Abstract: An isomerization process for converting an isomerization feed stream containing alkanes having about 4 carbon atoms to about 10 carbon atoms per molecule and cycloalkanes having about 5 carbon atoms to about 10 carbon atoms per molecule to at least one product hydrocarbon isomer. The isomerization feed stream, which contains at least one feed hydrocarbon and hydrogen, is contacted in an isomerization zone at effective isomerization conditions with a catalyst where deactivation of such catalyst occurs in the isomerization zone. The isomerization process includes the presence of an additive in the isomerization feed stream. The concentration of the additive is sufficient to alleviate or diminish the deactivation of the catalyst and to maintain a substantially constant conversion of the at least one feed hydrocarbon to the at least one product hydrocarbon isomer at effective isomerization conditions.

Abstract: Vent gases containing propane and HF obtained from a hydrocarbon alkylation operation are treated together with an alkylate either before or after it has been debutanized thus to remove HF from said vent gases and/or the vent gases are combined with a normal butane stream before it is treated to remove HF therefrom thus to remove HF from said vent gases. In any event described, the propane in the vent gases is advantageously recovered in the normal butane containing stream.

Abstract: In a hydrodesulfurization process having separate naphtha and distillate hydrodesulfurization zones, volatile fractions of the distillate hydrodesulfurization effluent are recycled to the naphtha feed stream before it combines with the hydrogen stream and enters the hydrodesulfurization zone and heavy fractions separated from the naphtha hydrodesulfurization effluent are combined with a diesel fuel oil fraction separated from the distillate hydrodesulfurization effluent. Alternatively, light fractions separated from the distillate hydrodesulfurization effluent are combined with a condensed liquid stream being returned to a distillation fractionation zone separating light fractions from the naphtha hydrodesulfurization effluent.

Abstract: In a system wherein a topped crude catalytic cracking system and a gas oil catalytic cracking system are operated, and the heavy cycle oils from each system are combined and the combined heavy cycle oil stream is solvent extracted to provide an aromatic extract suitable as feed for a carbon black operation, the aromaticity of the extract is increased by passing a substantial portion of the topped crude heavy cycle oil to the gas oil fractionator and recovering a heavy cycle oil from the gas oil fractionator as charge to solvent extraction.