Hydrolysis of Triglycerides Using Solid Acid Catalysts

Abstract

The commercial production of free fatty acids (FFAs) is carried out through the noncatalytic hydrolysis of triglycerides (TGs) using great amounts of superheated steam in large reactors made of expensive corrosion-resistant materials, making the process energy intensive and costly. In this study, the feasibility of a continuous reaction system using a solid acid for the hydrolysis of TGs at atmospheric pressure has been investigated. This research was to explore the viability of heterogeneous catalyzed hydrolysis of oils and fats for the synthesis of FFAs, a platform reaction of the oleochemical industry and a possible reaction in a novel two-step (hydrolysis−esterification) biodiesel synthesis process using low-cost feedstocks containing >5−15% FFAs. Tricaprylin (TCp) was used as a model compound representing TGs in order to obtain reliable intrinsic kinetics. Using tungstated zirconia (WZ) and the solid acid composite SAC-13 (Nafion resin nanoparticles supported on mesoporous silica) as catalysts, the hydrolysis of TCp was carried out at 110−150 °C in a semibatch reactor with continuous addition of water at low flow rates capable of achieving 100% selectivity of the carboxylic acid side chains on the triglyceride to HCp. The characteristics of the catalysts played an important role in reaction selectivity, apparent activation energy, and deactivation. Catalyst recycling experiments showed continuous activity loss for both catalysts. Characterization of the used catalysts indicated that deactivation was likely caused by the strong adsorption of bulky reaction intermediates on the catalytic acid sites, blocking reactant accessibility. For WZ, recalcination in air was an effective regeneration method resulting in the recovery of 100% of its original activity. Regeneration by calcination was not possible for SAC-13 due to its temperature sensitivity. Methanol washing of used WZ and SAC-13 catalysts only partially regenerated catalyst activity.