Abstract: A safe, effective, and economical method is provided for recovering olefins from cat-cracked gases without accumulating dangerous amounts of nitrogen oxides. A stream of cat-cracked gas first is scrubbed to remove acid gases, including nitrogen dioxide (NO.sub.2), and then is passed through a depropanizer fractionation tower. Hydrocarbons having four or more carbon atoms are recovered in the bottoms of the depropanizer, and the overhead from the depropanizer--which is composed of hydrocarbons having three or fewer carbon atoms--is sent to an absorber demethanizer tower. Hydrocarbons having two or more carbon atoms are recovered in the bottoms from the absorber demethanizer tower, where temperatures are no lower than about -45.56.degree. C. (-50.degree. F.). The overhead from the absorber demethanizer tower--which is composed of methane, hydrogen, and trace amounts of nitrogen oxide, C.sub.2, and absorbent (C.sub.3)--then is chilled to condense and recover trace amounts of C.sub.

Abstract: A process for the production of gaseous olefins which involves introducing a hydrocarbon feedstock stream into a high temperature thermal cracking zone to produce a high temperature cracked product stream, quenching the cracked product stream to stop the cracking reactions, injecting at least one HDD (hydrogen donor diluent) into the cracked product stream at or downstream of the point at which the reaction is quenched, recovering normally gaseous olefins from the cracked product stream, and recovering a liquid product stream containing a diminished asphaltene content.

Abstract: A process flow sequence for the reduction of polymer fouling while maintaining efficient production levels wherein a dual pressure, dual column configuration is used to effect the reduction in polymer fouling. The dual pressure, dual column configuration of the invention uses a high pressure and a separate low pressure to isolate the desired fractions while effecting a reduction in the production of fouling polymers.

Abstract: A process for the production of gaseous olefins which involves introducing a hydrocarbon feedstock stream into a high temperature thermal cracking zone to produce a high temperature cracked product stream, quenching the cracked product stream to stop the cracking reactions, injecting at least one HDD (hydrogen donor diluent) into the cracked product stream at or downstream of the point at which the reaction is quenched, recovering normally gaseous olefins from the cracked product stream, and recovering a liquid product stream containing a diminished asphaltene content.

Abstract: A process sequence for treating cracked gases of heavy feedstocks which preferentially produces propylene to the exclusion of propane, butanes and butenes. The process eliminates the need for a depropanizer with the attendant savings in capital and operating costs. In lieu of a conventional C3 splitter, the process features a depropylenizer, i.e. a distillation tower designed to separate propylene from propane, butanes and butenes. A hydrogenation unit to eliminate contaminants can be placed upstream of the depropylenizer or the depropylenizer can be split into two sections with the hydrogenation unit located between the two sections.