One-Pot Degradation of Cellulose into Furfural Compounds in Hot Compressed Steam with Dihydric Phosphates

Direct conversion of cellulose into furfural compounds (5-hydroxymethylfurfural and furfural) in hot compressed steam with the aid of phosphates was studied under temperatures of 250–330 °C and pressures of 0.5–3.5 MPa. The water in the steam could be adsorbed by cellulose to form water molecule layers, which could hydrolyze cellulose. Basic Na2HPO4 was found to be favorable for fragment product formation through hydrolysis of cellulose followed by retro-aldol condensation of saccharide, while the acidic dihydric phosphates (LiH2PO4, NaH2PO4, and Ca(H2PO4)2) were favorable for furfural compound formation through the hydrolysis–dehydration process. A total furfural compound yield of 34% was obtained under optimal conditions with the aid of NaH2PO4, accompanied by 16% solid residue formation. The solid residue containing dihydric phosphates could be used as phosphatic fertilizer.