Study On Molecular Structure Regulation And Properties Of Mesophase Pitch By Durene-Oligomer

In recent years,with the continuous development of coal and petrochemical industries,China has become a major producer and exporter of related products,while the production of by-products such as coal and petroleum pitch is also increasing year by year.Pitch is a mixture of aromatic-rich molecules that can be used to prepare high value-added mesophase pitch.Mesophase pitch has the advantages of high flatness,good spinnability,high yield and easy graphitization,which is an indispensable quality precursor for the preparation of high performance carbon materials.Mesophase pitch-based carbon fiber,foam carbon,carbon microspheres and other high-performance carbon materials are widely used in aerospace,military defense and new energy fields.However,the preparation technology of high-quality mesophase pitch is monopolized by a few developed countries,and a strict product embargo is imposed,making China’s high-end equipment manufacturing industry severely restricted.Therefore,it is of great strategic importance to investigate the production technology for the preparation of high quality mesophase pitch,and to study the modification of mesophase pitch and the related mechanism of its molecular regulation.In this study,the effect of Durene oligomer(DO)on the formation process of coal-based mesophase pitch was investigated by using refined coal tar pitch as raw material and different levels of DO as co-carbonization agent,and the mechanism of molecular modification of mesophase pitch by DO was proposed.The basic process conditions for the preparation of high-performance mesophase pitch were obtained by molecular design and experiments,and the resulting products were analyzed for polarization,softening point,family composition and spinnability.The basic process parameters for the preparation of coal-based mesophase pitch were investigated,and better basic process parameters were obtained by investigating the effects of thermal polycondensation temperature,holding time and system pressure on the mesophase pitch preparation process.The results showed that the pyrolysis products with high anisotropic content and moderate softening point could be obtained when the thermal polycondensation temperature was 370°C,the constant temperature reaction was 5H,and the system took the self-pressurization approach.The effects of DO addition on the formation process of mesophase pitch and the modification of molecular structure were investigated based on the better process conditions.The results showed that the introduction of DO led to the increase of the mesophase content,the optimization of the polarized weave and the more regular crystal structure of the products.According to the analysis of the test data,DO has a large number of short-chain alkane groups,which can easily break the bonds to form reactive molecular radicals when subjected to heat,and DO can also perform thermal condensation reactions to form DO macromolecules.These molecules can both graft with the limited reactive short-chain alkane groups of planar thick-ringed aromatic hydrocarbons and reduce the planarity of pitch molecules,and also interact with the pitch molecules in the process of mesophase pitch liquid crystal formation,which reduces the interaction force between thick-ringed aromatic hydrocarbon macromolecules and improves the molecular motility,thus to some extent destroying the regularity of molecular stacking,making its mobility better and promoting the mesophase pitch molecules formation.In view of the fact that the differences in molecular structure of the mesophase pitch are closely related to the differences in raw materials,petroleum pitch was chosen to investigate the effect of DO on the formation process and molecular structure regulation of petroleum-based mesophase pitch.The results showed that the addition of DO was also beneficial to the formation of petroleum-based mesophase pitch,but the softening point,anisotropy content,and crystal structure of the pyrolysis products were not consistent with those of the coal pitch experimental group.This may be because the molecular structure of petroleum pitch is less planar and contains more short alkyl side chains than that of coal pitch,which makes the modulation effect of DO on petroleum pitch molecules less.