Local Overheating Explains the Rate Enhancement of Xylose Dehydration under Microwave Heating

Abstract

The NH4Cl-assisted dehydration of xylose to furfural was studied using traditional and microwave heating. Significant differences in rate, pH profiles, and selectivity profiles were observed between both heating systems. A comparative kinetic analysis showed 7-13 times higher first-order rate constants for the xylose dehydration reaction under microwave heating. Dedicated experiments with varying irradiation power and liquid mixing intensity suggested that the differences are due to the development of overheated areas under microwave heating. This hypothesis was supported by modeling the rate enhancement observed under microwave heating using a simple kinetic model that assumes a minor overheated fraction amid a bulk liquid at target temperature.