SELECTIVE CONVERSION OF FRUCTOSE TO METHYL LEVULINATE USING SULPHATED ZIRCONIA-ALUMINA BINARY OXIDES

Abstract

Biomass constitutes a huge reservoir of renewable organic carbon that can be used for sustainable production of value-added chemicals and polymeric materials. Levulinate esters are biomass derived platform chemicals with potential applications as fuel additives, fragrances, and plasticizers. Moreover, they can be derivatized to produce herbicides, cancer therapeutics and surfactants. In this study, sulphated ZrO₂-Al₂O₃ binary oxides were synthesized by a modified co-precipitation method and found to be highly active and selective for direct conversion of fructose to methyl levulinate. The samples were characterized using powder x-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods. The synthesized sulphatedbinary oxideswere amorphous with large mesopores (≥ 3.4 nm) and high pore volumes (0.121-0.315 cm³g^-1). The synthesized materials were used for conversion of fructose to methyl levulinate, with methanol as a solvent, in a continuously stirred pressurized reactor. The most active catalyst (ZA20), containing 20% alumina,selectively converted fructose to methyl levulinate with a high yield of 65% after 1 h at 200^oC. The optimal catalyst loading, reaction time, and temperature were 40 mg, 30 min and 200^oC, respectively. The catalysts were gradually deactivated with successive reuse due to surface deposition of humins but were easily regenerated by calcination in static air at 500^oC for 3 h. However, activity was not fully recovered after regeneration, presumably due to leaching of sulphate species in the polar solvent media. The formation of ethers during conversion was negligible suggesting that methanol can be recycled after distillation.