JPS6343473B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of electrolyzing, particularly a method of electrolyzing an aqueous liquid such as an aqueous alkali chloride solution, water, or hydrochloric acid while pressurizing it. In the following, a detailed explanation will be given particularly regarding the case of alkali chloride electrolysis, but it goes without saying that the present invention is not limited to only alkali chloride electrolysis. In recent years, as a method for obtaining alkali hydroxide by electrolyzing an aqueous alkali chloride solution, the diaphragm method has become mainstream in place of the mercury method from the viewpoint of pollution prevention. As for the diaphragm method, instead of using asbestos as a diaphragm, several methods have been proposed in which an ion exchange membrane is used for the purpose of obtaining alkali hydroxide with higher purity and higher concentration. On the other hand, energy conservation has been progressing worldwide in recent years, and from this point of view, in this type of technology, it is desired to reduce the electrolysis voltage as much as possible. Various methods have been proposed to reduce the electrolytic voltage, such as considering the material, composition, and shape of the anode and cathode, or specifying the composition of the ion exchange membrane and the type of ion exchange group used. . Although all of these methods have certain effects, most of them have an upper limit where the concentration of alkali hydroxide obtained is not very high, and if this is exceeded, the electrolysis voltage will suddenly increase and the current efficiency will increase. However, they have not always been industrially fully satisfactory, such as causing a decrease in electrolytic voltage, or poor durability and durability of the electrolytic voltage drop phenomenon. Recently, an alkali chloride aqueous solution is electrolyzed using an electrolytic cell in which an anode and a cathode made of a gas- and liquid-permeable porous layer are closely attached to the surface of a fluorine-containing cation exchange membrane to obtain alkali hydroxide and chlorine. A method is proposed. (Refer to Japanese Patent Application Laid-open No. 112398/1983)
This method enables electrolysis at a lower voltage than conventional methods because it can reduce as much as possible the electrical resistance caused by the electrolyte and the bubbles based on generated hydrogen and chlorine gas, which were considered to be unavoidable in this type of technology. This is an excellent method for doing so. In this method, the anode and cathode are bonded to and embedded in the surface of the ion exchange membrane, and the gas generated by electrolysis at the contact interface between the membrane and the electrode easily leaves the electrode, and the electrolyte is It is made gas and liquid permeable so that it can penetrate. Such porous electrodes usually consist of a porous body formed into a thin layer by uniformly mixing active particles as anodes or cathodes with a substance that binds them, preferably graphite or other conductive material. ing. However, according to the inventor's study, when using an electrolytic cell in which such an electrode is directly bonded to an ion exchange membrane, for example, the anode in the electrolytic cell comes into contact with hydroxide ions that diffuse back from the cathode chamber. In addition to conventional chlorine resistance, alkali resistance is required, and special and expensive materials must be selected. In addition, the lifespans of electrodes and ion exchange membranes are usually very different, so if they are combined, both will have to be discarded when one of them reaches the end of its lifespan. In this case, the economic loss is large. The present inventor continued research on an electrolysis method that does not have these disadvantages and has a cell voltage as low as possible, and found that the surface of the cation exchange membrane has gas and liquid permeability that does not have electrode activity. When an aqueous alkali chloride solution is electrolyzed in an electrolytic cell in which a porous layer is formed and an anode or a cathode is placed through the porous layer,
It has been unexpectedly found that alkali hydroxide and chlorine can be obtained at low voltages and the above objects can be substantially solved. Although the above findings provide an innovative means for lowering the electrolysis voltage, the present inventors further investigated methods for electrolysis at lower voltages, and as a result, they discovered the present invention. It is ivy. Thus, the present invention provides an anolyte and an electrolytic cell comprising a cation exchange membrane having a gas- and liquid-permeable porous layer with no electrode activity disposed on at least one surface between the anode and the cathode. The gist of this method is to electrolyze the catholyte while pressurizing it. Although it is not yet fully understood why the method of the present invention enables low-voltage electrolysis, it is important to note that the porous layer, which is permeable to gases and liquids and has no electrode activity, is provided on the surface of the cation exchange membrane. However, the present inventors speculate that this is due to favorable changes in the electrochemical properties of the cation exchange membrane surface under pressure. Furthermore, the known effects of electrolysis under high pressure employed in the method of the present invention, such as the achievement of even lower electrolysis voltages due to high temperature electrolysis, and the thermoeconomic advantages due to heat recovery from high temperature electrolysis products. This is also a significant secondary effect of the method of the present invention. The cation exchange membrane used in the present invention is mechanically reinforced with a porous layer that is permeable to gas and liquid and has no electrode activity on its surface, so it can withstand higher pressures than ordinary cation exchange membranes. It is something. However, considering the durability of the cation exchange membrane, the degree of pressurization is preferably kept to 15 kg/cm ² or less. In the method of the present invention, the pressures in the anode and cathode chambers do not necessarily need to be the same and can be changed arbitrarily; however, for the reasons mentioned above, the pressure difference between them is 5
It is best to keep it below Kg/ ^cm2 . To explain the present invention in more detail below, in the present invention, the electrode disposed through the gas- and liquid-permeable porous layer is made of expanded metal such as titanium or tantalum, ruthenium, iridium, etc. in the case of an anode. , coated with platinum group metals such as palladium, platinum, their alloys, and their oxides, or porous plates, mesh bodies, etc. made of platinum group metals such as platinum, iridium, rhodium, their alloys, and their oxides. A known anode may be used as appropriate. Among these anodes, when using an anode coated with expanded metal such as titanium with platinum group metals, their alloys, or oxides of these metals or alloys, electrolysis can be performed at particularly low voltages. Therefore, it is preferable. In the case of a cathode, for example, a substrate such as iron coated with platinum group metals such as platinum, palladium, and rhodium or alloys thereof, mild steel, nickel, stainless steel, etc. Used in the form of expanded metal, etc. Among these cathodes, it is preferable to use a cathode containing a platinum group metal, an alloy thereof, or nickel as an active ingredient, since electrolysis can be expected particularly at low voltage. On the other hand, the gas- and liquid-permeable, corrosion-resistant porous layer used in the present invention is inactive as an anode or a cathode, respectively. That is, it is made of a material, for example, a non-conductive material, which has a greater chlorine overvoltage or hydrogen overvoltage than the electrodes disposed through the porous layer. Examples of the material include titanium,
Zirconium, niobium, tantalum, vanadium,
Manganese, molybdenum, tin, antimony, tungsten, bismuth, indium, cobalt, nickel, beryllium, aluminum, chromium,
Iron, gallium, germanium, selenium, yttrium, silver, lanthanum, cerium, hafnium,
Oxides and nitrides of lead, thorium, rare earth elements, etc.
Carbides may be used alone or in mixtures, and on the anode side, oxides, nitrides, and carbides such as titanium, zirconium, niobium, tantalum, vanadium, manganese, molybdenum, tin, antimony, tungsten, and bismuth may be used alone or in combination. Mixtures and the like are preferred. On the cathode side, titanium, zirconium, niobium,
Oxides, nitrides, and carbides of tantalum, indium, tin, manganese, cobalt, nickel, etc. alone or in mixtures are preferred. When forming the porous layer of the present invention from these materials, the above-mentioned materials are used in powder or particulate form, preferably combined with a suspension of a fluorine-containing polymer such as polytetrafluoroethylene. . At this time, if necessary, a surfactant is used to uniformly mix the two to form a porous layer. These mixtures are suitably formed into a layer and then bonded and preferably embedded by applying pressure and heat to the surface of the ion exchange membrane. In addition, the physical properties of these porous layers are almost the same on both the cathode and anode sides, with an average pore diameter of 0.01~
2000μ, porosity 10-99%, air permeability coefficient 1×10 ^-5
~10 mol/cm ² ·min·cmHg is suitable. If any of these physical properties deviate from the above range, the desired low electrolytic voltage cannot be expected, or
Both are unfavorable because there is a risk that the electrolytic voltage drop phenomenon may become unstable. Among the above physical properties, the average pore diameter is 0.1 to 1000μ, the porosity is 20 to 98%, and the air permeability coefficient is 1×10 ^-4 to 1 mol/cm ²・min・cmHg.
It is preferable to employ this method because stable electrolytic operation can be expected especially at low voltage. In addition, the thickness of such a porous layer is strictly determined by the material used and its physical properties, but generally
It is appropriate to use 0.1 to 500μ, preferably 1 to 300μ. If the thickness deviates from the above range, the electrical resistance may increase, gas may be difficult to escape, or
This is not preferable because it makes it difficult to move the electrolyte. In the present invention, the anode placed through the porous layer is provided in contact with the surface of the porous layer. In this way, it is provided through a porous layer, and the electrode may be either the anode or the cathode, but
When provided on both the anode side and the cathode side of the ion exchange membrane, it is particularly preferable for lowering the electrolytic cell voltage. In addition, when either the anode or the cathode is provided on the ion exchange membrane via the porous layer of the present invention, the counter electrode should have the same composition and shape as in the case of producing ordinary alkali chloride. Adopted. In fact, as a means of providing an electrode through the porous layer, for example, the powder forming the porous layer is applied to the ion exchange membrane by screen printing or the like, and then the ion exchange membrane is bonded with heat and pressure. A method of forming a porous layer on the surface of the porous layer and pressing an electrode against the surface of the porous layer is used. The ion exchange membrane used in the present invention is made of a polymer containing a cation exchange group such as a carboxyl group, a sulfonic acid group, a phosphoric acid group, or a phenolic hydroxyl group, and such a polymer includes a fluorine-containing polymer. It is particularly preferable to adopt Examples of fluorine-containing polymers containing ion exchange groups include vinyl monomers such as tetrafluoroethylene and chlorotrifluoroethylene, and perfluorinated polymers having reactive groups that can be converted into ion exchange groups such as sulfonic acid, carboxylic acid, and phosphoric acid groups. A copolymer of a vinyl monomer with a perfluorinated vinyl monomer having an ion exchange group such as a sulfonic acid, carboxylic acid, or phosphoric acid group is preferably used. Further, a membrane polymer of trifluorostyrene having an ion exchange group such as a sulfonic acid group introduced therein, or a polymer having a styrene dibylbenzene introduced with a sulfonic acid group can also be used. Among these monomers, it is particularly preferable to use monomers that can form the following polymerized units (a) and (b), since highly pure caustic alkali can be obtained with relatively high current efficiency. . (a) (-CF ₂ -CXX ¹ )-, (b)

[Formula] Here, X is fluorine, chlorine, hydrogen or -CF ₃ , X' is X or CE ₃ (CF ₂ ) _n , and m is 1 to 5
, and Y is selected from the following: ―P―A,―O―(CF ₂ )― _n (―P, Q, R)―A where P is―(CF ₂ )― _a (―CXX ¹ )― _b (―CF ₂ )― _c
, Q is (-CF ₂ -O-CXX ¹ )- _d , and R is (-
CXX ¹ ―O―CF ₂ )― _e , and (P, Q, R) are P,
This indicates that at least one of Q and R is arranged in an arbitrary order. X, X ¹ are the same as above, and n
=0-1, a, b, c, d, e are 0-6.
A is -COOH, or -CN, -COF, -COOR,
Represents a functional group that can be converted to -COOH by hydrolysis or neutralization, such as -COOM, -CONR ₂ R ₃ . R ₁ is an alkyl group having 1 to 10 carbon atoms, M is an alkali metal or quaternary ammonium group, R ₂ ,
R ₃ represents hydrogen or an alkyl group having 1 to 10 carbon atoms. Preferred representative examples of the above Y include the following, in which A has a structure in which A is bonded to carbon containing fluorine. (-CF ₂ )- _x A, -O(-CF ₂ )- _x A,

【formula】

【formula】

x, y, z are all 1 to 10, and z, R _f are -
It is a group selected from F or a perfluoroalkyl group having 1 to 10 carbon atoms, and A is the same as above. 1 g of dry resin composed of these copolymers
When using a fluorine-containing cation exchange membrane with a carboxylic acid group concentration in the membrane of 0.5 to 2.0 milliequivalents,
For example, even if the concentration of caustic soda is 40% or more,
Its current efficiency reaches over 90%. The concentration of carboxylic acid groups in the film per gram of the above dry resin is 1.12.
When the amount is 1.7 milliequivalents, it is particularly preferable because caustic soda having a high concentration as described above can be obtained stably over a long period of time with high current efficiency. In order to achieve such ion exchange capacity, the above (a) and
In the case of a copolymer consisting of the polymerized units (b), it is preferred that the polymerized units (b) account for 1 to 40 mol%, particularly 3 to 25 mol%. Preferred ion exchange membranes used in the present invention are:
From a non-crosslinkable copolymer obtained by copolymerizing the above-mentioned fluorinated olefin monomer with a polymerizable monomer having a carboxylic acid group or a functional group convertible to a carboxylic acid group. The molecular weight thereof is preferably about 100,000 to 2,000,000, particularly 150,000 to 1,000,000. Further, in order to produce such a copolymer, one or more of the above-mentioned monomers may be used, and the resulting film may be modified by further copolymerizing a third monomer. For example, CF ₂ =
By using CFOR _f (R _f is a perfluoroalkyl group having 1 to 10 carbon atoms), flexibility can be imparted to the obtained film, or CF ₂ =CF−CF=CF ₂ , CF ₂
By using a divinyl monomer such as =CFO(CF ₂ ) _l~3 CF=CF ₂ in combination, the resulting copolymer can be crosslinked and mechanical strength can be imparted to the membrane. The copolymerization of the fluorinated olefin monomer and a polymerizable monomer having a carboxylic acid group or a functional group convertible to the carboxylic acid group, as well as a third monomer, can be carried out by any known method. . That is, polymerization can be carried out by catalytic polymerization, thermal polymerization, radiation polymerization, etc., using a solvent such as a halogenated hydrocarbon, if necessary.
Furthermore, there is no particular restriction on the method for forming an ion exchange membrane from the obtained copolymer, and suitable known methods such as press molding, roll molding, extrusion molding, solution casting, dispersion molding, powder molding, etc. can be adopted. The film thus obtained has a thickness of 20 to 500μ,
Preferably, it is appropriate to make it 50 to 400μ. In addition, if the copolymer is not a carboxylic acid group itself but a functional group that can be converted into a carboxylic acid group before or after the copolymer film formation process, preferably after film formation, by appropriate treatment accordingly. , these functional groups are converted to carboxylic acid groups. For example, --CN, --
COF, ―COOR ₁ , ―COOM, ―CONR ₂ R ₃ (M,
R ₁ to _{R 3} are the same as above), it is converted into a carboxylic acid group by hydrolysis or neutralization with an acid or alkali alcohol solution, and when the functional group is a double bond, -COF It is converted into a carboxylic acid group by reacting with ₂ . Furthermore, the cation exchange membrane used in the present invention may optionally contain an olefin polymer such as polyethylene or polypropylene, preferably polytetrafluoroethylene, or a copolymer of ethylene and tetrafluoroethylene during membrane formation. It can also be molded by mixing fluoropolymer.
Alternatively, it is also possible to reinforce the membrane by using fabrics such as cloth, net, nonwoven fabric, or porous film made of these polymers as a support, or by using metal wires, nets, or porous materials as a support. be. The alkali chloride used for electrolysis is generally sodium chloride, but other alkali metal chlorides such as potassium chloride and lithium chloride are also available. Next, the present invention will be explained by examples. Example 1 73mg of tin oxide powder with a particle size of 44μ or less was suspended in 50cc of water, and a polytetrafluoroethylene (PTFE) suspension (DuPont, trade name Teflon) was added to this.
30J) so that PTFE becomes 7.3 mg, and after adding one drop of nonionic surfactant (Rohm & Haas, trade name: Triton X-100),
After stirring using an ultrasonic stirrer under ice cooling, the porous
A porous tin oxide thin layer was obtained by suction filtration on a PTFE membrane. The thin layer had a thickness of 30 μ, a porosity of 73%, an air permeability coefficient of 3.8×10 ^-3 mol/cm ² ·min·cmHg, and contained 5 mg/cm ² of tin oxide. On the other hand, using the same method as above, nickel oxide of 44μ or less was contained at 7mg/ ^cm2 , thickness was 35μ, and porosity was 73.
%, air permeability coefficient 3.5×10 ^-3 mol/cm ²・min・cm
A thin layer of Hg was obtained. Next, each thin layer is
An ion exchange membrane made of a copolymer of tetrafluoroethylene and CF ₂ = CFO (CF ₂ ) ₃ COOCH ₃ with 1.45 meq/g resin and a thickness of 250 μ has a porous structure on both sides.
The PTFE membrane is stacked on the outside of the ion exchange membrane, and the porous thin layer is attached to the ion exchange membrane by applying pressure at a temperature of 160℃ and a pressure of 60Kg/ ^cm2 .
Thereafter, the porous PTFE membrane was removed to obtain an ion exchange membrane with porous layers of tin oxide and nickel oxide adhered to each surface. The ion exchange membrane was immersed in a 25% by weight aqueous sodium hydroxide solution at 90° C. for 16 hours to hydrolyze the ion exchange membrane. After that, 40 meshes of platinum wire mesh was brought into pressure contact with the tin oxide side and 20 meshes of nickel wire mesh was brought into contact with the nickel oxide side, and the platinum wire mesh side was used as an anode and the nickel wire mesh side was used as a cathode. An electrolytic cell was assembled using the exchange membrane structure. The anode chamber of this electrolytic cell was pressurized to 2Kg/ ^cm2.
A 4N saline solution and water pressurized to 2 kg/cm ² were supplied to the cathode chamber, and electrolysis was carried out at 94° C. and with the current density varied as shown below. At this time, the concentration of caustic soda in the catholyte was maintained at 35% by weight. The cell voltage at this time is shown below along with the current density. Current density (A/dm ² ) Cell voltage (V) 10 2.65 20 2.82 30 3.00 40 3.14 Comparative example Same as Example 1 except that both the anolyte and catholyte were not pressurized and electrolysis was performed under atmospheric pressure. I did electrolysis. The results are shown below. Current density (A/dm ² ) Cell voltage (V) 10 2.74 20 2.96 30 3.18 40 3.35 Example 2 Electrolysis was carried out in the same manner as in Example 1, except that both the anolyte and catholyte were pressurized to 5 kg/cm ² Ivy. The results are shown below. Current density (A/dm ² ) Cell voltage (V) 10 2.63 20 2.80 30 2.97 40 3.10 Example 3 Same as Example 1 except that the anolyte was pressurized to 5Kg/cm ² and the catholyte was pressurized to 3Kg/cm ² Electrolysis was performed using The results are shown below. Current density (A/dm ² ) Cell voltage (V) 10 2.64 20 2.82 30 2.99 40 3.12

Claims (1)

[Scope of Claims] 1. An anode of an electrolytic cell comprising a cation exchange membrane provided on at least one side with a porous layer having no electrode activity and permeable to gases and liquids, disposed between an anode and a cathode. A method of electrolyzing liquid and catholyte while pressurizing them. 2. The electrolysis method according to claim 1, wherein the anolyte is an aqueous alkali chloride solution and the catholyte is an aqueous caustic alkali solution or water.