Dimethyl carbonate synthesis from propylene carbonate with methanol using Cu-Zn-Al catalyst

Abstract

In the present study, Cu-Zn-Al (CZA) hydrotalcite catalysts prepared by the coprecipitation method and calcined at 300, 500 and 800°C (named as CZA300, CZA500 and CZA800) were used for the synthesis of dimethyl carbonate (DMC) from methanol and propylene carbonate (PC) in a batch reactor. The physicochemical characteristics of the catalysts were analyzed by various methods such as X-ray diffraction (XRD), liquid nitrogen adsorption-desorption textural analysis, energy dispersive atomic spectra (EDAX), scanning electron microscope (SEM), Fourier transformation infrared (FTIR), and NH3- and CO2-temperature-programmed desorption (TPD). The average pore diameter of CZA300, CZA500, and CZA800 catalysts was found to be 55.6, 52.5, and 49.3 Å, respectively. Pore volume distribution analysis revealed that the CZA300 and CZA500 have bimodal pore distribution with pores centered at 36 ± 1 Å and 131 ± 2 Å. CZA300 catalyst has the highest amount of basic sites in weak and strong regions whereas CZA500 catalyst has the highest amount of basic sites in the moderate region. Overall, an increase in the calcination temperature decreased the quantity of basic and acidic sites. CZA catalyst calcined at 300°C (CZA300), was found to possess the highest basicity, and was found to be most effective during transesterification of PC to form DMC. CZA300 catalyst was further used to study the effect of catalyst dose, reaction time, methanol/PC molar ratio, reaction temperature, and reusability of the catalyst on PC conversion, turn over frequency (TOF), and DMC selectivity. PC conversion of 70% and DMC selectivity of 94% were observed at the optimum operating condition of reaction time = 4 h, methanol/PC molar ratio = 10, catalyst dose = 3 wt % of PC, and temperature = 160°C.