Synthesis/separation of 5-hydroxymethylfurfural converted from fructose promoted by H2O-CO2 biphasic system with solid catalysts: Experimental and kinetic modeling approaches

5-Hydroxymethylfurfural (5-HMF) is an industrially valuable compound typically produced by dehydration of fructose converted from cellulosic biomass. However, the formation of 5-HMF is accompanied by its conversion into by-products, such as levulinic and formic acids, decreasing its yield. Therefore, biphasic processes are attracting much attention allowing the efficient simultaneous synthesis and separation of 5-HMF. In this study, a biphasic system using water with high-pressure carbon dioxide, the most environmentally friendly solvents, combining with a solid catalyst is used to achieve 5-HMF synthesis and separation at lower temperatures and shorter duration than previous studies. The main experiment was operated by a semibatch reactor with a continuous flow of CO2. Additionally, three experiments, i) measurement of the partition coefficient of 5-HMF between the two phases, ii) 5-HMF synthesis in H2O-CO2 biphasic batch system, and iii) 5-HMF extraction in H2O-CO2 biphasic semibatch system, were conducted to complement the main experiment. All results from complement experiments were used as parameters in the kinetic modeling. As the result, the maximum yield of 5HMF (36.6 %) was achieved at a temperature of 403 K, a pressure of 25 MPa, and a reaction time of 180 min. Finally, the optimal conditions for the semibatch experiment for 5-HMF synthesis and separation could be estimated from the kinetic models with parameters determined in this work. The obtained results suggested that this yield can be further improved by increasing the reaction time, which should be confirmed by further experimental studies.