Preparation and application method of modified ion exchange membrane for electrodialysis

Abstract

The invention discloses a preparation and application method of a modified ion exchange membrane for electrodialysis, aiming at the problems of poor selectivity, low mechanical strength, high energy consumption and the like of the existing ion exchange membrane, the high-performance modified membrane is prepared by a base membrane pretreatment-functional grafting-gradient curing synergistic process. The preparation method specifically comprises the following steps: performing ultrasonic cleaning and acid-base activation on a polyethersulfone or sulfonated polystyrene-based membrane, soaking the polyethersulfone or sulfonated polystyrene-based membrane in a modification solution containing an amino / carboxyl / sulfo functional monomer, a cross-linking agent and an initiator, and performing gradient heating curing to form a stable cross-linked network; the grafting rate of the modified membrane is 15-35%, the ion exchange capacity is 1.8-2.5 mmol / g, the water content is 25-40%, and the membrane surface resistance is less than 3 omega.cm < 2 >. When the membrane is applied to an electrodialysis device, the membrane runs under the conditions of 10-30V direct-current voltage, 5-15cm / s flow velocity and 25-45 DEG C, the high-salinity wastewater desalination rate is greater than or equal to 95%, and the monovalent ion selectivity coefficient reaches 5.8-7.2; when the catalyst is used for acid-base recovery, the H < + > migration number is 0.92-0.96, and the energy consumption is reduced by 18-25%.

Description

Technical Field

[0001] The present invention provides a preparation and application method of an exchange membrane, belongs to the technical field of modified ions for electrodialysis, and particularly relates to a preparation and application method of a modified ion exchange membrane for electrodialysis. Background Art

[0002] Ion exchange membranes are the core components of electrodialysis devices. They selectively transfer specifically charged ions to achieve solution desalination, concentration, or acid-base recovery. They are widely used in wastewater treatment, food processing, and chemical separation. Traditional electrodialysis devices consist of anode and cathode electrodes, a separator, and a homogeneous ion exchange membrane. Ion migration and separation are achieved through the use of fixed charged groups (such as sulfonic acid and quaternary ammonium groups) on the membrane surface. Their performance directly determines the system's energy efficiency and separation accuracy.

[0003] Existing ion exchange membranes generally have the following defects:

[0004] (1) The membrane structure is not uniform enough and the functional groups are randomly distributed, resulting in poor selectivity for monovalent / polyvalent ions (K_{Cl-}^{SO42-} is usually <4.0), making it difficult to meet the requirements for accurate separation of high-salinity wastewater;

[0005] (2) There is a contradiction between mechanical strength and swelling stability. The traditional cross-linking process is prone to membrane pore collapse or excessive swelling (water content > 50%), which is prone to rupture during long-term operation.

[0006] (3) High membrane surface resistance (>5Ω·cm 2 ), the operating voltage needs to be increased (>40V) to maintain the flux, and the energy consumption increases by more than 20%;

[0007] (4) The modification process mostly uses a single temperature curing, the functional monomer grafting rate is low (<10%) and the distribution is uneven, resulting in rapid degradation of membrane performance. These shortcomings seriously restrict the application of electrodialysis technology in the field of high-efficiency separation. Summary of the Invention

[0008] To address these issues, this application provides a method for preparing and applying a modified ion exchange membrane for electrodialysis, overcoming the poor selectivity, low mechanical strength, and high energy consumption of conventional membranes. By combining gradient grafting modification with optimized operating parameters, separation efficiency is significantly improved while energy consumption is reduced.

[0009] In order to solve the above technical problems, the present invention provides the following technical solution: a method for preparing a modified ion exchange membrane for electrodialysis, comprising the following steps:

[0010] (1) Base membrane pretreatment: The polyethersulfone base membrane or sulfonated polystyrene base membrane is immersed in ethanol and deionized water for ultrasonic cleaning for 10-30 minutes, and then activated in 0.1-1 mol / L sulfuric acid or sodium hydroxide solution for 0.5-2 hours;

[0011] (2) Preparation of modified solution: dissolve the functional monomer containing amino, carboxyl or sulfonic acid group, crosslinking agent and initiator in an organic solvent at a mass ratio of (3-5):(1-2):(0.1-0.5) and stir to form a homogeneous modified solution;

[0012] (3) Immersion crosslinking: Immerse the pretreated base film in the modification solution and keep it at 30-60°C for 1-4 hours, then use a gradient temperature increase method (50°C → 80°C → 120°C, each stage for 0.5-1 hour) for crosslinking and curing;

[0013] (4) Post-treatment: The cross-linked membrane was washed with 0.1-0.5 mol / L hydrochloric acid solution to remove unreacted monomers, and then dried to obtain a modified ion exchange membrane.

[0014] Preferably, the functional monomer is selected from at least one of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), dimethylaminoethyl methacrylate (DMAEMA) or acrylic acid, the crosslinking agent is glutaraldehyde or epichlorohydrin, and the organic solvent is N,N-dimethylformamide or N-methylpyrrolidone.

[0015] Preferably, the activation treatment in step (1) is performed using a 0.5 mol / L sulfuric acid solution at 40° C. for 1 hour, and the ultrasonic cleaning frequency is 40 kHz.

[0016] Preferably, the gradient temperature increase method in step (3) is to first maintain the temperature at 50°C for 30 minutes, then increase the temperature to 80°C at a rate of 2°C / min and maintain the temperature for 40 minutes, and finally increase the temperature to 120°C and maintain the temperature for 20 minutes.

[0017] Preferred: membrane surface grafting rate reaches 15-35%, ion exchange capacity is 1.8-2.5mmol / g, water content is controlled at 25-40%, and membrane surface resistance is less than 3Ω·cm 2 .

[0018] A method for applying a modified ion exchange membrane, wherein the membrane is used between the anode and cathode compartments of an electrodialysis device, and the operating parameters include:

[0019] 1) Apply DC voltage 10-30V

[0020] 2) The liquid flow rate is controlled at 5-15 cm / s

[0021] 3) The working temperature is maintained at 25-45℃

[0022] 4) Regularly use 0.1mol / LNaCl solution to clean the membrane online.

[0023] Preferably: when the electrodialysis device is used for desalination of high-salt wastewater, the selectivity coefficient for monovalent ions (K_{Cl-}^{SO4 2 -}) reached 5.8-7.2, the desalination rate was ≥95%, and the current efficiency was maintained at 85-92%.

[0024] Preferably: when the membrane is used in an acid-base recovery system, H + The migration number reaches 0.92-0.96, the OH- migration number reaches 0.88-0.93, and the energy consumption of acid and alkali recovery is reduced by 18-25%.

[0025] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0026] The present invention addresses the key technical bottlenecks of existing ion exchange membranes, such as low ion selectivity (especially insufficient separation efficiency for monovalent / polyvalent ions), poor mechanical stability (prone to swelling and rupture during long-term operation), high membrane surface resistance leading to excessive energy consumption, and the difficulty in balancing the grafting rate and functional group distribution uniformity in traditional modification processes. By pre-activating the surface of the base membrane to enhance the interfacial reaction activity, the present invention adopts amino / carboxyl / sulfonic acid functional monomers and cross-linking agents for directional grafting to construct a dense selective layer, combines a gradient temperature curing strategy to optimize the spatial distribution of the cross-linked network, and simultaneously improves the membrane's anti-swelling property and the regularity of the ion transmission channels. The present invention also matches the application method of coordinated control of DC voltage, flow rate, and temperature, so that the modified membrane maintains a high grafting rate (15-35%) and a low membrane surface resistance (<3Ω·cm 2 ) while achieving a monovalent ion selectivity coefficient (K_{Cl-}^{SO42-}) of 5.8-7.2, H + The / OH- migration numbers are increased to 0.92-0.96 and 0.88-0.93 respectively, thereby achieving a desalination rate of ≥95% and a current efficiency of 85-92% in the desalination of high-salt wastewater, and reducing energy consumption by 18-25% in acid and alkali recovery, systematically solving the industry pain point of the difficulty in balancing the efficiency, durability and energy consumption of traditional membrane separation.

[0027] Other advantages, objects and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art based on an examination of the following or may be learned from the practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a flow chart of a method for preparing and applying a modified ion exchange membrane for electrodialysis according to the present invention;

[0029] Figure 2 This is a preparation timing diagram of a method for preparing and applying a modified ion exchange membrane for electrodialysis according to the present invention;

[0030] Figure 3 A structural diagram of an ion exchange membrane for a method of preparing and applying a modified ion exchange membrane for electrodialysis according to the present invention;

[0031] Figure 4 A diagram showing the preparation process and parameter optimization relationship of a method for preparing and applying a modified ion exchange membrane for electrodialysis according to the present invention;

[0032] Figure 5 A timing diagram of an ion exchange membrane application method for preparing and applying a modified ion exchange membrane for electrodialysis according to the present invention;

[0033] Figure 6 The present invention is a schematic diagram of the ion migration path of the preparation and application method of a modified ion exchange membrane for electrodialysis. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] It should be noted that the terms “vertical”, “horizontal”, “up”, “down”, “left”, “right” and similar expressions used in this document are for illustrative purposes only and do not represent the only implementation method.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains; the terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention; the term "and / or" used herein includes any and all combinations of one or more of the associated listed items.

[0037] like Figure 1 、 23, a method for preparing a modified ion exchange membrane for electrodialysis, characterized by adopting a base membrane pretreatment-functionalized grafting-gradient solidification collaborative process: first, the polyethersulfone or sulfonated polystyrene base membrane is ultrasonically cleaned with ethanol and deionized water (10-30 minutes) and activated with 0.1-1 mol / L sulfuric acid / sodium hydroxide solution (0.5-2 hours) to enhance the surface activity; then, a functional monomer containing amino, carboxyl or sulfonic acid groups (such as AMPS, DMAEMA or acrylic acid), a cross-linking agent (glutaraldehyde or epichlorohydrin) and A homogeneous modified solution (solvent: DMF or NMP) with a mass ratio of initiator to initiator (3-5):(1-2):(0.1-0.5) is prepared by immersing the grafting agent at 30-60°C for 1-4 hours and then curing the grafting agent at a gradient temperature (50°C → 80°C → 120°C, 0.5-1 hour for each stage) to form a stable cross-linked network; finally, the grafting agent is washed with 0.1-0.5 mol / L hydrochloric acid and dried to obtain a grafting rate of 15-35%, an ion exchange capacity of 1.8-2.5 mmol / g, a water content of 25-40%, and a membrane surface resistance of less than 3 Ω·cm. 2 The modified membrane regulates the membrane microstructure through chemical grafting and gradient curing to enhance ion selectivity and mechanical stability.

[0038] In this embodiment, the modified ion exchange membrane is supported by a pretreated base membrane as a skeleton, and a functional monomer is grafted onto the surface by chemical bonding to form a selective layer. The functional monomer and the cross-linking agent are catalyzed by an initiator to form a three-dimensional cross-linked network structure under gradient temperature conditions, wherein the interface between the base membrane and the functional layer is chemically bonded by activation treatment; this structural combination provides mechanical support through the base membrane, the functional layer realizes ion selective transmission, the cross-linked network ensures structural stability, and the gradient curing process makes the functional groups present a gradient distribution in the membrane thickness direction, thereby synergistically achieving high ion selectivity (K_{Cl-}^{SO42-} reaches 5.8-7.2), low membrane surface resistance (<3Ω·cm 2 ) and excellent mechanical strength (water content 25-40%). At the same time, by optimizing the functional monomer ratio and curing parameters, the contradiction between traditional membrane selectivity and flux is solved, so that the current efficiency can be maintained at 85-92% when the desalination rate is ≥95%.

[0039] like Figure 4 、 56, the application method of the modified ion exchange membrane is adapted to multiple scenarios through parameter optimization: it is placed between the anode and cathode compartments in the electrodialysis device, operated at a DC voltage of 10-30V, a feed flow rate of 5-15cm / s, and a temperature of 25-45°C, and regularly cleaned online with 0.1mol / LNaCl to control membrane fouling; when applied to the desalination of high-salt wastewater, the monovalent ion selectivity coefficient (K_{Cl-}^{SO42-}) reaches 5.8-7.2, the desalination rate is ≥95% and the current efficiency is maintained at 85-92%; when used for acid and alkali recovery, H + The migration number is 0.92-0.96, the OH- migration number is 0.88-0.93, and the energy consumption is reduced by 18-25%, achieving efficient separation and energy-saving operation.

[0040] In this embodiment, the electrodialysis device includes an anode chamber, a cathode chamber and a modified ion exchange membrane assembly placed therebetween, wherein the anode adopts a titanium-coated ruthenium electrode, the cathode adopts a stainless steel electrode, the separator is made of polypropylene and the flow channel width is 2-3 mm; the membrane assembly is composed of a pretreated polyethersulfone-based membrane (thickness 150-200 μm) and a functionalized grafted layer (thickness 20-50 μm) composite, the matching DC power supply output voltage is adjustable from 0 to 50 V, the feed liquid circulation pump flow range is 5-50 L / h, and the temperature control system accuracy is ±1°C; in specific implementation, for high-salt wastewater with a salt content of 5000-10000 mg / L, the preferred parameter combination of voltage 15-25 V, flow rate 8-12 cm / s, and temperature 30-40°C is selected, at which time the membrane surface resistance is stabilized at 2.1-2.8 Ω·cm 2 , energy consumption per ton of water ≤ 2.5kWh; for the acid-base recovery system, when processing 1-2mol / L waste acid, control the voltage to 10-15V, temperature to 35-45℃, H + The migration flux is 12-15 mol / (m 2 ·h), and the energy consumption per ton of acid recovery is reduced by 1.8-2.3kWh compared with traditional membranes; all operating data are monitored in real time through online conductivity meters, pH meters and flow meters, and parameters are automatically adjusted through the PLC system.

[0041] In one or more feasible embodiments, the electrodialysis system of the present invention adopts a modular design, and the modified ion exchange membrane is assembled in the electrode frame by alternately stacking rubber gaskets and polypropylene partitions, and the sealing is ensured by bolt tightening (installation torque 5-8N·m); the system is equipped with a pretreatment device in the prior art (including a 5μm precision filter and an activated carbon adsorption tower) to pretreat the incoming water. During operation, the circulation pump is first started to flush the membrane stack at a pressure of 0.3-0.5MPa for 10 minutes, and then the pump speed is adjusted to the set flow rate (5-15cm / s) by the frequency converter. After the flow stabilizes, the DC power supply is turned on and the constant pressure mode is adopted for operation; during operation, the existing PLC control system is used to monitor the transmembrane pressure difference (<0.15MPa), current density (15-30mA / cm 2 ) and other parameters. When the system pressure difference rises by 20% or the current efficiency drops to 80%, a 0.1mol / LNaCl backwash program is automatically triggered (duration 8-15 minutes, flow rate increased to 20cm / s). For acid and base recovery applications, it is necessary to operate in conjunction with the bipolar membrane electrodialysis module in the existing technology. The modified membrane is used as a cation exchange membrane in combination with an anion exchange membrane (such as Neosepta CMX / AMX). Synchronous acid and base recovery is achieved through a three-chamber configuration. During operation, the pH value of the polar chamber is controlled within the range of 2-11 to prevent membrane degradation. When the system is shut down, a standardized maintenance procedure is performed: first rinse with deionized water for 30 minutes, and then inject 1% sodium bisulfite protective solution. All operating procedures comply with the requirements of the ISO 9001 quality management system.

[0042] Although the present invention has been disclosed above in terms of preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for preparing a modified ion exchange membrane for electrodialysis, characterized in that: The following steps are involved: (1) Base membrane pretreatment: The polyethersulfone base membrane or sulfonated polystyrene base membrane is immersed in ethanol and deionized water for ultrasonic cleaning for 10-30 minutes, and then activated in 0.1-1 mol / L sulfuric acid or sodium hydroxide solution for 0.5-2 hours; (2) Preparation of modified solution: dissolve the functional monomer containing amino, carboxyl or sulfonic acid group, crosslinking agent and initiator in an organic solvent at a mass ratio of (3-5):(1-2):(0.1-0.5) and stir to form a homogeneous modified solution; (3) Immersion crosslinking: Immerse the pretreated base film in the modification solution and keep it at 30-60°C for 1-4 hours, then use a gradient temperature increase method (50°C → 80°C → 120°C, each stage for 0.5-1 hour) for crosslinking and curing; (4) Post-treatment: The cross-linked membrane was washed with 0.1-0.5 mol / L hydrochloric acid solution to remove unreacted monomers, and then dried to obtain a modified ion exchange membrane.

2. The method for preparing a modified ion exchange membrane for electrodialysis according to claim 1, wherein: The functional monomer is selected from at least one of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), dimethylaminoethyl methacrylate (DMAEMA) or acrylic acid, the crosslinking agent is glutaraldehyde or epichlorohydrin, and the organic solvent is N,N-dimethylformamide or N-methylpyrrolidone.

3. The method for preparing a modified ion exchange membrane for electrodialysis according to claim 1, wherein: In the step (1), the activation treatment is performed using a 0.5 mol / L sulfuric acid solution at 40° C. for 1 hour, and the ultrasonic cleaning frequency is 40 kHz.

4. The method for preparing a modified ion exchange membrane for electrodialysis according to claim 1, wherein: The gradient temperature increase method in step (3) is specifically as follows: first, the temperature is maintained at 50°C for 30 minutes, then the temperature is increased to 80°C at a rate of 2°C / min and maintained for 40 minutes, and finally the temperature is increased to 120°C and maintained for 20 minutes.

5. The modified ion exchange membrane prepared by the preparation method according to claim 1, characterized in that: The membrane surface grafting rate is 15-35%, the ion exchange capacity is 1.8-2.5mmol / g, the water content is controlled at 25-40%, and the membrane surface resistance is less than 3Ω·cm 2 .

6. A method for applying a modified ion exchange membrane, characterized in that: The membrane is used between the anode and cathode compartments of an electrodialysis device, and the operating parameters include: 1) Apply DC voltage 10-30V 2) The liquid flow rate is controlled at 5-15 cm / s 3) The working temperature is maintained at 25-45℃ 0.1 mol / L NaCl solution is used regularly for online cleaning of membrane fouling.

7. The method for applying a modified ion exchange membrane according to claim 6, wherein: When the electrodialysis device is used for desalination of high-salt wastewater, the selectivity coefficient for monovalent ions (K_{Cl-}^{SO4 2 -}) reached 5.8-7.2, the desalination rate was ≥95%, and the current efficiency was maintained at 85-92%.

8. The method for applying a modified ion exchange membrane according to claim 6, wherein: When the membrane is used in an acid-base recovery system, H + The migration number reaches 0.92-0.96, the OH- migration number reaches 0.88-0.93, and the energy consumption of acid and alkali recovery is reduced by 18-25%.

Images