JPS63312988A - Production of alkali hydroxide - Google Patents

Abstract

PURPOSE:To produce an aq. alkali hydroxide soln. having a high concn. and an aq. acid soln. with superior current efficiency when an aq. soln. of an alkali metal salt is electrolyzed to produce an aq. alkali hydroxide soln., by using a three-chamber type electrolytic cell provided with a cation exchange membrane having a specified multilayered structure. CONSTITUTION:When an aq. soln. of an alkali metal salt such as Na2SO4 is electrolyzed in a diaphragm system electrolytic cell to produce 35-55wt.% aq. NaOH soln. from the cathode and an aq. H2SO4 soln. from the anode, the aq. soln. of Na2SO4 or the like is fed to the intermediate chamber of the three- chamber type electrolytic cell provided with a cation exchange membrane consisting of two layers on the cathode side and an anion exchange membrane on the anode side. The first layer of the cation exchange membrane is made of a hydrocarbon-based cross-linked polymer having corrosion resistance to >=35wt.% aq. NaOH soln., e.g., a sulfonated styrene-divinylbenzene copolymer or a fluorine-contg. linear polymer having -SO3M or -OM groups (M is an alkali metal). The second layer has 2-7wt.% hydration rate in 45wt.% aq. NaOH soln., >=5mum thickness and -CO2M groups. The cation exchange membrane is stretched in the cell so that the first layer confronts the cathode.

Description

[Detailed Description of the Invention] [Industrial Application Field] Undeveloped IJI relates to a method for producing an aqueous alkali hydroxide solution, and in particular, in the royal ion exchange membrane method, an acid aqueous solution is supplied from the anode and relatively from the cathode. The present invention relates to a method for producing highly concentrated alkali hydroxide.

[Prior art] In the production of alkali hydroxide and chlorine by electrolyzing an aqueous alkali chloride solution, the so-called ion-exchange elimination method alkaline electrolysis uses a fluorine-containing cation exchange membrane as a diaphragm, which produces high purity and high concentration. Alkali hydroxide has become popular internationally in recent years because it can be produced with lower energy consumption than conventional methods.

On the other hand, in the production of alkali hydroxide and acid by electrolyzing an aqueous solution of alkali metal salts such as Glauber's Salt, unlike alkali chloride electrolysis, the ion exchange membrane does not need to have corrosion resistance (particularly chlorine resistance); Royal electrolysis is carried out in which hydrogen-based anion exchange II and cation exchange membranes are placed on the anode and cathode sides, respectively. However, when a conventional sulfonated cation exchange membrane of styrene-divinylbenzene copolymer is used, electrolysis can be performed with high current efficiency only when the alkali hydroxide concentration on the cathode side is only 10 to 15% by weight.

In order to obtain highly concentrated alkali hydroxide with high current efficiency, a fluorine-containing cation exchange membrane that has at least a carboxylic acid group on the cathode side, which is used for alkaline chloride electrolysis, is used on the cathode side of royal electrolysis. Even if the concentration is about 38, high current efficiency can be obtained at low voltage over a long period of time.
It has been found that this is limited to the production of up to 40% by weight of alkali hydroxide. According to the inventor's research,
The eJIV of alkali hydroxide is 9 up to approximately 40% by volume.
Although a high current efficiency of 4 to 98% can be obtained, it has been found that when the concentration is higher than that, the current efficiency suddenly decreases. In addition, when the concentration is high, the membrane resistance suddenly increases, the electrolytic voltage rises, and when operated for a long period of one week to one year, the current efficiency gradually decreases. Ta. When the ion exchange capacity of the cathode surface of a membrane operated for a long period of time with such a high concentration of alkali hydroxide is kept constant at 61, it becomes clear that the ion exchange capacity of the surface decreases due to the decomposition of the carboxylic acid groups. became. Thus, in the case of a cation exchange membrane having a carboxylic acid group on the cathode side of the membrane, it is not preferable to produce alkali hydroxide at a high concentration as described in (a) in a single-day process.

However, with high current efficiency and high concentration of alkali hydroxide,
If it can be produced at a low electrolytic voltage, the energy conventionally required for concentrating alkali hydroxide can be saved or eliminated.

[Problem to be Solved by the Invention 1] The present invention is directed to electrolysis of an aqueous alkali metal salt solution at a higher concentration than the cathode, preferably at a concentration of 42% by weight or more, particularly at a concentration of 4% by weight or more.
In producing alkali hydroxide with a concentration of 5% by weight or more, we use an ion exchange membrane that not only achieves high current efficiency in the initial stage but also maintains high current efficiency even after long-term operation. The purpose is to provide a manufacturing method.

[Means for Solving Problem E] The present invention has been made to solve the above-mentioned problem, and has a thickness of 5JL with alkali resistance.
The first layer cation exchanger having M and/or -OM groups (X is an alkali metal), the water content in the 45 wt % MaOH aqueous solution is 2 to 7 wt %, and the thickness is 5 ml. A cation exchange membrane consisting of at least two layers, the second layer having a -CO2N group (M is an alkali metal), the first layer facing the cathode chamber, and the anode side having: The present invention provides a method for producing alkali hydroxide, which comprises supplying an aqueous alkali metal salt solution to an intermediate chamber of a pressure chamber type electrolytic cell equipped with an anion exchange membrane for electrolysis.

More specifically, the concentration of alkali hydroxide is preferably 35
The present invention relates to a method for producing alkali hydroxide with a concentration of more than 42% by weight, particularly 42% by weight or more.

The cation exchanger having alkali resistance, which is disposed toward the cathode side of the cation exchange membrane used in the present invention, is a cation exchanger having corrosion resistance against alkali hydroxide containing 35% by weight or more, particularly 42% by weight or more. Any exchanger can be used, preferably sulfonated styrene-divinylbenzene copolymer, hydroxystyrene-divinylbenzene copolymer 1
Hydrocarbon-based crosslinked bodies such as -503M group and -CRfRf
Examples include fluorine-containing linear polymers having an ON group.

The thickness of the first layer having the alkali-resistant cation exchange resin layer of the cation exchange membrane used in the present invention is 5 μm or more,
Preferably it is 10-200 gta. If it is thinner than 5gm, sufficient current efficiency cannot be obtained when producing alkali hydroxide of 45% by weight or more, and deterioration of carboxylic acid groups due to high concentration of alkali cannot be prevented.2
Exceeding the 00p layer is not preferable because the membrane resistance increases and the electrolytic voltage increases.

The first layer made of an alkali-resistant cation exchange resin can be used as an ion exchange resin alone, but it is important to improve the peeling resistance between the first layer and the second layer, which will be described later, and to improve the mechanical strength of the first layer.
For example, various additives can be added to the first ion exchange resin layer for the purpose of improving brittleness.

As such additives, alkali-resistant polymers having substantially no ion exchange groups, webs, fibrils, particles, etc. of alkali-resistant inorganic compounds can be used. The fiber diameter or small fiber diameter and particle diameter constituting the web are preferably equal to or less than r, preferably one-third or less of the thickness of the first layer. Examples of the alkali-resistant inorganic compounds added to the first layer include hydroxides, oxides, nitrides, and carbides of titanium, zirconium, niobium, tantalum, indium, tin, manganese, nickel, and cobalt, nitrides of silicon,
selected from carbides and mixtures thereof. In addition, examples of alkali-resistant polymers without ion exchange groups include polyolefins such as polyethylene and bopropylene, polyvinyl fluoride, polytrifluoroethylene, polytetrafluoroethylene, polyvinylidene fluoride, and tetrafluoroethylene/hexafluoride. Examples include fluorine-containing carbon polymers such as (propylene) I-polymer, tetrafluoroethylene/perfluoropropyl vinyl ether copolymer, and tetrafluoroethylene/perfluoromethyl vinyl ether copolymer. The alkali-resistant polymer or alkali-resistant inorganic substance preferably has a volume ratio (volume of alkali-resistant substance y!/(volume of alkali-resistant substance + volume of cation exchange resin)) of 75% in the first layer. Below, more preferably 20 to 60%,
Preferably, it is appropriate to contain it uniformly. In this case, the average particle diameter of the particles or the average wire diameter of the fibrils is not more than half the thickness of the first layer, and not more than 20 mm,
In particular, it is preferable that it is 10 or less. If it deviates from this range, the reason is not clear, but it will cause a decrease in current efficiency or a decrease in durability. It is also possible to add soluble additives to the first layer. Soluble additives, such as S
i02, AI, Al(OH)3, particles and other alkali-soluble inorganic substances, hydrocarbon-based or fluorine-containing low-molecular-weight organic compounds, polymers, surfactants, etc. (hereinafter referred to as pore-forming agents). Preferably 5 to 85% by volume, especially 20 to 80% by volume of the cation exchanger or its precursor forming one layer.
An example of this method is to prepare a sample containing % by volume and immerse it in a solution containing an alkali and/or water to elute the above-mentioned pore-forming agent. The porous layer thus obtained preferably has small pore penetration, at least in a state where it is not wet with a liquid such as water or an aqueous alkali solution after film formation.
In the present invention, the permeability of the pores is determined by the Gurley number, that is, the pressure difference is 0 for the porous body in a dry state after film formation.
．． 1001 air under 0132kg/c proverb 2 is 6.4
It is evaluated by the number of seconds it takes to pass through an area of 5 cm2, and its f〆1
It is preferable that the permeability is 1000 or more. If the permeability is larger than this, alkali hydroxide at a higher concentration than the cathode chamber will penetrate to the surface of the carboxylic acid layer, which is undesirable. Under actual electrolytic conditions, , in some cases, the porous layer is.

It does not matter if fine pores are formed due to the influence of ion flow, etc.

According to the research of the present inventors, even if the first layer is not a porous cation exchanger, 42% by weight or more, especially 4%
Circulation is to achieve high current efficiency with a NaOH aqueous solution of 5% by weight or more, but by making the first layer porous,
Furthermore, it has become possible to stably obtain high current efficiency over a long period of time. Although the mechanism is not necessarily clear, it is thought that the provision of pores in the first layer relieves the stress that causes peeling and cracking of the first layer.

Next, as the second layer of the cation exchange membrane used in the present invention, a cation exchanger having -GO2M (M is an alkali metal) with a thickness of about 5 L is used.

-GO? As a cation exchanger containing '14 groups,
Crosslinked polymers such as copolymers of acrylic acid, methacrylic acid and divinylben; copolymers of acrylic acid, methacrylic acid and ethylene; copolymers of perfluorovinyl ether carboxylic acid ester and tetrafluoroethylene; A linear polymer is exemplified. Among them, a linear polymer containing a COyH group copolymerized with ethylene or tetrafluoroethylene is preferable because a high current efficiency can be obtained with a high concentration of alkali hydroxide, and a linear polymer containing a -002M group is preferable. However, the reason why it exhibits high current efficiency in high concentration alkali hydroxide is not clear, but because the linear polymer shrinks in high concentration alkali hydroxide and the water content decreases, ions in the membrane This is interpreted to be because the pores through which the particles pass through become smaller.

Thus, the second layer of the cation exchange membrane contains 45% by weight M
It is preferable that the water content in the aOH aqueous solution is in the range of 2 to 7% by weight, preferably 2.5 to 5% by weight; outside this range, the water content will be higher than above.I! : Flow efficiency cannot be obtained. Here, in the present invention, the water content in 45 wt% MaOH means that the cation exchanger 11 is immersed in a 45 wt% MaOH aqueous solution at the electrolysis operating temperature for 18 hours, and then cooled to 25°C. After that, the weight after wiping off the alkaline aqueous solution on the membrane surface is
The weight when the membrane was soaked in ion-exchanged water at 90°C for 16 hours and vacuum-dried at 130°C for 16 hours was b.
When g, moisture content (%) = (a - b) / bXloo!
L means something that can be gained.

As a polymer containing one GO2M group giving such a water content, the ion exchange capacity is 0.6 to 1.8 meq/
g dry resin, preferably 0.85-1.8 meq/
(meth)acrylic acid ethylene copolymer of dry resin,
(meth)acrylic acid-propylene copolymer or CO2
Thickness of Mal-containing perfluorocarbon nail combination: 5 to 30
0 gta is used.

The cation-exchangeable fluorine-containing polymer used in the first and second layers of the cation-exchange membrane used in the present invention is composed of a copolymer of at least two types of monomers, preferably the following ( It consists of a copolymer having the polymerized units of (a) and (b).

(() −(CF2JXX')−, (0) −(C
F2-CX) -+4 Cocote, x, x' are -F, -CI, -H or -C
F3TE, A is -9O314, -CRfRf'ON or -co2x (represents hydrogen, alkali metal, Rf, Rf
' represents a perfluoroalkyl group having 1 to 10 carbon atoms) or a group that can be converted into these groups by hydrolysis etc., and Y is selected from the following, where z and z' are -F or 1161-10 perfluoroalkyl group,!
+y, 2 represents an integer from 1 to 10.

-(CF2)! −, −0−(CFz)x−, −(0−C
F2-OF)x-.

-(0-OF-Oh)y-0-(CF)z-ZZ゛Furthermore, in addition to the polymerized units (a) and (b), the following polymerized units may be included.

lCF? (:F)--(CF2-CF)-0-Z
(0-CF2-CF)

The l-blended fluoropolymer is preferably a hydrolyzed perfluorocarbon polymer, and preferred examples thereof include CF2=CF2 and CF2-
CFOFG20F (CFz)OGF20F2S02
Copolymer with F, CF2 = CF2 and CFz-CFO
(CFz) Copolymer with 2-5SO2F, CFz -C
F2 and CF2F CFOFC2CF2C (CF3)
Copolymer with 20H, CF2-CF2 and 0F2=CF
OCCF2 )2-5GO7CH3 copolymers, and further copolymers with CF2-CF2 and CF2-CFOCF2CF(C
F+)0(CFz)? A copolymer with -GO2CH3 is exemplified.

The first layer and the second layer can be laminated by various methods. For example, separate films consisting of the first layer and the second layer or their derivatives are laminated by a similar press. method, a method of laminating the first layer and the second layer by coextrusion while recirculating (U.S. Pat. No. 4,437,952), a method of laminating the first layer and the second layer by coextrusion in advance; A method may be employed in which a solution or monomer containing a cation exchanger or its precursor constituting the other layer is applied, and then dried or polymerized to form a layer.

In the cation exchange membrane used in the present invention, in addition to the first layer and the second layer, a third layer can be further laminated if necessary. As such a preferred example, the second layer has a thickness of 30 to 350 pm on the anode side.
A layer made of a hydrocarbon polymer or a fluorine-containing polymer having an ion exchange group of 03M group or -GO2M group (M is an alkali metal) and has a lower specific resistance than the second layer is preferable.

Further, on the anode side of the second layer or the third layer, a thickness of 10 to 4
A fourth layer of a porous fluorine-containing polymer having a porosity of 50 uLra from 30 to 95% and having one surface and the inside made hydrophilic can be laminated. By stacking such a third layer and a fourth layer, the mechanical strength of the film can be stabilized to a greater degree than that of a film consisting only of the first layer and the second layer.

Furthermore, in addition to -■-, the cation exchanger 11 used in the present invention has the following properties: A bonding layer can be provided if necessary.

Furthermore, if necessary, a reinforcing material such as a web made of a heat-resistant and alkali-resistant polymer such as polypropylene or polytetrafluoroethylene may be embedded in the layer preferably on the anode side of the cation exchange membrane of the present invention. can.

The J2 cation exchange membrane can be used as is, but
Preferably, at least one surface of the cation exchange membrane, particularly preferably at least the cathode side surface of the ion exchange membrane, is treated to release hydrogen gas, thereby improving the long-term stability of current efficiency. The voltage under electrolysis can be further reduced.

As a method of treating the surface of the ion exchange membrane for gas release, there is a method of forming fine irregularities on the membrane surface (as described by Tokko Sho H.
-28495), a method of supplying a liquid containing iron, zirconia, etc. to an electrolytic cell and depositing hydrophilic inorganic particles on the membrane surface (Japanese Patent Application Laid-Open No. 152980/1983), A method of providing a porous layer containing particles that do not have any
No. 185), etc. are exemplified.

The cation exchange membrane thus formed forms a royal electrolytic cell by arranging the first layer facing the cathode and arranging the anion exchange membrane on the anode side.

The anion exchange membrane used on the anode side is not particularly limited, but preferably has corrosion resistance against the acid aqueous solution generated at the anode and contains hydrogen ions in order to increase the efficiency of acid production. A poorly permeable anion exchange membrane is used.

Such anion exchange membranes include vinylpyridine-divinylbenzene copolymer membranes, vinylimidazole-divinylbenzene copolymer membranes, polyamine-epoxy condensation membranes,
Cross-linked weakly basic anion exchange membrane of silane containing 7 amino groups and silane condensation membrane containing epoxy group 1, fluorine-based anion exchange membrane -(CF2-CF2)x-(CF2-0F)V
Examples include -(OC12CF)m-0(CF2)n-AF3 (A is a quaternary ammonium group and/or a functional group containing a primary to tertiary amino group).

In this way, an aqueous alkali metal salt solution is supplied to the intermediate chamber divided by the anion exchange membrane and the cation exchange membrane, water or diluted alkali hydroxide solution is supplied to the cathode chamber divided by the cation exchange membrane, and anion By supplying water or a diluted aqueous solution to an anode chamber separated by an exchange membrane and electrolyzing it, highly concentrated alkali hydroxide can be produced from the cathode and an acid aqueous solution can be produced from the anode chamber.

As the anode and cathode of the electrolytic cell used in the present invention, conventionally known electrode materials can be used.
In addition, an electrode material having excellent corrosion resistance is appropriately selected.

[Example] Example 1 Ion exchange capacity 1.33 milliequivalents/g dry resin CF
2 =lCF? /CF2-CFO(C:Fz)3-C
OOCH3 copolymer (copolymer A) with a thickness of 200
Ion exchange capacity 1.1 meq/g dry resin CF2 = CF2 / 7 CFs on gm film CFOC
FzCF(Oh)O(CF2)2sO3H (copolymer B
) and an ethanol mixture containing Z'02 particles with an average particle size of 5 at a volume ratio of 372, and by drying,
Copolymer B with a thickness of 501L11 and 202 parts of Zr0 were formed and heat-pressed at 120°C, followed by hydrolysis with a caustic soda solution to obtain a cation exchange membrane.

On the other hand, the anion exchange membrane contains 20 parts of divinibenzene, 4-
A polypropylene support was impregnated with a 7mer solution consisting of 38 parts of vinylpyridine and 42 parts of styrene and polymerized to obtain a weakly basic anion exchange membrane having a thickness of 150 tL.

On the layer side of the thus obtained cation exchange membrane made of copolymer B and ZrO2 with a thickness of 50IL11, 5LIS30 was added.
Panchitometal manufactured by No. 4 in 52% by weight of -Y soda,
A low hydrogen overvoltage cathode obtained by etching at 150°C for 52 hours and an anion exchange membrane were placed on the anode side of a punched titanium metal coated with noble metal oxidation.
Thickness divided by cation exchange membrane and anion exchange membrane io
While supplying a 3.5N Na2SOs aqueous solution to the intermediate chamber of the am, the NaOH concentration in the cathode chamber was maintained at 45% by volume, and the sulfuric acid concentration in the anode chamber was maintained at 4N, at 90°C and at a current density of 30A/
When electrolyzed at dm2, the sliding voltage was 4.5V, and I
The current efficiency for JY soda production was 95%, and the current efficiency for sulfuric acid production was 85%.

Comparative Example 1 In Example 1, copolymer B was added to one side of the cation exchange membrane.
Electrolysis was carried out in the same manner except that a mixed layer of Zr02 and Zr02 was not formed. As a result, at a sliding voltage of 4.8 V, the current efficiency for producing 7% soda was 88% and the current efficiency for producing sulfuric acid was 85%.

Example 2 40 pot thickness of copolymer A (carboxyl group 1.33 meq/g) and copolymer B (sulfonic acid group 11 meq/g)
) of 180! Next, on the copolymer A side, a polytetrafluoroethylene porous body with a pore diameter of 065 and a film thickness of 30 μL and a porosity of 80% was laminated, and an ethanol solution of copolymer B was added to the porous body. A layer of copolymer B was formed inside the porous body by repeatedly spraying and then hydrolyzed with a caustic potash solution.

A royal electrolytic cell was assembled in the same manner as in Example 1, with the porous layer side filled with copolymer B of the cation exchange membrane thus obtained facing the cathode. While supplying 4N sodium nitrate to the intermediate chamber, maintaining the NaOH concentration in the cathode chamber at 45% by weight and the nitric acid concentration in the anode chamber at 8N/1, the temperature was 50°C and the current density was 10.
When electrolyzed at A/da2, the current efficiency for producing caustic soda was 95% and the current efficiency for producing nitric acid was 88% at a sliding voltage of 4.2V.

Comparative Example 2 Electrolysis was carried out in the same manner as in Example 2, except that the Copolymer B 180 membrane used in Example 2 was used alone. the result,
/・Flow rate of Y-based soda production was 65%.

Example 3 Ion exchange capacity 1.4 milliequivalents/g dry resin was deposited on a 100 l thick film of ethylene-acrylic copolymer with a pore size of 0. A laminated polypropylene porous body with a thickness of 80 lp and a porosity of 70% was then impregnated and polymerized with a 7-mer solution containing styrene BO%, divinylbenzene 5%, and dioctyl phthalate 35%, followed by sulfonation treatment. did.

Electrolysis was carried out in the same manner as in Example 2, except that the porous body side impregnated with the sulfonated styrene-divinylbenzene polymer of the cation exchange membrane thus obtained was placed toward the cathode side, and a 45% MaOH solution was introduced from the cathode chamber. was generated with a current efficiency of 94%.

Comparative Example 3 Electrolysis was carried out in exactly the same manner as in Example 3 except that the porous material was not laminated and the styrene-divinylbenzene impregnation polymerization was not performed.
It was produced at 0%.

Comparative Example 4 Electrolysis was carried out in the same manner as in Example 3, except that a sulfonated membrane (thickness 150 JLm) of co-ffi combination of styrene and divinylhensen was used as the cation exchange IQ.
A 45% MaOH solution was produced from the cathode chamber at a current efficiency of 40%.

Procedure Uho Seisho (Method) ■, Indication of the case Patent Application No. 149151 of 1988 2, Name of the invention Process for producing alkali hydroxide 3, Person making the amendment Relationship with the case Patent applicant address Chiyoda, Tokyo 2-1-2 Marunouchi Ward Name
(004) Asahi Glass Co., Ltd. 6. Number of inventions increased by amendment None 7. Specification subject to amendment 8. Contents of amendment As per the engraving and attached sheet of the specification originally attached to the application (no change in content)

Claims (3)

[Claims] (1) -SO_ with a thickness of 5 μm or more with alkali resistance
a first layer cation exchanger having 3M (M represents an alkali metal) and/or -OM group and 45% by weight MaO
The water content in the H aqueous solution is 2 to 7% by weight, and the thickness is 5μ
A cation exchange membrane consisting of at least two layers including a second layer having m or more -CO_2M groups (M is an alkali metal) is arranged with the first layer facing the cathode chamber, and the anode side A method for producing alkali hydroxide, which comprises supplying an aqueous alkali metal salt solution to an intermediate chamber of a three-chamber electrolytic cell equipped with an anion exchange membrane for electrolysis. (2) The second layer of the cation exchange membrane has a thickness of 5 to 300μ
2. The method according to claim 1, wherein the layer is a linear polymer containing -CO_2M groups and has an ion exchange capacity of 0 to 1.8 meq/g dry resin. (3) The alkali metal salt solution is supplied to an intermediate chamber divided by an anion exchange membrane and a cation exchange membrane, and the acid aqueous solution is divided by a cation exchange membrane from the anode chamber divided by an anion exchange membrane. The method according to claims (1) and (2), for producing a 35 to 55% by weight alkali hydroxide solution from the cathode chamber.