CA1057233A - Method of electrolyzing alkali metal halide solution and apparatus therefor - Google Patents

Abstract

ABSTRACT

A method for electrolyzing an alkali metal halide solution is disclosed wherein a horizontal diaphragm electrolytic cell is employed. A
diaphragm having a water-permeability of not more than 0.02 ml/cm2.cm H2O.
hr. is used, and water or an electrolytic solution is supplied to the under-side of the diaphragm during electrolysis.

Description

~7Z33 This invention relates to a method for electrolyzing an aqueous solution of an alkali salt, and more specifically to a method for electroly~ing an alkali metal halide solution in a horizontal diaphragm cell using a diaphragm having a low water-permeability, characteri~ed ;
in that water or an electrolytic solution is continuously or intermittently supplied to the underside of the diaphragm.
In the conventional electrolysis of alkali salts, the most prevalent method is by using a vertical-type elec-trolytic cell using an absestos diaphragm. In this method, halogen gas generated on the anode surface and hydrogen gas generated at the cathode surface rise through the ; solution on both sides of the diaphragm. Consequently, the effective area of passing electricity decreases, and the voltage between electrodes increases. Furthermore, it is usually the practice in this method to pass an aqueous solution of an alkali salt from an anode compartment to a cathode compartment in order to prevent bases from diffusing from the cathode compartment to the anode compartment through the diaphragm. Therefore, the concentrationæ of bases generated in the cathode compartment, such as sodium hydroxide, potassium hydroxide, or other alkali hydroxides, decrease, ~,~ and products containing alkali salts as impurities are formed. In order bo remove bhese impurities, a complicated procedure is eubsequently required, especially in a step of concentrating the caustic -;' aIkalies. Even when this procedure is taken, it is still~ impossible to reduce the content of the impurities to -. ~ , -: :- .
an extent comparable to that of a product obtainea by the ' " . .

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16~57;~3;3 mercury method. Furthermore, an extracting operation, for example, is re-quired to remove the impurities.
`; With a view to preventing the inclusion of impuri-ties, attempts have been made to use a cation permselective membrane (cation exchange mem-brane). The use of the cation exchange membrane results in the prevention of -diffusion of bases from a cathode compartment to an anode compartment, and in a high level of current efficiency maintained during electrolysis. Since the cation exchange membrane has a low water-permeability, the amounts of im-purities that come into the product are reduced, and also alkali hydroxides of high concentrations can be obtained. In this case also, the defects in-heren-t in the vertical structure of the electrolytic cell cannot be avoided, and the loss caused by a decrease in the effective area of passing electricity becomes greater with increasingcurrent density.
Ordinary cation exchange membranes now under development cannot completely prevent the diffusion of bases, and therefore, there is a de-crease in current e~ficiency due to the diffusion of bases.
~ In order to overcome such structural disadvantages, U.S. Patent ~o. -!;~ 3,770,611 proposes a horizontal diaphragm cell in which a diaphragm is dis-~ posed horizontall~ to divide the cell into an upper anode compartment and a :~` 20 ~ lowar cathode compartment.
In the vertical electrolytic cell, as a~orementioned, a halogen gas and hydrogen~gas evolved at the anode and the cathode, respectively, rise ~ ~ beaide the surfaces of the anode and cathode that are disposed vertically.
`~ As a result, the effective area for passing electricity is reduced. In the ~ horizontal electrolytlc cell, on the other hand, the anode and the cathode ;~, are disposed horizontally, therefore, a halogen gas evolved at the anode is ~ removed from the cell substantially without passing beside the anode surface, ~. ~r9 and it causes no substantial trouble~ r~ hydrogen evolved at the cathode sur~ace is also removed from '' ' '. ' ' . -'` . ~.,. " . :

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~L05~233 .
the cell from the space under the cathode, and does not cause any substantial trouble. Another advantage is that a space can be pro-vided between the cathode and a reservoir for a catholyte (a solution containing caustic aIkalies) within the cathode compartment, and therefore, caustic alkalies are prevented from diffusing into the ` 1 anode comp~rtment. However, when a diaphragm having a low water-permeabili~yor being substantially devoid of water-permeability is ~-used ln the horizontal electrolytic cell, and especially when the cell is operated at a high current density, there is a great rise in tem-perature~ Consequent.ly, the moisture content of the underside of the diaphragm and at the cathode surface decreases and at times becomes very low, which in turn results in a rise in electric resistance and thus a rise in the electric voltage of the electrolytic cell, thereby ~;
causing a reduction in current e~ficiency. In an extreme case, the electrolysis ~ails.
An object of this invention is to produce aIkali hydroxides having reduced amounts of alkali salt as impurities by electrolysis in accordance with the diaphragm method.
Another object of this invention is to provide an electrolyzing ~?` 20 method using a horizontal electrolytic cell and a diaphragm having a ~` i ~ ....
low water-permeability.
'~ Still another obJect of this invention is to provide a method in which an ion-exchange membrane is used as a diaphragm having a low water-permeability~

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Still another object of this invention is to provide a method for electrolyzing alkali salt solutions while continuously or intermittently supplying water or an electrolytic solution to the underside of a diaphragm having a low water-permeability placed in a horizontal electrolytic cell.
Yet another object of this invention is to provide an apparatus suitable for performing the method of this invention.
Other objects of this invention alsng with its advantages will become apparent from the follo~ing description.
In the present invention, the same apparatus ~ -and operating procedure as the conventional horizontal electrolytic cells are used in many respects. The elec- ;
trolytic apparatus used in this invention is one in which an anode compartment including an anoda is disposed on the upper side and a cathode compartment including a cathode, .~ on the lower side. Usually, a multiplicity of such units ~ -., . :.
are superimposed, and used in the form of a multiple tier -`1~ horizontal diaphragm cell.
he present invention provides a method for ;~
electrolyzine an alkali halide solution using a horizontal diaphragm electrolytic cell using a diaphragm having a water-permeability, as defined hereinbelow, of not more than 0.02 ml/cm /cmH O/hr, characterized in that water ~ -1 or an electrolytic solution (these may be generically ~ :
-I termed "liquid" herelnafter) is supplied to the underside ~ of the diaphragm. TWhere an electrolytic solution is '' ' .

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~57Z33 :

supplied, it is desirable to use the catholyte solution in order to prevent the inclusion of impurities in the product. The liquid may be supplied from a separate source outside the electrolytic cell or alter- -natively the catholyte sol~tion in the catholyte reservoir of the lower .,' ~ :
part of the cathode compartment may be supplied either directly or after being taken out of the cell.
Since diaphragms of such a low water-permeability are used :
in this invention, the electrolysis is usually carried out in such a manner that alkali salts supplied to the anode compartment in the form of aqueous solution are consumed in an amount of not more than 60%, preferabl~ 10 to 30~, and the remainder of the alkali salts are withdrawn from the anode compartment as waste liquids and provided for reuse.
The invention will be specifically described by reference to the accompanying drawings în which: . :
Figure 1 is a sectional view showing a known horizontal dlaphragm-type electrolytic cell;
Figure 2 is a sectional view showing the apparatus of this :
, . ,:
:~ invention in which the liquid is supplied ~o the underside of the , 20 diaphragm by spraying it in atomized form from the bottom of the cell;
~ ,,:
~ Figure 3 is a sectional view showing another embodiment of , ~
-~ the apparatus of thls invention in which the liquid is directly intro-~'1 duced to the underside of the diaphragm from outside the electrolytic cell;

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: ,' '~ ,' ' ,. ' ~L~57233 Figure 4 is a sectional view of the apparatus of this invention in which the liquid is discharged from the side wall of the cathode compartment;
Figure 5 is a sectional view of the apparatus of this invention in which the catholyte solution is taken ~- out from the catholyte reservoir by a siphon and supplied .
- to the underside of the diaphragm;
Figure 6 is a view showing a similar structure to the apparatus shown in Figure 3, wherein a levelling device is provided in order to supply the liquid smoothly;
Figure 7 is a view showing a liquid supply system ~-, for practicing the present invention with good efficiency;
and :
Figure 8 is a view showing an example of a liquid maintaining device.
There are only specific e:mbodiments of this .1 invention, and various changes and:modi~ications are possible to those skilled in the art without departing from the spirit and scope o~ this invention. - --: ', . ' '- .
In the drawings, the reference numeral 1 :
.: represents a diaphragm; 2, a cathode; ~, an anode; 5, a ~ .
feed inlet for an alkali salt solution; 6, an outlet for ~ :
. .
halogen gas to be generated by electrolysis; 7, an outlet for hydrogen gas; 8, an outlet for alkali hydroxides; 9, ~ ~
an anode compartment; 10, a cathode compartment; 11, a . ~.
pipe for supplying the liquid from outside the electrolytic ~:.
cell; 12 9 an inlet, preferably a spray nozzle, for supplying . .

the liquid to the underside of the diaphragm and the cathode :: ~
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.: ' ': -~L~5~Z33 in the form of droplets uniformly; 13, a capillary tube; 14, a device for maintaining the water level constant; 15, an outlet for withdrawing the alkali salt solution; 3, a device for maintaining the liquid disposed in , contact with the diaphragm 1 and the cathode 2, which can hold the supplied liquid and is maintained in the wet state so as to avoid an increase in electrical resistance and therefore an increase in electrical voltage of the electrolytic cell that would otherwise be caused by its drying; l$ a device ~or supplying the liquid to the underside of the diaphragm and ~he cathode by tapping the surface of the catholyte solution in the catholyte reservoir; 17, a power transmitting device; 18, a drive device; 19, a device for actuating a switch in response to changes in electric voltage; and 20, a switch to be actuated by the switch actuating device 19.
As shown in Figure 1, in a well-known horizontal electrolytic cell, an aqueous solution of an alkali salt is introduced into an anode compartment partitioned by a diaphragm, for example asbestos paper, and it is electrolyz-ed while being passed to a cathode compartment. If desired a part of the anolyte is discharged from the anolyte outlet of an anode compartment.
Halogen gas evolved in the anode compartment is discharged from the outlet. -~
On the other hand, in the cathode compartment, hydrogen ions derived from ~- -water are reduced on the cathode generally disposed in contact with the -diaphragm or in close proximity to it, and hydrogen gas is generated. ~he ' ' .
` alkali hydroxide solution is diluted with the aqueous salt solution that has passed through the diaphragm, and withdrawn from the outlet of the ~ catholyte reservoir. The solution is generally an alkali hydroxide solution `~ .' . .
containing alkali hydroxides in a concentration of 0.5 to 4 normal and -~lkali salts of 50 to 200 mol% based on alkali hydroxides. Hydrogen . .
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gas is withdrawn ~rom the outlet.
In actual operation, a multiplicity of cell units as shown in Figure 1 are stacked, and one of such units will be described below. This, however, is not intended in any ~ay to limit the number of cell units used in this invention.
The most basic embodiment of the present invention is shown in Figures 2 to 7, in which an electrolytic cell very similar to the well-known horizontal electrolytic cells is used. Thus, the conventional horizontal electrolytic cell can be easily modified for the practice of the present invention. In order to obtain high purity aIkali hydroxides, there is used a diaphragm which permits the permeation of only a very small amount of water. The permeating water consists of water permeating by the difference in pressure according to head under the electrolyzing conditions and water ~-permeating by diffusion. The water-permeability of the diaphragm used in this invention is not more than 0.02 ml., preferably not more than 0.01 ml., in terms of pressure difference o~ing to head of 1 cm of water per hour per cm . Most effectiw ly, the amount of water permeating through such a dia-phragm should be negligible. In the present specification and the appended ~ :.: . ;- .
claimj the value exprossed in a unit of m}/cm /cmH20/hr.is defined as -water-permeability. Accordingly, it is essential in the present invention to use a diaphragm having a water-permeability of not more than 0.02 ml/cm /
cmH20/hr., prefer bl~ not more than 0.01 ml/cm /cmH20/hr., more preferably -, ' ,: ' ; '' , :: .. ' : ~ '' " ',:
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as close to zero as possible.
Generall~, it is preferred to use cation exchange membranes. Such an ion exchange membrane consists of a substance resulting from the chemical bonding of a cation exchange group such as a suLfonic group, carboxyl group, phosphoric acid group, or phenolic hydroxyl group to a polymer having high chemical resistance and oxidation resistance. This ion exchange membrane usuaLly has a water-permeability of not more than 0.02 ml/cm /cmH20/
hr. For example, this membrane consists o~ a divinylbenzeneacr~lic acid copolymer, a sulfonated high molecuLar subs1;ance such as a divinylbenzene-styrene copoLymer, polyolefine, polyvinyl f]Luorocarbon ether or perfluoro-ethylene-styrene copolymer, or a composite of a cation exchange resin and another polymer. Nafion (tradename for the product of E. I. du Pont de Nemours ~ Co.) is a pre~erred diaphragm. Similar cation exchange membranes . ~. .: .
having fluorine atoms bonded thereto are also preferred. These membranes ~ ;
have desirable high degrees of electrolytic conductivity and high alkaLi ~ -~; ion transport numbers. The cation exchange membranes are disclosed, for example, in United States Patents Nos. 2,636,851, 3,017,338, 3,496,o77, ~;- 3,560,568, 2,976,807, and 3,282,975, and Brltish Patent No. 1,184,321.
`~ It is also essential that water or an electrolytic solution ~ -be supplied continuously or intermittently to the underside of the diaphragm, ~;~ or both to the u~derside of the dlaphragm and to the cathode.
Examples of the method of supplying water or the : : ~ '".:''' .
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. - 10 - . . s ,: ., ~6)S7233 electrolytic solution are shown in Figures 2 to 7, but other means can also be applied.
As shown in Figures 2 to 4 and 6, water or the electrolytic solution may be supplied from outside the electrolytic cell. Alternatively, the catholyte solution may be directly fed as illustra~ed in Figures 5 and 7.
The modes of supplying water or the electrolytic solution include, for example, one wherein it is supplied in the form of droplets by a spray nozzle (Figure 2); one wherein the liquid is supplied under pressure from a ~et outlet (Figure 4), one wherein the liquid is sprayed uniformly by a sprinkler statistically, or it is supplied by gravity (Figures 3 and 6); one wherein it is supplied by a capillary action (Figure 5); and one wherein the liquid is scattered by tapping the liquid in the catholyte reservoir using a rotating blade, for example (Figure 7). These modes of liquid ~upply may be used individually or in combinations in the presenb invention.
The liquid to be supplied is water or an electrolytic solution. In particular, by supplying water or an alkali ~ `
hydroxide solution in a suitable concentration, the alkali hydroxide to be withdrawn from the electrolytic cell as a product can be ad~usted to the desired concentration.
The minimum amount required of the liquid to be supplied , :.
; to the underside of the diaphragm is one required to maintain good conductivity for passing electricity between the anode and the cathode. Since a diaphragm having a low water-permeability is used in this invention, sufficient electric conductivity for the electrolytic solution cannot , . .
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be maintained only by the water which passes through the diaphragm in the --form of water of hydration of the alkali metal ion ~usually, 2 to 8 :-molecules of water per alkali metal ion) and the water present in the alkali sa~t solutisn passing through the diaphragm.
Accordingly, the water passing through the diaphragm should be supplemented with a supply of wa-ter or aqueous solution as described above in order to secure the minimum required amount of water. In general, , ::
` the temperature becomes higher when the electrolysis is carried out at a high current densi-ty, and the evaporation of water from the vicinity of the underside of the diaphragm becomes vigorous, with the consequence that the minimum amount required of the liquid tends to be larger. The minimum ~, required amount of the liquid to be supplied is determined by the minimum amount required to prevent a rise in voltage during electrolysis. In ; determaning this, there is employed a method wherein a standard voltage is ;
set within a predetermined range of the voltage of the electrolytic cell, for example, 2 to 5 volts, and a voltage value higher than the predetermined value, for example, by 10%, preferably by 5~, is set as an upper limit volt-age, and when the electroly ing voltage exceeds the upper limit, the liquid is s~pplied until the voltage returns to the standard voltage, or the liquid , 20 is supplied continuously or intermittently so that the electroIyzing voltage is maintained within the range of the standard voltage predetermined.
The provision of the liquid maintaining device 3 in con-tact with the underside of the diaphragm and the surface ,j .,.

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-.' :, : ' .: ' ` . ~ i ., , . . . , ., ; .. ! ' ~S7%33 of the cathode is also a preferred embodiment in this invention. Several examples of this embodiment are shown in Figures 3 to 6, and several examples of providing the liquid maintaining device are shown in Figure 8.
Figure 8 is an enlarged view showing the provis.on of the liquid ..
maintaining device between the diaphragm and the cathode. The liquid maintaining device is one which has the ability to maintain the wet state ..
and has a relatively high corrosion resistance to alkali hydroxides, and its .
material and shape are not restricted in particular. Examples of the material of the liquid maintaining device are inorganic fibrous materials such as :-asbestos or glass fibers, or woven fabrics, non-woven fabrics, mats or battings, thereof; porous open-cellular substances composed of a resin having .:.
a relatively high resistance to alkali such as vinylidene chloride resins, ~
polyolefin resins, fluorine-containing resins, polyester resins or polyamide .
resins, woven fabrics or non-woven fabrics composed o~ fibers made from such resins, porous ceramics or minerals such as biscuit wares or porous ; stones, and porous metals. Generally, these materials have the ability to ; hold the liquid by a capillary action or the hydrophilic nature of their surfaces. . . `
~ The cathode can be constructed in a porous structure having a . `
;~ 20 porosity of, say, at least 50%, preferably at least 60%. From the viewpoint :~
: ~ of the current efficiency and the mechanical strength, it is preferred that s the porosity of the cathode should be not more than about 90%. By using :~ a porous metal or wire gauze having pores permitting :
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~1~57233 passage of solution and having an average unit pore area of not more than 1 cm , preferably not more than 3 mm as the cathode, it can maintain the liquid by itself without using a liquid maintaining device. ~eedless to say, such a cathode can be used together with another liquid maintaining device.
In one preferred embodiment of the present invention as shown in Figure 7, the liquid is supplied to the underside of the diaphragm by actuating the liquid supply means 16, such as rotary blades, through drive means 18 and power transmitting means 17 to be operated by the closing or opening of the switch 20 to be actuated -in response to signals from the device 19 which automatically measures the voltage between the anode and the cathode and emits signals when the voltage exceeds the predetermined I upper voltage or returns to values within the predetermined range. ~hen sufficient electric conductivity within the diaphragm and between the d~aphragm and the cathode is restored, and the voltage becomes normal below the upper limit, the switch is automatically opened to stop the supply of the liquid. By using such a device, the electrolysis of aIkali salts solutions can be performed in stable con-, dition with good current efficiency. ~
;~' The alkali salt solutions to be electroly~ed by -~i the method of this invention are salts formed between `~q alkali metals selected from lithium, sodium, potassium, ~ -~, .,1 rubidlum and cesium and halogens selected from chlorine, i bromine and iodine. Typical examples of such salts are -~ sodium chloride, potassium chloride, sodium bromide and ' ! . :
'`~ `' ~ - 14 -.

~L~S~33 potassium bromide. With certain alkali salts, the halogen cannot be recovered as a gas by electrolysis, but this does not affect the principle of this invention.
Thus, according to this invention, aIkali hydroxides can be obtained as solutions of high concentra-tions such as 2~ to 15~, and the concentration of salts present as impurities can be reduced to not more than 10 mol% based on caustic alkali, for example to less than :-1%.
The following Examples illustrate the present invention without any intention to limit the present -in~ention.
Example 1 A saturated saline water was electrolyzed using a horizontal electrolytic cell made of an acrylic acid resin shown as Figure 2 (effective area of diaphragm lO0 mm x lO0 mm~. The cell was modified to secure a water supply pipe to the cathode compartment, and an Rh-Ti anode and ;' a cathode in the form of an Ni porous plate having a porosity of 71~ were used. A 3M aqueous solution of sodium hydroxide , ~ was continuously fed in the atomized form to the underside `~ of the diaphragm and to the cathode a~ a rate of 25 ml/min.
A part of the caustic withdrawn from the cathode compart-ment wa~ used for analysis. A predetermined amount of . - .
water was continuously supplied to the catholyte reservoir so as to maintain the concentration of the caustic soda withdrawn from the tank at 3 N. The diaphragm used was `~ a cation exchange membrane of a fluorine resin type having ; a water-permeability of substan~ially zero. The : :

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electroly~ing conditions and the results obtained are shown in Table 1 below.
The above procedure was repeated except that instead of the 3N caustic soda, water was fed to the underside of the diaphragm and to the cathode in the atomized form, and instead of the water to be supplied ;
to the reservoir of the catholyte solution in the above procedure, water was intermittently sprayed at a rate of 200 ml./hour.
;; In either case, similar results were obtained.
~ The results shown in r~able 1 were averages of ; values after operating for 2 months.
Table 1 Concentration of salt solution 310 g/Q
fed Electro- pH of the salt solution fed 4 lyzing Concentration of the250 g/Q
con- salt solution discharged ditions Electrolyzing temperature 60C

Amount of pure water fed 200 ml/hour Current density 20 A/dm .... ~ , Goncentration of caustic 120 g/Q
Results soda formed Concentration of sodium elec- chloride in the caustic soda 0.08 g/Q
solution formed -~; ~ Current efficiency based on 93% :
caustic soda 1~ Electric voltage of electro- 3.8 V
_ _ lytic cell Example 2 ~ he procedure of Example 1 was repeated except that an Ni wire gauz.e having a porosity of 64% was used as the cathode. The current efficiency was 92%, and the voltage of the electrolytic cell was ~.1 V.

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Comparative Example 1 The procedure of Example 2 was repeated except that water was neither supplied to the cathode compart-ment nor sprayed. A catholyte solution having an NaOH
concentration of above 40% could be obtained, but the voltage of the cell was as high above 7, and the current efficiency was as low as 60%. The operation for a short period of time could be performed, but because ~aOH of high concentration passed through the cathode and the j 10 diaphragm surface, and the amount of the liquid was small, an electric current had difficult~ of flowing, and the voltage xose, and further the current efficiency was : . ~
poor. Accordingly, this operation is not economical, and is not suitable for use in commercial operation.
~, : .
~ Example 3 ., ~ . .
Electrolysis was performed using a horizontal electrolytic oell made of chlorinated polyvinyl chloride ~ ;~
resin (effective area of diaphragm 500 mm x 500 mm), a ~ .
, porous plate cathode~having a porosity Of 71%, and an Rh-Ti -~

; 20 anode. An alkali :olution was performed in the same wa~ ~

-~I as in Example l using a sulfonic acid-type cation ;
~ 1 - ~ ..
-~ exchange membrane made of styrene-divinylbenzene copolymer with pol~propylene as a backing material and having a 1 :: :.:
water-permeability of substantially zero. The electrolyzing -conditions and the results obtained are shown in Table l ,. .

l - 17 -!

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~L~S'723,3 Table 2 _ Concentration of the salt 310 g/Q
solution fed lyzing pH of the salt solution fed 4.5 con- Concentration of the salt ditions solution discharged250 g/Q
Electrolyzing temperature 80C
Amount of pure water fed 5 Q/hour Current density 30 A/dm .... __ _ _ Concentration of sodium 170 g/Q
hydroxide formed Results Concentration of sodium 0.3 g/Q
of chloride in the resulting elec- sodium hydroxide solution trolysis Current efficiency 89%
based on sodium hydroxide Voltage of the 4.4 V
electrolytic cell ¦
, : .
When pure water was not fed into the cathode compartment in this Example, the concentration of sodium ~ hydroxide formed was 590 g/Q, and the operation could be ;`; performed continuously.
Example 4 A horizontal electrolytic cell made of an acrylic acid resin (the effective area of diaphragm 100 mm x 100 mm) was used which included an Rh-Ti anode and a cathode of i~ : ' ~ 10 an ~i porous plate. A cation exchange membrane of the .. ..
sulfonic acid type with styrene/divinyl benzene copolymer having a water-permeability of less than 0.02 was brought into contact with the cathode with a water maintain-ing material made of a polypropylene non-woven fabric disposed therebetween. The liquid was fed to the diaphragm ~`

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~57Z33 using four siphons made o~ polyvinyl chloride tubes and each having a diameter of 4 mm. The electrolyzing condi- :
tions and the results obtained are shown in Table 3, Table 3 .' ' ' . _ . . . ~
~ Concentration of the salt -. ~ solution fed 310 g/~
. pH of the salt solution fsd 4 -:
o Concentration of the salt . .~ solutio~ discharged 260 g/~ : :
.. ~ Electrolyzing temperature 60C. .
: h Amount of pure water fed 200 m~,/hour Curren-t density 20 A/dm Concentration o~ sodit~m ~; o hydroxide formed 120 g/~ `~
Concentration o~ sodium :.
o chloride in the sodium hydro- 0.3 g/~
xide solution formed .
Current ef~iclency based on o sodium hydroxide 93% .`.
:~ Voltage o~ the electrolytic .. ~ ::
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1, ~ - , ' .~ ~ ComparatLye Exam~le 2 ~; , . . .
~'~ Electrolysis was per~ormed under the same condi- ~:
.. .~ . . :
tions as in Example 4 using a vertical elect~olytic cell :
(the ef~ecti~e area of the diaphragm 200 mm x 50 mm), ~

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The current ef~iciency was 88%9 and the voltage of the electrolytic cell was 409 V.

The procedure of Example 4 was repeated except that ~ tead of the polypropylene non-woven fabric, there was used a porous film obtained by molding a mixture of a polypropylene resin, a surface active agent and magnesium carbonate, and extracting the molded article with 2N ;-hydrochloric acid. The current ef~iciency was 94~'9 and the voltage of the electrolytic cell was 4~3 V.

: ' .
Electrolysis was performed using a horizontal electrolytic cell (the effective area o~ diaphragm 500 mm x 500 mm) made of a thermall~y stable vinyl chloride 1~
resin including an Rh-Ti anode and a cathode made of a 6-mesh wire gauze. The diaphragm consisted o~ a sul~onic acid type cation exchange membrane made of a styrene/
divinylbenzene with polypropylene as a backing material.
The method of supplying water was the same as in Example 4.
The electrolyzing conditions and the results obtained are ~-~
shown in Table 4.

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~ ~,'`', - ` ' ~g~S7Z33 Table 4 ...:

Concentration of the salt solu . ~ tion fed 310 g/~
~ .~ .~ :' ~ pH of the salt solution fed 4.5 - ~ Concentration of the salt solution :~
~ .~ discharged 260 g/~ ` -: . ~ Electrolyzing temperature 80C~
Amoun,t of pure water fed 5 ~/hour . ~ Current density 30 A/~m~ `
,~ ~ : ~ :: ' "' -'' Concentration o~ sodium hydroxi.de :~.
' ! ~ ~ormed ` 180 g/~ ;
j h Concentration of sodium chloride :.
. ~ in the resulting sodium hydroxide :: ::
solution o.3 g/~
o Current efficiency based o:n sodLum hydroxide 88% .

., . . ~ .

Electrolysis was carried out under the conditio~s shown in Table 5 using a horiz~ntal electrolytic cell (the ef~e~tive area ~f diaphragm lOq mm x 100 mm) made o~ a~
ac~yliG a~ld re~in a~d ha~ing: ~he struoture shown i~ Fi~ure ~7~ ~The results are ~how~ in Table 5, ~ :
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Table 5 _~_ ~ ::
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Concentration of the salt solution .^
. ~ed 210 g/~
.~ pH of salt solution fed 4 Concentrat.ion of the sal~ :
solution discharged 250 g/~

. ~ Ll O Electrolyzing temperature 60 C. :~
Current density 30 A/dm2 ~' ~ ~ '~' ~
: . Concentration of sodium hydroxide formed 130 g/~ ..
Concentration of sodium chloride 1 ~ ~ in the resulting sodium hydroxide ~-. ~ ~ solution 0.2 g/~
Current efficienc~ ba~ed on sodium hydroxide 91% . .
Voltage o~ the electrolytic cell 4~5 - 4.7 , . ~i ~ ....... _ ~ ~ . ~, . _ ~ . .

: Electrolysis was per~ormed under the conditions shown in Table 6 in the same way as in Example 1 except :~
~:~ thàt a saturated potassium chloride solution was used -~
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: ~: instead o~ the saturated saline water. ~ ~
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Table 6 ~.

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Concentration of the sal-t ~olution .~ pH o~ the salt solution ~ed 4 Concen~,ration o~ the salt -:
solution discharged 0 -:
~ ~ Electrolyzing temperature 60 C~
.~ ~ t~ Amt~unt of pure water ~ed 200 ml/hour Current density 2~ A/dm2 ::-:'. :.' ,-' :-.- .~" . -Concentration o~ potassium hydroxide ~ormed 154 g/~
~: ~ ~ .~ Concentration of potassium :~ ~ ~ ~ chloride in the resul-ting potassium .-:
: ~ - ~, ~ hydroxide solution 0.1 g/~ ~ :
. ~ ~ ~D Current ef~iciency based on : ~ ~ ~ potassium hydroxide 94 %
Voltage o~ the elec-trolyt:Lc cell 3.7 V .:.
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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for electrolyzing an alkali metal halide solution using a horizontal diaphragm electrolytic cell, wherein a diaphragm having a water-permeability of not more than 0.02 ml/cm2/cmH2O/hr is used, and water or an electrolytic solution is supplied continuously or intermittently to the under-side of the diaphragm during electrolysis.

2. The method of claim 1 wherein said diaphragm is a cation exchange membrane.

3. The method of claim 1 wherein said water or electrolytic solution is supplied when the voltage of the electrolytic cell exceeds a predetermined standard voltage.

4. The method of claim 1 wherein said electrolytic solution is a catholyte solution.

5. A method for electrolyzing an alkali metal halide solution using a horizontal electrolytic cell, wherein a cation exchange membrane having a water-permeability of not more than 0.02 ml/cm2/cmH2O/hr is used as a diaphragm, a wire gauze or porous plate having a porosity of at least 50%
is used as a cathode, and water or an alkali hydroxide solution is supplied to the undersides of the cathode in the form of atomized spray or jet during electrolysis.

5. A method for electrolyzing an alkali metal halide solution using a horizontal electrolytic cell, wherein a cation exchange membrane having a water-permeability of not more than 0.02 ml/cm2/cmH2O/hr is used as a diaphragm, a liquid maintaining material is disposed in contact with the underside of the cation exchange membrane and the cathode surface, and water or an electrolytic solution is supplied to the liquid maintaining material during electrolysis.

7. A horizontal diaphragm electrolytic cell including a diaphragm having a water-permeability of not more than 0.02 ml/cm2/cm?H2O?Hr and means for supplying a liquid to the underside of the diaphragm.

8. The electrolytic cell of claim 7 wherein said means for supplying the liquid is a sprayer, siphon, rotating blade or sprinkler.