Conversion of cellulose into 5-hydroxymethylfurfural in an H2O/tetrahydrofuran/cyclohexane biphasic system with Al2(SO4)3 as the catalyst

A simple and efficient biphasic system comprising H 2 O, tetrahydrofuran (THF), cyclohexane (CHX) and Al 2 (SO 4 ) 3 was employed to convert cellulose into 5-hydroxymethylfurfural (HMF). The volume ratio of the organic phase to the aqueous phase (V org /V aque ), concentration of Al 2 (SO 4 ) 3 in the aqueous phase (C[Al 2 (SO 4 ) 3 ] aque ) and concentration of Al 2 (SO 4 ) 3 in the organic phase (C[Al 2 (SO 4 ) 3 ] org ) of the biphasic system played critical roles in the conversion of cellulose into HMF. In the biphasic systems with H 2 O/THF/Al 2 (SO 4 ) 3 of 4/18/0.4 and H 2 O/THF/CHX/Al 2 (SO 4 ) 3 of 3/16/3/0.4, > 80% of the added H 2 O was dissolved in the organic phase, whereas most of the added Al 2 (SO 4 ) 3 remained in the 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. Graphical abstract