Low pressure chilling train for olefin plants

A method of processing a cracked gas feedstream containing hydrogen and C 1 to C 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 6 and heavier hydrocarbons forming a vapor stream containing the hydrogen, the C 1 to C 3 hydrocarbons and at least some of the C 4 and C 5 hydrocarbons. The C 4 and C 5 components act as an absorption liquid to lower the light ends partial pressure permitting the condensation of C 2 and C 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 2 and C 3 components in the bottoms.