Cocarbonization of Low Sulfur Vacuum Residue and FCC Decant Oil Aided by Additive Pitch of High Aromaticity

Cocarbonization of a low sulfur vacuum residue (LSVR) and a fluid catalytic cracking decant oil (FCC-DO) with the aid of Ashland A-240 pitch was studied, using tube bomb reactor at a temperature range of 460-480°C, under pressure of 8 kg/cm², to eliminate bottom mosaic-coke which was formed in the process with the given particular LSVR and FCC-DO. Addition of A-240 was highly effective to reduce the mosaic-coke, 30 and 5% added being found to eliminate completely at 480 and 460°C, respectively. The bottom mosaic-coke formed by LSVR alone was removed with less amount of A-240. Addition of A-240 tended to increase coefficient of thermal expansion(CTE) of the resultant lump coke at the optimum temperature, as compared to that obtained without A-240. The formation mechanism of bottom mosaic-coke is presumed to be that the heaviest asphaltene of high reactivity in the LSVR is carbonized into QI spheres of low solubility, in the somewhat paraffinic matrix, because of insufficient aromaticity of the FCC-DO, at the early stage of the carbonization. Spheres formed under such circumstances precipitate to the bottom without any growth or coalescence, forming the mosaic-coke. Higher aromaticity of the matrix mediates such QI to carbonize together, allowing formation of homogeneous texture in the whole area of resultant coke. Influence of carbonization temperature on CTE is briefly discussed in relation to their reactivity of blended feedstocks, based on the mechanism leading to production of needle coke.