Properties of Fluid Catalytic Cracking Decant Oils of Different Origins in Their Single Carbonization and Cocarbonization with a Petroleum Vacuum Residue

Eight decant oils of fluid catalytic cracking (FCC-DO) were compared in terms of their structure and carbonization properties in their single carbonization and cocarbonization with a low sulfur vacuum residue (LSVR) to reveal structure-reactivity correlation in the needle coke production. Although eight oils all provided (at 500°C under 16 kg/cm²of pressure) lumps of needle cokes in a tube bomb, their coefficients of thermal expansion (CTE) ranged from -0.15 X 10^-6(shrink, oil E) to 0.6 x 10^-6°C^-1(oil A). Their cocarbonization with LSVR at 480°C under 8 kg/cm²provided lump cokes of variable quality in terms of CTE and amount of bottom mosaic cokes. It should be noted that the best FCC-DO in its single carbonization was not always a better partner in the cocarbonization. In the cocarbonization, the best FCC-DO (G) gave a needle coke with the low CTE of 0.6 X 10^-6°C^-1and no bottom mosaic cokes while the worst oil (A2) gave a CTE of 1.2 X 10^-6°C^-1and bottom mosaic coke 1.4 mm thick. The oils consisted principally of saturate and light and heavy aromatic fractions, the contents of which varied from one oil to another. Among the fractions, the aromatic fractions were the major source of the coke, as indicated by a fair correlation of their content and aromaticity with their coke yield in the single carbonization. The saturate fraction appears to participate in the carbonization reaction as a poor solvent for the mesophase formation. The oil of the better partner in the cocarbonization was less paraffinic, and its aromatic fraction carried some alkyl groups of rather short chains. The roles of FCC-DO in the cocarbonization, particularly in the formation of bottom mosaic texture, are discussed, emphasizing the importance of the dissolution of the mesophase derived from the most reactive portion of asphaltene in the residue.