Dehydration of fructose to 5-hydroxymethylfurfural in sub-critical water over heterogeneous zirconium phosphate catalysts.

Dehydration of fructose to 5-hydroxymethylfurfural in a batch-type process with sub-critical water (sub-CW) was performed in the presence of different laboratory-made zirconium phosphate solid acids at 240 degrees C. A direct relation was found between increasing the crystallinity and decreasing the surface area of solid acids. However, irrespective of the different surface areas, similar catalytic behaviors were observed. Meanwhile, calcination of the samples showed no improvement in the activity of the solid acids. In the presence of the amorphous form of zirconium phosphate, about 80% of fructose was decomposed in sub-critical water at 240 degrees C after 120 s, and the selectivity of the dehydration reaction of fructose to 5-hydroxymethylfurfural rose to 61%. No rehydration products were identified. Soluble polymers and furaldehyde were the only major and minor side products found, respectively. Finally it was found that zirconium phosphate solid acids were stable under sub-CW conditions, and they can easily be recovered without changing their catalytic properties.