JPH031389B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a cation exchange membrane for alkali metal salt electrolysis. The characteristics required for such a cation exchange membrane are generally a dense diaphragm with excellent chemical resistance, a low diffusion constant for salts, and a low electrical resistance. The electrolytic diaphragm currently in common use is mainly made of asbestos, which is solidified and molded with an adhesive. Regardless of the chemical resistance of asbestos, these diaphragms generally have the disadvantage of being surprisingly poor in durability.Moreover, they also have high water permeability, and because they are a type of filtration diaphragm, salt diffusion is large, and current efficiency is low. Moreover, the concentration and purity of the product will not be high. One method for reducing salt diffusion and water permeability is to reduce the water permeability and diffusion constant of the diaphragm, but at the same time the electrical resistance increases. In the end, it is an industrial practice to suppress diffusion by regulating the flow method of the electrolyte so that the raw material flows to the product side through a diaphragm. In this case, the concentration of salts in the product, for example caustic, is significantly higher. Next, it is expected that an ion exchange membrane will be used as a membrane material with essentially a small diffusion constant and low electrical resistance, which is selective in the permeation of ions. Since it is hydrogen-based, it has no durability under the harsh conditions of electrolytic reactions and cannot be used industrially. On the other hand, there is also a proposal to use a porous film of fluorine-based polymer as an organic polymer membrane with excellent chemical resistance. In this case, the pore size, pore density, etc. are important factors, and the characteristics of fluororesins include poor wettability with aqueous solutions and inherently high electrical resistance. The present inventors believe that there is no substitute for fluororesin in that it has the absolute properties required for an electrolytic diaphragm, such as chemical resistance and oxidation resistance, and we have developed an ion-exchange base for this. As a result of conducting research on electrolytic diaphragms that incorporate this, we discovered an electrolytic diaphragm with extremely superior current effects. The present invention provides a monomer unit consisting of perfluoroalkyl vinyl ether with a cation exchange group.
SO ₃ M [where M is hydrogen or an alkali metal]
A unit in which a cation exchange group -COOM [where M is hydrogen or an alkali metal] is bonded to a monomer unit consisting of perfluoroalkyl vinyl ether, and a monomer unit of tetrafluoroethylene in the polymer chain. The object of the present invention is to provide a perfluorocarbon-based cation exchange membrane for alkali metal salt electrolysis comprising: The present invention also provides a unit in which a cation exchange group -SO ₃ M [where M is hydrogen or an alkali metal] is bonded to a monomer unit made of perfluoroalkyl vinyl ether, and a unit in which a cation exchange group -SO 3 M (M is hydrogen or an alkali metal) is bonded to a monomer unit made of perfluoroalkyl vinyl ether. A perfluorocarbon-based cation exchange membrane comprising a unit bonded with a group -COOM [where M is hydrogen or an alkali metal] and a monomer unit of tetrafluoroethylene in a polymer chain, and the ion exchange membrane a thin layer of a low molecular weight amino group-containing compound selected from diethylaminoethanol, triethanolamine, tetraethylenebentamine, and glycine bonded in the form of acid amide or acid addition salt to the surface of the alkali metal salt electrolytic solution. It provides an ion exchange membrane. The cation exchange membrane of the present invention falls within the category of ordinary cation exchange membranes in that it is mainly composed of a membrane bonded with cation exchange groups, and is similar to the fluororesin-based membrane in that it bonds fluorine atoms. It forms a diaphragm and has extremely excellent chemical resistance and oxidation resistance. Furthermore, the low current efficiency of conventional electrolytic diaphragms made of fluororesin into which cation exchange groups have been introduced can be significantly improved, and at the same time, the diffusion of electrolyte substances to be treated, such as salts, can be reduced. Although it is not necessarily clear why the present invention provides a current effect that is unimaginable for conventional fluororesin-based cation exchange electrolysis membranes, the inventors of the present invention have speculated as follows. There is. In other words, in a fluororesin-based cation-exchange electrolytic membrane, the diffusion of salts and bases due to the concentration gradient on both sides of the membrane caused by the electrolytic reaction is controlled by anions; This is because the diffusion resistance of the cation exchange membrane to bases is lower than that of other salts and acids, resulting in an increase in the amount of base diffusion. On the other hand, in the present invention, since it is a perfluorocarbon-based cation exchange membrane, it has extremely excellent chemical resistance and oxidation resistance. combined diethylaminoethanol, triethanolamine,
In the case of a cation exchange membrane having a thin film of a low-molecular amino group-containing compound (having anion exchange property) selected from tetraethylenebentamine and glycine, the cation exchange membrane is made of a thin film of a low-molecular amino group-containing compound (having anion exchange property) selected from tetraethylenebentamine and glycine. Instead of hydroxide ions, cations such as sodium ions are used as coions in an anion exchange thin layer (thin layer of an amino group-containing compound) to suppress the diffusion of hydroxide ions and make them extremely small. In the end, by controlling the diffusion of the base by cations, the diffusion is reduced, and thus the current efficiency of base production is thought to be improved. Moreover, in the above cation exchange membrane, since the layer of the low molecular amino group-containing compound bonded to the surface is a thin layer, the electrical resistance of the diaphragm is substantially lower than that of a cation exchange membrane without the thin layer. It is no different from a diaphragm. In the above cation exchange membrane, when the bonding layer of the low-molecular amino group-containing compound becomes thick, it becomes a so-called composite ion exchange membrane, and desalination and further Electrical resistance may increase due to water hydrolysis, etc. Therefore, in this cation exchange membrane, the thickness of the bonding layer of the low molecular weight amino group-containing compound containing the anion exchange group is 0.5, and the electrical resistance of the membrane measured at a direct current of 1 Amp/dm ² in normal saline is 0.5. The electrical resistance of the membrane should be no more than 10 times, preferably no more than 7 times, the electrical resistance of the membrane measured at 1000 AC cycles in a specified saline solution. In the present invention, as long as the low molecular weight amino group-containing compound is bonded to the surface of the perfluorocarbon-based cation exchange membrane composed of the above units -, the positional relationship between the two is not limited. Therefore, a thin layer of a low-molecular-weight amino group compound is formed on both sides or one side of a membrane-like cation-exchange resin layer, or one or more layers of low-molecular-weight amino group compounds are formed in a sandwich-like manner between a plurality of cation-exchange resin layers. A thin layer of group-containing compounds may also be formed. In the present invention, the means for producing the perfluorocarbon-based cation exchange membrane consisting of the above-mentioned ~ is not particularly limited, and any known method may be employed. In general, the formula [However, p and q are 0 or positive integers, and
is halogen, OR (R represents hydrogen, ammonium, or alkali metal)] The monomers shown are subjected to radical polymerization, ionic polymerization,
A method in which a polymer obtained by copolymerization by radiation polymerization or the like is formed into a film shape and hydrolyzed as necessary is preferably employed. Of course, the perfluorocarbon-based cation exchange membrane of the present invention has the above formulas (1) and (2) as monomers.
As a result, it is not necessary to use a monomer unit consisting of perfluoroalkyl vinyl ether, and a cation exchange group -SO ₃ M [wherein M is hydrogen or an alkali metal] is bonded to a monomer unit consisting of perfluoroalkyl vinyl ether. The monomer unit contains a cation exchange group -COOM [However, M
is hydrogen or an alkali metal], and a constituent element of a monomer unit of tetrafluoroethylene may be present. Furthermore, the low-molecular amino group-containing compounds used in the cation exchange membrane provided by the present invention, in which a low-molecular amino group-containing compound is bonded in a thin layer to the perfluorocarbon-based cation exchange membrane, include diethylaminoethanol, triethanolamine, and the like. , tetraethylenepentamine, and glycine, which can be used alone or in combination. In addition, some low-molecular-weight amino-group-containing compounds other than those listed above may be used together with these amino-group-containing compounds, but this may impair the excellent effects produced by combining the above-mentioned low-molecular-weight amino group-containing compounds. It should not be a thing. The method for manufacturing a cation exchange membrane by bonding the low molecular weight amino group-containing compound to the perfluorocarbon cation exchange membrane in a thin layer is not particularly limited, but can usually be carried out by the following method. (1) An amino group-containing compound is attached to the surface layer of a cation exchange membrane having a cation exchange group and reacted to form an amino group on the substantial surface of the cation exchange membrane in the form of an acid addition salt or an acid amide bond. A method of bonding group-containing compounds. (2) An amino group-containing compound is added to a perfluorocarbon film (hereinafter referred to as the raw film) that has a functional group that can become a cation exchange group by hydrolysis, such as -SO ₂ Y, -COY (where Y is a halogen atom). A method in which a cation exchanger is introduced by attaching and reacting to bond to the substantial surface of the raw membrane in the form of an acid addition salt or acid amide bond, and then hydrolyzing the raw membrane. The amino group-containing compound used in the present invention can be used as it is or diluted with a solution, and the method of attachment is to immerse the membrane in the treated material (amino group-containing compound) or its solution, or to attach them. Means such as spraying or coating may be used on the membrane surface. Further, the bonding of the amino group-containing compound is due to an acid amide bond or an acid addition salt bond, but some other bonds or simple physical adsorption may also occur at the same time. Note that the layer of the amino group-containing compound may extend slightly from the surface of the cation exchange membrane to its vicinity. In this case, if the reaction progresses too far inside the film, this is undesirable as it leads to an increase in electrical resistance. Therefore, it is necessary to control the reaction under appropriate reaction conditions using a poor solvent for the membrane and, if necessary, in the presence of a catalyst. In order to use such a cation exchange membrane for electrolysis of an aqueous alkali metal salt solution, the cation exchange membrane of the present invention is arranged between the anode and the cathode, a solution of alkali salts is poured into the anode chamber, and a caustic alkali is poured into the cathode chamber. Caustic alkali can be obtained by electrolyzing alkaline salts with high current efficiency by flowing a solution of It can also be applied to three-chamber electrolysis, in which an ion exchange membrane is arranged to form a three-chamber electrolytic cell, and alkali salts are passed through the anode chamber and the intermediate chamber to obtain caustic alkali through electrolysis with high current efficiency. . At this time, naturally, chlorine gas and oxygen gas can be obtained from the anode. However, since the membrane of the present invention inherently has oxidation resistance, it is economically more suitable for use in two-chamber electrodialysis than in three-chamber electrodialysis. In the following Examples, some examples thereof will be shown, but the present invention is not limited in any way by the following Examples. The measurement was performed using 0.5N NaCl as a property of the membrane.
Electrical resistance at 25℃ inside (measured with direct current at 1A/ ^dm2 )
and the transference number (calculated using Nernst's formula from the membrane voltage in a 0.5N NaCl 2.5N NaCl system). For electrodialysis, unless otherwise specified, the effective current-carrying area
It was carried out using two or three chambers using a 1 dm ² chamber. Note that the amount of current applied was measured using a digital coulometer. Further, pure water was injected so that the caustic alkali generated at the cathode had a constant concentration. Example 1 Perfluoro(3,6-dioxa-4-methyl-7-octensulfonyl fluoride) was purified from Journal of American Chemical Society 82
It was produced according to the method described in Vol., p. 6181 (1960). That is, by a conventional method, BrCF ₂ -CF ₂ Br was dropped into methanol in which zinc powder was dispersed, and the generated tetrafluoroethylene was dried, then cooled with liquid oxygen and trapped to obtain tetrafluoroethylene. Next, into the newly distilled sulfur trioxide sealed in an autoclave, the tetrafluoroethylene obtained above is pressurized in an amount equal to or more than the same mole as the sulfur trioxide, the two are reacted, and perfluorosaltone is obtained by distillation. Ta. Next, 0.2 parts by volume of triethylamine was added to 70 parts by volume of perfluorosultone to open the ring of perfluorosultone to obtain FOCCF ₂ SO ₂ F. Next, FOCCF ₂ SO ₂ F was subjected to an addition reaction with hexafluoropropylene oxide in a tetraglyme solvent in the presence of cesium fluoride. (n is 1 and 2) were obtained. obtained A double bond was formed according to Japanese Patent Publication No. 41-7949. That is, the compound obtained above was placed in a rotary distillation apparatus and heated until no gas was generated from the distillation apparatus. The exhaust gas produced by the reaction is condensed by cold condensation, and then distilled. (boiling point 118℃) (boiling point 159°C) was obtained. The mixing ratio of the two vinyl compounds having different boiling points was 9 for the former and 1 for the latter. next, was synthesized according to the method described in Japanese Patent Publication No. 45-22327. That is, 425 g of commercially available perfluoromalonic acid fluorite (FOCCF ₂ COF) was mixed with 150 c.c. of diethylene glycol dimethyl ether and 30 g of cesium fluoride.
The mixture was placed in a glass reactor with a gas inlet. After cooling the reactor and reducing the pressure, 734 g of hexafluoropropylene oxide was charged into the reactor and condensed. Then, the temperature was gradually raised to room temperature to complete the reaction and distillation was performed. The reaction product is

[Formula] is the main component, and part of it is

[Formula] was generated. The obtained two types of compounds were placed in a polyethylene bottle, and water was gradually added to convert the acid fluoride groups to carboxylic acid groups. Next, hydrogen fluoride was removed under heating and reduced pressure, and then the potassium hydroxide solution was neutralized and dried under reduced pressure to synthesize a dipotassium salt. The compound obtained above was placed in a round-bottomed glass container, heated to 200° C. with stirring under reduced pressure of 0.5 mmHg inside the flask, and the reaction product was collected in a trap connected to the glass container and cooled with liquid oxygen.
Distill what is in this trap and get CF ₂ = CFOCF ₂ CF ₂ COF.

Two compounds with the formulas were obtained. The production ratio of the former to the latter was 1/12. The perfluoroalkyl vinyl ether sulfonyl fluoride and perfluoroalkyl vinyl ether carbonyl fluoride obtained as described above were mixed in the presence of tetrafluoroethylene according to the method described in Japanese Patent Publication No. 45-26303 (Examples 5 and 6). Copolymerization was carried out. That is, as a solvent, 1,
Using 2,2-trichlorofluoroethane, 200 c.c. of solvent, 61.3 g of perfluoroalkyl vinyl ether sulfonium fluoride, and perfluoroalkyl were placed in a stainless steel autoclave coated with 500 c.c. of polytetrafluoroethylene. vinyl ether carbonyl fluoride
Add 35g and then 400mg of azobisbutyronitrile
was added, kept at 70°C with stirring, thoroughly degassed with nitrogen gas, and then added 15 kg/cm ² of tetrafluoroethylene.
When the reaction pressure was increased to 7.5 kg/cm 2 and left for 24 hours, the reaction pressure had decreased to 7.5 kg/cm ² . Thereafter, the mixed solution of polymer and monomer was taken out of the autoclave, the monomer was rotated, and the solvent was distilled off to obtain about 39 g of polymer. The polymer obtained above was heated and compressed at 210°C to form a 0.3 mm film. As a result of measuring the infrared absorption spectrum of this film, absorption of -SO ₂ F and -COF was observed. With this result,
It was found that the obtained polymer had the following structure. [However, p is 0 or 1, and q is 1 or 2.] The above film was immersed in a 2N-NaOH ethyl alcohol solution at 25°C for 8 hours to be hydrolyzed.
Cation exchange membranes each having carboxylic acid and sulfonic acid were used. The sulfonic acid group exchange capacity of this cation exchange membrane was 0.45 meq/g dry membrane (Na type), and the carboxylic acid group exchange capacity was 0.49 meq/g dry membrane (Na type). Separately, the film obtained as described above before hydrolysis is immersed in a diethylaminoethanol solution to react and bond triethanolamine to the substantial surface of the film, and then hydrolyzed in the same manner as above. A cation exchange membrane having amino groups on the surface was obtained. Salt water electrolysis was performed using the two types of cation exchange membranes obtained above. Salt water electrolysis was carried out using a two-chamber electrolytic cell with an effective current-carrying area of 1 dm ² . The anode is an insoluble anode made of a titanium plate coated with ruthenium oxide and titanium oxide, and the cathode is an insoluble anode made of a titanium plate coated with ruthenium oxide and titanium oxide.
A Ni plate was used. The membrane is sandwiched between the anode chamber and the cathode chamber, and in order to keep the concentration of saline solution as the anolyte and caustic soda as the catholyte constant, pure water is added from outside the cathode chamber to keep it constant. 6.0
cm・sec ^-1 , and the cathode chamber also flows at a flow rate of 6.0 cm・sec ^-1 .
The temperature was kept at 70°C. The current density was 20A/ ^dm2 . Obtain 4.0N NaOH from the cathode chamber and convert NaOH
The current efficiency of acquisition and NaCl in NaOH was determined.
The results were as shown in Table 1. In addition, the obtained cation exchange membrane was used as an anion exchange membrane using Neocepta AF-4T (Tokuyama Soda
0.2N-KOH and 0.2N in a multi-chamber cell using
-The mixed solution of NaCl was subjected to electrodialysis at a current density of 2 A/dm ² . The results are also shown in Table 1.

[Table] Example 2 Using the pre-hydrolyzed film obtained in Example 1, triethanolamine, tetraethylenebentamine, or the low-molecular amino group of glycine shown in Table 2 was used instead of diethylaminoethanol in Example. Electrolysis of saline solution was carried out in the same manner as in Example 1 except that the contained compounds were used. The results were as shown in Table 2.

【table】

Claims (1)

[Claims] 1. A monomer unit consisting of perfluoroalkyl vinyl ether has a cation exchange group -SO ₃ M
[However, M is hydrogen or an alkali metal] is bonded to a monomer unit consisting of a perfluoroalkyl vinyl ether, and a cation exchange group -
COOM [However, M is hydrogen or an alkali metal]
1. A perfluorocarbon-based cation exchange membrane for alkali metal salt electrolysis, comprising a unit in which these are bonded together, and a monomer unit unit of tetrafluoroethylene in a polymer chain. 2 A cation exchange group -SO ₃ M is added to the monomer unit consisting of perfluoroalkyl vinyl ether.
[However, M is hydrogen or an alkali metal] is bonded to a monomer unit consisting of a perfluoroalkyl vinyl ether, and a cation exchange group -
COOM [However, M is hydrogen or an alkali metal]
A perfluorocarbon-based cation exchange membrane comprising a unit in which is bonded, and a monomer unit unit of tetrafluoroethylene in a polymer chain;
an alkali metal comprising a thin film of a low molecular weight amino group-containing compound selected from diethylaminoethanol, triethanolamine, tetraethylenepentamine, and glycine bound to the surface of the cation exchange membrane in the form of an acid amide or an acid addition salt; Cation exchange membrane for salt electrolysis.