Treatment Of Lignin With Imidazolium Acetate Ionic Liquid Aqueous Solution

Lignocellulosic biomass,as an important renewable source,is mainly composed of cellulose,lignin and hemicellulose.Lignin is the only natural polymer with aromatic structure in nature.Its development and utilization is promising.Delignification using "ionic solvent"have attracted comprehensive attention,which is characterized by the environmental-friendly solvent—ionic liquid as the treatment system and the selective dissolution of lignin.The studies of the variation of lignin structure are very important for understanding the treatment with "ionic solvent".Thus,in this work,the treatment with imidazolium acetate ionic liquid was carried out with the enzymatic-hydrolysis-lignin as the feedstock.Effects of cation type,ionic liquid content and pH value of solutions on lignin recovery and chemical structure were fully investigated,and the mechanism of lignin treatment with ionic liquid aqueous solutions was discussed.Based on the experimental results,the following conclusions can be obtained:1)Type of cation,ionic liquid content,basicity of ionic liquid and pH value of solutions greatly influenced the treatment process and the structure of regenerated lignin;2)During the lignin treatment with imidazolium acetate aqueous solutions,molecular weight of the recovered lignin decreased,and its distribution became narrow.The minimum molecular weight and distribution of the recovered lignin(PDI=5.01-9.62)can be obtained in the case of the treatment with 1-ethyl-3-methylimidazolium acetate([C2mim]OAc,50%-90%content)aqueous solutions;3)In comparison with that with the pure ionic liquid,the recovery of regenerated lignin was higher with treatment of enzymatic-hydrolysis-lignin using imidazolium-based ionic liquid aqueous solutions.And,the influences of treatment with ionic liquid aqueous solutions on the destruction of the bonds in lignin and chemical structure of the regenerated lignin were obvious different from the treatment with the pure ionic liquid,suggesting that the treatment with ionic liquid aqueous solutions followed the different mechanisms.4)The molecular weight of the recovered lignin increased and its distribution became wide(PDI=514.47-31.84)with the treatment using choline acetate([OHEN1,1,1]OAc)of low pH value,and there was little influence of adding water on the recovery of regenerated lignin.It indicating that type of cation affected the treatment of lignin.