A process for treating an effluent gas stream arising from a manufacturing operation that produces an olefin or an olefin derivative. The process involves compressing the feed gas stream, which comprises an olefin, a paraffin, and a third gas, to produce a compressed stream, then cooling and condensing the compressed stream. The condensation step produces a liquid condensate and an uncondensed gas stream. The liquid condensate is then passed through a membrane separation step. The membrane separation of the condensate results in an olefin-enriched stream, which may be recycled for use within the manufacturing operation, and an olefin-depleted stream, which may be purged from the process.