Note: Descriptions are shown in the official language in which they were submitted.
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.
2.
, ~, ~., ~
.,.~,,. i
AD-4750
~ 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
CF3
CF2=CFOCF2CFOCF2fFOCF2CF2S02F,
CF3 CF3
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 .
CF3
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
_~ ..
R2
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.
EXAMPLE 1
In this and the ~ollowing examples a film is
employed o~ a copolymer of tetraXluoroethylene and
CF2=CFOCF21FOCF2CF2S02F
CF3
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.
EXAMPLE 3
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.
EXAMPLE 7
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.
EXAMPLE 9
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,
AD-4750
~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 -
.
