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 V org/V aque (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.

aqueous phase under the reaction temperature, jointly leading to high V org /V aque , high C[Al 2 (SO 4 ) 3 ] aque and low C[Al 2 (SO 4 ) 3 ] org in the biphasic system. All of these results yield the excellent performance of these biphasic systems in the conversion of cellulose into HMF. The addition of CHX into the biphasic system can decrease the solubility of Al 2 (SO 4 ) 3 in the organic phase, thus improving the stability of HMF in the reaction system. The influences of catalyst usage, reaction temperature and time, and cellulose/ solvent ratio were all explored, and a high HMF yield of 71.2% was obtained in the H 2 O-THF-CHX biphasic system with an H 2 O/THF/CHX volume ratio of 3/16/3 under optimized conditions.

A simple and efficient biphasic system consisting of H2O, tetrahydrofuran (THF), cyclohexane (CHX) and Al2(SO4)3 was employed to convert cellulose into 5-hydroxymethylfurfural (HMF) with high yield of 71.2%. The real volumes of organic phase (Vorg) and aqueous phase (Vaque) of the biphasic system at reaction temperature were measured to found out that over 80% of the added H2O was dissolved into the organic phase at reaction temperature, leading to high Vorg/Vaque (over 44/1) and high concentration of Al2(SO4)3 (over 0.34 g/mL) in aqueous phase. The high concentration of Al2(SO4)3 in aqueous phase could efficiently catalyze the conversion of cellulose into HMF, while the high Vorg/Vaque could protect the formed HMF from rehydration, all of which are responsible for the high efficiency of the system on conversion of cellulose into HMF. The addition of CHX into reaction mixture could decrease the solubility of Al2(SO4)3 and H2O in the organic phase, which could improve the stability of HMF in the reaction system, resulting higher yield of HMF from cellulose. Because of the high Vorg/Vaque of the reaction system, one microemulsion-like system and liquid film catalytic model are proposed for the cellulose-to-HMF process.