Biodiesel production over lime. Catalytic contributions of bulk phases and surface Ca species formed during reaction

Abstract

Lime is pointed out as an effective catalyst for biodiesel production by oil methanolysis. Several Ca phases are formed during reaction. Each Ca phase has different contribution to the catalyzed process.Using CaO as a catalyst, S shape kinetics curve was observed and the induction period can be ascribed to the Ca(OH)2 formation. When Ca(OH)2, prepared by contacting CaO with H2O, is used as catalyst the initial period with a slow rate of transesterification has almost vanished. Besides, if the catalyst surface is totally converted into methoxide species the induction period is longer than the analogous obtained with CaO. This is an indication that the methoxide species strongly bonded to Ca are less reactive.The calcium diglyceroxide material (CaO_diglyc), prepared by contacting CaO with a mixture of methanol and glycerol, displays a totally different kinetics curve with no induction period. The faster kinetics and the Ca species detected in the glycerin phase seem to underline a non-negligible homogeneous process contribution.The characterization of the post-reaction catalysts underlines the relevance of the surface and bulk catalyst modifications. Calcium hydroxide can be pointed out as the active phase whereas calcium diglyceroxide is responsible for the catalyst deactivation due to calcium leaching.