Study On The Process Of Catalytic Preparation Of C6 Sugars From Cellulose By Easy Recovery Acid Catalyst In Mixed Solvent System

Hydrolysis of cellulose into C6 sugars is the key and rate-limiting step in bioethanol production.The traditional inorganic acid catalyzed cellulose hydrolysis has many problems,such as large corrosion,difficult separation of sugar and acid,low sugar yield and high cost.In view of this,this study developed a gamma-valerolactone/water(GVL/H₂O)two-phase solvent system to realize the reuse of acid catalyst and the reduction of system cost in the process of efficient hydrolysis of cellulose to hexarbon sugar.Solid lignosulfonate acid was prepared by condensation-hydrothermal carbonization and high-temperature pyrolysis carbonization with cheap lignosulfonate as carrier.The results showed that the prepared SLS-based solid acids were of amorphous carbon structure and contained acidic functional groups(-OH,-COOH and-SO₃H),with certain catalytic activity.However,the catalytic activity of solid acid(C-PSA)prepared by phosphoric acid activation-pyrolysis is more excellent.In the solvent system of GVL/H₂O(80/20),the C6 sugar yield can reach 50.5%at 205?for 5min.FT-IR,XRD,BET,NH₃-TPD and SEM indicated that C-PSA had a larger specific surface area and higher acidity(0.536 mmol/g),and phosphoric acid activation promoted the formation of C-PSA mesoporous structure(pore diameter:3.062nm).The C6 sugar selectivity of GVL/H₂O(80/20)dual-phase system was more excellent.At the optimal temperature of 200?,the C6 sugars selectivity was up to 57%,which was higher than that of the pure water solvent system.Since the solid-solid mass transfer rate of solid acid and cellulose is limited,the process of combining 2,5-Furandicarboxylic acid(FDCA)with GVL/H₂O two-phase solvent system is proposed:The results showed that the highest C6 sugar yield was 72.9%(glucose 40.1%,fructose 32.8%)after reaction at 200?for 30 min in GVL/H₂O(60/40)solvent system.XRD of cellulose residue shows that FDCA can effectively reduce the crystallinity of cellulose during hydrolysis.After recycling,80%of FDCA crystals can be reused,and the recovered crystal purity can reach 100%.On the basis of efficient hydrolysis of cellulose,the process of cellulose hydrolysis combined with solid acid and double solvent can realize the goal of high value and sustainable utilization of biomass.