Method of making semi-permeable asymmetric membranes for reverse osmosis

• US 3,954,925 A
• Filed: 09/19/1974
• Issued: 05/04/1976
• Est. Priority Date: 12/20/1972
• Status: Expired due to Term

• Current Assignee: Gkss-Forschungszentrum Geesthacht GmbH
• Original Assignee: Gesellschaft Fur Kernenergie In Schiffbau U Schiffahrt mbH
• Inventors: Boddeker, Karl W.
• Primary Examiner(s): Anderson, Philip
• Application Number:
  US05/507,471
• Time in Patent Office: 593 Days
• Field of Search: 264/41, 264/49, 264/217, 210/500 M
• US Class Current: 264/41
• CPC Class Codes: B01D 2323/16 Swelling agents
• CPC Class Codes: B01D 61/025 Reverse osmosis; Hyperfiltration
• CPC Class Codes: B01D 67/0011 Casting solutions therefor
• CPC Class Codes: B01D 67/00113 Pretreatment of the casting solutions, e.g. thermal treatment or ageing
• CPC Class Codes: B01D 71/16 Cellulose acetate

Abstract

A method of making semi-permeable asymmetric membranes for desalting water in conformity with the method of reverse osmosis from a cellulose acetate casing mixture to which as modifying component there is added ammonia, preferably in gaseous condition, as swelling substance. Preferably a solution of cellulose acetate in acetone is employed into which the gaseous ammonia is introduced up to the desired concentration at room temperature, e. g. of 22° C. Casting of the film followed by a brief evaporation period prior to gelling the film in cold water is done at room temperature.

Claims

1. In a phase-inversion a method of making semi-permeable asymmetric membranes for the desalination of water according to the reverse osmosis method, the improvement comprising in combination the steps of preparing a pourable cellulose acetate solution consisting essentially of cellulose acetate and acetone at a ratio within the range of from 1:

2 to 1;

3, and adding thereto ammonia within the range of from 2 to 5% by weight as the sole swelling agent.

2. A method in combination according to claim 1, in which said cellulose acetate is a secondary cellulose acetate, and in which said ammonia is introduced into said cellulose acetate solution in gaseous anhydrous condition at room temperature.

3. A method in combination according to claim 1, in which the membranes being produced are cast at normal room temperature followed by a brief evaporation period likewise at room temperature, immersed in cold water and finally subjected to a heat treatment.

4. A method in combination according to claim 3, in which the membrane properties are controlled by varying the ammonia content, the evaporation period, and the heat treating temperature.

5. A method in combination according to claim 4, in which the heat treating step involves heating at a temperature of between 70°

and 85°

C for approximately 5 minutes.