The Product Evolution Of Lignin Pyrolysis Catalyzed By Ionic Liquid At Low Temperature

As the scale of industrial development continues to expand,the exploitation and application of fossil fuels continue to increase,due to the growth cycle of fossil fuels of hundreds of millions of years,excessive exploitation of fossil fuels will cause mankind to face the problem of fossil energy exhaustion within a few hundred years.In addition,the burning of fossil fuels intensifies the carbon cycle in the earth’s environment,and the destruction of earth’s vegetation leads to the accumulation of CO₂ and other substances in the atmosphere,which further gives rise to the intensification of the greenhouse effect,the melting of polar glaciers,and the rise of sea level.Therefore,the development and utilization of clean energy is particularly significant.In recent years,some of the energy problems have been alleviated by the construction of hydropower,wind power,tidal power,photovoltaic power,nuclear power and other facilities,but that is not nearly enough.High demand for energy and increasing environmental requirements make all walks of life need to come up with ideas together to break through technical problems.Biomass refers to a variety of organisms formed through photosynthesis,and is the fourth largest energy source after coal,oil and natural gas.Biomass has huge reserves,which is the link between inorganic environment and organic environment.It is of great significance to study the energy-oriented application of biomass owing to the large reserves and wide sources.Lignocellulose is an important part of biomass.Lignocellulosic biomass is mainly composed of three major components of cellulose,hemicellulose and lignin,of which cellulose content is as high as 40-80%,hemicellulose is followed by 15-30%,lignin is 10-25%,and there is a big difference between the constituent units and composition structure of the three,it is necessary to analyze the three components separately.In the study of biomass energy,thermochemical conversion method is popoular for its high efficiency and high conversion rate,but it also has the drawback of high energy consumption,so it is urgent to develop appropriate catalysts to reduce energy consumption.Room temperature ionic liquids are in a liquid state at room temperature or near room temperature,with good ionic conductivity and thermal conductivity,high thermal stability,selective dissolving power and designability,providing a new idea for lignocellulose pyrolysis technology.In this paper,the experimental and computational research on the mechanism of low temperature catalytic lignin cracking of ionic liquids is carried out,and three mechanisms of catalytic cracking of lignin by ionic liquids are obtained:temperature gradient zoning regulation mechanism,catalyst activity selective regulation mechanism and electrochemical regulation mechanism.The main research results of this paper are as follows:（1）With reference to related literature,the design and synthesis of[Hmim]Br,[Hmim]Cl,[Hmim]PF₆,[Hmim]BF₄,[Hmim]Tf₂N,[Hmim]CuCl₂,[Hmim]FeCl₄ were carried out.Through the thermal stability analysis of ionic liquids,two functional ionic liquids[Hmim]Tf₂N and[Hmim]FeCl₄ with excellent performance were selected for subsequent lignin cracking experiments.And the characterization analysis was carried out.（2）Through the experimental study of[Hmim]FeCl₄ and[Hmim]Tf₂N ionic liquids on the temperature gradient cracking of lignin,it was found that[Hmim]FeCl₄ has stronger catalytic performance,However,the products of[Hmim]Tf₂N catalytic cracking had more types and wider temperature zoning,and specific products were generated at each temperature gradient.In particular,there is a clear division between the typical products vanillin and guaiacol,vanillin is generated at200～260℃,guaiacol is produced at 260～320℃.（3）The results show that vanillin is generated at 1～3V voltage interval and guaiacol is generated at 1～5V voltage interval by electrochemical enhanced ionic liquid[Hmim]Tf₂N at low temperature catalytic lignin cracking experiment at 230℃.By comparing the GC-MS data of the two,it was found that in the comparison of peak area,vananthine reached its maximum at 3V and guaiacol reached its maximum at 4V,therefore,the structure of the product could be regulated by voltage.（4）β-O-4 type lignin dimer was used to study the regulation mechanism of lignin cracking by quantum chemical calculation.By calculating the bond lengths and bond energies of Cα-Cβ,C1-Cαandβ-O-4 bonds,it is found that the experimental results are consistent with the calculated results,so it is feasible to regulate the temperature gradient in different regions.Through structural optimization of ligands of active groups in lignin-ionic liquid,the results showed that[Hmim]FeCl₄had a stronger catalytic effect,which was consistent with the experimental results.It is found that the calculation results with the experimental results through to speculate that the reaction path calculation,the reasons were analyzed for the difference between the ideal reaction conditions and the actual conditions,and the electrochemical oxidation of guaiacol to produce vanillin made the yield of vanillin increase significantly under electrochemical control,which assisted to prove the feasibility of electrochemical control.