CA1071571A - Fluorinated ion exchange membrane containing n-monosubstituted sulfonamido groups - Google Patents
Fluorinated ion exchange membrane containing n-monosubstituted sulfonamido groupsInfo
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- CA1071571A CA1071571A CA284,465A CA284465A CA1071571A CA 1071571 A CA1071571 A CA 1071571A CA 284465 A CA284465 A CA 284465A CA 1071571 A CA1071571 A CA 1071571A
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Abstract
ABSTRACT OF THE DISCLOSURE
Pendant side chains containing sulfonyl groups attached to carbon atoms having at least one fluorine atom connected thereto are present as N-monosubstituted sulfon-amido groups in fluorinated polymers. Films of the polymers may serve for ion exchange purposes generally, and in particular as membranes in electrolysis cells. Composite films having one surface of such polymer have shown outstanding application as membranes in chlor-alkali cells with high current efficiency and minimization of anion transport of hydroxyl ions.
Pendant side chains containing sulfonyl groups attached to carbon atoms having at least one fluorine atom connected thereto are present as N-monosubstituted sulfon-amido groups in fluorinated polymers. Films of the polymers may serve for ion exchange purposes generally, and in particular as membranes in electrolysis cells. Composite films having one surface of such polymer have shown outstanding application as membranes in chlor-alkali cells with high current efficiency and minimization of anion transport of hydroxyl ions.
Description
BACKGROUND OF THE INVENTION
Fluorinated ion exchange membranes are known in the art wherein the ion e~change polymer precursor con~ains pendan~ side chains in sulfonyl fluoride form. These groups are converted to ionic form such as by hydrolysis with an alkaline material or by treatment with ammonia. An example of such prior art teaching is disclosed in Connolly and Gresham U.S. Patent 3,282,8750 Additionally, in the prior art is disclosed a tech-nique of treating cation exchange polymers for modificationof the property of relative cationic transport. This teaching is set forth in Miz~tani et al. U.S. Patent 3,647,o86 in preparation of an ion exchange membrane wherein permeation selection of different classes of cations is improved. As set forth in the Mizutani et al. patent, a cation exchange polymer of a high molecular weight polymer contains chemically bonded acid amide groups. These groups are present at the "substantial surface" to satisfy the equation:
A x 100 = 15 - 10 5%
A -~ B
wherein (per gram of dry membrane) A is the number of acid amide bonds and B is the number of cation exchange groups.
The reaction is controlled such that the formation of the acid amide bonds takes place only at the surface or as set for~h in the patent at the "substantial surface".
SUMMARY OF THE INVENTION
The precursor fluo-rinated polymers employed herein are of the type disclosed in Connolly et al. U~S.PI 3,282,875;
Resnick U.S.P. 3,560,568 and Grot U~S.P. 3,718~627 with pendant sulfonyl groups present as -S02F preferably or generically as -S02X with X representing fluorine or chlorine.
Fluorinated ion exchange membranes are known in the art wherein the ion e~change polymer precursor con~ains pendan~ side chains in sulfonyl fluoride form. These groups are converted to ionic form such as by hydrolysis with an alkaline material or by treatment with ammonia. An example of such prior art teaching is disclosed in Connolly and Gresham U.S. Patent 3,282,8750 Additionally, in the prior art is disclosed a tech-nique of treating cation exchange polymers for modificationof the property of relative cationic transport. This teaching is set forth in Miz~tani et al. U.S. Patent 3,647,o86 in preparation of an ion exchange membrane wherein permeation selection of different classes of cations is improved. As set forth in the Mizutani et al. patent, a cation exchange polymer of a high molecular weight polymer contains chemically bonded acid amide groups. These groups are present at the "substantial surface" to satisfy the equation:
A x 100 = 15 - 10 5%
A -~ B
wherein (per gram of dry membrane) A is the number of acid amide bonds and B is the number of cation exchange groups.
The reaction is controlled such that the formation of the acid amide bonds takes place only at the surface or as set for~h in the patent at the "substantial surface".
SUMMARY OF THE INVENTION
The precursor fluo-rinated polymers employed herein are of the type disclosed in Connolly et al. U~S.PI 3,282,875;
Resnick U.S.P. 3,560,568 and Grot U~S.P. 3,718~627 with pendant sulfonyl groups present as -S02F preferably or generically as -S02X with X representing fluorine or chlorine.
2.
, ~, ~., ~
.,.~,,. i ~ 7~
In the present disclosure at least a portion of the pendant side chains which contain a sulfonyl group at-tached to a carbon atom having at least one fluorine atom connected thereto are converted to N monosubstituted sul-*onamido groups.
The ion exchange membranes of the present disclo sure which contain N-monosubstituted sulfonamido groups as active ion exchange sites are highly desirable in comparison with prior art ion exchange membranes for several distinct reasons. The ion exchange sites may be introduced into the polymer in membrane or film form in a relatively short period of time in comparison to introduction of sulfonamido groups in the prior art teachings~ Most importantly~ out~
standing efficiencies in a chlor-alkali cell have been ob- -tained with the N-monosubstituted sulfonamido groups in comparison to sulfonamide groups obtained by treatment with ammonia and other ion exchange groups obtained by hydrolysis of pendant sulfonyl groups.
Conversion at the surface of the polymer of the pendant -S02X groups with X as fluorine or chlorine takes place such that a~ least the majority of the reactive sites are convertedD In the case of use of the polymer-in ion ex~
change for a chlor-alkall cell most desirably essentially complete or complete conversion of the sulfonyl halide groups takes place on only a single surface of a film. Thereafter, unreacted sulfon~1 halide groups on a second film surface are hydrolyzed to convert them to ionic form~ In an alternate manner sulfonyl halide groups on one surface may be hydrolyzed prior to conversion of the sulfonyl halide groups on the other surface of the film to N-monosubstituted sulfonamido groups.
, ~, ~., ~
.,.~,,. i ~ 7~
In the present disclosure at least a portion of the pendant side chains which contain a sulfonyl group at-tached to a carbon atom having at least one fluorine atom connected thereto are converted to N monosubstituted sul-*onamido groups.
The ion exchange membranes of the present disclo sure which contain N-monosubstituted sulfonamido groups as active ion exchange sites are highly desirable in comparison with prior art ion exchange membranes for several distinct reasons. The ion exchange sites may be introduced into the polymer in membrane or film form in a relatively short period of time in comparison to introduction of sulfonamido groups in the prior art teachings~ Most importantly~ out~
standing efficiencies in a chlor-alkali cell have been ob- -tained with the N-monosubstituted sulfonamido groups in comparison to sulfonamide groups obtained by treatment with ammonia and other ion exchange groups obtained by hydrolysis of pendant sulfonyl groups.
Conversion at the surface of the polymer of the pendant -S02X groups with X as fluorine or chlorine takes place such that a~ least the majority of the reactive sites are convertedD In the case of use of the polymer-in ion ex~
change for a chlor-alkall cell most desirably essentially complete or complete conversion of the sulfonyl halide groups takes place on only a single surface of a film. Thereafter, unreacted sulfon~1 halide groups on a second film surface are hydrolyzed to convert them to ionic form~ In an alternate manner sulfonyl halide groups on one surface may be hydrolyzed prior to conversion of the sulfonyl halide groups on the other surface of the film to N-monosubstituted sulfonamido groups.
3.
An important advantage of the present polymer and the method of preparation in comparison to treatment wlth ammonia of the prior art is elimination of extensive treat-ment times. A considerable time period for treatment is necessary for ammonia which ranges upwards from several hours while treatment with the amines to form the N-monosubstituted sulfonamido groups will be of the order of minutes. Flexibility ls af~orded with the amines which form the ~-monosubstltuted sulfonamido groups since the treatment techniques generally can involve liquid or gaseous contact. Also, wlth short periods o~ reaction a continuous process may be realized rather than batch convers~on.
An outstanding advantage has been obtalned wlth ionic groups present as N-monosubstituted sulfonamido gro,ups in comparison with the ionic groups present as the sul~onamide.
With a surface conversion by reaction with an amine to obtain N-monosubstituted sulfonamido groups rather than treatment with ammonia to obtain the sulfonamide, a dramatic increase in current e~ficiency has been obtained in application in a chlor-alkali cell. This improvement is considered to be of predominant importance in commercial applicability in reducing the cost of producing a unit o~ chlorine and caustic.
Illustratively, in a chlor-alkali plant producing 1000 tons per day of chlorine~ the direct savings in elec-trlcal power for only a 1% increase in efficlency are significant.
DETAILED DESCRIPTION
_ A need has developed in the chlor-alkali industry for the use of improved ion exchange materials which can replace existing separators which have been used for decades ~ . ~
~ ~p~ D~4750 without substan~ial improvement in design.
In the environmerlt of a chlor-alkali cell, the membrane mus~ be able to withstand a hostile environment for a polymeric material such as exposure to a hlghly alka-line pH as well as exposure to chlorine. Generally, hydro-carbon ion exchange membranes are totally unsatisractory for this usage since the membrane cannot withstandithis enviro~nent.
For commercial usage in the chlor alkali industry, a film must go beyond the ability to be operable for pro~
longed time periods in the production of chlorine and caustic.
A most important criteria is the current efficiency with the polymer in conversion of the brine in the electrolytic cell to the desired products. Therefore, improvement in current efficiency can translate into pronounced savings in the cost of production of each unit of chlorine and caustic. Addi-tionally, from a commercial standpoint the cost of production of each unit will be determinative of the commercial suitability of an ion exchange membrane.
The ion exchange polymers of the present disclosure possess pendant side chains conkaining sulfonyl groups at-tached ~o carbon atoms having at least one fluorine atom connected thereto with the pendant chains present as N-monosubstituted sulfonamido groupsO The polymers are prepared from monomers which are fluorinated or fluorine substituted vinyl compounds~ The polymers are made from at least two monomers with at least one of the monomers coming from each of the two groups described below. The ~irst group i5 fluorinated vinyl compounds such as vinyl fluoride, hexa-fluoropropylene 9 vinylidene fluoride 9 trifluoroethylene, chlorotrifluoroe~hylene, perfluoro(alkyl vinyl ether~
tetrafluoroethylene and mixtures thereof. In the case o~
use of copolymers in electrolysis of brine~ the precursor vinyl monomer desirably will not con~ain hydrogen.
The second group is the sulfonyl-containing monomers containing the precursor -S02F or -S02Cl~ One example of such a comonomer is CF2=CFS02F. Additional examples can be represented by the general formula CF2=
CFR~S02F wherein Rf ls a bifunctional perfluorinated radical comprising 2 to 8 carbon atoms. The particular chemical content or structure of the radical linking the sulfonyl group to the copolymer chain is not critical but such must have a fluorine atom attached to the carbon atoms to which is attached the sulfonyl groupO If the sulfonyl group is attached directly to the chain, the carbon in the chain to which it is attached must have a fluorine atom attached to it.
Other atoms connected to this carbon can include fluorine, chlorine, or hydrogen although generally hydrogen will be excluded in use of the copolymer ~or ion exchange in a chlor-alkali cell. The Rf radical of the formula above can be either branched or unbranched, i.e., straigh~-chained and can have one or more ether linkages. It is preferred that the vinyl radical in this group of sulfonyl fluoride contain-ing comonomers be joined to the Rf group through an ether llnkage, i.e., that the comonomer be of the formula CF2=CFORfS02F. Illustrative of such sulfonyl fluoride containing comonomers are CF2=CFOCF2CF2S02F, CF2=CFoCF2TFOcF2cF2s02 CF2=CFOCF2CFOCF2fFOCF2CF2S02F, AD-1~750 CF2=CFC~2CF2S02F, and CF2-CF0CF21F0C~2cF2s02 fF2 bF3 . ...
The most preferred sulfonyl fluoride containing comonomer is perfluoro(3,6-dioxa-L~-methyl-7-octenesulfonyl fluoride), CF2 -cFocF2cFocF2cF2so2F .
The sulfonyl containing monomers are disclosed in such references as U. S0 P. 3,282,875 to Connolly et al., U~S.PO
3,041,317 to Gibbs et al., and in U~S.P~ 3,718,627 to Grot and in U~S.P. 3,560,568 to Resnick.
The preferred copolymers utilized in the film are perfluorocarbon although others can be utilized as long as there is a fluorine atom attache~ to the carbon atom which is attached to the sulfonyl group o~ the polymer. The most preferred copol~mer is a copolymer Or tetrafluoroethylene and perfluoro(3 9 6-dioxa-~-methyl-7-octenesulfonyl fluoride) which comprises 10 to 60 percent, preferably, 25 to 50 percent by weight of the latter.
The copolymer used in the present invention is - prepared by general polymerizakion techniques developed for homo- and copolymerizations o~ fluorinated ethylenes, partic-ularly those employed for tetrafluoroethylene which are described in the literature. Nonaqueous techniques for preparing the copolymers of the present inven~ion include that of U. S. P0 3,01~1~317, issued to H~ Mo Gibbs and R. N.
Griffin on June 26~ 1962, that is~ by the polymerization o~
a mixture of the major monomer therein, such as D-~750 tetrafluoroethylene, and a fluorinated ethylene containing sulfonyl fluoride in the presence of a free radica:L initiator, preferably a perfluorocarbon peroxide or aæo compound~ at a temperature in the range 0-200C~ and ak pressures in the range 1-2007 or more atmospheres. The nonaqueous polymeriza-tion may9 if desired, be carried out in the presence of a fluorinated solvent. Suitable fluorinated solvents are inert9 liquid9 perfluorinated hydrocarbons7 such as per-fluoromethylcyclohexane, perfluorodimethylcyclobutane~
perfluorooctane, perfluorobenzene and the like.
Aqueous techniques for preparing the copolymer of this invention include contacting the monomers with an aqueous medium containing a free~radical initiator to obtain a slurry of polymer particles in non-water~wet or granular form9 as disclosed in U0 SO Patent 2,3939967, issued to Mo M~
Brubaker on February 5, 1946; or contacting the monomers with an aqueous medium containing both a free-radical initia-tor and a telogenically inactive dispersing agent, to obtain an aqueous colloidal dispersion of polymer particles, and coagula~ing the dispersion9 as disclosed9 for example, in U. S~ P~ 2,5595752, issued to K. L. Berry on July 10, 19519 and U. S. PO 2,593~$839 issued to J~ ~. Lontz on April 22, 19520 Upon formation of the intermediate polymer9 the pendant sulfonyl groups are present as ~SO?X with X defining fluorine or chlorine and preferably fluorineO It is a re-quirement in ~oth the intermediate and :Einal fluorinated polymers disclosed herein that the sulfonyl groups are at-tached to carbon ato~s having at least one fluorine atom connected theretoO These carbon atoms serve to link the sulfonyl group to the copolymer~chain or alternatively, th~
8.
~P7~Y~
carbon atom~ form a portlon o~ the backbone chain ln the copolymer. After formation o~ the intermed1ate polymer, the sul~onyl group~ are converted to N-monosubstituted ~ul~onamido group3.
In order to obtain ion exchange properties, the ~ole criticality o~ the N-monosubstituted groups is to functlon a~ an ion exchange site. me group employed ls not consldered critical from the standpoint of operability~ However, a di~ference in results will be obtained dependent upon the group employed, e.g., a varia-tion in current e~flciency with minimization o~ anion transport together with a variation ln the power required for each unit of product from a chlor-alkali cell. Additionally, i~ the N-mono~ubstituted sul~onamido group is unstable. e.g., in use of a chlor-alkall cell~ reaction and conversion of the group ean occur to a stable ion exchange sit~.
As illustrative examples o~ ~uitable groups a~ ~-monosubstituted ~ulfonamido group~ are those disclosed in M~zutani ~t al U.S.p. 3,647,o86. Although this pr~or art patent disclose~ reaction of both primar~ and secondary amines with the ion exchange polymer, the reacted amines are no~ re-quired to function as ion exchange groups in direct contrast to the disclosed groups in the polymer~ o~ the present appli-cationO
me amine~ useful in the invention are primaryamine~ o~ the type disclosed in Mlzutani et al. U.S.P~ 3,647,o860 Therefore, these amines are o~ the ~ormula H wherein H-N~R
R is alkyl, haloalkyi, alkyl substituted by either hydroxy, ~mino, carboxy~ alkoxy, pho~phonlc acid, ~ulfonic acid, nitro, nitrile, carb~moyl, ~ulfonic acid amide or pho~phonic acid ~D 475 amide~ aryl, aryl substituted by hydroxy, amino9 carboxy, phosphonic acid, alkoxy, sul~onic acid, nitro5 nitrile, carbamoyl, sulfonic acid amide, carbamoyl or phosphonic acid amide, a heterocyclic group or aralkyl~ In addition to the amides listed above~ the corresponding esters are likewise suitable. Illustrative of suitable ~ groups are straight and branch chained alkyls, benzyl and ~Rl _~ ..
wherein both Rl and R2 lndependently of the other can rcpre-s~nt alkyl, aryl ? aralkyl or hydrogen4 Illustratively, both Rl and R2 may include alkyl. Suitable amines include those of di-9 tri- and poly-functional types. Generally, amines containing alkyl groups have been found most satisfactory such as methyl amine and diamines of the type NH2(CH2)nNH2 wherein n is 2 to lO. The length of the chain is not con-sidered critical as illustratively alkyls may contain l to lO
carbon atoms or 2 to lO carbon atoms for alkylene in the case of diamines.
It is within the scope of this disclosure to include ~he salts of the N-monosubstituted sulfonamido groups~ Suit~
able salts include those with alkaline earth and alkali metal cations. Preferred metals include sodium and potassiumO
To obtain the conversion of the inkermediate pendant sulfonyl group, -S02X with X previously defined, the precursor polymer may be treated with the amine in either liquid or gaseous formO
Both reactive and inert carriers and solvents for the amine may be employed~ The reactive carrier will compete 10.
wikh the amine in conversion of the pendant sul~onyl halide sites on the precursor polymer. A reactive carrier contains active hydrogen such as water. Primary alcohols are not considered suitable since they react rapidly with the intermediate pendant sulfonyl halide groups lowering the concentration of the desired lon exchange sites. The competitive reaction may also produce ion exchange sites in the fluorinated polymer disclosed herein since the sulfonyl halide is converted to -S03 .
~ile outstanding advantages have been obtained with essentially complete conversion of the active sulfonyl halides in a polymer layer or surface to form the N-monosubstituted sul~onamido groups, it is within the scope of this disclosure to convert only a minimum of 40% or about a ma~ority of these sulfonyl groups to this form. The remaining groups are desirably converted to other active ion exchange groups For example, water employed as a carrier with ~he amine w~ll promote a competing reaction with the sulfonyl halide.
Inert solvents may be desirably employed which contaln no active hydrogen atoms and do n~t promote a competing reaction. Examples include dimethyl formamide, dimethyl sulfoxide~ tetramethylene sulfone, hexamethyl phos-phoramide3 diglyme, acetonitrile and general classes of ethers and nitriles.
Pressure and temperature together with the carrier or solvent, if employed, will determlne the efficiency and time of conversion of the sulfonyl groups and will tend to influence the degree of penetration of the amine into the polymer.
However, pressure and temperature are not ,~,"~; ,...
considered critical in the framework of obtaining conversion of the pendant -S02X groups but rather upon the rate of reaction and degree of penetration of the amine, Illus-tratively~ room temperature conversion has been found ko be satisfactory for most amines~ Pressure, below at or above atmospheric pressure may be employed, Wikh gaseous treatment, the proper combination of pressure and temperature wlll be employed to obtain the amlne in the gaseous state. With gaseous treatment~ an inert gas as a carrier may be employed.
For purposes of explanation in the reaction proce-dure, it is considered from physical observation after reaction with the amine that a sharp line of demarca~ion exists bet~ween converted sulfonyl halide groups and unconverted sulfonyl halide groups if the intermediate polymer does not or is not allowed to completely react. This observation is based upon staining the reacted polymer with a cationic active dye such as Sevron Red. In the present context~ a sharp l~ne of demar-cation refers to observation of a stained boundary with a cationic active dye.
The ion exchange polymer film of the present disclo-sure in a chlor~alkali cell desirably has a single surface converted to the N-monosubstituted sulfonamido form, In such event, the N-monosubstituted sulfonamido surface converted to the salt form faces the cathode portion of the cell producing caustic. This surface of the membrane serves to minimize anion transport of hydroxyl ions and acts as a barrier for such transport. Also~ the formation of a sur~ace layer, rather than total conversion, has been found to reduce the overall electrical resistance of the polymer leading to highly desirable results from ~he . ~ . . i . .
7~
standpoint of electrical power consumption. Such surface conversions have led to a significant increase of the ef-ficiency and a significant decrease in power consumption such as in comparison with sulfonyl groups converted with ammonia to the sul~onamide ~orm. Current efficiencies approaching and exceeding gO% are considered obtainable from a commercial standpoint with the amine reaction. A comparison with methyl amine treatment as opposed to ammonia treatment has shown an increase o~ efficiency of the order o* 4-5% and greater.
Similarly~ use of a diamine such as ethylenediamine has given comparable or better results.
An o~ltstanding advantage has been found in terms of electrical ef~iciency in a chlor-alkali cell with the fluorinated polymers of the type disclosed herein with pendant groups present as N-monosubstituted sulfonamido groups and salts thereo~. However, an equally impor~ant criterion in a chlor-alkali cell is the amount o~ power required for each unit o~ chlorine ancl caustic. It is con-sidered that the polymers of the type disclosed herein permit one by a proper combination o~ operating conditions to realize an excellent and une~ected reduction in power. Since the power requirement ~which may be expressed in watt-hours) is a function of both cell voltage and current efficiency~ low cell vo~tages are desirable and necessary~ However, a polymer without a high current ef~iciency cannot operate effectively ~rom a commercial standpoint even with extremely low cell voltages. Additionally, a polymer with an inherent high current efficiency allows one by a proper combination o~ para-meters as in fabrication into the film ancl/or operation of the electrolytic cell to realize the potential theoretical .
reduction in power. Illustratively, the polymer can be ~abricated at a ~ower equivalent weight which may result in some loss of current e~iciency which is more than com-pensated by a reduction in voltage.
In use of the ion exchange polymer of the present disclosure, it has been found that a composite ~ilm or lam-inate is most desirable. The pendant sul~onyl groups on one sur~ace of the film are reacted with an amine and converted to N-monosubstituted sulfonamido groups. Since these groups have high electrical resistance in a chlor-alkali cell, these groups are further reacted with ~ base to the salt ~orm.
Highly desirable salts include those with a~ka~i and alkaline earth metals with sodium and potassium pre~erred. The other sur~ace of the film and the remaining sul~onyl halide groups are converted to other ion exchange grcups as by hydrolysis.
In the case of alkali or alkaline earth salts of the N-monosubstituted sul~onamido groups, the salts may be represented by the formula (-S02NR)sT ~Iherein R is as pre-viously defined, T is an alkali or alkaline earth metal and s is the valence of T.
With a composite film or membrane the thickness o~
the N-monosubstituted sul~onamido l~yer is not considered critical but normally will be at least 200 angstroms in thick-ness. With a composite ~ilm or laminate, the thickness of the N-monosubstitu~ed sulfonamido layer will normally range from .01% to 80% o~ the film with 0.1 to 30~ desirable with the use o~ the film or laminate in the chlor-alkali cell.
Additionally~ in use of the composite ~ilm or mem-brane in the cell, it is a requirement that the layer with the N-monosubstituted sulfonamido groups or salt therecf faces the cathode portion o~ the cell in which caustic is produced.
The results and stability of the membrane are drastically di~ferent wlth reversal of the ~ilm in a composite structureO
The use of ion exchange films in a chlor-alkali cell ls known as disclosed ~n German patent application 2 251 660 o* R,L. Dotson and K.L. O'Leary~ published Aprll 26~ 1973 and Netherlands patent applicatlon 72.17598 of Hooker Chemical Corp,, published June 29, 19730 In a similar fashion as these teachingsg a conventional chlor-alkali cell is employed wlth the critical distinction of the polymeric film in a housing separating the anode and cathode portions o~ the cell from which chlorlne and caustic are respectively produced from brine flowing within the anode portion of the cell.
While the above description has been directed to use in a chlor-alkali cell, it is within the scope of this disclosure to produce alkali and alkallne earth metal hydroxides and halogen as chlorine from a solution of the alkali and alkaline earth metal salt. While efficiencies 1n current and power consumption di~fer, the operating conditions of the cell are similar to those disclosed in the ~erman and Netherlands applications, It is within the scope o~ this disclosure that more than sur~ace conversion of the polymer may take place with the disclosed amines set Porth herein. A high degree o~ penetra-tion into the polymer may take place by the amine and essentially complete reaction by the amine with conversion of the pendant sulfonyl groups may take place. The N-monosubstituted sulfonamido groups ~unction for lon exchange purposes as an active ion exchange site. A polymer with completely converted sulfonyl groups may be laminated to a ~luorinated polymer containing pendant -S02F groups~ There-a~ter, these pendant S02F groups may be converted to active ion exchange sites.
However, it is desirable that essentially all of the pendant sulfonyl groups react with the amine and are converted to N-monosubstituted sulfonamido groups. In the present context "essentially completely converslon" or "essentially all groups present as N-monosubstituted sulfon~
amido groups" refers to a conversion of at least 90% of the orlginal sulfonyl halide groups to the N-monosubstituted sul-fonamide form. As employed in the present context, "complete conversion" or "all groups present as N-monosubstituted sulfon-amldo groups" re~ers to a conversion of at least 9g~ o~ theoriginal sulfonyl halide groups to the ~-monosubstltuted sulfonamide form. The expressions are applicable to mono-substituted sulfonamides in the neutral and salt forms. All of the above conversions, including the minimum of 40~, pref-erably relate to the composition of a layer at least 1 ~ in depth.
In the treatment with amine, extremely short reaction times are em~loyed which are of the order of minutes such as 3 to 15 minutes to obtain a 0.5 mil thickness of conversion in the intermediate polymer. In contrast with the same type of intermediate polymer disclosed in Grot U.S.P. 3 784 399 a contact time as high as 24 hours is disclosed with a mlnimum contact time with liquid ammonia of les~ than three hours, This 3-hour treatment would obtain a conversion of about 0.5 mil of the polymer. Additionally, extremely low temperature must be employed with liquid ammonia with the resulting ~ -disadvantage of complicated techniques.
With only surface conversion of the sul~onyl halide groups, further conversion of the remaining sulfonyl halide 30 groups to the ionic f'orm is most desirable. The prior art techniques of conversion of the -S02X ~roups with X as defined may be undertaken such as by hydrolysis. The techniques set forth in Connolly & Gresham U.S.P. 3 282 875 and/or Grot ; -16~
, , ~ .
~7~
U.S.P. 3,784,399 may be employed. Illustratively~ the unconverted sul~onyl groups of the polymer may be converted to the foxm -(S02NHJmQ wherein Q is H, N~4~ cation of an alkali metal and/or cation of an alkaline earth metal and m is the valence of Q. Additionally, the unconverted sulfonyl groups may be ~ormed to -(S03~nMe wherein Me is a cation and n is the valence of` the cation. Pre~erred de~initions of Q
include NH~ and/or cation of an alkaline metal particularly sodium or potassium. Pre*erred definitions o~ Me include potassium, sodium and hydrogenO
The polymer is preferably employed in the form of a film and desirably thicknesses of the order of 0.002 to .02 inch may be u~ilized. Excessive ~ilm thicknesses will aid ln obtaining higher strength but with the resulting deficiency o~ increased elec~rical resistance.
It is known in the prior art as U.S.P. 3,647,086 issued to Mizutani et al. to treat a membrane with an amine to impart acid amide groups. HoweverJ the disclosed cation exchange membranes do not have ability to withstand the environment o~ a chlor-alkali cell for any appreciable time period and are totally unacceptable for this use. This patent discloses that the acid amide groups are to be presen-t at the "substantial sur~acel' in a concentration based on the formula A + ~ x ~00 = 15 - 10 5~
wherein (per gram of dry membranes) A is the number o~ acid amide bonds/gram of drled membrane and B is the number of cation exch-ange groups, said acid amide bonds being composed of a cation exchange group and an amine having at least one amino group 17.
~D-4750 .
containing at least one hydrogen atom bonded to a nitrogen atom.
In the use of cation exchange membranes of this U. S0 P. 3,61~7~086~ an object is to provide an ion exchange membrane which effects permeation selection of different classes of cations and most particularly, cations with small valences.
From the disclosure of the patent, it is apparen-t that functioning is not contemplated of the acid amide group as an ion e~change site. For example, for the acid amide group to function as an ion exchange siteg a basic and prefer-ably highly basic pH is necessary. Since permeation selection of different classes of cations is solely contempla~ed and is the reason for the low degree of reaction by the amine with the base pol~ner9 use of the membrane solely at high pH is not disclosed. The property of ion exchange is a func-tion o~ the pK value which is an indication of acidity and is the negati~e logarithm of the dissociation constant of the nitrogen hydrogen bond.
In direct contrast to t,he disclosure of Mizutani et al. U.S.P. 3,647,086, N-monosubstituted sulfonamido groups and salts thereof are required to function as ion exchange sites in the fluorina~ed polymer. Furthermore,this function of the group is the reason for the high conversion rates of the sul-fonyl groups which can be of the order of lOO~o~ This difference in ion exchange as opposed to non-ion exchange is true of the same pendant groups on different types of polymers, i.e~, a group of the formula ~S02N~ wherein R jncludes Rl and R2 in accordance with U.S.P~ 39647,086. However~ th2 secondary amines disclosed in this pa~ent are not employed herein~ ~lso7 secondary amines cannot yield acid amides that function as ion ~715~dl exchange groups at any pH. Thus~ it may be summarized that the purpose of Mizutani et al. U.S.P. 3,647,o86 is not to obtain an ion exchange site by reaction of the amine while in the present disclosuYe it is absolu~ely essential.
Additionally, with the class of pol~ners disclosed herein, it is requlred that the N-monosubsti.tuted sulfonamido group or ~alt thereof be attached to a carbon atom containing a ~luorine atom. ThereXore, the pK value o~ the pendan~ group will be lowered indicating a higher acidityO The pH at which the ~luorinated polymer will ~unc~ion ~or ion exchange purposes is likewise lowered.
As previously discussed, utility ~or the disclosed ~luorinated pol~ner with N-monosubstituted sulfonamido groups and salts thereo~ is to Xunction ~or ion exchange. Therefore, general utility of the pol~ner ~or ion exchange is directly contemplated. Illustratively, permeation selection of cations is directly encompassed. One method o~ determination o~
cation exchange propertles iæ a measurement o~ permselectivity with separation o~ the same cations in solutions but at di~-~erent concentra~ions. This involves cation transpor~ andpermselectivity m~asurement of no voltage would indicate the polymer does not ~unction ~or ion exchange.
To further illustrate the innovative aspects o~ the present invention, the following examples are provided.
In this and the ~ollowing examples a film is employed o~ a copolymer of tetraXluoroethylene and CF2=CFOCF21FOCF2CF2S02F
and is referred to as precursor polymer containing pendant 19.
sulfonyl ~luoride groups. The equivalent weight of the polymer is given and illustratively at a mole ratio of tetra~luoro-ethylene to the other monomer o~ 7:1, an eq~valent weight of 1146 would be obtained. Equivalent weight is the weight of the polymer in grams con~aining one eq~valent o~ poten-tial ion exchange capacity.
To a stopper Erlenmeyer flask was added 50 cc. o~
a 40~ aqueous solution o~ methylamine and the precursor ~luorinated polymer containing pendant sul~onyl ~luoride groups ~EW 1151). Stlrring took place at room temperature ~or 16 hours ~ollowed by washing with water. Infrared spectra by attenu&ted total reflectance (ATR) indicated the conversion o~ sul~onyl ~luoride groups to -S03 and ~S02NHCH3.
EXAMPLE ?
In a simllar procedure as Example 1, a 100 ml.
round bottom ~lask was fitted with a magnetic stirrer and water cooled condenser topped by an N2 bubbler. To the ~lask was added ~0 mls o~ 40% aqueous methyl amine and the pre-cursor ~luo~lnated polymer containing pend~nt sul~onyl~luoride group (E~l 1151). Stirring took place at room temperature ~rom 3 hours ~ollowed by washing with water and drying in a vacuum oven. Infrared (ATR) spectra indicated conversion of the sulfonyl fluoride groups to -S03 and mostly -S02NHCH3 groups.
A 100 ml. round bot~om flask was ~itted with a g&S
inlet tube~ magnetic stirrer and ~ater cooled condenser topped by an N2 bubbler. Into the flask was added 50 ml. o~
.
dlmethylformamide into which was bubbled methylamine ~or one hal~ hour.
The precursor fluorinated polymer containing 20.
7~
pendant sulfonyl fluoride groups (EW 1163) was added to the flask with stirring of the ~lask taking place at room temperature ~or one hour. The film was washed with water and dried. Infrared (ATR) spectra indicated the sulfonyl groups were con~erted to -S02NHCH3.
EXAMP~E 4 A 200 ml. round bottom ~lask was fitted with a gas lnlet tube~ magne~ic stirrer and water-cooled condenser topped by an N2 bubbler. 100 mlO ~ di~ethylsulfoxide (DMS0) were added~ Anhydrous methylamine was bubbled into the DMS0 un~il the bubble rate into the solvent equaled the bubbl0 rate out.
Precursor fluorins~ted polymer containing pendant sulfonyl fluoxide groups (EW 1163) was added with stirring for various time intervals to obtain v&rying penetration to obtain -S02~CH3 indicated by staining in accordance with the ~ollowing Table.
Duration of mil-S0 NHC~ taverage) contact (minutes) ~ 3 .1 3 .5 ~9 7 1~3 9 1.7 11 1.8 EX~MPLE 5 The precursor ~luorina~ed pol~mer containing pendant sulfonyl M uoride groups ~EW 1198) i~ the form of a bag was treated with gaseous methylamine by inserting a tube into the bagO The bag was purged ~th N2 ~ollowed by evacuation. Gaseous methylamine at about one atmosphere 21.
~D-~750 pressure was introduced and allowed to stand for 20 minutes. The ba~ was evacuated, purged with N2 and washed with waterA Staining indicated the sulfonyl fluoride groups had been converted to a depth of 1.7 mils with a sharp dis-crete layer of pendant -S02F considered to be underneathO
EX~PLE 6 Employing similar apparatus as in Example 1, 25 ml.
of dimethylsulfoxide and 25 ml. of cyclohexamine were added to ~ -a 100 ml~ flask. Precursor fluorinated polymer containing pendant sulfonyl fluoride groups (EW 1163~ was introduced into the flask which was stirred at 26C~ for one and three hours respectively.
The films were washed and dried followed by staining ~ith Sevron~Red which indicated the respective films had surface layers of pendant groups in the form of -S02NH-C6H
of 0.10 and 0. 23 mil respectively.
Pr~cursor fluorinated polymer containing pendan~
sulfonyl fluoride groups (E~=1063) was added to an evacuated `~20 100 ml. ~lask. Ethylamine was added to give a pressure of one atmosphere and further ~dditions made to keep the pressure at one atmosphere. After 30 minut~s the flask was evacuated and the polymer film washed with water and dried~ Infrared (ATR) spectra indicated the sulfonyl groups on the surface were converted to -S02NHC~I~CH3. Staining with Sevron~Red showed ~he surface layer to be 1~7 mils in thiclmess.
EXAMPLF, 8 Precursor f]uorinated polymer containing pendant sul-fonyl fluoride groups (EW=1163j was added to a flask containing 10 g. of 1~6-diaminohexane (hexamethyldiamine) and l~0 g. of diethyleneglycoldimethyl ether~ Stirring took place for one 22.
~D~4750 hour at 25 .followed by washing with H20 and drying in a vacuum oven~ Infrared (~TRj spec-tra indic~ted that the sulfonyl groups on the surface were all converted to sub-stituted sulfonamido groups. Staining with Sevro~Red showed the surface layer to be 0.21 mil in thickness.
Precursor fluorinated polymer containing pendant sulfonyl fluoride groups (EW-1163) was added to a flask containing 50 g. of 1,6-diaminohexaneO Stirring took place for one hour at 60-65 followed by washing with water and drying in a vacuum oven~ Staining with Sevron~Red showed a surface layer of 2.2 mil in thicl~ess.
EX~PL~S 10 to 12 Following the general procedure of Example 1, separate pieces of blown film of S mils thickness as pre-cursor fluorina.ted polymer containing pendant sulfonyl fluoride groups (~T~J=1150) were contacted on one surface respectively ~nth liquid triethylene tetramine, aniline and liquid hydra~ine (98% concentration). The contact times with triethylene tetramine and aniline were both 5 minutes while contact time with hydra~ine was 7 minutes.
Thereafter all pieces of the filrn were hydrolyzed in a solution containing 15% sodium hydroxide and 30~0 di-methyl sulfoxide. Use of the triethylene tetramine and aniline samples in a permselectivity measurement on 3N vs~
lN KCl respectively gave 25~8 m~ and 26.3 mV.
For a separate permselectivity measuremen-t9 all samples after hydrolysis with the 15% sodium hydroxide, were converted ~o the ll fo~l by cont,act with HCl followed bY:'conver-sion to the K~ form b~ boiling in potassillm carbonate solution for 30 minutesO The orig:inal treated tri.ethy].ene tetramine9 23, ~a~
aniline and hydrazîne polymers~respectively yield voltages of 18,7 mV7 1906 mV and 19~7 mV0 ~ .
A 5 mil fi]m of precursor ~luorinated polymer containing pendant sulfonyl fluoride groups (~W-llO~) was placed in a Pyrex3 baking dish. Ethylenediamine (99~0 purity) was poured on top of the film so as to contact on]y the top surface, The surface of the liquid was covered with a second9 similar film to minimize the exposure to moisture~
After 15 minutes at room temperature, the amine was poured off~ the ~ilm rinsed first ~ith diglyme, then benzene and ~înally with warm ~ater at about ~O~C~ Staining;f~ a cross section of the ~ilm with Sevro~ed indicated reaction to a dep~h of 007 mil The remaining pendant sulfonyl fluoride groups were converted to -S03K groups by immersing the film in a solution of 15~o potassium hydroxide and 30~0 dimethyl sul~oxide in water for 6 hours at 60C~
The film was clamped in a chlor-alkali cell with the amine treated side toward the cathodeO The chlor-alkali electrolysis cell ~las constructed of two identical half cell housings made ~rom Teflon~ T~ resin into which were mounted in the respective cell housings a dimensionally stable anode and a perforated stainless steel cathode~ The clamped film gave an active area of the electrodes and membrane of 4 x 4 inches. The electrol~tes saturated brine and sodium hydroxide were circula-ted through respective cell halves with a temperature maintained at 85C~ by heaters installed in the circulatory lines. Fresh ~rine was pumped into -the anode section of the cell and distilled water was pumped into the ~0 AD~4750 ~ 7~
cathode section o the cellO
In operation of the cell a current efficiency of 91% was realized at a cell voltage of 3.6 volts~ A sodium hydroxide concentration o~ 14~ was obtained.
~X~MPLE 14 Using the procedure described in Example 5, one surface of a 6.6 mil precursor fluorinated polymer film of an EW of 1198 was converted to a depth of 107 mils to the N-methyl sulfonamide form. After conversion of the remaining -S02F groups to the -S03K form the film was tested in a chlor~alkali cell as described in Example 13. A current ef-ficiency of 86% at a cell voltage of 3.8 volts and a sodium hydroxide concentration of 12% was obtained. ~-A S mil thick precursor fluorinated polymer film of an E~Y of 1200 was completely converted to the N-methyl sulfonamide form by treating with gaseous methyl-amine for 6 hoursO
When tested in a chlor-alkali cell as described 2~ in Example 13, a current efficiency of 89~ at a cell volt-age o 4.5 ~olts and a sodium hydroxide concentration of 14%
was obtained.
~ lthough the invention has been described by way of specific embodiments7 it is not intended to be limi~ed thereto. As will be apparent to those skilled in the ar-t, numerous embodiments can be made wnthout de-parting from the spirit o the invention or the scope of the following claims.
25.
7~ :
me application is a division of copending appll-cation Seri al No. 211,312, ~iled 11th October, 1974.
_ 26 -.
An important advantage of the present polymer and the method of preparation in comparison to treatment wlth ammonia of the prior art is elimination of extensive treat-ment times. A considerable time period for treatment is necessary for ammonia which ranges upwards from several hours while treatment with the amines to form the N-monosubstituted sulfonamido groups will be of the order of minutes. Flexibility ls af~orded with the amines which form the ~-monosubstltuted sulfonamido groups since the treatment techniques generally can involve liquid or gaseous contact. Also, wlth short periods o~ reaction a continuous process may be realized rather than batch convers~on.
An outstanding advantage has been obtalned wlth ionic groups present as N-monosubstituted sulfonamido gro,ups in comparison with the ionic groups present as the sul~onamide.
With a surface conversion by reaction with an amine to obtain N-monosubstituted sulfonamido groups rather than treatment with ammonia to obtain the sulfonamide, a dramatic increase in current e~ficiency has been obtained in application in a chlor-alkali cell. This improvement is considered to be of predominant importance in commercial applicability in reducing the cost of producing a unit o~ chlorine and caustic.
Illustratively, in a chlor-alkali plant producing 1000 tons per day of chlorine~ the direct savings in elec-trlcal power for only a 1% increase in efficlency are significant.
DETAILED DESCRIPTION
_ A need has developed in the chlor-alkali industry for the use of improved ion exchange materials which can replace existing separators which have been used for decades ~ . ~
~ ~p~ D~4750 without substan~ial improvement in design.
In the environmerlt of a chlor-alkali cell, the membrane mus~ be able to withstand a hostile environment for a polymeric material such as exposure to a hlghly alka-line pH as well as exposure to chlorine. Generally, hydro-carbon ion exchange membranes are totally unsatisractory for this usage since the membrane cannot withstandithis enviro~nent.
For commercial usage in the chlor alkali industry, a film must go beyond the ability to be operable for pro~
longed time periods in the production of chlorine and caustic.
A most important criteria is the current efficiency with the polymer in conversion of the brine in the electrolytic cell to the desired products. Therefore, improvement in current efficiency can translate into pronounced savings in the cost of production of each unit of chlorine and caustic. Addi-tionally, from a commercial standpoint the cost of production of each unit will be determinative of the commercial suitability of an ion exchange membrane.
The ion exchange polymers of the present disclosure possess pendant side chains conkaining sulfonyl groups at-tached ~o carbon atoms having at least one fluorine atom connected thereto with the pendant chains present as N-monosubstituted sulfonamido groupsO The polymers are prepared from monomers which are fluorinated or fluorine substituted vinyl compounds~ The polymers are made from at least two monomers with at least one of the monomers coming from each of the two groups described below. The ~irst group i5 fluorinated vinyl compounds such as vinyl fluoride, hexa-fluoropropylene 9 vinylidene fluoride 9 trifluoroethylene, chlorotrifluoroe~hylene, perfluoro(alkyl vinyl ether~
tetrafluoroethylene and mixtures thereof. In the case o~
use of copolymers in electrolysis of brine~ the precursor vinyl monomer desirably will not con~ain hydrogen.
The second group is the sulfonyl-containing monomers containing the precursor -S02F or -S02Cl~ One example of such a comonomer is CF2=CFS02F. Additional examples can be represented by the general formula CF2=
CFR~S02F wherein Rf ls a bifunctional perfluorinated radical comprising 2 to 8 carbon atoms. The particular chemical content or structure of the radical linking the sulfonyl group to the copolymer chain is not critical but such must have a fluorine atom attached to the carbon atoms to which is attached the sulfonyl groupO If the sulfonyl group is attached directly to the chain, the carbon in the chain to which it is attached must have a fluorine atom attached to it.
Other atoms connected to this carbon can include fluorine, chlorine, or hydrogen although generally hydrogen will be excluded in use of the copolymer ~or ion exchange in a chlor-alkali cell. The Rf radical of the formula above can be either branched or unbranched, i.e., straigh~-chained and can have one or more ether linkages. It is preferred that the vinyl radical in this group of sulfonyl fluoride contain-ing comonomers be joined to the Rf group through an ether llnkage, i.e., that the comonomer be of the formula CF2=CFORfS02F. Illustrative of such sulfonyl fluoride containing comonomers are CF2=CFOCF2CF2S02F, CF2=CFoCF2TFOcF2cF2s02 CF2=CFOCF2CFOCF2fFOCF2CF2S02F, AD-1~750 CF2=CFC~2CF2S02F, and CF2-CF0CF21F0C~2cF2s02 fF2 bF3 . ...
The most preferred sulfonyl fluoride containing comonomer is perfluoro(3,6-dioxa-L~-methyl-7-octenesulfonyl fluoride), CF2 -cFocF2cFocF2cF2so2F .
The sulfonyl containing monomers are disclosed in such references as U. S0 P. 3,282,875 to Connolly et al., U~S.PO
3,041,317 to Gibbs et al., and in U~S.P~ 3,718,627 to Grot and in U~S.P. 3,560,568 to Resnick.
The preferred copolymers utilized in the film are perfluorocarbon although others can be utilized as long as there is a fluorine atom attache~ to the carbon atom which is attached to the sulfonyl group o~ the polymer. The most preferred copol~mer is a copolymer Or tetrafluoroethylene and perfluoro(3 9 6-dioxa-~-methyl-7-octenesulfonyl fluoride) which comprises 10 to 60 percent, preferably, 25 to 50 percent by weight of the latter.
The copolymer used in the present invention is - prepared by general polymerizakion techniques developed for homo- and copolymerizations o~ fluorinated ethylenes, partic-ularly those employed for tetrafluoroethylene which are described in the literature. Nonaqueous techniques for preparing the copolymers of the present inven~ion include that of U. S. P0 3,01~1~317, issued to H~ Mo Gibbs and R. N.
Griffin on June 26~ 1962, that is~ by the polymerization o~
a mixture of the major monomer therein, such as D-~750 tetrafluoroethylene, and a fluorinated ethylene containing sulfonyl fluoride in the presence of a free radica:L initiator, preferably a perfluorocarbon peroxide or aæo compound~ at a temperature in the range 0-200C~ and ak pressures in the range 1-2007 or more atmospheres. The nonaqueous polymeriza-tion may9 if desired, be carried out in the presence of a fluorinated solvent. Suitable fluorinated solvents are inert9 liquid9 perfluorinated hydrocarbons7 such as per-fluoromethylcyclohexane, perfluorodimethylcyclobutane~
perfluorooctane, perfluorobenzene and the like.
Aqueous techniques for preparing the copolymer of this invention include contacting the monomers with an aqueous medium containing a free~radical initiator to obtain a slurry of polymer particles in non-water~wet or granular form9 as disclosed in U0 SO Patent 2,3939967, issued to Mo M~
Brubaker on February 5, 1946; or contacting the monomers with an aqueous medium containing both a free-radical initia-tor and a telogenically inactive dispersing agent, to obtain an aqueous colloidal dispersion of polymer particles, and coagula~ing the dispersion9 as disclosed9 for example, in U. S~ P~ 2,5595752, issued to K. L. Berry on July 10, 19519 and U. S. PO 2,593~$839 issued to J~ ~. Lontz on April 22, 19520 Upon formation of the intermediate polymer9 the pendant sulfonyl groups are present as ~SO?X with X defining fluorine or chlorine and preferably fluorineO It is a re-quirement in ~oth the intermediate and :Einal fluorinated polymers disclosed herein that the sulfonyl groups are at-tached to carbon ato~s having at least one fluorine atom connected theretoO These carbon atoms serve to link the sulfonyl group to the copolymer~chain or alternatively, th~
8.
~P7~Y~
carbon atom~ form a portlon o~ the backbone chain ln the copolymer. After formation o~ the intermed1ate polymer, the sul~onyl group~ are converted to N-monosubstituted ~ul~onamido group3.
In order to obtain ion exchange properties, the ~ole criticality o~ the N-monosubstituted groups is to functlon a~ an ion exchange site. me group employed ls not consldered critical from the standpoint of operability~ However, a di~ference in results will be obtained dependent upon the group employed, e.g., a varia-tion in current e~flciency with minimization o~ anion transport together with a variation ln the power required for each unit of product from a chlor-alkali cell. Additionally, i~ the N-mono~ubstituted sul~onamido group is unstable. e.g., in use of a chlor-alkall cell~ reaction and conversion of the group ean occur to a stable ion exchange sit~.
As illustrative examples o~ ~uitable groups a~ ~-monosubstituted ~ulfonamido group~ are those disclosed in M~zutani ~t al U.S.p. 3,647,o86. Although this pr~or art patent disclose~ reaction of both primar~ and secondary amines with the ion exchange polymer, the reacted amines are no~ re-quired to function as ion exchange groups in direct contrast to the disclosed groups in the polymer~ o~ the present appli-cationO
me amine~ useful in the invention are primaryamine~ o~ the type disclosed in Mlzutani et al. U.S.P~ 3,647,o860 Therefore, these amines are o~ the ~ormula H wherein H-N~R
R is alkyl, haloalkyi, alkyl substituted by either hydroxy, ~mino, carboxy~ alkoxy, pho~phonlc acid, ~ulfonic acid, nitro, nitrile, carb~moyl, ~ulfonic acid amide or pho~phonic acid ~D 475 amide~ aryl, aryl substituted by hydroxy, amino9 carboxy, phosphonic acid, alkoxy, sul~onic acid, nitro5 nitrile, carbamoyl, sulfonic acid amide, carbamoyl or phosphonic acid amide, a heterocyclic group or aralkyl~ In addition to the amides listed above~ the corresponding esters are likewise suitable. Illustrative of suitable ~ groups are straight and branch chained alkyls, benzyl and ~Rl _~ ..
wherein both Rl and R2 lndependently of the other can rcpre-s~nt alkyl, aryl ? aralkyl or hydrogen4 Illustratively, both Rl and R2 may include alkyl. Suitable amines include those of di-9 tri- and poly-functional types. Generally, amines containing alkyl groups have been found most satisfactory such as methyl amine and diamines of the type NH2(CH2)nNH2 wherein n is 2 to lO. The length of the chain is not con-sidered critical as illustratively alkyls may contain l to lO
carbon atoms or 2 to lO carbon atoms for alkylene in the case of diamines.
It is within the scope of this disclosure to include ~he salts of the N-monosubstituted sulfonamido groups~ Suit~
able salts include those with alkaline earth and alkali metal cations. Preferred metals include sodium and potassiumO
To obtain the conversion of the inkermediate pendant sulfonyl group, -S02X with X previously defined, the precursor polymer may be treated with the amine in either liquid or gaseous formO
Both reactive and inert carriers and solvents for the amine may be employed~ The reactive carrier will compete 10.
wikh the amine in conversion of the pendant sul~onyl halide sites on the precursor polymer. A reactive carrier contains active hydrogen such as water. Primary alcohols are not considered suitable since they react rapidly with the intermediate pendant sulfonyl halide groups lowering the concentration of the desired lon exchange sites. The competitive reaction may also produce ion exchange sites in the fluorinated polymer disclosed herein since the sulfonyl halide is converted to -S03 .
~ile outstanding advantages have been obtained with essentially complete conversion of the active sulfonyl halides in a polymer layer or surface to form the N-monosubstituted sul~onamido groups, it is within the scope of this disclosure to convert only a minimum of 40% or about a ma~ority of these sulfonyl groups to this form. The remaining groups are desirably converted to other active ion exchange groups For example, water employed as a carrier with ~he amine w~ll promote a competing reaction with the sulfonyl halide.
Inert solvents may be desirably employed which contaln no active hydrogen atoms and do n~t promote a competing reaction. Examples include dimethyl formamide, dimethyl sulfoxide~ tetramethylene sulfone, hexamethyl phos-phoramide3 diglyme, acetonitrile and general classes of ethers and nitriles.
Pressure and temperature together with the carrier or solvent, if employed, will determlne the efficiency and time of conversion of the sulfonyl groups and will tend to influence the degree of penetration of the amine into the polymer.
However, pressure and temperature are not ,~,"~; ,...
considered critical in the framework of obtaining conversion of the pendant -S02X groups but rather upon the rate of reaction and degree of penetration of the amine, Illus-tratively~ room temperature conversion has been found ko be satisfactory for most amines~ Pressure, below at or above atmospheric pressure may be employed, Wikh gaseous treatment, the proper combination of pressure and temperature wlll be employed to obtain the amlne in the gaseous state. With gaseous treatment~ an inert gas as a carrier may be employed.
For purposes of explanation in the reaction proce-dure, it is considered from physical observation after reaction with the amine that a sharp line of demarca~ion exists bet~ween converted sulfonyl halide groups and unconverted sulfonyl halide groups if the intermediate polymer does not or is not allowed to completely react. This observation is based upon staining the reacted polymer with a cationic active dye such as Sevron Red. In the present context~ a sharp l~ne of demar-cation refers to observation of a stained boundary with a cationic active dye.
The ion exchange polymer film of the present disclo-sure in a chlor~alkali cell desirably has a single surface converted to the N-monosubstituted sulfonamido form, In such event, the N-monosubstituted sulfonamido surface converted to the salt form faces the cathode portion of the cell producing caustic. This surface of the membrane serves to minimize anion transport of hydroxyl ions and acts as a barrier for such transport. Also~ the formation of a sur~ace layer, rather than total conversion, has been found to reduce the overall electrical resistance of the polymer leading to highly desirable results from ~he . ~ . . i . .
7~
standpoint of electrical power consumption. Such surface conversions have led to a significant increase of the ef-ficiency and a significant decrease in power consumption such as in comparison with sulfonyl groups converted with ammonia to the sul~onamide ~orm. Current efficiencies approaching and exceeding gO% are considered obtainable from a commercial standpoint with the amine reaction. A comparison with methyl amine treatment as opposed to ammonia treatment has shown an increase o~ efficiency of the order o* 4-5% and greater.
Similarly~ use of a diamine such as ethylenediamine has given comparable or better results.
An o~ltstanding advantage has been found in terms of electrical ef~iciency in a chlor-alkali cell with the fluorinated polymers of the type disclosed herein with pendant groups present as N-monosubstituted sulfonamido groups and salts thereo~. However, an equally impor~ant criterion in a chlor-alkali cell is the amount o~ power required for each unit o~ chlorine ancl caustic. It is con-sidered that the polymers of the type disclosed herein permit one by a proper combination o~ operating conditions to realize an excellent and une~ected reduction in power. Since the power requirement ~which may be expressed in watt-hours) is a function of both cell voltage and current efficiency~ low cell vo~tages are desirable and necessary~ However, a polymer without a high current ef~iciency cannot operate effectively ~rom a commercial standpoint even with extremely low cell voltages. Additionally, a polymer with an inherent high current efficiency allows one by a proper combination o~ para-meters as in fabrication into the film ancl/or operation of the electrolytic cell to realize the potential theoretical .
reduction in power. Illustratively, the polymer can be ~abricated at a ~ower equivalent weight which may result in some loss of current e~iciency which is more than com-pensated by a reduction in voltage.
In use of the ion exchange polymer of the present disclosure, it has been found that a composite ~ilm or lam-inate is most desirable. The pendant sul~onyl groups on one sur~ace of the film are reacted with an amine and converted to N-monosubstituted sulfonamido groups. Since these groups have high electrical resistance in a chlor-alkali cell, these groups are further reacted with ~ base to the salt ~orm.
Highly desirable salts include those with a~ka~i and alkaline earth metals with sodium and potassium pre~erred. The other sur~ace of the film and the remaining sul~onyl halide groups are converted to other ion exchange grcups as by hydrolysis.
In the case of alkali or alkaline earth salts of the N-monosubstituted sul~onamido groups, the salts may be represented by the formula (-S02NR)sT ~Iherein R is as pre-viously defined, T is an alkali or alkaline earth metal and s is the valence of T.
With a composite film or membrane the thickness o~
the N-monosubstituted sul~onamido l~yer is not considered critical but normally will be at least 200 angstroms in thick-ness. With a composite ~ilm or laminate, the thickness of the N-monosubstitu~ed sulfonamido layer will normally range from .01% to 80% o~ the film with 0.1 to 30~ desirable with the use o~ the film or laminate in the chlor-alkali cell.
Additionally~ in use of the composite ~ilm or mem-brane in the cell, it is a requirement that the layer with the N-monosubstituted sulfonamido groups or salt therecf faces the cathode portion o~ the cell in which caustic is produced.
The results and stability of the membrane are drastically di~ferent wlth reversal of the ~ilm in a composite structureO
The use of ion exchange films in a chlor-alkali cell ls known as disclosed ~n German patent application 2 251 660 o* R,L. Dotson and K.L. O'Leary~ published Aprll 26~ 1973 and Netherlands patent applicatlon 72.17598 of Hooker Chemical Corp,, published June 29, 19730 In a similar fashion as these teachingsg a conventional chlor-alkali cell is employed wlth the critical distinction of the polymeric film in a housing separating the anode and cathode portions o~ the cell from which chlorlne and caustic are respectively produced from brine flowing within the anode portion of the cell.
While the above description has been directed to use in a chlor-alkali cell, it is within the scope of this disclosure to produce alkali and alkallne earth metal hydroxides and halogen as chlorine from a solution of the alkali and alkaline earth metal salt. While efficiencies 1n current and power consumption di~fer, the operating conditions of the cell are similar to those disclosed in the ~erman and Netherlands applications, It is within the scope o~ this disclosure that more than sur~ace conversion of the polymer may take place with the disclosed amines set Porth herein. A high degree o~ penetra-tion into the polymer may take place by the amine and essentially complete reaction by the amine with conversion of the pendant sulfonyl groups may take place. The N-monosubstituted sulfonamido groups ~unction for lon exchange purposes as an active ion exchange site. A polymer with completely converted sulfonyl groups may be laminated to a ~luorinated polymer containing pendant -S02F groups~ There-a~ter, these pendant S02F groups may be converted to active ion exchange sites.
However, it is desirable that essentially all of the pendant sulfonyl groups react with the amine and are converted to N-monosubstituted sulfonamido groups. In the present context "essentially completely converslon" or "essentially all groups present as N-monosubstituted sulfon~
amido groups" refers to a conversion of at least 90% of the orlginal sulfonyl halide groups to the N-monosubstituted sul-fonamide form. As employed in the present context, "complete conversion" or "all groups present as N-monosubstituted sulfon-amldo groups" re~ers to a conversion of at least 9g~ o~ theoriginal sulfonyl halide groups to the ~-monosubstltuted sulfonamide form. The expressions are applicable to mono-substituted sulfonamides in the neutral and salt forms. All of the above conversions, including the minimum of 40~, pref-erably relate to the composition of a layer at least 1 ~ in depth.
In the treatment with amine, extremely short reaction times are em~loyed which are of the order of minutes such as 3 to 15 minutes to obtain a 0.5 mil thickness of conversion in the intermediate polymer. In contrast with the same type of intermediate polymer disclosed in Grot U.S.P. 3 784 399 a contact time as high as 24 hours is disclosed with a mlnimum contact time with liquid ammonia of les~ than three hours, This 3-hour treatment would obtain a conversion of about 0.5 mil of the polymer. Additionally, extremely low temperature must be employed with liquid ammonia with the resulting ~ -disadvantage of complicated techniques.
With only surface conversion of the sul~onyl halide groups, further conversion of the remaining sulfonyl halide 30 groups to the ionic f'orm is most desirable. The prior art techniques of conversion of the -S02X ~roups with X as defined may be undertaken such as by hydrolysis. The techniques set forth in Connolly & Gresham U.S.P. 3 282 875 and/or Grot ; -16~
, , ~ .
~7~
U.S.P. 3,784,399 may be employed. Illustratively~ the unconverted sul~onyl groups of the polymer may be converted to the foxm -(S02NHJmQ wherein Q is H, N~4~ cation of an alkali metal and/or cation of an alkaline earth metal and m is the valence of Q. Additionally, the unconverted sulfonyl groups may be ~ormed to -(S03~nMe wherein Me is a cation and n is the valence of` the cation. Pre~erred de~initions of Q
include NH~ and/or cation of an alkaline metal particularly sodium or potassium. Pre*erred definitions o~ Me include potassium, sodium and hydrogenO
The polymer is preferably employed in the form of a film and desirably thicknesses of the order of 0.002 to .02 inch may be u~ilized. Excessive ~ilm thicknesses will aid ln obtaining higher strength but with the resulting deficiency o~ increased elec~rical resistance.
It is known in the prior art as U.S.P. 3,647,086 issued to Mizutani et al. to treat a membrane with an amine to impart acid amide groups. HoweverJ the disclosed cation exchange membranes do not have ability to withstand the environment o~ a chlor-alkali cell for any appreciable time period and are totally unacceptable for this use. This patent discloses that the acid amide groups are to be presen-t at the "substantial sur~acel' in a concentration based on the formula A + ~ x ~00 = 15 - 10 5~
wherein (per gram of dry membranes) A is the number o~ acid amide bonds/gram of drled membrane and B is the number of cation exch-ange groups, said acid amide bonds being composed of a cation exchange group and an amine having at least one amino group 17.
~D-4750 .
containing at least one hydrogen atom bonded to a nitrogen atom.
In the use of cation exchange membranes of this U. S0 P. 3,61~7~086~ an object is to provide an ion exchange membrane which effects permeation selection of different classes of cations and most particularly, cations with small valences.
From the disclosure of the patent, it is apparen-t that functioning is not contemplated of the acid amide group as an ion e~change site. For example, for the acid amide group to function as an ion exchange siteg a basic and prefer-ably highly basic pH is necessary. Since permeation selection of different classes of cations is solely contempla~ed and is the reason for the low degree of reaction by the amine with the base pol~ner9 use of the membrane solely at high pH is not disclosed. The property of ion exchange is a func-tion o~ the pK value which is an indication of acidity and is the negati~e logarithm of the dissociation constant of the nitrogen hydrogen bond.
In direct contrast to t,he disclosure of Mizutani et al. U.S.P. 3,647,086, N-monosubstituted sulfonamido groups and salts thereof are required to function as ion exchange sites in the fluorina~ed polymer. Furthermore,this function of the group is the reason for the high conversion rates of the sul-fonyl groups which can be of the order of lOO~o~ This difference in ion exchange as opposed to non-ion exchange is true of the same pendant groups on different types of polymers, i.e~, a group of the formula ~S02N~ wherein R jncludes Rl and R2 in accordance with U.S.P~ 39647,086. However~ th2 secondary amines disclosed in this pa~ent are not employed herein~ ~lso7 secondary amines cannot yield acid amides that function as ion ~715~dl exchange groups at any pH. Thus~ it may be summarized that the purpose of Mizutani et al. U.S.P. 3,647,o86 is not to obtain an ion exchange site by reaction of the amine while in the present disclosuYe it is absolu~ely essential.
Additionally, with the class of pol~ners disclosed herein, it is requlred that the N-monosubsti.tuted sulfonamido group or ~alt thereof be attached to a carbon atom containing a ~luorine atom. ThereXore, the pK value o~ the pendan~ group will be lowered indicating a higher acidityO The pH at which the ~luorinated polymer will ~unc~ion ~or ion exchange purposes is likewise lowered.
As previously discussed, utility ~or the disclosed ~luorinated pol~ner with N-monosubstituted sulfonamido groups and salts thereo~ is to Xunction ~or ion exchange. Therefore, general utility of the pol~ner ~or ion exchange is directly contemplated. Illustratively, permeation selection of cations is directly encompassed. One method o~ determination o~
cation exchange propertles iæ a measurement o~ permselectivity with separation o~ the same cations in solutions but at di~-~erent concentra~ions. This involves cation transpor~ andpermselectivity m~asurement of no voltage would indicate the polymer does not ~unction ~or ion exchange.
To further illustrate the innovative aspects o~ the present invention, the following examples are provided.
In this and the ~ollowing examples a film is employed o~ a copolymer of tetraXluoroethylene and CF2=CFOCF21FOCF2CF2S02F
and is referred to as precursor polymer containing pendant 19.
sulfonyl ~luoride groups. The equivalent weight of the polymer is given and illustratively at a mole ratio of tetra~luoro-ethylene to the other monomer o~ 7:1, an eq~valent weight of 1146 would be obtained. Equivalent weight is the weight of the polymer in grams con~aining one eq~valent o~ poten-tial ion exchange capacity.
To a stopper Erlenmeyer flask was added 50 cc. o~
a 40~ aqueous solution o~ methylamine and the precursor ~luorinated polymer containing pendant sul~onyl ~luoride groups ~EW 1151). Stlrring took place at room temperature ~or 16 hours ~ollowed by washing with water. Infrared spectra by attenu&ted total reflectance (ATR) indicated the conversion o~ sul~onyl ~luoride groups to -S03 and ~S02NHCH3.
EXAMPLE ?
In a simllar procedure as Example 1, a 100 ml.
round bottom ~lask was fitted with a magnetic stirrer and water cooled condenser topped by an N2 bubbler. To the ~lask was added ~0 mls o~ 40% aqueous methyl amine and the pre-cursor ~luo~lnated polymer containing pend~nt sul~onyl~luoride group (E~l 1151). Stirring took place at room temperature ~rom 3 hours ~ollowed by washing with water and drying in a vacuum oven. Infrared (ATR) spectra indicated conversion of the sulfonyl fluoride groups to -S03 and mostly -S02NHCH3 groups.
A 100 ml. round bot~om flask was ~itted with a g&S
inlet tube~ magnetic stirrer and ~ater cooled condenser topped by an N2 bubbler. Into the flask was added 50 ml. o~
.
dlmethylformamide into which was bubbled methylamine ~or one hal~ hour.
The precursor fluorinated polymer containing 20.
7~
pendant sulfonyl fluoride groups (EW 1163) was added to the flask with stirring of the ~lask taking place at room temperature ~or one hour. The film was washed with water and dried. Infrared (ATR) spectra indicated the sulfonyl groups were con~erted to -S02NHCH3.
EXAMP~E 4 A 200 ml. round bottom ~lask was fitted with a gas lnlet tube~ magne~ic stirrer and water-cooled condenser topped by an N2 bubbler. 100 mlO ~ di~ethylsulfoxide (DMS0) were added~ Anhydrous methylamine was bubbled into the DMS0 un~il the bubble rate into the solvent equaled the bubbl0 rate out.
Precursor fluorins~ted polymer containing pendant sulfonyl fluoxide groups (EW 1163) was added with stirring for various time intervals to obtain v&rying penetration to obtain -S02~CH3 indicated by staining in accordance with the ~ollowing Table.
Duration of mil-S0 NHC~ taverage) contact (minutes) ~ 3 .1 3 .5 ~9 7 1~3 9 1.7 11 1.8 EX~MPLE 5 The precursor ~luorina~ed pol~mer containing pendant sulfonyl M uoride groups ~EW 1198) i~ the form of a bag was treated with gaseous methylamine by inserting a tube into the bagO The bag was purged ~th N2 ~ollowed by evacuation. Gaseous methylamine at about one atmosphere 21.
~D-~750 pressure was introduced and allowed to stand for 20 minutes. The ba~ was evacuated, purged with N2 and washed with waterA Staining indicated the sulfonyl fluoride groups had been converted to a depth of 1.7 mils with a sharp dis-crete layer of pendant -S02F considered to be underneathO
EX~PLE 6 Employing similar apparatus as in Example 1, 25 ml.
of dimethylsulfoxide and 25 ml. of cyclohexamine were added to ~ -a 100 ml~ flask. Precursor fluorinated polymer containing pendant sulfonyl fluoride groups (EW 1163~ was introduced into the flask which was stirred at 26C~ for one and three hours respectively.
The films were washed and dried followed by staining ~ith Sevron~Red which indicated the respective films had surface layers of pendant groups in the form of -S02NH-C6H
of 0.10 and 0. 23 mil respectively.
Pr~cursor fluorinated polymer containing pendan~
sulfonyl fluoride groups (E~=1063) was added to an evacuated `~20 100 ml. ~lask. Ethylamine was added to give a pressure of one atmosphere and further ~dditions made to keep the pressure at one atmosphere. After 30 minut~s the flask was evacuated and the polymer film washed with water and dried~ Infrared (ATR) spectra indicated the sulfonyl groups on the surface were converted to -S02NHC~I~CH3. Staining with Sevron~Red showed ~he surface layer to be 1~7 mils in thiclmess.
EXAMPLF, 8 Precursor f]uorinated polymer containing pendant sul-fonyl fluoride groups (EW=1163j was added to a flask containing 10 g. of 1~6-diaminohexane (hexamethyldiamine) and l~0 g. of diethyleneglycoldimethyl ether~ Stirring took place for one 22.
~D~4750 hour at 25 .followed by washing with H20 and drying in a vacuum oven~ Infrared (~TRj spec-tra indic~ted that the sulfonyl groups on the surface were all converted to sub-stituted sulfonamido groups. Staining with Sevro~Red showed the surface layer to be 0.21 mil in thickness.
Precursor fluorinated polymer containing pendant sulfonyl fluoride groups (EW-1163) was added to a flask containing 50 g. of 1,6-diaminohexaneO Stirring took place for one hour at 60-65 followed by washing with water and drying in a vacuum oven~ Staining with Sevron~Red showed a surface layer of 2.2 mil in thicl~ess.
EX~PL~S 10 to 12 Following the general procedure of Example 1, separate pieces of blown film of S mils thickness as pre-cursor fluorina.ted polymer containing pendant sulfonyl fluoride groups (~T~J=1150) were contacted on one surface respectively ~nth liquid triethylene tetramine, aniline and liquid hydra~ine (98% concentration). The contact times with triethylene tetramine and aniline were both 5 minutes while contact time with hydra~ine was 7 minutes.
Thereafter all pieces of the filrn were hydrolyzed in a solution containing 15% sodium hydroxide and 30~0 di-methyl sulfoxide. Use of the triethylene tetramine and aniline samples in a permselectivity measurement on 3N vs~
lN KCl respectively gave 25~8 m~ and 26.3 mV.
For a separate permselectivity measuremen-t9 all samples after hydrolysis with the 15% sodium hydroxide, were converted ~o the ll fo~l by cont,act with HCl followed bY:'conver-sion to the K~ form b~ boiling in potassillm carbonate solution for 30 minutesO The orig:inal treated tri.ethy].ene tetramine9 23, ~a~
aniline and hydrazîne polymers~respectively yield voltages of 18,7 mV7 1906 mV and 19~7 mV0 ~ .
A 5 mil fi]m of precursor ~luorinated polymer containing pendant sulfonyl fluoride groups (~W-llO~) was placed in a Pyrex3 baking dish. Ethylenediamine (99~0 purity) was poured on top of the film so as to contact on]y the top surface, The surface of the liquid was covered with a second9 similar film to minimize the exposure to moisture~
After 15 minutes at room temperature, the amine was poured off~ the ~ilm rinsed first ~ith diglyme, then benzene and ~înally with warm ~ater at about ~O~C~ Staining;f~ a cross section of the ~ilm with Sevro~ed indicated reaction to a dep~h of 007 mil The remaining pendant sulfonyl fluoride groups were converted to -S03K groups by immersing the film in a solution of 15~o potassium hydroxide and 30~0 dimethyl sul~oxide in water for 6 hours at 60C~
The film was clamped in a chlor-alkali cell with the amine treated side toward the cathodeO The chlor-alkali electrolysis cell ~las constructed of two identical half cell housings made ~rom Teflon~ T~ resin into which were mounted in the respective cell housings a dimensionally stable anode and a perforated stainless steel cathode~ The clamped film gave an active area of the electrodes and membrane of 4 x 4 inches. The electrol~tes saturated brine and sodium hydroxide were circula-ted through respective cell halves with a temperature maintained at 85C~ by heaters installed in the circulatory lines. Fresh ~rine was pumped into -the anode section of the cell and distilled water was pumped into the ~0 AD~4750 ~ 7~
cathode section o the cellO
In operation of the cell a current efficiency of 91% was realized at a cell voltage of 3.6 volts~ A sodium hydroxide concentration o~ 14~ was obtained.
~X~MPLE 14 Using the procedure described in Example 5, one surface of a 6.6 mil precursor fluorinated polymer film of an EW of 1198 was converted to a depth of 107 mils to the N-methyl sulfonamide form. After conversion of the remaining -S02F groups to the -S03K form the film was tested in a chlor~alkali cell as described in Example 13. A current ef-ficiency of 86% at a cell voltage of 3.8 volts and a sodium hydroxide concentration of 12% was obtained. ~-A S mil thick precursor fluorinated polymer film of an E~Y of 1200 was completely converted to the N-methyl sulfonamide form by treating with gaseous methyl-amine for 6 hoursO
When tested in a chlor-alkali cell as described 2~ in Example 13, a current efficiency of 89~ at a cell volt-age o 4.5 ~olts and a sodium hydroxide concentration of 14%
was obtained.
~ lthough the invention has been described by way of specific embodiments7 it is not intended to be limi~ed thereto. As will be apparent to those skilled in the ar-t, numerous embodiments can be made wnthout de-parting from the spirit o the invention or the scope of the following claims.
25.
7~ :
me application is a division of copending appll-cation Seri al No. 211,312, ~iled 11th October, 1974.
_ 26 -.
Claims (15)
1. An improved process for production of halogen and metal hydroxide of an alkali, alkaline earth metal, or combination thereof, by electrolysis of a halide of said metal employing separate anode and cathode sections in an electrol-ytic cell, said improvement comprising passing ions of said metal through an ion exchange fluorinated polymer film contain-ing ion exchange sites wherein at least one film surface contains pendant side chains and includes sulfonyl groups attached to carbon atoms having fluorine atoms connected thereto, said surface containing essentially all of the ion exchange sites as the salt of said metal of N-monosubstituted sulfonamido groups.
2. The improved process of Claim 1 wherein the entire film contains essentially all of the ion exchange sites as the salt of said metal of N-monosubstituted sulfonamido groups.
3. The improved process of Claim 1 wherein the film surface containing said salt faces the cathode section and a second film surface facing the anode section contains pendant side chains and includes sulfonyl groups attached to carbon atoms having fluorine atoms connected thereto, said surface containing at least a majority of the sulfonyl groups as -(SO2NH)mQ or (-SO3)nMe, Q and Me represent ions of said metal, and m and n represent the valence of said metal.
4. An electrolytic cell comprising a housing with separate anode and cathode sections being separated by an ion exchange fluorinated polymer membrane with pendant side chains and including sulfonyl groups attached to carbon atoms having fluorine atoms connected thereto, essentially all of the exch-ange sites on at least one surface of the membrane being present as N-monosubstituted sulfonamido groups or the salt thereof.
5. The cell of Claim 4 wherein said groups are present as a salt of an alkali or alkaline earth metal.
6. An electrolytic cell comprising a housing with separate anode and cathode sections, said cell being separated by fluorinated polymer film containing ion exchange sites with pendant side chains and including sulfonyl groups attached to carbon atoms having fluorine atoms connected thereto, wherein facing the cathode section a first film surface contains essentially all of the ion exchange sites as N-monosubstituted sulfonamido groups or salt thereof and a second film surface facing the anode section contains at least a majority of the sulfonyl groups as (-SO2NH)mQ or -(SO3)nMe wherein Q is selected from the group consisting of H, NH4, cation of an alkali metal, cation of an alkaline earth metal and combinat-ions thereof, m is the valence of Q, Me is a cation, and n is the valence of the cation.
7. A film of fluorinated ion exchange polymer with ion exchange sites being present on at least a first surface comprising pendant side chains and including sulfonyl groups attached to carbon atoms having at least one fluorine atom connected thereto, at least 40% of said ion exchange sites being present as N-monosubstituted sulfonamido groups or salt thereof.
8. The film of Claim 7 wherein a second surface of the film contains the groups in non-ionic form wherein said pendant sulfonyl groups are present as -SO2X with X
representing fluorine or chlorine.
representing fluorine or chlorine.
9. The film of Claim 8 wherein X is fluorine.
10. The film of Claim 7 wherein a second surface of the film contains at least a majority of the sulfonyl groups of the polymer in the (-SO2NH)mQ form, or -(SO3)nMe wherein Q is selected from the group con-sisting of H, NH4. cation of an alkali metal, cation of an alkaline earth metal and combinations thereof, m is the valence of Q, Me is a cation and n the valence of the cation.
11. The film of Claim 10 wherein essentially all of said groups on the first surface are present as the salt of an alkali or alkaline earth metal.
12. The film of Claim 11 wherein all of said groups on the first surface are present as the salt of an alkali or alkaline earth metal.
13. The film of Claim 10 wherein the sulfonyl groups on the second surface are present as -SO3Na.
14. The film of Claim 11 wherein the sulfonyl groups on the second surface are present as -SO3Na.
15. The film of Claim 12 wherein the sulfonyl groups on the second surface are present as -SO3Na.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA284,465A CA1071571A (en) | 1973-10-15 | 1977-08-08 | Fluorinated ion exchange membrane containing n-monosubstituted sulfonamido groups |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US40636173A | 1973-10-15 | 1973-10-15 | |
| CA284,465A CA1071571A (en) | 1973-10-15 | 1977-08-08 | Fluorinated ion exchange membrane containing n-monosubstituted sulfonamido groups |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1071571A true CA1071571A (en) | 1980-02-12 |
Family
ID=25668550
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA284,465A Expired CA1071571A (en) | 1973-10-15 | 1977-08-08 | Fluorinated ion exchange membrane containing n-monosubstituted sulfonamido groups |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1071571A (en) |
-
1977
- 1977-08-08 CA CA284,465A patent/CA1071571A/en not_active Expired
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