Kinetics of Mixed Ethanol/n‑Butanol Esterification of Butyric Acid with Amberlyst 70 and p‑Toluene Sulfonic Acid

Esterification of butyric acid with ethanol, n-butanol, and ethanol/n-butanol mixtures was studied using Amberlyst 70 cation-exchange resin and homogeneous p-toluene sulfonic acid as catalysts. The kinetics of individual alcohol esterification were first examined in batch reactions at different temperatures and catalyst loadings, and then esterification in ethanol/n-butanol mixtures of varying concentration ratios was characterized. Both nonideal solution and ideal solution kinetic models were developed. These models accurately predict the esterification of butyric acid by the individual alcohols; a simple additive combination of the individual alcohol esterification kinetics properly describes mixed alcohol esterification, indicating that the alcohols do not compete with each other or inhibit esterification when present together. When solution density is included in the kinetic rate expression to account for the actual concentration of −OH groups in ethanol and n-butanol, butyric acid esterification kinetics with the two alcohols are described by a common rate constant. This rate constant also predicts butyric acid esterification kinetics with other alcohol combinations, suggesting a generalized esterification rate constant for simple alcohol esterification of butyric acid over Amberlyst 70 catalyst. These results provide significant predictive capabilities for simulating processes such as reactive distillation processes for mixed alcohol esterification.