Pretreatment of CaO Catalyst for Transesterification of Croton Megalocarpus Oil

Abstract

Transesterification of oils to produce FAME has traditionally been carried out using homogeneous catalysts. However the use of homogeneous catalysts has serious environmental implications and attempts are being made to identify a suitable heterogeneous catalyst. Alkaline earth metal oxides have been studied as an alternative, and CaO is found to be the most suitable because of its readily available and easy to handle. Study was made to see the effectiveness of CaO as a catalyst for FAME. It was found that CaO and NanoCaO contain a significant amount of hydroxide and carbonate leading to very poor activity. CaO was calcined to eliminate the hydroxide and carbonate. Calcination of CaO was
carried out at 500, 700, 800 and 900oC, and the resulting samples analyzed through XRD. Results indicated that amounts of hydroxide and carbonate decreased as the calcination temperature was increased, and at calcination temperatures above 800oC sample consisted mostly of calcium oxide. CaO was hydrated with water and the resulting hydroxide was calcined to re-obtain calcium oxide. This re-oxidized catalyst was found to have a lower BET surface area, but a higher activity. CaO, NanoCaO and Re-oxidized CaO were characterized through BET surface area, XRD, TEM, and basicity by Hammett indicator method. Transesterification of Croton Megalocarpus oil was carried out with methanol using a 9:1 methanol to oil molar ratio at 60oC for 3 hours using 2% catalyst. Product was analyzed for FAME by GC. Uncalcined catalyst gave a very low yield of 3 %. Yields for calcined catalysts ranged from 28 to 35%. Results indicate that pretreatment of CaO through calcination
and re-oxidation increase the catalytic activity. It also shows that basicity of catalyst is a better indicator of activity as compared to
BET surface area. Re-oxidized CaO catalyst with a lower BET surface area had a higher basicity, and a higher activity.