Modification And Application Of Coal Based Mesophase Pitch Blended With Biomass Tar Pitch

China is rich in coal resources.The output of coal tar from coal liquefaction is very high.Coal tar pitch（CTP）is the residual liquid after tar distillation,in addition to the preparation of metallurgical industry anode and carbon products,it can be prepared coal based mesophase pitch and carbon materials.However,because of the high C/H atomic ratio,the high quinoline insoluble（QI）and nitrogen and sulfur heteroatoms in coal tar pitch,it is necessary to be refined and modified to be used as raw materials for the preparation of high quality mesophase pitch and carbon materials.Biomass tar pitch（BTP）is a distillation product of biomass tar,which has low carbon atom content,high hydrogen atom content,low nitrogen and sulfur atom content,and high light component content.The composition of coal tar pitch can be changed by adding BTP to coal tar pitch.In the co-carbonization process,BTP can provide more hydrogen ions and reduce the content of heteroatom.By hydrogen dissolution and transfer to form more alkyl side chains or cycloalkanes,reducing the viscosity of the system.In other words,BTP may help overcome the defect of low hydrogen content in CTP and introduce naphthenic and aliphatic side chain structure.In addition,the lower contents of heteroatoms and QI in BTP are also favorable to generate high-quality mesophase pitch.This paper has used theoretical knowledge of physical chemistry,solvent extraction and liquid phase carbonization theory to study the possibility,method and mechanism of using BTP to modify CTP to modulate mesophase pitch structure.The structure change of the mesophase pitch prepared by co-carbonization after CTP and BTP mixed refining was studied,and the mixing and modification mechanism of BTP was explored.On this basis,the structure and properties of the carbon materials prepared by the mixed mesophase pitch were studied.The main research work of this thesis:The mixture of CTP and BTP pitch was used as raw material,the process technology of refining pitch by pressure solvent method was proposed.The content and yield of QI of refined pitch under different pressures were tested.The morphology,particle size and viscosity of the removal system were characterized and measured by nano particle size analyzer,scanning electron microscope and high temperature viscosity tester.The effect of pressure on flocculation and sedimentation of solid particles was studied.High quality mesophase pitch was prepared by co-carbonization with refined mixed pitch.The structure and properties of the mesophases pitch prepared under different BTP addition ratios,temperature and pressure were characterized by thermogravimetric analysis,infrared spectroscopy,¹H-NMR and polarizing microscopy.The relationship between sample mass change and carbonization temperature and pressure,the proportion of modified substance,the formation mechanism of mesophase and the kinetics of mesophase carbonization reaction were studied.Using mesophase pitch as raw material to prepare mesophase pitch needle coke,using polarizing microscope,scanning electron microscope to observe the microstructure of the needle coke prepared by different BTP addition ratio,coking temperature and coking pressure,testing the thermal expansion coefficient and true density of the needle coke.Mesophase carbon microspheres were prepared from mixed pitch of CTP and BTP by carbonization.The microstructure of mesophase carbon microspheres prepared with different BTP addition ratio,carbonization temperature and carbonization time were observed by polarizing microscope.The morphology and structure characteristics of carbon microspheres were determined by X-ray diffraction,Raman spectroscopy and laser particle size analysis.The main conclusions of this thesis are:（1）Mixed pitch with biomass pitch could effectively remove the QI from the raw pitch using the pressurized solvent method.Under the same temperature conditions,increasing system pressure could significantly increase the refined pitch yield.Pressure had little effect on QI content of refined pitch.As the pressure increased,the solvent’s ability to dissolve pitch components,especially heavy components increased,which increased the yield of refined pitch.Higher pressure also slightly increased the viscosity of the system,which made it difficult for some QI particles to settle.（2）Using BTP and CTP mixed pitch as raw materials,100%mesophase pitch could be produced through high temperature and high pressure liquid phase carbonization,and the anisotropic area completely presented a wide-area streamlined structure.The raw material pitch modified by BTP could form a mesophase pitch with better optical structure.The addition ratio of BTP was 15%,which had the best effect.The addition of biomass pitch increased the H/C atomic ratio and oxygen content of the mixed refined pitch,decreased the S and N content,and decreased the softening point and viscosity.Biomass pitch was rich in alkyl and cycloalkyl functional groups.A large nμmber of smaller molecular species generated during the pyrolysis process help reduced the softening point and viscosity of the mesophase pitch.During the carbonization process,the hydrogen transfer reaction could maintain a low viscosity and extend the polymerization time.Through the study of thermal decomposition kinetics,the activation energy of the refined mixed pitch modified with biomass pitch was reduced from 91.27 to 62.84 k J/mol.The overall reaction activity after the modified and refined mixed pitch was improved;the carbonization reaction speed was slow,which was conducive to the growth and coalescence of mesophase.（3）The mesophase pitch prepared by BTP modified CTP was beneficial to the preparation of high performance needle coke.Due to the adequate mixing and rearrangement of large planar aromatic hydrocarbon molecules at the appropriate viscosity during heat treatment,the more tightly arranged unidirectional needle bundle structure was more developed.Therefore,the CTE value decreased from 1.54×10^-6/^oC to 0.96×10^-6/^oC.The crosslinking reaction between free radicals caused by oxygen-containing functional groups in BTP would result in the formation of more condensed macromolecules,which would lead to the increase of coking yield.Under the carbonization temperature of 490 ^oC,carbonization pressure of 0.2 MPa and reaction time of 6 h,the best properties of needle coke were prepared with 15%BTP.（4）Mesophase carbon microspheres were prepared with mixed pitch of CTP and BTP as raw materials.For the mesophase carbon microspheres prepared at 410 ^oC for 7h,the addition of BTP significantly increased the yield of mesophase carbon microspheres,which was mainly because BTP provided additional nucleation domain for the formation of carbon microspheres,thus prolonged the formation of mesophase in the pyrolysis process.Pyrolysis conditions also had a great influence on the morphology and yield of mesophase carbon microspheres.When BTP-CTP mixture was at 410 ^oC,the particle size of mesophase-carbon microspheres prepared increases with the increase of carbonization time.When the carbonization time exceeded 8 h,the MCMB began to merge with each other.When the carbonization time was 7 h,the yield of mesophasic carbon microspheres was the highest,the yield of MCMB-15 was42.8 wt.%,and the average particle size was 12.31μm.Compared with the mesophase carbon microspheres prepared by CTP,the mesophase carbon microspheres prepared by CTP and BTP mixed pitch has larger layer spacing and more defect sites.