(583a) Investigation of Esterification of Biomass Pyrolysis Acids Over Sulfonic Acid-Functionalized Mesoporous Silicas

Esterification of carboxylic acids with alcohols is of great industrial interest due to the enormous practical importance of organic ester products. Additionally, esterification also provides a potential route to stabilize bio-oil produced from the fast pyrolysis of biomass since carboxylic acids are a key constituent in bio-oil that can catalyze reactions such as esterification, acetalization and polymerization, which results in the instability of bio-oil during aging. Compared with homogeneous catalysts such as sulfuric acid, heterogeneous acidic catalysts would be advantageous due to easier separation and recyclability. In the strategy for developing highly active heterogeneous acidic catalyst, organosulfonic acid-functionalized mesoporous silicas are proven to be promising candidates. In this presentation, detailed studies on the kinetics and mechanism of acetic acid esterification over organosulfonic acid-functionalized SBA-15 are discussed, since acetic acid is a prevalent carboxylic acid in bio-oil.

Varying concentrations of sulfonic acid moieties were incorporated into the mesopores of SBA-15 via the one-step co-condensation method. The reaction performance of the functionalized mesoporous silicas was evaluated for the esterification of acetic acid with methanol. In the kinetic studies, the reaction orders for acetic acid and methanol as well as the activation energy were determined. A series of pyridine poisoning experiments were performed to establish the reaction mechanism of esterification over SO3H-SBA-15, i.e., single-site or dual-site mechanism. Since water is a significant component in bio-oil, an investigation of the effect of water on the esterification was performed. SO3H-SBA-15 was found to be more water tolerant than the homogeneous catalyst H2SO4 through a series of experiments with addition of varying levels of water, suggesting that the heterogenous catalyst is a better candidate for pretreating bio-oil.