Abstract: A method of processing a cracked gas feedstream containing hydrogen and C.sub.1 to C.sub.6 and heavier hydrocarbons is described using a relatively low pressure as compared to conventional cryogenic separation processes. At pressures below 27 bars, the feedstream is dried and cooled in a series of steps to initially separate out essentially all of the C.sub.6 and heavier hydrocarbons forming a vapor stream containing the hydrogen, the C.sub.1 to C.sub.3 hydrocarbons and at least some of the C.sub.4 and C.sub.5 hydrocarbons. The C.sub.4 and C.sub.5 components act as an absorption liquid to lower the light ends partial pressure permitting the condensation of C.sub.2 and C.sub.3 components at higher temperature levels and permitting the operation at lower pressures. The vapor stream is then further cooled and separated in another series of steps and processed in a demethanizer column in a manner to provide a high pressure hydrogen and methane overhead product and a high recovery of C.sub.2 and C.sub.

Abstract: A low pressure cryogenic process is disclosed for recovering C.sub.2 and heavier hydrocarbons and particularly olefins from a refinery offgas containing hydrogen, methane, nitrogen oxide in addition to the C.sub.2 and heavier hydrocarbons. The conventional high pressures are eliminated and the temperatures are maintained higher than the temperature at which nitrated gums can form while still maintaining high olefin recovery. The feed is deethanized or depropanized to remove the C.sub.4 and heavier hydrocarbons at a temperature above the nitrated gum formation temperature. The overhead is then demethanized in a column using an enriching zone above the rectifying zone with a feed of C.sub.2 or heavier paraffins between these two zones.