US4812270A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Novel water softening membranes
Assignee: Dow Chemical Co
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Filing: 1988-06-13
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Granted: 1989-03-14
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Expires: 2008-06-13
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
2026-11-09 04:07
CPC Classifications
B; B01; B01D; B01D67/00; B01D67/0081; B01D67/0088; B01D67/0093; B01D67/00933; B01D2323/00; B01D2323/30; Y; Y10; Y10S; Y10S264/00; Y10S264/48
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
129 words
A process comprising making a membrane having properties for enabling water softening, by, (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 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
129 words
A process comprising making a membrane having properties for enabling water softening, by, (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 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
35 words
The process as described in claim 1 wherein the acid treatment in step (b) increases the water flux of the membrane by at least about 50 percent at the recited MgSO 4 reverse osmosis conditions.
Claim 4
Dependent Claim
34 words
The process as described in claim 1 wherein the sum of the water flux in gfd and MgSO 4 rejection in percent for the acid-treated membrane in step (b) is at least about 90.
Claim 5
Dependent Claim
15 words
The process as described in claim 1 wherein the polyamide is a crosslinked aromatic polyamide.
Claim 6
Dependent Claim
27 words
The process as described in claim 4 wherein the acid in step (a) is selected from the group consisting of phosphoric acid, phosphorous acid and sulfuric acid.
Claim 7
Dependent Claim
21 words
The process as described in claim 5 wherein the polyamide is a poly(phenylene diamine trimesamide) and the acid is phosphoric acid.
Claim 8
Dependent Claim
27 words
The process as described in claim 6 wherein the rejection enhancing agent is tannic acid or a hydrolyzable tannin which contacts the membrane in an aqueous medium.
Claim 9
Dependent Claim
30 words
The process as described in claim 6 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 10
Dependent Claim
36 words
The process as described in claim 6 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 11
Dependent Claim
39 words
The process as described in claim 6 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.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1992-03-13 | 1992-09-12 | 1993-03-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-03-13 | 1996-09-12 | 1997-03-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-03-13 | 2000-09-12 | 2001-03-14 | $7700.00 | Window Closed / Lapsed |