a process can include polymerizing propylene in a polymerization zone , withdrawing an effluent , and sending the effluent to a separation zone . a stream can be sent from the separation zone to a splitter to produce an overhead and a bottom stream . the overhead can be recycled to the polymerization zone , and the bottom stream can be sent to a membrane separation zone to produce a permeate and a purge . optionally , the bottom stream can be washed in a scrubber , and an overhead of the scrubber can be sent to the membrane separation zone . the permeate can be recycled to the polymerization zone . a process can include providing a membrane separation zone to a polypropylene manufacturing facility that includes a polymerization zone , a separation zone , a splitter , and optionally a scrubber . the membrane separation zone cab be fed a bottoms steam of the splitter or an overhead of the scrubber .