Ionomeric membrane

• US 20060223894A1
• Filed: 03/14/2006
• Published: 10/05/2006
• Est. Priority Date: 03/17/2005
• Status: Active Grant

• Current Assignee: Solvay Solexis SPA (Solvac SA)
• Original Assignee: Solvay Solexis SPA (Solvac SA)
• Inventors: Ghielmi, Alessandro, Arcella, Vincenzo, Vaccarono, Paola
• Granted Patent: US 8,536,237 B2
• Time in Patent Office: Days
• US Class Current: 521/27
• CPC Class Codes: B01D 71/32 containing fluorine atoms
• CPC Class Codes: B01D 71/82 characterised by the presence of specified groups, e.g. introduced by chemical after-treatment
• CPC Class Codes: C08J 2327/12 containing fluorine atoms
• CPC Class Codes: C08J 5/2237 containing fluorine
• CPC Class Codes: H01M 8/1025 having only carbon and oxygen, e.g. polyethers, sulfonated polyetheretherketones [S-PEEK], sulfonated polysaccharides, sulfonated celluloses or sulfonated polyesters
• CPC Class Codes: H01M 8/1039 halogenated, e.g. sulfonated polyvinylidene fluorides
• CPC Class Codes: H01M 8/1081 starting from solutions, dispersions or slurries exclusively of polymers
• CPC Class Codes: Y02E 60/50 Fuel cells
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

An ionomeric membrane formed of a sulphonic (per)fluorinated ionomer wherein the sulphonic groups are at the end of short side chains (SSC), said ionomer having: equivalent weight between 700 and 1600 g/eq;

• • side chains of formula: —O—CF₂—CF₂—SO₃³¹ M⁺, wherein M is hydrogen or an alkaline metal; said membrane having the following combination of properties: size variations, for both the orthogonal directions xy of the plane, lower than 15%, measured after dipping of the ionomeric membrane, dried at 105° C. under vacuum for one hour, in demineralized water at 100° C. for 30 minutes; the membrane, dipped at the temperature of 50° C. for 22 hours in a water/ethanol mixture containing 40% by weight of alcohol, remains integral.

Claims

1. An ionomeric membrane formed of a sulphonic (per) fluorinated ionomer with sulphonic groups at the end of short side chains (SSC), having:

equivalent weight from 700 to 1,600 g/eq, preferably from 750 to 1,200 g/eq;

side chains of formula;

—

O—

CF₂—

CF₂—

SO₃⁻

M⁺, wherein M is hydrogen or an alkaline metal;

size variations, in both orthogonal directions xy of the plane, lower than 15%, more preferably lower than 10%, measured after dipping of the ionomeric membrane, dried at 105°

C. under vacuum for one hour, in demineralized water at 100°

C. for 30 minutes;

remaining integral after dipping at the temperature of 50°

C. for 22 hours in a water/ethanol mixture containing 40% by weight of alcohol.

2. Membranes according to claim 1, wherein the (per) fluorinated ionomers usable for preparing the membranes are obtainable from ionomers having the following units:

(A) monomeric units deriving from one or more fluorinated monomers containing at least one ethylenic unsaturation;

(B) fluorinated monomeric units containing —

SO₂F groups having formula CF₂═

CF—

O—

CF₂CF₂SO₂F, in amounts such that the ionomer has the equivalent weight in the above range;

by hydrolysis of the —

SO₂F groups to obtain the —

SO₃H groups.

3. Membranes according to claim 1, wherein the fluorinated monomers (A) are selected from:

vinylidene fluoride (VDF);

C₂-C₈ perfluoroolefins, preferably tetrafluoroethylene (TFE);

C₂-C₈ chloro- and/or bromo- and/or iodo-fluoroolefins, preferably chlorotrifluoroethylene (CTFE) and bromotrifluoroethylene;

CF₂═

CFOR_f1 (per) fluoroalkylvinylethers (PAVE), wherein R_f1 is a C₁-C₆ (per) fluoroalkyl, preferably tri-fluoromethyl, bromodifluoromethyl, pentafluoropropyl;

CF₂═

CFOX perfluoro-oxyalkylvinylethers, wherein X is a C₁-C₁₂ perfluoro-oxyalkyl having one or more ether groups, preferably perfluoro-2-propoxy-propyl.

4. Membranes according to claim 1, wherein the sulphonic fluorinated ionomers contain from 0.01% to 2% by moles of monomeric units deriving from a bis-olefin of formula:

R₁R₂ C═

CH—

(CF₂)_mCH═

CR₅R₆;

 

 

(I)

wherein;

m=2-10, preferably 4-8;

R₁, R₂, R₅, R₆, equal to or different from each other, are H or C₁-C₅ alkyl groups.

5. Membranes according to claim 1, wherein the ionomers contain TFE as monomer (A).

6. A process for preparing the composite membrane according to claim 1, comprising the following steps:

1) preparation of a liquid dispersion comprising a (per) fluorinated ionomer, in acid or salified form, wherein the ionomer concentration is, in per cent by weight, between 0.5% and 40%, preferably between 0.5% and 25%;

2) deposit of the dispersion obtained in

     1) on a surface of a support to form a layer or film, the support being inert under the conditions used in the process of the present invention;

3) optional removal of the solvent for at least 80% by weight, preferably for at least 90%, still more preferably for at least 95% by weight with respect to the initial solvent of the used dispersion, obtaining a raw membrane on the support;

4) thermal treatment at temperatures from 130°

to 280°

C., preferably from 140°

to 180°

C., obtaining the membrane on the support;

5) detachment of the membrane from the support.

7. A process according to claim 6, wherein in step 1) the solvent used for preparing the liquid dispersion comprising the (per) fluorinated ionomer is selected from C₁-C₃;

preferably C₃, alcohols, n-propanol and/or iso-propanol;

or from mixtures, preferably with water, of said C₁-C₃ alcohols.

8. A process according to claim 7, wherein the dispersion is prepared by using organic solvents miscible with water and/or with C₁-C₃ alcohols.

9. A process according to claim 8, wherein the used solvents are fluoropolyoxyalkenes having one hydrogen atom at one or at both the chain end groups having boiling point between 80°

C. and 120°

C.

10. A process according to claim 6, wherein in step 2) the inert support, preferably non porous and with smooth surfaces, has the following properties:

it has size variations in each of the two directions xy of the plane, measured for 15 minutes at the temperature used in step

     4), not higher than 2%, preferably lower than 1%;

preferably the support substantially maintains unchanged its mechanical properties during the thermal treatment of the process step

     4).

11. A process according to claim 6, wherein in step 3) the solvent removal is carried out by operating at temperatures from 25°

C. to 95°

C., until obtaining a residual solvent content in the limits indicated in step

     3).

12. Electrochemical cell comprising the membrane of claim 1.

13. Use of the membrane of claim 1 in electrochemical cells.

14. Use according to claim 13, wherein the electrochemical cells are fuel cells.