Effect of salt addition on cellulose conversion into 5-hydroxymethylfurfural in metal chloride aqueous solution

Metal chloride aqueous solution is an effective method to promote the conversion of cellulose into 5-hydroxymethylfurfural (HMF). In this work, the influences of sodium chloride (NaCl) and lithium chloride (LiCl) on the conversion of cellulose into HMF in ferric chloride (FeCl3) aqueous solution were investigated. The conversion of glucose and fructose in FeCl3-NaCl and FeCl3-LiCl aqueous solutions were studied, and the interaction between active species and cellobiose was characterized by UV spectrum and electrospray ion mass spectrometry to explore salt addition on the reaction of cellulose conversion and the active specie. Results showed that the yield of HMF converted from cellulose in FeCl3 aqueous solution was low, while the yield of HMF was significantly increased when NaCl or LiCl added to the system. In FeCl3-NaCl aqueous solutions, the yield of HMF reach a maximum of 40.0% at a concentration of 0.02 M FeCl3, and hydrolysis of cellulose was the key step in the conversion of cellulose; In FeCl3-LiCl aqueous solutions, the yield of HMF reach a maximum of 36.7% at a concentration of 0.06 M FeCl3, and isomerization of glucose was the controlling step. The characterization results illustrated that the addition of NaCl or LiCl changed the active species in FeCl3 aqueous solutions, and [Fe (OH)2]+ and [FeCl2(OH) + Li]+ were the active species in FeCl3-NaCl and FeCl3-LiCl aqueous solution for cellulose conversion, respectively.