Pressure effects on the yield and on the microstructure formation in the pyrolysis of coal tar and petroleum pitches

Abstract

The pyrolysis of coal tar and petroleum pitches was studied under nitrogen pressures from 2 to 150 bar at temperatures between 300 and 600°C. The resulting residues were investigated by TGA, polarized-light microscopy and X-ray diffraction. It is shown that increasing pressure does not only increase the coke yield but also lowers the temperature at which pyrolysis is completed. This “chemical” effect of pressure is stronger with petroleum pitch. Increasing the pressure also improves preorder and graphitizability of the residues. Simultaneously, the microstructure becomes coarser and more Isotropie, i.e. that the enlarged areas of optical anisotropy exhibit no preferred orientation.