The use of catalysts in biomass upgrading processes to reduce oxygen content is an essential part of the pursuit of replacing fossil fuels with more sustainable resources. In this work, esterification of butyric acid and butanol catalyzed by solid acid resins was studied as a model reaction using 10 mL glass batch reactors. The catalysts used were hydrogen form AmberlystTM 15 and AmberlystTM 46 ion exchange resins. Additionally, solvents of different polarity were used to study the influence of the interaction of solvent and catalyst on the reaction mechanism. The solvents used were toluene (nonpolar) and tetrahydrofuran (polar, aprotic). In the presence of toluene, the reaction was approximately first-order with respect to both butanol and butyric acid. However, in the presence of tetrahydrofuran, the reaction was approximately zero-order with respect to both butanol and butyric acid. This difference in reaction order signifies a difference in either the rate-determining step or the identity of the abundant surface species, and it is therefore a manifestation of a difference in reaction mechanism due to solvation effects. The measured turnover frequencies were also much lower in the presence of tetrahydrofuran than in the presence of toluene. Additionally, it was found that, in the presence of toluene, the measured turnover frequency over AmberlystTM 15 was lower than that over AmberlystTM 46, even when correcting for concentration variance. This difference in turnover frequency is attributed to differences in the activity coefficient of the surface-bound transition state due to slight differences in the polymer resin structure which impact the solvation of the transition state. It has been observed that solvation effects can be related to the catalyst itself as well as to the reaction solvent.

Solvation effects in liquid-phase esterification reactions catalyzed by hydrogen form ion exchange resins

ACS Spring 2022

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