Study On Pretreatment Of Medium-low Temperature Coal Tar Pitch And Preparation Of Needle Coke

With the continuous development of the graphite electrode industry,the demand for needle coke has risen sharply,while domestic needle coke is mostly produced by using high temperature coal tar pitch as raw material,and the source of raw materials is relatively simple.After pyrolysis of low-rank coal in China,the obtained heavy-weight coal tar heavy component-asphalt by-product has the characteristics of abundant output and low impurity content.Therefore,the development of needle coke technology using medium-low temperature coal tar pitch as raw material can not only broaden the source of raw materials for needle coke,but also provide a wider utilization route for heavy components of medium-low temperature coal tar,which is of great significance and value.In this paper,medium-low temperature coal tar pitch of>300℃was used as raw material,and the raw materials were pretreated by solvent extraction and catalytic hydrogenation.The effects of different ratios of solvent to oil,ratios of aromatic to alkane and hydrogenation temperature on the yield,QI content and group composition distribution of refined asphalt were investigated.Secondly,raw material asphalt（CTP）,solvent extraction refined asphalt（RCTP₁）and catalytic hydrorefined asphalt（RCTP₂）were used as raw materials.After carbonization and calcination,the influence of raw material composition on needle-coke structural properties was investigated.Finally,using RCTP₁ as raw material,the effects of carbonization and calcination process parameters on the properties of coke and needle coke structure were investigated,and a better process was optimized.Research indicates:（1）In the solvent extraction process,when the ratios of aromatic to alkane is 1.2:1,the ratio of the solvent to oil is 1.6:1,the extraction temperature is 80℃,the stirring time is 1 h,the standing time is 10 h,and the standing temperature is 80℃,the refined asphalt yield is 60%.The QI content decreased from 0.81%to 0.03%,the group composition distribution was adjusted to n-heptane solubles（HS）42.483%,n-heptane insoluble-toluene solubles（HI-TS）54.031%,toluene insoluble-quinoline solubles（TI-QS）3.45%.In the catalytic hydrogenation process,when the reaction pressure is 9MPa and the temperature is 360℃,the yield of refined asphalt reaches 47.526%,and the QI is basically removed.The distribution of the group composition is adjusted to HS 57%,HI-TS 40%,TI-QS 2.8%.Both pretreatment methods made the refined asphalt reach the requirement of preparation of needle coke（QI<0.1%）,and through the elemental and infrared spectrum analysis,it was found that the solvent extraction method is more suitable as a needle coke pretreatment process.（2）Three different needle cokes（NK-CTP,NK-RCTP₁ and NK-RCTP₂）were obtained at a carbonization temperature of 460℃,a carbonization heating rate of 1℃/min,a system pressure of 1 MPa,a constant temperature time of 800 min,a calcination temperature of1200℃,a calcination rate of 5℃/min,and a calcination constant temperature of 5 h.,among which NK-CTP₁ has good structural properties,indicating that RCTP₁ is suitable as a raw material for the preparation of medium-low temperature coal tar pitch-based needle coke.（3）Using RCTP₁ as raw material,the carbonization process conditions suitable for the preparation of medium-low temperature coal tar pitch-based needle coke were as follows:polymerization temperature 480℃,constant temperature time 900 min,heating rate0.75℃/min and heat polymerization pressure 1.5 MPa,and observed by SEM,obtaining a semi-coke with good density.After high temperature calcination,the preferred calcination conditions are optimized:calcination temperature 1450℃,constant temperature time 5 h,25-900℃heating rate is 3℃/min,900-1450℃heating rate is 5℃/min.Further,a highly ordered,wide-area streamline-type fibrous calcined coke product having a true density of 2.143 g·cm^-3and a specific resistance of 578μ?·m was obtained.