US4147622A
Expired / Lapsed
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Process for manufacturing membranes for osmotic separation
Assignee: Sartorius Membranfilter GmbH
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Filing: 1977-03-18
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Granted: 1979-04-03
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Expires: 1997-03-18
Abstract
Abstract An asymmetrical permselective cellulose triacetate membrane has outstanding properties for desalination of seawater by reverse osmosis. It is made by casting a solvent solution of the cellulose triacetate in a solvent mixture of at least 40% acetone, a solvent for the triacetate and a swelling agent for the triacetate. The swelling agent, preferably formamide, must be added as the last component of the solution. After exposing the cast solution to evaporation for 2-90 seconds, it is precipitated in cold water, and then optionally tempered at 50°-100° C. in water which may contain a modifying agent, and dried.
Inventors
- 👤 Dietmar G. Nussbaumer
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 23:19
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; B01D2323/00; B01D2323/15; B01D2323/16; Y; Y02; Y02A; Y02A20/00; Y02A20/124; Y02A20/131
Claims Analysis
Total Claims: 41
Claim 1
Independent Claim
153 words
A process for manufacturing asymmetrical selectively permeable cellulose triacetate membranes with a skin layer on at least one side of the membrane, comprising: casting a low-molecular cellulose triacetate, having a viscosity, measured as a 2% solution in methylene chloride methanol 9:1, at 25° C., of a maximum of 10 cp and having an acetyl content of at least about 43%, dissolved in a mixture of solvents, to form a membrane, said solution consisting essentially of at least 50% acetone, a solvent for the cellulose triacetate, and a swelling agent for the cellulose triacetate, whereby the swelling agent is added to the solution as the last component, the concentration of the triacetate in the solution being 12-20%, and the swelling agent 5-15%, and the ratio of acetone to solvent being at least 1.25:1; exposing the cast membrane to evaporation for 2 to 90 seconds; and precipitating in cold water of room temperature or below.
Claim 2
Dependent Claim
153 words
A process for manufacturing asymmetrical selectively permeable cellulose triacetate membranes with a skin layer on at least one side of the membrane, comprising: casting a low-molecular cellulose triacetate, having a viscosity, measured as a 2% solution in methylene chloride methanol 9:1, at 25° C., of a maximum of 10 cp and having an acetyl content of at least about 43%, dissolved in a mixture of solvents, to form a membrane, said solution consisting essentially of at least 50% acetone, a solvent for the cellulose triacetate, and a swelling agent for the cellulose triacetate, whereby the swelling agent is added to the solution as the last component, the concentration of the triacetate in the solution being 12-20%, and the swelling agent 5-15%, and the ratio of acetone to solvent being at least 1.25:1; exposing the cast membrane to evaporation for 2 to 90 seconds; and precipitating in cold water of room temperature or below.
Claim 3
Dependent Claim
27 words
A process in accordance with claim 1 further including the step of tempering the cast membrane in water at 50° to 100° C. after said precipitating step.
Claim 4
Dependent Claim
16 words
A process in accordance with claim 2 wherein said tempering water has a modifying agent therein.
Claim 5
Dependent Claim
14 words
A process in accordance with claim 3 wherein the tempering temperature is 60°-100° C.
Claim 6
Dependent Claim
20 words
A process in accordance with claim 4 wherein said tempering step is performed in water containing up to 15% sulfolane.
Claim 7
Dependent Claim
77 words
A process in accordance with claim 4 wherein said modifying agent in said tempering water comprises a water-soluble ester, an alkane or alkene carboxylic acid or a lactone thereof or formamide saturated in said water up to 20%, a monovalent C 1 -C 3 alcohol in the water up to 45%, butanol saturated in the water, dioxane or C 3 -C 5 ketone up to 20% in the water, or sulfolane up to 15% in the water.
Claim 8
Dependent Claim
33 words
A process in accordance with claim 6 wherein said ester, or said acids or their lactone contain up to 5 carbon atoms in the alkane or alkene part and/or in the ester residue.
Claim 9
Dependent Claim
49 words
A process in accordance with claim 6 wherein the concentration of said modifying agent in the tempering water is 2-10% for said esters, carboxylic acids, lactones, formamides or sulfolane, 5-10% for dioxane and C 3 -C 5 ketones, 30-45% for C 1 -C 3 alcohols and saturation for butanol.
Claim 10
Dependent Claim
16 words
A process in accordance with claim 6 wherein said modifying agent is acetic acid or diacetin.
Claim 11
Dependent Claim
26 words
A process in accordance with claim 9 wherein the concentration of said acetic acid is approximately 10% or the concentration of said diacetin is approximately 4-6%.
Claim 12
Dependent Claim
22 words
A process in accordance with claim 2 wherein said tempering water is substantially pure water and the tempering temperaure is 70°-100° C.
Claim 13
Dependent Claim
31 words
A process in accordance with claim 11 further including the step of pretreating the formed membrane in formamide after said precipitating step and prior to said tempering step in pure water.
Claim 14
Dependent Claim
24 words
A process in accordance with claim 2 further including the step of treating the cast membrane with glycerol and water following said tempering step.
Claim 15
Dependent Claim
16 words
An asymmetrical selectively permeable cellulose triacetate membrane prepared in accordance with the process of claim 13.
Claim 16
Dependent Claim
16 words
An asymmetrical selectively permeable cellulose triacetate membrane prepared in accordance with the process of claim 2.
Claim 17
Dependent Claim
26 words
In the process of single-stage seawater desalination by reverse osmosis using a selectively permeable membrane, the improvement wherein said membrane is the membrane of claim 15.
Claim 18
Dependent Claim
20 words
A process in accordance with claim 2, further including the step of drying the formed membrane following said precipitating step.
Claim 19
Dependent Claim
16 words
An assymetrical selectively permeable cellulose triacetate membrane prepared in accordance with the process of claim 17.
Claim 20
Dependent Claim
26 words
In the process of single-stage seawater desalination by reverse osmosis using a selectively permeable membrane, the improvement wherein said membrane is the membrane of claim 18.
Claim 21
Dependent Claim
24 words
A process in accordance with claim 1 further including the step of treating the cast membrane with glycerol and water following said precipitating step.
Claim 22
Dependent Claim
20 words
A process in accordance with claim 20 wherein said treating step comprises immersing the cast membrane in 10% aqueous glycerol.
Claim 23
Dependent Claim
17 words
A process in accordance with claim 1 wherein said precipitating water is ice water at 0°-1° C.
Claim 24
Dependent Claim
24 words
A process in accordance with claim 1 wherein said cellulose triacetate in said solution contains up to 30% of its weight of cellulose diacetate.
Claim 25
Dependent Claim
30 words
A process in accordance with claim 1 wherein said solvent for the cellulose triacetate which is in the mixture with the acetone and the swelling agent is dioxane or dimethylsulfoxide.
Claim 26
Dependent Claim
23 words
A process in accordance with claim 1 wherein the ratio of acetone to said solvent for cellulose triacetate is no more than 17.5:1.
Claim 27
Dependent Claim
18 words
A process in accordance with claim 25 wherein said ratio of acetone to solvent is 1.25:1 to 3:1.
Claim 28
Dependent Claim
13 words
A process in accordance with claim 1 wherein said swelling agent is formamide.
Claim 29
Dependent Claim
18 words
A process in accordance with claim 27 wherein the concentration of said formamide in the solution is 8-12%.
Claim 30
Dependent Claim
34 words
A process in accordance with claim 1 wherein the length of time of said exposing step is 2-30 seconds and further including the step of drying the formed membrane immediately following said precipitating step.
Claim 31
Dependent Claim
19 words
A process in accordance with claim 29 wherein the length of time of said exposing step is 5-15 seconds.
Claim 32
Dependent Claim
22 words
A process in accordance with claim 1 wherein the atmosphere above the membrane during casting is maintained partially saturated with solvent vapor.
Claim 33
Dependent Claim
23 words
A process in accordance with claim 1 further including the step of aging the solution prior to said casting step for 12-48 hours.
Claim 34
Dependent Claim
15 words
A process in accordance with claim 32 wherein said aging is for approximately one day.
Claim 35
Dependent Claim
16 words
An asymmetrical selectively permeable cellulose triacetate membrane prepared in accordance with the process of claim 1.
Claim 36
Dependent Claim
23 words
In the process of ultrafiltration of hyperfiltration using a selectively permeable membrane, the improvement wherein said membrane is the membrane of claim 34.
Claim 37
Dependent Claim
24 words
A process in accordance with claim 1 wherein said solvent for the cellulose triacetate which is in the mixture with the acetone is dimethylsulfoxide.
Claim 38
Dependent Claim
42 words
A process in accordance with claim 36 wherein said casting solution is prepared at a temperature of -10° to -40° C. and only 2 to 6% dimethylsulfoxide is used as said solvent for the cellulose triacetate, based on the total casting solution.
Claim 39
Dependent Claim
20 words
A process in accordance with claim 1, further including the step of drying the formed membrane following said precipitating step.
Claim 40
Dependent Claim
16 words
An asymmetrical selectively permeable cellulose triacetate membrane prepared in accordance with the process of claim 38.
Claim 41
Dependent Claim
23 words
In the process of ultrafiltration of hyperfiltration using a selectively permeable membrane, the improvement wherein said membrane is the membrane of claim 39.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1982-04-02 | 1982-10-02 | 1983-04-03 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1986-04-02 | 1986-10-02 | 1987-04-03 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1990-04-02 | 1990-10-02 | 1991-04-03 | $7700.00 | Window Closed / Lapsed |