Patent US4307135A successfully refreshed from Google Patents.
US4307135A
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Process for preparing an asymmetric permselective membrane
Assignee: United States Department of the Interior
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Filing: 1980-04-08
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Granted: 1981-12-22
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Expires: 2000-04-08
Abstract
Abstract Asymmetric reverse osmosis membranes are made from synthetic aromatic polyimides having a relatively high predominance of polar groups in the polymer backbone. A polar/non-polar group ratio of from 2:2 to 2:7 per imidized nitrogen link is required. Such membranes can be fabricated using conventional casting equipment by providing a solution of the polyimide in a good solvent and a poor solvent, the poor solvent being compatible with solution components at poor solvent/good solvent ratios of at least 1:1 up to about 7:1, casting a film of such solution, and partially evaporating the exposed surface of the cast film for 100+/-30 seconds prior to gelation.
Inventors
- 👤 Ronald L. Fox
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 05:48
CPC Classifications
B; B01; B01D; B01D71/00; B01D71/06; B01D71/58; B01D71/62; B01D71/64
Claims Analysis
Total Claims: 5
Claim 1
Independent Claim
143 words
A process for preparing an asymmetric permselective membrane consisting essentially of a synthetic aromatic polyimide derived from the co-condensation of benzophenone3,3',4,4'-tetracarboxylic acid dianhydride and a mixture of either (1) di(4-aminophenyl)methane and toluene diamine or (2) 4,4'-methylenebis (phenyl isocyanate) and toluene diisocyanate, said process comprising: (a) providing a solution of about 18 to 25 weight percent of said polyimide in about 20 to 10 weight percent of N,N'-dimethylformamide and about 60 to 70 weight percent of dioxane, said formamide being a good solvent for said polyimide; (b) casting a film of said polyimide solution onto a suitable surface; (c) partially evaporating the solvent system from the exposed film surface for 100±30 seconds; and (d) gelling the polyimide film by immersion in water maintained at 15° to 32° C., whereby a thin, dense permselective polyimide skin is formed over a relatively thick, porous polyimide layer.
Claim 2
Dependent Claim
143 words
A process for preparing an asymmetric permselective membrane consisting essentially of a synthetic aromatic polyimide derived from the co-condensation of benzophenone3,3',4,4'-tetracarboxylic acid dianhydride and a mixture of either (1) di(4-aminophenyl)methane and toluene diamine or (2) 4,4'-methylenebis (phenyl isocyanate) and toluene diisocyanate, said process comprising: (a) providing a solution of about 18 to 25 weight percent of said polyimide in about 20 to 10 weight percent of N,N'-dimethylformamide and about 60 to 70 weight percent of dioxane, said formamide being a good solvent for said polyimide; (b) casting a film of said polyimide solution onto a suitable surface; (c) partially evaporating the solvent system from the exposed film surface for 100±30 seconds; and (d) gelling the polyimide film by immersion in water maintained at 15° to 32° C., whereby a thin, dense permselective polyimide skin is formed over a relatively thick, porous polyimide layer.
Claim 3
Dependent Claim
37 words
A process in accordance with claim 1 wherein said polyimide solution contains up to 2 weight percent of a pore former selected from the group consisting of water soluble alcohols, ketones and mineral acids or salts thereof.
Claim 4
Dependent Claim
26 words
A process in accordance with claim 1 wherein said polyimide film is cast at a speed within the range of 0.5 to 1.5 feet per minute.
Claim 5
Dependent Claim
26 words
A process in accordance with claim 1 wherein, during immersion, the total included angle of said film to the water line ranges between 100° to 135°.
References Cited (Backward Citations)
US3615024A
Cited
US3852388A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1984-12-21 | 1985-06-22 | 1985-12-22 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1988-12-21 | 1989-06-22 | 1989-12-22 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1992-12-21 | 1993-06-22 | 1993-12-22 | $7700.00 | Window Closed / Lapsed |