Transesterification of Croton Megalocarpus Oil by Heterogeneous Catalysis and Microwave Irradiation – Reaction Kinetics and Process Optimization

Abstract

Use of biomass such as vegetable oils in the biodiesel synthesis decreases the need for fossil energy, provides an outlet for utilizing the abundant resources effectively and economically, results in a cleaner fuel that is biodegradable, renewable, and non-toxic. Biodiesel is produced by catalytic transesterification of vegetable oils. Homogeneous catalysts have problems of downstream processing and heterogeneous catalysts are being developed as they are environmentally better option to produce biodiesel. Transesterification of Croton megalocarpus oil was studied using homogeneous NaOH and heterogeneous alkaline earth BeO, Nano MgO, MgO, Nano CaO, CaO, Reoxidized CaO, SrO and BaO catalysts. The objective was to study the effect of key process variables on Fatty acid methyl esters (FAME) yield, to study the reaction kinetics, to optimize the reaction process, to compare conventional and microwave heating modes, and to compare batch and continuous reaction processes. Characteristic surface, bulk and chemical properties of the heterogeneous catalysts were obtained which included surface area, pore properties, scanning electron micrography, X-ray diffraction, basic strength and basicity. Transesterification reaction variables were reaction temperature, reaction time, catalyst concentration, methanol to oil ratio and microwave power. Gas chromatography was used for FAME analysis. Polymath 6.1, Matlab R2009b, and Design Expert 9 were used for data analysis. Process variable reaction temperature was 313, 323, 333, 343K; catalyst concentration was 0.5, 1.0, 1.5, 2 mass%; and methanol to triglyceride molar ratio 6, 9, 12, and 15. Highest reaction time for conventional heating was 180 min, and for microwave irradiation 5 min. Highest FAME yield for NaOH catalyst was 98% for conventional heating and 96% for microwave irradiation. For heterogeneous catalysts highest FAME yield for BaO, SrO, Nano CaO, CaO RO, CaO, Nano MgO, MgO and BeO under conventional heating were 83%, 77%, 74%, 42%, 32%, 25%, 20% and 4%; and for microwave irradiation were 78%, 72%, 62%, 24%, 19%, 7%, 6% and 3% respectively. Reaction order, rate constant and activation energy were obtained, for homogenous and heterogeneous catalysts, and for conventional heating and microwave irradiation. FAME yields for continuous transesterification were similar to batch process. Central Composite Design was used to optimize process variables and FAME yield presented in Response Surface Methodology surface and contour plots. FAME was analyzed for properties as a biodiesel fuel and it satisfied the international standards. Study established that Croton megalocarpus oil was a suitable feedstock for transesterification reaction, heterogeneous catalysts have a potential to replace conventional homogenous catalyst, and microwave irradiation was superior to conventional heating. Further studies on leaching, recyclability, modification of calcium oxide catalyst and scale-up of microwave irradiation were recommended.