Conversion of carbohydrates biomass into levulinate esters using heterogeneous catalysts

The catalytic performances of common solid acids (ZSM-5(25), ZSM-5(36), NaY, H-mordenite, Zr 3 (PO 4 ) 4 , SO 4 2 - /ZrO 2 , SO 4 2 - /TiO 2 , and TiO 2 ) for the conversion of carbohydrates such as glucose to methyl levulinate in near-critical methanol were investigated to develop an environmentally benign catalyst with high activity. Among these catalysts employed, sulfated metal oxides (especially SO 4 2 - /TiO 2 ) were found to be a type of potential catalysts for prospective utilization, which showed remarkably high selectivity and yield of methyl levulinate and had negligible undesired dimethyl ether formation from the dehydration of methanol. With SO 4 2 - /TiO 2 as the catalyst, methyl levulinate in ca. 43, 33 and 59   mol% yields could be obtained from sucrose, glucose and fructose, respectively, at 473   K for 2   h reaction time with a catalyst loading of 2.5   wt.%. The heterogeneous catalyst ( SO 4 2 - /TiO 2 ) was easily recovered by filtration and exhibited good catalytic activities after calcination in five cycles of reusing. The surface structure and acidity variations of the fresh and recycled SO 4 2 - /TiO 2 catalysts after calcination were characterized by XRD and NH 3 -TPD techniques. The results indicate that the catalyst crystallization structure was preserved after multiple cycles, the acid amount and acid strength of the catalyst reduced gradually as the increasing of recycling times.