Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to a process for electrolyz-
ing an aqueous solution of an alkali metal chloride.
A cation exchange membrane made of a perfluorocarbon co-
polymer having sulfonic acid groups as ion exchange groups
has been prepared by fabricating a film of a copolymer of
tetrafluoroethylene and perfluoro-3,6-dioxa-4-methyl-7-octene-
sulfonyl fluoride and hydrolyzing the film. The cation exchange
membrane is commercially available under the trademark Nafion
manufactured bv Du Pont. I~hen this cation exchange membrane is
used for the electrolysis of an aqueous solution of an alkali
metal halide, high current efficiency is not possible because
of the high hydrophilic characteristic of sulfonic acid group.
A cation exchange membrane made of a perfluorocarbon polymer
having sulfonic acid groups whose surface on the cathode side
has sulfonamido groups has been proposed to overcome this
problem. The current efficiency for producing 30% sodium
hydroxide may be about 90%.
A cation exchange membrane made of a perfluorocarbon
polymer having carboxylic acid groups has been proposed. A
high current efficiency such as 95% is possible in the produc-
tion of sodium hydroxide at high concentrations such as 40%.
However, carboxylic acid groups have lower acidity than sul-
fonic acid groups even though carboxylic acid groups are
bonded to a perfluorocarbon polymer. Therefore, dissociation
is low under the acidic conditions providing a low ion exchange
capacitv. Even though the current efficiency is about 95%,
oxy~en at a minimum amount of about 2% is present in the
chlorine generated from the anode compartment. In order to
overcome this, the electrolysis is carried out with the add-
ition of hydrochloric acid to the anode compartment. In the
electrolysis, the anode compartment is under strong acidic
conditions having a pH of less than 2. When the cation ex-
."~ -- 1
~,.~j, "
~L5~
change membrane of a perfluorocarbon polymer havin~ carboxylicacid groups is used under such strong acidic conditions, the
cell voltage is disadvantageously increased. In order to
overcome this, it has been proposed to partially convert a
perfluorocarbon polymer having sulfonic acid groups to intro-
duce carboxylic acid groups. However, it is not possible to
prepared a membrane having sulfonic acid groups which has an
ion exchange capacitv of more than 1.0 me~./g. dry resin
because of the mechanical strength of the membrane and accord-
ingly, a membrane having carboxylic acid groups obtained bymodifying a membrane having sulfonic acid groups does not have
a large ion exchange capacity.
It is preferable to use a cation exchange membrane made
of a perfluorocarbon polymer having carboxylic acid groups and
having a large ion exchange capacity, such as 1.1 to 2.0
meq./g. drv resin, to produce an alkali metal hydroxide in
high concentration. The above-mentioned method is not satis-
factory.
A membrane obtained by laminating a membrane made of a
perfluorocarbon polymer having sulfonic acid groups and a
membrane made of a perfluorocarbon polymer having carboxylic
acid groups has been proposed. However, the membrane may
be peeled off due to different swelling degrees of the two
types of the polymer decreasing the characterisitics of the
membrane.
~he present invention provides a process for electrolyz-
ing an aqueous solution of an alkali metal chloride at high
current efficiency to produce an alkali metal hydroxide in
high concentration and at a low cell voltage using a cation
exchange membrane having a large ion exchange capacity.
According to the present invention there is provided in
~ .~
:
a process for electrolyzing an aqueous solution of an alkali
metal chloride using a cation exchange membrane having two
layers of a first layer made of a fluorocarbon polymer having
ta) groups of the formula -O(CF2) COOM where M represents H,
an alkali metal atom or -NH4; and n=2 to 5 and a second layer
made of a fluorocarbon polymer having (b) groups of the formula
~O(CF2)nSO3M where M and n are defined above such that the
layer having (b) groups of the formula -O(CF2)nSO3M face in an
anode compartment, the improvement in which the layer having
(b) groups of the formula -O(CF2) SO3M is formed by treating
a cation exchange membrane having (a) groups of the formula
-O(CF2)nCOOM and an ion exchange capacity of 1.1 to 2.0 meq./g.
dry resin to convert (a) groups of the formula -O(CF2)nCOOM
in one layer into groups of the formula -O(CF2) I where n=2 to
5 and further to convert the groups into groups of the formula
-O(CF2) SO3M where M and n are defined above.
It is preferable to use a cation exchange membrane having
the first layer made of a fluorocarbon polymer having ta)
groups of the formula -O(CF2) COOM and the second layer made
of a fluorocarbon polymer having ~b) groups of the formula
-OtCF2) SO3M in thickness a ratio of the second layer to the
total layer ranging from 0.2 to 0.9 because of the low cell
voltage and high current efficiency in producing an alkali
metal hydroxide at high concentration.
The cation exchange membrane has the structure of a pair
of parallel plane layers. The component having (a) groups of
the formula -O(CF2)nCOOM can remain in the second layer having
~b) groups of the formula -O(CF2) SO3M. It is also possible
to have a boundary region in which the ratio of -the component
having (a) groups to the component having (b) groups continuous-
ly varies.
:`
The process for preparing the cation exchange membrane used
in the process of the present invention will be illustrated.
-- 3 --
" '
~' .
In the first step for preparing the cation exchange mem-
brane, a fluorocarbon polymer having carboxylic acid groups
is prepared. A monomer having carboxylic acid groUps or a
functional group which can be converted into carboxvlic acid
groups may be used in the preparation. Suitable carboxylic
acid type functional monomers (i) include fluorovinyl mono-
mers having the formula
CF2=CX--~OCF2CFYt-aO t CF2~
wherein a=0 to 3; n=2 to 5; X represents F or -CF3; Y repre-
sents F or a C1-C10 perfluoroalkyl group; A represents -C~,
-COF, -COORl, -COOM or -COONR2R3; Rl represents C1-C10 alkyl
group; R2 and R3 respectively represent H or Rl; M represents
H or an alkali metal atom or -NH4.
Is is espeeially preferable to use a fluorovinyl compound
having the formula (I) wherein X is F; Y is -CF3, a=0 to 1;
A is -COF or -COORl and Rl is a Cl-C5 alkyl group. Typical
fluorovinyl compounds inelude CF2=CFO(CF2)2_3COOCH3; CF2=CFO-
(CF2)2_3COF; CF2=CFO(CF2)2 3COOC2H5; CF2=CFOCF2CF(CF3)0(CF2)-
2_3COOCH3; and CF2=CFOcF2cF(cF3)0(cF2)2-3coF-
In the production of the fluorocarbon polymer having car-
boxylic acid groups, a fluorinated olefin (ii) such as tetra-
fluoroethylene, trifluorochloroethylene, hexafluoropropylene,
trifluoroethylene and vinylidene fluoride is also used. It
is especially preferable to use tetrafluoroethylene.
Two or more types of the carboxylic acid type functional
monomers and two or more types of the fluorinated olefins can
be used. It is also possible to add one or more other monomers
such as olefins having the formula CH2=CR4R5, wherein R4 and
R5 respectively represent H, a Cl-C8 alkyl group or an aromatic
group; fluorovinyl ethers having the formula, CF2=CFORf, wherein
Rf re~resents a Cl-C10 perfluoroalkyl group; and divinyl mono-
mers such as CF2=CF-CF=CF2 and CF2=CFO(CF2)1_40CF=CF4.
In the production of the fluorocarbon polymer by copoly-
merizing the functional monomer (i) and the fluorinated olefin
(ii) and if necessary, a third monomer, the ion exchange
capacity is controlled by the proportion of the monomers, to be
in a range of 1.1 to 2.0 meq./g. dry resin, preEerably 1.1 to
1.5 meq./g. dry resin.
The copolymerization of the monomer (i), and the monomer
(ii) and if necessary with the third monomer can be carried
out by various processes. The copolymerization is carried out
by conventional processes in the presence of a polymerization
initiator source, such as a peroxide compound, an azo compound,
ultraviolet rays and ionized high energy rays with or without
an inert organic solvent or an aqueous medium. The copolymer-
ization ca~ be carried out by various processes such as bulkpolymerization, solution polymerization, suspension polymeriza-
tion and emulsion ~olvmerization. The resulting copolymer
is fabricated to form a membrane. The fabrication can be
carried out by conventional processes, such as the press
molding process and the roll molding process. The thickness
of the membrane is preferably in the range of 20 to 500~,
especially 50 to 300~. For increasing the mechanical
strength, it is possible to reinforce the membrane with a
reinforcing substrate, such as woven fabric or a net. When
the functional groups of the resulting copolymer are fun-
ctional groups which can be converted into carboxvlic acid
groups, such as ~CN, -COF, -COORl and -COOR2R3, tlle functional
groups, can be converted into carboxylic acid groups by a
suitable process, such as hydrolysis with an alcoholic solution
of an a~cid or a base.
In the second step of the preparation of the cation ex
change membrane used in the process of the present invention,
only one surface of the membrane made of the fluorocarbon
polymer having groups of the formula -O(CF2)nCOOM obtained
~,
.. . .
in the first step is treated to convert the groups of the formu-
la -O~CF2) COOM into groups of the formula -O(CF2) I. The
reaction con~itions shoul~ be controlled ~o give a desired thick-
ness of the reaction layer. The following alternative treatments
may be carried out:-
(1) A single surface of the membrane is coated with an aqueous
solution of NaOH to convert groups of the formula -O(CF2) COOH
into groups of the formula -O(CF2) COONa, then it is treated
with an a~ueous solution of AgNO3 to convert the groups into
groups of the formula -O(CF2)nCOOAg and the membrane is then
dried and heated in the presence of I2 to eliminate CO2
groups.
(2) A single surface of the membrane is coated with an aqueous
solution of Ag2O to convert the groups of the formula -O(CF2) -
COOH into groups of the formula -O(CF2)nCOOAg and the membrane
is dried and heated in the presence of I2 to eliminate CO2
groups; and
(3) A single surface of the membrane having the groups of the
formula -O(CF2) COOCH3 is treated with an a~ueous solution of
NaOH to hydrolyze the groups, the groups are conver-ted into
groups of the formula -O(CF2) COOAg and the membrane is dried
and h~ated in the presence of I2 to eliminate CO2 groups.
/\
l~hen the membrane having the groups of the formula
-O(CF2)nCOOAg in one layer is heated in the presence of I2,
the reaction time is in the range of 5 minutes to 20 hours,
preferably 10 minutes to 5 hours and the reaction temperature
is in the range of 150 to 250C, preferably 170 to 220C.
It is also possible to react I2 with the groups o~ the formula
-O(CF2)nCOOH ~n one side of the membrane in the pxesence of a
radical initiator,such as benzoyl peroxide ~*~ dicumylperoxide.
The resultinq membrane having groups of the formula -O(CF2) I
in one layer and groups of the formula -O(CF2)nCOOH or -O(CF2)
COOCH3 in the other layer is treated by the third step. In
the third step, the groups of the formula -O(CF2)nI are con-
verted by the following reactions:-
(1) The membrane having groups o~ the formula -O(CF2)nI is
dipped into anhydrous dimethylsulfoxide with a Zn-Cu couple
and SO2 is fed into contact with the membrane. The reaction
is as follows.
1 ) Me2SO
RfI + Zn-Cu-~SO2 ~ RfSO Cl
2) C12, MeOH 2
In a nitrogen gas atmosphere, the Zn-Cu couple is produced
in anhydrous dimethylsulfoxide by reacting Zn powder with
copper acetate. The membrane having groups of the formula
-O(CF2)nI is dipped in the solution and SO2 is bubbled to
effect reaction. After the reaction, the membrane is dipped
into methanol dissolving C12 to form groups of the formula
-O(CF2) SO2Cl. The ratio of Zn powder to copper acetate may
be about 100:1. The molar ratio of the groups of the formula
-O(CF2)nI to the Zn-Cu couple may be less than 1. The reaction
time with SO2 is preferably in the range of 10 minutes to
20 hours, especially 1 hour to 10 hours, and the reaction
temperature is preferably in a range of 0 to 100C, especially
20 to 50C. The temperature in the step of contacting with
C12 is preferably in a range of 0 to 50C and the time of con-
tacting is preferably in a range of 5 minutes to 20 hours.
(2) NascH3/(cH3)2s2 is dissolved in an aprotic solvent and the
membrane having the groups of th~ formula -O(CF2)nI is dipped
into the solution to convert the groups into groups of the
formula -O(CF2)nSCH3. ~he membrane is oxidized to convert
the groups into groups of the formula -O(CF2)nSO3H. The reac-
tions are as follows:-
(CH )
RfI + CH3SNa - 3 RfSCH3
RfSCH3_ KMnO4 - CH3COOH ~ RfSO2CH
2 3 KMnO4 aq. ~ RfSO~K
35RfSO3K_ ~ RfSO3H
,~
~; ?
In the reaction of the groups of the formula -O(CF2)nI,
the reaction temperature is preferably ln the range of 50
to 150C; the reaction time is preferably in the range of 1
to 100 hours. It is preferable to carry out the reaction
in a polar aprotic solvent such as dimethylsulfoxide. The
resulting methvlsulfide type membrane may be oxidized with
a mixture of KMnO4-CH3COOH or H2O2-CH3COOH to produce the
corresponding methylsulfone type membrane. The reaction tem-
perature is preferably in the range of -10C to 150C and the
reaction time is preferably in the range of 5 minutes to
200 hours. The ~qnO4-CH3COOH system is especially preferable
because the reaction is easily performed at a reaction tem-
perature of 0 to 20C for a reaction time of 1 to 5 hours. The
corresponding potassium sulfonate type membrane is obtained
by refluxing the methylsulfone type membrane in an aqueous
solution of KMnO4. The salt type membrane can be converted
to the acid type ~embrane bv the conventional process such
as the treatment with hydrochloric acid.
The following processes can be also used:-
(3) Ultraviolet rays are applied to the surface of the layer
having the groups of the formula -O(CF2)nI in the presence of
(CH3S)2 to convert the groups into groups of the formula
-O(CF2)nSCII3. The groups of the formula -O(CF2)nSCH3 are
converted into groups of the formula -O(CF2)nSO3i3 by the
oxidation as process (2).
(~) The membrane having the groups of the formula -O(CF2)nI
is dipped into a system containing Rfl (Rf represent a per-
fluoroal~yl ~roup) and sulfur is added to the system to con-
vert the groups into groups of the formula -O(CF2)nSSRf.
Ultraviolet rays are applied to the membrane in the presence of
mercury to convert the groups into groups of the formula
~O(CF2)nSHgSRf and the membrane is oxidized with hydrogen per-
oxide to convert the groups into groups of the formula -O(CF2)-
nSO3H.
(5) The memhrane having groups of the formula -O(CF2) SSRf
-- 8
. . .
in one layer obtained by the process (~4) is treated with
water containing chlorine to convert the groups into groups
of the formula -O(CF2)nS02Cl and the membrane is then hydrolyzed
to convert the groups into groups of the formula -O(CF2) SO3-
Na.
(~) The membrane having the groups of the formula -O(CF2)nI
is dipped in a solution containing phenyl magnesium bromide
and SO2 gas is bubbled in the solution and then, the membrane
is hydrolyzed and treated with chlorine to convert the groups
into groups of the formula -O(CF2)nSO2Cl. The membrane is
further hydrolyzed to convert the groups into groups of the
formula -O(CF2)nSO3Na.
(7) The membrane having the groups of the formula -O(CF2)nI
is dipped into an aqueous solution o~ sodium sulfide and re-
fluxed to convert the groups into groups of the formula
-O (CF2) nS3Na -
When the membrane having a first layer having carboxylic
acid groups or derivative groups and a second layer having
sulfonic acid groups or derivative groups is used,pos.sibly as a
result of hydrolysis, in the electrolysis of an aqueous solution
of an alkali metal chloride, the cell voltage is relatively
low and the current efficiencv is remarkably hi~h even though
hydrochloric acid is added to the anode compartment.
The present invention will be further illustrated by the
following Examples and References.
Example 1
In a stainless steel autoclave, the copolymerization of
CF2=CF2 and CF2=CFOCF~CF(CF3)OCF2CF2COOCH3 was carried out in
1,1,2-trichloro-1,2,2-tri~luoroethane in the presence of per-
fluoropropionyl peroxide as the initiator. The resulting co-
pol~mer was press-molded at 250C to obtain a trallsparent
membrane having a thickness of 200~(I). The membrane (I)
_ 9 _
~ ,,:i
was hydrolyzed in a solution of 10~KOH-methanol (1:1 vol/vol).
It was confirmed by a titration, to have a carboxylic acid
salt con-tent of 1.2 meq./g. drv resin.
Two sheets of the membranes (I) were held between frames
of acrylic resin with a packing made of polytetrafluoro-
ethylene. The membranes held by the frames were dipped in a
2~NaOlT a~ueous solution at room temperature for 60 minutes
to hvdrolyze one surface of each of the two sheets only.
The membrane obtained is referred to as membrane (II). It
was confirmed that one layer having a thickness of about 10
in the membrane (II) was colored by treating with a bath of
Crystal violet the residual being a colorless layer.
The membrane (II) was dipped into a lN-AgNO3 aqueous
solution to convert the groups of the formula -COONa in the
one layer having a thickness of 10~ into groups of the
formula -COOAg and was washed with water and dried at 80C
in a vacuum. The membrane having groups of the formula
-COOAg in one layer having a thickness of 10~ was treated
with I2 at 180C for 1 hour. The resulting membrane was
washed with methanol and dried. According to the infrared
spectrography, the peak for -CF2cOoAg at 1650 cm 1 disappeared
and the peak for -CF2I at 910 cm 1 was found. The membrane
is referred to as membrane (III).
Membrane (III) was dipped into a suspension prepared by
reacting Zn powder with copper acetate in anhydrous dimethyl-
sulfoxide in a nitrogen gas atmosphere, and then, SO2 gas was
bubbled in at 45~C for 6 hours. After the reaction, the mem-
brane was taken out and dipped into methanol dissolving C12
at 30~C for 15 hours. The membrane was washed with methanol
and dried. According to the infrared spectrography, the peak
for -CF2I at 910 cm 1 substantially disappeared and the peak
for -CF2SO2Cl at 1420 cm was found. The membrane was re-
-- 10 --
,
.
ferred to as membrane (IV).
Membrane (IV) was dipped into 10~KOH-methanol (1:1 vol/
vol) at 60C for 16 hours to effect hydrolysis.
The resulting cation exchange membrane was used to form
an eleetrolytic cell with the converted surface facing the
anode side. The electrolytic cell was a -two compartment -type
cell having an anode eompartment and a eathode compartment
with the cation exchange membrane having an effective area
of 36 cm (8 cm x 4.5 em), an anode made of a metal having
low chlorine overvoltage, and a eathode made of iron. A
saturated aqueous solution of sodium ehloride and hydroehloric
acid were fed into the anode eompartment and water was fed
into the eathode eompartment to obtain a 36% sodium hydroxide
solution. The conversion of sodium chloride was 50g6 and an
electrolysis was carried out at 85C at a eurrent density of
30 A/dm2. In the eleetrolysis, the pH at the outlet of the
brine was 2Ø The eurrent effieieney was 94% and the eell
voltage was 3.7 V.
Referenee 1
The membrane (I) obtained in the proeess of Example 1
was dipped in 10%KOH-methanol (1:1 vol/vol) at 60C for 16
hours to effect hydrolysis. The eleetrolysis of an aqueous
solution of sodium ehloride was earried out to yield a 36%
sodium hydroxide solution under the eonditions of Example 1
exeept using the resulting eation exchange membrane. The
eurrent effieieney was 94% and the eell voltage was 4.1 V.
Example 2
.
The membrane (III) obtained in the process of Example 1
was dipped into a solution of sodium methanethiolate and
dimethyl sulfide (1:5) in dimethylsulfoxide to effect reation
at about 110C for 40 hours. After the reaction, the membrane
-- 11 --
..
was dipped into a solution of KMnO4-CH3COOH to effect reaction
at 20C for 10 hours. The membrane was dipped into an a~ueous
solution of KMnO~ under reflux for 15 hours and then, th~
membrane was dipped into 10%KOH-methanol (1:1 vol/vol) at
5 ~0C for 16 hours to hydrolyze the membrane.
The electrolysis of an aqueous solution of sodium chloride
was carried out under the conditlons of Example 1 except
using the resulting cation exchange membrane. The current
efficiency was 94% and the cell voltage was 3.8 V.
Example 3
In a stainless steel autoclave, the copolymerization of
CF2=CF2 and CF2=CFOCF2CF(CF3)OCF2CF2COOCH3 was carried out
in 1,1,2-trichloro-1,2,2-trifluoroethane in the presence of
perfluoropropionyl peroxide as the initiator. The resulting
copolymer was press-molded at 250C to obtain a transparent
membrane having a thickness of 200~(I). The membrane (I) was
hydrolyzed in a solution of 10%KOH-methanol (1:1 vol/vol~.
It was confirmed by a titration to have a carboxylic acid
salt content of 1.2 meq./g. dry resin. Two sheets of the
membrane (I) were held between frames of acrylic resin with
a packing of polytetrafluoroethylene. The membranes held by
the frames were dipped into a 2%NaOH aqueous solution at 50C
for 60 minutes to hydrolyze only one sur-face of each of the
two sheets. The membrane is referred to as membrane (V).
It was confirmed that one layer having a thickness of
about 150~ in the membrane (V) was colored by treating with
a bath of Crystal violet the remainder being a colorless
layer.
Membrane (V) was dipped into an lN-AgNO3 aqueous solution
to convert the groups of the formula -COONa in the one layer
having a thickness of 150~ into groups of the formula ~COOAg
and was washed with water and dried at 80C in a vacuum. The
- 12 -
membrane having groups of the formula -COOAg in one layer
having a thickness of 150~ was treated with I2 at 180C for
6 hours. The resulting membrane was washed with methanol and
dried. According to infrared spectrography, the peak for-
-CF2COOAg at 1650 cm disappeared and the peak for -CF2I at
910 cm 1 was found. The membrane is referred to as membrane
(VI).
Membrane (VI) was dipped into a suspension prepared by
reacting Zn powder with copper acetate in anhydrous dimethyl-
sulfoxide in a nitrogen gas atmosphere, and then S02 gas was
bubbled therethrough at 45C for 18 hours. After the reaction,
the membrane was taken out and dipped into methanol dissolving
C12 at 30C for 20 hours. The membrane was washed with
methanol and dried. According to infrared spectrography,
the peak for -CF2I at 910 cm 1 substantially disappeared
and the peak for -CF2S02Cl at 1420 cm was found. The mem-
brane was referred to as membrane (VII).
Membrane (VII) was dipped into 10%KOH-methanol (1:1 vol/
vol) at 60C for 16 hours to effect hydrolysis.
The resulting cation exchange membrane was used to form
an electrolytic cell with the converted surface to the anode
side. The electrolytic cell was a two compartment type cell
having an anode compartment and a cathode compartment with
the cation exchange membrane having an effective area of 36
cm (8 cm x 4.5 cm), an anode made of a metal having a low
chlorine overvoltage and a cathode made of iron. A saturated
aqueous solution of sodium chloride and hydrochloric acid
were fed in-to the anode compartment and water was fed into
the cathode compartment to obtain 45% sodium hydroxide. The
conversion of sodium chloride was 50% and the electrolysis
was carried out at 85C at a current density of 30 ~/dm2. The
current efficiency was 94% and the cell vol-tage was 3.9 V.
:~5~
Reference 2
The membrane (I) obtained in the process of E~ample 1
was dipped in 10%KOH-methanol (1:1 vol/vol) at 60C for 16
hours to effect hydrolysis. The electrolysis o~ an aqueous
solution of sodium chloride was carried out to obtain 45~
sodium hydroxide under the conditions of Fxample 3, except
using the resulting cation exchange membrane. The current
efficiency was 88% and the cell voltage was 4.7 V.
Example 4
~ wo sheets of the membrane (I) obtained in the process of
Example 1 were held between frames made of acrylic resin with
a packing made of polytetrafluoroethylene, and were dipped
into a 2%NaOH aqueous solution at 30C for 90 minutes to
hydrolyze only one surface of each of the two sheets. The
membrane is referred to as membrane (VIII).
It was confirmed that one layer having a thickness of
about 50~ in the membrane (VIII) was colored by treating
with a bath of Crystal violet the residual being a colorless
layer.
Membrane (VIII) was dipped into a lN-AgNO3 aqueous solu-
tion to convert the groups of the formula -COONa in the one
layer having a thickness of 50~ into yroups of the formula
-COOAg and was washed with water and dried at 80C in a
vacuum. The membrane having groups of the formula -COOAg in
one layer having a thickness of 50~ was treated with I2 at
180C for 3 hours. The resulting membrane was washed with
methanol and dried. According to infrared spectrography, the
peak for -CF~COOAg at 1650 cm 1 disappeared and the peak for
--1
-CF2I at 910 cm was found. The membrane was referred to as
membrane (IX).
The membrane (IX) was dipped into a solution of sodium
- 14 -
methanethiolate and dimethyl disulfide (1:5) in dimethyl-
sulfoxide to effect reaction at about 110C for 60 hours.
The resulting membrane was dipped into a solution of KMnO~-
CH3COOH at 20C for 10 hours. The membrane was dipped into
a KMnO4 aqueous solution under reflux for 15 hours and the
membrane was dipped into 10~KOH-methanol (1:1 vol/vol) at
60C for 16 hours to effect hydrolysis.
In accordance with the process of Example 3 except using
the resul~ing cation exchange membrane, -the electrolysis was
carried out to obtain 42~ sodium hydroxide. The current
efficiency was 94~ and the cell voltage was 3.9 V.
Example 5
In an apparatus of a middle pressure mercury lamp for
internal irradiation, the membrane (VI) obtained in Example
3 was charged together with dimethyldisulfide so as to irra-
diate the surface of the membrane having the groups of the
formula -CF2I. The membrane (VI) was dipped in dimethyl-
disulfide at 60C for 1 day to sw211 the membrane and then
the mercury lamp was actuated to irradiate the membrane at
40C for 3 weeks. After the irradiation, the membrane was
taken out and oxidized with an aqueous solution of KMnO4 and
hvdrolyzed with potassium hydroxide as set forth in Example
2 to obtain a cation exchange membrane.
The electrolysis of an aqueous solution of sodium chloride
was carried out under the conditions of Example 3 except
using the resulting cation exchange membrane. The current
efficiency was 94% and the-cell voltage was 4.0 V.
Example 6
In a stainless steel autoclave, membrane (~I) obtained in
Example 3 and, perfluoro-l-iodooctane were charged and heated
at ~0C for 1 day to swell the membrane. The autoclave was
,.~
cooled to the ambient tempera-ture, sulfur was added and the
autoclave was further heated at 250DC for 72 hours to effect
reaction of the membrane. After the reaction, the treated
surface of the resultin~ membrane was irradiated by a middle
pressure mercury lamp in a chlorine gas atmosphere for 3
weeks. The resulting membrane was dipped into water and
chlorine gas was bubbled for 1 week. According to infrared,
spectrography, the peak for -CF2I at 910 cm disappeared
and the peak for -CF2SO2Cl at 1420 cm was found. The mem-
brane was h~ydrol~7zed b~ dipping it in 10%I~OH-methanol at
60C for 16 hours to obtain the cation exchange membrane.
The electrolysis of an aqueous solution of sodium chloride
was carried out under the conditions of Example 3 except
using the resulting cation exchange membrane. The current
efficiency was 94% and the cell voltage was 3.9 V.
- 16 -
~ .
