Analyzing esterification kinetics of model bio-oil with ethanol catalyzed by a green catalyst

Abstract

Fast pyrolysis of biomass is a potential method for the production of bio-oils as a renewable liquid fuel. Bio-oils contain a large number of organic compounds, particularly carboxylic acids, which cause corrosiveness and instability that are troublesome for storage and for the transportation of fuel. Upgrading is an important process to transform bio-oils into high-quality biofuels. Contained organic acids are treated with alcohol to convert them into esters by esterification which may be considered as a good intermediate bio-oil upgrading method. This work presents a kinetic study for 12-tungstosilicic acid (a type of heteropoly acid, HPA) catalyzed esterification of a model bio-oil with ethanol. The main compound of the agro-residue-derived bio-oil was illustrated by oleic acid. The kinetic study was investigated under the molar ratio between ethanol to oleic acid of 9.11:1 and catalyst loading of 10 wt% condition with the varied reaction temperature in the range of 35-75°C. The result showed that a pseudo-first-order was suitable to represent the kinetic model for esterification of the model bio-oil. By fitting between the experimental results and kinetic model, the activation energy (Ea) and the pre-exponential factor (A) were found to be 31.5 kJ/mol and 432 min−1, respectively. This comparatively low activation energy equated to other catalytic esterification proved that the HPA catalyst (12-tungstosilicic acid) considered here was an assured green catalyst for esterification in the bio-oil upgrading process.