Energy efficient production of 5-hydroxymethylfurfural (5-HMF) over surface functionalized carbon superstructures under microwave irradiation

Microwave (MW)-assisted process intensification of catalytic conversion of saccharides is a promising route for energy efficient production of value-added chemicals and fuels. This work presents the development of the MW-responsive catalysts (i.e., the acid functionalized spherical carbon superstructure, SCS) for converting fructose to 5-HMF effectively and efficiently under MW irradiation. Under a mild MW condition (at 70 °C, atmospheric pressure), the SCS catalyst (with surface sulfonic and carboxylic acid groups) achieved fructose conversion of ~ 97.8% and selectivity to 5-HMF of ~ 90.6% after 5 min reaction time with good recyclability, being significantly higher than that obtained by the system under the conventional heating. Importantly, the MW-assisted system showed very high energy efficiency coefficient of 1.01 mmol kJ⁻¹ L⁻¹ compared to that (0.09 mmol kJ⁻¹ L⁻¹) of the conventional thermal catalysis. The mechanism of process intensification of the system developed may be attributed to the combination of the dipole polarization of the MW-responsive sulfonic groups and the selective heating of the MW-absorbing SCS support under the MW condition.