Conversion of Cellulose into 5-Hydroxymethylfurfural in a Biphasic System Catalyzed by Aluminum Sulfate and Byproduct Characterization

The production of 5-hydroxymethylfurfural (HMF) from cellulose is a crucial step in the production of high-value chemicals and fuels from renewable cellulosic biomass. In this study, the influences of the H2O/organic solvent ratio, the type of organic solvents, the addition of NaCl, and the type and concentration of catalysts on the catalytic conversion of cellulose into HMF in biphasic systems were comprehensively studied, and the highest HMF yield of 45.7% was obtained from cellulose in the H2O–tetrahydrofuran (THF) biphasic system with Al2(SO4)3 as the catalyst. Further investigation reveals that the excellent performance of the H2O–THF–Al2(SO4)3 reaction system was ascribed to the high Vorg/Vaque (60/1), high C[Al2(SO4)3]aque (0.38 g/mL), and low C[Al2(SO4)3]org (10–4 g/mL) of the reaction system. Moreover, the byproduct formed during the conversion of cellulose in the H2O–THF–Al2(SO4)3 reaction system was characterized by liquid chromatography–mass spectrometry (LC–MS) and LC–MS2 to detect considerable initial polymers. One plausible mechanism of glucose conversion in the H2O–THF biphasic system was proposed based on the detected compounds.