Journal of Biofuels DOI : 10.5958/j.0976-4763.4.2.010 Vol. 4 Issue 2, July-December 2013 pp. 79-87 Alkaline Catalytic Transesterification for Palm Oil Biodiesel and Characterisation of Palm Oil Biodiesel BaskarThangaraj 1 *, Kasturi Bai Ramachandran 1, Samuel Paul Raj 2 1 Department of Bio-Energy, 2 Department of Natural Resources and Waste Recycling, School of Energy, Environment and Natural Resources, Madurai Kamaraj University, Madurai-625021, Tamil Nadu, India *Corresponding author email id: biodieselbaskar@yahoo.co.in ABSTRACT Biodiesel produced by the transesterification of vegetable oils, waste cooking oils and animal fats, is a promising alternative fuel for diesel engines due to fossil fuel depletion and environmental degradation. Biodiesel was prepared from palm oil by transesterification of the crude oil with methanol in the presence of NaOH as catalyst. Maximum conversion efficiency (>95%) was achieved using 1:5 molar ratio of oil to methanol at 60ºC. Important fuel properties of methyl ester of palm oil (Biodiesel) compared well with other methyl esters and American Society for Testing and Materials (ASTM) D 6751 standards. The fatty acid methyl esters profiles in the reaction mixture were quantified by gas chromatography using mass spectroscopy and high-performance liquid chromatographyanalytical techniques. Key words: Palm oil, Biodiesel, Transesterification, Palm oil methyl esters, Alternative fuel 1. INTRODUCTION The world has been confronted with twin crisis of depletion of fossil fuel resources and increasing environmental degradation[1]. Fossil fuels have been the prime sources for the purposes of transportation, agriculture and power generation for commercial, domestic and industrial activities for more than a century. Indiscriminate extraction and consumption of fossil fuels have led to the reduction in petroleum reserves. This situation has created the need to find an alternative fuel for diesel engines, which should not only be sustainable, but also environment friendly[2]. The alternative fuel must be technically feasible, economically competitive, environmentally acceptable and readily available. Fatty acid methyl esters are called biodiesel derived from renewable source like vegetable oils and they have gained importance as alternative fuels for diesel engines[3]. Biodiesel (fatty acid methyl esters) is produced by transesterification (also called methanolysis) of vegetable oils (triglycerides) and fats with methanol in the presence of an acid and a base catalyst. In addition, the process yields glycerol. The transesterification reaction is a reversible reaction hence higher stoichiometric ratio is practically used to increase the concentration of the product (biodiesel) and to precede the equilibrium towards the right side [4]. The overall stoichiometric view of this process is presented below in Figure 1. Figure 1: Schematic diagram of transesterification reaction IndianJournals.com 79
BaskarThangaraj, Kasturi Bai Ramachandran, Samuel Paul Raj Alkali catalysts are the most effective transesterification reaction catalysts, as compared with acid catalysts. Sodium and potassium hydroxides are commonly used alkaline catalysts[5]. Almost all biodiesel are produced using base-catalysed transesterification as it is the most economical process requiring only low temperatures and pressures and also producing high (> 95%) yield. In this present work, biodiesel is derived from the palm oil and its properties are analysedon parwith other methyl esters. Biodiesel is blended with conventional diesel [or ordinary diesel (OD)] at various proportions to determine the kinematic viscosity at the temperature range up to 95ºC. The effect of palm oil to methanol molar ratio was investigated. The quantification of the methyl ester profile of the biodiesel produced was analysed by gas chromatography with mass spectroscopy (GC-MS) and high-performance liquid chromatography (HPLC). 2. MATERIALS AND METHODS 2.1. Materials Palm oil was purchased from a local market in Madurai, Tamil Nadu, India. All the chemicals were brought from SD-Fine Chemicals India Pvt. Ltd., India. 2.2. Equipments A magnetic stirrer with mantle heater was used to perform the transesterification reaction. The quantification of methyl esters in the product of transesterification of palm oil was carried out by using GC-MS and HPLC equipped with refractive-index UV-spectrophotometer (SHIMADZU, Japan). The kinematic viscosity of the biodiesel produced was determined by the Redwood viscometer. 2.3. Experimental Analyses The fatty acid methyl ester profile of the product obtained by transesterification of palm oil was analysed using HPLC (SHIMADZU, JAPAN) equipped with refractive-index UV-spectrophotometric detector and GC-MS (Thermo Finnigan Trace). 2.4. HPLC Analysis For separation, the main column ODS-C18 (analytical-shim-pack CLC-OCTA DECYL SILANE) (4.6 mm 1D * 25 cm) and guard column Shim-Pack G-ODS (4 mm 1D * 1 cm) maintained at the temperature of 30ºC were used and methanol, used as the carrier solvent, was passed through them at a flow rate of 1 ml/(min). A volume of 20 μl of the sample was injected and each constituent was quantified by comparing the peak areas with their respective standards. The methyl esters in the product were quantified by Silica Gel (reverse phase) HPLC. 2.5. GC-MS Analysis A RTX-5 capillary column (internal diameter 0.25 mm, length 15 m) was used and a temperature range of 80-280 C was considered. The temperature raiseof 10 C/min was used for separation with 1 ml/min flow rate of helium as carrier gas. The sample injection volume was 1 ml and each constituent was quantified by comparing the peak areas with their respective standards. 2.6. Transesterification Set Up for Biodiesel Synthesis A reflux condenser system was used as the laboratory-scale reactor for this experimental purpose. A magnetic stirrer with mantle heater arrangement was used for heating and stirring the mixture in the reflux. The mixture was stirred at the same speed for all the test runs. A temperature range of 50-60ºC was maintained during this experiment. 80 Vol. 4 Issue 2, July-December 2013
Alkaline Catalytic Transesterification for Palm Oil Biodiesel and Characterisation of Palm Oil Biodiesel 2.7. Methods Palm oil was filtered to remove any suspended particles. It is necessary to heat the oil while filtering so as to enable easy flow. Then, the oil was heated to remove the moisture content, if present. The lower the water content in the oil, greater will be the quality of the biodiesel. After the pretreatment of the oil, it was transesterified using alkali catalyst (preferably sodium hydroxide) with methanol at a temperature range of 50-60ºC for 1 h. The tranesterified oil was allowed to settle down and cool for at least half an hour or preferably, longer. After cooling, the fatty acid methyl esters (biodiesel) were floating on top, while the denser glycerine settled at the bottom of the container. Then, the biodiesel was decanted carefully from the container. The semi-liquid glycerine was dark brown coloured, while the biodiesel was pale yellow coloured; once the biodiesel was formed, it was diverted to a separate container. It was easy to retrieve the biodiesel completely once the glycerine had solidified. The separated biodiesel was washed with water to remove any catalyst (NaOH) or soap residue; the product should have a ph of 7. Washing thrice with ordinary tap water was enough to remove the catalyst. When washing for the first time, it is best to add a small amount of dilute acetic acid or phosphoric acid before adding water. The acid brings the ph of the solution closer to neutral because it neutralisers and drops out any NaOH suspended in the biodiesel. Finally, after washing, the biodiesel appeared clearer as any remaining soap was removed from the solution. 3. RESULTS AND DISCUSSION 3.1. Synthesis of Palm Oil Biodiesel A volume of 100 ml of the oil was taken in a two-necked round bottom flask. One neck was connected toacondenser for avoiding methanol loss and the other neck held a thermometer. The oil was heated and stirred at 60ºC. The oil required 17 ml (5 moles) of methanol to get dissolved and 0.4 gm of NaOH to form sodium methoxide. Heating and stirring was continued for 60 min at atmospheric pressure in the closed vessel by reflux condensation system. On completion of this reaction, the product was poured into a separating funnel for the separation of biodiesel and glycerine. Two layers were separated, the lower layer, which contains impurities and glycerol (dark red), was drawn off and the top layer (pale yellow) contained methyl esters (biodiesel), as shown in Figure 2. Figure 2: Palm oil biodiesel separation Journal of Biofuels 81
BaskarThangaraj, Kasturi Bai Ramachandran, Samuel Paul Raj The biodiesel so obtained was then washed three times with ordinary tap water to remove the entrained impurities and glycerol before adding a small amount of dilute acetic acid to the solution for attaining a neutral ph [ph=(7)]. The solution was again taken in a separating funnel, where in the lower layer of water was discarded and the top layer (biodiesel) was separated. Finally, the biodiesel was heated at a high temperature of 120ºC for excess methanol recovery and water evaporation by distillation process. 3.2. Properties of Methyl Esters of Palm Oil The fuel properties of palm oil biodiesel are incomparison with ASTM standard biodiesel (D 6751) and other sources of biodiesel, as presented in Table 1. The obtained results show that the transesterification process has improved the fuel properties of the oil with respect to the physical and chemical properties, such as specific gravity, viscosity, flash point, pour point, total sulphur content, ash content, copper strip corrosion, carbon residue, sediment and water content. The kinematic viscosity of biodiesel is 5.03 cst, which is near to petroleum diesel (1.2-3.00 cst) and other methyl esters. The flash point of palm oil biodiesel is higher than of other methyl esters excluding Jatropha curcas oil biodiesel. The density of fuel is lowered (0.865 g/m 3 ) by transesterification compared with other methyl esters. 3.3. Effect of Palm Oil to Methanol Molar Ratio The molar ratio of alcohol to vegetable oil is one of the important factors that affect the conversion efficiency as well as production cost of biodiesel. The conversion efficiency is defined as the yield of the process represented in terms of percentage. Molar ratio is the number of moles of alcohol to the number of moles of triglycerides in the oil. Theoretically, transesterification reaction requires 3 moles of alcohol for each mole of oil. However, in practice, the molar ratio should be higher than that of stoichiometric ratio in order to drive the reaction towards completion[5]. That is, 3.43 moles of methanol is required for the completion of the reaction. Thus, the optimal Table 1: The properties of palm oil biodiesel compared with other methyl esters and ASTM D6751 standard biodiesel S. Fuel properties Palm oil Jatropha Pongamia Soya Canola ASTM D 6751 No. biodiesel curcas oil pinnata oil bean oil oil standard biodiesel biodiesel biodiesel biodiesel biodiesel -6-7 (8) (8) -9 1 Ash, percent by mass NIL 0.014 0.005 0.001 0.002 NA 2 Carbon residue percent 0.02 0.02 NA 0.2 0.02 < 0.05 by mass 3 Pour point 1.5 C NA NA NA NA - 4 Copper strip corrosion for Not worse NA NA 1 B 1A < No.3 at 50 C 3 h at 100 C than no.1 7 Flash point (Cleveland 170 C 191 150 153 162 >100 open cup) C 8 Kinematic viscosity at 40 C 5.03 4.84 at 30ºC 4.8 4.2 4.475 1.9-6.0 (Red-wood viscometer) 9 Sediment, percent by mass NIL NA NA NA NA - 10 Density or specific gravity 0.865 0.879 NA 0.885 0.888 - at 15 C, g/m 3 11 Total sulphur, percent by mass 0.013 NA NA 0.00014 0.0004 < 0.05 12 Water content, percent NIL 0.16 NA 0.04 0 < 0.05 by volume NA not available 82 Vol. 4 Issue 2, July-December 2013
Alkaline Catalytic Transesterification for Palm Oil Biodiesel and Characterisation of Palm Oil Biodiesel amount of 5 moles of methanol gives a higher efficiency of around 95%. The effect of palm oil to methanol ratio is represented in Figure 3. Figure 3: Effect of palm oil to methanol molar ratio 3.4. Effect of Heating and Dilution on Kinematic Viscosity of Blends Viscosity is one of the most important physical properties of a fuel. The effects of viscosity can be seen in the quality of atomisation and combustion as well as in engine wears. The higher viscosity of biodiesel fuel is reported to be responsible for the premature injector fouling, leading to poor atomisation. The quality of fuel atomisation is significantly affected by viscosity[8]. The viscosities of palm oil methyl esters (POMEs) and various blends of biodiesel with OD (20, 40, 60 and 80%) were measured at a temperature range of up to 95ºC, as shown in figure 4. It can be seen that the viscosity of POMEs was decreased due to blend with OD. The viscosity reduction is observed to increase with the increase in diesel content of the blend. The viscosity of B 20 (20% Palm oil biodiesel + 80% OD) has 3.81 cst at 40ºC, which is too close to OD, while the and other blends B 40, B 60 and B80 are having viscosity values close to OD only at above 50ºC. The viscosity of the blends decreased with increase in temperature and became close to that of OD at temperature ranges above 40ºC. The kinematic viscosity values of OD, palm oil and its methyl esters were measured at a temperature range up to 95 o C, as shown in Figure 5. The viscosity of palm oil biodiesel is close to OD at a temperature above 60 o C. Generally, the oil has higher viscosity (i.e 10 times greater) than that of its methyl esters (biodiesel). 3.5. Analytical Monitoring of Palm Oil Biodiesel There are various analytical methods developed for analysing mixtures containing fatty acid methyl esters (biodiesel) obtained by transesterification of vegetable oils. Various analytical instruments like GC-MS, HPLC-MS, FT-IR (Fourier transform- infrared spectroscopy) and NMR (Nuclear magnetic resonance) are used for quantifying the Journal of Biofuels 83
BaskarThangaraj, Kasturi Bai Ramachandran, Samuel Paul Raj Figure 4: Kinematic viscosities of palm oil methyl esters-diesel blend Figure 5: Kinematic viscosities of palm oil methyl esters and palm oil in comparison with ordinary diesel 84 Vol. 4 Issue 2, July-December 2013
Alkaline Catalytic Transesterification for Palm Oil Biodiesel and Characterisation of Palm Oil Biodiesel mixtures of fatty acid methyl esters. In this study, GC-MS and HPLC were chosen for analysing the synthesised biodiesel. 3.6. GC-MS Analysis The quantification of palm oil biodiesel was carried out by using GC MS and the spectrum is presented in Figure 6. There are five methyl ester compounds were identified by this technique, such as tetradecanoic acid, palmitic acid, linoleic acid, oleic acid and stearic acid methyl esters. This analysis concluded that finally all the fatty acids were converted into corresponding methyl esters and the transesterification reaction attained maximum of 100 % efficiency. Figure 6: GC-MS analysis of palm oil biodiesel 3.7. HPLC Analysis The amount of methyl esters in the transesterification of palm oil was analysed by HPLC, as shown in Figure 7, and its quantification in percentage results are presented in Table 2. Five major peaks appeared in this spectrum similar to GC-MS spectrum. Both the spectra have provided similar results for the transesterification of palm oil. This confirmed the formation of the biodiesel product. 4. CONCLUSION Biodiesel constitutes alkyl esters of fatty acids obtained from virgin or used edible, non-edible and animal fats. It is a renewable and non-toxic fuel. It contains no petroleum compounds, but it can be blended at various proportions Journal of Biofuels 85
BaskarThangaraj, Kasturi Bai Ramachandran, Samuel Paul Raj Figure 7: HPLC analysis of palm oil biodiesel Table 2: Quantification of palm oil methyl esters Retention time(min) Area (%) 2.087 1.1 3.477 30.0 4.010 17.8 4.830 10.4 5.233 40.8 with petroleum diesel to create a biodiesel blend or can be used in its pure form. In this study, biodiesel is derived from the low-cost edible oil of palm. Alkaline transesterification process is developed to convert FFA (free fatty acid) oils to its esters. The advantage of this method is that lower reaction temperature and time duration are required. It has been also found that the conversion efficiency is strongly affected by the molar ratio of methanol to oil. The molar ratio of 1:5 favours the completion of alkaline-catalysed esterification process within an hour. Maximum methyl ester conversion (95%) is achieved at the reaction temperature range of 50 60ºC. The physical and chemical properties of biodiesel are analysed. The viscosity of biodiesel is found to be closer to that of petroleum diesel. The flash point of biodiesel (170ºC) is greater than that of diesel. The experimental study revealed the production of biodiesel from palm oil by alkaline transesterification process and evaluated its characteristics by comparing it with other methyl esters and ASTM D 6751 standard biodiesel. The quantification and confirmation of methyl esters were carried out by GC-MS and HPLC analyses. ACKNOWLEDGMENT The authors gratefully acknowledge the financial support fromthe Tamil Nadu State Council for Science and Technology (TNSCST), Chennai, Tamil Nadu, India. 86 Vol. 4 Issue 2, July-December 2013
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