Carbonization and liquid-crystal (mesophase) development. 6. Effect of pre-oxidation of vitrinites upon coking properties

• Published in: Fuel (Guildford) 1975-01, Vol.54 (2), p.105-112
• Main Authors: Goodarzi, Fariborz, Hermon, Gail, Iley, Margaret, Marsh, Harry
• Format: Article
• Language: English
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/0016-2361(75)90065-4

The effects of atmospheric oxidation at 378 K upon the carbonization of a coking and a caking vitrinite have been examined in terms of the origins and extents of development of anisotropic material. The vitrinites, oxidized from 1 to 40 days, were carbonized to temperatures between 618 and 878 K, in open boats under nitrogen at atmospheric pressure, and in sealed gold tubes at maximum pressures of 140 to 310 MPa. Optical microscopy was used to observe, qualitatively, changes in reflectance and in shape and size of the anisotropic material of the carbonized product; morphological changes were monitored by scanning electron microscopy. For both vitrinites, whereas one day of oxidation destroyed coking properties and almost all of the anisotropic development in the open-boat carbonizations, the pressure carbonizations were not significantly affected until after five days of oxidation. Anisotropy still developed by mesophase growth from the plastic phase of carbonization, to produce the shaped, botryoidal material characteristic of pressure carbonizations. Thereafter, although in the pressure carbonizations the particles of coking vitrinite only fused slightly at interfaces to form a coherent product, marked increases occurred in reflectance and in observed anisotropy, showing maxima at nine days of oxidation. Results are interpreted on the assumption that oxidation cross-links the macromolecular structure of the vitrinite substance. The effect of high pressure during carbonization after five days of oxidation is to preserve and perfect the original basic anisotropy of the vitrinites initially stabilized by the cross-linkage of oxygen atoms.