Microwave-assisted hydrothermal degradation of fructose and glucose in subcritical water

The microwave-assisted hydrothermal treatment of fructose and glucose is studied under subcritical conditions, in a temperature window between 180 °C and 250 °C. The suitability of microwave heating as well as the impact of the reaction variables temperature and time on the extent of the substrate conversion and on the product composition are elucidated. With rate constants of 3.6*10−3 s−1 (fructose) and 5.2*10−4 s−1 (glucose) at 220 °C the decomposition of fructose took place about eight times faster than that of glucose. 5-HMF was found to be the major decomposition product for both monosaccharides, with maximum yields of 47% 5-HMF (for fructose) and 30% (for glucose) at a maximum selectivity of 65% and 50%, respectively. All other liquid monomeric products like levulinic acid, furfural and trihydroxy benzene are formed at cumulative yields below 16%.

► The hydrothermal conversion of fructose and glucose was studied.
► Temperature and time were studied as major reaction variables.
► Fructose decomposition took place eight times faster than that of glucose.
► 5-HMF was the major reaction product with a selectivity of up to 65%.