Research For Preparation And Properties Of Mesophase Pitch Based On Coal Tar Pitch

In China,there is such a huge amount of coal tar reserves,so that the production of coal tar pitch as a primary carrier for carbon materials is also extremely rich.It is of great significance to the development of carbon materials if we can bring into play the excellent performance of coal tar pitch.Among all the researches on coal tar pitch,the study on mesophase pitch had been a popular subject.Mesophase pitch,a coal tar production with high utilization rate,is often used as a precursor to create high performance carbon materials.Therefore,in order to obtain a better quality downstream products,the study on preparation and properties of mesophase pitch is also of great importance.In this paper,modified coal tar pitch was chosen as an experimental raw material,and the mesophase pitch was successfully prepared by thermal polymerization method.Then,the properties of polymerization products in different reaction conditions were studied systematically.And then,the proper preparation condition of mesophase pitch were determined due to the former analysis.Furthermore,the kinetics of modified coal tar pitch pyrolysis and getting mesophase pitch from CTP01 was also analyzed.The following are the main results.Firstly,the modified coal tar pitch named CTP01 and CTP02 were chosen as research object.The chemical composition and relative properties of the two raw materials were characterized by infrared spectrometer?FTIR?,elemental analyzer?EA?and thermogravimetric analyzer?TGA?,then related physical parameters were also analyzed by softening point tester and solvent extraction methods.All results showed that both materials can be selected as raw materials for the preparation of mesohpase pitch,because they both contain polycyclic aromatic hydrocarbons,aliphatic compounds and a high hydrogen/carbon ratio.However,when compared to CTP02,CTP01 had an obviously advantage to the formation of mesophase pitch due to its lower softening point,lower ash content,lower coking value and better filudity.Therefore,CTP01 was utilized as a raw material to prepare mesophase pitch in next research.Moreover,based on TGA analysis,the preparation temperature of mesophase pitch was determined during 350?⁵00?.Secondly,mesophase pitch was prepared by CTP01 through direct thermal polycondensation method.We selected reaction temperature and constant time as two main control parameters to analyze the products obtained under different conditions,so as to determine whether mesophase pitch was generated.First,FTIR showed that in an appropriate range,the higher heat temperature and the longer constant time,the more favorable polymerization reaction occurred between the aromatic rings.Then,the morphology of products at each stage were revealed by polarizing microscopy?PM?and scanning electron microscopy?SEM?.And the results showed that the formation of mesophase pitch had three steps,which contained formation of small spheres,growth of small spheres and fusion of small spheres.And then,X-ray diffraction?XRD?showed that the structure of CTP01 had some changes after heat treatment,the internal large aromatic molecules packed more closely than CTP01,the products had been initially carbonized and the graphite-like structure had already appeared.At last,under autogenous pressure,as reaction temperature was 420?,reaction time was 5 h and stirring rate was 100 r·min^-1,the mesophase pitch was successfully prepared by CTP01.The product in this condition was a mesophase pitch with a wide-range structure,which softening point was over 300?,yield coefficient was 72.17%,toluene insoluble?TI?was 94.82%and quinoline insoluble?QI?was93.17%,respectively.Finally,in order to determine the pyrolysis mechanism of CTP01 and CTP02,three kinetic models,Coats-Redfern model,DAEM model and Flynn-Wall-Ozawa model,were utilized to analyze the pyrolysis kinetics of raw coal tar pitch.The results showed that at three heating rate(5 K·min^-1,10 K·min^-11 and 20 K·min^-1),the two kinds of pitch were in line with the first-order function equation f?X?=-ln?1-X?under Coats-Redfern model.Then,from DAEM model,the activation energy E enhanced with the increasing of conversion rate X.Since X=0.4,the pyrolysis reactions of two materials had entered into thermal polymerization stage,the strengthening trend of activation energy was more significant and CTP02 fitted well with this model.At the same time,the average activation energy can be calculated by Flynn-Wall-Ozawa model,CTP01 was 103.38 kJ·mol^-1,and CTP02 was 95.84 kJ·mol^-1.CTP01 accorded well with this model and the change trend of activation energy E and conversion rate X was consistent with that in DAEM model.Furthermore,the kinetics of heat treatment process for getting mesophase pitch from CTP01 was also discussed.The results showed that the formation of this mesophase pitch confirmed to the first-order reaction kinetics.