Membrane-augmented polypropylene manufacturing
AssigneeMembrane Technology and Research, Inc.
InventorsRichard W. Baker, Andre R. Da Costa, Ramin Daniels, Ingo Pinnau, Zhenjie He
Life of this patent
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Abstract
A process for polypropylene manufacturing, including treating a vent stream from the polymerization reactor, to recover propylene for return to the reactor. The process involves using a gas separation membrane to separate propylene from propane in the reactor vent stream. The membrane separation step results in a residue stream typically containing as much as 30% propane or more, which is vented from the polymerization process, and a permeate stream containing 95% or less propylene, which is recirculated to the polymerization reactor.
Claims33
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.
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 by no more than about 10% compared to the gas stream;
- (f) withdrawing from the feed side a residue stream enriched in propane compared to the gas stream;
- (g) recirculating at least a portion of the permeate stream as feed to the polymerization reactor;
- the process being characterized in that the permeate stream has a propylene concentration that is lower than 95%.
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, the membrane being selected from the group consisting of inorganic membranes, solid polymer electrolyte membranes, perfluorinated dioxole polymer membranes, perfluorinated dioxolane polymer membranes and perfluorinated cyclic ether polymer membranes;
- (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;
- (g) recirculating at least a portion of the permeate stream as feed to the polymerization reactor;
- the process being characterized in that the permeate stream has a propylene concentration that is lower than 95%.
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 by at least about 10% compared with the gas stream;
- (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.
Dependencies are inferred from the claim text.