A Study On Preparation Of Needle Coke

Needle coke is the main raw material for large-scale industrial electrode for the steel, aluminum, rockets, spacecraft and so on, and it can be prepared from coal-tar pitch. The medium coal tar pitch, which contains a large number of quinoline insolubles (QI) that needs to be completely removed, can be prepared for needle coke under appropriate conditions.In this study, the size distribution of QI particles in medium coal tar pitch was determined. Then the QI particles were removed through solvent sedimentation and centrifugal separation. The effect of operating conditions on the removal of QI has been investigated. Under the appropriate temperature and pressure conditions needle coke was synthesized using the pitch of low QI content, and the laws of operating conditions on the quality of needle coke was studied by scanning electron microscopy of the micro-structure of needle coke. The results show that:(1) The QI particle size, 90% of which is below 4μm, is too small to be removed by conventional filtering methods;(2) Using the 2~# solvent, increasing the sedimentation time, raising the temperature and the weight proportion of solvent can reduce the viscosity and density of the pitch solution, and thus the quinoline insolubles (QI) can be more effectively removed. The sedimentation temperature should not be beyond 350℃, or the medium pitch would be polymerized;(3) Using mixture of anthracene oil and heavy diesel oil as mixed solvents, the small QI particles flocculate and become bigger particles which can be removed effectively through the centrifugal separation method; Increasing the heavy oil proportion or the solvent ratio, the viscosity and density of pitch solution decline in favor of the separation of QI; For pure heavy oil solvent, the QI content of purified pitch declines with the increasing of solvent ratio; Under the conditions that the centrifugation rotate speed is 4000rpm, the centrifugation temperature is from 70℃to 80℃, the solvent ratio is not lower than 1.0 and in 1 min, the QI content of purified pitch is below 0.01%;(4) In the thermal polymerization process, the lower temperature, the slower heating rate and sufficient time are conducive to mesophase formation, and thus the bigger planar molecules are made. The proper pressure on coking reactor will make the amount of light group suitable and air gap in coke is formed, which is conducive to the formation of fibrous tissue. The direction of movement under heat treatment of coal tar pitch can make thick planar aromatic molecules into a liquid crystal. To achieve the lowest energy state of the system, the small mesophase ball is formed under the surface tension of liquid crystal, and then well-structured needle coke is formed.