Effect Of Polymerization Mode On Mesophase Formation Of Coal Pitch

Mesophilic bituminous carbon fibers have high modulus and high thermal conductivity,making them an ideal material for aerospace and defense applications.However,due to the weak research foundation,it is difficult to realize the stabilization of mesophase pitch based carbon fiber continuous filament in China at present.As a precursor of various high-performance carbon materials,the synthesis of spinnable mesophase pitch is the key.At present,the synthesis method of mesophase asphalt is mainly direct thermal polycondensation,but at the later stage of polymerization,the reactivity of asphalt molecules increases with the increase of molecular weight,and the self-acceleration phenomenon makes the reaction process difficult to control,resulting in a wide molecular weight distribution and poor spinnability of the product.Therefore,it is necessary to explore new synthetic methods and devices to optimize the preparation conditions of mesophase asphalt.In this paper,coal asphalt was used as raw material to carry out thermal condensation in a riser reactor to strengthen the separation effect of asphalt components.The formation process of mesophase asphalt was explored through multi-temperature zone polymerization,and the effects of reaction temperature,constant temperature time and component migration on the reaction were analyzed.The specific research contents and conclusions are as follows:（1）Mesophase asphalt was synthesized by isothermal polymerization with isotropic coal pitch as raw material.The formation of mesophase at different heights in the reactor and the variation of each component were investigated.The optical morphology,softening point,molecular structure,group composition structure,density and viscosity of asphalt products were tested in order to explain the migration of asphalt components in the vertical direction and its effect on polymerization kinetics.The results show that gravity deposition effect has taken place during the formation of mesophase pellets,and the reaction speed in the lower part is higher than that in the upper part,because the molecular weight in the bottom increases gradually and the reaction speed is accelerated.At the bottom of the 10 th h,the large molecular weight components converged with each other,and the molecular weight increased greatly.The asymmetric of PHS electron cloud intensified,and the activation energy decreased,leading to the self-acceleration effect.At the same time,a large amount of gas was generated to drive the upward migration of the light components,leading to the obvious separation of the coal asphalt components.The content of benzene soluble component（BS）of asphalt component decreases continuously,while the content of pyridine insoluble component（PI）increases continuously,and the content of benzene insoluble pyridine insoluble component（BI-PS）first increases and then decreases,and the content is small.（2）On the basis of isothermal polymerization,non-isothermal polymerization was used in the second part to suppress the self-accelerating effect of bottom bitumen molecules at the later stage of reaction.Firstly,a schematic diagram of the action mechanism of the riser reactor was drawn based on the basic law of meso-phase asphalt generation process.The viscosity test results showed that temperature conditions had a great influence on the reactivity of coal pitch molecules,and the migration law of components was verified.Meso-phase asphalt was synthesized at 420℃,400℃,350℃/300℃ in the reaction kettle,and the optical texture,softening point,density,component structure and functional group properties of the asphalt products were characterized.The results show that the mesophase synthesized by non-isothermal polymerization can be deposited to the bottom of the reactor,which can effectively inhibit the further condensation of asphalt molecules and improve the composition distribution of mesophase asphalt to a certain extent.At the bottom of300℃ for 10 h,asphalt products with good fluidity can be obtained,the mesophase content is higher than 70%,and the group composition data are BS: 37.47%;BI-PS: 13.53%;PI: 49%,the content of recombinant fraction（PI）was significantly reduced.Therefore,proper temperature conditions should be strictly controlled for polycondensation of coal pitch.Mesophase asphalt with good spinning performance can be obtained by reasonably decreasing temperature and prolongating reaction time.