Dehydration of fructose to 5-hydroxymethylfurfural over H-mordenites

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 degrees 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.