CARBONIZATION OF COAL-TAR PITCH UNDER CONTROLLED-ATMOSPHERE .1. EFFECT OF TEMPERATURE AND PRESSURE ON THE STRUCTURAL EVOLUTION OF THE FORMED GREEN COKE

The carbonization of an industrial coal-tar pitch was studied, by usin g a tube bomb, as a function of carbonization temperature (520 degrees C-580 degrees C) and inert gas pressure (1-20 bar) and resultant gree n cokes were evaluated according to yield and observation under polari zed light microscopy. At 520 degrees C, green cokes present large isot ropic domains as well as Brooks and Taylor's spheres whatever the pres sure applied, indicating that the pyrolysis duration seems to be too s hort to obtain an entirely anisotropic texture. When carbonization tem perature increases, samples present an entirely anisotropic texture. A n increase of carbonization pressure from 5 to 10 bar leads to a sharp increase of the coke yield and of the uniaxial arrangement, this latt er being progressive with increasing pressure at 550 degrees C and app earing only at pressures greater than 15 bar at 580 degrees C. Carboni zation temperature and pressure are intimately correlated. The tempera ture increase involves a higher solidification rate, whereas the press ure increase delays the volatile departure and consequently the solidi fication rate. It is necessary to obtain a compromise between them so as to produce green cokes with oriented uniaxial texture.