Optimisation of transesterification of Croton megalocarpus oil over alkaline earth catalysts using conventional and microwave irradiation by response surface methodology

Abstract

Croton megalocarpus oil is a non-edible oil with potential to produce biodiesel in East Africa. Transesterification of the oil and methanol to produce fatty acid methyl ester (FAME) was studied using heterogeneous alkaline earth BaO, SrO, CaO, Nano CaO, Reoxidised CaO (CaO RO), MgO, Nano MgO, BeO catalysts; by conventional heating and by microwave irradiation. Catalysts were characterised by surface area, porosity, basic strength and basicity. FAME yield was obtained through Gas chromatography. Central Composite Design (CCD) was used to optimise process variables (reaction temp. /time, methanol-to-oil ratio, catalyst conc.) for the highest FAME yield through Response Surface Methodology (RSM) plots. Conventional heating gave a higher maximum yield, in the order: BaO(83%) > SrO(77%) > Nano CaO(74%) > CaO RO(42%) > CaO(32%) > Nano MgO(25%) > MgO(20%) > BeO(–). Yields were in order of the observed catalyst basicity, and independent of surface area. New catalyst CaO RO obtained from CaO showed higher activity. BeO showed no activity (<5%). Microwave irradiation gave slightly reduced maximum yields for BaO(78%), SrO(72%) and Nano CaO(62%). However, no such maxima were observed for other catalysts for the chosen reaction time. Microwave was found to be a superior heating mode due to highly reduced reaction times