Methods and apparatus for the formation of heterogeneous ion-exchange membranes

• US 6,503,957 B1
• Filed: 11/19/1999
• Issued: 01/07/2003
• Est. Priority Date: 11/19/1999
• Status: Expired due to Fees

• Current Assignee: SnowPure, LLC
• Original Assignee: Electropure, Inc.
• Inventors: Bernatowicz, Joseph M., Snow, Michael J., OʼHare, Ronald J.
• Primary Examiner(s): Zitomer, Fred
• Application Number:
  US09/444,055
• Time in Patent Office: 1,145 Days
• Field of Search: 521/27, 521/25, 524/80, 524/81, 524/502, 524/509
• US Class Current: 521/27
• CPC Class Codes: B29C 48/40 using two or more parallel screws or at least two parallel non-intermeshing screws, e.g. twin screw extruders
• CPC Class Codes: C08J 2323/12 Polypropene
• CPC Class Codes: C08J 5/2275 Heterogeneous membranes

Abstract

The present invention provides methods and apparatus for the formation of heterogeneous ion-exchange membranes by prescribed in-line compounding and extrusion of a polymeric binder and heat sensitive ion-exchange resin. The ion-exchange resin is incorporated, at a late process stage, into the melted matrix polymer at relatively low temperature and residence time prior to transfer to a die head for extrusion. In the presently preferred embodiment, the in-line compounding apparatus comprises a twin-screw compounding extruder, for effecting late stage kneading and mixing of ion-exchange resin and optional additives to the polymer melt, prior to compression to transfer the blended polymer melt to a die head for extrusion. Accordingly, the final properties of the resultant heterogeneous ion-exchange membrane are enhanced as the blended polymer melt material is not exposed to excessive heat and shear history. Resultant heterogeneous ion-exchange membranes and apparatus for treatment of fluid streams utilizing such membranes are also provided.

Claims

1. A method for the formation of an improved heterogeneous ion-exchange membrane comprising:

a) feeding a supply of a polymer binder to an in-line compounding extruder, having means for melting, kneading and transferring the polymer binder to a sheet die head for sheet extrusion;

said extruder further having means for feeding and blending additives in-line to the melted polymer binder at a prescribed processing stage;

b) maintaining the polymer binder within said extruder at a temperature range of between about the softening point of said polymer binder and the melting point of said polymer binder to form a melted matrix polymer;

c) kneading the melted polymer binder to form a homogeneous matrix;

d) subsequently adding and mixing a powdered ion-exchange resin, to the melted matrix polymer derived from step c) to form a heterogeneous blended melt within said extruder, wherein said ion-exchange resin has a residence time within said extruder of less than about two minutes; and

e) transporting the blended melted polymer matrix derived from step d) directly into a sheet die head for continuous sheet extrusion.

2. The method for the formation of an improved heterogeneous ion-exchange membrane as defined in claim 1, and further including the step of washing the sheet extrusion in a deionized water bath at a temperature of from about 180 degrees F. for at least two hours until expansion is effected.

3. The method for the formation of a heterogeneous ion-exchange membrane as defined in claim 1, wherein said powdered ion-exchange resin is added to the melted matrix polymer in a range of between about 20% to about 80% by weight.

4. The method for the formation of a heterogeneous ion-exchange membrane as defined in claim 1, wherein the polymer binder is polypropylene polymer.

5. The method for the formation of a heterogeneous ion-exchange membrane as defined in claim 1, wherein the powdered ion-exchange resin has an average size of 200 mesh.

6. The method for the formation of a heterogeneous ion-exchange membrane as defined in claim 1, wherein polymer binder is metallocene polypropylene polymer having a narrow molecular weight distribution and having a melting point below about 130 degrees C.

7. The method for the formation of a heterogeneous ion-exchange membrane as defined in claim 1, wherein the powdered ion-exchange resin has an average size of 325 mesh.

8. The method for the formation of a heterogeneous ion-exchange membrane as defined in claim 1, wherein the powdered ion-exchange resin is of Type I.

9. The method for the formation of a heterogeneous ion-exchange membrane as defined in claim 1, wherein the powdered ion-exchange resin is of Type II.

10. The method for the formation of a heterogeneous ion-exchange membrane as defined in claim 1, wherein the powdered ion-exchange resin is of Type III.

11. The method for the formation of a heterogeneous ion-exchange membrane as defined in claim 1, wherein the powdered ion-exchange resin is anionic.

12. The method for the formation of a heterogeneous ion-exchange membrane as defined in claim 1, wherein the powdered ion-exchange resin is cationic.

13. The method for the formation of a heterogeneous ion-exchange membrane as defined in claim 1, wherein the powdered ion-exchange resin is amphoteric.

14. The method for the formation of a heterogeneous ion-exchange membrane as defined in claim 1, wherein the powdered ion-exchange resin is a mixture of ion-exchange materials selected from the group consisting of:

Type I, Type II, Type III, anionic, cationic, amphoteric and mixtures thereof.