KR20040013627A - Preparation method of Polyethylene/Polystyrene cation-exchange membrane - Google Patents

Abstract

PURPOSE: A method for preparing a polyethylene/polystyrene cation exchange membrane is provided, to improve the ion permeation selectivity without the addition of a chemical crosslinking agent. CONSTITUTION: The method comprises the steps of depositing a nonporous low density polyethylene film in a polymerization solution containing styrene and a photoinitiator to swell the polyethylene film; irradiating the swollen polyethylene film with the UV ray at a room temperature for 35-100 min to polymerize it; and introducing a sulfonate group (SO3-) as a cation exchange group by sulfonation. Preferably the photoinitiator is selected from the group consisting of 1,2-diphenylethanedione, benzophenone, benzyl dimethyl ketal, hydroxydimethyl acetophone and α-hydroxydicyclohexyl phenyl methanone, and the content is 0.01-0.1 parts by weight based on 1 parts by weight of styrene.

Description

Preparation method of polyethylene / polystyrene cation exchange membrane {Preparation method of Polyethylene / Polystyrene cation-exchange membrane}

The present invention relates to a method for producing a polyethylene / polystyrene cation exchange membrane, and more particularly, to improve the conventional paste method and monomer absorption method by absorbing styrene and photoinitiator in a non-porous low density polyethylene (PE) film, after irradiation by copolymerizing, by performing a sulfonation reaction sulfonic acid group (-SO ₃ ^-) in the strongly acidic cation exchanger to increase the ion transmission excellent selectivity without the addition of a chemical cross-linker by performing the relatively simple manufacturing process for introducing the reduction of manufacturing cost It relates to a method for producing a cation exchange membrane that can be.

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 (-NR 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 etc. are mentioned. In particular, as the demand for ion exchange membranes as polymer electrolyte fuel cells expands in recent years, interest in ion exchange membranes has increased. In general, commercial membranes should have high ion selective permeability (> 0.95-0.98), low electrical resistance (<3.0-4.0 Ω · cm 2), adequate water content, high mechanical strength and chemical resistance.

Existing commercial membranes, for example, Neosepta ^trademark (Tokuyama Co. Ltd., Japan), Selemion ^trademark (Asahi Glass Company, Japan), etc. as a base material is a copolymer of styrene-divinylbenzene or styrene-butadiene The ion exchange membrane was prepared by using the copolymerization process of the bulk polymerization method, the latex method, and the 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 styrene-divinylbenzene is polymerized alone, a plasticizer should be used because the brittleness is increased and mechanical properties are deteriorated. Furthermore, in order to obtain a thin film, a constant container is required, which increases the overall manufacturing cost of the film. Becomes

In the latex method, a latex of styrene-butadiene copolymer is dipped on a support and dried to form a base film through crosslinking using an oxidative crosslinking method. Ion exchange groups are introduced into the base membrane through sulfonation, chloromethylation, and quaternary amination reactions.The method is based on the mechanical and electrochemical properties of the membranes due to the emulsifiers remaining in the latex of the styrene-butadiene polymer. It is very likely to cause poor performance.

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 styrene-divinylbenzene monomer to obtain a paste. In order to obtain physical properties, a plasticizer must be added. This complexity in the manufacturing process acts as a factor to increase the manufacturing cost of the film.

In order to improve this problem, the inventors of the present invention invented in Korean Patent Application No. 2001-75488 prepared a monomer solution containing an initiator, and then adsorbed to a porous film to polymerize at a predetermined temperature and react the membrane structure with time. A method of preparing a cation exchange membrane by a monomer absorption method of a new concept that can control desired selectivity and mechanical properties by controlling. This method has the advantage that the ion exchange membrane can be prepared by a relatively simple manufacturing process compared to the conventional paste method, but chemical crosslinking agent must be added to improve the selectivity to the solute of the membrane.

Accordingly, the present invention seeks to develop a new concept of film production process that does not degrade the performance of the membrane and a new type of production process capable of crosslinking without the addition of a chemical crosslinking agent.

As described above, the inventors of the present invention have a simpler manufacturing process than the conventional paste method and the monomer absorption method, thereby reducing manufacturing costs, and attempting to develop a film manufacturing process having superior electrochemical characteristics and mechanical performance as compared to commercial membranes. As a result, the conventional paste method and monomer absorption method have been improved to absorb styrene and photoinitiator into a nonporous low density polyethylene film which exhibits both monomer absorbency and photocrosslinkability properties. strong adult sulfonyl group (-SO ₃ ^-) in the exchange by introducing contrast to conventional monomers absorption method and developed a process for the production of chemical cross-linking agent it is not needed the cation exchange membrane.

1 is a manufacturing process diagram of the PE / polystyrene cation exchange membrane of the present invention.

2 is a graph showing the change in polymerization amount according to the UV irradiation time of the PE / polystyrene cation exchange membrane of the present invention.

Figure 3 is a graph of the change in membrane resistance and ion exchange capacity according to the polymerization amount of the PE / polystyrene cation exchange membrane of the present invention.

4 is a graph showing the relationship between the water content and the ion exchange capacity according to the polymerization amount of the PE / polystyrene cation exchange membrane of the present invention.

5 is a graph comparing the PE / polystyrene cation exchange membrane and the commercial cation exchange membrane (CMX, Tokuyama Corp., Japan) voltage-current curve of the present invention.

According to the present invention, after dipping and swelling a non-porous low density polyethylene film in a polymerization solution including styrene and a photoinitiator, the swelled low density polyethylene film is irradiated for 35 to 100 minutes at room temperature, and then photopolymerized through a sulfonation reaction. and the introduction of a manufacturing method of polyethylene / polystyrene cation exchange membrane according to the ^{feature-sulfonic} acid group (-SO ₃₎ by a cation exchanger.

Referring to the present invention in more detail as follows.

The present invention uses a non-porous low density polyethylene film that exhibits the properties of monomer absorption and photocrosslinkability, which replaces the conventional photodegradable non-porous PVC film as a support, absorbs the monomer and the photoinitiator, and then polymerizes and sulfonates by irradiating with ultraviolet rays. Since the introduction of ionic groups through the reaction, it does not use a paste unlike the conventional paste method, and at the same time combines the monomer absorption method and the ultraviolet polymerization method, which shows the characteristics of the high ion permeability selective membrane without the addition of a chemical crosslinking agent, unlike the conventional monomer absorption method. A method for producing a cation exchange membrane.

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 onto a PVC cloth, and then It is a method of introducing an ion exchange group by copolymerizing at a temperature of. Neosepta ^registered ion exchange membrane (Tokuyama Co. Ltd.), which occupies many markets worldwide, is a membrane produced through such a process, and its performance is reported to be relatively excellent. However, since this paste method requires the use of a plasticizer and PVC powder to improve the mechanical strength, the manufacturing cost increases. On the other hand, the recently reported monomer absorption method has the advantage of not using a paste, which has the advantage of reducing the manufacturing cost by simplifying the manufacturing process, but in order to improve the permeation selectivity, Vinylbenzene) has been added.

On the contrary, in the present invention, the method of manufacturing the cation exchange membrane of the present invention is the same as that of the monomer absorption method in that styrene is absorbed into the support of the non-porous film to polymerize the monomer present in the free volume of the support film. Unlike the monomer absorption method, a photoinitiator is used instead of the thermal polymerization initiator as an initiator, and is characterized by polymerizing monomers present in the free volume by irradiating ultraviolet rays. 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 is formed It is done. Therefore, the selective permeability can be improved by the crosslinking reaction during the polymerization process without the need to improve the selective permeability through the addition of a chemical crosslinking agent used in the conventional paste method or monomer absorption method. . Moreover, the non-porous support used at this time is characterized by using a low density polyethylene, a photocrosslinkable polymer instead of the conventional photodegradable polyvinyl chloride (PVC) to enhance the mechanical strength.

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

First, a solution for polymerization is prepared. Styrene, a monomer, contains a large amount of 4-t-butylcatechol (TBC), a polymerization inhibitor, and is mixed with 6.0 N sodium hydroxide (NaOH) solution at a ratio of 10: 1 and separated by a separating funnel. . This process is repeated until the color of the NaOH solution phase does not change. Photoinitiators were used without further purification and other reagents were also used without further purification.

The polymerization solution contains 0.01 to 0.1 parts by weight of the photoinitiator based on 1 part by weight of styrene. As the photoinitiator, 1,2-diphenyl ethanedione, 1.2-diphenyl ethanedione, benzophenone, benzil dimethyl ketal, hydroxyl dimethyl acetophone or α-hydroxycyclo Hexyl phenylmethanone (α-hydroxy cyclohexyl phenyl methaneone) and the like can be used. If the amount of the photoinitiator is less than 0.01 parts by weight, the molecular weight can be increased, but the polymerization rate is very slow, so long time ultraviolet irradiation is required, resulting in a decrease in mechanical properties (increased brittleness) due to excessive crosslinking reaction. . On the contrary, if the amount of the photoinitiator exceeds 0.1 parts by weight, the polymerization rate is increased, but due to the formation of low molecular weight with the influence of the remaining photoinitiator, the mechanical properties and the electrochemical properties are reduced.

Next, a nonporous low density polystyrene film is dipped in the polymerization solution to swell. As the support, a support that is swelled in the vinyl monomer and is not decomposed by ultraviolet rays can be used. 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 the mechanical property is remarkably deteriorated because decomposition occurs during ultraviolet irradiation. Therefore, the present invention is characterized by using a non-porous low-density polyethylene as a support that swells in the vinyl monomer and can induce crosslinking upon ultraviolet irradiation. As described above, the non-porous low density polyethylene film used as a support in the present invention is a low density polyethylene film having a weight average molecular weight of about 35,000 g / mol. As mentioned above, it is good to use a density of 0.906-0.930g / cm <^3> and 40-50% of crystallinity.

The monomer and the initiator are allowed to stand at room temperature for 0.5 to 8 hours, preferably 1 to 6 hours, so that the monomer and the initiator are sufficiently sorbed to the low density polyethylene to reach an equilibrium state. Low-density polyethylene, sorbed and at 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. The two glass plates are sealed with tape to prevent the monomer from spilling during polymerization. This is placed in an ultraviolet polymerization apparatus to which a 400W mercury ultraviolet lamp (wavelength of 150 to 400 nm) is attached and irradiated with ultraviolet rays to polymerize. At this time, the distance from the ultraviolet light is maintained at 10 to 50 cm. If the distance is less than 10 cm, deformation of the sample occurs due to heat generation from ultraviolet light. If the distance exceeds 50 cm, the adsorbed monomers do not polymerize on the low density polyethylene due to the 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 preferably 35 to 100 minutes, more preferably 40 to 70 minutes. If the UV irradiation time is less than 35 minutes, the polymerization is incompletely formed. On the contrary, if the UV irradiation time exceeds 100 minutes, excessive polymer formation causes 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. Leave at room temperature for at least one day to remove this unreacted monomer.

A 1: 1 mixture of 97% chlorosulfonic acid and 98% sulfuric acid is then prepared for the sulfonation reaction. The base membrane prepared in the polymerization step is then deposited in this solution and sulfonated for 10 to 200 minutes, preferably 30 to 150 minutes, at a temperature of 40 to 60 ° C. 10 to 200 minutes in 98% sulfuric acid, preferably 30 to 100 minutes, 10 to 100 minutes in 40% sulfuric acid, preferably 20 to 50 minutes, and finally to remove byproducts generated in the sulfonation process. Wash several times in ultrapure water. In order to completely convert the sulfonic acid remaining in the membrane into the form of sodium sulfonate, the reaction is carried out in an aqueous solution of 1-5N NaOH for 1-5 hours. After washing sufficiently in ultrapure water, it is stored in 0.5N NaCl aqueous solution.

In addition, water content, ion exchange capacity, electrical resistance, etc., which are typical methods for characterizing an ion exchange membrane, were measured, and it was confirmed that the membrane was successfully manufactured using FT-IR. In addition, transport numbers and IV (current-voltage) curves for cations (Na ⁺ ) were measured to measure ion selectivity of the prepared membranes.

The cation exchange membrane prepared through the preparation method of the present invention exhibits low electrical resistance (<1 Ωcm ² ) and high ion selectivity (about 0.98 or more of transport water for Na ⁺ ions) and at the same time excellent mechanical strength (tensile strength: 203.2 kgf). / cm ² ) was superior to the conventional commercial cation exchange membrane CMX cation exchange membrane (Tokuyama Corp., Japan).

As described above, the present invention utilizes the property that the non-porous low density polyethylene film swells in the monomer solution without using a paste, and improves the permeability without adding a chemical crosslinking agent by using a low density polyethylene film for optical crosslinking as a support. A homogeneous cation exchange membrane was developed. In addition, the manufacturing process can reduce the manufacturing cost because the paste process in the paste method can be omitted by partially using the recently developed monomer absorption method.

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

Example 1 and Comparative Examples 1-2

The polymerization solution was prepared by adding 0.06 parts by weight of benzophenone (BP) as a photoinitiator to 1 part by weight of styrene monomer. 0.3 parts by weight of a non-porous low density polyethylene film (LDPE, Daehan Co., Ltd., 60 μm thick) was immersed in a solution for polymerization at room temperature for 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. This was 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 irradiation time of the ultraviolet ray was 20 minutes (Comparative Example 1), 30 minutes (Comparative Example 2), and 40 minutes (implementation). As Example 1), polymerization was carried out. When the polymerization was completed, it was separated from the glass plate and left for one day to remove the unreacted monomer.

In order to introduce a cation exchanger into the base membrane prepared by the polymerization reaction, it was immersed in a 1: 1 mixed solution of 97% chlorosulfonic acid and 98% sulfuric acid and sulfonated at 50 ° C. for 120 minutes. When the sulfonation reaction was completed, to remove the by-products generated in the sulfonation process was left for 30 minutes in 98% sulfuric acid, 30 minutes in 40% sulfuric acid, and finally washed sequentially in ultrapure water for 30 minutes. Then, in order to completely convert the sulfonic acid remaining in the membrane into the form of sodium sulfonate, it was immersed in a 2M aqueous NaOH solution for 2 hours, washed sufficiently in ultrapure water and stored in a 0.5M aqueous NaCl solution.

Characterization of each of the membranes prepared by the above method 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], and the results are shown in Table 1 below.

[Measurement Method of Membrane]

(1) Water content: The difference between the wet weight of the membrane and the weight difference after drying for 24 hours in an oven at 60 ° C. was calculated by dividing the weight after drying.

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

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

(4) Transport water and I-V curve: 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, and the IV curve (Fig. 5) using the same cell. The voltage difference across the membrane was measured while increasing the current density, and 0.025M NaCl aqueous solution was used as the electrolyte.

Type of membrane Water content Ion exchange capacity [meq./g-dry mem.] Membrane Resistance [Ω · cm ² ] Na ⁺ Transports Comparative Example 1 0.35 0.65 200 - Comparative Example 2 0.45 0.98 20 0.990 Example 1 0.90 1.80 0.96 0.992 Commercial Membrane [CMX, Tokuyama co.] 0.45 1.60 3.00 0.980

As shown in Table 1, in Example 1 according to the present invention shows that the electrochemical properties are equivalent to or better than CMX (Tokuyama co., Japan) commercial membrane.

Figure 2 is a graph showing the change in polymerization amount according to the ultraviolet irradiation time of the cation exchange membrane of the present invention, shows the polymerization behavior through the polymerization fraction on the low density polyethylene according to Example 1 and Comparative Examples 1 and 2. Here, the polymerization fraction is evaluated by the weight part of the polystyrene polymerized with respect to 1 weight part of low density polyethylene as a support, and is defined by the following formula.

Wr = [Wps / Wpe]

Where Wr: polymerization fraction, Wps: weight of polymerized polystyrene (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.

FIG. 3 shows the relationship between the ion exchange capacity and the membrane resistance as a function of the polymerization fraction according to Example 1 and Comparative Examples 1 to 2. FIG. Increasing the polymerization fraction shows that the desired ion exchange membrane can be prepared by increasing the ion exchange capacity and decreasing the membrane resistance, thereby leading to an increase in the polymerization fraction.

4 shows the relationship between the ion-exchange amount and the water content rate using the polymerization fraction according to Example 1 and Comparative Examples 1 to 2 as a function. The increase in the polymerization fraction means that polystyrene is increased on the LDPE, which means that a large amount of ion exchange groups can be introduced through sulfonation. Therefore, the membrane into which the ion exchanger introduced in a large amount is superior in the hydration ability compared to the membrane into which a small amount of the ion exchanger is introduced, thus showing an increase in water content.

5 is a graph comparing voltage-current curves using the cation exchange membrane of Example 1 and a commercial membrane (CMX, Tokuyama Co., Japan). As shown in this graph, the electrical resistance of the commercial membrane is lower in all areas. That is, the voltage-current slope in the ohmic region (below the limit current density) shows that the film resistance of the present invention is larger than that of the commercial film, so that the film resistance is small with respect to the applied current. This low and somewhat high limit current demonstrates that the ion exchange groups are more uniformly distributed on the surface of the ion exchange membrane of the present invention than in the commercial membrane.

As described above, the present invention utilizes the property that the non-porous low density polyethylene film swells in the monomer solution without using a paste, and performs UV polymerization using an ultraviolet crosslinked support, thereby providing high ion permeability without adding a chemical crosslinking agent. By producing a cation exchange membrane, the manufacturing process is simpler than the conventional paste method and the monomer absorption method, the manufacturing cost can be reduced, and the electrochemical properties and mechanical performance is superior to the commercial membrane.

Claims (3)

After dipping and swelling a non-porous low density polyethylene film in a polymerization solution including styrene and a photoinitiator, the swelled low density polyethylene film was irradiated for 35 to 100 minutes at room temperature and photopolymerized, followed by a sulfonation reaction to a cation exchanger. sulfonic acid group (-SO ₃ ^-) the introduction method of producing a polyethylene / polystyrene cation exchange membrane characterized in that. The polyethylene / polystyrene cation according to claim 1, wherein the photoinitiator is selected from 1,2-diphenyl ethanedione, benzophenone, benzyldimethyl ketal, hydroxyldimethylacetophone and α-hydroxycyclohexylphenylmethanone. Method of producing an exchange membrane. The method according to claim 1, wherein the photoinitiator is contained in an amount of 0.01 to 0.1 parts by weight based on 1 part by weight of styrene.