Electrodialysis device for enriching low-concentration weak acid-base solution and enrichment method thereof

Abstract

The application provides an electrodialysis device for enriching a low-concentration weak acid-base solution and an enrichment method thereof, comprising oppositely arranged anodes and cathodes, an anode membrane arranged on the side of the anodes, a cathode membrane, a first separation net and at least one repeating membrane unit arranged on the side of the cathodes and between the first separation net and the anode membrane; the repeating membrane unit comprises a second separation net, an anion membrane, an ion-conductive separation net and a cation membrane arranged in sequence, the ion-conductive separation net comprises a separation net body and ion-conductive material filled in the separation net body, and the ion-conductive material is anion-conductive material or cation-conductive material. The ion-conductive material is applied to the electrodialysis system, the conductivity of the feed liquid is enhanced, and the concentration of charged ions in the raw solution can be efficiently realized under the action of an applied direct current electric field. Compared with the original method, the technical solution has higher current efficiency, higher unit processing capacity, higher recovery liquid concentration and lower energy consumption.

Description

Technical Field

[0001] This invention relates to the technical field of electrochemical separation, specifically to an electrodialysis device and method for enriching low-concentration weak acid and alkali solutions. Background Technology

[0002] In actual production processes, low-concentration salt, alkali, and acid solutions are frequently generated. Due to their low concentration, they cannot be used directly. These low-concentration solutions are typically diluted with water to meet emission standards before being discharged, which creates considerable environmental pressure and also signifies a significant waste of resources.

[0003] In recent years, electrodialysis technology has gained increasing attention and has been gradually applied to specific fields for treating ionic aqueous solutions. It uses an applied DC electric field as the driving force and leverages the selective permeability of cation and anion membranes to allow the directional migration of cations and anions, thereby enriching or concentrating the aqueous solution. Weak acids and bases are highly soluble in water and exist in an ionic state, making them suitable for electrodialysis. However, the weak dissociation of weak acids and bases results in poor conductivity in these solutions, leading to poor performance, high energy consumption, and low concentrations during electrodialysis treatment. This limits the further widespread adoption of electrodialysis technology in this field. Summary of the Invention

[0004] This invention addresses the problem of enriching or concentrating low-concentration weak acid and base solutions by providing an electrodialysis device and method for enriching such solutions. By applying ion-conductive materials to the electrodialysis (ED) system, the conductivity of the feed solution is enhanced. Under an applied DC electric field, the concentration of charged ions in the feed solution can be achieved efficiently. Compared to previous methods, this invention offers higher current efficiency, higher throughput per unit area, higher recovered solution concentration, and lower energy consumption.

[0005] The present invention provides an electrodialysis device for enriching low-concentration weak acid and base solutions, comprising an anode and a cathode arranged opposite to each other, an anode membrane disposed on one side of the anode, a cathode membrane, a first screen disposed on one side of the cathode, and at least one repeating membrane unit disposed between the first screen and the anode membrane.

[0006] The repeatable membrane unit includes a second separator, an anion exchange membrane, an ion-conductive separator, and a cation exchange membrane arranged sequentially. The other side of the second separator is an anode membrane or a cation exchange membrane, and the other side of the cation exchange membrane is a first separator or a second separator.

[0007] The ion-type conductive mesh includes a mesh body and an ion-type conductive material filled in the mesh body. The ion-type conductive material is either an anionic conductive material or a cationic conductive material.

[0008] The side of the anion exchange membrane facing the anode is a concentration chamber containing a low-concentration weak acid solution or a low-concentration weak base solution. Between the anion exchange membrane and the cation exchange membrane is a dilute chamber containing a low-concentration weak acid solution or a low-concentration weak base solution. An ion-type conductive mesh is located in the dilute chamber. The dilute chamber is connected to a desalination solution tank, and the concentration chamber is connected to a concentrate tank.

[0009] The anionic conductive material of the ion-type conductive mesh adsorbs hydrogen ions generated by the weak acid solution in the dilute chamber and allows the hydrogen ions to pass through the cation membrane into the concentrated chamber. The weak acid anions in the weak acid solution migrate towards the anode and pass through the anion membrane into the concentrated chamber to combine with hydrogen ions, thereby achieving the directional migration of low-concentration weak acid and the enrichment of low-concentration weak acid solution.

[0010] The cationic conductive material of the ion-type conductive mesh adsorbs hydroxide ions generated by the weak alkaline solution in the dilute chamber and allows the hydroxide ions to pass through the anion exchange membrane into the concentrated chamber. The weak alkaline cations in the weak alkaline solution migrate towards the cathode and pass through the cation exchange membrane into the concentrated chamber to combine with hydroxide ions, thereby achieving the directional migration of low-concentration weak bases and the enrichment of low-concentration weak acid solutions.

[0011] The electrodialysis device for enriching low-concentration weak acid and alkali solutions according to the present invention, as a preferred embodiment, uses any one or more of the following low-concentration weak acids: formic acid, acetic acid, propionic acid, butyric acid, oxalic acid, malonic acid, succinic acid, benzoic acid, malic acid, maleic acid, tartaric acid, lactic acid, salicylic acid, ascorbic acid, taurine, propanesulfonic acid, boric acid, phosphoric acid, and hypochlorous acid.

[0012] The electrodialysis device for enriching low-concentration weak acid and base solutions according to the present invention, as a preferred embodiment, is any one or more of the following: ammonia monohydrate, dimethylamine, trimethylamine and aniline.

[0013] The electrodialysis device for enriching low-concentration weak acid and alkali solutions according to the present invention, as a preferred embodiment, uses one or more of the following anionic conductive materials: cation exchange resin, cation conductive mesh, and cation membrane fragments.

[0014] Cationic conductive materials include one or more of the following: anion exchange resins, anion conductive meshes, and anion membrane fragments.

[0015] In the electrodialysis device for enriching low-concentration weak acid and base solutions according to the present invention, the concentrations of the low-concentration weak acid and weak base are preferably 0.5% to 5%.

[0016] The mesh body is a continuous and dense mesh with an effective open area in the middle, and the thickness of the mesh body is 0.5mm~10mm;

[0017] Both the first and second meshes are continuous and dense on all four sides, with an effective open area in the middle, which can form a turbulent layer when the solution flows through them. The thickness of the first and second meshes is 0.5mm~1mm.

[0018] The number of repeating membrane units ranges from 1 to 200.

[0019] This invention provides an enrichment method for an electrodialysis device used to enrich low-concentration weak acid and base solutions, comprising the following steps:

[0020] S1. Prepare a low-concentration weak acid solution or a low-concentration weak base solution to obtain the stock solution;

[0021] S2. Assemble the anode, cathode, anode membrane, cathode membrane, first separator and at least one repeating membrane unit to obtain an electrodialysis device for enriching low-concentration weak acid and alkali solutions.

[0022] S3. Add the original solution to the desalination tank in the desalination chamber and the concentrate tank in the concentration chamber respectively. Circulate the solution using a water pump and turn on the DC power supply to form a DC electric field for enrichment. After the concentration in the concentrate tank reaches the target, an enriched weak acid solution or weak alkali solution is obtained. The desalination tank contains a residual solution with reduced concentration. The enrichment method of an electrodialysis device for enriching low-concentration weak acid and alkali solutions is completed.

[0023] The enrichment method of the electrodialysis device for enriching low-concentration weak acid and base solutions according to the present invention, as a preferred embodiment, involves filtering the low-concentration weak acid solution and the low-concentration weak base solution in step S1, resulting in a clear and transparent initial solution as the original solution.

[0024] In the preferred embodiment of the enrichment method of the electrodialysis device for enriching low-concentration weak acid and alkali solutions according to the present invention, in step S3, the initial volume ratio of the original solution added to the desalination solution tank and the concentrate tank is 1:100 to 1:1.

[0025] Step S3 also includes adding an inorganic solution as an electrode solution to the electrodialysis device that enriches low-concentration weak acid and base solutions.

[0026] The inorganic solution is any one or more of the following: sodium sulfate, sodium nitrate, sodium hydroxide, potassium hydroxide, potassium sulfate, potassium nitrate, potassium hydroxide, hydrochloric acid, sulfuric acid, nitric acid, hypophosphoric acid, and the concentration of the inorganic solution is 0.5% to 5%.

[0027] In the preferred embodiment of the electrodialysis method for enriching low-concentration weak acid and alkali solutions described in this invention, in step S3, the operating current density of the electrodialysis device for enriching low-concentration weak acid and alkali solutions is 10~1000 A / m. 2 The operating voltage of a single group is 0.5~1V.

[0028] In the preferred embodiment of the enrichment method of the electrodialysis device for enriching low-concentration weak acid or alkali solutions according to the present invention, in step S3, the concentration of the residual liquid is 0.1% to 1%, and the concentration of the enriched weak acid or alkali solution is 3% to 15%.

[0029] The present invention has the following advantages:

[0030] (1) Formic acid, acetic acid, ammonia monohydrate and other weak acid-base solutions have low conductivity and can only partially ionize in aqueous solution. They mainly exist as hydrogen ions, weak acid radicals, weak acid molecules or hydroxide ions, weak base cations and weak base molecules. Under the action of a DC electric field, the hydrogen ions generated by the ionization of weak acids in the desalination solution are adsorbed by anionic conductive materials, thereby realizing the process of "adsorption-desorption-migration" and further passing through the cation membrane into the concentrate chamber. Meanwhile, the weak acid radicals in the original solution migrate towards the positive electrode and pass through the anion membrane into the concentrate chamber, where they combine with hydrogen ions to realize the directional migration of weak acids. The principle of the "adsorption-desorption-migration" process of weak bases is the same.

[0031] In this process, anionic conductive materials construct rapid hydrogen ion migration channels, and cationic conductive materials construct rapid hydroxide ion migration channels, accelerating the migration rate. At the same time, as hydrogen ions or hydroxide ions migrate out, it is beneficial to the decomposition of weak acid molecules or weak base molecules in the desalination solution, generating more hydrogen ions or hydroxide ions, thereby further promoting the migration of hydrogen ions or hydroxide ions.

[0032] (2) Inspired by electrodeionization (EDI) technology, this invention applies ion-conductive materials to an electrodialysis (ED) system, enhancing the conductivity of the feed solution. Under the action of an external DC electric field, it can efficiently concentrate charged ions in the feed solution. Compared with the original method, this invention significantly increases current efficiency, increases the unit processing capacity, and reduces energy consumption; the concentration of the concentrate is increased, reducing the overall water volume and water usage. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of an electrodialysis device for enriching low-concentration weak acid and alkali solutions.

[0034] Figure 2 A flowchart of an enrichment method for an electrodialysis device used to enrich low-concentration weak acid and base solutions.

[0035] Figure 3 Example 1 of an electrodialysis device for enriching low-concentration weak acid and alkali solutions: Comparison of operating current densities.

[0036] Figure label:

[0037] 1. Anode; 2. Cathode; 3. Anode membrane; 4. Cathode membrane; 5. First separator; 6. Repeating membrane unit; 61. Second separator; 62. Anion exchange membrane; 63. Ion-type conductive separator; 64. Cation exchange membrane. Detailed Implementation

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Example 1

[0039] like Figures 1-2 As shown, an electrodialysis device and method for enriching low-concentration weak acid and base solutions are described. The first step involves preparing 6 L of 1% acetic acid solution with glacial acetic acid and 3 L of 2% solution with concentrated sulfuric acid.

[0040] Step 2: Assemble the ion-conducting membrane 63 using 2~5.0 mmol / g cation exchange resin. Then, assemble the repeatable membrane unit 6 using the second membrane 61, the anion exchange membrane 62, the ion-conducting membrane 63, and the cation exchange membrane 64.

[0041] An electrodialysis device for enriching low-concentration weak acid and alkali solutions is assembled by assembling anode 1, cathode 2, anode membrane 3, cathode membrane 4, first separator 5, and repeating membrane unit 6, and then connected to instruments and equipment.

[0042] Step 3: Add 1L of 1% acetic acid solution to the concentrate tank, 5L of 1% acetic acid solution to the desalination tank, and 3L of 2% dilute sulfuric acid solution to the electrode solution tank, and start the circulation. Turn on the DC power supply, set the voltage to 1V / group, and the maximum operating current to 200A / m. 2 After running the experiment for 30 minutes, the DC power supply and water pump were turned off in sequence, and the liquid in each water tank was collected.

[0043] Based on the experimental results, the operating current density during the process was calculated to be 56~112 A / m. 2 The partial pressure of a single membrane unit is 1V / unit, the concentration of the recovered solution is 2.7%, and the unit throughput (based on pure acetic acid) is 104.5g / (m³). 2 ·h), unit DC energy consumption (based on pure acetic acid) 765.7kwh / t.

[0044] In comparison, the parameters of existing electrodialysis systems are as follows: recovered solution concentration 1.8%, operating current density 34~65 A / m³. 2 Unit throughput (based on pure acetic acid) 39.2 g / (m³) 2 ·h), unit DC energy consumption (based on pure acetic acid) 1276.2kwh / t.

[0045] The comparison chart of operating current density is as follows Figure 3 As shown.

[0046] Example 2

[0047] like Figures 1-2 As shown, an electrodialysis device and method for enriching low-concentration weak acid and base solutions are disclosed.

[0048] Step 1: Prepare 20L of 3% formic acid solution and 5L of 2% dilute sulfuric acid solution.

[0049] Step 2: Assemble an ion-type conductive mesh 63 using a 0.5~3.0 mmol / g cation conductive mesh. Then, assemble a repeatable membrane unit 6 using a second mesh 61, an anion membrane 62, an ion-type conductive mesh 63, and a cation membrane 64.

[0050] An electrodialysis device for enriching low-concentration weak acid and alkali solutions is assembled by assembling anode 1, cathode 2, anode membrane 3, cathode membrane 4, first separator 5, and repeating membrane unit 6, and then connected to instruments and equipment.

[0051] Step 3: Add 1L of 3% formic acid solution to the concentrate tank, 3L of 3% formic acid solution to the desalination tank, and 3L of 2% dilute sulfuric acid solution to the electrode solution tank, and start the circulation. Turn on the DC power supply, set the voltage to 1V / group, and the maximum operating current to 300A / m. 2 When the concentration of the desalination solution drops to 1%, replace it with the initial solution at 3%, and continue running until the concentration of the concentrate no longer rises. Then, turn off the DC power supply and the water pump in sequence, and collect the liquid from each water tank.

[0052] Based on experimental results, the operating current density during the process was calculated to be 114~280 A / m. 2 The partial pressure of a single membrane unit is 1V / unit, the concentration of the recovered solution is 9.8%, and the unit throughput (based on pure formic acid) is 206.0 g / (m³). 2 ·h), unit DC energy consumption (calculated as pure formic acid) 971.0 kWh / t.

[0053] In comparison, the parameters of existing electrodialysis systems are as follows: recovered solution concentration 6.3%, operating current density 94~195 A / m³. 2 Unit throughput (calculated as pure formic acid) 103.0 g / (m³) 2 ·h), unit DC energy consumption (calculated as pure formic acid) 1456.5kwh / t.

[0054] Example 3

[0055] like Figures 1-2 As shown, an electrodialysis device and method for enriching low-concentration weak acid and base solutions are disclosed.

[0056] Step 1: Prepare 20L of 2% formic acid solution and 5L of 2% dilute sulfuric acid solution.

[0057] Step 2: Assemble an ion-conductive membrane 63 using 0.5~3.0 mmol / g cation-conductive membrane fragments. Then, assemble a repeatable membrane unit 6 using a second membrane 61, an anion membrane 62, an ion-conductive membrane 63, and a cation membrane 64.

[0058] An electrodialysis device for enriching low-concentration weak acid and alkali solutions is assembled by assembling anode 1, cathode 2, anode membrane 3, cathode membrane 4, first separator 5, and repeating membrane unit 6, and then connected to instruments and equipment.

[0059] Step 3: Add 1L of 2% formic acid solution to the concentrate tank, 3L of 2% formic acid solution to the desalination tank, and 3L of 2% dilute sulfuric acid solution to the electrode solution tank, and start the circulation. Turn on the DC power supply, set the voltage to 1V / group, and the maximum operating current to 300A / m. 2 When the concentration of the desalination solution drops to 1%, replace it with the initial 2% formic acid solution and continue running until the concentration of the concentrate no longer rises. Then, turn off the DC power supply and water pump in sequence and collect the liquid from each water tank.

[0060] Based on the experimental results, the operating current density during the process was calculated to be 10⁸~2¹² A / m. 2 The partial pressure of a single membrane unit is 1V / unit, the concentration of the recovered solution is 8.9%, and the unit throughput (based on pure formic acid) is 169.9g / (m³). 2 ·h), unit DC energy consumption (calculated as pure formic acid) 1059.3kwh / t.

[0061] In comparison, the parameters of the unmodified electrodialysis system are as follows: recovered solution concentration 5.4%, operating current density 89~174 A / m³. 2 Unit throughput (calculated as pure formic acid) 87.1 g / (m³) 2 ·h), unit DC energy consumption (calculated as pure formic acid) 1664.5kwh / t.

[0062] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An electrodialysis device for enriching low-concentration weak acid and alkali solutions, characterized in that: It includes an anode (1) and a cathode (2) arranged opposite to each other, an anode membrane (3) disposed on one side of the anode (1), a cathode membrane (4) and a first mesh (5) disposed on one side of the cathode (2) in sequence, and at least one repeating membrane unit (6) disposed between the first mesh (5) and the anode membrane (3). The repeatable membrane unit (6) includes a second mesh (61), an anion membrane (62), an ion-type conductive mesh (63) and a cation membrane (64) arranged in sequence. The other side of the second mesh (61) is the anode membrane (3) or the cation membrane (64), and the other side of the cation membrane (64) is the first mesh (5) or the second mesh (61). The ionic conductive mesh (63) includes a mesh body and an ionic conductive material filled in the mesh body, wherein the ionic conductive material is an anionic conductive material or a cationic conductive material; The anion exchange membrane (62) facing the anode (1) is a concentration chamber for a low-concentration weak acid solution or a low-concentration weak alkali solution. The anion exchange membrane (62) and the cation exchange membrane (64) are located in a dilute chamber for a low-concentration weak acid solution or a low-concentration weak alkali solution. The ion-type conductive mesh (63) is located in the dilute chamber. The dilute chamber is connected to a desalination liquid tank, and the concentration chamber is connected to a concentrate tank. The anionic conductive material is one or more of the following: cation exchange resin, cation conductive mesh, cation membrane fragments; The cationic conductive material is one or more of the following: anion exchange resin, anion conductive mesh, and anion membrane fragments. The concentrations of the low-concentration weak acid and the low-concentration weak base are 0.5% to 5%; In the electrodialysis device for enriching low-concentration weak acid and alkali solutions, under the action of a DC electric field, hydrogen ions generated by the ionization of low-concentration weak acid in the desalination tank are adsorbed by the anionic conductive material of the ion-type conductive mesh (63), thereby realizing the "adsorption-desorption-migration" process, and further passing through the cation membrane (64) into the concentration chamber; while the weak acid radical ions in the low-concentration weak acid stock solution migrate towards the anode (1) and pass through the anion membrane (62) into the concentration chamber to combine with hydrogen ions, thereby realizing the directional migration of low-concentration weak acid and the enrichment of low-concentration weak acid solution; In the electrodialysis device for enriching low-concentration weak acid and base solutions, under the action of a DC electric field, hydroxide ions generated by the ionization of low-concentration weak base in the desalination tank are adsorbed by the cationic conductive material of the ion-type conductive mesh (63), thereby realizing the process of "adsorption-desorption-migration". They further pass through the anion membrane (62) into the concentration chamber. The weak base cations in the low-concentration weak base solution migrate towards the cathode (2) and pass through the cation membrane (64) into the concentration chamber to combine with hydroxide ions, thereby realizing the directional migration of low-concentration weak base and the enrichment of low-concentration weak base solution.

2. The electrodialysis device for enriching low-concentration weak acid and alkali solutions according to claim 1, characterized in that: The low-concentration weak acids include, but are not limited to, the following: formic acid, acetic acid, propionic acid, butyric acid, oxalic acid, malonic acid, succinic acid, benzoic acid, malic acid, maleic acid, tartaric acid, lactic acid, salicylic acid, ascorbic acid, taurine, boric acid, phosphoric acid, hypochlorous acid, propanesulfonic acid, boric acid, phosphoric acid, and hypochlorous acid.

3. The electrodialysis device for enriching low-concentration weak acid and alkali solutions according to claim 1, characterized in that: The low-concentration weak base is any one or more of the following: ammonia monohydrate, dimethylamine, trimethylamine, and aniline.

4. The electrodialysis device for enriching low-concentration weak acid and alkali solutions according to claim 1, characterized in that: The mesh body is a continuous, dense mesh with an effective open area in the middle, and the thickness of the mesh body is 0.5mm~10mm. The first mesh (5) and the second mesh (61) are both meshes that are continuous and dense on all four sides, with an effective hollow area in the middle, and can form a turbulent layer when the solution flows through them. The thickness of the first mesh (5) and the second mesh (61) is 0.5mm~1mm. The number of repeating membrane units (6) is 1 to 200.

5. The enrichment method of an electrodialysis device for enriching low-concentration weak acid-base solutions according to any one of claims 1 to 4, characterized in that: Includes the following steps: S1. Prepare a low-concentration weak acid solution or a low-concentration weak base solution to obtain the stock solution; S2. Assemble the anode (1), the cathode (2), the anode membrane (3), the cathode membrane (4), the first mesh (5), and at least one repeating membrane unit (6) to obtain the electrodialysis device for enriching low-concentration weak acid and alkali solutions; S3. The original solution is added to the desalination tank in the desalination chamber and the concentrate tank in the concentration chamber, respectively. The solution is circulated by a water pump and a DC electric field is formed by turning on the DC power supply to enrich the solution. After the concentration in the concentrate tank reaches the target, an enriched weak acid solution or weak alkali solution is obtained. The desalination tank contains a residual solution with reduced concentration. The enrichment method of an electrodialysis device for enriching low-concentration weak acid and alkali solutions is completed.

6. The enrichment method of an electrodialysis device for enriching low-concentration weak acid-base solutions according to claim 5, characterized in that: In step S1, the low-concentration weak acid solution and the low-concentration weak base solution are filtered, and the original solution is a clear and transparent initial solution.

7. The enrichment method of an electrodialysis device for enriching low-concentration weak acid-base solutions according to claim 5, characterized in that: In step S3, the initial volume ratio of the stock solution added to the desalination tank and the concentrate tank is 1:100 to 1:1; Step S3 further includes adding an inorganic solution as an electrode solution to the electrodialysis device enriched with low-concentration weak acid and base solutions. The inorganic solution is any one or more of the following: sodium sulfate, sodium nitrate, sodium hydroxide, potassium hydroxide, potassium sulfate, potassium nitrate, potassium hydroxide, hydrochloric acid, sulfuric acid, nitric acid, hypophosphoric acid, and the concentration of the inorganic solution is 0.5% to 5%.

8. The enrichment method of an electrodialysis device for enriching low-concentration weak acid-base solutions according to claim 5, characterized in that: In step S3, the operating current density of the electrodialysis device for enriching low-concentration weak acid and alkali solutions is 10~1000 A / m. 2 The operating voltage of a single group is 0.5~1V.

9. The enrichment method of an electrodialysis device for enriching low-concentration weak acid-base solutions according to claim 5, characterized in that: In step S3, the concentration of the residual liquid is 0.1% to 1%, and the concentration of the enriched weak acid solution or weak base solution is 3% to 15%.

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