Layered zeolites intercalated with quaternary ammonium salts as catalysts for esterification of glycerol

Abstract

This research aimed to study the preparation of MCM-22 intercalated with quaternary ammonium salts, including tetrapropylammonium hydroxide (TPAOH), tetrabutylammonium hydroxide (TBAOH), tetrabutylammonium acetate (TBAAC), and cetyltrimethylammonium bromide (CTAB). MCM-22(P) was synthesized by using hydrothermal method. MCM-22 and ITQ-2 were attained by calcination and delamination of MCM-22(P), respectively. The intercalation of MCM-22 with CTAB and TPAOH or TBAOH can be prepared by refluxing MCM-22(P) with the solution of TPAOH/CTAB or TBAOH/CTAB, respectively, at 80 ℃ for 16 h. MCM-22 and ITQ-2 were impregnated with phosphotungstic acid (HPW). The synthesized catalysts were characterized by means of X-ray diffraction (XRD), thermogravimetric/differential thermal analysis (TG/DTA), nitrogen adsorption-desorption technique, scanning electron microscopy (SEM), and acidity measurement. Effects of quaternary ammonium salt, phosphotungstic acid amount, molar ratio of glycerol to lauric acid, reaction temperature, catalyst amount, and reaction time on lauric acid conversion and products distribution were investigated. Due to an enhancement of the catalyst acidity, it was found that 40HPW/ITQ-2 giving the highest monoglycerides yield of 45.5% at the lauric acid conversion of 57.4% under the suitable conditions, the molar ratio of glycerol/lauric acid of 1, the catalyst mass of 4 wt.% based on weight of lauric acid, the reaction time of 5 h at 110 ℃.