Permeable membranes for enhanced gas separation

Claim 2

A composite membrane having enhanced gas separation characteristics comprising: (a) a porous polymeric support layer in asymmetric form, having a relatively thin, dense semipermeable skin region and a less dense, porous non-selective support region that serves to preclude the collapse of the skin region under pressure, said skin region being capable of selectively permeating a more readily permeable component of a feed gas mixture to be separated at a desirably high permeation rate; and (b) a separation layer deposited on said skin region without alteration of the structure of said support layer, said separation layer having a selectivity for said more readily permeable component equal to or greater than that of the material of said asymmetric support layer, the resulting composite membrane exhibiting separation characteristics equal to or higher than the intrinsic separation characteristics of the material of said asymmetric support layer, whereby said composite membrane exhibits enhanced gas permeability and separation characteristics.

Claim 3

A composite membrane having enhanced gas separation characteristics comprising: (a) a porous support layer in asymmetric form, having a relatively thin, dense semipermeable skin region and a less dense, porous non-selective support region that serves to preclude the collapse of the skin region under pressure, said skin region being capable of selectively permeating a more readily permeable component of a feed gas mixture to be separated said support layer, after being formed, in a desired porous form, washed and dried, being exposed in essentially dry form to an elevated temperature approaching the glass transition temperature of the support layer material under non-swelling conditions for a short period of time sufficient to modify the membrane structure to create asymmetry therein and to increase its compaction resistance and collapse pressure, without causing the collapse of said membrane; and (b) a separation layer deposited on the outer surface of said skin region, said separation layer having a selectivity for said more readily permeable component equal to or greater than that of the skin region of said asymmetric support layer, said separation layer thus determining the separation characteristics of the composite membrane, whereby said composite membrane exhibits enhanced selectivity and permeability characteristics, and advantageous combinations of selectivity and permeability, together with desirable compaction resistance and collapse pressure on a repeatable basis, enhancing the uniformity and reliability of the composite membrane for use in gas separation operations.

Claim 4

A composite membrane having enhanced gas separation characteristics comprising: (a) a porous support layer in asymmetric form, having a relatively thin, dense semipermeable skin region and a less dense, porous non-selective support region that serves to preclude the collapse of the skin region under pressure, said skin region being capable of selectively permeating a more readily permeable component of a feed gas mixture to be separated said support layer, after being formed, in a desired porous form, washed and dried, being exposed in essentially dry form to an elevated temperature approaching the glass transition temperature of the support layer material under non-swelling conditions for a short period of time sufficient to modify the membrane structure to create asymmetry therein and to increase its compaction resistance and collapse pressure, without causing the collapse of said membrane; and (b) a separation layer deposited on the outer surface of said skin region, said separation layer having a selectivity for said more readily permeable component equal to or greater than that of the skin region of said asymmetric support layer, said separation layer thus determining the separation characteristics of the composite membrane, whereby said composite membrane exhibits enhanced selectivity and permeability characteristics, and advantageous combinations of selectivity and permeability, together with desirable compaction resistance and collapse pressure on a repeatable basis, enhancing the uniformity and reliability of the composite membrane for use in gas separation operations.

Claim 5

The composite membrane of Claim 1 or 2 in which said membrane is in hollow fiber form.

Claim 6

The composite membrane of any one of the preceding Claims in which said separation layer comprises a polymeric material.

Claim 7

The composite membrane of any one of the preceding Claims in which said support layer comprises polysulfone.

Claim 8

The composite membrane of Claim 3 in which said support layer comprises polysulfone and said separation layer comprises a poly­meric material.

Claim 9

The composite membrane of Claim 2 in which said non-swelling condi­tions comprise a heated gas atmosphere at a temperature of not more than about 20°C less than said glass transition temperature of the support layer material.

Claim 10

The composite membrane of Claim 7 in which said support layer com­prises polysulfone and said heated gas atmosphere comprises hot, essentially dry air, said support layer being exposed to said eleva­ted temperature for a period of from about 5 seconds to about 5 mi­nutes.

Claim 11

The composite membrane of Claim 2 in which the support layer is ex­posed to said elevated temperature under non-swelling conditions by passing the membrane through a bath of non-swelling liquid for a period of time not sufficient to cause the collapse of said support layer.

Claim 12

The composite membrane of Claim 9 in which said support layer com­prises polysulfone in hollow fiber form.

Claim 13

The composite membrane of Claim 4 or 6 in which said separation layer comprises cellulose acetate.

Claim 14

The composite membrane of Claim 4 or 6 in which said separation layer comprises a polyarylate.

Claim 15

The composite membrane of Claim 12 in which said separation layer comprises sulfonated polysulfone.

Claim 16

The composite membrane of Claim 12 in which said separation layer comprises brominated polyphenyleneoxide.

Claim 17

In the process of preparing a polymeric membrane capable of selectively permeating a more readily permeable component of a feed gas mixture in which said membrane is produced in a desired porous form, washed and dried, the improvement comprising exposing said membrane in essentially dry form to an elevated temperature approaching the glass transition temperature of the membrane material under non-swelling conditions for a period of time sufficient to modify the membrane structure to form asymmetry therein, with increased compaction resistance and collapse pressure, whereby the uniformity and reliability of the treated membrane is enhanced for use in gas separation operations.

Claim 18

In the process of preparing a polymeric membrane capable of selectively permeating a more readily permeable component of a feed gas mixture in which said membrane is produced in a desired porous form, washed and dried, the improvement comprising exposing said membrane in essentially dry form to an elevated temperature approaching the glass transition temperature of the membrane material under non-swelling conditions for a period of time sufficient to modify the membrane structure to form asymmetry therein, with increased compaction resistance and collapse pressure, whereby the uniformity and reliability of the treated membrane is enhanced for use in gas separation operations.

Claim 19

The process of Claim 15 in which said non-swelling conditions comprise a heated gas atmosphere.

Claim 20

The process of Claim 16 in which said inert gas atmosphere is at a temperature of not more than about 20°C less than said glass transition temperature of the membrane material.

Claim 21

The process of Claim 17 in which said temperature is from about 15°C to about 1°C less than said glass transition temperature.

Claim 22

The process of Claim 15 in which said polymeric membrane comprises polysulfone.

Claim 23

The process of Claim 17 in which said heated gas atmosphere comprises hot, essentially dry air.

Claim 24

The process of Claim 16 in which the membrane is exposed to said elevated temperature for a period of from about 5 seconds to about 5 minutes.

Claim 25

The process of Claim 21 in which said period of time is from about 30 seconds to about 4 minutes.

Claim 26

The process of Claim 15 in which the membrane is exposed to said elevated temperature under non-swelling conditions by passing the membrane through a bath of non-swelling liquid for a period of time not sufficient to cause the collapse of said membrane.

Claim 27

The process of Claim 23 in which said non-swelling liquid comprises silicone oil, and including washing and drying the treated membrane.

Claim 28

The process of Claim 24 in which said treated membrane is in hollow fiber form.

Claim 29

The process of Claim 23 and including depositing a separation material on the outer skin region of the treated membrane to form a separation layer thereon, said separation layer having a selectivity for the more readily permeable component of a gas mixture to be separated that is equal to or greater than the intrinsic separation characteristics of the material of the asymmetric support layer.

Claim 30

The process of Claim 23 and including depositing a separation material on the porous membrane prior to the treatment thereof to form asymmetry therein, said separation layer having a selectivity for the more readily permeable component of the gas mixture to be separated that is equal to or greater than the intrinsic separation characteristics of the material of said porous membrane.

Claim 31

The process of Claim 26 in which said asymmetric treated membrane comprises polysulfone in hollow fiber form.

Claim 32

The process of Claim 28 in which said non-swelling conditions comprise a hot air atmosphere.

Claim 33

The process of Claim 28 in which said non-swelling conditions comprise an inert gas atmosphere.

Claim 34

In the process for the separation of a more readily permeable component of a feed gas mixture from a less readily permeable component thereof by contacting said feed gas mixture with the feed side of a composite membrane having gas separation characteristics, and separately withdrawing the more readily permeable component from the composite membrane as a permeate stream and said less readily permeable component as a non-permeate stream, the improvement comprising employing a composite membrane comprising: (a) a porous polymeric support layer in asymmetric form, having a selectively thin, dense semipermeable skin region and a less dense, porous non-selective support region that serves to preclude the collapse of the skin region under pressure, said skin region being capable of selectively permeating a more readily permeable component of the feed gas mixture to be separated at a desirably high permeation rate; and (b) a separation layer deposited on said skin region without alteration of the structure of the support layer, said separation layer having a selectivity for said more readily permeable component greater than that of the material of the asymmetric support layer, the resulting composite membrane exhibiting separation characteristics equal to or higher than the intrinsic separation characteristics of the material of the asymmetric support layer, whereby said composite membrane exhibits enhanced gas permeability and separation characteristics in desired gas separation operations.

Claim 35

In the process for the separation of a more readily permeable component of a feed gas mixture from a less readily permeable component thereof by contacting said feed gas mixture with the feed side of a composite membrane having gas separation characteristics, and separately withdrawing the more readily permeable component from the composite membrane as a permeate stream and said less readily permeable component as a non-permeate stream, the improvement comprising employing a composite membrane comprising: (a) a porous polymeric support layer in asymmetric form, having a selectively thin, dense semipermeable skin region and a less dense, porous non-selective support region that serves to preclude the collapse of the skin region under pressure, said skin region being capable of selectively permeating a more readily permeable component of the feed gas mixture to be separated at a desirably high permeation rate; and (b) a separation layer deposited on said skin region without alteration of the structure of the support layer, said separation layer having a selectivity for said more readily permeable component greater than that of the material of the asymmetric support layer, the resulting composite membrane exhibiting separation characteristics equal to or higher than the intrinsic separation characteristics of the material of the asymmetric support layer, whereby said composite membrane exhibits enhanced gas permeability and separation characteristics in desired gas separation operations.

Claim 36

The process of Claim 31 in which the composite membrane is in hollow fiber form.

Claim 37

The process of Claim 32 in which said support layer comprises polysulfone.

Claim 38

The process of Claim 31 in which said porous polymeric support layer, after initial formation in a desired porous form, washing and drying, is exposed in essentially dry form to an elevated temperature approaching the glass transition temperature of the support layer material under non-swelling conditions for a period of time sufficient to modify the membrane so as to increase its compaction resistance and collapse pressure, without causing the collapse of said support layer.

Claim 39

The process of Claim 34 in which said non-swelling conditions comprise a heated gas atmosphere.

Claim 40

The process of Claim 34 in which said support layer comprises polysulfone and said composite membrane is in hollow fiber form.

Claim 41

The process of Claim 31 in which said feed gas mixture comprises air, said permeate gas comprises oxygen, and said non-permeate gas comprises nitrogen.

Claim 42

The process of Claim 31 in which said feed gas mixture comprises a mixture of hydrogen and nitrogen, said permeate gas comprises hydrogen, and said non-permeate gas comprises nitrogen.

Claim 43

The process of Claim 38 in which said feed gas mixture comprises a mixture of carbon dioxide and methane, said permeate gas comprises carbon dioxide, and said non-permeate gas comprises methane.

Claim 44

An asymmetric membrane having enhanced gas separation characteristics comprising a relatively thin dense semipermeable skin region and a less dense, porous non-selective support region that serves to preclude the collapse of the skin region under pressure, said skin region being capable of selectively permeating a more readily permeable component of a feed mixture to be separated at a desirably high permeation rate, said membrane having been formed initially in a desired porous form, washed and dried, and having been exposed in essentially dry form to an elevated temperature approaching the glass transition temperature of the membrane material under non-swelling conditions for a period of time sufficient to modify the membrane structure to create asymmetry therein and to increase its compaction resistance and collapse pressure, whereby said asymmetric membrane exhibits enhanced selectivity and permeability characteristics, and advantageous combinations of selectivity and permeability, together with desirable compaction resistance and collapse pressure, on a repeatable basis, enhancing the uniformity and reliability of the membrane for use in gas separation operations.

Claim 45

An asymmetric membrane having enhanced gas separation characteristics comprising a relatively thin dense semipermeable skin region and a less dense, porous non-selective support region that serves to preclude the collapse of the skin region under pressure, said skin region being capable of selectively permeating a more readily permeable component of a feed mixture to be separated at a desirably high permeation rate, said membrane having been formed initially in a desired porous form, washed and dried, and having been exposed in essentially dry form to an elevated temperature approaching the glass transition temperature of the membrane material under non-swelling conditions for a period of time sufficient to modify the membrane structure to create asymmetry therein and to increase its compaction resistance and collapse pressure, whereby said asymmetric membrane exhibits enhanced selectivity and permeability characteristics, and advantageous combinations of selectivity and permeability, together with desirable compaction resistance and collapse pressure, on a repeatable basis, enhancing the uniformity and reliability of the membrane for use in gas separation operations.

Claim 46

The membrane of Claim 40 in which the membrane material comprises polysulfone.

Claim 47

The membrane of Claim 40 in which said desired form comprises hollow fiber form.

Claim 48

The membrane of Claim 40 in which said non-swelling conditions comprise a heated gas atmosphere at a temperature of not more than about 20°C less than said glass transition temperature of said membrane material.

Claim 49

The membrane of Claim 40 in which said heated gas atmosphere comprises hot, essentially dry air.

Claim 50

The membrane of Claim 40 in which said non-swelling conditions comprise a bath of non-swelling liquid, the exposure of said membrane thereto being for a period of time not sufficient to cause the collapse of said membrane.