Sulfated zirconia: an efficient solid acid catalyst for esterification of myristic acid with short chain alcohols

Sulfated zirconia (SZ) catalysts prepared by a two-step sol-gel method and calcined at 600-700 degrees C were evaluated for esterification of myristic acid with methanol using varied acid to alcohol ratio, reaction temperature and catalyst concentration. An exceptionally small concentration of SZ catalysts (0.125-0.5 wt% to acid) exhibited 98-100% conversion of myristic acid with methanol at 60 degrees C after 5 h. The conversion was decreased with an increase in the alkyl chain of alcohol from methanol to butanol, however, similar conversion was achieved by increasing the reaction temperature to 90 degrees C. The ester formation was selective, irrespective of alcohol and other reaction variables. The calcination temperature has strong influence on the structural, textural and acidic features and thus on the activity and re-usability of SZ catalysts. The reaction is sensitive to moisture present in methanol or reaction mixture. The studied reaction is Bronsted acid catalyzed and the SZ catalyst having higher number of Bronsted acid sites was re-used successfully without significant loss in activity; whereas the SZ catalyst having lower number of Bronsted acid sites showed a decrease in activity (similar to 28%) after five reaction cycles. The results clearly indicated the necessity of higher number of Bronsted acid sites for better performance and recycling of the SZ catalysts for esterification of myristic acid with methanol under the conditions studied.