Modified dolomites as catalysts for palm kernel oil transesterification

Abstract

Heterogeneously catalyzed transesterification of palm kernel oil with methanol over various modified dolomites has been studied at 60 °C. The modification of dolomite was performed via a conventional precipitation method using various nitrate salt solutions of alkali earth metals and trivalent metals. Influences of a variety of metals, calcination temperature of the parent dolomite, methanol/oil molar ratios, reaction time, catalyst amount, and catalyst reuse have been investigated. The results indicated that the calcination temperature of the parent dolomite is a crucial factor affecting the activity and the basicity of the resulting catalyst. The catalyst modified from dolomite calcined at 600 and 700 °C, followed by the precipitation from Ca(NO 3) 2 and the subsequent calcination at 800 °C, exhibited the most active catalyst, giving the methyl ester content as high as 99.9% under the suitable reaction conditions, the methanol/oil molar ratio of 15, amount of catalyst of 10 wt.%, and reaction time of 3 h. As suggested by the TGA results, the high activity of the catalyst should be due to the presence of two active CaO sites generated from the precipitated Ca(OH) 2 located in the crystalline phase of dolomite and from CaCO 3 remaining after the calcination of the parent dolomite at 600–700 °C.