| With the depletion of fossil resources and the increasingly severe environmental problems,the research that converting lignocellulosic biomass into biofuels and high value-added chemicals have attracted extensive interests.Due to the complex structure of lignocellulosic biomass,developing an efficient,“green” and industrial-feasible pretreatment process is crucial.Deep eutectic solvent(DES)is promising for biorefiney because of their low cost,low toxicity,biodegradability,tunability of the properties and easy recyclability.Firstly,this work studied the relationship between the properties of different DESs and their corresponding pretreatment efficiency.By using a series of DESs with fixed choline chloride or lactic acid as hydrogen bond acceptor(HBA),polyols,monocarboxylic acids and dicarboxylic acids as hydrogen bond donor(HBD)for rice straw pretreatment,both HBD and HBA exhibited important influence on the pretreatment efficiency of DESs.The DESs containing more hydroxyl groups and amino groups shows weak biomass deconstruction ability because of the strong inter-molecular hydrogen bonding effect within solvent.The presence of strong electron-withdrawing groups in the DESs improved the pretreatment efficiency of DESs.In addition,the results suggest that the removal rate of xylan is negatively correlated with the pKa value of HBD,and increasing temperature is beneficial to rice straw deconstruction in most of the DESs;the cellulose biodigestibility is positively correlated with xylan removal,and rice staw pretreatment with strongly acidic DESs could remove a large amount of xylan,thus resulting in excellent cellulose biodigestibilities.The relationship between structure and function of DESs in biomass deconstruction established in this work can provide beneficial information for developing new DESs in this field.The effect of HBA/HBD molar ratio on the deconstruction,transformation and the subsequent enzymatic hydrolysis of the biomass was studied in lactic acid-choline chloride(LC)system.The results show that cellulose riched materials(CRMs),ligninriched materials(LRMs),and hemicellulose riched materials(HRMs)can be easily obtained from the pretreatment mixture after experiencing a simple separation,followed with ethanol and water fractionation.Increasing the HBD/HBA molar ratio of pretreatment can increase the removal of xylan and lignin and obtain higher purity of the biomass components.When the pretreatment was conducted at 120 ° C by using LC 3:1and LC 5:1 as solvents,more than 70% of the lignin and xylan can be removed,the high purity(>85%)of lignin in LRMs was achieved.A comparison study between LC and its corresponding lactic acid solution proves that both HBA choline chloride and HBD lactic acid have a non-negligible effect on biomass fractionation.Additionally,LC can be reused and achieved a high recovery rate(90%).After 5 cycles,high glucose yields(60-70%)were reached due to a high stability of DES.This study gives further understanding of the structure and function relationship of DESs in biomass fractionation,reveals the role of HBD and HBA in lignin and hemicellulose removal,and helps to design a new solvent system for better biorefinery,which laies the theoretical foundation for achieving efficient biomass fractionation and further conversion of its major components. |
