Purification of coal tar pitch by a combined thermal condensation and filtration method

Raw coal tar pitch with an ash content of 1100 ppm and a quinolone insoluble (QI) fraction of 8 wt% was first thermally condensed at 420℃ for different times, then dissolved in pyridine at 100℃ for 1 h under stirring and finally filtered under a pressure of 0.1-0.3 MPa with meshes of different sizes to lower the ash and QI contents. The effects of the thermal condensation time and aperture size of the mesh on the purification efficiency were investigated. Results indicated that the ash content of the refined pitch first decreased and then increased slightly, but the pitch yield decreased with condensation time. The ash content and yield of refined pitch decreased with decreasing the aperture size. The purification efficiency was improved greatly by thermal condensation. SEM observation of the surface morphology of the residue revealed that mesophase spheres formed by heterogeneous nucleation during the thermal condensation had the ability to adsorb ash components and primary QI to decrease their contents in the refined pitch. The slight increase of the ash content with a condensation time greater than 5 h was caused by coalescence of mesophase spheres to form large spheres and domains, which decreased their adsorbing ability. A refined pitch with an ash content of 90 ppm and a QI content of 0.6 wt% was obtained using a condensation time of 5 h and a mesh aperture size of 13 μm, which meets the requirement for preparing most advanced carbon materials.