Carbonization in the tube bomb leading to needle coke: II. Mechanism of cocarbonization of a petroleum vacuum residue and a FCC-decant oil

Abstract

Cocarbonization of a FCC decant oil (FCCDO) and a vacuum residue of low sulfur crude (LSVR) was studied at 460 and 480°C through the sequential microscopic observation and analyses of the carbonization intermediates produced in a tube bomb to discuss how the best needle coke was produced from their mixture of a particular ratio subjective to the carbonization temperature. The cocarbonization moderates the reactivity of LSVR to allow the formation of the mesophase of low viscosity comparable to that from FCCDO alone as indicated by the solubility change and allows at same time more evolution of gas at the solidification stage which may originate from LSVR. Thus, the better uni-axial arrangement of mesophase components is achieved in the cocarbonization, leading to the production of better needle coke. Such a cocarbonization is strongly influenced by the carbonization temperature, defining the best ratio of the mixing at the respective temperature because of the reactivity subjective to the temperature. The formation mechanism of the bottom mosaic coke is also discussed from a view of solubility of the reactive portion of the asphaltene in the cocarbonization matrix.