Selective conversion of hemicellulose into furfural over low-cost metal salts in a γ-valerolactone/water solution

Abstract

Thermochemical conversion of biomass into platform chemicals and fuels is recognized as the most promising process for the partial substitution of fossil resources. Notably, selective liquefaction is a critical step for the integrated utilization of waste lignocellulosic biomass resources. Herein, we demonstrated an efficient and environmentally benign liquefied process for converting hemicellulose and waste lignocellulosic residues into furfural in a γ-valerolactone/water solution using inexpensive Al2(SO4)3 as the catalyst. Due to the synergistic effect between the γ-valeroctone (GVL) and active acid center which was derived from the metal salt, more than 50.2 mol% yield of furfural could be obtained from xylan, accompanying with 95.5 wt% of xylan conversion in GVL/H2O (m/m = 9:1, 40.0 g in total) at 140 °C for 3 h. A combination of 27Al NMR spectroscopy and electrospray ionization tandem mass spectrometry (ESI-Q-TOF-MS/MS) revealed that the [Al(OH)2(aq)]+ species contributed to the isomerization and dehydration processes. In addition, the existence of an appropriate amount of water was believed to be responsible for promoting the destruction of hemicellulose and restrain the formation of humins. The liquefied system sheds light on its considerable potential for the industrial utilization of agriculture and forestry lignocellulosic residues.