Abstract: Process flow sequences for the reduction of equipment fouling in the fractional distillation of light end hydrocarbon components, such as those produced by pyrolysis or steam cracking, wherein conventional multiple hydrogenation unit configurations are replaced with upstream hydrogenation unit configurations. The upstream hydrogenation units of the invention are located at either side draws or in the reboiler circuit of deethanizers, in front-end demethanizer and front-end deethanizer sequences, or depropanizers, in front-end depropanizer sequences and obviate the need for most of the conventionally used hydrogenation units downstream.

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.