 MJ/kg) was lower compared to petroleum-based diesel fuel (42.0 MJ/kg) because of oxygen content in methyl ester. The presence of oxygen in the biodiesel fuel enhances combustion process while using in internal combustion engine. It results cetane number of biodiesel is generally higher than conventional diesel. Carbon residue of RSO methyl ester in this study is also lower. Thus, biodiesel from RSO can be used directly or blended with diesel fuel for use in diesel engines without any modification. 4. Conclusions: This study has demonstrated that SCM treatment method is a feasible process in producing biodiesel from RSO with using non catalyst. Because of the absence Table 5.Properties of biodiesel from RSO Property Units Test Method Specific Gravity, 30 o C Kinematic Viscosity, 40 o C Sulfur Content Copper Corrosion (40 o C, 3h) Cetane Number Cloud Point Carbon Residue Acid Value Phosphorus Content Iodine Value Ash Content Heating Value mm 2 /s % mass o C % mass mg KOH/g % mass g I 2 /100g % mass MJ/kg ASTM D4052 ASTM D445 ASTM D5453 ASTM D130 ASTM D613 ASTM D2500 ASTM D4530 ASTM D664 ASTM D4951 TCVN 7869 ASTM D482 ASTM D240 Biodiesel Standard ASTM D max No. 3 max 47 min 3 to max 0.8 max max 120 max Biodiesel from RSO a < < Fuel type Rubber seed oil ME Rubber seed oil ME Rape seed oil ME Cotton seed oil ME Jatropha oil ME Rice bran oil ME Waste cooking oil ME Diesel Table 6.Comparison of fuel properties ofrso methyl ester (ME), other MEs and diesel fuel Specific Gravity Viscosity(mm 2 /s) of catalyst, the purification of products after transesterification is much simpler and more environmentally friendly.the effects of solvent to feed ratio, temperature reaction and time reaction on methyl ester content in SCM transesterification reaction were also investigated and discussed. The ester conversion increased with increasing the Heating Value (MJ/kg) Cetane Number Carbon Residue (wt. %) Reference This study [4] [4] [4] [1] [1] [1] [1] temperature reaction and the molar ratio of methanol to RSO. The maximum methyl ester content in biodiesel was 92.7%, which was achieved at the optimal reaction conditions: temperature of 280 o C, pressure of 85 bar, molar ratio of methanol to feed of 42:1 within 20 min reaction duration. With fuel properties meeting ASTM D6751 standard, biodiesel

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