A method for preparing high-purity acid by closed-loop coupling of bipolar membrane electrodialysis and diffusion dialysis

Abstract

This invention provides a method for preparing high-purity acid through closed-loop coupling of bipolar membrane electrodialysis and diffusion dialysis, belonging to the field of membrane separation technology. This invention utilizes bipolar membrane electrodialysis (BMED) for acid production and concentration, and distilled distillate (DD) for purification and cation rejection. The high-purity acid solution purified from DD is used as the acid receiving liquid in the DMED, forming a synergistic cycle of "acid production-purification-concentration." This compensates for the decrease in acid concentration during DD purification and avoids using pure water as the acid receiving liquid, thus reducing pure water consumption. Furthermore, the residual acid after DD purification is used as a replenishing liquid in the DMED salt chamber, reducing wastewater generation.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a method for preparing high-purity acid by closed-loop coupling of bipolar membrane electrodialysis and diffusion dialysis. Background Technology

[0002] Bipolar membrane electrodialysis (BMED) is an advanced electro-driven membrane process that uses a direct current electric field to dissociate water and generate hydrogen. + and OH - By combining anion exchange membranes and cation exchange membranes, salt solutions (taking NaCl as an example) are converted into corresponding acids (HCl) and bases (NaOH).

[0003] A typical three-chamber BMED unit includes an acid chamber, a salt chamber (feed chamber), and an alkali chamber; a schematic diagram is shown below. Figure 1 As shown: NaCl solution is circulated into the salt chamber. Under the influence of an electric field, Cl... - It enters the acid chamber through the anion exchange membrane and reacts with H+ generated by the bipolar membrane. + Combine to form HCl; Na + It enters the alkaline chamber through the cation exchange membrane and reacts with OH-. - This process generates NaOH. This technology has advantages such as requiring no external acid or alkali, relatively low energy consumption, and enabling the resource-based conversion of salts. It has already been applied in fields such as industrial waste salt treatment and organic acid salt conversion.

[0004] However, in actual operation, the BMED acid chamber product (HCl) often contains cations (Na+). + The leakage problem is mainly caused by factors such as: the anion exchange membrane's resistance to monovalent cations (Na+). + The retention of ions is not 100%, especially under high concentration gradients or long-term operation. Monovalent ions can permeate into the acid chamber in trace amounts through membrane defects, water channels, or the Donnan dialysis effect; bipolar or anion membranes may experience slight reverse ion migration under high current densities; impurities in the feed solution or membrane aging further exacerbate leakage. Leakage results in the presence of impurity ions (Na+) in the acid product. + When the concentration is in the hundreds to thousands of mg / L, the acid purity decreases and cannot meet the requirements for high-purity acid.

[0005] Diffusion dialysis (DD) uses a concentration gradient as the driving force, allowing solutes to diffuse from a side with a high concentration to a side with a low concentration. A diffusion membrane is used to selectively pass ions through the membrane, purifying the solute. A DD system includes a feed tank, a feed chamber, and a recovery chamber, with a diffusion membrane between the feed chamber and the recovery chamber. Impurities in the feed tank circulate through the feed chamber, while pure water flows counter-currently through the recovery chamber. Solutes from the impurities pass through the diffusion membrane into the recovery chamber, while impurities remain in the feed chamber, thus purifying the solute.

[0006] Existing technology introduces the acid solution generated by BMED into the DD system to reduce impurity cations in the acid solution; a schematic diagram is shown below. Figure 2 As shown: The acid solution produced in the BMED acid chamber is used as a raw material and passed into a DD system with an anion exchange membrane as the diffusion membrane. Pure water is used as the receiving liquid for diffusion dialysis to produce an ultrapure acid solution and impurity cations (Na+). + Acid solution. However, the DD system has a fatal flaw: DD is driven by concentration difference, so the concentration of the permeate is inevitably lower than that of the original solution, resulting in a significant decrease in the acid concentration in the ultrapure acid solution, and high-concentration acid cannot be obtained; the DD receiver side needs to continuously replenish pure water as the receiving liquid, which significantly increases the amount of pure water used and the amount of wastewater generated. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing high-purity acid through closed-loop coupling of bipolar membrane electrodialysis and diffusion dialysis. The method provided by this invention can obtain high-concentration, high-purity acid with low pure water consumption and minimal wastewater generation.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing high-purity acid by closed-loop coupling of bipolar membrane electrodialysis and diffusion dialysis, comprising the following steps: (1) A salt solution is introduced into the salt chamber of the bipolar membrane electrodialysis device, an acid receiving solution is added into the acid chamber, a DC electric field is turned on to perform electrodialysis, and an acid solution is obtained in the acid chamber. (2) The acid solution obtained in step (1) is introduced into the raw material storage tank of the diffusion dialysis device, and then flows through the raw material chamber and diffuses with the pure water flowing in the opposite direction in the recovery chamber. Residual acid is obtained at the outlet of the raw material chamber and filtrate is obtained at the outlet of the recovery chamber. An anion exchange membrane is provided between the raw material chamber and the recovery chamber. The residual acid is used as a replenishing solution for the salt solution and is introduced into the salt chamber of the bipolar membrane electrodialysis device; the filtrate is used as an acid receiving solution and is introduced into the acid chamber of the bipolar membrane electrodialysis device. (3) Repeat steps (1) to (2) until the acid concentration and cation content of the acid solution produced by the acid chamber of the bipolar membrane electrodialysis device reach the target value, and collect the acid solution as high-purity acid.

[0009] Preferably, in step (2), the flow rate of acid through the raw material chamber is 1 to 4 times that of pure water through the recovery chamber.

[0010] Preferably, the circulation rate of the acid solution in step (2) is 1~3 L / h·m 2 .

[0011] Preferably, the acid concentration of the acid solution in step (1) is 1.5~3.5 mol / L.

[0012] Preferably, the circulation rate of the salt solution in step (1) is 3~7 L / h.

[0013] Preferably, the acid concentration of the residual acid in step (2) is 0.1~0.6 mol / L.

[0014] Preferably, the current density of the DC electric field in step (1) is 500~800 A / m. 2 .

[0015] Preferably, the concentration of the salt solution in step (1) is 10-12%.

[0016] Preferably, in step (2), the residual acid is concentrated and then introduced into the salt chamber of step (1) as a supplementary solution.

[0017] Preferably, the concentration process is a reverse osmosis process.

[0018] This invention provides a method for preparing high-purity acid by closed-loop coupling of bipolar membrane electrodialysis and diffusion dialysis, comprising the following steps: (1) passing a salt solution into the salt chamber of a bipolar membrane electrodialysis device, adding an acid receiving solution into the acid chamber, turning on a DC electric field to perform electrodialysis, and obtaining an acid solution in the acid chamber; (2) introducing the acid solution obtained in step (1) into the raw material storage tank of a diffusion dialysis device, and then flowing through the raw material chamber to perform diffusion dialysis with pure water flowing counterclockwise in the recovery chamber, obtaining residual acid at the outlet of the raw material chamber, and obtaining filtrate at the outlet of the recovery chamber; an anion exchange membrane is provided between the raw material chamber and the recovery chamber; the residual acid is passed into the salt chamber of the bipolar membrane electrodialysis device as a supplementary solution for the salt solution; the filtrate is passed into the acid chamber of the bipolar membrane electrodialysis device as an acid receiving solution; (3) repeating steps (1) to (2) until the acid concentration and cation content of the acid solution produced in the acid chamber of the bipolar membrane electrodialysis device reach the target values, and collecting the acid solution is high-purity acid. This invention utilizes BMED (Bio-Mechanical Distillation) for acid production and concentration, and DD (Distilled Distillate) for purification and cation retention. The high-purity acid solution after DD purification is used as the acid receiving solution for DMED, forming a synergistic cycle of "acid production-purification-concentration." This compensates for the decrease in acid concentration during DD purification and avoids using pure water as the acid receiving solution, thus reducing pure water consumption. Furthermore, the residual acid after DD purification is used as a replenishing solution for the DMED salt chamber, reducing wastewater generation. Results from the embodiments show that the hydrochloric acid concentration prepared by the method provided by this invention can reach above 3 mol / L, with Na... + The content is not higher than 50 mg / L. Attached Figure Description

[0019] Figure 1 A schematic diagram of the process for preparing acids and bases for bipolar membrane electrodialysis; Figure 2 This is a schematic diagram of the existing technology that combines bipolar membrane electrodialysis with diffusion dialysis. Figure 3 This is a schematic diagram of the process for preparing high-purity acid in an embodiment of the present invention. Detailed Implementation

[0020] All raw materials used in this invention are not particularly restricted in their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0021] There are no particular restrictions on the purity of any of the raw materials used in this invention, but industrially pure raw materials are preferred.

[0022] This invention provides a method for preparing high-purity acid by closed-loop coupling of bipolar membrane electrodialysis and diffusion dialysis, comprising the following steps: (1) A salt solution is introduced into the salt chamber of the bipolar membrane electrodialysis device, an acid receiving solution is added into the acid chamber, a DC electric field is turned on to perform electrodialysis, and an acid solution is obtained in the acid chamber. (2) The acid solution obtained in step (1) is introduced into the raw material storage tank of the diffusion dialysis device, and then flows through the raw material chamber and diffuses with the pure water flowing in the opposite direction in the recovery chamber. Residual acid is obtained at the outlet of the raw material chamber and filtrate is obtained at the outlet of the recovery chamber. An anion exchange membrane is provided between the raw material chamber and the recovery chamber. The residual acid is used as a replenishing solution for the salt solution and is introduced into the salt chamber of the bipolar membrane electrodialysis device; the filtrate is used as an acid receiving solution and is introduced into the acid chamber of the bipolar membrane electrodialysis device. (3) Repeat steps (1) to (2) until the acid concentration and cation content of the acid solution produced by the acid chamber of the bipolar membrane electrodialysis device reach the target value, and collect the acid solution as high-purity acid.

[0023] In this invention, a salt solution is introduced into the salt chamber of a bipolar membrane electrodialysis device, an acid receiving solution is added to the acid chamber, a DC electric field is turned on to perform electrodialysis, and an acid solution is obtained in the acid chamber.

[0024] In an embodiment of the present invention, the bipolar membrane electrodialysis device is a three-chamber bipolar membrane electrodialysis device.

[0025] In this invention, the concentration of the salt solution is preferably 10-12%. A salt solution concentration within this range is beneficial for the stable production of acid. Salt molecules in the salt chamber ionize into anions and cations. Under the drive of an electric field, anions enter the acid chamber, and cations enter the alkali chamber. Therefore, during BMED operation, the concentration of the salt solution will continuously decrease, requiring the replenishment of solute or a high-concentration salt solution to maintain the salt solution concentration within the aforementioned range. In this embodiment of the invention, the salt solution is a NaCl solution with an initial concentration of 12%; when the concentration of the NaCl solution falls below 10%, a 12% NaCl solution is added.

[0026] In this invention, the circulation flow rate of the salt solution is preferably 3~7 L / h, more preferably 4~6 L / h; as one embodiment of this invention, the circulation flow rate of the salt solution can be 3 L / h, 4 L / h, 5 L / h, 6 L / h, or 7 L / h. A circulation flow rate within the above range can avoid uneven salt concentration and is beneficial for improving acid production efficiency.

[0027] In this invention, the current density of the DC electric field is preferably 500~800 A / m. 2 More preferably 600~700 A / m 2 As one embodiment of the present invention, the current density of the DC electric field can be 550 A / m. 2 600A / m 2 650A / m 2 700A / m 2 Or 750A / m 2 A direct current electric field electrolyzes water molecules into H+. + and OH - This drives the directional migration of ionized anions and cations from the salt, resulting in acid in the acid chamber and alkali in the alkali chamber. A DC electric field with a current density within the aforementioned range is beneficial for improving acid production efficiency.

[0028] In one embodiment of the present invention, the acid receiving solution can be pure water when the BMED system is turned on, and the pure water can be electronic grade pure water.

[0029] In this invention, the acid concentration of the acid solution is preferably 1.5~3.5 mol / L, more preferably 1.5~2.5 mol / L; as one embodiment of this invention, the acid concentration of the acid solution can be 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L, or 3.5 mol / L. An acid concentration within the above range is beneficial for the stable operation of the system.

[0030] In one embodiment of the present invention, the acid concentration of the acid solution can be increased with the increase of running time.

[0031] In one embodiment of the present invention, the concentration of the alkali solution in the bipolar membrane electrodialysis chamber can be controlled to be no higher than 2 mol / L; the concentration of the alkali solution can be controlled by replacing the receiving liquid in the alkali chamber with pure water.

[0032] As one embodiment of the present invention, the effective area of ​​the BMED membrane stack in the bipolar membrane electrodialysis can be 2m². 2 .

[0033] After obtaining the acid solution, the present invention introduces the acid solution into the raw material storage tank of the diffusion dialysis device, and then flows through the raw material chamber to perform diffusion dialysis with pure water flowing in the opposite direction in the recovery chamber. Residual acid is obtained at the outlet of the raw material chamber, and filtrate is obtained at the outlet of the recovery chamber. An anion exchange membrane is provided between the raw material chamber and the recovery chamber. The residual acid is introduced into the salt chamber of the bipolar membrane electrodialysis device as a replenishing solution for the salt solution; the filtrate is introduced into the acid chamber of the bipolar membrane electrodialysis device as an acid receiving solution.

[0034] As one embodiment of the present invention, the acid solution is introduced into the raw material storage tank of diffusion dialysis in a continuous manner or in a manner in which all the acid solution is introduced into the raw material storage tank of diffusion dialysis at one time; when the acid solution is continuously introduced into the raw material storage tank of diffusion dialysis, the introduction flow rate can be the same as the acid receiving liquid replenishment flow rate of the acid chamber.

[0035] In this invention, the preferred circulation rate of the acid solution is 1~3 L / h·m. 2 More preferably 2L / h·m 2 A circulating flow rate of acid within the above range is beneficial for acid purification.

[0036] In this invention, the flow rate of the acid solution through the raw material chamber is preferably 1 to 4 times that of the pure water flow rate through the recovery chamber, more preferably 2 to 3 times. The faster the flow rate of the acid solution through the raw material chamber relative to the flow rate of the pure water flow rate through the recovery chamber, the more acid enters the filtrate. When the relationship between the flow rate of the acid solution through the raw material chamber and the flow rate of the pure water flow rate through the recovery chamber is within the above-mentioned range, it is beneficial to increase the concentration of acid in the filtrate.

[0037] In this invention, the acid concentration of the residual acid is preferably 0.1~0.6 mol / L, more preferably 0.2~0.5 mol / L; as one embodiment of this invention, the acid concentration of the residual acid can be 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, or 0.6 mol / L. An acid concentration within the above range is beneficial for increasing the acid concentration in the filtrate.

[0038] In this invention, the residual acid is preferably concentrated before being introduced into the salt chamber of a bipolar membrane electrodialysis system as a makeup solution; the concentration treatment is preferably reverse osmosis treatment. Reverse osmosis treatment of the residual acid can increase the concentration of cations in the residual acid, which is beneficial for controlling the concentration of the salt solution in the salt chamber and improving the stability of acid production.

[0039] In one embodiment of the present invention, the reverse osmosis treatment can use an acid-resistant reverse osmosis device, with an operating pressure of 2-5 MPa and a recovery rate of 70-90%; the conductivity of the reverse osmosis permeate is less than 100 μS / cm. The pure water produced by reverse osmosis can be used as pure water for diffusion dialysis.

[0040] As one embodiment of the present invention, the concentration treatment of the residual acid can be carried out in stages. When the concentration of acid and the content of cations in the acid chamber reach the target value and no further purification is required, the residual acid is concentrated. Alternatively, the residual acid can be concentrated after each DD operation.

[0041] In one embodiment of the present invention, the total effective area of ​​the DD membrane stack for diffusion dialysis can be 8m². 2 .

[0042] This invention determines the system operation based on the acid concentration and cation content of the acid solution in the acid chamber. When the acid concentration and cation content reach the target values, the collected acid solution is high-purity acid solution. When the acid concentration and cation content do not reach the target values, the system continues to operate until the acid concentration and cation content reach the target values.

[0043] This invention utilizes BMED to produce and concentrate acid, and DD for purification and cation retention. The high-purity acid solution after DD purification is used as the acid receiving liquid for DMED, forming a synergistic cycle of "acid production-purification-concentration". This compensates for the deficiency of acid concentration decrease during DD purification and avoids using pure water as the acid receiving liquid, thus reducing the amount of pure water used. Moreover, the residual acid after DD purification is used as the replenishment liquid for the DMED salt chamber, reducing the amount of wastewater generated.

[0044] A schematic diagram of the operation of preparing high-purity acid by closed-loop coupling of bipolar membrane electrodialysis and diffusion dialysis in an embodiment of the present invention is shown below. Figure 3 As shown: NaCl solution is passed into the salt chamber, and pure water is passed into the alkali chamber to form NaOH solution. Pure water is then passed into a diffusion dialysis device to purify the acid solution produced in the acid chamber, resulting in residual acid containing impurities and diffusion dialysis permeate. The diffusion dialysis permeate is used as the acid receiving liquid in the acid chamber and is concentrated. When the concentration and cation content of the acid solution reach the target values, no further purification is required to obtain a high-purity acid solution.

[0045] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0046] Example 1 Device components: BMED membrane stack: effective area 2m 2 It contains salt chambers, acid chambers, and alkali chambers; DD membrane stack: Total effective area 8m² 2 It includes a raw material room and a recycling room, with a circulating storage tank and metering pump on the raw material side; Acid-resistant reverse osmosis unit: acid-resistant membrane module, operating pressure 2~5MPa, recovery rate 70~90%; Closed-loop pipelines, metering pumps, flow meters, concentration / ion detectors.

[0047] A closed-loop coupling method for preparing high-purity hydrochloric acid (Na₂O₃) using bipolar membrane electrodialysis and diffusion dialysis + For methods involving content ≤50mg / L and concentration ≥3mol / L, the steps are as follows: A 12% NaCl solution (initial volume 100L, circulation rate 5L / h) was circulated into the BMED salt chamber. Add 8L of electronic-grade pure water to the BMED acid chamber as the initial acid receiving solution; Add 45L of electronic-grade pure water to the BMED alkalinity chamber; Apply current density 650A / m 2 The process was continued until the hydrochloric acid concentration in the acid chamber reached 2.5 mol / L and the Na+ concentration reached 100 mol / L. + Content 1500 mg / L; All hydrochloric acid from the BMED acid chamber was transferred to the DD circulating storage tank. DD purification startup: The liquid in the circulating storage tank flows at a rate of 2 L / h·m 2 The fluid circulates through the raw material chamber and the recovery chamber at a rate of 0.5 L / h·m. 2 8L of pure water is introduced at a flow rate; the filtrate is continuously refluxed back to the BMED acid chamber. BMED continues to operate, receiving and concentrating the reflux filtrate; When the NaOH concentration in the alkali chamber reaches 2 mol / L, overflow recovery and replenishment with pure water are performed; when the concentration in the salt chamber is below 10%, fresh NaCl solution (concentration 12%) is added. Repeat the above export-purification-reflux operation 3 times; when the hydrochloric acid concentration in the BMED acid chamber is ≥3.0 mol / L (target concentration), Na + When the content is ≤50mg / L, the system operation is stopped, and the discharged acid is high-purity acid; The residual acid (concentration 0.6 mol / L, Na) + All water with a concentration of 1200 mg / L is extracted and first pumped into an acid-resistant reverse osmosis unit for concentration treatment. The resulting concentrated water is then added to the BMED salt chamber, and the permeate (conductivity <100 μS / cm) is reused in the DD recovery chamber.

[0048] As can be seen from the above embodiments, the method provided by the present invention can obtain a high-concentration, high-purity acid solution with low pure water consumption and low wastewater generation.

[0049] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing high-purity acid by closed-loop coupling of bipolar membrane electrodialysis and diffusion dialysis, comprising the following steps: (1) A salt solution is introduced into the salt chamber of the bipolar membrane electrodialysis device, an acid receiving solution is added into the acid chamber, a DC electric field is turned on to perform electrodialysis, and an acid solution is obtained in the acid chamber. (2) The acid solution obtained in step (1) is introduced into the raw material storage tank of the diffusion dialysis device, and then flows through the raw material chamber and diffuses with the pure water flowing in the opposite direction in the recovery chamber. Residual acid is obtained at the outlet of the raw material chamber and filtrate is obtained at the outlet of the recovery chamber. An anion exchange membrane is provided between the raw material chamber and the recovery chamber. The residual acid is used as a replenishing solution for the salt solution and is introduced into the salt chamber of the bipolar membrane electrodialysis device; the filtrate is used as an acid receiving solution and is introduced into the acid chamber of the bipolar membrane electrodialysis device. (3) Repeat steps (1) to (2) until the acid concentration and cation content of the acid solution produced by the acid chamber of the bipolar membrane electrodialysis device reach the target value, and collect the acid solution as high-purity acid.

2. The method according to claim 1, characterized in that, In step (2), the flow rate of acid through the raw material chamber is 1 to 4 times that of pure water through the recovery chamber.

3. The method according to claim 1, characterized in that, In step (2), the flow rate of the acid solution is 1~3 L / h·m 2 .

4. The method according to claim 1, characterized in that, The acid concentration of the acid solution in step (1) is 1.5~3.5 mol / L.

5. The method according to claim 1, characterized in that, In step (1), the circulation rate of the salt solution is 3~7 L / h.

6. The method according to claim 1, characterized in that, The acid concentration of the residual acid in step (2) is 0.1~0.6 mol / L.

7. The method according to claim 1, characterized in that, The current density of the DC electric field in step (1) is 500~800 A / m. 2 .

8. The method according to claim 1, characterized in that, The concentration of the salt solution in step (1) is 10-12%.

9. The method according to claim 1, characterized in that, In step (2), the residual acid is concentrated and then introduced into the salt chamber of step (1) as a supplementary solution.

10. The method according to claim 9, characterized in that, The concentration process is a reverse osmosis process.

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