US4765897A
Expired / Lapsed
US
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Polyamide membranes useful for water softening
Assignee: Filmtec Corp
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Filing: 1986-04-28
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Granted: 1988-08-23
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Expires: 2006-04-28
Abstract
Abstract A novel water softening membrane and process for making the same is described. The membrane can be prepared by treating a polyamide reverse osmosis membrane with a strong mineral acid followed by treatment with a rejection enhancing agent. The resulting membrane at transmembrane pressures of 50 psi can attain a magnesium sulfate rejection with a 0.2 percent aqueous solution of more than 90 percent with a water flux of more than 15 gallons per square foot per day.
Inventors
- 👤 John E. Cadotte
- 👤 David R. Walker
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 01:15
CPC Classifications
B; B01; B01D; B01D67/00; B01D67/0081; B01D67/0088; B01D67/0093; B01D67/00933; B01D71/00; B01D71/06; B01D71/56; B01D2323/00; B01D2323/30; Y; Y10; Y10T; Y10T428/00; Y10T428/31504; Y10T428/31536; Y10T428/31725; Y10T428/3175
Claims Analysis
Total Claims: 33
Claim 1
Independent Claim
130 words
A membrane useful for water softening which is prepared by a process comprising: (a) contacting a crosslinked polyamide discriminating layer of a reverse osmosis membrane with an aqueous solution of a compatible strong mineral acid; (b) maintaining the membrane in contact with the acid at an elevated temperature for a period sufficient to produce a membrane having a water flux of at least about 8 gfd and a MgSO 4 rejection of at least about 65 percent when tested under reverse osmosis conditions at 50 psi and 25° C. using an aqueous solution of 0.2 weight percent MgSO 4 ; and (c) contacting the membrane from step (b) with a rejection enhancing agent so as to produce a membrane having a MgSO 4 rejection of at least about 85 percent.
Claim 2
Dependent Claim
130 words
A membrane useful for water softening which is prepared by a process comprising: (a) contacting a crosslinked polyamide discriminating layer of a reverse osmosis membrane with an aqueous solution of a compatible strong mineral acid; (b) maintaining the membrane in contact with the acid at an elevated temperature for a period sufficient to produce a membrane having a water flux of at least about 8 gfd and a MgSO 4 rejection of at least about 65 percent when tested under reverse osmosis conditions at 50 psi and 25° C. using an aqueous solution of 0.2 weight percent MgSO 4 ; and (c) contacting the membrane from step (b) with a rejection enhancing agent so as to produce a membrane having a MgSO 4 rejection of at least about 85 percent.
Claim 3
Dependent Claim
36 words
The membrane as described in claim 1 with the proviso that the sum of the water flux in gfd and MgSO 4 rejection in percent after acid treatment in step (b) is at least about 90.
Claim 4
Dependent Claim
15 words
The membrane as described in claim 2 wherein the polyamide is a crosslinked, aromatic polyamide.
Claim 5
Dependent Claim
16 words
The membrane as described in claim 3 wherein the membrane is a thin film composite membrane.
Claim 6
Dependent Claim
15 words
The membrane as described in claim 4 wherein the membrane is a flat sheet membrane.
Claim 7
Dependent Claim
24 words
The membrane as described in claim 5 wherein the membrane from step (b) is assembled in a spiral membrane device prior to step (c).
Claim 8
Dependent Claim
24 words
The membrane as described in claim 6 wherein the polyamide is a poly(phenylene diamine trimesamide) and the acid in step (a) is phosphoric acid.
Claim 9
Dependent Claim
17 words
The membrane as described in claim 7 wherein the rejection enhancing agent is a tannic acid colloid.
Claim 10
Dependent Claim
16 words
The membrane as described in claim 7 wherein the rejection enhancing agent is styrene/maleamic acid copolymer.
Claim 11
Dependent Claim
36 words
The membrane as described in claim 7 wherein the rejection enhancing agent is a copolymer of hydroxyethyl methacrylate and methyl methacrylate or methacrylamide and including up to 20 weight percent of other compatible ethylenically unsaturated monomers.
Claim 12
Dependent Claim
39 words
The membrane as described in claim 7 wherein the rejection enhancing agent is a coacervate prepared from a first polymer bearing a plurality of sulfonium or quaternary ammonium groups and a second polymer bearing a plurality of carboxylate groups.
Claim 13
Dependent Claim
14 words
The membrane as described in claim 4 wherein the membrane is a tubular membrane.
Claim 14
Dependent Claim
32 words
The membrane as described in claim 2 wherein the acid in step (a) is phosphoric acid in a concentration in the range from about 50 to about 85 weight percent aqueous solution.
Claim 15
Dependent Claim
27 words
The membrane as described in claim 1 wherein the acid in step (a) is selected from the group consisting of phosphoric acid, phosphorous acid and sulfuric acid.
Claim 16
Dependent Claim
52 words
The membrane as described in claim 1 wherein the reverse osmosis membrane in step (a) has a sodium chloride rejection of at least about 90 percent and a flux of at least about 10 gfd when tested with an aqueous solution of 2,000 ppm sodium chloride at 200 psi and 25° C.
Claim 17
Dependent Claim
15 words
The membrane as described in claim 1 wherein the polyamide is a poly(phenylene diamine trimesamide).
Claim 18
Dependent Claim
46 words
The membrane as described in claim 1 wherein the membrane has a water flux of at least about 15 gfd and a rejection of at least about 90 percent when tested with an aqueous solution of 0.2 percent magnesium sulfate at 50 psi and 25° C.
Claim 19
Dependent Claim
15 words
The membrane as described in claim 1 wherein the rejection enhancing agent is a colloid.
Claim 20
Dependent Claim
38 words
The membrane as described in claim 18 wherein the rejection enhancing agent is a tannic acid colloid which contacts the membrane in an aqueous acidic medium at a pH in the range from about 2 to about 5.
Claim 21
Dependent Claim
30 words
The membrane as described in claim 1 wherein the rejection enhancing agent is a styrene/maleamic acid copolymer or a C 5 to C 7 hydroxyalkyl methacrylate polymer, copolymer or terpolymer.
Claim 22
Dependent Claim
15 words
The membrane as described in claim 1 wherein the rejection enhancing agent is a coacervate.
Claim 23
Dependent Claim
96 words
A membrane useful for water softening comprising: (a) a porous support layer; (b) a crosslinked, aromatic polyamide discriminating layer affixed to the support layer, the discriminating layer having a first surface not in direct contact with the support layer; and (c) a rejection enhancing agent coating at least part of the first surface of the discriminating layer, wherein the membrane has a water flux of at least about 15 gfd and a rejection of at least about 90 percent when tested with an aqueous solution of 0.2 percent magnesium sulfate at 50 psi and 25° C.
Claim 24
Dependent Claim
96 words
A membrane useful for water softening comprising: (a) a porous support layer; (b) a crosslinked, aromatic polyamide discriminating layer affixed to the support layer, the discriminating layer having a first surface not in direct contact with the support layer; and (c) a rejection enhancing agent coating at least part of the first surface of the discriminating layer, wherein the membrane has a water flux of at least about 15 gfd and a rejection of at least about 90 percent when tested with an aqueous solution of 0.2 percent magnesium sulfate at 50 psi and 25° C.
Claim 25
Dependent Claim
15 words
The membrane as described in claim 22 wherein the polyamide is a poly(phenylene diamine trimesamide).
Claim 26
Dependent Claim
18 words
The membrane as described in claim 23 wherein the support layer is a porous polysulfone or polyether sulfone.
Claim 27
Dependent Claim
18 words
The membrane as described in claim 24 wherein the membrane is in the form of a flat sheet.
Claim 28
Dependent Claim
17 words
The membrane as described in claim 25 wherein the membrane is present in a spiral membrane device.
Claim 29
Dependent Claim
18 words
The membrane as described in claim 25 wherein the membrane is present in a plate and frame device.
Claim 30
Dependent Claim
17 words
The membrane as described in claim 25 wherein the rejection enhancing agent is a tannic acid colloid.
Claim 31
Dependent Claim
30 words
The membrane as described in claim 25 wherein the rejection enhancing agent is a styrene/maleamic acid copolymer or a C 5 to C 7 hydroxyalkyl methacrylate polymer, copolymer or terpolymer.
Claim 32
Dependent Claim
36 words
The membrane as described in claim 25 wherein the rejection enhancing agent is a copolymer of hydroxyethyl methacrylate and methyl methacrylate or methacrylamide and including up to 20 weight percent of other compatible ethylenically unsaturated monomers.
Claim 33
Dependent Claim
39 words
The membrane as described in claim 25 wherein the rejection enhancing agent is a coacervate prepared from a first polymer bearing a plurality of sulfonium or quaternary ammonium groups and a second polymer bearing a plurality of carboxylate groups.
References Cited (Backward Citations)
US3551331A
Cited
US3853755A
Cited
US3886066A
Cited
US3877978A
Cited
US4259183A
Cited
US4277344A
Cited
US4567009A
Cited
US4520044A
Cited
US4618533A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1991-08-23 | 1992-02-22 | 1992-08-23 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1995-08-23 | 1996-02-22 | 1996-08-23 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1999-08-23 | 2000-02-22 | 2000-08-23 | $7700.00 | Window Closed / Lapsed |