Preparation Of Spinnable Mesophase Pitch From Coal Tar Pitch Via Hydrogenation Modification

Mesophase pitches have been widely used in manufacturing of carbon fibers with high modulus and high thermal conductivity due to their special nematic liquid crystal structure.Coal tar pitch is one of the main raw materials for preparing mesophase pitch because of its wide source and low price.However,the poor rheological properties and mosaic optical texture of the present coal tar-derived mesophase pitch because of the high aromaticity of the feedstock and its high content of heteroatoms such as N?S and so on,which severely limits its application in carbon fibers.Therefore,it is necessary to modify the coal tar pitch when used as feedstocks of spinnable mesophase pitch.In this paper,tetrahydronaphthalene(THN)was used for hydrogenation treatment of the coal tar pitch,and the influence of hydrogenation process on the performance as well as the molecular structure of coal tar pitch was investigated.Further,the influence of the hydrogenation treatment on the basic performance and spinnability of the prepared mesophase pitch was discussed.The main conclusions are as follows:(1)With the increase of THN mass ratio increase from 5% to 30% in the hydrogenation process,the softening point of hydrogenated coal tar pitches decrease gradually,and the rheological properties and thermal stability are improved.The molecular analysis showed that the hydrogen to carbon ratio(H/C)of hydrogenated coal pitch increased with the increase content of THN,and the "S" heteroatom was significantly removed in the hydrogenation process.At the same time,more naphthenic structures and alkyl groups were introduced,which was the main reason for the improvement of the performance of hydrogenated coal pitch.(2)With the increase of THN content from 5% to 30% in the hydrogenation process,the softening point and viscosity of the resultant mesophase pitches gradually decrease,the optical texture size increase while the isotropic component content of the prepared mesophase pitches decreases.The softening point of mesophase pitch CTP-30-MP is as low as 296?,and it show a large domain optical texture with anisotropic component content more than 98vol%.The molecular structure analysis show that the naphthenic structure and alkyl groups increase with the THN content increase during hydrogenation,as well as the homogeneity of molecular weight distribution in the consequent mesophase pitches.(3)The spinnability of the coal tar pitch-derived mesophase pitches developed obviously because of the improvement of their rheological properties and molecular homogeneity by hydrogenation process.The as-spun mesophase pitch fibers was then pre-oxidized,carbonized and graphitized,and their mechanical properties were tested.The carbonized fibers' tensile strength reached 1.1GPa and the tensile modulus reached82 GPa.The carbon fibers after graphitization have a tensile strength of 2.7GPa,a tensile modulus of 530 GPa and a thermal conductivity of 537W/(m·K).