Study On The Preparation And Growth Mechanism Of Petroleum Pitch-Based Carbonaceous Mesophase

Mesophase pitch is a thermotropic liquid crystal structure formed by stacking plenty of aromatic molecular sheets.Because of the easy graphitization,it is the precursor material of many high-performance carbon materials.Also,due to its wide range of sources and low price,petroleum pitch has always been an important raw material for preparing mesophase pitch.Since the composition of petroleum pitch is extremely complex,researches on its structure and properties,and its influence on the formation of mesophase pitch,have always been the focus of research in this field.This thesis has separated Petroleum pitch into different groups according to different solubility,aiming to analyze the components and explore the main composition structure of each group composition.The composition of each group was mixed in different proportions for comparative experiments,and the influence of each component on the development of mesophase pitch was compared and analyzed,and the role of each composition in the formation of mesophase was visually revealed.The mesophase pitch was prepared with petroleum pitch as a raw material.The growth process of the mesophase as well as the influence of polymerization time and decompression time on mesophase pitch were studied;and tetralin was used as hydrogenation agent to adjust the structure and properties of mesophase.The main findings of this paper are as follows:1.By using n-heptane,toluene,pyridine and quinoline to separate petroleum pitch into n-heptane solubles(HS),n-heptane insoluble-toluene solubles(HI-TS),toluene insoluble-pyridine solubles(TI-PS),pyridine insoluble matter(PI),it is found that the content of each group composition in petroleum pitch accounts for 12.29%,79.44%,5.59%,and 2.68%respectively,and the content of quinoline insoluble(QI)is almost zero.2.The chemical reactivity of each group composition and the ability to develop mesophase were compared,then they were mixed in proportions to examine their ability to form mesophase.HS does not have the ability to form an intermediate phase at 400-430℃.Its main function might be reducing the viscosity of the reaction system and providing convenient conditions for the flow of other fused ring aromatics.HI-TS is the core component that forms mesophase pitch and can independently generate mesophase pitch.TI-PS allows mesophase pitch to have a larger sheet size.PI could affect the development process of the mesophase and cause the intermittent growth of mesophase pitch,resulting in the mesophase pitch generated later tends to form an inlaid structure.3.Petroleum pitch and its various group components were used as raw materials;and the mesophase pitch was prepared by static atmospheric pressure method.The effect of reaction time on the product was studied.After the reaction time exceeds 8 h,the mesophase content is very high,and the soft point is also greatly increased.When the reaction time reaches 12 h,the mesophase content of the product is about 100%,but the soft point could reach more than 400℃.The comparison results show that after the bulk mesophase pitch grows to a certain scale,there are still plenty of isotropic phases.When the mesophase content is close to 100%,the mesophase could be excessively polycondensed,and then soft point could be raised.The sharp increase in viscosity could affect the subsequent development of mesophase pitch,making it easy to form an inlaid structure.4.Petroleum pitch as the raw material,the mesophase pitch is prepared by the pressure-decompression two-stage thermal polycondensation method.The effect of decompression time on the product was studied.Through optimization of conditions,under the conditions that the pressure in the pressurization section is 2 MPa,the pressurization period is 2 h,and the decompression period is 4 h,the mesophase content of the obtained product is close to 100%,and the soft point can reach 300℃.The mesophase structure presents a densely packed fine fiber shape.5.Tetralin as hydrogenation agent was used to adjust the structure and properties of mesophase pitch.The mesophase pitch with domain-like structure was prepared under the conditions that the pressure in the pressurization section was 2 MPa,the pressurization period was 2 h,the decompression period was 4 h,and the hydrogenation agent content was 5-15%.The soft point was all less than 280℃.It shows that the introduction of hydrogenation agent successfully lowered the soft point of mesophase pitch,and changed its texture morphology,which transformed it from a mosaic structure to a wide-area structure.