Study On Rheology Of Imidazolium Ionic Liquid-lignin-aqueous Solution

As a renewable resource,lignocellulosic biomass has a wide distribution,high content and other characteristics,mainly composed of cellulose,lignin and hemicellulose.The use of aqueous ionic liquids to pretreat lignocellulosic biomass?Ionosolv process?has received extensive attention from researchers at home and abroad in recent years.The method is characterized by the selective dissolution and separation of lignin.By studying the rheological properties of ionic liquid-lignin-water solution and analyzing the nano-microstructure of lignin macromolecules in aqueous solution of ionic liquids,it is helpful to understand the dissolution process of lignin,thus to further optimize and design the aqueous pretreatment process of ionic liquid.Based on this,this work used enzymatic hydrolysis lignin?EHL?and alkali lignin?AL?as raw materials,using a rotational viscometer to investigate the flow of lignin-1-butyl-3-methylimidazolium chloride?[C₄C₁im]Cl?-water solution,to investigate the effect of factors such as lignin concentration,shear rate and temperature on solution flow and macromolecular chain configuration.It was found that factors such as lignin concentration,shear rate,molecular weight and temperature could affect the viscosity of lignin-[C₄C₁im]Cl-water solution;with the increase of lignin concentration,the viscosity of lignin-[C₄C₁im]Cl-water solution increased,and in the high concentration area,the viscosity increased greatly.When the dilute solution area rises to the sub-concentrate solution area,there is a lignin macromolecule overlap concentration?c*?,and with the change of temperature and[C₄C₁im]Cl content,c*also changes;when the temperature rises,c*increases;while the lignin concentration increases,the overlapping concentration c*decreases,which is related to molecular chain motion and molecular chain density.For different types of lignin,the molecular weight affects the viscosity of the solution.The molecular chain is long and complex for the large molecular weight,and the solution tangles to form segments,which is not conducive to fluid flow,and the viscosity increases in the macroscopic performance.For the different lignin-[C₄C₁im]Cl-water solutions,the shear rate has a significant effect on the viscosity of the solution.Using the power law equation to calculate the non-Newtonian index n,it was found that these lignin-[C₄C₁im]Cl-water solutions all have shear thinning characteristics,indicating that the lignin macromolecular chains in the solution move with the fluid orientation and disentangling phenomenon occurs.The study also found that the viscosity of the lignin-[C₄C₁im]Cl-aqueous solution decreases to varying degrees when the temperature is increased.The Arrhenius equation was used to fit the curve,and the Inn and 1/T curves were plotted to obtain the corresponding viscous activation energy E_?.The results showed that the enzymatic hydrolysis lignin-[C₄C₁im]Cl-water had a higher E_?than that of alkali lignin-[C₄C₁im]Cl-water solution,indicating that the viscosity-temperature sensitivity of enzymatic hydrolysis lignin-[C₄C₁im]Cl-water solution was better.