Overall Transesterification Rate of Oil in Methanol-Oil Two-Phase System: A Simultaneous Diffusion-Reaction Model

Abstract

This short paper aims to clarify the main factor controlling overall transesterification rate of vegetable oil (triglycerides) with methanol catalyzed by homogeneous acid catalyst. In this reaction system, methanol droplets are dispersed in oil continuous phase. Most of the catalyst is existing in methanol droplets. The authors formulated a simultaneous diffusion-reaction model by focusing on the following processes: (1) dissolving of oil into methanol droplets at the oil-methanol interface, (2) inward diffusion of oil in methanol droplets, and (3) simultaneous transesterification of oil with the inward diffusion. In order to prove this model, firstly, the intrinsic transesterification kinetics were determined in methanol/oil/2-butanone/sulfuric acid system at 298, 308, and 323 K. 2-Butanone and sulfuric acid were used as a co-solvent and a catalyst, respectively. Secondly, transesterification of oil with methanol catalyzed by sulfuric acid was carried out in ordinary two-phase system at 298, 308, and 323 K. The authors successfully simulated the two-phase reaction results from the homogeneous kinetics by applying the model developed in this paper. It was found that the overall transesterification rate is controlled by the intrinsic kinetics.