Methanolysis Optimization of Cottonseed Oil to Biodiesel Using Heterogeneous Catalysts

Abstract

This paper presented the process optimization for heterogeneous catalysts transesterification of refined cottonseed oil catalyzed by calcium oxide (CaO) and magnesium oxide (MgO) impregnated on Saw Dust Ash (SDA) using Response Surface Methodology Central Composite Design (RSMCCD). The five transesterification process variables studied were: catalyst concentration (4-8 wt% oil), methanol/oil molar ratio (4:1-8:1), reaction temperature (45-85oC), reaction time (3-5h), and agitation speed (200-300rpm). It was revealed that the reaction temperature gave the most significant effect on the yield of Fatty Acid Methyl Ester (FAME), followed by methanol/oil molar ratio. There were also significant interaction effects between catalyst concentration and methanol/oil molar ratio, catalyst concentration and agitation speed, methanol/oil molar ratio and reaction temperature, methanol/oil molar ratio and reaction time, methanol/oil molar ratio and agitation speed, reaction time and agitation speed for CaO/SDA transesterified reaction while for MgO/SDA transesterified reaction the significant interaction effect between variable is methanol/oil molar ratio and reaction time. Based on the optimized conditions, the highest yield of 90% for CaO/SDA transesterified reaction and 77% for MgO/SDA transesterified reaction were predicted using the following variables catalyst concentration, CaO/SDA = 6wt% and MgO/SDA = 8wt%, methanol/oil molar ratio = 6:1(CaO/SDA) and 8:1 (MgO/SDA), reaction temperature = 65oC, reaction time = 4h and agitation speed = 250rpm. Experimental validation of the predicted optimum conditions gave an actual yield of 86% (CaO/SDA) and 73.3% (MgO/SDA). The small errors between the predicted and actual optimum yield (4.7% (CaO/SDA) and 5.2% (MgO/SDA)) indicated that the model were valid and accurate in representing the actual experimental values and also in predicting yield at any conditions within the range studied. The results proved the efficacy of saw dust ash impregnated with CaO and MgO in transesterification reaction.

Keywords

• refined cottonseed oil
• saw dust ash
• free fatty acid methyl ester
• response surface methodology
• central composite design
• heterogeneous catalysts