Patent ID: 6168649
Filing Date: 2001-01-02
Classification: B01D,C01B

Abstract:
A method of separating a noble gas from oxygen, nitrogen, or carbon dioxide, or a mixture thereof, using three membranes, comprising the steps of: a) contacting one side of a first semi-permeable membrane comprising a thin discriminating layer selected from the group consisting of polycarbonate, polyester, and polyestercarbonate, said first semi-permeable membrane exhibiting an oxygen/noble gas permselectivity of at least 21, with a feed gas mixture under pressure; b) maintaining a pressure differential across the first membrane under conditions such that a component of the feed gas selectively permeates through the first membrane from a high pressure side of the first membrane to a low pressure side of the first membrane; c) removing a first permeated gas, which is enriched in a faster permeating component, from the low pressure side of the first membrane; d) removing a first retentate gas, which is enriched in a slower permeating component, from the high pressure side of the first membrane; e) contacting one side of a second semi-permeable membrane comprising a thin discriminating layer selected from the group consisting of polycarbonate, polyester, and polyestercarbonate, said second semi-permeable membrane exhibiting an oxygen/noble gas permselectivity of at least 21, with the first retentate gas under pressure; f) maintaining a pressure differential across the second membrane under conditions such that a component of the first retentate gas selectively permeates through the second membrane from a high pressure side of the second membrane to a low pressure side of the second membrane; g) removing a second permeated gas, which is enriched in a faster permeating component, from the low pressure side of the second membrane and recycling it to the feed gas mixture under pressure; h) removing a second retentate gas, which is more enriched in a slower permeating component, from the high pressure side of the second membrane; i) re-pressurizing the first permeated gas to produce a re-pressurized first permeated gas; j) contacting one side of a third membrane comprising a thin discriminating layer selected from the group consisting of polycarbonate, polyester, and polyestercarbonate, said third membrane exhibiting an oxygen/noble gas permselectivity of at least 21, with said re-pressurized first permeated gas; k) maintaining a pressure differential across the third membrane, under conditions such that a component of the re-pressurized permeated gas selectively permeates through the third membrane from a high pressure side of the third membrane to a low pressure side of the third membrane; l) removing permeated gas, which is enriched in a faster permeating component, from the low pressure side of the third membrane; m) removing a third retentate gas, which is enriched in a slower permeating component, from the high pressure side of the third membrane and recycling it to the feed gas mixture under pressure; and n) storing the second retentate gas.