CARBONIZATION OF PETROLEUM FEEDSTOCKS (CARBONACEOUS MESOPHASE, ASPHALTENES)

The properties of the petroleum cokes are determined by their crystalline structure, which principally depends on the nature of the mesophase formed during the liquid-phase carbonization of the precursors. This study was aimed at investigating the relationships between the chemical nature of the petroleum feedstocks and the mesophase development during carbonization.; Ashland 240 pitch and a range of petroleum heavy residua were characterized by solvent fractionation, elemental analysis, Fourier Transform Infrared Spectroscopy, ('1)H and ('13)C Nuclear Magnetic Resonance Spectroscopy.; The samples were carbonized in tubing bomb reactors under essentially isothermal conditions. The carbonization temperature and time were varied, usually in the range 673-773 K and 0.25-12 h, respectively.; The aromatic feedstocks gave rise to a high degree of mesophase development producing semi-cokes similar in optical texture to needle coke. The paraffinic feedstocks, on the other hand, produced semi-cokes, the optical textures of which ranged from that of sponge to shot coke.; The semi-coke (pyridine insolubles) formation from the feedstocks and their asphaltene fractions was found to be first-order with respect to the concentration of pyridine solubles over a wide conversion range. The calculated apparent activation energies and preexponential factors varied between 152 and 224 kJ/mole and 3.4 x 10('11) and 1.5 x 10('15) h('-1), respectively. An inverse relationship was observed between the rate of carbonization of the asphaltenes and the degree of mesophase development.; The degree of mesophase development during the carbonization of the feedstock asphaltenes increased consistently with the increasing hydrogen aromaticity over the whole range of the feedstocks used. The carbon aromaticity of the asphaltenes, on the other hand, did not appear to be a significant parameter for the mesophase development.; The principal conclusion from this study is that the mesophase development during carbonization critically depends on the chemical constitution of the petroleum feedstocks. The molecular nature of the asphaltene fractions determines the extent of mesophase development during the carbonization of the petroleum heavy residua. In this respect, the hydrogen aromaticity of the asphaltenes appears to be a good measure for the feedstock quality in terms of resulting coke structure and properties.