Esterification Of Solketal And Levulinic Acid Over Heterogeneous Acid Catalysts

Abstract

This work studied the esterification of solketal (SK) and levulinic acid (LA) over heterogeneous acid catalysts, including Amberlyst 15, Amberlyst 36 wet, HUSY zeolite, HMS-SO3H and NR/HMS-SO3H. The effect of reaction conditions on the reactants conversion and products distribution were studied such as reaction time, molar ratio of SK: LA, reaction temperature and catalyst loading. Gas chromatography with mass spectroscopy (GC-MS) was used to identify the chemical structure all of components in the products mixture. The products mixture is composed of solketal levulinate (SL), hemi-acetal of solketal levulinate (H-SL), glycerol levulinate (H-SL) and oligomers (LGO). SL is considered as the primary product. Nuclear magnetic resonance (NMR) was used to identify the chemical structure of LGO. These oligomers was terminated by three different end groups, including keto terminal (KT), glycerol-ketal terminal (GKT), and glycerol-ester terminal (GET). However, water which located inside the catalyst and generated from esterification cause of hydrolysis and other larger products formation. Glycerol was found in all of experiments. It was obtained from SK hydrolysis. Typically, esterification is a spontaneous reactionม but it was provided a low of the reactants conversion and products yield, and also takes long reaction time so adding acid catalyst is used. Esterification is an endothermic reaction so increasing the reaction temperature, the reactants conversion and product yield was increased. The effect of SK: LA molar ratio was enhanced the reaction forward and LGO was found as a major component. The effect of catalyst loading can be controlled the product selectivity. The optimum reaction conditions were used Amberlyst 15 as a catalyst at 5 wt.% respect to LA and reaction temperature at 120 ºC for 5 h to achieve the higher conversion and minimize the glycerol formation.