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

Abstract

A simple and efficient biphasic system comprising H2O, tetrahydrofuran (THF), cyclohexane (CHX) and Al2(SO4)3 was employed to convert cellulose into 5-hydroxymethylfurfural (HMF). The volume ratio of the organic phase to the aqueous phase (Vorg/Vaque), concentration of Al2(SO4)3 in the aqueous phase (C[Al2(SO4)3]aque) and concentration of Al2(SO4)3 in the organic phase (C[Al2(SO4)3]org) of the biphasic system played critical roles in the conversion of cellulose into HMF. In the biphasic systems with H2O/THF/Al2(SO4)3 of 4/18/0.4 and H2O/THF/CHX/Al2(SO4)3 of 3/16/3/0.4, > 80% of the added H2O was dissolved in the organic phase, whereas most of the added Al2(SO4)3 remained in the aqueous phase under the reaction temperature, jointly leading to high Vorg/Vaque, high C[Al2(SO4)3]aque and low C[Al2(SO4)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 Al2(SO4)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 H2O–THF–CHX biphasic system with an H2O/THF/CHX volume ratio of 3/16/3 under optimized conditions.