Publication

Fatty acid methyl ester (FAME) production via transesterification of triglycerides (TGs) over a heterogeneous acid catalyst is mediated by carbon dioxide in an expanded methanol system. A representative TG, triolein, is used to determine the mechanisms and interactions responsible for the improved yields over Nafion-NR50 in these system conditions. Namely, the system mass transfer limitations, reaction kinetics, and interphase partitioning behavior are explored by varying mixing conditions and catalyst characteristics over a time series of 4 h. It is found that CO2 enhances mass transfer leading to improved reaction yields and product profiles due to increased substrate transport to and from the catalyst surface. CO2 also contributes to catalyst expansion, leading to greater exposure of active sites and faster reaction kinetics. Initial reaction rate constants using methanol-soaked Nafion reflect pseudo-first-order kinetics. Finally, the substrate-reagent mediating properties of CO2 are discussed in reference to the varying reaction rates of TG and intermediate products. All three of these mechanisms contribute to CO2's multifaceted role in facilitating heterogeneously catalyzed reactions.