Esterification of ethanol and lactic acid with WO3 on montmorillonite catalysts for ethyl lactate production

Abstract

This research aims to study the characteristics, catalytic properties and stability of tungsten oxide (13.5 wt%) supported on montmorillonite (W/MMT) catalysts prepared by using three different calcination temperatures including 375 (W/MMT375), 475 (W/MMT475) and 575 (W/MMT 575) °C. All catalysts were examined in esterification of ethanol and lactic acid at 80 °C. Characterization studies showed that the W/MMT475 catalyst exhibited the highest acidity, followed by W/MMT375 and W/MMT575, respectively. However, from the surface area result, W/MMT375 exhibited the highest surface area, followed by W/MMT475 and W/MMT575, respectively. When all catalysts were tested in esterification of ethanol and lactic acid, it revealed that the W/MMT375 catalyst was found to have the highest yield of ethyl lactate around 43.2 %. Then, the suitable catalyst (W/MMT375) was further improved by adding two different promoters such as zirconium (W-Zr/MMT375) and platinum (W-Pt/MMT375). Based on NH3 temperature-programmed desorption, it indicated that the W-Pt/MMT375 catalyst had the highest acidity. When two catalysts were tested in esterification of ethanol and lactic acid, the result showed that the W-Pt/MMT 375 catalyst exhibited higher yield of ethyl lactate (ca.48 %) than W-Zr/MMT 375. Finally, the catalytic stability of the catalysts including W/MMT 375 and W-Pt/MMT 375 was performed around 3 cycles in esterification of ethanol and lactic acid. It was found that the yield of ethyl lactate for each reuse was decreased. The characteristics of the spent W/MMT 375 and W-Pt/MMT 375 catalysts after each cycle up on the catalyst external structure, which is perhaps related to textural properties of catalyst did not affect by the reaction test within 3 cycles of reuse. However, the decrease of moderate to strong acid site related with the catalytic activity was significant.