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.

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To reveal the hydrothermal conversion routes of the biomass-derived furanic compounds, the soluble products formed during the hydrothermal conversion of 5-hydroxymethylfurfural (HMF), furfural, and furfuryl alcohol were analyzed by liquid chromatography–mass spectrometry (LC–MS) and LC–MS/MS. Multiple carbocyclic compounds containing hydroxy group and carbonyl group were detected, with a molecular mass in the range of 154–272 Da and carbon chain of the length 8–15. The formation of these soluble carbocyclic compounds was proposed to involve hydrolytic ring-opening of the furanic ring, intermolecular aldol condensation, intramolecular aldol condensation, and C–C cleavage reaction. The C–C cleavage reaction was proposed to occur on the dicarbonyl structure of the formed primary polymers.

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.

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