Upgrading of biomass pyrolysis oil model compound via esterification: Kinetic stydy using heteropoly acid

Abstract

© 2019 The Authors. Published by Elsevier Ltd. Bio-oils from biomass fast pyrolysis consisted of many oxygenated compounds and water that limited direct use of bio-oils as transportation fuel by their corrosiveness, instability and low in heating value, especially organic acids. Catalytic esterification may be applied to upgrade bio-oils to biofuel by converting organic acids into esters. This work reported experimental kinetic data of the esterification of a bio-oil model compound with ethanol over a heteropoly acid catalyst (HPA). Acetic acid (85% w/w) and phenol (15% w/w) were used to represent biomass derived bio-oil. In a typical reaction, the mixture of bio-oil model compound and ethanol at molar ratio of 5:1 was used as the reaction solution. The catalyst was applied at a 4% w/w of acetic acid while the reaction temperature was varied in the range of 35-75oC. It was found that the esterification reaction of bio-oil model compound could be represented by a pseudo-homogeneous kinetic model. By fitting the kinetic model with the experimental results, the activation energy, Ea = 30.4 kJ/mol and the pre-exponential factor, A = 241 min-1 were obtained. These values were relatively low compared to those using some of homogeneous or heterogeneous catalysts commonly used in esterification of bio-oil. The HPA catalyst (tungstosilicic acid) proved to be a promising new type of catalyst for bio-oil upgrading via esterification.