Fundamental Study On Coal Tar Pitch Refining And Preparation Of Needle Coke

Needle coke is mainly used to produce high power and ultra-high power graphite electrode in steel making industry.Although China has carried out a series of research on coal-based needle coke,introduced some advanced foreign technology and production lines,and made certain progress.But due to the blockade of needle coke core technology from the United States,Japan and other countries,the development of coal-based needle coke technology is slow,and the product quality and production scale cannot meet the needs of the development of the steel industry.The pretreatment of raw materials,as a key technique in needle coke production,can fundamentally determine the quality of needle coke.Due to the insufficient research on the refining and modification mechanism of raw materials,the research progress of high-performance carbon materials represented by needle coke in China is slow.Therefore,this study uses China's rich coal tar pitch as raw material to study the mechanism and process conditions of solvent-based asphalt refining and needle coke preparation,analyze the basic characteristics of coal tar pitch,explain the dissolution mechanism of coal tar pitch refining,and optimize the refining process conditions.To study the carbonization reaction kinetics of refined asphalt,as well as the preparation and characterization of high-performance needle coke,providing theoretical support and proeess conditions for industrial production of needle coke in China.The advanced analytical equipments such as Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),visible ultraviolet spectrophotometer,fluorescence spectroscopy,thermal analysis(TG/DTG),gas chromatography/mass spectrometry(GC/MS),laser particle size analyzer were used for the analysis and characterization of coal tar pitch.Based on the fine analysis of asphalt raw materials,this study has used colloid formation and asphalt carbonization theory to systematically study the formation and destruction process of colloid in the process of coal tar pitch refining,carbonization kinetics of refined asphalt and preparation of needles.The process conditions of the coke preparation are optimized.The microstructure of the needle coke was analyzed by a polarizing microscope,and the coefficient of thermal expansion(CTE)and true density of the needle coke were measured.Studies have shown that the quinoline solubles(QS),toluene solubles(TS)and n-heptane solubles(HS)of coal tar pitch contain abundant 2-4 ring polycyclic condensed aromatic hydrocarbons,and the molecular structure is mainly a linear structure,that is,an aromatic hydrocarbon molecule with a low degree of condensation,which can be used as a high-quality raw material for preparing needle coke.In the study of micelles in coal tar pitch toluene solution,it is concluded that the formation of micelles is divided into three stages,namely nucleation,agglomeration and equilibrium stages.In the nicleation stage,the molecules of the asphalt solution are closely arranged in a certain order to form a stable system of the original micelles with the larger molecular aromatic layer as the core and the outward aromatic layer gradually decreasing;in the clustering stage system,the rubber core exists in a large amount and forms a gel.The micelle release rate and the association rate are equal in the asphalt solution in the equilibrium stage,and the micelle formation reaches a kinetic equilibrium.Under the influence of extermal temperature and solvent,when the rate of the nucleus absorbing material is greater than the rate of diffusion,the nucleus is in the growth stage,that is,the nucleation and agglomeration stage,When the two rates are equal,they are in the equilibrium phase.The rise in temperature could increase the instability of the micellar system.In addition,the alkane in the mixed solvent can break the thermodynamic equilibrium of the system,destroy the colloidal structure,cause flocculation and sedimentation,and facilitate solid-liquid se:paration.When the mixed solvent of toluene and n?heptane has a n-heptane content of 10%,a solvent solute ratio of 2:1,a settling time of 7 h,and a dissolved static settling temperature of 60?,a refined H/C having a higher H/C ratio can be obtained.Inspired by this,the industrial tar fraction and kerosene mixed solvent were used to purify coal tar pitch under the condition of 1:1 of aromatie to aliphatie sovlents and of 2.5:1 of the solvent to pitch.The high-quality refined asphalt was succesfully obtained for preparing needle coke.The thermal decomposition characteristics of coal tar pitch before and after refining show that the intensive reactions take place at 350?550?,and the slow heating rate is beneficial to increase the yield of coke.The coal tar pitch is refined to obtain refined asphalt,and its activation energy is reduced from 92.32 kJ/mol to 73.63 kJ/mol.After purification,the coal tar pitch activity is improved,and the carbonization reaction speed is relatively stable,which facilitates the growth and fusion of the mesophase.Under the condition of carbonization temperature of 500?and pressure of 0.4 MPa,the needle-like coke prepared from refined asphalt exhibits a well-oriented,streamlined wide-area fusion structure with a thermal expansion coefficient below 0.7×10-6?-1 and a true density above2.13 g/cm3.