Fluid Catalytic Cracking Catalyst Demetallization and Reactivation, Modeling of Catalytic Cracking, and Use of Microwaves to Heat Fluid Beds
The fluid catalytic cracking unit (FCCU), the major conversion unit in an oil refinery, uses a silica-alumina zeolite catalyst to convert heavy hydrocarbons to light hydrocarbons. A small fraction of the catalyst must be continually replaced with fresh catalyst to maintain activity. The most detrimental of the contaminant metals are nickel and vanadium, which are deposited from the hydrocarbon feed during the cracking process and affect the deactivation rates. The deactivation rate of the catalyst followed a first order expression at constant metal addition and constant partial pressure of water in the regenerator.
FCCU catalyst demetallization processes remove contaminant metals from the equilibrium fluid cracking catalyst (ECAT), increasing the ECAT activity and reducing its deactivation rate. The purpose of catalyst demetallization is to reduce the FCCU fresh catalyst addition rate and reduce the FCCU operating cost. Three processes were evaluated and optimized, and one of these three processes, the DEMET process was selected for commercial development. In the DEMET process developed at Chalmers, the ECAT is first reacted with H2S at 840 OC, then reacted with Cl2 at 340 OC, nitrogen stripped and then washed with water to remove the metal chlorides. Maintaining the catalyst at 840 OC in the commercial unit was difficult due to severe corrosion of the alloy-steel sulfider shell. This problem was solved by heating the catalyst with microwaves, while keeping the shell cool with internal insulation. To understand the value of the DEMET it was necessary to predict the FCCU yields, and for this purpose a computer model (MOD) was developed to predict the commercial yields of an FCCU using demetallization or other catalyst reactivation technology. Catalytic cracking, catalyst demetallization and alternatives, pilot plant vanadium and nickel deposition studies, commercial DEMET results, FCCU computer modeling and fluid bed microwave heating are described and evaluated in this thesis.
nickel and vanadium deposition
and microwave heating