Hydrolysis of Regenerated Cellulose from Ionic Liquids and Deep Eutectic Solvent over Sulfonated Carbon Catalysts

Abstract

The efficient hydrolysis of cellulose into its monomer unit such as glucose or valuable cello-oligosaccharides is the critical step for the cost-effective production of biofuels and biochemicals. However, the current cellulose hydrolysis process involves high energy-demanding pretreatment (e.g., ball-milling) and long reaction times (>24h). Herein, we investigated the feasibility of the dissolution/regeneration (DR) of cellulose in ionic liquids (ILs) and deep eutectic solvent (DES) as an alternative to ball-milling pretreatment for the effective hydrolysis of cellulose. Because chlorine-based solvents are reported to be most active for biomass pretreatment, [EMIM]Cl and [DMIM]DMP were selected as the IL molecules, and choline chloride-lactic acid was selected as the DES molecule. The level of the crystallinity reduction of the regenerated cellulose were analyzed by the XRD and SEM measurements. The hydrolysis kinetics of the regenerated cellulose from ILs and DES were examined at 150 °C using sulfonated carbon catalysts and compared with the ball-milled cellulose. Overall, the cellulose pretreatment using the ILs and the DES had similar or superior kinetics for cellulose hydrolysis to the conventional ball milling treatment, suggesting a possibility to replace the current high energy-demanding ball-milling process with the energy-saving DR process. In addition, the utilization of supercritical carbon dioxide-induced carbonic acid as an in-situ acid catalyst for the enhanced hydrolysis of cellulose was presented for the first time.