Note: Descriptions are shown in the official language in which they were submitted.
~OS9~16Z
BACKGROUND OF THE INVENTION
___________________________
1. Field of the Invention
This invention relates to a method for electrolyzing
halides of monovalent alkali metals using an electrolytic dia-
phragm, and more specifically, to a method for electrolyzing
halides of monovalent alkali metals using a cation exchange
membrane composed of a graft copolymer of a polyolefin main chain
to which a side chain composed mainly of a hydroxystyrene compound
having the following formula is grafted:
Cl~= CH 2
l~
(OH)n
wherein n is an integer of 1 or 2.
2. Description of the Prior Art
.
In the method of electrolyzing an aqueous solution of
an alkali metal halide in an electrolytic cell including an anode,
a cathode, a diaphragm disposed between them for separating the
electrolytic cell into an anode compartment and a cathode compart-
ment, and means provided outside of the cell for passing an
electric current between the anode and the cathode, the feeding
of the aqueous solution of the alkali metal halide into the anode
compartment and the subsequent passing of a current between both
electrodes result in the conversion of the halogen ion to halogen
at the anode. The alkali metal ion moves to the cathode compart-
ment vla the diaphragm, and an alkali metal hydroxide and hydrogen
gas are generated on the cathode. Previously, a porous diaphragm
made of asbestos has frequently been used for this purpose. How-
ever, since the asbestos porous diaphragm does not possess selec-
tive permeability between positive and negative ions and between
~059~6Z
monovalent and polyvalent ions, a part of the hydroxide ion formed
in the cathode compartment diffuses into the anode compartment
through the diaphragm to cause a reduction in current efficiency.
At the same time, very small amounts of divalent or higher cations
such as iron, magnesium or calcium contained as impurities also
move to the cathode compartment together with the alkali metal
ion, and thus cannot be removed. Thus, in order to prevent
diffusion of hydroxide ions into the anode compartment, a technique
is employed of flowing a part of the anodic solution into the
cathode compartment through the diaphragm. However, an enormous
cost in the subsequent concentrating and purifying steps is
required because the aqueous solution of the alkali metal hydroxide
obtained in the cathode compartment contains a large quantity
of the alkali metal halide and traces of polyvalent metal ions,
and the concentration of the resulting alkali metal hydroxide
cannot be increased.
It is known that the use of a cationic exchange membrane
as the diaphragm obviates the above defect. If a cation exchange
membrane having an ideal selective permeability to monovalent
cations is used as a diaphragm, alkali metal hydroxides in high
concentrations can be obtained from the cathode compartment with-
out involving the above difficulties because the cation exchange
membrane does not permit the permeation of hydroxide ions,
halogen ions and polyvalent metal ions such as iron or magnesium.
However, it is very difficult in practice to produce membranes
having an ideal permselectivity to monovalent cations. Conven-
tional cation exchange membranes have proved to be not entirely
feasible for one or more reasons. For example, these membranes
cannot ensure sufficient current efficiency or sufficient purity
or concentration of the product. Moreover, since the membranes
1059~62
are exposed to severe conditions, they do not have sufficient
endurance for use for prolonged periods of time.
SUMMARY OF THE INVENTION
____________ ___________
An object of this invention is to provide a method for
electrolyzing alkali metal halides using a diaphragm having
excèllent performance.
Another object of this invention is to provide an
electrolytic diaphragm having high permselectivity to monovalent
cations, mechanical strength and durability.
The present invention provides a method for electro-
lyzing alkali metal halides using a cation exchange membrane as
a diaphragm, the cation exchange membrane being composed of a
graft copolymer of a polyolefin main chain to which a side chain
composed mainly of a hydroxystyrene compound of the following
formula tI) is grafted:
f~H=CH2
~OH)n (I)
wherein n is an integer of 1 or 2.
DETAILED DESCRIPTION OF THE INVENTION
_____________________________________
The graft copolymer used in this invention can be cross-
linked or sulfonated, or both cross-linked and sulfonated.
The diaphragm used in this invention can be produced,
for example, by the following method.
The polyolefin used in this invention can be an aliphatic
3Q
hydEocarbon polymer, especially those polymers of monomer units
1059062
1 having 2 to 10 carbon atoms, such as polyethylene, polypropylene
or polybutene; aromatic hydrocarbon polymers, especially polymers
of compounds represented by~the general formula (II)
Rl~ / R2
/ C = C \ (II)
wherein Rl, R2 and R3 each represents a hydrogen atom or an alkyl
group having 1 to 10 carbon atoms, and A is an aryl group having
the formula R6 ~ R4 or ~ in which R4, R5,
R~4 R~5
R6, R'4, R'5 and R'6 each represents a hydrogen atom or an alkyl
group having 1 to 10 carbon atoms, such as polystyrene, poly(a-
methylstyrene) or poly(tert-butylstyrene); alicyclic hydrocarbon
polymers, especially polymers of the compound represented by the
general formula (III)
R7CH = CHR8 (III)
in which R7 and R8 each represents a hydrogen atom or an alkyl
group having 1 to 10 carbon atoms, and at least one of R7 and R8
is a cycloalkyl group, such as polyvinyl cyclohexane; or copolymers
derived from two or more aliphatic, alicyclic or aromatic monomers
that constitute the above polymers. The polyolefin that makes up
the main chain of the graft copolymer can have branched chains.
The range of the degree of polymerization of these
polymers is such that the polymers are solid at normal temperatures
(e.g., 20-30C). The polymers can be used in various desired forms
such as powders, granules, fibers or films. If a polymer in a film
form is used, the product can be used directly as a diaphragm.
~)59~162
The hydroxystyrene compound that constitutes the
hydroxystryene side chain of the graft copolymer can be any
isomer, or a mixture of these isomers. A suitable proportion
of the hydroxystyrene compound side chain is about 5 to 500~
by weight, preferably 20 to 200% by weight, based on the poly-
olefin main chain. Instead of the hydroxystyrene compound, an
acyloxystyrene can be grafted to the polyolefin main chain with
subsequent hydrolysis of the acyloxy group. Examples of suitable
acyloxystyrenes are mono-, or 1,2-, 1,3- or 3,4-diacetoxystyrene,
mono-, or 1,2-, 1,3- or 3,4-dipropionyloxystyrene, mono-, or 1,2-,
1,3- or 3,4-dibutyryloxystyrene, and mono-, or 1,2-, 1,3- or 3,4-
dibenzoyloxystyrene. MoSt generally, para-acetoxystyrene or 3,4-
diacetoxystyrene is used.
In order to reduce the water content of the graft co-
polymer containing the hydroxystyrene compound side chain and to
increase the current efficiency thereof, the graft copolymer can,
if desired, be cross-linked using a difunctional compound reactive
with phenolic hydroxy groups, a polyene compound having at least
2 polymerizable double bonds in the molecule, or an organic
sulfonic acid compound.
Examples of suitable difunctional compounds are di-
epoxides, for example, aliphatic, aromatic and alicyclic di-
epoxides, such as ethylene glycol diglycidy] ether, diethylene
glycol diglycidyl ether, bisphenol A diglycidyl ether, cyclo-
hexane diol diglycidyl ether, and epoxy resins; diisocyanates
such as hexamethylene diisocyanate, tolylene diisocyanate,
xylylene diisocyanate, diphenylmethane-4,4'-diisocyanate, or
hexahydrotolylenediisocyanate; and acid dihalides such as
adipoyl dichloride, terephthaloyl dichloride and hexahydro-
terephthaloyl dichloride. A suitable amount of the difunctionalcompound is about 0.01 to 0.5 equivalent per equivalent of the
phenolic hydroxy group.
~059C~6Z
1 Examples of suitable organic sulfonic acid compounds
are aliphatic or aromatic sulfonic acids having 1 to 20 carbon
atoms or their alkyl esters, such as benzensulfonic acid, methyl
benzenesulfonate, para-toluenesulfonic acid, methyl para-toluene-
sulfonate, ethanesulfonic acid, and methyl ethanesulfonate.
When the graft copolymer is cross-linked with an organic
sulfonic acid compound, the graft copolymer is immersed in a
solution of the organic sulfonic acid compound, and react~d by
heating, or the copolymer is impregnated with this solution and
reacted by heating. A suitable reaction temperature is generally
about 100 to 150C. The reaction time differs according to the
end use of the copolymer, or the degree of cross-linking, but
generally, a suitable reaction time is about 5 minutes to 5 hours
or longer.
The polyene compound having at least two polymerizable
double bonds in the molecule can, for example, be an aliphatic
compound, an alicyclic compound containing double bonds in the
ring or in a substituent, and an aromatic compound containing
unsaturated substituents. Suitable aliphatic compounds are
aliphatic hydrocarbons, and aliphatic esters, such as diesters
formed between unsaturated acids and dihydric alcohols, diesters
formed between diacids and unsaturated alcohols, diesters formed
between unsaturated acids and unsaturated alcohols, diesters
formed between unsaturated acids and unsaturated diols, and
diesters formed between unsaturated dicarboxylic acids and un-
saturated alcohols, and the like. These compounds have 4 to 20
carbon atoms. Specific examples of the polyene compounds are
divinylbenzenes (o-, m- or p- isomers, or mixtures of these
isomers), isoprene, butadiene, cyclopentadiene, ethylidene
norbornene, diol esters of acrylic acid or methacrylic acid, or
1059~6Z t
divinyl esters of adipic acid. Of these, divinylbenzenes and
isoprene are used preferably. All of the o-, m- and p-isomers
of divinylbenzene can be used in this invention. Generally, a
mixture of these isomers is used. Generally, commercially
available divinylbenzene sometimes contains about 45~ by weight
of ethylvinylbenzene, but this mixture can be used as such in
the present invention.
A membrane composed of a graft copolymer of a polyolefin
as a main chain and a side chain composed of the hydroxystyrene
compound and the polyene compound grafted to the main chain, in
which the polyolefin is cross-linked by the polyene compound of
the side chain, can also be used as the diaphragm in accordance
with this invention. In this copolymer, too, the above-described
various polyolefins and polyene compounds, and the hydroxystyrene
compounds can be used as constituents of the copolymer. Irre-
spective of the method of introducing the polyene compound, the
amount of the hydroxystyrene compound and polyene compound is
preferably about 5 to 500~ by weight based on the polyolefin
main chain. If the amount is less than about 5%, the resulting
copolymer has insufficient properties as an electrolytic
diaphragm. On the other hand, if the amount is larger than about
500% by weight, the resulting graft copolymer has insufficient
strength and softness, and becomes difficult to use.
The grafting ratio, or the rate of introduction (based
on the polyolefin), of the polyene compound is generally about
0.5 to 100%. If the grafting ratio is less than about 0.5%, the
degree of cross-linking is low, and no outstanding effect is
obtained by incorporating the polyene compound. On the other
hand, if the grafting ratio is more than about 100~, cross-linking
becomes excessive, and the polymer generally tends to be hard,
1059062
1 brittle and tearable, and tends to have a high electric resist-
ance that makes the passage of electricity through the polymer
difficult. In view of the ion transport number, electric
resistance and strength of the membrane, an especially preferred
grafting ratio is about 20 to 200% for the hydroxystyrene compound,
and about 2 to 50~ for the polyene compound.
Preferably, the hydroxystyrene : polyene weight ratio
is about 200 : 1 to 1 : 1, especially 50 : 1 to 2 : 1.
Furthermore, an ion-exchange membrane of a sulfonated
product of the graft copolymer, either cross-linked or uncross-
linked, can also be used as a diaphragm in this invention. Inthese graft copolymers, sulfonic acid groups are introduced
mainly into the hydroxystyrene portion, but can be introduced
into the polyene compound portion grafted for cross-linking
purposes.
The rate of introduction of sulfonic acid groups is
not particularly limited, but generally, about 0.5 to 2 sulfonic
acid groups can be introduced per unit of the hydroxystyrene
compound. A suitable thickness of the membrane composed of the
~ graft copolymer or the sulfonated product thereof is about 0.05
to 0.5 mm (in a wet condition).
~e ~ O~rO ~C r
; The mcmbranc composed of the above graft copolymer or
its sulfonated product can be those prepared by any desired
method. For example, a membrane composed of the graft copolymer
containing a hydroxystyrene compound side chain can be prepared
by subjecting a polyolefin film to ionizing radiation in vacuo, in
air or in an inert gas such as nitrogen, and then immersed in a
solution of a hydroxystyrene compound monomer or an acyloxy-
styrene compound monomer or a mixture of these (when the acyloxy-
styrene compound monomer is used, the grafted acyloxystyrene is
-- 8 --
1059~62
hydrolyzed to convert the acyloxystyrene to the hydroxystyrene
compound). The membrane can also be obtained by immersing the
polyolefin film in a solution of the styrene compound monomer,
and applying ionizing radiation (when an acyloxystyrene compound
monomer is used, hydrolysis is carried out subsequently as
described above). Alternatively, a powdery or granular poly-
olefin is used in the above process instead of the film-form
polyolefin to obtain a powdery or granular graft copolymer, and
such a copolymer can be fabricated into film form using any
desired film-forming techniques such as press-forming or melt-
extrusion. If desired, the grafted copolymer obtained in a film
form is subjected to the above-described cross-linking treatment.
The cross-linking treatment using the polyene compound
can be performed easily by utilizing ionizing radiation as in
the case of the graft copolymerization.
In order to obtain a graft copolymer in which a side
chain composed of the hydroxystyrene compound and the polyene
compound is grafted to a polyolefin main chain and which is
cross-linked with the polyene compound of the side chain, a
solution containing both the styrene compound monomer and the
polyene compound monomer is used in the above-described method
for graft copolymexization using ionizing radiation, whereby
the styrene compounds and polyene compounds are both grafted
to the polyolefin, and cross-linking occurs by the polyene com-
pound so grafted.
The styrene compound and the polyene compound are used
for the graft copolymerization reaction as solutions in organic
solvents which uniformly dissolve the styrene compound and the
polyene compound, but do not dissolve the polyolefin. Examples
of suitable organic solvents are ketones such as acetone or
methyl ethyl ketone, esters such as ethyl acetate or butyl
~OS906Z
acetate, alcohols such as methyl alcohol, ethyl alcohol, propyl
alcohol or butyl alcohol, ethers such as tetrahydrofuran,
aromatic hydrocarbons such as benzene or toluene, aliphatic or
alicyclic hydrocarbons such as n~heptane or cyclohexane, or a
mixture thereof. Because these aliphatic or alicyclic hydro-
carbons have high affinity for the hydrocarbon polymers, they
swell the polymers and permit easy introduction of the monomer.
Thus, the grafting reaction is accelerated, and the grafting
becomes uniform. The amount of these hydrocarbons should be such
~ that they do not dissolve the polymer at the reaction temperatures,
and is determined according to the type of the polymer.
The concentration of the monomer in the reaction solu-
tion is not critical, but generally, a suitable concentration of
the monomer is about 0.1 to 80% by weight, preferably 5 to 50
by weight, based on the solution.
When the monomeric mixture to be grafted contains an
unsaturated compound such as ethyl vinylbenzene, for example,
such an unsaturated compound is also graft copolymerized and con-
tained in the side chain. The presence of unsaturated compounds
other than acyloxystyrene compounds, hydroxystyrene compounds
and polyene compounds, especially monounsaturated compounds
other than those having a polymerization inhibiting action, for
example, styrene, l-hexene and acrylic acid esters in addition
to ethyl vinylbenzene, does not adversely affect the reaction.
However, if the amount of such an unsaturated compound is too
large, the effect of the present invention is reduced. For
practical purposes, therefore, the amount of such a compound
can be about 30~ by weight or less based on the total monomeric
mixture.
The source of ionizing radiation can be ~-rays, X-rays,
electron beams, a-rays, or mixtures thereof. A suitable intensity,
-- 10 --
~059~6Z
1 that is, dose, of the ionizing radiation is about 103 to 1011
rads per hour. With electron beams, doses of as high as 109 to
1011 rads per hour can be used. Although lower doses can be used,
a long time is required to obtain the desired amount of irradia-
tion. Furthermore, higher doses can also be used, but are not
feasible because higher doses may result in the structural change
of the polyolefin, for example, excessive cross-linking, cleavage
of the main chain, and deformation and breakage of the polymer
by heat.
tO The use of electron beams generated from an electron
beam accelerator is especially effective since high dose
irradiation can be obtained within short periods of time. The
total dose of ionizing radiation required for graft copolymeriza-
tion is usually from about 105 rads to 101 rads.
The temperature employed for ionizing radiation must
be one at which the polyolefin is not dissolved and deformed.
In view of the life of the generated radicals (which is short
at high temperatures), a feasible temperature generally ranges
from about -100C to 40C. There is no particular lower limit
to this temperature except that arising due to economical and
technical problems.
The graft copolymerization reaction temperature
generally ranges from the temperature at which the reaction
mixture is a liquid, to about lbOC. If the reaction temperature
is too low, the time required for the reacti,on increases, and if
.i 9e~ 7~,0 ~
the reaction temperature is too high, gcll~e~ or homopolymeriza-
tion under heat tends to occur. A suitable temperature can be
selected so that such difficulties do not occur. For practical
purposes, temperatures of about 0 to 70C are suitable. Where
the ionizing radiation is applied in air, the graft copolymeriza-
tion is preferably carried out at a temperature of about 60C
-- 11 --
~059062
1 or more because the peroxide generated must be decomposed.
Ionizing radiation in advance in air or in a stream of nitrogen
is commercially advantageous.
The resulting graft copolymer, if desired, is washed
with an organic solvent, for example, an alcohol such as methanol,
ethanol or propanol, a ketone such as acetone or methyl ethyl
ketone, or an aromatic hydrocarbon such as benzene or toluene,
or mixtures of these solvents. Hydrolysis of graft copolymers
containing a side chain comprising the acyloxystyrene, similar
to an ordinary hydrolysis of phenol esters, is much easier to
perform than the hydrolysis of esters of primary alcohols, and
can be carried out easily under mild conditions. Specifically,
the graft copolymer is placed in a solution of an acid such as
hydrochloric acid, sulfuric acid or organic sulfonic acid or a
base such as sodium hydroxide or ammonia as a catalyst in water
or in a mixture of water and an organic water soluble solvent
to hydrolyze the acyloxy group of the side chain. Since the
hydrolysis is primarily carried out in a heterogeneous system,
it is preferably performed in a mixture of water and a water-
soluble organic solvent such as an alcohol or ketone in order
to increase the affinity between the substrate and the catalyst
and also to dissolve the organic acid that is split off in the
case of using an acidic catalyst. A suitable hydrolysis tempera-
ture is about 50 to 100C.
In order to obtain membranes composed of a sulfonated
product of the graft copolymer, either cross-linked or uncross-
linked, any known method for sulfonating phenols can be used.
For example, the sulfonation can be effected by
sulfonating the graft copolymer with concentrated sulfuric acid,
sulfuric anhydride, or chlorosulfonic acid, etc. in the presence
- 12 -
lOS9~6Z
1 or absence of a solvent. Examples of suitable solvents which can
be used in this process are halogenated hydrocarbons such as
chloroform or carbon tetrachloride, polar solvents such as
pyridine or dimethylformamide, or solvents such as ether or
dioxane. Catalysts such as silver sulfate can also be used
in this process.
When concentrated sulfuric acid is used, the film is
immersed in concentrated sulfuric acid, and allowed to react for
about 1 hour to about 10 days at about 0 to 40C. If heating
to a temperature of about 60C is carried out, the treating time
can be shortened. If the temperature is too high, the base
polymer is attacked with the properties of the polymer being
degraded. In order to achieve a mild reaction, up to about 80
by weight of a solvent such as acetic acid or dioxane can be
used. When fuming sulfuric acid containing about 5 to 60% by
weight of sulfuric anhydride is used, the film is suitably treated
at room temperature for about 2 to 10 hours. If the reaction
proceeds excessively, the base polymer is also attacked. Where
chlorosulfonic acid is used, the graft copolymer is dissolved
in a solvent such as chloroform, dioxane, carbon tetrachloride
or a mixture of these solvents in a concentration of about 1 to
60% by weight, and reacted at about 0 to 60C for about 1 hour
to 10 days. Then, the reaction product is washed with water.
The reaction conditions such as the temperature, the type of
reagent, the concentration, or the reaction time are controlled
as required so that the proportion of sulfonic acid groups
introduced becomes the desired value.
If the graft copolymer is treated with concentrated
sulfuric acid at room temperature for about 10 hours, about one
sulfonic acid group is introduced per hydroxystyrene group unit.
- 13 -
~OS9C3 62
When a strong sulfonating agent such as chlorosulfonic acid is
used, the treatment of the polymer in a solution of chloroform
or dioxane, etc. results in the introduction of about 2 sulfonic
acid groups per hydroxystyrene group unit, and a membrane having
a high ion-exchange capacity can be obtainedO
Membranes composed of the above graft copolymers or
their sulfonated products have reduced permeability to halogen
ions, low electric resistance, high permselectivity to monovalent
cations, high mechanical strength and high durability.
In the practice of the method of this invention, any
type of electrolytic cell including an anode, a cathode and a
cationic exchange membrane as hereinabove described and provided
between the electrodes can be used. For example, a two-compart-
ment electrolytic cell divided into an anode compartment and a
cathode compartment by the cationic exchange membrane, a three-
compartment electrolytic cell in which an anode compartment and
an intermediate compartment are separated from each other by a
non-selective diaphragm and the intermediate compartment and a
cathode are partitioned by the above cationic exchange membrane,
or a modified three-compartment or four-compartment electrolytic
cell built up by providing another non-selective diaphragm in
the cathode compartment of the above three-compartment electro-
lytic cell. The arrangement of the electrodes is also optional.
For example, they are arranged perpendicularly, or obliquely in
parallel to each other, or not in parallel to each other. E~owever,
unless there is a special reason to do otherwise, electrodes
provided in parallel to each other are generally used. The mode
of providing the cationic exchange membrane can also be varied
just as in the case of the electrodes, but usually, the membrane
is provided perpendicularly. Generally, an iron or iron-type
electrode is used as the cathode, and a graphite or dimensionally
- 14 -
~59062
stable electrode is used as the anode. The scope o this inven-
tion, however, is not limited and any appropriate selection of
these embodiments can be made.
An aqueous solution of an alkali metal halide to be
electrolyzed is fed into the anode compartment or the intermediate
compartment, and an electrolytic current is passed between the
electrodes whereby an alkali metal hydroxide is f~rmed in the
cathode compartment. At the surface of the cathode, hydrogen-
gas is formed, and at the surface of the anode, halogen is
10generated.
The alkali metal halides that can be electrolyzed by
the method of this invention are halides of monovalent alkali
metals. A suitable concentration of the solution electrolyzed
generally ranges from about 1~ by weight up to a saturated solu-
tion. A suitable current density is about 1 to 40 A~dm2.
When sodium chloride is electrolyzed using the cationic
exchange membrane in accordance with this invention, the tempera-
ture of the electrolytic cell can range from room temperature
to about 90C, and a suitable current density ranges from about
S to 30 A/dm . If, for example, sodium hydroxide in a concen-
tration of 15g by weight is to be produced at a current density
of 10 A/dm2 using a cationic exchange membrane having a thickness
of 0.15 mm, a current efficiency o~ 70 to 95% can be obtained,
and the resulting sodium hydroxide solution contains sodium
chloride in an amount of less than about 0.02~ by weight.
The following Examples are given to further illustrate
the present invention in detail but the invention is not to be
construed as being limited thereby. Vnless otherwise indicated,
all parts, percents, ratios and the like are by weight.
B - 15 -
1059062
1 EXAMPLE 1
An electrolytic cell made of poly(methyl methacrylate)
was used which was partitioned by a diaphragm having an effective
area of 10 cm2 into an anode compartment having a volume of 7 cm3
and a cathode compartment having a volume of 3.5 cm3 and in which
a graphite plate was used as an anode and a stainless steel plate
was used as a cathode. A solution feed opening and discharge
openings for the solution and gas were provided in each of the
anode compartment and the cathode compartment. Brine saturated
at room temperature with sodium chloride was fed into the anode
compartment at a rate of 15 ml/min., and a prescribed amount of
a O.lN aqueous solution of sodium hydroxide was circulated into
the cathode at a rate of 5 ml/min. Both of these solutions were
pre-heated by a coil immersed in a constant-temperature water
tank, and the temperature inside the tank was maintained at 70C.
Current of a specific den~ ty wa,s passed for a prescribed period
e o O/,~e
~- of time, and then the cathoritc was analyzed to examine the con-
centrations of sodium hydroxide and sodium chloride. On the
basis of the concentrations, the current efficiency was calculated.
Separately, a polyethylene film having a thickness of
0.1 mm was inserted into a glass ampoule, and subsequently, a
tetrahydrofuran-n-heptane mixed solution (1:2 by volume) contain-
ing 20 wt% of p-acetoxystyrene monomer was added thereto, followed
by heat-sealing the glass ampoule in vacuum. After irradiation
of ~-rays of 105 rad/hr at a temperature of 25C for 10 hours,
the resulting film was taken out of the glass ampoule and
sufficiently washed with acetone to remove the p-acetoxystyrene
homopolymer. The thus treated film was then refluxed in a con-
centrated hydrochloric acid-methanol mixed solution (1:4 by
volume) under heating for a period of 30 minutes, followed by
- 16 -
1059062
1 hydrolysis to obtain a film in which a p-hydroxystyrene side chain
was grafted at a grafting ratio of 52 wt~ (based on the poly-
ethylene). This film was further immersed in concentrated sul-
furic acid at a temperature of 25C for 72 hours and then sul-
fonated to obtain a cationic exchange membrane. The thus obtained
cationic exchange membrane was used as a diaphragm. This cationic
exchange membrane had a cation transport number of 0.97, an
electric resistance, in 0.5N sodium chloride, of 1.7~-cm2, and
an acidic ion-exchange capacity of 2.2 meq/g. A potential
was applied to the cell and after about 10 minutes a current of
1.0 A (lO A/dm2) was passed for 5 hours. It was found that the
concentration of sodium hydroxide in the catholyte was 16.8% by
weight, that the concentration of sodium chloride was 0.02~ by
weight, and that the current efficiency was 83%.
EXAMPLE 2
A polyethylene film having a thickness of 0.1 mm was
inserted in one leg of an H-type glass cell and a benzene-acetone
solution (2:1 by volume) containing 20 wt% of a p-acetoxystyrene
monomer was added to the other leg, followed by heat-sealing the
H-type glass cell in vacuum. The portion containing the monomer
solution was cooled and frozen, followed by covering sufficiently
with lead plates. Then the H-type cell was cooled to -30C and
electron beams of 20 Mrad were irradiated onto the polyethylene
film using an electron beam accelerator under the conditions,
i.e., of an acceleration voltage of 2 MeV, and an acceleration
current of lmA, at this temperature.
After irradiation of the polyethylene film, the
monomer solution was melted and transferred to the film
side, and reacted at room temperature (i.e., about 20 to
30C) for 24 hours. After completion of the reaction, the
cell was opened and the resulting film was then taken out,
followed by washing thoroughly with acetone. The
17 -
1C~59062
thus treated film was then hydrolyzed in the same manner as
described in Example 1 to obtain a film in which a p-hydroxy-
styrene side chain was graft-copolymerized at a grafting ratio
of 92 wt% (based on the polyethylene).
Electrolysis was then carried out in the same manner
as described in Example 1 using the film thus obtained as a
diaphragm. It was fou~d th,at the concentration of sodium
c~f~io~
hydroxide in the aathori-tc was 14.2% by weight and the concen-
tration of sodium chloride was 0.01% by weight. The current
efficiency was 74~.
EXAMPLE 3
Electrolysis was carried out in the same way as inExample 1 using the same diaphragm as in Example 1 except that
it was not sulfonated. It wa~ fpu~d that the concentration of
~ 70/~'e
sodium hydroxide in the c~ was 16.9% by weight, that the
concentration of sodium chloride was 0.01% by weight, and that
the current e~ficiency was 77%.
EXAMPLE 4
The same graft copolymer film as used in Example 1
except that the film was not sulfonated but was immersed in a 10
acetone solution of bisphenol A diglycidyl ether (containing 1%
of triethylenetetramine as a curing agent) for 2 hours, and then
taken out, followed by air-drying. The resulting film was further
heated to 100C for 30 minutes in an air thermostat to obtain
a cross-linked film.
Electrolysis was then carried out in the same manner
as described in Example 1 using the resulting cross-linked film
as a diaphragm. It wa~ f~und that the concentration of sodium
hydroxide in the oathor-~c was 16.8% by weight, and that the
concentration of sodium chloride was 0.005% by weight. The
current efficiency was 85%.
P~
l~S9(~62
EXAMPLE 5
Electrolysis was carried out in the same way as in
Example 1 using a diaphragm obtained by graft-copolymerizing a 0.1
mm thick polypropylene film with p-hydroxystyrene at a grafting
ratio of 98~ by weight in the same manner as described in Example 2.
It w~s fo~und that the concentration of sodium hydroxide in the
~athor~e was 16.0% by weight, that the concentration of sodium
chloride was 0.02% by weight, and that the current efficiency
was 76%.
EXAMPLE 6
Electrolysis was carried out in the same way as in
Example 1 using a diaphragm obtained by sulfonating the graft-
copolymer membrane obtained in Example 5. It ~as fQund that thec~o /~e
concentration of sodium hydroxide in the e*~e~itr-was 16.2% by
weight, that the concentration of sodium chloride was 0.02%, and
that the current efficiency was 78%.
EXAMPLE 7
Electrolysis was carried out continuously for 1000
hours using the same apparatus as used in Example 1 and a diaphragm
obtained by graft-copolymerizing a 0.2 mm thick polyethylene film
with p-hydroxystyrene at a grafting ratio of 105% by weight using
ionizing radiation from electron beams. The current density used
was 15 A/dm2. In order to completely prevent C12 from attacking
the ion-exchange membrane, a neutral porous diaphragm (made of a
fluorine resin) was provided to separate the ion-exchange membrane
in the anode compartment from the anode, and a suitable amount of
water was added to the cathode compartment ~o m 'ntain the con-
c~o ~o/,~
centration of sodium hydroxide in the c~tho~ite at 11% by weight,
and brine comprising saturated sodium chloride at room tempera-
ture ti.e., about 20-30C) was supplied between the ion-exchange
membrane and the neutral porous diaphragm. The
total current efficiency of the
-- 19 --
lOS9C3 6Z
1 continuous electrolysis for 1000 hours was 75~. The average
concentration of sodium chloride in the catholyte was 0.002%
by weight, and no reduction in current efficiency was observed
even at the end of the electrolysis.
EXAMPLE 8
Electrolysis was rarried out continuously for 1000
hours in the same way as in Example 7 using a diaphragm obtained
by sulfonating the graft copolymer membrane used in Example 7.
When the concentration of sodium hydroxide in the catholyte was
8~ by weight, the total current efficiency of the continuous
electrolysis for 1000 hours was 85%, and the concentrati~n of
sodium chloride in the catholyte was less than 0.001% by weight.
No reduction in current efficiency was observed even at the end
of the electrolysis.
EXAMPLE 9
A polyethylene film having a thickness of 0.2 mm was
cooled to -20C, and electron beams of 20 Mrad were irradiated
thereon under a nitrogen atmosphere. Subsequently, the resulting
polyethylene film was inserted into a glass ampoule and a solu-
tion in which a monomer mixture of p-hydroxystyrene and divinyl-
benzene (divinylbenzene content of 55 wt%, an m- to p- weight
ratio of about 2 : 1, and the remainder being mainly
ethylvinyl benzene) at a mixing ratio of 3 : 1 by weight
was dissolved in the same weight of benzene was added thereto,
followed by thorough degassing in vacuum by repeating a
freezing-melting procedure five times and heat-sealing. This
glass ampoule was then heated to 60C and the contents were
reacted for one hour. After completion of the reaction, the
seal of the glass ampoule was broken and the resulting film was
- 20 -
1C~59~62
1 then taken out, followed by washing thoroughly with acetone.
The thus treated film was then hydrolyzed in the same manner
as described in Example 1 to obtain a film at a total grafting
ratio of 75 wt% (based on the polyethylene). As a result of
analysis, the p-hydroxystyrene content was 69 wt% in the total
of the graft copolymer.
Electrolysis was then carried out in the same manner
as described in Example 1 using the film thus obtained as a
diaphragm. It was found that the concentration of sodium
hydroxide in the catholyte was 17.2% by weight, that the concen-
tration of sodium chloride was 0.02~ by weight, and that the
current efficiency was 87%.
EXAMPLE lO
Electrolysis was carried out in the same way as in
Example 1 using a diaphragm obtained by sulfonating the same
graft copolymer membrane as used in Example 9 in a 50% by weight
dioxane solution of chlorosulfonic acid at 70C for 5 hours.
It was found that the concentration of sodium hydroxide in the
cath~lyte was 17.3% by weight that the concentration of sodium
chloride was 0.03% by weight, and that the current efficiency
was 88%.
EXAMPLE 11
Electron beams of 30 Mrad were irradiated on a poly-
propylene film having a thickness of 0.1 mm in air.The resultin~
film was subjected to grafting and hydrolysis in the same manner as
described in Example 9 to obtain a film at a total grafting ratio
of 115 wt% (based on the polypropylene), the p-hydroxystyrene
content being 91 wt~ in the total of the graft copolymer.
Electrolysis was then carried out in the same manner
as described in Example 1 using the polypropylene film thus
- 21 -
1059~)6Z
obtained as a diphragm. It wa~f o d that the concentration
;~ C O ~
of sodium hydroxide in the c~t-h~rit~ was 17.0~ by weight, that
the concentration of sodium chloride was 0.02~ by weight, and
that the current efficiency was 85%.
EXAMPLE 12
On a polyethylene film having a thickness of 0.2 mm
was grafted p-acetoxystyrene in the same manner as described in
Example 5, and subsequently, divinylbenzene (in which a benzene-
acetone mixed solution containing 3 wt% of divinylbenzene usedas a monomer solution) was further grafted thereon in the same
manner as described in Example 5. The thus treated film was
then hydrolyzed to obtain a film at a total grafting ratio of
90 wt% (based on the polyethylene). The p-hydroxystyrene content
was 94 wt~ and the divinylbenzene content was 6 wt~ in the total
of the graft copolymer, respectively.
Electrolysis was then carried out in the same manner
as described in Example 1 using the polyethylene film thus
obtained as a diaphragm. It was~ fou~d that the concentration
~Dof~o /~/7'C~
of sodium hydroxide in the aathoritc was 18.4~ by weight, that
the concentration of sodium chloride was 0.01% by weight, and
that the current efficiency was 89.5%.
EXAMPLE 13
Electrolysis was carried out in the same way as in
Example 1 except that a suitable amount of water was added to
the cathode compartme~t to~ maintain the concentration of sodium
hydroxide in the cathor-tc constant at 12~ by weight, and the
current density was adjusted to 15 A/dm2.
When a membrane prepared by graft copolymerizing a
0.2 mm thick polyethylene film with p-hydroxystyrene and divinyl-
benzene at a total grafting ratio of 102~ by weight (based on the
- 22 -
~059062
polyethylene), the p-hydroxystyrene content being 73% by weight
in the total of the graft copolymer, using ionizing radiation
from electron beams, was used as a diaphragm, the concentration
of sodium chloride in the catholyte was 0.002% by weight, and
the current efficiency was 92%.
When a membrane prepared by graft copolymerizing the
same polyethylene film as used above with p-hydroxystyrene alone
at a grafting ratio of 74% by weight was used as a diaphragm,
the concentration of sodium chloride in the catholyte was 0.008%
by weight, and the current efficiency was 77%.
ExAMæLE 14
_
Electrolysis was carried out in the same way as in
Example 13 using a diaphragm prepared by sulfonating the same
graft copolymer membrane as used in Example 13 having both p-
hydroxystyrene and divinylbenzene grafted thereto, in a 50% by
weight dioxane solution of chlorosulfonic acid at 70C for 5
hours. It was found that the concentration of sodium chloride
in the catholyte was 0.002% by weight, and the current efficiency
was 92%.
EXAMPLE 15
Electrolysis was.carried out in the same way as in
Example 13 using a diaphragm prepared by graft copolymerizing a
0.1 mm thick polypropylene film with p-hydroxystyrene and di-
vinylbenzene using ionizing radiation from electron beams at a
total grafting ratio of 125~ by weight, the p-hydroxystyrene
content being 97% by weight in the total of the graft copolymer.
It was found that the concentration of sodium chloride in the
catholyte was 0.002% by weight, and the current efficiency was
88%.
- 23 -
105906Z
EXAMPLE 16
Electrolysis was carried out in the same way as in
Example 13 using a diaphragm obtained by sulfonating the same
graft copolymer membrane as used in Example 15 in a 50% by weight
dioxane solution of chlorosulfonic acid at 70C for 5 hours.
It w~s~fo~nd that the concentration of sodium chloride in the
cathoritc was 0.001% by weight, and the current efficiency was
90% .
_~MP~E 17
The grafting reaction and the hydrolysis were carried
out on a polystyrene film having a thickness of 0.1 mm in the same
manner as described in Example 9 except that a mixed solution of
methanol and benzene (2 : 1 by volume) was used. Thus, a film
having a total graft copolymer content of 85 wt% (based on the
polystyrene) and a p-hydroxystyrene content of 90 wt% in the
total of the graft copolymer was obtained.
Electrolysis was then carried out in the same manner
as described in Example 13 using the resulting polystyrene film
as a diaphragm. It ~a~ ~ound that the concentration of sodium
chloride in the cathorit~ was 0.002% by weight, and the current
efficiency was 85%.
ExAMæLE 18
The graft copolymerization was carried out on a poly-
ethylene film having a thickness of 0.2 mm in the same manner as
described in Example 9 (but the divinylbenzene content was 90%
by weight, with the remainder being ethylvinyl benzene). Thus,
a film having a total grafting ratio of 82% by weight (based
on the polyethylene) and a p-hydroxystyrene content of 72% by
weight in the total of the graft copolymer was obtained.
- 24 -
~05906Z
1 Electrolysis was then carried out in the same manner
as described in Example 13 using the resulting film as a
diaphragm. It was found that the concentration of sodium
chloride in the catholyte was 0.002~ by weight and the current
efficiency was 94%.
EXAMPLE l9
~ lectrolysis of a saturated potassium chloride solution
was carried out in the same manner as described in Example 18
using the same apparatus and the same diaphragm as described in
Example 18. The concentration of potassium hydroxide was 12%
by weight, the concentration of potassium chloride was 0.02~ by
weight and the current efficiency was 98% by weight.
EXAM2LE 20
An electrolytic cell made of poly(methyl methacrylate)
was used which was partitioned by a diaphragm having an effective
area of lO cm2 into an anode compartment having a volume of 7 cm3
and a cathode compartment having a volume of 3.5 cm3 and in which
a graphite plate was used as an anode and a stainless steel plate
was used as a cathode. A solution feed opening and discharge open-
ings for the solution and gas were provided in each of the anode
compartment and the cathode compartment. Brine which was saturated
with sodium chloride at room temperature (i.e., about 20 to 30C)
and in which magnesium chloride was dissolved to the concentration
of 20 ppm was fed into the anode compartment at a rate of 15
ml/min, and a prescribed amount of a O.lN aqueous solution of
sodium hydroxide was circulated into the cathode compartment at
a rate of 5 ml/min. Both of these solutions were preheated by
a coil immersed in a constant-temperature water tank, and the
temperature inside the tank was maintained at 70C. Current of
a specific density was passed for a prescribed period of time,
- 25 -
1~591~62
1 and then the catholyte was analyzed to examine the concentrations
of sodium hydroxide, sodium chloride and magnesium hydroxide~ On
the basis of the concentrations, the current efficiency was
calculated.
Separately, one leg of a glass H-tYpe cell (diameter
10 mm, thickness 0.5 mm) was charged with a 0.1 mm thick poly-
ethylene film washed thoroughly with acetone and the other leg
was charged with a solution of a mixture of 3,4-diacetoxystyrene
and divinylbenzene (containing 55% by weight of divinylbenzene
with an m- to p-weight ratio of about 2 : 1, and the remainder
being mainly ethylvinylbenzene)in a weight ratio (3,4-diacetoxy-
styrene : divinylbenzene) of 9 : 1 in two times its weight
of a mixture of benzene and acetone (in a benzene : acetone
volume ratio of 3 : 1). By repeating a freezing-melting
procedure five times, the cell was thoroughly degassed in vacuo,
and then heat-sealed. The monomer solution part was frozen,
and sufficiently covered with a lead plate. While the
entire H-type cell was being cooled at -30C, electron beams in
a dose of 30 Mrads were applied to the polyethylene film at an
acceleration voltage of 1.5 MeV using an electron beam accelerator.
After the irradiation, the monomer solution was transerred to
the film-containing portion to dip the film in the solution and
allow it to react for 24 hours at 25C. After the reaction, the
cell was opened. The film was withdrawn, and thoroughly washed
with benzene and acetone.
The thus obtained film was then placed in a 100 ml of
flask equipped with a cooling tube. Subsequently, 50 ml of a
mixture of concentrated hydrochloric acid and methanol in a
mixing ratio by weight of 1 : 4 was added, and the flask was
heated for 30 minutes over a hot water bath. As a result of the
- 26 -
105906Z
1 calculation from the difference in the weight of this film before
and after the hydrolysis treatment, a grafting ratio of 3,4-
dihydroxystyrene per se was 73% by weight, and a total grafting
ratio was 98% by weight.
Electrolysis was then carried out using the resulting
polyethylene film as a diaphragm. A potential was applied to the
cell and after about 10 minutes a current of 1.0 A (10 A/dm2) was
~-~ passed for 5 hours. ~t w~s found that the concentration of sodium
O ~f e
hydroxide in the cathoritc was 17.2~ by weight, that the con-
centrations of sodium chloride and magnesium hydroxide were 0.02%by weight and 6 ppm, respectively, and that the current efficiency
was 84.5%.
EXAMPLE 21
The graft copolymerization reaction was carried out on
a polyethylene film having a thickness of 0.2 mm using a mixed
solution of 3,4-dihydroxystyrene and divinylbenzene (containing
90% by weight of divinylbenzene) by means of ionizing radiation
from electron beams to obtain a film having a total grafting
ratio of 105~ by weight (based on the polyethylene) and a 3,4-
dihydroxystyrene content of 82% by weight.
Electrolysis was then carried out in the same manneras described in Example 20 using the thus treated polyethylene
film as a diaphragm. In the above experiment, a neutral porous
diaphragm was provided to separate the diaphragm of the graft
copolymer as described above in the anode compartment from the
anode, and brine was supplied between the diaphragm of the graft
copolymer and the neutral porous diaphragm. It~ s,f nd that
c~G
the concentration of sodium hydroxide in the cathorite was 19.2%
by weight, that the concentration of sodium chloride was 0.005%
by weight, and that the concentration of magnesium hydroxide was
2 ppm. Further, the current efficiency was found to be gl%.
- 27 -
1059~6Z
EXAMPLE 22
Electrolysis was carried out in the same manner as
described in Example 20 using a diaphragm obtained by graft-
copolymerizing a polyethylene film having a thickness of 0.2 mm
with a 3,4-dihydroxystyrene side chain at a grafting ratio of
95% by weight using ionizing radiation from electron beams. It
' was ~o,un~ that the concentration of sodium hydroxide in the
o~thor-i-t~ was 15.5~ by weight, that the concentration of sodium
chloride was 0.01% by weight, and the concentration of magnesium
hydroxide was 4 ppm. Further, the current efficiency was found
to be 79%.
EXAMPLE 23
Electrolysis was carried out in the same manner as
described in Example 20 using a diaphragm obtained by graft-
copolymerizing a polypropylene film having a thickness of 0.2 mrn
with a 3,4-dihydroxystyrene side chain at a grafting ratio of
92% by weight using ionizing radiation from electron beams. It
was f~u~d that the concentration of sodium hydroxide in the
c"~f~o /~
oathorito was 16.2~ by weight, that the concentration of sodium
chloride was 0.02~ by weight, and that the concentration of
magnesium hydroxide was 5 ppm. Further, the current efficiency
was found to be 75%.
EXAMPLE 24
A 0.2 mm thick polyethylene film was placed in a glass
ampoule, and a solution of a mixture of 3,4-diacetoxystyrene and
divinylbenzene in a weight ratio (3,4-diacetoxystyrene : divinyl-
benzene) of 9 : 1 in 9 times its weight of a mixture of benzene
and acetone in a benzene : acetone volume ratio of 3 : 1 was
placed in the ampoule. The ampoule was sufficiently degassed in
vacuo by repeating a freezing-melting procedure five times and
- 28 -
~OS906Z
1 then heat-sealed. Using a cobalt 60 source, ~-rays were applied
to the ampoule at a dose of 1.1 x 105 rads/hour for 24 hours.
Then, the film was taken out of the ampoule, washed sufficiently
with benzene and acetone to remove a by-product copolymer composed
of 3,4-diacetoxystyrene and divinylbenzene. The grafted film was
hydrolyzed in the same manner as described in Example 20. The
grafting ratios of 3,4-diacetoxystyrene and divinylbenzene cal-
; culated from the difference in weight of the grafted film before
and after the hydrolysis were 50~ and 19%, respectively.
Electrolysis was then carried out in the same manner
as described in Example 20 using the thus obtained polyethylene
film as a diaphragm. It was/fo~nd that the concentration of
~O/Jf
~!s sodium hydroxide in the c~thoritc was 17.5% by weight, that the
concentration of sodium chloride was 0.02~ by weight, and that
the concentration of magnesium hydroxide was 4 ppm. Further,
the current efficiency was found to be 82%.
EXAMPLE 25
The grafting reaction and the hydrolysis were carried
out on a polyethylene film having a thickness of 0.2 mm in the
same manner as described in Example 20 except that using a
cobalt 60 source, ~-rays were applied at a dose of 1.1 x 105
rads/hour at room temperature (i.e., about 20 to 30C) for 24
hours instead of the electron beams, and that a monomeric solu-
tion of 3,4-dihydroxystyrene in 2 times its weight of a mixture
of benzene and acetone (3:1 by volume) was used, to obtain a
film in which a 3,4-dihydroxystyrene side chain was graft-
copolymerized at a grafting ratio of 64% by weight (based on
the polyethylene). The resulting film was further sulfonated
with concentrated sulfuric acid at room temperature for 72 hours
to obtain a cationic exchange membrane.
- 29 -
1~9~16Z
1 Electrolysis was then carried out in the same manner
as described in Example 20 using the resulting cationic exchange
membrane as a diaphragm. It was found that the concentration of
cr~ f~o/,~7~e
sodium hydroxide in the ea~ ~e was 17.2% by weight, that ~he
concentration of sodium chloride was 0.02% by weight, and that
the concentration of magnesium hydroxide was 6 ppm. The current
efficiency was also found to be 84.5~.
SUPPLEMENTARY DISCLOSURE
As noted in the above examples, when an electrical
potential is applied to the electrolytic cell there is an
initial period of approximately 10 minutes before the desired
operating current is obtained. This may be explained by the
fact that when using the membranes composed of the graft co-
polymers or the sulfonated products thereof of the present
invention, the hydrogen ion of the hydroxy group of the hydroxy-
styrene side chain is inevitably replaced with an alkali metal
ion. Thus the electrolysis does not proceed smoothly until
the hydrogen atoms are replaced. Once replacement occurs the
desired current level can be maintained.
To obviate this problem it is possible to control the
voltage applied across the cell during this initial period.
The preferred technique, however, is to affirm~tivcly replace
the hydrogen ions with alkali metal ions prior to electrolysis.
This is done by contacting the membrane with an aqueous
solution of an alkali metal hydroxide such as sodium hydroxide,
potassium hydroxide and lithium hydroxide having a concentration
of about 0.1 to 12N, an aqueous solution of an alkali metal
hydroxide at the concentration as described above, additionally
containing an organic solvent which can be uniformly mixed with
- 30 -
`" 1059~6Z
1 the above described aqueous solution and which is also capable
of swelling the membrane, or a solution of an alkali metal
hydroxide, at the concentration as described above, dissolved
in a lower aliphatic alcohol having 1 to 4 carbon atoms at a
temperature of room temperature (e.g., about 20-30C) to about
90C for a period about 30 minutes to about 5 hours. Suitable
examples of organic solvents which can be employed include
methanol, ethanol, dioxane, tetrahydrofuran, acetone, methyl- -
ethylketone, etc. Further, suitable examples of lower aliphatic
alcohols which can be employed include methanol, ethanol, etc.
When the membranes used are composed of sulphonated
products containing sulphonic acid groups, the hydrogen atom
of the sulphonic acid group similarly is also inevitably replaced
by an alkali metal ion at the beginning of the electrolysis or
in the replacement treatment as set forth above.
When!the~membr~nes are employed which are composed of
graft copolymers which are produced by grafting side chains
composed mainly of an acyloxy styrene onto a polyolefin and
hydrolyzing the resulting graft copolymer in the presence of an
alkali metal hydroxide as a catalyst, the hydrogen atom of the
hydroxy group o~ the hydroxystyrene side chain thus produced
in the membranes is already replaced by an alkali metal ion.
Therefore, in such a case, no particular replacement treatment is
needed and the use of such copolymers as membranes results
in an electrolysis which proceeds smoothly at the desired
current level as soon as the potantial is applied to the cell.
The following examples are given to further illustrate
in detail the above embodiments of the present invention but the
invention is not to be construed as being limited thereby.
Unless otherwise indicated, all parts, percents, ratios and the
like are by weight.
B
i~S9~62
` 1 EXAMPLE 26
. . _
The method of manufacturing a membrane and the
electrolysis were carried ou~ in the same way as in Example 2
e,,~7,Yge
except that the cationic ~ membrane to be used as a diaphragm
was subjected to a pretreatment in which the membrane was
immersed in 0.5N sodium hydroxide solution at a temperature
of 8`0C for a period of 2 hours prior to the electrolysis. The
membrane had a cation transport number of 0.97, an electrical
resistance in 0~5N sodium chloride, of 1.7~ -cm2, and an
acidic ion-exchange capacity of 2.2 meq/g. The current of
l.0 A(lOA/dm2) was passed for 5 hours with a constant current
level throughout tha~ t~m,e. The concentration of sodium
~ /,~f~
hydroxide in the c~h~te, the concentration of sodium
chloride and the current efficiency were the same as found in
Example 2.
EXAMPLE 27
The method of manufacturing a membrane and the
electrolysis were carried out in the same way as in Example 7
except that the membrane which was to be used as a diaphragm
was subjected to a pretreatment, before electrolysis, comprising
immersing the diaphragm in a mixture of a lN sodium hydroxide
aqueous solution and dioxane (l:l by volume). The results were
the same as found in Example 7 except that there was no initial
period where the current level was less than the desired rate.
EXAMPLE 28
The method of manufacutring a membrane and the electro-
lysis were carried out in the same way as in Example 21 above
except that the polyethylene film was subjected to pretreatment,
before electrolysis, in which the film was immersed in a mixture
of a lN sodium hydroxide solution comprising water and dioxane
(1:1 by volume) at a temperature of 80C for a period of 2 hours.
- 32 -
1059~6Z
1 There was no initial period where the current level was not
at the desired rate. The results were the same as found in
Example 21.
While the invention has been described in detail
and with reference to specific embodiments thereof, it will be
apparent to one skilled in the art that various changes and
modifications can be made therein without departing from the
spirit and scope thereof.
- 33 -
i~
