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US4026978A
Expired / Lapsed
US
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Method of making asymmetric cellulose triacetate membranes
Assignee: United States Department of the Interior
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Filing: 1975-07-17
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Granted: 1977-05-31
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Expires: 1995-07-17
Abstract
Abstract Asymmetric cellulose triacetate semipermeable membranes cast from a solution of cellulose triacetate having an acetyl content of at least 43 percent in a solvent mixture having a ratio of dioxane to acetone of at least about 1.5 to 1, which solution also contains a swelling agent in the form of a low molecular weight alcohol or a low molecular weight mono- or poly-basic acid. Solvent is evaporated from one surface of the cast film to form a dense gel layer and the film is immersed in water to provide an asymmetric semipermeable membrane having a high salt-rejection capability and good flux.
Inventors
- 👤 Charles R. Mungle
- 👤 Ronald L. Fox
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 14:54
CPC Classifications
B; B01; B01D; B01D71/00; B01D71/06; B01D71/08; B01D71/12; B01D71/14; B01D71/16; B01D67/00; B01D67/0002; B01D67/0009; B01D67/0011
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
140 words
A method for making an asymmetric cellulose triacetate semipermeable membrane, which method comprises forming a solution of cellulose triacetate having an acetyl content of 43.5 percent, by dissolving said cellulose triacetate in a solvent mixture of acetone and dioxane wherein said casting solution contains a ratio of dioxane to acetone of about 3.8 to 1 and also contains a swelling agent consisting of a mixture of methanol and maleic acid, casting said solution to form a film, evaporating solvent from one surface of said film for sufficient time to form a dense gel layer at said surface, and then treating said film with water to form a gel, and thereafter annealing said gelled film by immersion in water at a temperature of about 85° C., to thereby provide an asymmetric semipermeable membrane having a high salt-rejection capability and good flux.
Claim 2
Independent Claim
140 words
A method for making an asymmetric cellulose triacetate semipermeable membrane, which method comprises forming a solution of cellulose triacetate having an acetyl content of 43.5 percent, by dissolving said cellulose triacetate in a solvent mixture of acetone and dioxane wherein said casting solution contains a ratio of dioxane to acetone of about 3.8 to 1 and also contains a swelling agent consisting of a mixture of methanol and maleic acid, casting said solution to form a film, evaporating solvent from one surface of said film for sufficient time to form a dense gel layer at said surface, and then treating said film with water to form a gel, and thereafter annealing said gelled film by immersion in water at a temperature of about 85° C., to thereby provide an asymmetric semipermeable membrane having a high salt-rejection capability and good flux.
Claim 3
Dependent Claim
27 words
A method for making an asymmetric semipermeable membrane in accordance with claim 1 wherein said evaporation is carried out for between about 25 and about 90 seconds.
Claim 4
Dependent Claim
29 words
A method for making a semipermeable membrane in accordance with claim 2 wherein said evaporation is carried out at a temperature between about 15° C. and about 35° C.
Claim 5
Dependent Claim
31 words
A method for making a semipermeable membrane in accordance with claim 3 wherein said solution being cast is maintained at a temperature of between about 0° C. and about 30° C.
Claim 6
Dependent Claim
30 words
A method for making an asymmetric semipermeable membrane in accordance with claim 1 wherein said solution contains cellulose triacetate in an amount between about 11 and about 18 weight percent.
Claim 7
Dependent Claim
48 words
A method for making a semipermeable membrane in accordance with claim 1 wherein said solution contains cellulose triacetate in an amount between about 15.5 and about 16.5 weight percent and has a viscosity between about 200 and about 2000 poises at the temperature at which casting takes place.
References Cited (Backward Citations)
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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) | 1980-05-30 | 1980-11-29 | 1981-05-31 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1984-05-30 | 1984-11-29 | 1985-05-31 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1988-05-30 | 1988-11-29 | 1989-05-31 | $7700.00 | Window Closed / Lapsed |