Investigation of Esterification of Biomass Pyrolysis Acids Over Sulfonic Acid-Functionalized Mesoporous Silicas

Bio-oil produced from fast pyrolysis of biomass contains significant amount of carboxylic acids which are corrosive and also can catalyze reactions such as acetalization and polymerization resulting in the instability of bio-oil during storage. Esterification, which is an acid-catalyzed reaction, provides a potential route to stabilize bio-oil. Ideally, heterogeneous acid catalysts would be utilized for this reaction rather than homogeneous catalysts such as sulfuric acid. A possible heterogeneous acid catalyst systemis organosulfonic acid-functionalized mesoporous silicas. In this presentation, detailed studies are presented on the kinetics and mechanism of acetic acid esterification with methanol and ethanol over organosulfonic acid-functionalized mesoporous silicas, since acetic acid is a prevalent carboxylic acid in bio-oil. The esterification of acetic acid with methanol and ethanol were examined. In the kinetic studies, the reaction orders for acetic acid and alcohol, as well as the activation energy were determined. Varying concentrations of acidic sites were employed to investigate the mechanism for acetic acid esterification with methanol and ethanol, i.e., a single-site or dual-site mechanism. In addition, since water is a significant component in pyrolysis bio-oil, an investigation of the effect of water on the esterification was also performed.