Plastic-Derived Solid Acid Catalysts for the Production of Methyl 2-Hydroxyisobutyrate via Esterification

Abstract

In this study, we successfully prepare solid acid catalysts using plastic as the starting material for the production of methyl 2-hydroxyisobutyrate (HBM) through the esterification of 2-hydroxyisobutyric acid (HBA) and methanol. Polyethylene (PE) and polyvinyl chloride (PVC) are sulfonated at different temperatures (X) to obtain sulfonated polymer catalysts (SPE_X and SPVC_X). Various characterizations clearly confirm the introduction of sulfonic acid groups (-SO3H groups), which serve as active sites in this reaction, on the PE and PVC surfaces via sulfonation. For the SPVC_X catalysts, an excessively high sulfonation temperature facilitate the loss of chlorine groups (-Cl groups) via dehydrochlorination, resulting in a decrease in catalytic activity. In particular, the -Cl groups improve the acidic properties and accessibility of reactants to the -SO3H groups of the SPVC_X catalysts, leading to a high HBM yield. Therefore, the SPVC_120 catalyst show the highest HBM yield (ca. 75%) because of the abundant -SO3H and -Cl groups on the catalyst surface. Furthermore, the catalytic performance of the SPVC_120 catalyst surpassed those of commercial ion-exchange resins such as Amberlyst-15 and Nafion NR50, which are representative solid acid catalysts for esterification.