Porous composite cation exchange membrane for diffusion dialysis alkali recovery as well as preparation method and application of porous composite cation exchange membrane

Abstract

The invention discloses a porous composite cation exchange membrane for diffusion dialysis alkali recovery and a preparation method and application thereof. The membrane is a series of porous composite cation separation membranes which are obtained by blending chloromethylated polyether sulfone and sulfonated aromatic hydrocarbon polymer, modifying with an amine cross-linking agent and grafting with 1, 3-propane sultone. The composite cation exchange membrane provided by the invention is subjected to amine crosslinking to form pores with the membrane, so that pore size screening and separation of OH <-> and WO4 < 2-> are facilitated, and the separation factor is increased; sulfonic acid groups are introduced through grafting modification of 1, 3-propane sultone, and permeation of acid radical ions is reduced through electrostatic repulsion. Meanwhile, the obtained composite cation exchange membrane has the characteristics of high mechanical strength, excellent thermal stability and low cost, and has excellent performance in the aspects of efficient alkali recovery, ion selectivity optimization, enhanced durability and the like. The method has great application potential in the field of diffusion dialysis alkali recovery.

Description

Technical Field

[0001] The present invention relates to the technical field of new chemical materials, and particularly relates to a porous composite cation exchange membrane for diffusion dialysis alkali recovery, and a preparation method and application thereof. Background Art

[0002] The rapid development of industrialization and modern manufacturing has brought severe challenges to the treatment of alkali-containing waste liquid, posing a threat to environmental protection and sustainable utilization of resources. Such waste liquid is widespread in many industries such as papermaking, chemical engineering, food processing, and metal surface treatment, and is characterized by high pH value and strong corrosiveness. In the production processes of tungsten ore and aluminum ore smelting, papermaking, artificial fiber production, and leather processing, etc., due to the use of alkaline raw materials, a large amount of alkali-containing waste liquid is inevitably generated. For example, in tungsten ore smelting, the alkali decomposition method is adopted, and an alkaline solution is used to leach tungsten salts, generating a large amount of such waste liquid. The papermaking industry uses sodium hydroxide to dissolve lignin to extract pulp, and also discharges a large amount of alkali-containing waste liquid. If directly discharged without treatment, it will not only waste alkaline raw materials but also seriously damage the ecological environment. Efficient treatment of alkali-containing waste liquid and promotion of waste alkali resource utilization are crucial for ecological balance and sustainable development. Untreated discharge will seriously pollute ecological systems such as water bodies and soil, not only harming the environment but also wasting potential recyclable resources. Therefore, relevant industries urgently need to seek efficient and environmentally friendly treatment solutions for alkali-containing waste liquid.

[0003] Traditional alkaline waste liquid treatment methods mainly include neutralization, sedimentation, evaporation and concentration, etc. The acid-base neutralization method is easy to operate and has a wide range of applications. However, the acidic reagent corrodes the equipment, affects production safety in the long term, and produces by-products containing chlorine, sulfur and carbon, which are prone to cause secondary pollution and waste acid-base resources. The flocculation sedimentation method has a low cost and a simple process. However, a large amount of sediment is generated during the flocculation process, increasing the difficulty of subsequent treatment, and the consumption of flocculants is large, resulting in resource waste. The evaporation and concentration method can better recover and utilize alkaline waste liquid. The process is direct and the operation is convenient. However, it has high energy consumption, high operating costs, and limited treatment efficiency, which limits its large-scale application. Although these methods can reduce the alkalinity and pollutant concentration of waste liquid, they face problems such as large consumption of chemical drugs, high risk of secondary pollution, and high treatment costs, and it is difficult to meet the requirements of environmental protection and economic benefits. Especially when the waste liquid is rich in recoverable alkaline substances and useful chemical components, the limitations of traditional treatment methods are more obvious, and valuable resources cannot be effectively recovered. In view of the limitations of traditional methods, membrane separation technology has increasingly become an important research direction for alkaline waste liquid treatment and resource recovery due to its advantages of high efficiency, low energy consumption and environmental protection. Membrane separation technology can effectively separate water, alkaline compounds and pollutants in waste liquid through physical sieving without additional chemical agents, avoiding secondary pollution. In addition, membrane technology also has the characteristics of simple operation, small floor area and flexible process, and can be customized and optimized for different waste liquids. Diffusion dialysis technology is a membrane separation method based on the driving force of solution concentration gradient, and mainly relies on cation exchange membrane (CEM) to achieve the directional migration of ions and the recovery of alkaline resources. The most important point is that this method does not rely on external electric energy, only uses the solution concentration difference as the driving force, makes the separation process proceed spontaneously, and has extremely low energy consumption. Therefore, it has obvious advantages in reducing treatment costs. In the context of increasingly tight energy resources, this characteristic of not requiring additional energy input makes diffusion dialysis a more economical and environmentally friendly alkali recovery technology. Summary of the Invention

[0004] Aiming at the problem of the trade-off effect between the alkali dialysis coefficient (U OH- ) and the high separation factor (S) in the diffusion dialysis alkali recovery membrane in the prior art, the present invention provides a porous composite cation exchange membrane for diffusion dialysis alkali recovery, its preparation method and application.

[0005] The present invention adopts the following technical solutions: A porous composite cation exchange membrane for diffusion dialysis alkali recovery and its preparation method, characterized by comprising the following steps: S1. Blend chloromethylated polyethersulfone (CMPES) and sulfonated aromatic hydrocarbon polymer in different mass ratios and dissolve them in an organic solvent. After standing for 12 h, filter with non-woven fabric, ultrasonic for 10 min, and then stand for 12 h to obtain a casting solution completely free of bubbles. Coat it on a substrate and then place it in pure water to obtain a porous cation exchange membrane. S2. Immerse the porous cation exchange base membrane in an aqueous solution of amine cross-linking agent at a certain temperature for a certain time to obtain an amine cross-linked porous cation exchange membrane. S3. Place this membrane in a solution of 1,3 - propanesultone (PS) with a certain concentration, and immerse it at a certain temperature for a certain time to obtain a porous composite cation exchange membrane.

[0006] Furthermore, in step S1, the sulfonated aromatic hydrocarbon polymer is any one of sulfonated polyethersulfone (SPES), sulfonated polyphenylene oxide (SPPO), sulfonated polysulfone (SPSF), and sulfonated polyether ether ketone (SPEEK), and the mass ratio of the sulfonated aromatic hydrocarbon polymer to chloromethylated polyethersulfone is 100:(1 - 100).

[0007] Furthermore, in step S1, the organic solvent is any one of N - methylpyrrolidone (NMP), N,N - dimethylformamide (DMF), and dimethyl sulfoxide (DMSO), and the concentration of the obtained casting solution is 10 - 35 wt%; in step S1, the substrate is a glass plate or a polytetrafluoroethylene plate; the coating method is one of blade coating, spin coating, or casting. In step S2, the immersion temperature is 40 - 80 °C; the amine cross-linking agent is any one of ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), polyethyleneimine (PEI), and tetraethylenepentamine (TEPA), the concentration of the aqueous solution of the amine cross-linking agent is 0.1 - 1.0 M; the certain immersion time is 1 h - 24 h. Furthermore, in step S3, the concentration of the 1,3 - propanesultone solution is 0.1 - 1.0 M; the solvent of the 1,3 - propanesultone solution is one of ethanol and methanol; the immersion temperature is 40 - 80 °C; the immersion time is 1 h - 24 h.

[0008] A porous composite cation exchange membrane for diffusion dialysis alkali recovery prepared by the above method.

[0009] Application of the above porous composite cation exchange membrane in diffusion dialysis alkali recovery. The self - made diffusion dialysis device in the laboratory is as Figure 1 shown, which consists of a feed chamber (left side), a cation exchange membrane, a pure water chamber (right side), and a stirring device. Clamp the membrane to be tested between the two chambers (the effective area is 5.7 cm 2), the feed chamber and the pure water chamber are respectively filled with 100 mL of simulated alkaline waste liquid (1.0 mol L -1 NaOH / 0.1 mol L -1 aqueous Na2WO4 solution) and ultrapure water. The entire device is placed in a 25 °C constant temperature water bath. After diffusion dialysis for 1 h, the concentrations of NaOH and Na2WO4 in the two chambers are detected.

[0010] The technical solution of the present invention has the following advantages compared with the prior art: A. It can overcome the Trade-off effect between the alkali dialysis coefficient (U OH- ) and the separation factor (S). By adopting amine cross-linking modification and using the pores formed by it for pore size screening, this is beneficial to the separation of OH - and WO4 2- , and improve the S value. Graft modification with 1,3-propane sultone can introduce sulfonic acid groups onto the amine-crosslinked porous cation exchange membrane, reduce the permeation of acid radicals through electrostatic repulsion, improve the separation selectivity, and achieve the simultaneous improvement of U OH- and S.

[0011] B. The composite membrane obtained by the present invention enhances the stability of CEMs, adapts to complex working conditions, improves the mechanical strength, thermal stability and alkali resistance of the membrane, enabling it to operate stably for a long time in a high-temperature and high-concentration alkali environment. The phase inversion method, a scalable preparation method, is adopted to simplify the production steps, improve the production efficiency and reduce the cost.

[0012] C. The raw materials for preparing the composite membrane of the present invention are either commercially available or can be synthesized at low cost, thus significantly reducing the membrane preparation cost and facilitating its large-scale application. Description of the Drawings

[0013] Figure 1 Self-made diffusion dialysis alkali recovery device diagram.

[0014] Figure 2 FTIR spectra of 25wt%-CMPES / SPES-1 / 1-PEI-12h-PS-yh (y = 0, 4, 12, 24) series of porous membranes.

[0015] Figure 3 XPS wide spectra of 25wt%-CMPES / SPES-1 / 1-PEI-12h in Comparative Example 2 and 25wt%-CMPES / SPES-1 / 1-PEI-12h-PS-12h composite porous membrane in Example 3. (a) 25wt%-CMPES / SPES-1 / 1-PEI-12h, (b) 25wt%-CMPES / SPES-1 / 1-PEI-12h-PS-12h.

[0016] Figure 4 IEC results diagram of 25wt%-CMPES / SPES-a / b-PEI-12h-PS-12h series composite porous cation exchange membranes. Specific implementation mode

[0017] The present invention can be implemented in many different forms and should not be construed as limited to the embodiments set forth herein. On the contrary, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the present invention to those skilled in the art. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0018] Example 1: This example provides a method for preparing a porous composite cation exchange membrane for diffusion dialysis alkali recovery, including the following steps: 2 g of CMPES and 2 g of SPES were blended and dissolved in 12 g of NMP at a mass ratio of 1:1 to obtain a 25 wt% casting solution. After standing for 12 h, it was filtered with non-woven fabric, ultrasonicated for 10 min, and then stood for 12 h to obtain a casting solution completely free of bubbles. After taking an appropriate amount of the casting solution and pouring it onto a glass plate, it was uniformly coated with a wet film preparation device and placed in pure water to obtain a porous cation exchange membrane; the porous cation exchange base membrane was immersed in an aqueous solution of 1.0 M PEI amine crosslinking agent at 60 °C for 4 h to obtain an amine-crosslinked porous cation exchange membrane; this membrane was placed in a mixed solution of 190 mL of 1.0 M 1,3-propanesultone ethanol solution and 10 mL of 1.0 M NaOH aqueous solution, and immersed at 60 °C for 12 h to obtain a porous composite cation exchange membrane, denoted as membrane 25wt%-CMPES / SPES-1 / 1-PEI-4h-PS-12h. The Figure 1 diffusion dialysis device shown was used for the alkali recovery performance test. The results show that the reached 17.1×10 -3 mh -1 , and the separation factor S reached 12.5. While maintaining a high separation factor, this membrane also maintained excellent ion flux, which is of great significance for practical applications.

[0019] Comparative Example 1: This example provides a composite membrane, and its preparation method includes the following steps: 2 g of CMPES and 2 g of SPES were blended and dissolved in 12 g of NMP at a mass ratio of 1:1 to obtain a 25 wt% casting solution. After standing for 12 h, the solution was filtered through non-woven fabric, ultrasonicated for 10 min, and then stood for 12 h to obtain a casting solution with all bubbles removed. An appropriate amount of the casting solution was poured onto a glass plate and evenly coated with a wet film applicator, and then placed in pure water to obtain a porous cation exchange membrane; denoted as membrane 25wt%-CMPES / SPES-1 / 1. The Figure 1 laboratory self-made diffusion dialysis device shown in

[0020] was used for the alkali recovery performance test. The laboratory self-made diffusion dialysis device consists of a feed chamber (left side), a cation exchange membrane, a pure water chamber (right side), and a stirring device. The membrane to be tested was clamped between the two chambers (effective area: 5.7 cm2), and the feed chamber and the pure water chamber were respectively filled with 100 mL of simulated alkali-containing waste liquid (1.0 mol L-1 NaOH / 0.1 mol L-1 Na2WO4 aqueous solution) and ultrapure water. The whole device was placed in a constant temperature water bath at 25 °C. After diffusion dialysis for 1 h, the concentrations of NaOH and Na2WO4 in the two chambers were detected.

[0020] The results showed that the of this membrane was 22.5×10 -3 m h -1 , and the separation factor S was 5.62. Although the selectivity S of the membrane only reached 5.62, due to its large free volume and relatively high ion exchange capacity, its was relatively high, far better than that of the dense CMV, indicating that the porous substrate membrane has great potential for improving the treatment efficiency of alkali-containing waste liquid.

[0021] Comparative Example 2: This example provides a composite membrane, and its preparation method includes the following steps: 2 g of CMPES and 2 g of SPES were blended and dissolved in 12 g of NMP at a mass ratio of 1:1 to obtain a 25 wt% casting solution. After standing for 12 h, the solution was filtered through non-woven fabric, ultrasonicated for 10 min, and then stood for 12 h to obtain a casting solution with all bubbles removed. An appropriate amount of the casting solution was poured onto a glass plate and evenly coated with a wet film applicator, and then placed in pure water to obtain a porous cation exchange membrane; the porous cation exchange substrate membrane was immersed in a 1.0 M PEI amine cross-linking agent aqueous solution at 60 °C for 12 h to obtain an amine-crosslinked porous cation exchange membrane, denoted as membrane 25wt%-CMPES / SPES-1 / 1-PEI-12h. Figure 1 The laboratory self-made diffusion dialysis device shown in was used for the alkali recovery performance test. The results showed that the -3 of this membrane was 16.4×10 -1, the separation factor S is 12.5. This is because as the PEI modification time increases, the free space volume in the membrane gradually decreases, which in turn leads to a gradual reduction in the ion transport channels in the membrane, increasing the ion transport resistance.

[0022] Example 2: This example provides a porous composite cation exchange membrane for diffusion dialysis alkali recovery and its preparation method, which is characterized by including the following steps: 2 g of CMPES and 2 g of SPES were blended and dissolved in 12 g of NMP in a mass ratio of 1:1 to obtain a 25 wt% casting solution. After standing for 12 h, it was filtered through non-woven fabric, ultrasonicated for 10 min, and then stood for 12 h to obtain a casting solution with completely removed bubbles. After taking an appropriate amount of the casting solution and pouring it onto a glass plate, it was evenly coated with a wet film preparation device and placed in pure water to obtain a porous cation exchange membrane; the porous cation exchange base membrane was immersed in a 1.0 M aqueous solution of PEI amine cross-linking agent at 60 °C for 12 h to obtain an amine-crosslinked porous cation exchange membrane; this membrane was placed in a mixed solution of 190 mL of 1.0 M 1,3-propanesultone ethanol solution and 10 mL of 1.0 M NaOH aqueous solution, and immersed at 60 °C for 4 h to obtain a porous composite cation exchange membrane, denoted as membrane 25wt%-CMPES / SPES-1 / 1-PEI-12h-PS-4h. Figure 1 The alkali recovery performance was tested using the self-made diffusion dialysis device shown in the figure. The results show that the reached 17.1×10 -3 mh -1 , and the separation factor S reached 12.6. Compared with the test results of membrane 25wt%-CMPES / SPES-1 / 1-PEI-4h-PS-12h in Example 1, the and S of this membrane both increased.

[0023] Example 3: This example provides a porous composite cation exchange membrane for diffusion dialysis alkali recovery and its preparation method, which is characterized by including the following steps: 2 g of CMPES and 2 g of SPES were blended and dissolved in 12 g of NMP at a mass ratio of 1:1 to obtain a 25 wt% casting solution. After standing for 12 h, it was filtered with non-woven fabric, ultrasonicated for 10 min and then stood for 12 h to obtain a casting solution with completely removed bubbles. An appropriate amount of the casting solution was poured onto a glass plate and evenly coated with a wet film forming apparatus, and then placed in pure water to obtain a porous cation exchange membrane; the porous cation exchange base membrane was immersed in an aqueous solution of 1.0 M PEI amine crosslinking agent at 60 °C for 12 h to obtain an amine crosslinked porous cation exchange membrane; this membrane was placed in a mixed solution of 190 mL of 1.0 M 1,3 - propanesultone ethanol solution and 10 mL of 1.0 M NaOH aqueous solution, and immersed at 60 °C for 12 h to obtain a porous composite cation exchange membrane, denoted as membrane 25wt%-CMPES / SPES-1 / 1-PEI-12h-PS-12h. Figure 1 The self-made laboratory diffusion dialysis device shown in reached 20.2×10 -3 mh -1 , and the separation factor S reached 13.7. Compared with the test results of the membrane 25wt%-CMPES / SPES-1 / 1-PEI-12h-PS-8h in Example 2, the and S of this membrane were further increased.

[0024] Example 4: This example provides a porous composite cation exchange membrane for diffusion dialysis alkali recovery and its preparation method, which is characterized by including the following steps: 2 g of CMPES and 2 g of SPES were blended and dissolved in 12 g of NMP at a mass ratio of 1:1 to obtain a 25 wt% casting solution. After standing for 12 h, it was filtered with non-woven fabric, ultrasonicated for 10 min and then stood for 12 h to obtain a casting solution with completely removed bubbles. An appropriate amount of the casting solution was poured onto a glass plate and evenly coated with a wet film forming apparatus, and then placed in pure water to obtain a porous cation exchange membrane; the porous cation exchange base membrane was immersed in an aqueous solution of 1.0 M PEI amine crosslinking agent at 60 °C for 12 h to obtain an amine crosslinked porous cation exchange membrane; this membrane was placed in a mixed solution of 190 mL of 1.0 M 1,3 - propanesultone ethanol solution and 10 mL of 1.0 M NaOH aqueous solution, and immersed at 60 °C for 24 h to obtain a porous composite cation exchange membrane, denoted as membrane 25wt%-CMPES / SPES-1 / 1-PEI-12h-PS-24h. Figure 1 The self-made laboratory diffusion dialysis device shown in reached 20.3×10 -3 mh -1, the separation factor S reaches 13.3. Compared with the test results of 25wt%-CMPES / SPES-1 / 1-PEI-12h-PS-12h in Example 3, the increases and S decreases. This is because as the PS modification time increases, the number of -SO3 - groups is larger, and the transport of Na + increases, resulting in the driving force of the potential difference for WO4 2- gradually approaching the repulsive force of the -SO3 - group for WO4 2- , leading to a decrease in the ability of the membrane to intercept WO4 2- ions, so its S begins to decline.

[0025] Example 5: This example provides a porous composite cation exchange membrane for diffusion dialysis alkali recovery and its preparation method, which is characterized by including the following steps: CMPES and SPES are blended and dissolved in 12 g of NMP according to a mass ratio of 6:4 to obtain a 25wt% casting solution. After standing for 12 h, it is filtered with non-woven fabric, ultrasonicated for 10 min, and then standing for 12 h to obtain a casting solution with completely removed bubbles. After taking an appropriate amount of the casting solution and pouring it on a glass plate, it is uniformly scraped with a wet film preparation device and placed in pure water to obtain a porous cation exchange membrane; the porous cation exchange base membrane is soaked in a 1.0 M aqueous solution of PEI amine cross-linking agent at 60 °C for 12 h to obtain an amine-crosslinked porous cation exchange membrane; this membrane is placed in a mixed solution of 190 mL of 1.0 M 1,3-propanesulfonic acid lactone ethanol solution and 10 mL of 1.0 M NaOH aqueous solution, and soaked at 60 °C for 12 h to obtain a porous composite cation exchange membrane, denoted as membrane 25wt%-CMPES / SPES-6 / 4-PEI-12h-PS-12h. Figure 1 The alkali recovery performance test is carried out by using the self-made diffusion dialysis device shown in the figure. The results show that the reaches 16.3×10 -3 mh -1 , and the separation factor S reaches 12.2.

[0026] Example 6: This example provides a porous composite cation exchange membrane for diffusion dialysis alkali recovery and its preparation method, which is characterized by including the following steps: SPES and CMPES were blended and dissolved in 12 g of NMP at a mass ratio of 4:5 to obtain a 25 wt% casting solution. After standing for 12 h, it was filtered with non-woven fabric, ultrasonicated for 10 min, and then stood for 12 h to obtain a casting solution with completely removed bubbles. An appropriate amount of the casting solution was poured onto a glass plate and evenly coated with a wet film applicator, and then placed in pure water to obtain a porous cation exchange membrane. The porous cation exchange base membrane was immersed in a 1.0 M aqueous solution of PEI amine crosslinking agent at 60 °C for 12 h to obtain an amine-crosslinked porous cation exchange membrane. This membrane was placed in a mixed solution of 190 mL of 1.0 M 1,3-propanesultone ethanol solution and 10 mL of 1.0 M NaOH aqueous solution and immersed at 60 °C for 12 h to obtain a porous composite cation exchange membrane, denoted as membrane 25wt%-CMPES / SPES-5 / 4-PEI-12h-PS-12h. The alkali recovery performance was tested using a diffusion dialysis device. The results showed that the reached 19.6×10 -3 mh -1 , and the separation factor S reached 13.4.

[0027] Example 7: This example provides a porous composite cation exchange membrane for alkali recovery by diffusion dialysis and its preparation method, which is characterized by including the following steps: CMPES and SPES were blended and dissolved in 12 g of NMP at a mass ratio of 4:6 to obtain a 25 wt% casting solution. After standing for 12 h, it was filtered with non-woven fabric, ultrasonicated for 10 min, and then stood for 12 h to obtain a casting solution with completely removed bubbles. An appropriate amount of the casting solution was poured onto a glass plate and evenly coated with a wet film applicator, and then placed in pure water to obtain a porous cation exchange membrane. The porous cation exchange base membrane was immersed in a 1.0 M aqueous solution of PEI amine crosslinking agent at 60 °C for 12 h to obtain an amine-crosslinked porous cation exchange membrane. This membrane was placed in a mixed solution of 190 mL of 1.0 M 1,3-propanesultone ethanol solution and 10 mL of 1.0 M NaOH aqueous solution and immersed at 60 °C for 12 h to obtain a porous composite cation exchange membrane, denoted as membrane 25wt%-CMPES / SPES-4 / 6-PEI-12h-PS-12h. Figure 1 The alkali recovery performance was tested using the self-made diffusion dialysis device shown in the figure. The results showed that the reached 22.4×10 -3 mh -1 , and the separation factor S reached 15.2.

[0028] Example 8: This example provides a porous composite cation exchange membrane for alkali recovery by diffusion dialysis and its preparation method, which is characterized by including the following steps: CMPES and SPES were blended and dissolved in 12 g of NMP at a mass ratio of 35:65 to obtain a 25 wt% casting solution. After standing for 12 h, it was filtered through a non-woven fabric, ultrasonicated for 10 min, and then stood for 12 h to obtain a casting solution with completely removed air bubbles. An appropriate amount of the casting solution was poured onto a glass plate and evenly coated with a wet film preparation device, and then placed in pure water to obtain a porous cation exchange membrane; the porous cation exchange base membrane was soaked in a 1.0 M aqueous solution of PEI amine crosslinking agent at 60 °C for 12 h to obtain an amine-crosslinked porous cation exchange membrane; this membrane was placed in a mixed solution of 190 mL of 1.0 M 1,3-propanesultone ethanol solution and 10 mL of 1.0 M NaOH aqueous solution, and soaked at 60 °C for 12 h to obtain a porous composite cation exchange membrane, denoted as membrane 25wt%-CMPES / SPES-35 / 65-PEI-12h-PS-12h. Figure 1 The alkali recovery performance test was carried out using the self-made laboratory diffusion dialysis device shown. The results show that the reached 24.4×10 -3 mh -1 , and the separation factor S reached 16.6.

[0029] Example 9: This example provides a porous composite cation exchange membrane for diffusion dialysis alkali recovery and a preparation method thereof, which is characterized by including the following steps: CMPES and SPES were blended and dissolved in 12 g of NMP at a mass ratio of 3:7 to obtain a 25 wt% casting solution. After standing for 12 h, it was filtered through a non-woven fabric, ultrasonicated for 10 min, and then stood for 12 h to obtain a casting solution with completely removed air bubbles. An appropriate amount of the casting solution was poured onto a glass plate and evenly coated with a wet film preparation device, and then placed in pure water to obtain a porous cation exchange membrane; the porous cation exchange base membrane was soaked in a 1.0 M aqueous solution of PEI amine crosslinking agent at 60 °C for 12 h to obtain an amine-crosslinked porous cation exchange membrane; this membrane was placed in a mixed solution of 190 mL of 1.0 M 1,3-propanesultone ethanol solution and 10 mL of 1.0 M NaOH aqueous solution, and soaked at 60 °C for 12 h to obtain a porous composite cation exchange membrane, denoted as membrane 25wt%-CMPES / SPES-3 / 7-PEI-12h-PS-12h. Figure 1 The alkali recovery performance test was carried out using the self-made laboratory diffusion dialysis device shown. The results show that the reached 24.6×10 -3 mh -1 , and the separation factor S reached 15.7. As the proportion of SPES gradually increased, the continuously increased to 24.7×10 -3 m h -1, meanwhile, membrane S first increases and then decreases, and reaches a maximum value of 16.6 when the mass ratio of SPES / CMPES is 65 / 35; this is because the increase in SPES will increase the sulfonic acid group content of the membrane and improve the ion exchange capacity of the membrane, while the decrease in S after 7 / 3 is because the free space volume of the membrane is too large to better block the transport of WO4 2- ions.

[0030] Example 9: A composite membrane was prepared by a method similar to that of Example 2, except that the amine crosslinking agent was changed to ethylenediamine and the solvent of the PS solution was changed to methanol to obtain similar results.

[0031] Example 10: A composite membrane was prepared by a method similar to that of Example 4, except that SPES was changed to SPPO and the solvent of the PS solution was changed to methanol to obtain similar results.

[0032] Example 11: A composite membrane was prepared by a method similar to that of Example 4, except that SPES was changed to SPPO and the amine crosslinking agent was changed to EDA to obtain similar results.

[0033] Example 12: A composite membrane was prepared by a method similar to that of Example 4, except that SPES was changed to SPPO, the amine crosslinking agent was changed to EDA, and the soaking time of the PS ethanol solution was changed to 24 h to obtain similar results.

[0034] Example 13: A composite membrane was prepared by a method similar to that of Example 5, except that SPES was changed to SPPO and the amine crosslinking agent was changed to DETA to obtain similar results.

[0035] Example 14: A composite membrane was prepared by a method similar to that of Example 6, except that SPES was changed to SPEEK, the amine crosslinking agent was changed to TETA, and the soaking time of the amine crosslinking agent was changed to 8 h to obtain similar results.

[0036] Example 15: A composite membrane was prepared by a method similar to that of Example 6, except that SPES was changed to SPSF, the amine crosslinking agent was changed to EDA, and the doctor blade coating was changed to the casting method to obtain similar results.

[0037] Example 16: A composite membrane was prepared by a method similar to that of Example 1, except that SPES was changed to SPSF, the mass ratio of SPSF to CMPES was changed to 40:60, and the concentration of the amine crosslinking agent was changed to 0.5 M to obtain similar results.

[0038] Example 17: A composite membrane was prepared using a method similar to that of Example 1, except that SPES was changed to SPSF, the mass ratio of SPSF to CMPES was changed to 20:80, the concentration of the PS ethanol solution was changed to 0.5 M, and the soaking time of the PS solution was changed to 24 h to obtain similar results.

[0039] Example 18: A composite membrane was prepared using a method similar to that of Example 1, except that SPES was changed to SPPO, the mass ratio of SPPO to CMPES was changed to 80:20, the concentration of the PS ethanol solution was changed to 0.5 M, and the soaking time of the PS solution was changed to 24 h to obtain similar results.

[0040] Example 19: A composite membrane was prepared using a method similar to that of Example 3, except that SPES was changed to SPPO, the mass ratio of SPPO to CMPES was changed to 80:20, the amine crosslinking agent was changed to TETA, the concentration of the TETA solution was changed to 0.5 M, and the soaking time of the PS solution was changed to 24 h to obtain similar results.

[0041] Example 20: A composite membrane was prepared using a method similar to that of Example 4, except that the amine crosslinking agent was changed to TETA, the concentration of the TETA solution was changed to 0.8 M, and the soaking time of the amine crosslinking agent was changed to 4 h to obtain similar results.

[0042] Innovatively, the present invention blends chloromethylated polysulfone (CMPES) with sulfonated aromatic hydrocarbon polymers such as polysulfone (SPES, SPPO, SPSF, etc.) to enhance the hydrophilicity and ionic conductivity of the material and improve the transport rate of OH- ions (U OH- ). And by controlling the ratio of SPES to CMPES and the membrane structure, the OH- selectivity is improved, the penetration of acid root ions is reduced, and the separation factor (S) is increased. It can overcome the trade-off effect between the alkali dialysis coefficient and the separation factor S. Through amine crosslinking modification and using the pores formed by it for pore size screening, this is beneficial for the separation of OH - and WO4 2- , and the S value is increased. Graft modification with 1,3-propane sultone can introduce sulfonic acid groups onto the amine-crosslinked porous cation exchange membrane, reduce the permeation of acid roots through electrostatic repulsion, improve the separation selectivity, and achieve and the simultaneous increase of S.

[0043] The composite membrane obtained by the present invention enhances the stability of CEMs, adapts to complex working conditions, improves the mechanical strength, thermal stability and alkali resistance of the membrane, enabling it to operate stably for a long time in a high-temperature and high-concentration alkali environment. The phase inversion method, a scalable preparation method, is adopted to simplify the production steps, improve the production efficiency and reduce the cost.

[0044] The raw materials for preparing the composite membrane of the present invention are either commercially available or can be synthesized at low cost, thus significantly reducing the membrane preparation cost and facilitating its large-scale application.

[0045] Figure 2 FTIR spectra of the 25wt%-CMPES / SPES-1 / 1-PEI-12h-PS-yh (y = 0, 4, 12, 24) series of porous membranes. For CMPES, the characteristic peaks at 1575 cm -1 , 1480 cm -1 are attributed to the C═C vibration characteristic peaks of the benzene ring on its main chain; the characteristic peak at 754 cm -1 is attributed to the C-Cl vibration characteristic peak of the benzyl chloride group. The characteristic peak of the C-N single bond appears in the range of 1654 cm -1 ; at the same time, the characteristic peaks of the sulfonic acid groups belonging to SPES appear at 1124 cm -1 and 1029 cm -1 , and both increase with the increase of the PS modification time, which is consistent with the experimental expectation.

[0046] Figure 3 XPS wide spectra of the 25wt%-CMPES / SPES-1 / 1-PEI-12h and 25wt%-CMPES / SPES-1 / 1-PEI-12h-PS-12h porous membranes after PS treatment for 12h. It can be seen that the membrane contains C, N, O, S, and Cl species elements, and the contents of S and O elements increase significantly, proving that the PS molecules are successfully cross-linked into the membrane, which is in line with the experimental expectation.

[0047] Figure 4 IEC results of the 25wt%-CMPES / SPES-a / b-PEI-12h-PS-12h series of composite porous cation exchange membranes. As the proportion of SPES with sulfonic acid groups in the base membrane increases, the IEC of the membrane further increases; this is attributed to more sulfonic acid groups brought by a larger proportion of SPES, providing more ion exchange channels.

[0048] Obviously, the above embodiments are only examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A preparation method of a porous composite cation exchange membrane for diffusion dialysis alkali recovery, characterized in that It includes the following steps: S1. Blend chloromethylated polyethersulfone and sulfonated aromatic hydrocarbon polymer in different mass ratios and dissolve them in an organic solvent. After standing for 12 h, filter with non-woven fabric, ultrasonic for 10 min and then stand for 12 h to obtain a casting solution with completely removed bubbles. Coat it on a substrate and then put it into pure water to obtain a porous cation exchange membrane; S2. Immerse the porous cation exchange base membrane in an aqueous solution of an amine cross-linking agent at a certain temperature for a certain time to obtain an amine-crosslinked porous cation exchange membrane; S3. Place this membrane in a 1,3-propanesultone solution with a certain concentration, immerse it at a certain temperature for a certain time to obtain a porous composite cation exchange membrane.

2. The preparation method according to claim 1, characterized in that, In step S1, the sulfonated aromatic hydrocarbon polymer includes any one or more of sulfonated polyethersulfone, sulfonated polyphenylene oxide, sulfonated polysulfone and sulfonated polyether ether ketone. The mass ratio of the sulfonated aromatic hydrocarbon polymer to chloromethylated polyethersulfone is 100:1 - 100.

3. The preparation method according to claim 1, wherein: In step S1, the organic solvent includes any one of N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide. The concentration of the obtained casting solution is 10 - 35 wt%.

4. The preparation method according to claim 1, characterized in that: In step S1, the substrate is a glass plate or a polytetrafluoroethylene plate; the coating method is any one of knife coating, spin coating or casting method.

5. The preparation method according to claim 1, characterized in that: The amine cross-linking agent is any one of ethylenediamine, diethylenetriamine, triethylenetetramine, polyethyleneimine and tetraethylenepentamine. The concentration of the aqueous solution of the amine cross-linking agent is 0.1 - 1.0 M.

6. The preparation method according to claim 1, wherein: In step S2, the immersion temperature is 40 - 80 °C; the immersion time is 1 h - 24 h.

7. The preparation method according to claim 1, wherein: In step S3, the concentration of the 1,3-propanesultone solution is 0.1 - 1.0 M; the solvent of the 1,3-propanesultone solution is any one of absolute ethanol and methanol.

8. The preparation method according to claim 1, characterized in that: In step S3, the immersion temperature is 40 - 80 °C; the immersion time is 1 h - 24 h.

9. A porous composite cation exchange membrane for diffusion dialysis alkali recovery prepared by the preparation method according to any one of claims 1 - 8.

10. Application of the porous composite cation exchange membrane according to claim 9 in diffusion dialysis alkali recovery.

Images