Carbon-based solid acids catalyze the synthesis of ethylene glycol monoacetate from ethylene glycol and acetic acid

Abstract

Activation is essential for improving the structure and surface functional groups of carbon-based solid acids (CSA) during the preparation of carbon materials. This paper compared the catalytic activity of CSA treated non-, KOH-, H3PO4-, and ZnCl2-activation in esterification of ethylene glycol (EG) and acetic acid (HAc) to synthesize ethylene glycol monoacetate (EGMA). The catalysts were characterized using N2 isothermal adsorption–desorption, acid-base titration, Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), Raman spectrometer, X-ray photoelectron spectroscopy (XPS), and X-ray diffractometer analysis (XRD). The results showed that activation treatment clearly enhanced the CSA’s specific surface area and significantly influenced the distribution of surface functional groups. Notably, the CSA activated with H3PO4 had a markedly higher density of –SO3H groups than the non- activated, KOH- activated, and ZnCl2-activated CSA. The high density of –SO3H on the catalyst surface is advantageous for the synthesis of EGMA from EG and HAc, making the H3PO4-activated CSA the best performer. The reaction conditions were optimized on H3PO4-activated CSA, resulting in a 74.1% conversion of EG and an 81.8% selectivity of EGMA at 100 °C for 30 min, and the EG/HAc molar ratio of 1:2. H3PO4-activated CSA was not obviously deactivated even after five cycles, and the decrease of its catalytic performance was related to the leaching of –SO3H on the catalyst surface. Overall, these findings suggest that H3PO4-activated CSA offers the benefits of less cost, a simpler preparation method, and greater catalytic activity compared to other catalysts, making it a desirable option for the synthesis of EGMA.