Patent ID: 6271319
Filing Date: 2001-08-07
Classification: B01D,B01J,C08F

Abstract:
A process for making polypropylene, comprising the steps of:(a) polymerizing propylene in a polymerization reactor,(b) withdrawing from the reactor an effluent comprising polypropylene, propylene and propane;(c) subjecting the effluent to at least one separation step, thereby producing a raw polymer stream and a gas stream;(d) passing at least a portion of the gas stream across a feed side of a membrane selective for propylene over propane;(e) withdrawing from a permeate side of the membrane a permeate stream enriched in propylene compared to the gas stream;(f) withdrawing from the feed side a residue stream enriched in propane compared to the gas stream, and having a propane concentration of at least about 30%;(g) recirculating at least a portion of the permeate stream as feed to the polymerization reactor; the process being characterized in that the type of membrane used to carry out step (d) excludes facilitated transport membranes with liquid carriers.