MICROTEXTURAL STUDY OF COKES FROM HYDROPYROLYSIS OF COALS

Two bituminous non-coking coals were selected to investigate the contr ibution of pressure and gas atmosphere (hydrogen and helium) on their textural and microtextural evolution during carbonization in a 100 g f ixed bed semi batch unit. Microtextural analysis was carried out by tr ansmission electron microscopy (TEM) with the help of 002 dark field i mages, whereas the texture was established by polarizing optical micro scopy (OM). The results indicate a good coherence between OM and TEM a nd the complementary nature of these two techniques. If pressure is th e predominant factor, the role of the nature of the gas atmosphere is nevertheless significant. These two parameters act on balance between formation and diffusion of the suspensive medium (the metaplast) respo nsible for the reorientation of the polyaromatic basic structural unit s (BSU). Increase of pressure leads to the formation of larger molecul ar orientation domains (MOD) than those obtained at atmospheric pressu re. For the same gas pressure, the MOD obtained in the cokes from hydr opyrolysis are smaller, and these cokes are optically more isotropic. This could be explained by the formation of a suspensive medium, too l ight to be efficient for BSU reorientation and, therefore, for the for mation of the coke microtexture.