Esterification of bio-based succinic acid in biphasic systems: Comparison of chemical and biological catalysts

Abstract

Different chemical and biological catalysts were screened for the biphasic esterification of aqueous solutions of succinic acid with 1-octanol. Among them, DBSA, Nafion NR-50 and Novozym 435 were found to be the most attractive catalysts. The pH, the temperature and the catalyst concentration had high impacts on the reaction rates. The optimization of the reaction conditions with a single-variable approach for the chemical catalysts and a Response Surface Methodology for the enzyme allowed an increase of the rates by a factor 1.5 for DBSA, 2.3 for Nafion NR-50 and 1.3 for Novozym 435. Real fermentation broths produced from recombinant Escherichia coli could be successfully esterified with conversions up to 93% for DBSA and 70% for Nafion NR-50 and Novozym 435 as catalysts. Finally, DBSA was selected as the cheapest and most active option. Besides, the esters were isolated with a purity of 83% from fermentation broth solutions. DBSA also catalyzed the esterification of succinic acid from fermentation broth with many alcohols creating a broad spectrum of interesting esters. The esters might then be used as end-product, hydrolyzed back to pure succinic acid or hydrogenated.