Dehydration of fructose to 5-hydroxymethylfurfural over H-mordenites Original Research Article

Dehydration of fructose to 5-hydroxymethylfurfural was performed in a batch mode in the presence of a series of dealuminated H-form mordenites as catalysts, at 165°C, and in a solvent mixture consisting of water and methyl isobutyl ketone (1:5 by volume). Under the operating conditions used, the reaction was not controlled by external or internal diffusional limitations. Fructose conversion and selectivity to 5-hydroxymethylfurfural were found to depend on acidic and structural properties of the catalysts used as well as on the micropore vs. mesopore volume distribution of those catalysts. A maximum in the rate of conversion of fructose was observed for the H-mordenite with a Si/Al ratio of 11. A maximum in the selectivity to 5-hydroxymethylfurfural was observed only for H-mordenites with a low mesoporous volume. The high selectivity obtained (>90%) was correlated with the shape selectivity properties of H-mordenites (bidimensional structure), and particularly with the absence of cavities within the structure allowing further formation of secondary products. The influence of the microporosity vs. mesoporosity on the selectivity to 5-hydroxymethylfurfural was also studied, the formation of mesopores upon dealumination procedures being damaging to obtain a high selectivity. A significant increase in the selectivity (10%) was also obtained by simultaneous extraction of 5-hydroxymethylfurfural with methyl isobutyl ketone circulating in a countercurrent manner in a continuous catalytic heterogeneous pulsed column reactor. Finally, taking into account the most recent results reported in the literature and our own results, it is possible to revise the mechanism of the dehydration of fructose.