KR100542295B1 - Preparation method of polyethylene / polyvinylbenzyl chloride anion exchange membrane - Google Patents

Abstract

The present invention relates to a method for producing polyethylene / polyvinylbenzyl chloride anion exchange membrane, and more particularly, vinylbenzyl chloride and swelling-promoting monomer, using a non-porous low density polyethylene film which simultaneously exhibits monomer absorbency and photocrosslinkability as a support. After absorbing divinylbenzene and photoinitiator, polymerizing by irradiation with ultraviolet rays and introducing an anion ion group through quaternary amination reaction to produce an anion exchange membrane, eliminating the conventional paste process and replacing the thermal polymerization process The present invention relates to a method for producing a homogeneous polyethylene / polyvinylbenzyl chloride anion exchange membrane by using a non-porous low density polyethylene film as a support and increasing the permeability.

Anion exchange membrane, vinyl benzyl chloride, monomer absorption method, UV polymerization method, low density polyethylene, photoinitiator

Description

Preparation method of polyethylene / polyvinylbenzyl chloride anion exchange membrane {Preparation of Polyethylene / Polyvinylbenzyl chloride anion-exchange membrane}             

1 is a manufacturing process chart of the polyethylene / polyvinyl benzyl chloride anion exchange membrane of the present invention.

2 is a graph showing the change in polymerization amount according to the UV irradiation time of the polyethylene / polyvinylbenzyl chloride anion exchange membrane of the present invention.

3 is a graph showing the change in membrane resistance and ion exchange capacity according to the styrene content of the polyethylene / polyvinylbenzyl chloride anion exchange membrane of the present invention.

4 is a current-voltage characteristic curve of the polyethylene / polyvinylbenzyl chloride anion exchange membrane of the present invention.

5 is a graph showing the chronopotentry characteristics of the polyethylene / polyvinylbenzyl chloride anion exchange membrane of the present invention.

The present invention relates to a method for producing polyethylene / polyvinylbenzyl chloride anion exchange membrane, and more particularly, vinylbenzyl chloride and swelling-promoting monomer, using a non-porous low density polyethylene film which simultaneously exhibits monomer absorbency and photocrosslinkability as a support. After absorbing divinylbenzene and photoinitiator, polymerizing by irradiation with ultraviolet rays and introducing an anion ion group through quaternary amination reaction to produce an anion exchange membrane, eliminating the conventional paste process and replacing the thermal polymerization process The present invention relates to a method for producing a homogeneous polyethylene / polyvinylbenzyl chloride anion exchange membrane by using a non-porous low density polyethylene film as a support and increasing the permeability.

An ion exchange membrane is a kind of polymer separation membrane that can selectively separate anions or cations depending on the species of ion-exchangeable groups introduced into the membrane. For the cation exchange membranes used as commercial, large adult strong acid sulfonic acid group as the ion exchange group (-SO ₃ ^-) and the weak acid is a carboxylic acid group (-COO ^-) becomes is divided into, mainly in the case of strong base anion exchange membrane 4 Adults The primary ammonium group (-N ⁺ R ₃ ) will have an ion exchange group. The separation process using the ion exchange membrane is capable of relatively high purity separation and purification compared to the separation method using distillation or chemical treatment, has low energy consumption and simple equipment, so that the equipment investment cost is low and the continuous process is possible. It is attracting attention as a separate purification process in various industrial fields because of its excellent processing capacity per hour. Current applications of ion exchange membranes in industry include electrodialysis and water-splitting electrodialysis for desalination and purification, and diffusion dialysis and ultrapure water production to recover acids from pickling liquor. Electrodeionization and the like. In particular, in recent years, interest in ion-exchange membranes has been increasing, suggesting the possibility that the ion-exchange membranes can exhibit excellent performance as polymer electrolyte fuel cells. In general, commercial membranes should have high ion selective permeability (> 0.95-0.98), low electrical resistance (<1.0-4.0 Ω · cm 2), adequate water content, high mechanical strength and chemical resistance.

Existing commercial membranes such as NEOSEPTA® ^trademark (Tokuyama Co. Ltd., Japan), SELEMION® ^trademark (Asahi Glass Company, Japan), etc., are copolymers of vinylbenzyl chloride-divinylbenzene or vinylbenzyl as a base material. The copolymer of chloride-butadiene was prepared by using a bulk polymerization method, a latex method, or a paste method. Ion-exchange membranes using these methods have relatively good electrochemical properties. However, these manufacturing processes cause an increase in manufacturing cost due to the complexity of the process.

In the case of bulk polymerization, when polymerizing with vinylbenzyl chloride-divinylbenzene alone, a plasticizer should be used because brittleness is increased and mechanical properties are deteriorated. Moreover, in order to obtain a thin film, a uniform container is required, which increases the overall cost of manufacturing the film. It becomes a factor.

In the latex method, a latex of vinyl benzyl chloride-butadiene copolymer is dipped on a support and dried to form a base film through crosslinking using an oxidative crosslinking method. Thereafter, an ion exchange group is introduced through a quaternary amination reaction, and this method is likely to cause deterioration of the mechanical and electrochemical properties of the membrane under the influence of the emulsifier remaining in the latex of the vinylbenzyl chloride-butadiene copolymer. This is very high.

On the other hand, the paste method is the most widely used method up to now as a manufacturing method of the ion exchange membrane. Although the paste method has better mechanical and electrochemical properties than the films obtained by the above-mentioned bulk polymerization method or latex method, powder is required in addition to the vinylbenzyl chloride-divinylbenzene monomer to obtain a paste. In order to obtain mechanical properties, a plasticizer and rubber must be added. This complexity in the manufacturing process acts as a factor to increase the manufacturing cost of the film.

In order to overcome these disadvantages, the present inventors prepared a monomer solution containing an initiator recently in a cation exchange membrane, and then adsorbed to a porous film to polymerize at a predetermined temperature and react the reaction with time to control the membrane structure to obtain desired selectivity and mechanical properties. A new concept of monomer absorption method has been developed to control physical properties (Korean Patent Application No. 2001-75488). The patent has the advantage that the ion exchange membrane can be prepared by a relatively simple manufacturing process compared to the conventional paste method, but in order to improve the selectivity to the solute of the membrane, a chemical crosslinking agent must be added, and further, the polymerization uses a thermal polymerization method. Since there is some inconvenience in the manufacturing process, there is a station of improvement.

Accordingly, the inventors of the present invention absorb the solution for polymerization containing vinylbenzyl chloride, swelling accelerator monomer, divinylbenzene and photoinitiator in a nonporous low density polyethylene film and irradiate ultraviolet rays at room temperature to solve the above problems. In other words, after inducing the formation of a crosslinked product during the polymerization process, the introduction of an amine group into the anion exchanger through a quaternary amination reaction was found to improve the permeability by improving the crosslinking to complete the present invention.

Therefore, the present invention is a simple manufacturing process compared to the conventional paste method and the monomer absorption method can reduce the manufacturing cost, and the production method of polyethylene / polyvinyl benzyl chloride anion exchange membrane excellent electrochemical properties and mechanical performance compared to commercial membranes The purpose is to provide.

The present invention absorbs a solution for polymerization comprising vinyl benzyl chloride, a swelling accelerator monomer, divinylbenzene and a photoinitiator in a non-porous low density polyethylene film, and photopolymerizes by irradiating ultraviolet light at room temperature, and then through a quaternary amination reaction The method for producing polyethylene / polyvinylbenzyl chloride anion exchange membrane into which an amine group is introduced is characterized.

Referring to the present invention in more detail as follows.

The production method of the anion exchange membrane of the present invention is the same as the monomer absorption method in that the vinyl benzyl chloride is absorbed in the support of the non-porous film to polymerize the monomer present in the free volume of the support film, but is different from the conventional monomer absorption method. Alternatively, photoinitiators are used in place of thermal initiators as initiators, and swelling-promoting monomers are used to prepare homogeneous membranes with the promotion of the absorption of vinylbenzyl chloride on the support. As described above, the present invention is characterized in that the monomer and the photoinitiator are irradiated with ultraviolet light to polymerize the monomer present in the free volume. At this time, the polymerization behavior is different from the conventional monomer absorption method, in addition to the formation of the polymer of the monomer on the non-porous film, the formation of the polymer of the grafted monomer, the cross-linking between the film molecules and the cross-linking between the grafted polymer molecules It is done. Therefore, the conventional paste method and monomer absorption method to improve the selective permeability through the addition of a chemical crosslinking agent, in the present invention is characterized in that the selective permeability can be further improved by the crosslinking reaction during the polymerization process. Furthermore, the non-porous support used at this time is characterized by using a low density polyethylene, which is a photocrosslinkable polymer instead of the conventional photodegradable PVC, in order to enhance mechanical strength. Thereafter, the production process of introducing the ion exchanger is performed through the same quaternary amination reaction.

In the conventional paste method, a monomer (F-monomer), a crosslinking agent, an initiator, and a plasticizer capable of introducing an ion exchange group are mixed together with a polyvinyl chloride (PVC) powder to form a paste, and the paste is impregnated on a PVC cloth, and then The ion exchange group was introduced by copolymerization at a temperature of [Y. Mizutani, J. Membr. Sci., Vol. 49, pp 121-144, 1990. As a representative product manufactured by such a manufacturing method, Neosepta ^registered ion exchange membrane (Tokuyama Co. Ltd.), which occupies many markets worldwide, is reported to have relatively excellent performance. However, no matter how well mixed in preparing the paste containing the monomer and the PVC powder, the polymer film prepared after the polymerization cannot form a uniform phase. In addition, in order to manufacture a polymer film having excellent mechanical strength by the paste method, a plasticizer should be added as an essential ingredient in waste yeast, and the manufacturing process is complicated and the manufacturing cost is required, such as impregnating a paste into a PVC mesh cloth and forming a polymer film. Will rise.

On the other hand, the recently reported monomer absorption method has the advantage of not using a paste, the manufacturing process is simple and has the advantage of reducing the manufacturing cost, but in order to improve the permeation selectivity chemical crosslinking agent (eg, DVB) Has been added.

The present invention improves the paste method and the monomer absorption method to absorb the vinylbenzyl chloride, the swelling-promoting monomer and the photoinitiator in a non-porous low density polyethylene film and irradiate ultraviolet rays over a period of time to induce the formation of a crosslinked product during the polymerization process. Then, the present invention relates to the preparation of an anion exchange membrane having high permeation selectivity by introducing a strong alkali quaternary amine group (-N ⁺ R ₃ ) as an anion exchanger through a quaternary amination reaction.

In particular, the present invention uses a non-porous low-density polyethylene film having both monomer absorption and photocrosslinkability properties by replacing a conventional photodegradable non-porous PVC film as a support without using a paste. Alternatively, a homogeneous anion exchange membrane can be prepared that induces formation of a chemical crosslinked product during the polymerization process, thereby increasing permeation selectivity. In this case, chemical crosslinking occurs between low density polyethylene molecules and molecules, between low density polyethylene molecules and grafted polymer molecules, or between grafted polymer molecules.

The manufacturing method of the present invention as described above will be described in more detail based on the manufacturing process diagram shown in FIG.

First, a solution for polymerization is prepared. Vinyl benzyl chloride (F-monomer), which is used as a monomer capable of introducing an ion exchanger (F-monomer), contains a large amount of a polymerization inhibitor, and a polymerization inhibitor separation column was used to remove it. In addition, styrene and the chemical crosslinker divinylbenzene, which are swelling accelerator monomers of the support, were also removed through the polymerization inhibitor separation column. Photoinitiators were used without further purification and other reagents were also used without further purification.

The polymerization solution contains 70 to 95% by weight of vinylbenzyl chloride, 5 to 30% by weight of swelling accelerator monomer and 0 to 5% by weight of divinylbenzene, and 1 to 10 parts by weight of photoinitiator based on 100 parts by weight of the monomer described above. It is contained.

A nonporous low density polyethylene film is deposited and swelled in the polymerization solution. The nonporous low density polyethylene film used as the support is nonporous and has the property of being swollen to the vinyl monomer and not decomposed by ultraviolet rays. If the low density polyethylene film is porous, a nonporous material is used because pinholes may be concerned and a decrease in permeation selectivity of ions may be caused. In the case of using the existing non-porous PVC film as a support, it has the property of swelling in the vinyl monomer, but decomposes when irradiated with ultraviolet rays, resulting in poor mechanical properties. Therefore, the present invention is characterized by using a non-porous low density polyethylene as a support that swells in vinyl monomer and can induce crosslinking upon ultraviolet irradiation.

In particular, the present invention has another feature of using a swelling-promoting monomer to further promote swelling of the support in the polymerization solution to induce sorption of the monomer. In this case, swelling promoting monomers may be used such as styrene, 2-vinyl pyridium or 4-vinyl pyridium, and if the content is less than 5% by weight, vinylbenzyl chloride has a lower sorption to the support and thus the surface of the support. Only vinylbenzyl chloride can be sorbed so that a uniform membrane cannot be obtained. If the content exceeds 30% by weight, the content of vinylbenzyl chloride is relatively decreased, resulting in a decrease in ion exchange capacity and an increase in membrane resistance.

In addition, when the content of vinyl benzyl chloride used as a monomer in the present invention is less than 70% by weight, the ion exchange capacity is lowered. If the content is more than 95% by weight, a uniform membrane cannot be obtained.

In addition, divinylbenzene is used as a monomer that serves as a crosslinking aid, and if the content exceeds 5% by weight, it causes a decrease in mechanical properties due to an increase in brittleness.

The photoinitiator is 1,2-diphenyl ethanedione, 1,2-diphenyl ethanedione, benzophenone, benzyl dimethyl ketal, hydroxydimethylacetophenone, or α-hydroxy Cyclohexyl phenylmethanone (α-hydroxycyclohexyl phenyl methaneone) and the like can be used, if the amount is less than 1 part by weight, the molecular weight can be increased, but the polymerization rate is very slow and requires a long time ultraviolet irradiation, excessive crosslinking As the reaction proceeds, mechanical properties decrease (increase brittleness). If the content exceeds 10 parts by weight, the polymerization rate increases, but the mechanical effect is due to the formation of low molecular weight or acceleration of the photodegradation effect of the support with the influence of the remaining photoinitiator. It leads to deterioration of physical properties and electrochemical properties.

Thereafter, the monomer and the initiator are left at 0.5 to several hours or more, preferably 4 to 8 hours at room temperature, so that the monomer and the initiator are sufficiently sorbed to the nonporous low density polyethylene to reach an equilibrium state. Nonporous low density polyethylene that is sorbed to equilibrium increases flexibility with swelling. It is placed on a square glass plate that does not block ultraviolet rays and is covered with another glass plate. Then, the two glass plates are sealed with a tape to prevent leakage of the monomer during polymerization. This is placed in an ultraviolet polymerization apparatus to which a 400 W mercury ultraviolet light (wavelength: 150 to 400 nm) is attached. At this time, the distance from the ultraviolet light is maintained at 10 to 50 cm. At this time, if the distance is less than 10 cm, the sample is deformed due to heat generation from ultraviolet light. If the distance is more than 50 cm, the adsorbed monomers do not polymerize on the low density polyethylene due to a decrease in the amount of irradiation per unit area of the sample. Meanwhile, the temperature of the polymerization apparatus is maintained at room temperature by purging with nitrogen gas to minimize the influence of heat generated from ultraviolet light and to suppress side reactions. The irradiation time of ultraviolet rays is 10 to 60 minutes, preferably 20 to 50 minutes. If the UV irradiation time is less than 10 minutes, the polymerization is incompletely formed, and if it exceeds 60 minutes, excessive polymer formation leads to a decrease in mechanical strength. The base membrane thus prepared contains somewhat unreacted monomers, which acts as a major factor in determining the mechanical strength and morphology of the membrane. To remove this unreacted monomer, it is left at room temperature for one day to evaporate the unreacted monomer.

Thereafter, an anion exchange group is introduced to the base membrane through a quaternary amination reaction. As the anion exchanger, tertiary amines such as trimethyl amine, triethyl amine, diethyl phenyl amine and diphenyl ethyl amine are selected. The reaction time is 30 to 120 minutes, and the reaction temperature is 40 to 60 ° C, preferably 50 ° C. The membrane thus prepared contains side reactions, which is repeatedly washed several times in 0.5M HCl solution and 0.5M ammonium chloride, and then again in ultrapure water and stored in 0.5N NaCl solution.

The ion exchange capacity, electrical resistance, etc., which are typical methods for characterizing ion exchange membranes, were measured, and the membranes were successfully manufactured using FT-IR. In addition, anion (Cl ⁻ ) transport number, current-voltage curve (VI curve), chronopotentiometry, etc. were measured to measure ion selectivity of the prepared membrane.

As described above, the present invention does not use a paste unlike the conventional paste method, and unlike the conventional monomer absorption method, the monomer absorption method and the ultraviolet polymerization method exhibiting the characteristics of the high permeability-selective membrane through the formation of chemical crosslinking during the polymerization process. It is a manufacturing method of the anion exchange membrane which combined these.

The anion exchange membrane prepared through the production method of the present invention exhibits low electrical resistance (<1 μm ² ) and high ion selectivity (about 0.98 or more of transport water for Cl ⁻ ions) and exhibits excellent mechanical properties. It exhibits excellent properties on par with AMX anion exchange membrane (Tokuyama Co. Ltd., Japan) which is an anion exchange membrane.

Such a present invention will be described in more detail based on the following examples, but the present invention is not limited thereto.

Examples 1-3

The polymerization solution was prepared using vinylbenzyl chloride, divinylbenzene, and swelling accelerator styrene in the amounts shown in Table 1 below. 6 parts by weight of benzophenone (BP), a photoinitiator, was added to 100 parts by weight of the monomer. A nonporous low density polyethylene (LDPE) (530G or 630G, Samsung General Chemicals) having a thickness of about 60 μm was deposited over the polymerization solution thus prepared over 5 hours. The LDPE that reached the sorption equilibrium was placed on a glass plate capable of transmitting ultraviolet rays, and then the glass plate was covered thereon. In order to suppress the loss of the monomer during the polymerization process, a tape was sealed between the two glass plates. It was then placed in an ultraviolet polymerization apparatus to which a 400W ultraviolet mercury lamp (150-400 nm) was attached. At this time, the distance between the UV lamp and the glass plate was 25 cm, and the temperature of the polymerization apparatus was maintained at room temperature by purging nitrogen, and the ultraviolet ray was irradiated for 10 to 50 minutes to prepare each specimen, and then the base film.

In order to introduce an anion exchanger into the polymerized membrane under the above conditions, the reaction temperature was performed at 50 ° C. using a 10% by weight aqueous trimethylamine solution for 60 minutes. Since the membrane prepared as described above contained a side reaction material, it was repeatedly washed several times in 0.5M HCl aqueous solution and 0.5M ammonium chloride, and then washed again in ultrapure water, and stored in 0.5N NaCl aqueous solution. The characteristics of the prepared membrane were analyzed by the following method, and the analysis results are shown in Table 1 below.

Membrane characterization is described in J.-H., Choi, H.-J., Lee, and S.-H., Moon, J. Colloid & Interf. Sci., Vol. 238, p188, 2001; J.-H., Choi, S.-H., Kim, and S.-H., Moon, J. Colloid & Interf. Sci., Vol. 241, p120, 2001].

[Measurement Method of Membrane]

(1) Ion-exchange capacity: 1M HCl aqueous solution was impregnated for 24 hours or more, the membrane surface was washed, and then re-impregnated in 1M NaCl aqueous solution to determine the amount of hydrogen ions ion-exchanged inside the membrane by acidic titration (meq. g dry membrane).

(2) Electrical resistance: Calculated by using impedance value and phase angle measured by LCZ meter in 0.5M NaCl aqueous solution.

(3) Transport water, V-I curve, chronopotentiometry: It measured using the cell (film effective area: 0.785 cm <2>) of the structure which has both electrolyte tanks. The transport water was calculated by adding different concentrations of aqueous NaCl solution (0.001M / 0.005M NaCl) to both electrolyte baths and measuring the voltage difference between the Ag / AgCl electrodes fixed at both ends of the membrane.The VI curve was calculated using the same cell. The voltage difference across the membrane was measured while increasing, and 0.025M NaCl aqueous solution was used as the electrolyte.

Type of membrane Polymerization solution (% by weight) UV irradiation time (min) Ion exchange capacity [meq./g-dry mem.] Film resistance [ohm cm ² ] Cl ^- Transport [-] Vinylbenzyl chloride Divinylbenzene Styrene Example 1 94 One 5 60 1.30 4.01 > 0.98 Example 2 81 One 18 60 1.10 3.92 > 0.98 Example 3 71 One 28 60 0.98 3.72 > 0.98 Commercial membrane [AMX] - - - - 2.05 2.50 > 0.98

As shown in Table 1, the anion exchange membrane according to the present invention is compared with the electrochemical characteristics of AMX (Tokuyama co., Japan) which is a commercial membrane anion exchange membrane, it is confirmed that the electrochemical characteristics are equivalent to commercial membranes Could.

In addition, Figure 2 shows the polymerization behavior through the polymerization fraction on the low density polyethylene according to Examples 1 to 3. Herein, the polymerization fraction is evaluated by the weight part of vinylbenzyl chloride polymerized to 1 weight part of low density polyethylene as a support, and is defined by the following formula.

WG = [Wm / Wpe]

Where WG: polymerization fraction, Wm: weight of polymerized monomer (weight after polymerization-weight before polymerization), Wpe: weight of low density polyethylene (weight before polymerization)

The graph shows that the polymerization fraction increases with UV irradiation time, which shows that increasing the irradiation time can increase the amount of polymerization.

Figure 3 shows the relationship between the ion exchange capacity and the membrane resistance as a function of the styrene content according to Examples 1 to 3. Increasing the styrene content leads to a decrease in the ion exchange capacity, but it shows an advantage as an ion exchange membrane by reducing the membrane resistance.

4 shows typical I-V characteristics of the ion exchange membranes according to Examples 1-3. An increase in styrene content leads to a decrease in resistance and an increase in the limit current density.

5 shows typical chronopotentry properties of the ion exchange membranes according to Examples 1-3. Increasing the styrene content shows an increase in the transition time, which means an improvement in the surface uniformity of the film surface. In other words, the addition of the swelling-promoting monomer can be shown to improve the uniformity of the film.

As described above, the present invention utilizes the property that the non-porous low-density polyethylene film is swollen in the monomer solution without using a paste, and also performs ultraviolet polymerization using an ultraviolet crosslinked support to achieve high permeation through natural chemical crosslinking. By developing a membrane manufacturing method showing selectivity, the manufacturing process is simpler than the monomer absorption method, thereby reducing the manufacturing cost, and has the advantages of excellent electrochemical properties and mechanical performance compared to commercial membranes.

Claims (6)

A polymerization solution containing vinylbenzyl chloride, a swelling accelerator monomer, divinylbenzene and a photoinitiator is absorbed into a nonporous low density polyethylene film, photopolymerized by irradiating UV light at room temperature, and then subjected to a quaternary amination reaction to an amine group as an anion exchanger. Method for producing a polyethylene / polyvinyl benzyl chloride anion exchange membrane, characterized in that the introduction. The method of claim 1, wherein the polymerization solution contains 70 to 95% by weight of vinylbenzyl chloride, 5 to 30% by weight of swelling accelerator monomer, and 1 to 5% by weight of divinylbenzene. A method for producing a polyethylene / polyvinylbenzyl chloride anion exchange membrane, characterized by containing 1 to 10 parts by weight of a photoinitiator. The method of claim 1, wherein the swelling-promoting monomer is selected from styrene, 2-vinyl pyridium and 4-vinyl pyridium. The method of claim 1, wherein the photoinitiator 1,2-diphenyl ethanedione (1,2-diphenyl ethanedione), benzophenone (Benzophenone), benzyl dimethyl ketal, hydroxydimethylacetophenone (Hydroxy dimethyl acetophenone) ) And α-hydroxycyclohexyl phenyl methaneone. A method for producing polyethylene / polyvinylbenzyl chloride anion exchange membrane, characterized in that the selected. The method of claim 1, wherein the ultraviolet irradiation time is 10 to 60 minutes. The method of claim 1, wherein the anion exchanger is selected from trimethyl amine, triethyl amine, diethyl phenyl amine and diphenyl ethyl amine. Method for producing a polyethylene / polyvinyl benzyl chloride anion exchange membrane.

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