Abstract:In order to explore the mechanism of deep eutectic solvents (DESs) pretreatment of lignocellulosic biomass, seven DESs with choline chloride (ChCl) as hydrogen bond acceptor (HBA) and seven DESs with ethanolamine compounds as hydrogen bond donor (HBD) were employed to pretreat wheat straw. Their physical and chemical properties were measured, and the effects of different DES on the components and enzymatic hydrolysis efficiency of biomass were studied. The results indicated that the viscosity of DES was between 0.04~1.37 Pa·s, the conductivity was 0.29~3.57 ms/cm, and the pH of 5 mM DES was between 7.41~11.02 at 30 ℃; it was effective for lignin and xylan. The solubility of DES was as high as 425 mg/g and 523 mg/g at 90 ℃, and it was almost insoluble to cellulose. After these DES pretreatments, the enzymatic hydrolysis efficiency of polysaccharides in wheat straw was significantly improved, and the pretreatment effect depended on the pH value. Among them, [Choline chloride]: [ethylenediamine] was the most suitable solvent for pretreatment of wheat straw. After 4 h of pretreatment at 90 ℃, the removal rate of lignin was 83.14% and the yield of reducing sugar was 93.88%. A large amount of lignin and part of xylan were selectively removed from wheat straw without changing the crystal structure of cellulose, and the efficiency of subsequent enzymatic hydrolysis was significantly improved. It found that this type of DES is good for grass biomass and eucalyptus. After the pretreatment, the sugar yield was obviously improved (57.10~98.13%), but it was not effective for pine. This work would provide a theoretical basis for rational design novel DESs for biomass pretreatment.
