Study of related reactions for production of biodiesel using solid acid catalysts

Abstract

The focus of this research is to establish a better fundamental insight into heterogeneous catalysis for the reactions related to biodiesel production, in an attempt to design the catalyst systems more proficient and durable for applications concerning biodiesel synthesis. This research was to explore the viability of heterogeneous catalyzed hydrolysis of oils and fats for the synthesis of free fatty acids (FFAs), a platform reaction of the oleochemical industry and a possible reaction in a novel 2-step (hydrolysis-esterification) biodiesel synthesis process using low cost feedstocks containing > 5–15% FFAs. Using tungstated zirconia (WZ) and SAC-13 as catalysts, the hydrolysis of tricaprylin (TCp) was carried out at 110–150℃ in a semi-batch reactor with continuous addition of water at low flow rates. The characteristics of the catalysts played an important role in reaction selectivity, apparent activation energy, and deactivation. Hydrolysis and transesterification are two reactions which can occur during the synthesis of biodiesel. An investigation of the mechanistic pathways in hydrolysis and transesterification were carried out at 100–130°C and 120–180 psi. Using a reaction model discrimination procedure, it was found that both hydrolysis and transesterification on WZ could be successfully described by an Eley-Rideal single site mechanism with adsorbed TCp reacting with bulk phase water or methanol. This research also proven that surface nature of zirconia can play crucial roles on determining the catalytic activity of WZ catalysts. The solvothermal method for preparation of crystalline zirconia support can result in the formation of Zr-OH bond on its surface. This surface species related to the Zr-heteropolyacid, acting as strong BrØnsted acid sites. It consequently affected on the catalytic activity for esterification of dilute acetic acid and 1-heptanol.