Selective preparation of furfural from xylose over microporous solid acid catalysts

Dehydration of xylose into furfural was performed in a batch mode in the presence of I-I-form faujasites and mordenites as catalysts, at 170 degrees C and in a solvent mixture consisting of water and methylisobutylketone or toluene (1:3 by volume). In toluene used as the co-solvent, xylose conversion and selectivity to furfural were found to depend on both acidic and structural properties of the catalysts used, Under the operating conditions used, H-mordenite with a Si/Al ratio of 11 was found to be more selective for the formation of furfural from xylose than H-Y faujasite with a Si/Al of 15. As already shown in the case of the dehydration of fructose to 5-hydroxymethylfurfural, the better selectivity of H-mordenite, as compared to H-Y faujasite, results from the structural properties of these catalysts. The high selectivity obtained (90-95%) was correlated once again with the shape selective properties of H-mordenites and particularly with the absence of cavities within the structure allowing the further formation of secondary products. When methylisobutylketone is used as the co-solvent, lower selectivities to furfural are obtained, in spite of the better affinity of furfural for methylisobutylketone than for toluene. Nevertheless, the high selectivities obtained in a solvent mixture consisting of water and toluene then allow to consider a process of the kind previously described for the dehydration of fructose. (C) 1998 Elsevier Science B.V.