The effect of acidity of rapeseed oil on its transesterification

Abstract

The aim of this work is to study the transesterification of vegetable oils with a high acid number. Rapeseed oil was used as the raw material and its acid number was changed by the adding of oleic acid (from 0.89 to 12.25 mg KOH/g). Methanol was used for transesterification (molar ratio of oil to methanol 1:6) and potassium hydroxide was used as a catalyst. After the reaction time, the residue of catalyst was neutralized by gaseous carbon dioxide and methanol excess was removed. After the separation of two phases, each of them was analyzed (in ester phase: yield, content of methylester and acid number; in glycerol phase: yield, density, viscosity, content of glycerol, soaps, methylester, potassium carbonate and hydrogen carbonate). The obtained data was compared with theoretical material balances and effect on saponification of oil was calculated. The results show that the yield of methylester (biodiesel) is significantly affected by higher acid number, as well as enhanced soap formation. On the other hand, the conversion of the oil and acid number of the ester phase remain at constant values in studied borders.