Evaluating the kinetics of the esterification of oleic acid with homo and heterogeneous catalysts using in-line real-time infrared spectroscopy and partial least squares calibration

Abstract Biodiesel is a mixture of fatty acid alkyl esters with properties similar to petroleum-based diesel. Thus, biodiesel can be used as either a substitute for diesel fuel or, more commonly, in a fuel blend. Biodiesel production can be catalyzed with mineral acids or bases or enzymes. The use of real-time techniques for monitoring the reaction and evaluating the efficiency of the catalyst can be of great use for optimizing the reaction and monitoring the process. In the present work, an in-line real-time methodology was used to evaluate and compare the kinetics of a reaction catalyzed with homo (hydrochloric acid) and heterogeneous (the enzymes Novozym 435, Lipozyme RM, and Lipozyme TL) catalysts. The esterification of oleic acid with ethanol was used as the reaction model. The study used attenuated total reflexion/Fourier transform infrared (ATR/FT-IR) and a single partial least squares (PLS) regression model to evaluate the kinetics of the various catalysts, without multiple calibrations, with validation by GC–MS. Novozym 435, which showed complete conversion after 165 min, was the best catalyst for this reaction. Lipozyme RM and Lipozyme TL had inferior conversion after the same amount of time, in agreement with the literature. All enzymatic catalysts showed higher conversion than hydrochloric acid at the same reaction conditions.