Utilization of sesame oil for the production of bio-based fuels and lubricants

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1 Utilization of sesame oil for the production of bio-based fuels and lubricants G.S.Dodos*, F.Zannikos and E.Lois School of Chemical Engineering, Laboratory of Fuel Technology and Lubricants, National Technical University of Athens, 15780, Athens, Greece *Corresponding author: Tel: , Fax: Abstract The environmental awareness along with the need to increase the exploitation of renewable resources has led during the last decades to the development of biobased fuels and lubricants deriving mainly from vegetable oils and fats. The aim of this study was to utilize sesame oil as renewable feedstock for the production of biodiesel (Fatty Acid Methyl Esters) and biolubricants by applying a two stages sequential process. The overall results revealed that sesame oil methyl esters meet the EN14214 requirements with emphasis on the oxidation stability performance since it outstrips the 6h limit without the addition of antioxidant agents. Furthermore, sesame oil TMP esters exhibit very good lubricating properties and thus they can be utilized as lubricant basestock in the formulation of high added value biobased lubricants for special and environmentally sensitive applications. Key Words: Sesame oil; biodiesel; biolubricant; TMP esters. 1. INTRODUCTION The environmental issues associated with the use of petroleum products and the geopolitical strategies concerning crude oil manipulation are the driving forces behind the introduction of alternative fuels and lubricants from renewable raw materials that can contribute to the vertical organization of the national economies. Regarding fuels, biodiesel is the most widely used biofuel nowadays. Biodiesel is a renewable alternative fuel for diesel engines with non-toxic and biodegradable characteristics consisting of Fatty Acid Methyl Esters (FAME) mainly of vegetable oils and animal fat origin. The reduction of the CO 2 emissions by its use is one of the main advantages while the poor oxidation stability and contamination problem is a field still under investigation [1,2]. Higher levels of biodiesel-diesel blends have recently been introduced to the European market - with the maximum FAME concentration reaching the 7% v/v- and the mixing ratio is expected to increase more in the forthcoming years. On the other hand the area of environmentally acceptable lubricants represent one the most growing markets with an estimated growth of more than 6% per year in Europe [3]. The search for bio-based material as industrial and automotive lubricants has accelerated in recent years. Oleochemical esters is a class of products that improve the thermal and cold-flow instability of the neat vegetable oils and fulfill the basic requirements as lubricant basestocks. Among the esters used for the production of biolubricants are the polyol esters such as trimethylolpropane (TMP), pentaerythritol (PE), and neopentylpolyol (NPG). These biobased esters deliver good low temperature fluidity and although they cannot be used at extremely high temperatures still they can be suitable in less extreme applications [4]. Based on this background the aim of this study was to investigate the use of sesame oil as feedstock for the production of biodiesel (Fatty Acid Methyl Esters) and biolubricants. Sesame oil is rarely reported as a starting material for the synthesis of renewable substitutes for conventional petroleum products. The advantage of sesame oil over other commonly used vegetable oil would lie in its significant resistant to deteriorative changes due to the endogenous antioxidants it contains [5]. Proceedings of the 3 rd International CEMEPE & SECOTOX Conference Skiathos, June 19-24, 2011, ISBN

2 2. EXPERIMENTAL 2.1 Materials and Reagents Refined Sesame Oil (SEO) was obtained from domestic oil manufacturers and was used without further processing. The properties of the base oil are listed in Table 1. Methanol, 99.99% purity was obtained from Fisher Scientific. Sodium Methoxide, pure, anhydrous powder, was obtained from Acros Organics Trimethylolpropane (TMP), > 99% purity was obtained from Merck. Table 1. Physicochemical properties of Sesame Oil Property Units Sesame Oil Method Density at 15 C kg/m EN ISO KV at 40 C mm2/s EN ISO 3104 Water Content mg/kg 215 EN ISO Acid Value mg KOH/g 0.50 EN Pour Point o C -6 ASTM D Methodology Sesame oil was employed as a starting material for the production of biodiesel (FAME) and biolubricant in a two stages process as illustrated in Figure 1. At first the triglycerides were converted to sesame oil methyl esters (SEOME) via methanolysis. Afterwards, the biolubricant was synthesized by transesterification of the methylesters producing the sesame oil TMP esters (SEOTMPE). MeOH Sesame Oil Transesterification Sesame Oil Methyl Esters BIODIESEL MeOH TMP Transesterification Sesame Oil TMP Esters BIOLUBRICANT Figure 1. Simplified flow diagram illustrating the combined production of biodiesel and biolubricant from sesame oil as starting material. 624

3 2.2.1 Synthesis of SEOME - Biofuel The Sesame oil Methyl Esters (SEOME) were prepared by methanolysis of sesame oil using sodium methoxide (CH 3 ONa) as catalyst at a concentration of 0.75wt%. The reaction was carried out at 65 o C for 2h employing a 6:1 methanol/oil molar ratio. After the completion of the transesterification, the upper methyl esters phase was separated from the glycerol phase and was purified by washing with 5% w/w sulfuric acid (H 2 SO 4 ) followed by warm water. The excess of methanol was removed by rotary evaporator. The purified methyl esters were dried over anhydrous sodium sulphate (Na 2 SO 4 ) and after vacuum filtration the final SEOME were obtained Quality Assessment of SEOME The produced methyl esters were examined regarding their use as automotive fuel for diesel engines. The analysis was performed according to the specified requirements and test methods included in the European Standard EN The fatty acid composition of the SEOME was determined by gas chromatography using a DANI Master GC apparatus in accordance with EN Synthesis of SEOTMPE - Biolubricant For the production of an environmentally adapted lubricant basestock a second stage reaction was followed using part of the previously prepared sesame oil methyl esters (SEOME) as feedstock. The methylesters were converted to Trimethylolpropane (TMP) (tri-) esters via alkaline transesterification reaction following a methodology similar to the one reported in a previously published work of the authors [4]. It should be noted that during the second stage reaction the methanol produced was continuously removed and so it could be isolated and re-used for further production of methylesters Quality Assessment of SEOTMPE Following the purification, the synthesized TMP esters were evaluated regarding their physicochemical properties as potential lubricant basestocks. Determinations concerning kinematic viscosities (KV) at 40ºC and 100ºC, viscosity index (VI), pour point (PP), acid value (AV) and water content were carried out according to the respective ASTM and EN Standard Methods. The lubricating properties of the esters under boundary lubrication were evaluated by employing a High Frequency Reciprocating Rig (HFRR, PCS Instruments) apparatus. Samples were subjected to oscillating motion of 1.0mm amplitude and 50Hz frequency between a moving test ball and a fixed specimen under loading of 1kg. The sample temperature was 100 o C and the test duration was 1 hour. The air relative humidity was kept at 45% while the ambient temperature in the laboratory was approximately 25 o C. The coefficient of friction (CoF) and the Lubricating Film were continuously recorded and at the end of the test the average values were reported. The antiwear properties of the biolubricant were estimated by measuring the Mean Wear Scar Diameter (MWSD) on the test ball, using a Leica M165C stereoscope at 120x magnification. The MWSD was corrected to the standardized water vapour pressure of 1.4 kpa and the WS 1.4 value, in micrometers ( m), was reported. A conventional additive-free mineral base oil was used as a reference lubricating fluid. 3. RESULTS AND DISCUSSION 3.1. Fuel properties of SEOME The fatty acid profile and the quality parameters of the prepared SEOME are listed in Table 2 and Table 3 respectively. The fatty acid analysis of the methyl ester showed that SEOME is composed primarily of linoleic and oleic acids accounting for and wt%, respectively. The other main fatty acids are palmitic (8.96 wt%) and stearic (6.16 wt%) acids. Very low levels of linolenic acid have been detected (0.33 wt%). 625

4 Table 2. Fatty acid composition of sesame oil methyl ester Fatty Acids Chemical structure weight% Myristic C14:0 CH3(CH2)12COOH 0.11 Palmitic C16:0 CH3(CH2)14COOH 8.96 Palmitoleic C16:1 CH3(CH2)5CH=CH(CH2)7COOH 0.15 Stearic C18:0 CH3(CH2)16COOH 6.16 Oleic C18:1 CH3(CH2)7CH=CH(CH2)7COOH Linoleic C18:2 CH3(CH2)3(CH2CH=CH)2(CH2)7COOH Linolenic C18:3 CH3(CH2CH=CH)3(CH2)7COOH 0.33 Arachidic C20:0 CH3(CH2)18COOH 0.67 Gadoleic C20:1 CH3(CH2)8CH=CH(CH2)8COOH 0.21 Behenic C22:0 CH3(CH2)20COOH 0.13 Regarding the fuel properties it is obvious that SEOME satisfy the applicable requirements as automotive diesel fuel outlined in the European Standard EN The low levels of water and free fatty acids contained in the starting oil substantially reduced the undesirable saponification and neutralization side reactions during transesterification process. As a result the conversion was completed and the biodiesel yield was determined to be 98.2% which is well above the specified lower limiting value. The completion of the reaction is also depicted in the measured values of the density and the kinematic viscosity. Moreover, the sulphur and the water content as well as the acid value of the prepared SEOME are fairly lower than the maximum acceptable levels. Finally the methyl esters possess good low temperature characteristics given the CFPP determination. However, the most advantageous characteristic of SEOME is the remarkable high oxidation stability it exhibits in the Rancimat accelerated oxidation method. It is worth noticing that although the increased levels of poly-unsaturation detected should lead to a decrease in the oxidation stability - similarly to other FAMEs - [6], SEOME outstrip the minimum demand of 6h imposed by the EN specifications without the addition of any artificial antioxidant agent. The reason for this behaviour lies in the antioxidant activity of the lignands (sesamin,sesamolin) and the phenolic compounds that are naturally occurring in the sesame seed oil, which retard the aging process [5]. Table 3. Properties of sesame oil methyl ester (SEOME) Property Units SEOME EN14214 limits Method Ester Content % m/m 98.2 min 96.5 ΕΝ Density at 15 C kg/m EN ISO K.Viscosity at 40 C mm 2 /s EN ISO 3104 Total sulphur mg/kg 2.5 max 10.0 EN ISO Water Content mg/kg 120 max 500 EN ISO CFPP C -1 max +5 EN 116 Linolenic acid methyl ester % m/m 0.33 max 12 ΕΝ Oxidation Stability (110 C) hours 6.3 min 6 ΕΝ Acid Value mg KOH/g 0.2 max 0.50 EN Gross Calorific Value MJ/kg 40 - ASTM D

5 3.2. Lubricant Properties of SEOTMPE The quality parameters of the biobased lubricant are presented in Table 4 along with the standard methods adopted for the analyses. The high kinematic viscosity and density is due to triester structure of the SEOTMPE. The synthesized esters depict a very high viscosity index above 200, which is far beyond of what the majority of conventional petroleum base oils can achieve. A high VI value is a desirable characteristic since it is indicative of the resistance in the viscosity variation due to temperature change. Another important property for a lubricant basestock is the pour point, which is the lowest temperature at which it still flows. PP should be low enough in order to ensure pumpability in cold starting conditions. It can be seen that SEOTMPE possess quite satisfactory low temperature characteristics, due to high unsaturation of the molecule, demonstrating a pour point value of -12 C. Table 4. Properties of the Sesame oil TMP ester (SEOTMPE) Property Units SEOTMPE Method 15 C g/cm ASTM D C cst ASTM D C cst 7.93 ASTM D 445 Viscosity Index (VI) ASTM D 2270 Water Content mg/kg 90 EN ISO Pour Point (PP) C -12 ASTM D 97 Acid Value mg KOH/g 0.1 EN In the tribological measurements the superiority of the biolubricant over the conventional reference base oil in boundary lubrication is evident as demonstrated in the HFRR results listed in Table 5. SEOTMPE is more capable in reducing wear since it provided smaller WS1.4 value than the mineral oil. However, the most profound difference was found in the friction properties. The metalto-metal contact was substantially higher when the system was lubricated with the mineral oil since the reported friction coefficient (CoF) was and the contact resistance - given by the lubricating film percentage-was very poor (20%). On the other hand the SEOTMPE exhibited much better friction characteristics. The CoF was reduced to the value of and the contact resistance between the sliding surfaces ascended to the value of 87%. Figure 2 shows the evolution of the CoF and the film respectively during the HFRR tests. The superior boundary lubrication performance of the biolubricant is attributed to the ester functionality. The SEOTMPE contains fatty acids which are organic substances with polar end groups. The latter are absorbed physically or/and chemically into the metal surface resulting in a monolayer film formation with the non-polar end and causing a suppression of the surface energy that leads consequently to a reduction in the friction coefficient [7]. Table 5. Friction and antiwear properties of Sesame oil TMP esters Property SEOTMPE Mineral Oil WS 1.4 (μm) Friction Coef. (Aver.) Film (Aver.) 87% 20% 627

6 SEOTMPE Mineral Oil SEOTMPE Mineral Oil Friction Coef. 0.1 Film % Time (min) Time (min) Figure 2: Evolution of CoF and film percentage for SEOTMPE and reference Mineral Oil during the HFFR measurements. 4. CONCLUSIONS A two stage process was followed for the utilization of sesame oil as renewable feedstock for the biodiesel and biolubricant production. The natural oil was sequentially converted first to methyl esters (SEOME) and then to TMP triester (SEOTMPE). The produced SEOME and SETMPE were subsequently tested and evaluated with regards to their fuel and lubricating characteristics respectively. The results could be interpreted as follows. Sesame oil methyl esters meet the EN14214 automotive fuel requirements and could be a potential source for biodiesel fuel. The advantage lies mainly in the oxidation stability performance since SEOME exceeds the 6h limit, despite the high level of unsaturation. Sesame oil TMP esters exhibit high VI, good cold-flow characteristics and excellent boundary lubricating properties and thus they can be utilized as lubricant basestock in the formulation of high added value biobased lubricants for special and environmentally sensitive applications. References 1. S.A.Basha, K.R.Gopal, S.Jebaraj, A review on biodiesel production, combustion, emissions and performance, Renewable and Sustainable Energy Reviews G.S.Dodos, V.Perdiou, F.Zannikos, Effect of Biodiesel in the Microbiological Growth in the Diesel Fuel Supply Chain, 7 th Pan-Hellenic Scientific Conference on Chemical Engineering, Patras, Greece 3. Frost & Sullivan Report: Dokos L., 2007 European Biolubricant Market 4. G.S.Dodos, G.Anastopoulos, F.Zannikos, Tribological Evaluation of Biobased Lubricant Basestocks from Cottonseed and Soybean Oils, SAE Technical Paper Z. Konsoula, M. Liakopoulou-Kyriakides, Effect of endogenous antioxidants of sesame seeds and sesame oil to the thermal stability of edible vegetable oils, LWT - Food Science and Technology J.A. Waynick, Characterization of Biodiesel Oxidation and Oxidation Products: CRC Project no. AVFL-2b. National Renewable Energy Laboratory, NREL/TP A. Arngek and J. Vitintin, 2002, Lubricating Properties of Rapeseed-Based Oils, Journal of Synthetic Lubrication, 16 4,