Study On The Isolation Of Poplar Lignin By Deep Eutectic Solvent Pretreatment

Within the framework of green chemistry,solvents occupy a strategic place.Deep Eutectic Solvent(DES)is discovered as a noval green solvent.It has been widely used in electrochemical,biotransformation and other fields.This topic aims to study the solubility of DES with different compositions and ratios on lignocellulose.Through the configuration of various DES,the conductivity,viscosity and other properties were analyzed.The influence of the ratio and temperature on the dissolution performance of lignocellulose was studied.The dissolution and separation mechanism of lignocellulose in the DES system was explored.The method of separation of three components(cellulose,lignin,and hemicellulose)of poplar wood powder under atmospheric pressure and the separation of lignin from poplar wood chips under high pressure conditions were proposed.The chemical degradation and spectroscopy method characterizes the structural properties of the separated lignin.The paper also contains the application of cellulose separated by DES.The main findings of the paper are as follows:1)This paper prepares several common DES such as urea/choline chloride,lactic acid/choline chloride,acetamide/choline chloride,etc.,and studies its state and melting point at room temperature,and physical properties such as viscosity and conductivity at 50 ~oC.By comparing and analyzing the solubility of different DES systems on poplar wood powder,the study showed that the dissolution effect of lactic acid/choline chloride(LA/ChCl)was stronger than that of the other DES solvents.The dissolution rate of poplar wood powder exceeded 50%.The LA/ChCl not only has a strong solubility for poplar wood powder,but also has a good dissolution effect on pine powder and wheat straw powder.The dissolution rate can reach about 50%,indicating that LA/ChCl DES has good solubility for lignocellulosic materials.2)In this thesis,the dissolution properties of LA/ChCl under different pressures,temperature and time on poplar wood powder were studied systematically.The results have shown that the optimum process conditions:LA/ChCl molar ratio of 9:1,temperature of 120°C,and time of 6 h.The dissolution rates of hemicellulose and lignin were 97%and 95%,respectively,while cellulose was essentially insoluble,and achieved the separation of the three components on wood.The analysis showed that the crystalline structure of cellulose did not change,and the purity of DES separation lignin reached more than 95%.Infrared spectroscopy analysis of DES lignin showed that the structure of lignin changed after dissolution by LA/ChCl DES.The yield of DES lignin after nitrobenzene oxidation was significantly lower than that of the original lignin.A large number of non-condensed parts of lignin were degraded.Nuclear magnetic resonance analysis showed that theβ-O-4 ether bond in DES lignin was destroyed.The molecular weight distribution of lignin was regenerated by gel chromatography,and the molecular weight of lignin was significantly reduced.3)Based on LA/ChCl DES to selectively dissolve lignin in poplar wood powder,the paper continued to study the selective dissolution and separation of lignin from poplar wood chips by LA/ChCl DES cooking(high pressure).The paper also analyzed effect of high-efficiency separation of lignin from poplar wood chips under different cooking temperatures and cooking time.The removal of 78.3%of lignin in poplar wood chips was successfully achieved at a holding temperature of 150°C and a holding time of 3 h.The purity of lignin was more than 95%that at a holding temperature of 140°C and a holding time of 1.5 h.NMR analysis showed that theβ-O-4ether bond in lignin was destroyed,and the results were similar to those under normal pressure,but the result was more serious with the increase of temperature,indicating DES cooking is not only the dissolution of lignin,but also causes the degradation of lignin.4)The paper is based on LA/ChCl DES cooking to achieve the pulping of poplar wood chips(fiber separation).The yield of the poplar wood chips by DES at the holding temperature of 140°C and the holding time of 1.5 h is 48.8.%,the Kappa number of pulp was 35.5,and the cellulose polymerization was 1100.XRD analysis showed that the crystal structure of the pulp did not change.The bleached pulp was subjected to a papermaking process,and the formed paper had good physical properties.