streams that is streams 10 and 9 the light ends fractionation column 52 consists of at least one and preferably more theoretical liquid vapor equilibrium stages vapor enters the light ends fractionation column by way of stream 5 as a bottom feed while the top feed is by way of stream 23 a which is a liquid enriched by condensed methane the methane and lighter constituents and un recovered ethylene and ethane exit as a dew point vapor as a fourth residue stream 9 from the top tray or separation stage of the light ends fractionation column 52 the top feed through stream 23 a into the light ends fractionation column 52 and particularly the methane content thereof serves as a reflux in the column in flowing from stage to stage within column 52 the liquid methane is vaporized and in turn the liquid is progressively enriched in ethylene and ethane condensed from the upflowing bottom feed vapor from stream 5 the fourth liquid stream from the light ends fractionation column 52 stream 10 provides process cooling in exchanger 42 while it is itself warmed and then fed to the heavy ends fractionation column 56 for further separation the fourth residue gas stream 9 discharged from light ends fractionation column 52.