Direct degradation of cellulose to 5-hydroxymethylfurfural in hot compressed steam with inorganic acidic salts

Abstract

A novel method of direct degradation of cellulose into 5-hydroymethylfurfural (HMF) in hot compressed steam was introduced, with the inorganic acidic salts (NaHSO₄, KHSO₄, NaH₂PO₄ and KH₂PO₄) as catalysts. The water molecules in the steam were absorbed by the catalysts to form an acidic aqueous layer on the surface of the cellulose, where the cellulose was converted into HMF and spread into the gas phase. The relative humidity of steam could influence the reaction route by controlling the acidity of the aqueous layer. Low relative humidity of steam was favoured for the carbonization of cellulose, while high relative humidity was preferred for hydrolysis-dehydration of cellulose to form HMF. A moderate HMF yield of 30.4 mol% was obtained with NaH₂PO₄ as the catalyst. This novel methodology demonstrated an efficient and green HMF production from cellulose, without organic solvents and toxic transition metal cations.