JPH0119923B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for acid electrodialysis. Specifically, when electrodialyzing acids, an anion exchange membrane is used in which an anion exchange group based on a pyridine ring or a haloalkyl group is bonded, and the anion exchange group present in the surface layer of the anion exchange membrane has 6 carbon atoms. This is an acid electrodialysis method using an anion exchange membrane bound with one or more alkyl groups having a chain length of ~30. Ion exchange membranes can be used for electrodialysis, diffusion dialysis, reverse osmosis,
It is widely used industrially in separation techniques such as ultrafiltration. Recently, it has also been used as a diaphragm for electrode reactions. As the field of use of ion exchange membranes has expanded in this way, special properties have come to be required of ion exchange membranes as well. For example, in the field of acid electrodialysis, there is a demand for the development of anion exchange membranes with a small diffusion constant. That is, methods for concentrating and desalting acids by electrodialysis have been carried out industrially for various acids, and many proposals have been made. For example, Japanese Patent Application Laid-Open No. 11981/1983 proposes a method of electrodialyzing a solution containing an acid using an anion exchange membrane having a thin layer of a cation exchange material. Although this method is one of the excellent methods, it has been desired to develop an anion exchange membrane with a small acid diffusion constant. The present inventors have made earnest efforts to develop an anion exchange membrane having a small diffusion constant for the above-mentioned acids. the result,
We obtained the following knowledge. That is, we investigated the electrical resistance and acid diffusion constant of anion exchange membranes obtained by treating polymer membranes containing pyridine rings with various alkyl halides having a longer carbon number than conventionally used alkyl groups. , favorable results were obtained as a film in which the electrical resistance of the film was low and the acid diffusion constant was small in the range of carbon number from 6 to 30.
Since there is a correlation between the acid diffusion constant and the fixed ion concentration, it is clear that in the carbon number range of 6 to 30, the fixed ion concentration is high or a layer with a high fixed ion concentration exists. The above-mentioned favorable results are obtained not only when using a polymer film having a pyridine ring, but also when using a film having a halomethyl group with a mono-, di-, or trialkylamine having at least one chain length of 6 to 30 carbon atoms. It was also confirmed that the same phenomenon occurs even after treatment. Based on these results, we conducted further research and completed the present invention, which we have proposed here. That is, the present invention provides an anion exchange membrane having an anion exchange group based on a pyridine ring or a haloalkyl group bonded to it when electrodialyzing an acid. This is an acid electrodialysis method characterized by using an anion exchange membrane to which one or more types of alkyl groups having a chain length of 6 to 30 are bonded. The types of compounds (hereinafter referred to as long-chain alkylating agents) that can bond one or more types of alkyl groups having a chain length of 6 to 30 carbon atoms to the anion exchange group of the anion exchange membrane used in the present invention are as follows: Since it is naturally determined by the constituent components of the ion exchange membrane, it cannot be determined unconditionally. For example, in the case of vinylpyridine-based anion exchange membranes, long-chain alkyl halides are used, and in the case of haloalkyl group-based anion exchange membranes, long-chain alkylamines and trialkylstibines having at least one long-chain alkyl group are used. , trialkylphosphine, etc. are used. Generally, linear alkylating agents are more effective as these long-chain alkylating agents, but they do not necessarily have to be linear, and branched alkylating agents are also effective to varying degrees. In addition, a portion of the compound may be substituted with a relatively inert halogen or the like. The long chain alkylating agents used in this invention have between 6 and 30 carbon atoms. Although the reactivity of the alkylating agent varies depending on the degree of crosslinking of the polymer membrane used, styrene-divinylbenzene-vinylpyridine, styrene-divinylbenzene-vinylpyridine,
In a divinylbenzene-chloromethylstyrene film, as the degree of crosslinking increases, only the surface layer of the film reacts. Particularly preferred alkylating agents are compounds having a chain length of 8 to 20 carbon atoms. The fact that alkyl groups having 8 or more carbon atoms are particularly effective seems to be correlated with the micelle formation phenomenon observed in surfactants. This is because, as has been well known in the past, when the number of carbon atoms exceeds 8, mimol formation is observed in the surfactant solution. Therefore,
In the present invention, it is also possible that intramembrane micelles are formed near the anion exchange group. Typical manufacturing methods for the anion exchange membrane used in the present invention are as follows: (1) Styrene-divinylbenzene-vinylpyridine is made viscous by adding styrene-butazinine rubber, etc., and a radical polymerization initiator is added thereto to form a polymer. After coating vinyl chloride etc. on a cloth and polymerizing it to form a film, it is alkylated with a long-chain alkyl halide such as dodecylbroyide, and if necessary, a short-chain alkyl halide such as methyl iodide is applied. How to react with. (2) Add chloromethylstyrene to styrene-divinylbenzene, add fine powder such as polyvinyl chloride, add a radical polymerization initiator to this, apply it on the same cloth, heat polymerize it, and react with, for example, dioctylamine. After this, if necessary, react with trimethylamine, etc. (3) A method in which fine powder of polyvinyl chloride is heated with dimethyldodecylamine to cause the polyvinyl chloride and tertiary amine to react, and then heated and formed into a film. (4) Other methods include reacting lauryl bromide with a conventionally known anion exchange membrane obtained by reacting dimethylamine with a polymer membrane synthesized mainly of chloromethylstyrene-divinylbenzene-styrene. In addition, after reacting a polymer film having the same halomethyl group with trimethylamine, oxidation, heat treatment, etc.
A method of partially or completely decomposing a class ammonium base to convert it into a tertiary, secondary, or primary amino group and then reacting it with stearyl bromide or the like is adopted. Generally, from the viewpoint of obtaining a membrane with a high fixed ion concentration, a homogeneous ion exchange membrane is more desirable than a heterogeneous ion exchange membrane. The anion exchange membrane matrix can be any anion exchange membrane made by any of the conventionally proposed methods, and as long as it has the anion exchange group specified by the present invention, the fixed ion concentration can be It becomes a high performance anion exchange membrane. In addition, the amount of long-chain alkylating agent, such as long-chain alkyl halide or long-chain alkylamine, depends on its type, reaction conditions, chain length of alkyl group, reaction activity of halogen and amine, and the shape of the polymer film to be reacted. Although it varies depending on the substance, the type and structure of the polymer, the activity of the reaction site, etc., and the intended use of the obtained anion exchange membrane, the higher the reaction amount of the long-chain alkylating agent, the more the membrane will be fixed. The ion concentration increases, and at the same time the electrical resistance of the ion exchange membrane also increases. Furthermore, in order to increase the Donnan exclusion effect of the anion exchange membrane, it is effective to increase the concentration of fixed ions in the membrane at the membrane-liquid interface that contacts the solution. Based on this, we investigated the amount of various long-chain alkylating agents to be reacted, and found that
The alkylating agent may be present in at least one of the surface layers of the membrane, and the amount thereof may be bonded to anion exchange groups of 2% or more of the total ion exchange capacity of the membrane. If necessary, for example, add 1 vinylpyridine.
In the case of the anion exchange membrane used as a component, the remaining anion exchange groups are tertiary amino groups based on pyridine groups, which act as anion exchange groups when used in an acidic atmosphere, but in neutral Alternatively, it becomes inactive if used in an alkaline atmosphere. Therefore, a type of alkylating agent such as an alkyl halide that can easily react within a polymer matrix with a short carbon chain length such as methyl iodide, methyl bromide, ethyl iodide, ethyl bromide, dimethyl sulfate, etc. By reacting with the above, a polymer film having quaternary ammonium bases as most of the anion exchange groups can be obtained. In addition, when reacting something like dodecylamine to a polymer film such as chloromethylstyrene-styrene-divinylbenzene, it is necessary to A layer that cannot be completely reacted and has no electrical conductivity, that is, there is no anion exchange group, is formed inside the membrane or on the back side when only one side is reacted. Since such substances cannot actually be used, methylamine, dimethylamine, trimethylamine, trimethylstibine,
By reacting a compound with a short alkyl chain length such as trimethylphosphine, trimethylarsine, or triethylamine with the chloromethyl group present inside the polymeric membrane, it becomes able to function as an anion exchange membrane. As mentioned above, the anion exchange membrane used in the present invention has a high concentration of fixed ions in the ion exchange membrane or has a layer with a high concentration of fixed ions, so as a result, various ideal ion exchange membranes exhibit It exhibits behavior and characteristics different from conventional ion-exchange membranes, resulting in a high-performance membrane. That is, the amount of diffusion and leakage of acid used in electrodialysis is significantly small, and concentration and deoxidation of acid by electrodialysis can be carried out with high current efficiency. Furthermore, the presence of long-chain alkyl groups on the surface or inside of the membrane makes it difficult for ionic species with a large ionic radius to pass through. Specifically, the permeation amount of sulfate ions decreases relative to chlorine ions. Similarly, it becomes difficult for large organic anions to pass through the membrane, and at the same time, it has the effect of selectively adsorbing anionic surfactants and the like onto the membrane surface or within the membrane. The acid electrodialysis method in the present invention is not particularly limited, and can be carried out by using a conventionally known electrodialysis tank and employing a known method as is. Further, the type of acid is not particularly limited and may be any conventionally known acid. For example, using an acid as shown in JP-A-50-11981, the method described therein may be carried out. The content of the present invention will be specifically explained with reference to the following examples, but the content of the present invention is not restricted in any way by these examples. In the example, the electrical resistance of the membrane is 0.5N−NaCl
or 25.0℃ in 1.0N HCl, 1000 cycles AC
It was measured in Also, the ring ratio of the membrane is 0.5N−
It was calculated using the Nernst equation from the membrane potential generated between NaCl and 2.5N-NaCl. A two-chamber acrylic diffusion cell was used to measure the amount of acid and salt diffusion through the membrane, with pure water in one chamber and pure water in the other.
Arrange 3.5N-NaCl and stir both chambers at 1500 rpm at 25.0℃ to analyze the amount of salt that has diffused into the pure water. N
-HCl was placed on both sides of the membrane, acid was diffused under the same conditions, and the amount of acid diffused into pure water was analyzed to determine the diffusion constant D/δ from the following equation. D/δ=Q/ΔC・A・t D: Diffusion coefficient (cm ²・sec ^-1 ) δ: Film thickness (cm) Q: Diffusion amount (eq) ΔC: Concentration difference (eq ・cm ^-3 ) A: Membrane area (cm ² ) t: Dialysis time (sec) The current efficiency is determined by placing the membrane in the center of a two-chamber cell made of acrylic with silver-silver chloride electrodes, and applying 4.0N to the anode side of the membrane. After electrodialyzing HCl at a current density of 3 A/dm ² for 90 minutes using 0.416N HCl on the cathode side, the catholyte was analyzed to determine the change in concentration. The amount of electricity was determined using a coulometer and by calculating the current efficiency. The fixed ion concentration of the membrane was determined by equilibrating the anion exchange membrane with 1N hydrochloric acid and washing it several times with methanol to remove the hydrochloric acid adsorbed on the membrane.
After washing and ion exchange with 0.2N sodium nitrate, the washing solution was collected, concentrated, and the chlorine ions contained therein were quantified. The exchange capacity of the membrane was thereby measured (EC). On the other hand, the membrane was equilibrated in 0.5N saline water, weighed, wet weight (Wet W) was measured, and then 30
After drying under reduced pressure at °C for 16 hours, the weight of the membrane was measured (Dry W). The fixed ion concentration of the membrane was determined by EC/(Wet W) - (Dry W) (molar concentration). Furthermore, the selective permeability coefficients of sulfate radicals and chloride ions were measured. The measurement method is a two-chamber acrylic cell with a silver-silver chloride electrode, and a 0.500N-silver electrode in the anode chamber.
Filled with NaCl, 0.25N−Na ₂ SO ₄ in the cathode chamber,
Fill with 0.250N-NaCl mixed solution, 10mA/cm ²
Current was applied for 1.5 hours at a current density of , and the selective permeability coefficient of sulfate ions relative to chloride ions was calculated from the amount of sulfate radicals and chloride ions that permeated the membrane into the cathode chamber using the following formula. P ^SO _4Cl tSO ₄ /tcl/CSO ₄ /CCl tSO ₄ : Number of equivalents of SO ₄ ^-- that permeated the membrane tCl: Number of equivalents of Cl ^- that permeated the membrane CSO ₄ : Sulfate ion concentration in the cathode chamber CCl: Cathode chamber Chloride ion concentration Example 1 A paste consisting of 100 parts of polyvinyl chloride fine powder, 160 parts of 4-vinylpyridine, 10 parts of styrene, 15 parts of divinylbenzene with a purity of about 55%, 25 parts of dioctyl phthalate, and 3 parts of benzoyl peroxide. Apply the mixture to a plain woven polyvinyl chloride cloth and cover both sides with a polyvinyl alcohol sheet.
Polymerization was carried out at 90°C for 4 hours to obtain a polymer membrane. This membrane was dissolved in dodecyl bromide, n-hepetane at 45°C.
It was left immersed for 2 months. Then take it out and
- After thorough washing with hepetane, further washing with methanol, and conditioning with 1N hydrochloric acid and 0.5N saline, the electrical resistance was measured in 1N hydrochloric acid and found to be 6.4Ω-cm ² and the transference number to be 0.93. It was hot. Next, the quaternization rate of this membrane was measured and found to be 59% (after equilibration with 1N hydrochloric acid and thorough washing of the membrane with methanol, the ion-exchanged chlorine ions were eluted with 0.2N sodium nitrate. , then 5N of PH12
After equilibration with saline, the solution was thoroughly washed with methanol, chloride ions were eluted in the same manner, and the ratio of the two was determined. ). A membrane reacted with dodecyl bromide in exactly the same manner was mixed with 40 parts of methyl iodide and 60 parts of n-hexane.
The amount of permeated water in the membrane was measured after immersing the membrane in a 2-chamber acrylic cell for 16 hours at room temperature. The amount of movement through the membrane was calculated) 1.85×
10 ^-6 cc/sec×cm ² ． It was N. The diffusion constant of salt was determined using this membrane.
When the diffusion constant of hydrochloric acid was determined to be 6.86×10 ^-7 cm・sec ^-1 , it was 5.75×10 ^-6 cm・sec ^-1 . Next, the current efficiency of acid electrodialysis was measured and found to be 65%. For comparison, the styrene-divinylbenzene-4-vinylpyridine copolymer film was simply immersed in an alkylation bath of the same composition of methyl iodide and n-hexane, and its various properties were measured. The electrical resistance of the membrane in 9.5N−NaCl is 2.0Ω−cm ²
The transference number is 0.92, and the amount of permeated water is 9.21×10 ^-6 cc/sec×
cm ² , the diffusion constant of common salt is 3.94 × 10 ^-6 cm sec ^-1 , the diffusion constant of hydrochloric acid is 3.81 × 10 ^-5 cm sec ^-1 , and the current efficiency of acid electrodialysis is 12%. Ta. The fixed ion concentration of the membrane was determined by measuring the exchange capacity and water content of the membrane used in this example and a comparative membrane. The membrane was 6.5 molar. Example 2 6 parts of benzoyl peroxide was added to 10 parts of acrylonitrile rubber (manufactured by Nippon Zeon; Hiker 1042), 160 parts of chloromethylstyrene, and 40 parts of divinylbenzene with a purity of about 55%, and the mixture was mixed and dissolved uniformly. The mixture was applied to a plain woven polyvinyl chloride cloth, degassed, covered with polyvinyl alcohol sheets on both sides, and polymerized by heating in an autoclave at 90°C for 8 hours to form a polymer film. This was immersed in each of the amines shown in Table 1 and reacted at 80° C. for various hours, and then each performance was measured. The results are also listed in Table 1.

[Table] Membranes 2 and 3 were immersed in dioctylamine and trioctylamine, and then immersed in trimethylamine-acetone-water used in producing membrane 1 for 12 hours.
Example 3 100 parts of polyvinyl chloride fine powder, 80 parts of 4-vinylpyridine, 80 parts of 2-methyl-5-vinylpyridine
A paste mixture consisting of 10 parts of styrene, 15 parts of divinylbenzene with a purity of about 55%, 25 parts of dioctyl phthalate, and 3 parts of benzoyl peroxide was applied to a plain woven polyvinyl chloride cloth, and both sides were coated with polyvinyl alcohol. Cover with a sheet and heat at 90℃
Polymer film-like material was obtained by heating and polymerizing for a period of time. This membrane was immersed in various alkyl bromides shown in Table 2 at various temperatures, and then immersed in n-hexane and methyl iodide.
After 16 hours immersion at 25℃ in 60:40 (weight ratio),
The properties of each film were measured. The results are also listed in Table 2. Furthermore, Table 2 also shows the ratio of the chain length of the alkyl group and the diffusion constant of various alkyl bromide-treated membranes when the diffusion constant of hydrochloric acid of the membrane treated only with methyl iodide-hexane is 1.0. Shown as a ratio.

【table】

[Table] Example 4 The polymer membrane obtained in Example 1 was reacted with stearyl bromide under the following two different conditions. (1) A mixture of stearyl bromide with a purity of 95% or higher was reacted at 80°C for 10 hours. (2) It was left in stearyl bromide with a purity of 95% or higher at room temperature for two years. For the above two types of membranes, after reaction with stearyl bromide, 60:40 of methyl iodide and n-hexane
(weight ratio) to alkylate the remaining pyridine rings. When the fixed ion concentrations were determined by measuring the exchange capacity and water content of these two types of membranes, the membrane (1) had a molarity of 8.9, and the membrane (2) had a molarity of 15.5. Furthermore, the alkylation rate of the pyridine ring after reacting with stearyl bromide was 55% for (1) and 55% for (2).
It was 59%. Furthermore, the results of electrodialysis using hydrochloric acid with different concentrations were 60% for membrane (1) and 61% for membrane (2). Furthermore, for comparison, the immersion time in stearyl bromide was changed. That is, at 80℃ for 30 minutes, 2 hours,
I changed it to 4 hours. The quaternization rate was measured by a conventional method, and then immersed in methyl iodide and n-hexane by a conventional method. Next, the diffusion constant of hydrochloric acid was determined and was as shown in Table 3.

【table】

[Table] Also, when reacting this polymer film,
The mixture was placed in a stainless steel reactor capable of reacting on only one side, stearyl bromide was placed in one chamber, and the mixture was reacted at 80°C for 2 and 4 hours. 4
The grading rate was measured, and then the sample was immersed in methyl iodide and n-hexane by a conventional method. Next, the diffusion constant of hydrochloric acid was determined. The results are shown in Table 4.

[Table] When determining the diffusion constant of hydrochloric acid, the surface of the membrane reacted with stearyl bromide was diffused toward 4N hydrochloric acid.

Claims (1)

[Claims] 1. When electrodialyzing acids, an anion exchange membrane with an anion exchange group based on a pyridine ring or a haloalkyl group is used, and the anion exchange group present in the surface layer of the anion exchange membrane has 6 to 30 carbon atoms. 1. A method for electrodialyzing acids, which comprises using an anion exchange membrane to which one or more types of alkyl groups having a chain length of .