Coking Mechanisms Within RFCC Disengagers

In this article we review and analyze the causes of coking within Residua Fluidized Catalytic Cracking (RFCC) process disengagers. The existing literature points to the presence of fine catalyst particles and condensation of heavy fractions of RFCC products as the primary, physical causes of coking in these units. Chemical causes include condensation reactions of heavy aromatic hydrocarbons, resins, and asphaltenes as well as cyclization and polymerization of olefins and diolefins. Based on analysis of known coking mechanisms within RFCC disengagers, it is apparent that coking occurs by different mechanisms in the vapor and liquid phases of RFCC products. Therefore, the key to the inhibition of coke formation is to prevent the condensation of heavy fractions in the RFCC products and to decrease residence time of these products in the disengagers.