CN108067101B

CN108067101B - Method for manufacturing cation exchange alloy membrane

Info

Publication number: CN108067101B
Application number: CN201710878385.5A
Authority: CN
Inventors: 雷引林; 李南文; 卿波
Original assignee: Quzhou Lanran New Material Co ltd
Current assignee: Quzhou Lanran New Material Co ltd
Priority date: 2017-09-26
Filing date: 2017-09-26
Publication date: 2020-12-01
Anticipated expiration: 2037-09-26
Also published as: CN108067101A

Abstract

A method of making a cation exchange alloy membrane is described. Firstly, thermoplastic polyethylene-sulfonated polystyrene strong acid cation exchange resin powder, non-thermoplastic micron-sized weak acid cation exchange resin powder (or non-thermoplastic micron-sized weak base anion exchange resin powder), polyethylene powder and polyisobutylene powder are mixed, and then the mixture is subjected to banburying, open milling and sheet discharging, continuous rolling, cooling and cutting to obtain a single prefabricated membrane; and finally, clamping a piece of reinforcing mesh cloth by using two prefabricated membranes, and carrying out hot pressing to obtain the cation exchange alloy membrane product. The surface of the membrane is smooth, and the anti-pollution capability is strong; the thermoplasticity component and the non-thermoplasticity component form a star-shaped hollow polymer alloy structure, and the film resistance is low; the enhanced mesh cloth limits the swelling of the membrane in strong acid or strong alkaline solution, and the internal structure is compact. Is particularly suitable for electrodialysis application occasions under the environment of strong acid or strong alkaline solution.

Description

Method for manufacturing cation exchange alloy membrane

Technical Field

The invention belongs to the technical field of functional polymer film processing, and particularly relates to a method for manufacturing a cation exchange membrane, wherein a reinforcing mesh cloth is inlaid in the middle of the cation exchange membrane, and a main membrane material is of a starry sky type polymer alloy structure, so that the cation exchange membrane can meet the requirement of a long-term electrodialysis unit in a strong acid and strong alkali solution environment.

Background

The ion exchange membrane is widely applied to occasions of brackish water desalination, seawater concentration salt making, food special separation and desalination, industrial wastewater desalination, acid/alkali recovery and the like based on an electrodialysis technology. Previously, heterogeneous membranes were produced by mixing non-thermoplastic ion exchange resin powder with binders such as polyethylene and pressing the surface with a reinforcing mesh, because the production process was simple and the price was very low, they have been widely used in engineering. However, the ion exchange heterogeneous membrane has a loose structure and poor performance, and particularly the limit concentration of salt concentration is not high enough, such as the limit concentration of seawater concentration is not more than 12-14%. Therefore, a great deal of improvement has been made in the film-forming process of heterogeneous films. In particular, the chinese invention patent (application No. 201510570174.6) discloses a method for manufacturing a semi-homogeneous cation exchange membrane, which introduces a thermoplastic polyethylene-sulfonated polystyrene based strong acid cation exchange composite resin powder component, and provides a four-roll calendering process capable of continuously discharging the membrane, thereby not only improving the membrane structure, remarkably reducing the membrane surface resistance, and greatly improving the concentration performance (for example, the limit concentration for seawater concentration can reach 16-18%), but also remarkably improving the production efficiency and the product precision (for example, the thickness, the flatness, the smoothness, and the like).

However, the semi-homogeneous cation exchange membrane is still blended with a high proportion of non-thermoplastic strong acid cation exchange resin powder (the mass percentage can reach 40 percent), and the particle size is still too large (usually only can reach 200-300 meshes, and about 50-75 microns). This results in that under a strongly acidic or strongly alkaline solution environment, the strongly acidic resin powder having a large particle size is rapidly swollen or shrunk (specifically, swollen in a strongly acidic solution and shrunk in a strongly alkaline solution), and in a severe case, instantaneous disintegration of the film structure is caused. During the use process of repeatedly switching the environment of the long-term 'acid-base-salt' solution, phase separation occurs among the components of the membrane material due to the sharp 'swelling-shrinking' behavior, so that the compactness of the membrane structure is reduced and the concentration effect is reduced. Meanwhile, as with heterogeneous films, the semi-homogeneous film also adopts a method of respectively hot-pressing an upper surface and a lower surface into a thin mesh (generally adopting a polyester mesh with a thickness of 0.09-0.11 mm). The enhancement effect of the mesh cloth is not enough, and the swelling behavior of the membrane in the environment of strong acid or strong alkali solution is difficult to be really limited; on the other hand, the surface of the membrane is not smooth due to the clamping net on the surface, so that pollutants are easy to adhere to the membrane, and the anti-pollution capacity of the membrane is obviously reduced. The result is: such semi-homogeneous membranes, like heterogeneous membranes, are also difficult to use in strongly acidic and strongly basic environments for long periods of time, and in particular cannot be used for the removal or concentration of strong acids (e.g. hydrochloric acid) and strong bases (e.g. sodium hydroxide) after being placed in an electrodialysis stack for a long period of time.

Disclosure of Invention

The invention aims to remarkably improve the structural defects of a heterogeneous cation exchange membrane or a semi-homogeneous cation exchange membrane, and provides a method for manufacturing a cation exchange alloy membrane which has better compatibility of various membrane forming components and more reasonable membrane structure and can be filled into an electrodialysis set for long-term use in a strong acid and strong base solution environment on the premise of not remarkably increasing the cost of raw materials.

The purpose of the invention is realized by the following technical scheme: a method for producing a cation exchange alloy membrane, comprising the steps of: 1) uniformly mixing thermoplastic polyethylene-sulfonated polystyrene strong-acid cation exchange resin powder, non-thermoplastic micron-sized weak-acid cation exchange resin powder (or non-thermoplastic micron-sized weak-base anion exchange resin powder), polyethylene powder and polyisobutylene powder; 2) carrying out banburying, sheet discharging by a two-roll open mill, continuous calendering by a four-roll calender, cooling and cutting on the mixture in sequence to obtain a single prefabricated diaphragm; 3) and clamping a piece of reinforcing mesh cloth by using two prefabricated membranes, and carrying out hot-pressing fusion and cooling annealing by using a hot press to obtain the cation exchange alloy membrane product.

Significant improvements are made and specific benefits are achieved over heterogeneous or semi-homogeneous membranes. Firstly, only a small amount of non-thermoplastic micron-sized weak acidic cation exchange resin powder (or non-thermoplastic micron-sized weak basic anion exchange resin powder) is doped to replace a large amount of non-thermoplastic large-particle-size strong acidic cation exchange resin powder adopted in a heterogeneous membrane or a semi-homogeneous membrane, so that the sea-island structure of the main membrane materials of the two latter materials (the large-particle-size strong acidic resin powder can be regarded as an island, and the other thermoplastic components surrounded by the large-particle-size strong acidic resin powder can be regarded as a sea) is improved into the star-hollow structure required by the alloy membrane (the non-thermoplastic micron-sized resin powder can be regarded as a 'dotted star', and the other thermoplastic components can be regarded as 'hollow'); and the swelling degree of the micron-sized resin powder in an acid/alkali solution environment is further limited by controlling the appropriate exchange capacity of the micron-sized resin powder (rather than the highest exchange capacity as much as possible). This leads to a clear transformation of the membrane structure and a significant improvement of the swelling resistance by targeted changes of the group type (weak acid and weak base), group content (ion exchange capacity) and particle size of the non-thermoplasticable resin. Secondly, by optimizing the formula, the content of the resin powder which is not thermoplastic is reduced (the cation exchange capacity is reduced), the content of the thermoplastic polyethylene-sulfonated polystyrene strong-acid cation exchange resin powder is correspondingly increased (the cation exchange capacity is increased again), and the plasticity, the flexibility and the flatness of the prefabricated film obtained after the four-roll calendering are improved. Therefore, even if the net cloth is not required to be reinforced, the prefabricated film piece does not swell excessively in an acid/alkali solution environment to cause structural disintegration, and the surface is kept smooth and the film piece is kept flat all the time. Thirdly, two prefabricated membranes are embedded with a thicker reinforcing mesh cloth in a hot-pressing mode to replace a method for covering two thinner mesh cloths on the surface in a hot-pressing mode, wherein the method is adopted by heterogeneous membranes and semi-homogeneous membranes, so that the reinforcing effect of the reinforcing mesh cloth can be exerted to the maximum extent, meanwhile, the corrosion effect of acid/alkali treatment liquid in engineering application on the mesh cloth on the membrane surface can be greatly relieved, and the swelling degree of the membranes in an acid/alkali solution environment is limited to the greatest extent. The final definite effect is that the tolerance of the membrane to strong acid and strong alkali solution environment is obviously improved, so that the membrane can be applied to the electrodialysis removal or concentration process of strong acid or strong alkali for a long time.

Detailed Description

The method for manufacturing the cation exchange alloy membrane comprises the following 3 steps:

1) thermoplastic polyethylene-sulfonated polystyrene strong acid cation exchange resin powder, non-thermoplastic micron weak acid cation exchange resin powder (or non-thermoplastic micron weak base anion exchange resin powder), polyethylene powder and polyisobutylene powder are mixed uniformly.

The thermoplastic polyethylene-sulfonated polystyrene strong-acid cation exchange resin powder (hereinafter referred to as strong-acid resin powder) simultaneously contains a thermoplastic inert polyethylene component and a sulfonated polystyrene strong-acid cation exchange polymer component. During banburying melt blending, the polyethylene component in the mixture can partially overflow to be bonded with the polyethylene powder component and the polyisobutylene powder component which are added later; the sulfonated polystyrene component is partially compatible with the non-thermoplastically weak acidic micro cation exchange resin powder added later or more compatible with the non-thermoplastically weak alkaline micro anion exchange resin powder through acid-base charge attraction. That is, the thermoplastic strong acid resin powder can bond and fuse the rest components together, thereby ensuring that the sulfonic acid group which plays the main cation exchange function can be uninterruptedly connected in the membrane to form a space in the structure of a star-space type high molecular alloy. The strong acid resin powder is obtained by impregnating low-density polyethylene powder into a styrene polymer oil phase, and then carrying out suspension polymerization, sulfonation and pulverization, and the specific production method and the required use specifications (including particle size, exchange capacity, contents of each component and the like) can be in accordance with those described in the literature (chinese patent application No. 201510570174.6).

The nonformable micron-sized weakly acidic cation exchange resin powder (hereinafter, referred to as weakly acidic resin powder) may be obtained by pulverizing commercially available acrylic weakly acidic cation exchange resin, or may be obtained by pulverizing phenolic weakly acidic cation exchange resin, or by mixing these two resins in an arbitrary mass ratio and then pulverizing them. And, a wet resin of sodium type (not hydrogen type) is used, dried and then pulverized. It is well known that hydrogen-type resins are significantly less resistant to high temperatures than the sodium-type, and therefore are likely to be difficult to meet the high temperature requirements for thermoplastic processing. In general, a gel type resin, such as an acrylic weak acid resin type 110, or a phenolic weak acid resin type 122; porous resins such as acrylic weak acid resin of type D110; however, the gel type is preferably used in order to avoid the porous resin from having a pore structure (which remains partially after pulverization) that results in an insufficiently dense film product. The weakly acidic cation exchange sodium type resin used for the pulverization has a cation exchange capacity of 3 to 10mmol/g dry basis, preferably 4 to 7mmol/g dry basis. In general, the exchange capacity of a commercially available weak acid acrylic resin is relatively high (up to 10mmol/g dry basis) and the volume expansion rate of a high exchange capacity weak acid resin is also high (the percentage of volume expansion when switching from the sodium type to the hydrogen type), which results in a large volume change of the alloy film product when switching between acid/base solution environments. If the exchange capacity is too low (for example, less than 3mmol/g dry basis), the ion exchange capacity of the weak acid resin is not sufficiently exhibited, and the ion exchange capacity of the whole membrane is insufficient, so that the membrane surface resistance significantly increases. It is pointed out that in the strong alkaline solution environment, weak acid groups can play a better role in ion exchange; under the acidic environment, the ion exchange effect of weak acid groups is greatly weakened. However, the degree of swelling-shrinking of a weak acid resin with a moderate exchange capacity (as described above) is much less than that of a strong acid resin with a high exchange capacity (as used in cation exchange heterogeneous membranes and cation exchange semi-homogeneous membranes), whether in a strongly acidic or strongly basic solution environment. Meanwhile, the ion-exchange membrane has significantly higher ion conductivity in an acid/alkali solution environment than that in a salt solution (because of significant difference in migration rate between hydrogen ions and sodium ions and between hydroxide ions and chloride ions). Therefore, the cation exchange membrane doped with micron-sized weak acid resin powder has membrane surface resistance which is not too high in strong acid and strong alkaline solution environments (but is obviously higher in salt solution), so that the requirement of operating current density in electrodialysis application can be met. Nevertheless, the cation exchange alloy membrane incorporating micron-sized weak acid resin powder should be more suitable for use in a strongly alkaline environment (rather than a strongly acidic environment because the membrane is less swollen and has higher ion conductivity), such as the recovery of sodium hydroxide from alkaline waste streams using electrodialysis techniques.

The non-thermoplastic micron-sized weak base anion exchange resin powder (hereinafter referred to as weak base resin powder) can be obtained by crushing commercially available styrene system weak base anion exchange resin, can also be obtained by crushing epoxy system weak base anion exchange resin, or can be obtained by crushing acrylic system weak base anion exchange resin, and is obtained by mixing and crushing the three resins according to any mass ratio. And the resin is prepared by drying and crushing wet resin of chlorine type (instead of hydrogen-oxygen type). It is known that the high temperature resistance of the oxyhydrogen type resin is significantly inferior to that of the chlorine type. In general, a gel type resin such as an epoxy type weak base resin of type 335 or a styrene type weak base resin of type 301; porous resins such as acrylic weak base resins of type D315; but preferably of the gel type. The weak base anion exchange chlorine type resin used for grinding has an ion exchange capacity of 3 to 10mmol/g dry basis, preferably 4 to 8mmol/g dry basis. In general, the transition volume expansion ratio (percent volume expansion when switching from the chlorine to the hydrogen oxygen) of a weakly basic anion exchange resin is slightly less than that of a weakly acidic cation exchange resin of the same degree of crosslinking and exchange capacity. Particularly, the exchange capacity of the commercially available acrylic weak base resin is relatively high (up to more than 9mmol/g dry basis), and at this time, customization may be needed, namely, a product with the exchange capacity adjusted to be low (such as 4-8 mmol/g dry basis) is selected to avoid the transformation volume expansion rate of the resin powder from being too large. The transformation volume expansion rate of the non-thermoplasticity weak acid cation exchange resin (or non-thermoplasticity weak base anion exchange resin) used should be controlled below 30% in order not to affect the compactness of the alloy film product. Furthermore, the transformation volume expansion rate of the resin needs to be controlled to meet the requirements by customizing technical indexes of a framework system (acrylic, epoxy, styrene, phenolic aldehyde and the like), group types (weak acid and weak base), a crosslinking degree, ion exchange capacity and the like of the resin. It is also noted that weak base groups can exert a good ion exchange effect in a strongly acidic solution environment, but much less in a basic environment. However, the swelling-shrinking degree of the weak base resin with moderate exchange capacity (as mentioned above) is far smaller than that of the strong acid resin with high exchange capacity (as used in cation exchange heterogeneous membrane and cation exchange semi-homogeneous membrane) under the environment of strong acid or strong alkaline solution. Even if the exchange capacity of the cation exchange membrane is reduced by adding the weak base resin powder, the influence is not obvious as long as the adding amount is not large (for example, less than 10 percent), so that the surface resistance of the prepared membrane product is not too high in the strong acid or strong base solution environment. It should be noted that the cation exchange alloy membrane product incorporating the micron-sized weak base resin powder (rather than the micron-sized weak base resin powder) is more suitable for the strongly acidic environment (rather than the strongly basic environment because the weak base groups carried by the micron-sized resin powder can accelerate the electrically driven conduction of hydrogen ions due to hydrogen bonding), such as the recovery of strong acids such as hydrochloric acid, sulfuric acid or nitric acid from acidic waste liquid by electrodialysis technology.

The weakly acidic cation exchange resin (or weakly basic anion exchange resin) needs to be converted into a sodium type (or a chlorine type) and then dried, and the water content is lower than 2 percent, otherwise, the resin has too strong toughness and insufficient rigidity and is difficult to completely crush. The dried resin can be pulverized to below 100 mesh (150 micron) by an air flow pulverizing method, and then loaded into a ball mill for grinding for 3-8 hours. As long as the loading is appropriate, it is ensured that the particle size after comminution is substantially satisfactory, i.e. that more than 99% of the number of particles have a particle size of less than 3 microns (as measured by laser granulometry). Repeated experiments have proved that the grinding effect of the resin is better by using a ball mill method than by using a jet mill method or a freezing mill method. In most cases, the pulverization requirement can be directly achieved without laborious and time-consuming sieving (a 5000-mesh sieve is required). Only when the particle size of the micron-sized resin powder meets the requirement, a star-hollow type high molecular alloy structure like 'a point is numerous and a sky is full' can be formed macroscopically, so that the micron-sized powder is equivalent to 'star'. Therefore, the particle size requirement for comminution is of crucial importance.

The polyethylene powder is prepared by crushing low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE) or a mixture of the LDPE and the LLDPE. The polyisobutylene powder is B200 (produced by BASF corporation). The specification requirements of both materials can be in accordance with the literature (Chinese patent application No. 201510570174.6).

The mixture ratio of the four components is proper to obtain the star hollow polymer alloy film product. The preferable mixture ratio of the four is as follows: 100 parts of thermoplastic polyethylene-sulfonated polystyrene strong acid cation exchange resin powder, 5-20 parts of non-thermoplastic micron weak acid cation exchange resin powder (or non-thermoplastic micron weak base anion exchange resin powder), 10-25 parts of polyethylene powder and 0-10 parts of polyisobutylene powder. In the composition proportion of the semi-homogeneous cation exchange membrane, the addition amount of the non-thermoplastic strong acid resin powder is maximum (generally more than 40%); in the composition of the cation exchange alloy film described in this patent application, the thermoplastic strong acid resin powder is mainly (generally more than 60%) to play the main role of its thermoplastic film. This also indicates that, in the case of cation-exchange membranes, the strongly acidic sulfonic acid groups are still responsible for the main ion-exchange (electrically driven conduction) action, since otherwise the membrane surface resistance increases dramatically. The addition of a small amount of weak acid resin powder objectively plays a role in making up the cation exchange capacity of the membrane as a whole (particularly in a strongly alkaline solution), and mainly aims at utilizing the characteristic of less swelling of the weak acid resin. If the addition amount is too small, the definite effect of improvement cannot be achieved; if added too much, the exchange capacity of the membrane is significantly reduced. On the other hand, the amount of the weak base resin powder is usually less than the amount of the weak base resin powder, which would reduce the cation exchange capacity of the alloy film product (because the weak base groups form "ion pairs" with the strong acid groups). That is, whether the incorporated non-thermoplastic micron-sized particles are weak acid resin powder or weak base resin powder, it should exert a "positive effect" (e.g., decrease in volume expansion ratio to improve swelling property of the film) while limiting a "side effect" (e.g., decrease in ion exchange capacity), and therefore the content must be appropriate; and repeated tests prove that the addition amount of 5-20 parts is suitable. The polyethylene powder is added to improve the cohesiveness and compactness among membrane components; if only the thermoplastic strong acid resin powder is used, it is not sufficient to bond together the non-thermoplastic micron-sized resin powder by banburying, but only the latter is loosely embedded therein. However, if too much inert polyethylene powder is added, the powder will be "noisy", which causes the poor plasticity of the strong acid resin powder, and the strong acid resin powder will not exert its plasticity, and phase separation will occur during the thermoplastic process, i.e. it is difficult to form the effect of uniformly distributing sulfonic acid groups on the film matrix, and the opposite is true. The polyisobutylene powder is added to improve the toughness of the rolled sheet and ensure that the rolled sheet is smoothly filmed; the addition of small amounts of these ultra-high molecular weight elastomers generally significantly improves the bonding characteristics of the blended plastic system and the flexibility of the sheet. However, if the amount of non-thermoplastic resin powders of micron size is very small and the flexibility of the system is sufficient, it is also possible to add no such polyisobutylene powders. Depending on the particular processing conditions and equipment, small amounts of mold release agents (e.g., calcium stearate, polyethylene wax), antioxidants (e.g., pentaerythritol esters), and pigments (e.g., methyl orange) may also be added, but in most cases stable production is achieved without the need for such additives, resulting in acceptable film products. It is also noted that the mixing of these four components is preferably carried out using a high-speed mixer.

2) And (3) carrying out banburying, sheet discharging by a two-roll open mill, continuous calendering by a four-roll calender, cooling and cutting on the mixture in sequence to obtain a single prefabricated diaphragm.

The internal mixer can be a pressurized open internal mixer, the internal mixing temperature is 130-150 ℃, and the mixing time is 15-30 minutes. After banburying is finished, rapidly conveying the sintered lumpy materials to a continuously rotating two-roller open mill while the materials are hot; the temperature of the open mill is required to be set to be 120-140 ℃ in advance, and is generally 10-15 ℃ lower than the sealing temperature; then, the distance between the two rollers is adjusted to ensure that the thickness of the discharged sheet is 1-3 mm. And (3) conveying the discharged sheet to a feeding port of a four-roller calender while the discharged sheet is hot, supplementing materials in time, and respectively setting the temperature of the four rollers (which should be gradually reduced) and the distance between the rollers to realize continuous film discharging. The thickness of the membrane is controlled to be 0.12-0.32 mm; if the thickness of the membrane is too thin, the membrane is difficult to be discharged, abnormal conditions such as fragments, empty pieces (large empty parts) and the like are easy to occur, and if the thickness of the membrane is too thick, the application requirements of the electrodialysis combiner cannot be met.

3) And clamping a piece of reinforcing mesh cloth by using two prefabricated membranes, and carrying out hot-pressing fusion and cooling annealing by using a hot press to obtain the cation exchange alloy membrane product.

The two sheets of the prefabricated film sheets must have the same thickness in order to ensure the uniformity of the film product in the thickness direction, and preferably are two sheets adjacent to each other in the front and rear direction obtained by rolling and cutting the film product in the same batch by four rolls. Otherwise, the slight difference in thickness between the two prefabricated films is amplified by the subsequent hot pressing treatment, and finally the film product is bent towards the side with small swelling in the solution, and the flatness of the film is poor. The mesh silk material of the reinforced mesh cloth is terylene (polyester), chinlon (nylon) or polypropylene (polypropylene), and can also be obtained by mixing and weaving the mesh silk of the materials. Aiming at the strong acid or strong alkaline solution environment, the mesh fabric materials should be distinguished: if the silk screen is mainly used in a strong acid environment, the material of the silk screen is acid-resistant terylene; if the polyamide is mainly used in a strong alkaline environment, polyamide with alkali resistance is preferred; polypropylene is considered for use if both types of environments are frequently involved. It should be noted that although the polypropylene mesh cloth can simultaneously endure strong acid and strong alkaline solution environments, the enhancement effect on the membrane is inferior to that of terylene and nylon, i.e. the tensile strength of the mesh wire with the same wire diameter is inferior to that of the latter two. Common polyethylene mesh fabrics on the market can not be applied to the reinforcement of the alloy film product, and can be melted at the hot pressing temperature (even if the materials are ultra-high molecular weight polyethylene), and the tensile strength is inferior to that of terylene, chinlon and polypropylene. The thickness of the mesh cloth is slightly larger than that of the prefabricated film, and if the mesh cloth is too thin, the strength is insufficient, so that the swelling of the membrane is not limited enough; but the thickness of the prefabricated membrane cannot exceed 2 times, otherwise, the mesh mark is very obvious after hot pressing, and the membrane surface is extremely uneven. The mesh density of the mesh cloth is between 20 and 60 meshes, and the two prefabricated films are difficult to permeate the mesh cloth to realize complete fusion due to too large mesh number (too small meshes), so that a qualified reinforcing effect cannot be achieved; too small a mesh (too large a mesh) would result in too little mesh per unit width and still not achieve the overall reinforcement effect. Meanwhile, the mesh cloth with too small mesh number (for example, less than 20 mesh) is often large in wire diameter (for example, greater than 0.3 mm), so that the material of the membrane sheet right above and below the mesh is too small, and after swelling in the solution, a significant concave mesh screen mark appears (because the membrane material is less, the swelling is also less), and the flatness of the membrane surface is lost. The process conditions of hot pressing and cooling annealing can refer to the processing method of the semi-homogeneous cation exchange membrane, and are consistent with the description of the literature (Chinese patent application No. 201510570174.6). Finally, the thickness of the dry film of the prepared cation exchange alloy film is 0.3-0.6 mm. Furthermore, if no special requirement exists, the industrial standard of the heterogeneous membrane can be referred to, and the thickness is generally 0.38-0.42 mm; if the requirement on film strength or compactness is higher, the thickness of the film product can be properly increased, such as 0.5-0.6 mm.

The present invention is further illustrated by the following specific examples, but the present invention should not be construed as being limited to these examples.

Example 1:

preparing raw materials: 1) thermoplastic strong acid resin powder (polyethylene-sulfonated polystyrene strong acid cation exchange resin powder): it can be prepared by the method described in the literature (Chinese patent application No. 201510570174.6), and is provided by Eel environmental protection technology, Inc. of Hangzhou (particle size is below 50 mesh, and cation exchange capacity is 2.58mmol/g dry basis). 2) Weak base resin powder which is not thermoplastically moldable: soaking epoxy weak-base anion exchange resin (with particle size of 0.325-1.25 mm, anion exchange capacity of 7.5mmol/g dry basis, type 335, and customized by Shanghai Huazhen technology Co., Ltd.) in 4% hydrochloric acid, washing with water to neutrality, converting to chlorine type, and air-drying at 60-70 deg.C to constant weight; firstly, crushing by using an airflow crusher to pass through a stainless steel screen with 100 meshes, and then grinding for 6 hours by using a ball mill; sampling analysis, and measuring by laser particle size analysis: the number of particles with the particle size of less than 3 microns is more than 99.2 percent, and the product is judged to be qualified. 3) Polyethylene powder: reference is made to the method described in the literature (chinese patent application No. 201510570174.6) and provided by the angler environmental protection technologies ltd, hangzhou (particle size below 50 mesh, crushed LDPE pellets (yanshan petrochemical, model 1I 20A)). 4) Polyisobutylene powder: reference is made to the method described in the literature (chinese patent application No. 201510570174.6) and supplied by oer environmental protection technologies ltd, hangzhou (particle size 50 mesh or less, from bulk polyisobutylene powder of type B200 (basf)). 5) Reinforcing the mesh cloth: the terylene material, model number is DPP12S, the specific specification is listed in Table 1, purchased from Shanghai New iron chain Screen manufacturing Co.

Manufacturing an alloy film: a) weighing 30 kg of thermoplastic strong acid resin powder, 2.4 kg of non-thermoplastic weak base resin powder, 3.6 kg of polyethylene powder and 3 kg of polyisobutylene powder (the raw material ratio is shown in table 1), and uniformly mixing by using a high-speed mixer; b) putting into an internal mixer, pressurizing and internally mixing, naturally raising the temperature from 120 ℃ to 145 ℃, stopping internal mixing, and discharging; transferring the agglomerated lump materials to a two-roller open mill which continuously rotates and has a roller surface temperature of 120-125 ℃, and continuously pulling out a membrane with a thickness of about 2.0-3.0 mm; continuously and uninterruptedly putting the hot film into a feed inlet of a four-roll calender (the rotating speed of the four rolls is synchronous to 6-7 m/min, the temperature is 122, 119, 115 and 112 ℃ in sequence), and continuously discharging the film, wherein the width is 90-95 cm, and the thickness is 0.19-0.20 mm; the method comprises the following steps that after being peeled from a bottom roller of a four-roller calender, a membrane immediately passes through a five-roller cooling machine, edges are continuously cut by a cutting knife until the width is 81-82 cm, and the tail end of the membrane is automatically cut by a pulse cutting machine to obtain a prefabricated membrane with the length of 162-164 cm; c) two prefabricated membranes which are adjacent in membrane discharging sequence are clamped with a reinforcing mesh (84 multiplied by 168 cm), the whole membrane is placed on a stainless steel plate (180 cm in length, 90 cm in width and 2.0 mm in thickness) which is covered with a polyester protective film (180 cm in length, 90 cm in width and 0.125 mm in thickness) in advance, then the same polyester protective film and the same stainless steel plate are covered, 8-10 layers of membranes are superposed in this way, then the membranes are sent into an oil press, hot-pressed for 60 minutes at 155-160 ℃ and 15-18 MPa, circulated cooling water is introduced for cooling, the membranes are taken out, the steel plate and the polyester protective film are peeled off in sequence, and the cation exchange alloy membrane is prepared, and can be cut into 800 multiplied by 1600 mm according to the group standard of electrodialysis, and the average thickness is 0.43.

The results of the measurements are shown in Table 2, referring to the measurement method described in the industry Standard (HY/T034.2-1994). It can be seen that it has a low degree of dimensional swelling in both saline and strong acid, with a dry-wet dimensional increase of less than 3% in both the length and width directions; in strong alkali, the polyester mesh fabric is slowly degraded, so that the strengthening effect is gradually weakened, and the swelling degree is continuously increased along with the soaking time. Even so, the film sheet still keeps intact in appearance after being soaked in strong alkali for 15 days, maintains the flatness and the tensile strength, and has no obvious sign of disintegration. The surface resistance detection data of the membrane indicate that the surface resistance of the membrane in strong acid is lower than 5 omega cm²Can meet the requirements of electrodialysis application; in strong alkali, the swelling is continuous, and the detection data is unstable (the compactness is smaller and smaller, so that the detection method is suitable for the detection of the alkali metal ionsLosing practical application value). It is demonstrated that the cation exchange alloy membrane product prepared under the formula condition is more suitable for the electrodialysis removal or concentration process of strong acid (but not strong base).

Example 2:

replacing the epoxy weak base resin with type 335 in example 1 with an acrylic weak base resin with type D315 (particle size range 0.325-1.25 mm, anion exchange capacity 6.5mmol/g, custom made by Shanghai Huazhen science and technology Limited); changing the polyester mesh cloth with the model of DPP12S into the polyester mesh cloth with the model of DPP20S (purchased from Shanghai New iron chain Screen manufacturing Co., Ltd.); the rest of raw materials and the mixture ratio are unchanged compared with the example 1 (see the table 1 specifically). According to the same alloy film manufacturing process as described in example 1, a prefabricated film sheet with a thickness of 0.12 mm was first produced, and an alloy film product with a thickness of 0.30 mm was produced after hot pressing.

The results and rules for the performance measurements of the resulting film products are shown in Table 2, with reference to the measurements described in the industry standards, and are essentially the same as in example 1. Meanwhile, the film thickness is reduced, and qualified products of the alloy film can still be obtained (the dry film thickness is only 0.3 mm, and is obviously thinner than that of the alloy film in the example 1).

Example 3:

replacing 335 epoxy weak base resin of example 1 with 301 styrene weak base resin (particle size 0.325-1.25 mm, anion exchange capacity 5.2mmol/g, custom made by Shanghai Huazhen science and technology Limited); the "2.4 kg of the non-thermoplastic weak base resin powder, 3.6 kg of the polyethylene powder and 3 kg of the polyisobutylene powder" in example 1 were changed to "1.5 kg of the non-thermoplastic (301) weak base resin powder, 4.5 kg of the polyethylene powder and 1.5 kg of the polyisobutylene powder". Compared with the example 1, the other raw materials and the alloy film manufacturing process are unchanged (see table 1 specifically), a prefabricated film sheet with the thickness of 0.18 mm is prepared, and an alloy film product with the thickness of 0.41 mm is prepared after hot pressing.

The performance test data of the obtained film product are listed in table 2 by referring to the measurement method described in the industry standard, and the obtained conclusion and rule are basically consistent with those in example 1, which shows that the influence of the system of the micron-sized weak base resin powder which is not thermoplastic (from epoxy system to styrene system) is not obvious.

Example 4:

the epoxy weak base resin of type 335 in example 1 was changed to a phenolic weak base resin of type 122 (particle size range 0.325 to 1.25mm, cation exchange capacity 4.2mmol/g, custom made by Tianxing resins Co., Ltd., Unionian, N.Y.); the 2.4 kg of the non-thermoplastic weak base resin powder, 3.6 kg of the polyethylene powder and 3 kg of the polyisobutylene powder in the example 1 are changed into 3.6 kg of the non-thermoplastic (122) weak base resin powder, 4.8 kg of the polyethylene powder and 1.5 kg of the polyisobutylene powder; changing the polyester mesh fabric with the model of DPP12S into a polyamide mesh fabric with the model of JPP24 (purchased from Shanghai New iron chain Screen manufacturing Co., Ltd.); compared with the example 1, the other raw materials and the alloy film manufacturing process are unchanged (see table 1 specifically), a prefabricated film sheet with the thickness of 0.20 mm is prepared, and an alloy film product with the thickness of 0.46 mm is prepared after hot pressing.

The performance test data for the resulting film products are shown in Table 2, with reference to the measurement methods described in the industry standards. It can be seen that it has a low degree of dimensional swelling in saline, strong acids and strong bases, and a dry-wet dimensional increase rate of less than 3% in both the length and width directions. However, it should be noted that nylon mesh is slowly degraded even after long-term exposure to strong acid, so that the swelling degree in strong acid is very slowly increased (difficult to significantly show in short time) with the increase of soaking time. The detection of the surface resistance of the membrane shows that the surface resistance of the membrane in strong acid and strong alkali is lower than 4 omega cm²Can meet the requirements of electrodialysis application. Considering the characteristics of no strong acid resistance of the nylon mesh cloth and the fact that the weak acid resin powder is easy to have ion exchange effect in a strong alkaline environment, the cation exchange alloy membrane product prepared under the formula condition is suggested to be more suitable for being applied to the electrodialysis removal or concentration process of strong alkali (but not strong acid).

Example 5:

the epoxy weak base resin of type 335 in example 1 was changed to a phenolic weak base resin of type 110 (particle size range 0.325 to 1.25mm, cation exchange capacity 4.5mmol/g, custom made by Tianxing resins Co., Ltd., Unionian, N.Y.); the 2.4 kg of the non-thermoplastic weak base resin powder, 3.6 kg of the polyethylene powder and 3 kg of the polyisobutylene powder in the example 1 are changed into 3.0 kg of the non-thermoplastic (110) weak base resin powder, 4.2 kg of the polyethylene powder and 1.5 kg of the polyisobutylene powder; changing the polyester mesh fabric with the model of DPP12S into a polyamide mesh fabric with the model of JPP16 (purchased from Shanghai New iron chain Screen manufacturing Co., Ltd.); the rest of the raw materials and the manufacturing process of the alloy film are basically unchanged compared with the example 1 (see the table 1 specifically), a prefabricated film sheet with the thickness of 0.24 mm is prepared, and an alloy film product with the thickness of 0.58 mm is prepared after hot pressing.

The performance test data for the resulting film products are shown in Table 2, with reference to the measurement methods described in the industry standards. Comparison with example 4 shows that an increase in film thickness does not significantly affect the degree of dimensional swelling of the film in saline, strong acids and strong bases; and the surface resistance in strong acid and strong base is not greatly increased (still lower than 5 omega cm)²) It is also possible to meet the requirements of electrodialysis applications. For the same reasons as in example 4, it is suggested that the cation exchange alloy membrane product prepared under the formulation conditions is more suitable for the electrodialysis removal or concentration process of strong base.

Example 6:

the polyester scrim of type DPP12S from example 1 was replaced with a polypropylene scrim of the same weave gauge (see table 1, provided by heyday huatian screen ltd, nibo); an alloy film product with a thickness of 0.43 mm was also prepared from the prefabricated film sheet with a thickness of 0.19 mm prepared in example 1 by the same hot pressing process.

The performance test data for the resulting film products are shown in Table 2, with reference to the measurement methods described in the industry standards. Shows the dimensional swelling degree of the membrane in saline, strong acid and strong base, and the dry and wet dimensional increasing rate in the length direction and the width direction is lower than 3 percent; and the surface resistance of the film in strong acid and strong alkali is lower than 5 omega cm². Considering that the mesh cloth made of polypropylene material can simultaneously resist strong acid and strong alkaline solution environments at normal temperature, the cation exchange alloy film product prepared under the formula condition can be the same as that of the cation exchange alloy film productThe method is applied to the electrodialysis removal or concentration process of strong acid or strong base.

Example 7:

changing the nylon mesh fabric with the model number of JPP24 in the embodiment 4 into the polypropylene mesh fabric in the embodiment 6; also using the prefabricated film sheet having a thickness of 0.20 mm prepared in example 4, an alloy film product having a thickness of 0.44 mm was prepared using the same hot pressing process.

The results and rules for the performance measurements of the resulting film products are shown in Table 2, with reference to the measurements described in the industry standards, and are substantially the same as in example 6. And further explains that: the method can achieve the purpose of obviously reducing the swelling degree in strong acid and strong alkaline solutions no matter micron-sized weak acid resin powder or micron-sized weak base resin powder is doped.

Comparative example:

with reference to the method described in the literature (chinese patent application No. 201510570174.6) (specifically, refer to example 3), a semi-homogeneous cation-exchange membrane was prepared, the thickness of the prefabricated membrane sheet was 0.38 mm, and the thickness of the membrane product was 0.43 mm. The specific raw materials and formulation (see table 1) are as follows: 20 kg of non-thermoplastic strong acid resin powder (crushed by sodium 001 multiplied by 9 strong acid sulfonic acid styrene cation exchange resin to below 300 meshes, the cation exchange capacity is 4.37mmol/g), 9 kg of thermoplastic strong acid resin powder (the specification is the same as that of all the embodiments of the invention), 5 kg of LLDPE powder (the model is 20100J, Mitsui chemical), 5 kg of LDPE powder (the model is 1I20A, Yanshan petrochemical) and 1.4 kg of polyisobutylene powder. Compared with the embodiment of the invention, the main differences are as follows: a) replacing micron-sized non-thermoplastic weak base resin powder (or weak acid resin powder) with non-thermoplastic strong acid resin powder with particle size increased by at least one order of magnitude; b) the specific formula proportions are different in primary and secondary, and the addition amount of the non-thermoplastic component is maximum; c) the reinforcing mode of the mesh cloth is different, and the mesh cloth is embedded by covering the surface with two thin nets through hot pressing instead of the method of embedding the thick net in the embodiment of the invention.

The dimensional swelling of the semi-homogeneous film in saline, strong acids and strong bases was greater and the wet-dry dimensional increase in both the length and width directions was greater than 3% (and often greater if the heterogeneous film was used) as determined by reference to industry standard methods (test data are shown in table 2). In addition, in the strong alkaline solution, because the polyester thin mesh fabric covered on the surface is dissolved, the film mesh is separated and the film material is disintegrated (actually, the film material is torn by hands or broken). Further comparative studies, such as covering the surface with nylon or polypropylene thin mesh, have found that it is difficult to obtain a semi-homogeneous film product with a smooth surface and completely pressed film sheets by the mesh made of these materials because the mesh is not resistant to high temperature and heat pressure (much worse than terylene). Even if the part with better hot pressing condition is taken out, the membrane sheet can be separated from the middle part after being converted for a plurality of times (generally not more than 10 times) in the environment of strong acid and strong alkaline solution, and the strong acid resin powder with large particle size can be stripped out, so that the soaking solution becomes turbid instantly. This means that the heterogeneous membrane and the semi-homogeneous membrane of the "sea-island" structure cannot be applied to the electrodialysis process in a strongly acidic or strongly alkaline solution environment for a long period of time, as in the case of the alloy membrane of the "star-void" structure according to the present invention.

The above examples are intended to illustrate and explain the present invention, but not to limit the present invention. Any modifications and variations of the present invention may be made by those skilled in the art without departing from the spirit of the present invention and the scope of the appended claims.

Claims

1. A method for producing a cation exchange alloy membrane, comprising the steps of: 1) uniformly mixing 100 parts by mass of thermoplastic polyethylene-sulfonated polystyrene strong-acid cation exchange resin powder, 5-20 parts by mass of non-thermoplastic micron-sized weak-acid cation exchange resin powder or non-thermoplastic micron-sized weak-base anion exchange resin powder, 10-25 parts by mass of polyethylene powder and 0-10 parts by mass of polyisobutylene powder; 2) carrying out banburying, sheet discharging by a two-roll open mill, continuous calendering by a four-roll calender, cooling and cutting on the mixture in sequence to obtain a single prefabricated diaphragm; 3) clamping a piece of reinforcing mesh cloth by using two prefabricated membranes, and performing hot-pressing fusion and cooling annealing by using a hot press to obtain the cation exchange alloy membrane product;

the particle size of the non-thermoplastic micron-sized weak acid cation exchange resin powder or the non-thermoplastic micron-sized weak base anion exchange resin powder in the step 1 is controlled to be more than 99 percent of the particles with the particle size less than 3 microns;

the thickness of the single prefabricated membrane in the step 2 is 0.12-0.32 mm.

2. The method for producing a cation exchange alloy membrane according to claim 1, wherein the micron-sized weak acid cation exchange resin powder which is not thermoplastically moldable in step 1 is obtained by pulverizing a weak acid cation exchange sodium type resin, wherein:

the weak-acid cation exchange sodium type resin is selected from acrylic weak-acid cation exchange sodium type resin, phenolic weak-acid cation exchange sodium type resin or a mixture of the acrylic weak-acid cation exchange sodium type resin and the phenolic weak-acid cation exchange sodium type resin according to any proportion;

the weak acid cation exchange sodium type resin has an ion exchange capacity of 4-7 mmol/g dry basis.

3. The method for producing a cation exchange alloy membrane according to claim 1, wherein the micron-sized weak base anion exchange resin powder which is not thermoplastically moldable in step 1 is obtained by pulverizing a weak base anion exchange chloride type resin, wherein:

the weak base anion exchange chlorine type resin is selected from styrene weak base anion exchange chlorine type resin, epoxy weak base anion exchange chlorine type resin, acrylic weak base anion exchange chlorine type resin or a mixture of the styrene weak base anion exchange chlorine type resin, the epoxy weak base anion exchange chlorine type resin and the acrylic weak base anion exchange chlorine type resin according to any proportion;

the weak base anion exchange chlorine type resin has an ion exchange capacity of 4-8 mmol/g dry basis.

4. The method for manufacturing a cation exchange alloy membrane according to claim 1, wherein the mesh of the reinforcing mesh in step 3 is made of terylene, chinlon, polypropylene or is formed by weaving the three kinds of mesh in a mixed manner; the thickness of the reinforcing mesh cloth is larger than that of the prefabricated membrane, but is smaller than 2 times of the thickness of the prefabricated membrane.

5. The method for producing a cation exchange alloy membrane according to claim 1, wherein the dry membrane thickness of the produced cation exchange alloy membrane is 0.3 to 0.6 mm.