COMBINATION RESIDUE HYDRODESULFURIZATION AND ZEOLITE RISER CRACKING PROCESS

摘要

A multiple stage hydrodesulfurization process is described for the catalytic hydrodesulfurization and hydrodemetallization of a residual petroleum oil boiling above the gasoline range followed by a zeolite riser cracking process. The product of the hydrodesulfurization section comprises essentially material boiling above the gasoline range and comprises little material boiling below the initial boiling point of the residual oil feed. The hydrodesulfurization-demetallization section comprises an initial stage involving relatively high hydrogen pressure in the presence of a catalyst comprising a relatively low proportion of catalytically active hydrogenation metals. The process employs a final hydrodesulfurization stage in series having a relatively lower hydrogen pressure and a catalyst comprising a relatively higher proportion of hydrogenation metals. The stream entering the final hydrodesulfurization stage contains an amount up to 10, 20 or even 25 weight percent of the asphaltene content of the charge to the first stage while the effluent from the final stage is essentially free of asphaltenes. The metals content of the final stage effluent is so low that said effluent can be charged without blending with a distillate oil to a fluidized zeolite riser cracking unit (FCC) to produce gasoline and fuel oil. The zeolite catalyst make-up requirement due to metals accumulation on the zeolite catalyst is no greater than zeolite make-up requirement when a distillate gas oil comprises the entire feed to the reactor. The sulfur content of the final stage effluent is so low that the sulfur dioxide content in the zeolite regenerator flue gas is able to meet commercial requirements and so that the fuel oil range product of the FCC operation is sufficiently low that the FCC fuel oil product also meets commercial fuel oil sulfur specifications without requiring further hydrodesulfurization, whereby all hydrodesulfurization can precede the FCC step and no hydrodesulfurization is required after the FCC step. Of course, further desulfurization can follow the FCC step, if such is desired for a specialized requirement.