Electrodialysis method and apparatus

Abstract

The present invention belongs to the field of membrane separation technology, and relates to a method for electrodialysis avoiding hydrogen production, the method comprising the following steps: (1) adding a raw water solution to an electrodialysis device; and (2) adding an aqueous solution of different valence salts of a polyvalent metal M to a cathode chamber and an anode chamber of the electrodialysis device, wherein in the method, the molar ratio of the relatively high valence cations of metal M in the feed added to the cathode chamber to the relatively low valence cations of metal M in the feed added to the anode chamber is at least 1:10, wherein the metal M is selected from iron, nickel, manganese or cobalt, and wherein the metal M in the feed added to the cathode chamber is the same as the metal M in the feed added to the anode chamber. The present invention also includes an electrodialysis system for implementing the method of the present invention. The present invention can effectively inhibit the hydrogen production in the cathode chamber, thereby effectively reducing the explosion-proof level of the electrodialysis device, while achieving cost and energy consumption reduction.

Description

Technical Field

[0001] This invention relates to an electrodialysis method. More specifically, this invention relates to an electrodialysis method with improved safety. This invention also relates to an electrodialysis system. Background Technology

[0002] Electrodialysis is a membrane separation technology that uses ion exchange membranes and a direct current electric field to separate and purify ions in a solution. It is widely used in seawater desalination, wastewater treatment, and material purification. An electrodialysis unit consists of a cathode chamber and an anode chamber, as well as cathode membranes, anode membranes, and bipolar membranes positioned between the anode and cathode chambers. During electrodialysis, hydrogen gas is produced as a byproduct in the cathode chamber. Hydrogen gas, with its extremely wide explosion limits (4.0%~75.6%), significantly impacts the safety of the device. Therefore, electrodialysis units are generally designed according to Class A standards, resulting in relatively high plant costs. The design standards for other electrical equipment in the workshop are also raised, leading to higher overall investment costs and higher safety risks throughout the production process.

[0003] Therefore, an electrodialysis method is needed that can effectively suppress hydrogen production in the cathode chamber, thereby effectively reducing the explosion-proof rating of the electrodialysis device while simultaneously reducing cost and energy consumption. Additionally, an electrodialysis system suitable for implementing such a method is also required. Summary of the Invention

[0004] To address the problems in the prior art, this invention provides an electrodialysis method and an electrodialysis system. Through this method, hydrogen production in the cathode chamber is effectively suppressed, thereby improving process safety and reducing process costs.

[0005] This invention relates, in one aspect, to an electrodialysis method that avoids hydrogen production, the method comprising the following steps:

[0006] (1) Add the raw material aqueous solution to the electrodialysis device; and

[0007] (2) Add aqueous solutions of salts of different valence states of the polyvalent metal M to the cathode and anode chambers of the electrodialysis apparatus.

[0008] In the method described above, the molar ratio of the relatively high-valence cations of metal M added to the feed to the relatively low-valence cations of metal M added to the feed to the anode chamber is at least 1:10, preferably at least 1:1, and more preferably at least 10:1.

[0009] The metal M is selected from iron, nickel, manganese or cobalt, preferably iron, wherein the metal M added to the feed to the cathode chamber is the same as the metal M added to the feed to the anode chamber, and preferably the anions of different valence salts of the multivalent metal M are also the same.

[0010] On the other hand, the present invention relates to an electrodialysis system comprising an electrodialysis apparatus and a circulation apparatus, the electrodialysis apparatus comprising a cathode chamber and an anode chamber, the circulation apparatus being in fluid communication with the cathode chamber and the anode chamber of the electrodialysis apparatus, the circulation apparatus being used to receive and mix the material flow from the cathode chamber and the material flow from the anode chamber, and to recirculate the resulting mixture back to the cathode chamber and the anode chamber.

[0011] This invention effectively suppresses hydrogen production in the cathode chamber and oxygen production in the anode chamber. Furthermore, it improves the overall electrical efficiency of the device and reduces energy consumption. This is beneficial for both existing and newly constructed electrodialysis devices. For existing electrodialysis devices, it effectively enhances the overall safety; for newly constructed electrodialysis devices, this invention is even more important because it means that the method and system of this invention can reduce the explosion-proof rating of the device from Zone 0 to Zone 2 or even a non-explosion-proof zone, thereby effectively avoiding many of the measures and significant investments associated with explosion-proof zones. Generally speaking, a non-explosion-proof device can reduce investment by about half compared to a Zone 0 explosion-proof device. Attached Figure Description

[0012] Figure 1 This is an exemplary schematic diagram of a prior art electrodialysis implementation scheme.

[0013] Figure 2 This is an exemplary schematic diagram of an embodiment of the present invention.

[0014] Figure 3 This is an exemplary schematic diagram of another embodiment of the present invention. Detailed Implementation

[0015] The present invention will be further described in detail below through specific embodiments. These specific embodiments are given for illustrative purposes only and are not intended to limit the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

[0016] Electrodialysis method

[0017] A first aspect of the present invention relates to an electrodialysis method for avoiding hydrogen production, the method comprising the following steps:

[0018] (1) Add the raw material aqueous solution to the electrodialysis device; and

[0019] (2) Add aqueous solutions of salts of different valence states of the polyvalent metal M to the cathode and anode chambers of the electrodialysis apparatus.

[0020] In the method described above, the molar ratio of the relatively high-valence cations of metal M added to the feed to the cathode chamber to the relatively low-valence cations of metal M added to the feed to the anode chamber is at least 1:10, preferably at least 1:1.

[0021] The metal M is selected from iron, nickel, manganese or cobalt, wherein the metal M added to the feed to the cathode chamber is the same as the metal M added to the feed to the anode chamber, and preferably the anions of different valence salts of the multivalent metal M are also the same.

[0022] Step (1) of the method of the present invention is to add the raw material aqueous solution to the electrodialysis device. Any electrolyte aqueous solution suitable for electrodialysis can be used as the raw material aqueous solution of the present invention. In some exemplary embodiments, the raw material aqueous solution of the present invention can be desulfurization wastewater or an aqueous solution obtained after further treatment of desulfurization wastewater. For example, the raw material aqueous solution of the present invention can be an aqueous solution of alkali metal sulfate, an aqueous solution of bisulfate, an aqueous solution of hydrochloride, or a mixture thereof, or the main component of the raw material aqueous solution of the present invention is an aqueous solution of alkali metal sulfate, an aqueous solution of bisulfate, an aqueous solution of hydrochloride, or a mixture thereof. Lithium, sodium, and potassium are preferred alkali metals. It is particularly preferred that the raw material of the present invention is an alkali metal sulfate, such as lithium, sodium, and potassium sulfate. In a preferred embodiment, the raw material aqueous solution used in the method of the present invention is an aqueous solution of sodium sulfate.

[0023] In some preferred embodiments, the electrodialysis method of the present invention may further include a pretreatment step before step (1), wherein the pretreatment step pretreats the crude raw material (e.g., desulfurization wastewater), for example, by neutralization, precipitation, coagulation, filtration, etc., to obtain a raw material aqueous solution for step (1). For example, in some preferred embodiments, the electrodialysis method of the present invention pretreats the desulfurization wastewater before step (1) to remove impurities therein, such as possible COD, heavy metals, and F. - Ions, as well as insoluble particulate matter such as gypsum, silica, iron and aluminum hydroxides, are used to obtain an aqueous solution of raw materials for step (1).

[0024] The method of the present invention further includes step (2): adding an aqueous solution of a polyvalent metal M in different valence states to the cathode chamber and the anode chamber of the electrodialysis apparatus. The metal M is selected from iron (Fe), nickel (Ni), manganese (Mn), and cobalt (Co). More preferably, the metal M is iron (Fe).

[0025] In the method of the present invention, the metal M added to the feed to the cathode chamber is the same as the metal M added to the feed to the anode chamber. Preferably, the anions of the different valence salts of the multivalent metal M are also the same, that is, preferably, the different valence salts of the multivalent metal M added in step (2) are salts formed by different valence cations of the same metal M and the same anion. In a preferred embodiment, the different valence salts of the multivalent metal M are Fe 3+ salt and Fe 2+ The salts of metal M are salts in which the corresponding salt anions are monovalent or divalent anions, such as sulfate ions. In a particularly preferred embodiment, the salt of metal M with a relatively high valence state is Fe. 3+ The sulfate of metal M, the salt of which is Fe, is a relatively low valence state salt. 2+ sulfates.

[0026] In a preferred embodiment, the aqueous solution used in the method of the present invention is an aqueous solution of sodium sulfate, and the relatively high valence salt of metal M is Fe. 3+ The sulfate of Fe, namely Fe2(SO4)3, is the salt of metal M in a relatively low oxidation state, which is Fe. 2+ The sulfate, namely FeSO4.

[0027] In the method of the present invention, the molar ratio of the relatively high-valence cations of metal M added to the feed to the cathode chamber to the relatively low-valence cations of metal M added to the anode chamber is at least 1:10, for example at least 1:10, at least 1:8, at least 1:6, at least 1:4, at least 1:2, at least 1:1, at least 3:1, at least 5:1, at least 8:1, at least 10:1, at least 12:1, at least 15:1, at least 18:1, at least 20:1, at least 22:1, at least 25:1, at least 28:1, at least 30:1. The upper limit of the molar ratio of the relatively high-valence cations of metal M added to the cathode chamber to the relatively low-valence cations of metal M added to the anode chamber can be at most 50:1, for example at most 40:1. Alternatively, in the method of the present invention, the molar ratio of the relatively high-valence cations of metal M added to the feed to the cathode chamber to the relatively low-valence cations of metal M added to the anode chamber can be any value between these upper and lower limits. In a preferred embodiment, in the method of the present invention, the molar ratio of the relatively high-valence cations of metal M added to the feed to the relatively low-valence cations of metal M added to the anode chamber is at least 1:10, at least 1:1, or at least 5:1, or at least 10:1, for example in the range of 1:10 to 30:1, in the range of 1:10 to 20:1, for example in the range of 1:10 to 15:1.

[0028] Different valence salts of a polyvalent metal M can be added separately to the cathode and anode chambers of the electrodialysis apparatus in the form of aqueous solutions, or in the form of an aqueous solution containing a mixture of different valence salts of the polyvalent metal M. In one exemplary embodiment, as the initial feed to the electrodialysis apparatus, an aqueous solution of a relatively high valence salt of metal M is fed to the cathode chamber, and an aqueous solution of a relatively low valence salt of metal M is fed to the anode chamber. The initial feed refers to the feed added in step (2) when the electrodialysis method is started. In another exemplary embodiment, as the initial feed to the cathode and anode chambers, an aqueous solution containing a mixture of different valence salts of polyvalent metal M is fed to the cathode and anode chambers of the electrodialysis apparatus. Preferably, the aqueous solutions of the relatively high valence salts of metal M and the relatively low valence salts of metal M are first mixed, for example, in a buffer tank, and then the resulting mixed aqueous solution is fed to the cathode and anode chambers of the electrodialysis apparatus.

[0029] Unconstrained by any theory, the inventors of this invention have discovered that by adding aqueous solutions of different valence states of polyvalent metal M to the cathode and anode chambers of an electrodialysis apparatus during the electrodialysis process, and by ensuring that the molar ratio of the relatively high valence state cations of metal M in the feed added to the cathode chamber to the relatively low valence state cations of metal M in the feed added to the anode chamber is at least 1:10, preferably at least 1:1, hydrogen formation during electrodialysis can be effectively avoided, and cost savings and energy reduction can be achieved.

[0030] Preferably, after the electrodialysis method of the present invention starts operating, the feed stream from the cathode chamber is mixed with the feed stream from the anode chamber, and the resulting mixture is then fed into the cathode and anode chambers of the electrodialysis apparatus to form a cycle. According to the present invention, this cycle mode can greatly reduce operating costs. Moreover, after the electrodialysis method of the present invention starts operating, the total amount of aqueous solution of different valence states of polyvalent metal M is essentially not lost, which allows the present invention to continue operating after the electrodialysis method starts operating with almost no need to replenish the feed in step (2). In addition, such a cycle mode realizes the acid-base neutralization reaction, effectively avoiding the accumulation of acid and base in the cathode and anode chambers.

[0031] Therefore, in a preferred embodiment of the invention, the electrodialysis method further includes step (3): mixing the feed stream from the cathode chamber with the feed stream from the anode chamber in a circulation loop, and splitting the resulting mixture and adding it as feed to the cathode chamber and anode chamber of the electrodialysis apparatus, respectively, in step (2), wherein the molar ratio of the relatively high valence cations of metal M to the relatively low valence cations of metal M in the mixture is at least 1:10, preferably at least 1:1, more preferably at least 10:1. Preferably, the circulation loop includes a buffer tank, and the resulting mixture is split from the buffer tank and added as feed to the cathode chamber and anode chamber of the electrodialysis apparatus, respectively, in step (2). The molar ratio of the relatively high-valence cations to the relatively low-valence cations of metal M in the mixture obtained in the buffer tank is at least 1:10, preferably at least 1:1, for example at least 1:10, at least 1:8, at least 1:6, at least 1:4, at least 1:2, at least 1:1, at least 3:1, at least 5:1, at least 8:1, at least 10:1, at least 12:1, at least 15:1, at least 18:1, at least 20:1, at least 22:1, at least 25:1, at least 28:1, at least 30:1. The upper limit of the molar ratio of the relatively high-valence cations to the relatively low-valence cations of metal M in the obtained mixture can be at most 50:1, for example at most 40:1. The molar ratio of the relatively high-valence cations to the relatively low-valence cations of metal M in the obtained mixture can be any value between these molar ratios. In a preferred embodiment, the molar ratio of the relatively high-valence cation of metal M to the relatively low-valence cation of metal M in the resulting mixture is at least 1:10, at least 1:1, or at least 5:1, or at least 10:1, for example in the range of 1:10 to 30:1, in the range of 1:10 to 20:1, for example in the range of 1:10 to 15:1.

[0032] According to some preferred embodiments of the present invention, in the electrodialysis method of the present invention, by weight, in step (2), the feed flow rate of the anode chamber is controlled to be at least 3 times, preferably at least 5 times, the feed flow rate of the cathode chamber. For example, during the operation of the electrodialysis method of the present invention, by weight, in step (2), the feed flow rate of the anode chamber can be controlled to be at least 3 times, at least 4 times, at least 5 times, at least 6 times, at least 7 times, at least 8 times, at least 9 times, at least 10 times, at least 11 times, at least 12 times, at least 15 times, at least 18 times, at least 20 times, or at least 30 times the feed flow rate of the cathode chamber. As an upper limit, during the operation of the electrodialysis method of the present invention, by weight, in step (2), the feed flow rate of the anode chamber can be controlled to, for example, at most 40 times, at most 35 times, at most 30 times, or at most 25 times the feed flow rate of the cathode chamber. Alternatively, during the operation of the electrodialysis method of the present invention, the feed flow rate of the anode chamber can be controlled, by weight, in step (2) to be a multiple of the feed flow rate of the cathode chamber listed above. Preferably, during the operation of the electrodialysis method of the present invention, the feed flow rate of the anode chamber is controlled, by weight, in step (2) to be in the range of 5 to 10 times the feed flow rate of the cathode chamber.

[0033] Unrestricted by any theory, in the electrodialysis method of the present invention, controlling the feed flow rate of the anode chamber to be at least three times, preferably at least five times, the feed flow rate of the cathode chamber by weight can reduce the possibility of precipitation adhering to the membrane surface, thereby enabling the device to operate for a long time.

[0034] According to some preferred embodiments of the present invention, in the electrodialysis method of the present invention, the pH value at the anode chamber or anode chamber outlet is controlled to be 10 or higher, for example, the pH value at the anode chamber or anode chamber outlet is controlled to be 10 or higher, 10.1 or higher, 10.2 or higher, 10.3 or higher, 10.4 or higher, 10.5 or higher, 10.6 or higher, 10.7 or higher, 10.8 or higher, 10.9 or higher, 11 or higher, or any pH value between these values. Preferably, in the electrodialysis method of the present invention, the pH value at the anode chamber or anode chamber outlet is controlled to be 10.2 or higher, preferably in the range of 10.2 to 10.8. Since the pH is not exactly the same at different points in the anode chamber, the pH at the anode chamber outlet reflects the overall pH level in the anode chamber more comprehensively.

[0035] Unconstrained by any theory, the inventors of this invention have discovered that in the electrodialysis method of this invention, controlling the pH value at the outlet of the anode chamber to 10 or higher, preferably 10.2 or higher, and preferably in the range of 10.2 to 10.8, can effectively reduce or avoid precipitation in the anode chamber and reduce or avoid the impact on the resistance of the anode chamber.

[0036] According to some preferred embodiments of the present invention, in the electrodialysis method of the present invention, the pH value at the cathode chamber or cathode chamber outlet is controlled within the range of 2.5 to 6, for example, controlled as 2.5, 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4.0, 4.2, 4.4, 4.6, 4.8, 5.0, 5.2, 5.4, 5.6, 5.8, 6.0, or any pH value between these values. Preferably, in the electrodialysis method of the present invention, the pH value at the cathode chamber or cathode chamber outlet is controlled within the range of 3.5 to 5, more preferably within the range of 4 to 5, for example, controlled as 5. Since the pH is not exactly the same at different points in the cathode chamber, the pH at the cathode chamber outlet more accurately reflects the overall pH level in the cathode chamber.

[0037] Unconstrained by any theory, the inventors of this invention have discovered that in the electrodialysis method of this invention, controlling the pH value at the outlet of the cathode chamber within the range of 2.5 to 6, preferably within the range of 3.5 to 5, and more preferably within the range of 4 to 5, such as controlling it to 5, can effectively prevent precipitation in the anode chamber, thereby protecting the membrane near the anode chamber.

[0038] Figure 2 and Figure 3 The method of the present invention is illustrated schematically. Figure 2 In the exemplary embodiment shown, pipeline 1, pipeline 2, pipeline 3, pipeline 4, buffer tank 5, hydraulic jet pump 6, and the connecting passages between them constitute the circulation loop of the present invention. Figure 3 In the exemplary embodiment shown, pipelines 1, 2, 3, and 4, buffer tank 5, static mixer 7, and the connecting passages between them constitute the circulation loop of the present invention. During the initial feeding of the method of the present invention, salts of different valence states of the polyvalent metal M can be added to buffer tank 5 in aqueous solution form, and then the resulting mixture is sent to the cathode chamber and anode chamber of the electrodialysis apparatus via pipelines 1 and 2, respectively. After the method of the present invention has been running, the feed streams from the cathode chamber and the anode chamber are circulated back to buffer tank 5 via pipelines 3 and 4, and the resulting mixture is then used as feed from buffer tank 5 to the cathode chamber and anode chamber of the electrodialysis apparatus via pipelines 1 and 2, respectively. Preferably, a mixing mechanism, such as a hydraulic jet pump 6 or a static mixer 7, is provided upstream of buffer tank 5.

[0039] The electrodialysis method of this invention effectively achieves hydrogen-free electrode electrolysis and allows for the continuous recycling of salts of different valence states of a multivalent metal M. In particular, the different valence states of the multivalent metal M are continuously recycled throughout the electrodialysis process at an almost constant molar ratio. Furthermore, after the electrodialysis method of this invention begins operation, the total amount of aqueous solution containing the different valence states of the multivalent metal M is essentially not lost. In some preferred embodiments, the electrodialysis method of this invention effectively achieves hydrogen-free and oxygen-free electrode electrolysis and allows for the continuous recycling of salts of different valence states of the multivalent metal M. In addition, the method of this invention effectively avoids excessive precipitation in the anode chamber. Furthermore, by adjusting the flow rate, the possibility of precipitation adhering to the membrane surface can be further reduced, thereby protecting the membrane near the anode chamber and reducing or avoiding the impact on the resistance of the anode chamber.

[0040] Electrodialysis system

[0041] Another aspect of the invention relates to an electrodialysis system. The electrodialysis system of the present invention includes an electrodialysis apparatus and a circulation device, the electrodialysis apparatus including a cathode chamber and an anode chamber, the circulation device being in fluid communication with the cathode chamber and the anode chamber of the electrodialysis apparatus, the circulation device being used to receive and mix a flow from the cathode chamber with a flow from the anode chamber, and to recirculate the resulting mixture back to the cathode chamber and the anode chamber.

[0042] The electrodialysis apparatus of the present invention may be an electrodialysis apparatus known in the art or a newly manufactured electrodialysis apparatus, provided that it contains a cathode chamber and an anode chamber as commonly known in electrodialysis apparatuses, and an anode membrane, a cathode membrane and a bipolar membrane disposed between the anode chamber and the cathode chamber.

[0043] In a preferred embodiment, the electrodialysis apparatus of the present invention includes an anodic membrane, a cathode membrane, and a bipolar membrane. Preferably, the electrodialysis apparatus of the present invention may include one or more modules, more preferably multiple modules, such as at least 2, at least 3, at least 5, at least 10, at least 15, at least 20, or more modules. The number of modules can be selected according to actual operational needs. The modules include an anodic membrane, a cathode membrane, and a bipolar membrane.

[0044] In addition to the electrodialysis apparatus, the electrodialysis system of the present invention also includes a circulation device. The circulation device is in fluid communication with the cathode chamber and the anode chamber of the electrodialysis apparatus, and is used to receive and mix the feed stream from the cathode chamber and the feed stream from the anode chamber, and to recirculate the resulting mixture back to the cathode chamber and the anode chamber.

[0045] In some preferred embodiments, the circulation device of the present invention is provided with a mixing mechanism, preferably a static mixer or a hydraulic jet pump. In some preferred embodiments, the circulation device of the present invention is provided with a buffer tank. More preferably, the circulation device of the present invention includes a mixing mechanism and a buffer tank downstream of the mixing mechanism. The feed stream from the cathode chamber (where the ratio of high-valence ions to low-valence ions decreases due to electron gain in the electrode chamber) and the feed stream from the anode chamber (where the ratio of high-valence ions to low-valence ions increases due to electron loss in the electrode chamber) can first be thoroughly mixed in the mixing mechanism, for example, in a static mixer or a hydraulic jet pump, and then enter the buffer tank, where the ratio of high-valence and low-valence metal ions is restored to its initial configuration value, thus allowing for recycling. The resulting mixture is then pumped to the cathode chamber and the anode chamber.

[0046] In some preferred embodiments, the circulation device of the present invention can also be used to mix aqueous solutions of relatively high-valence salts of metal M and relatively low-valence salts of metal M, and feed the resulting mixture through the circulation device of the present invention into the cathode chamber and anode chamber of the electrodialysis device.

[0047] In some preferred embodiments, the circulation device of the present invention is used in the electrodialysis method to add aqueous solutions of different valence salts of a polyvalent metal M to the cathode and anode chambers of the electrodialysis device. The metal M added to the feed to the cathode chamber is the same as the metal M added to the feed to the anode chamber, and preferably the anions of the different valence salts of the polyvalent metal M are also the same; that is, the different valence salts of the polyvalent metal M in the circulation device are salts formed by different valence cations of the same metal M and the same anion, wherein the metal M is selected from iron, nickel, manganese, or cobalt, preferably iron, and preferably Fe. 3+ salt and Fe 2+ The salt, wherein the corresponding anion of the salt is a monovalent or divalent anion, such as sulfate ion.

[0048] In the circulation apparatus of the present invention, the molar ratio of the relatively high-valence cations of metal M added to the feed to the cathode chamber to the relatively low-valence cations of metal M added to the anode chamber is at least 1:10, preferably at least 1:1, for example at least 1:10, at least 1:8, at least 1:6, at least 1:4, at least 1:2, at least 1:1, at least 3:1, at least 5:1, at least 8:1, at least 10:1, at least 12:1, at least 15:1, at least 18:1, at least 20:1, at least 22:1, at least 25:1, at least 28:1, at least 30:1. The upper limit of the molar ratio of the relatively high-valence cations of metal M added to the cathode chamber to the relatively low-valence cations of metal M added to the anode chamber can be at most 50:1, for example at most 40:1. Alternatively, the molar ratio of the relatively high-valence cations of metal M added to the feed to the cathode chamber to the relatively low-valence cations of metal M added to the anode chamber can be any value between these molar ratios. In a preferred embodiment, the molar ratio of the relatively high-valence cations of metal M added to the feed to the relatively low-valence cations of metal M added to the anode chamber is at least 1:10, at least 1:1, or at least 5:1, or at least 10:1, for example, in the range of 1:10 to 30:1, in the range of 1:10 to 20:1, for example, in the range of 1:10 to 15:1.

[0049] In some preferred embodiments, the feed flow rate of the anode chamber is controlled to be at least 3 times, more preferably at least 5 times, the feed flow rate of the cathode chamber. For example, the circulation device of the present invention is configured such that, during operation of the electrodialysis method of the present invention, the feed flow rate of the anode chamber is controlled, by weight, to be at least 3 times, at least 4 times, at least 5 times, at least 6 times, at least 7 times, at least 8 times, at least 9 times, at least 10 times, at least 11 times, at least 12 times, at least 15 times, at least 18 times, at least 20 times, or at least 30 times the feed flow rate of the cathode chamber. As a maximum, the circulation device of the present invention is configured such that, during operation of the electrodialysis method of the present invention, the feed flow rate of the anode chamber can be controlled, by weight, to be, for example, at most 40 times, at most 35 times, at most 30 times, or at most 25 times the feed flow rate of the cathode chamber. Alternatively, the circulation device of the present invention is configured such that, during operation of the electrodialysis method of the present invention, the feed flow rate of the anode chamber can be controlled, by weight, to be a multiple of the above-listed values ​​of the feed flow rate of the cathode chamber. Preferably, the circulation device of the present invention is configured such that, during the operation of the electrodialysis method of the present invention, the feed flow rate of the anode chamber is controlled to be within the range of 10 to 20 times the feed flow rate of the cathode chamber by weight.

[0050] In some preferred embodiments, the electrodialysis system of the present invention is used to implement the electrodialysis method of the present invention.

[0051] Figure 2 and Figure 3 The electrodialysis system of the present invention is illustrated schematically. Figure 2 In the exemplary electrodialysis system shown, pipelines 1, 2, 3, and 4, buffer tank 5, hydraulic jet pump 6, and the connecting passages between them constitute the circulation device of the present invention. Figure 3 In the exemplary electrodialysis system shown, pipelines 1, 2, 3, and 4, buffer tank 5, static mixer 7, and the connecting passages between them constitute the circulation device of the present invention. Two branches, pipeline 1 and pipeline 2, branch off from the outlet pipeline of buffer tank 5. Pipeline 1 connects to the inlet of the cathode chamber of the electrodialysis device, and pipeline 2 connects to the inlet of the anode chamber of the electrodialysis device. The outlet of the cathode chamber of the dialysis device is fluidly connected to pipeline 3, and the outlet of the anode chamber of the dialysis device is fluidly connected to pipeline 4. Figure 2 In the exemplary electrodialysis system shown, the material flow in pipelines 3 and 4 is sent to a hydraulic jet pump 6, where it is mixed before being sent to a buffer tank 5. Figure 3 In the exemplary electrodialysis system shown, the material flow in pipelines 3 and 4 is sent to static mixer 7, mixed in static mixer 7, and then sent to buffer tank 5.

[0052] The circulation device in the electrodialysis system of this invention enables the recycling of material flow from the cathode and anode chambers, achieving acid-base neutralization reactions and preventing the accumulation of acids and bases in the cathode and anode chambers. After the system starts operating, it essentially does not lose the total amount of aqueous solution of different valence states of the polyvalent metal M, allowing the entire system to operate stably without generating hydrogen and oxygen, and reducing energy consumption. Furthermore, the electrodialysis system of this invention can improve both existing and newly built electrodialysis devices. For existing electrodialysis devices, the safety of the entire device can be effectively improved by adding the circulation device of this invention; while for newly built electrodialysis devices, this invention is even more important because it means that the method and system of this invention can reduce the explosion-proof rating of the device from Zone 0 to Zone 2 or even a non-explosion-proof zone, thereby effectively avoiding many measures and large investments associated with explosion-proof zones.

[0053] Embodiments of the present invention

[0054] In general, the present invention relates to the following embodiments:

[0055] Implementation Method 1

[0056] An electrodialysis method for avoiding hydrogen production, the method comprising the following steps:

[0057] (1) Add the raw material aqueous solution to the electrodialysis device; and

[0058] (2) Add aqueous solutions of salts of different valence states of the polyvalent metal M to the cathode and anode chambers of the electrodialysis apparatus.

[0059] In the method described above, the molar ratio of the relatively high-valence cations of metal M added to the feed to the relatively low-valence cations of metal M added to the feed to the anode chamber is at least 1:10.

[0060] The metal M is selected from iron, nickel, manganese or cobalt, and the metal M added to the feed to the cathode chamber is the same as the metal M added to the feed to the anode chamber.

[0061] Implementation Method 2

[0062] According to the electrodialysis method of Embodiment 1, in the method, the molar ratio of the relatively high-valence cations of metal M added to the feed of the cathode chamber to the relatively low-valence cations of metal M added to the feed of the anode chamber is at least 10:1.

[0063] Implementation Method 3

[0064] According to the electrodialysis method of Embodiment 1, the metal M is iron.

[0065] Implementation Method 4

[0066] According to the electrodialysis method described in Embodiment 1, the anions of different valence salts of the multivalent metal M are also the same.

[0067] Implementation Method 5

[0068] According to the electrodialysis method of Embodiment 1, aqueous solutions of salts of different valence states of a multivalent metal M are added from a buffer tank to the cathode chamber and the anode chamber.

[0069] Implementation Method 6

[0070] The electrodialysis method according to any one of embodiments 1 to 5, wherein the method further comprises:

[0071] (3) The feed stream from the cathode chamber and the feed stream from the anode chamber are mixed in a circulation loop, and the resulting mixture is split and added to the cathode chamber and anode chamber of the electrodialysis apparatus as feed for step (2), wherein the molar ratio of the relatively high valence cation of metal M to the relatively low valence cation of metal M in the mixture is at least 1:10.

[0072] Implementation Method 7

[0073] According to the electrodialysis method of Embodiment 6, the molar ratio of the relatively high valence cations of metal M to the relatively low valence cations of metal M in the mixture is at least 10:1.

[0074] Implementation Method 8

[0075] According to the electrodialysis method of embodiment 6, the circulation loop includes a buffer tank, and the resulting mixture is diverted from the buffer tank and added as feed to the cathode chamber and anode chamber of the electrodialysis apparatus, respectively, in step (2).

[0076] Implementation Method 9

[0077] According to any one of embodiments 1 to 5, 7 and 8, in the electrodialysis method, the feed flow rate to the anode chamber in step (2) is at least 3 times the feed flow rate to the cathode chamber by weight.

[0078] Implementation Method 10

[0079] According to the electrodialysis method of embodiment 9, the feed flow rate to the anode chamber in step (2) is at least 5 times the feed flow rate to the cathode chamber by weight.

[0080] Implementation Method 11

[0081] According to any one of embodiments 1 to 5, 7, 8, and 10, the electrodialysis method wherein the pH value at the outlet of the anode chamber is controlled to be 10 or higher.

[0082] Implementation Method 12

[0083] According to any one of embodiments 1 to 5, 7, 8, and 10, the electrodialysis method wherein the pH value at the cathode chamber outlet is controlled within the range of 2.5 to 6.

[0084] Implementation Method 13

[0085] According to the electrodialysis method of embodiment 12, the pH value at the outlet of the cathode chamber is controlled within the range of 3.5 to 5.

[0086] Implementation Method 14

[0087] According to any one of embodiments 1 to 5, 7, 8, 10, and 13, the electrodialysis method wherein different valence salts of the polyvalent metal M are Fe 3+ salt and Fe 2+ The salt, wherein the corresponding anion of the salt is a monovalent or divalent anion.

[0088] Implementation Method 15

[0089] According to any one of embodiments 1 to 5, 7, 8, 10, and 13, the aqueous solution of the raw material added in step (1) is an aqueous solution of Na2SO4, and the different valence salts of the polyvalent metal M added in step (2) are Fe2(SO4)3 and FeSO4.

[0090] Implementation Method 16

[0091] The electrodialysis method according to any one of embodiments 1 to 5, 7, 8, 10, and 13, wherein the method can further prevent oxygen generation.

[0092] Implementation Method 17

[0093] An electrodialysis system includes an electrodialysis device and a circulation device. The electrodialysis device includes a cathode chamber and an anode chamber. The circulation device is in fluid communication with the cathode chamber and the anode chamber of the electrodialysis device. The circulation device is used to receive and mix the material flow from the cathode chamber and the material flow from the anode chamber, and to recirculate the resulting mixture back to the cathode chamber and the anode chamber.

[0094] Implementation Method 18

[0095] According to the electrodialysis system of embodiment 17, the circulation device includes a buffer tank.

[0096] Implementation Method 19

[0097] According to the electrodialysis system of embodiment 17, the circulation device further includes a mixing mechanism.

[0098] Implementation Method 20

[0099] According to the electrodialysis system of embodiment 19, the mixing mechanism is selected from a static mixer or a hydraulic jet pump.

[0100] Implementation Method 21

[0101] According to the electrodialysis system of embodiment 19, the circulation device includes a buffer tank, and the mixing mechanism is located upstream of the buffer tank.

[0102] Implementation Method 22

[0103] According to any one of embodiments 17 to 21, the electrodialysis system includes an anodic membrane, a cathode membrane, and a bipolar membrane.

[0104] Implementation Method 23

[0105] According to any one of embodiments 17 to 21, the electrodialysis system includes one or more modules comprising an anodic membrane, a cathode membrane, and a bipolar membrane.

[0106] Implementation Method 24

[0107] According to any one of embodiments 17 to 21, the electrodialysis system wherein the circulation device is used to add aqueous solutions of salts of different valence states of a polyvalent metal M to the cathode chamber and the anode chamber of the electrodialysis apparatus, wherein the metal M added to the feed to the cathode chamber is the same as the metal M added to the feed to the anode chamber, wherein the metal M is selected from iron, nickel, manganese or cobalt.

[0108] Implementation Method 25

[0109] According to the electrodialysis system of embodiment 24, the circulation device is used to add aqueous solutions of different valence salts of polyvalent metal M to the cathode chamber and anode chamber of the electrodialysis device, wherein the metal M added to the feed to the cathode chamber is the same as the metal M added to the feed to the anode chamber, and the anions of the different valence salts of polyvalent metal M are also the same.

[0110] Implementation Method 26

[0111] According to the electrodialysis system of embodiment 25, the circulation device is used to add aqueous solutions of different valence salts of a polyvalent metal M to the cathode and anode chambers of the electrodialysis apparatus, wherein the different valence salts of the polyvalent metal M are Fe. 3+ salt and Fe 2+ The salt, wherein the corresponding anion of the salt is sulfate ion.

[0112] Example

[0113] The invention and its effects are further illustrated by the following examples. These examples are for illustrative purposes and should not be construed as limiting the invention. Unless otherwise specified, the proportions or percentages given in the examples are by weight.

[0114] Example 1 and Comparative Example 1

[0115] The general procedure for Example 1 is as follows:

[0116] Electrodialysis was performed using a self-assembled electrodialysis unit. The unit consisted of three modules. The current was controlled at 500mA (the current was stabilized by adjusting the voltage via a controller).

[0117] The electrodialysis method includes the following steps:

[0118] (1) Feed 7% (wt) Na2SO4 into the space between the anion and cation membranes of the electrodialysis system;

[0119] (2) Add 0.08 mol / L Fe2(SO4)3 aqueous solution to the cathode chamber of the electrodialysis system (flow rate S1), and add 0.4 mol / L FeSO4 aqueous solution to the anode chamber of the electrodialysis system (flow rate S2), wherein Fe 3+ / Fe 2+The molar ratio and flow rate ratio are shown in Table 1 below.

[0120] After one hour of operation, the pH value of the effluent was measured at the outlet positions of the anode and cathode chambers of the electrodialysis system, respectively. A combustible gas detector was used to measure the amount of hydrogen produced in the cathode chamber, and an oxygen concentration detector was used to measure the amount of oxygen produced in the anode chamber.

[0121] The general procedure of Comparative Example 1 is basically the same as that of Example 1, except that Comparative Example 1 does not include step (2).

[0122] The results are shown in Table 1.

[0123] Table 1

[0124]

[0125] Example 2

[0126] An electrodialysis method using a self-assembled electrodialysis unit is employed, which includes a circulation device. The electrodialysis unit comprises N modules consisting of an anodic membrane, a cathode membrane, and a bipolar membrane arranged sequentially. The circulation device includes pipelines 1, 2, 3, and 4, a buffer tank 5, and a static mixer 7. Two branches (pipelines 1 and 2) branch off from the outlet pipeline of buffer tank 5. Pipeline 1 connects to the inlet of the cathode chamber of the electrodialysis unit, and pipeline 2 connects to the inlet of the anode chamber. The fluid outlet of the cathode chamber is connected to pipeline 3, and the fluid outlet of the anode chamber is connected to pipeline 4. Pipelines 3 and 4 connect to the static mixer 7, which in turn connects to the buffer tank 5. A schematic diagram of the entire electrodialysis unit can be found [reference needed]. Figure 3 .

[0127] Electrodialysis method, the method includes the following steps:

[0128] - Feed 7% (wt) of Na2SO4 into the feed chamber of the electrodialysis system;

[0129] - A 0.4 mol / L aqueous solution of Fe2(SO4)3 and a 0.08 mol / L aqueous solution of FeSO4 were added to a buffer tank. After mixing in the buffer tank, the resulting mixture was sent to the cathode chamber and the anode chamber, respectively. At this time, the Fe content in the mixture was... 3+ / Fe 2+ The molar ratios are listed in Table 2;

[0130] - After loading, the operation begins by transporting the material discharged from the cathode chamber to the static mixer 7 via pipeline 3, and the material discharged from the anode chamber to the static mixer 7 via pipeline 4. After mixing in the static mixer 7, the mixture is then sent to the buffer tank 5. A portion of the mixture in the buffer tank 5 is sent to the cathode chamber via pipeline 1, and the remainder is sent to the anode chamber via pipeline 2. The weight-based flow ratio of pipeline 1 to pipeline 2 (pipeline 1 / pipeline 2) is listed in Table 2.

[0131] The pH values ​​of the cathode and anode chambers remained essentially constant during the operation of the method.

[0132] Example 3

[0133] The operation of Example 3 is the same as that of Example 2, except that the weight-based flow rate ratio of pipeline 1 and pipeline 2 is different (see Table 2).

[0134] Example 4

[0135] The operation of Example 4 is the same as that of Example 2, except that Fe in the mixture 3+ / Fe 2+ The molar ratios are different (see Table 2).

[0136] Example 5

[0137] The operation of Example 5 is the same as that of Example 4, except that the weight-based flow rate ratio of pipeline 1 and pipeline 2 is different (see Table 2).

[0138] Example 6

[0139] The operation of Example 6 is the same as that of Example 2, except for the number of modules N (see Table 2).

[0140] Example 7

[0141] The operation of Example 7 is the same as that of Example 2, except for the number of modules N (see Table 2).

[0142] Example 8

[0143] The operation of Example 8 is the same as that of Example 2, except for the number of modules N (see Table 2).

[0144] Table 2

[0145]

Claims

1. An electrodialysis method that avoids hydrogen production, characterized in that... The method includes the following steps: (1) Add the raw material aqueous solution to the electrodialysis device; and (2) Add aqueous solutions of salts of different valence states of the polyvalent metal M to the cathode and anode chambers of the electrodialysis apparatus. In the method described above, the molar ratio of the relatively high-valence cations of the multivalent metal M added to the feed to the cathode chamber to the relatively low-valence cations of the multivalent metal M added to the feed to the anode chamber is at least 1:

10. The multivalent metal M is selected from iron, nickel, manganese or cobalt, and the multivalent metal M added to the feed to the cathode chamber is the same as the multivalent metal M added to the feed to the anode chamber.

2. The electrodialysis method according to claim 1, wherein in the method, the molar ratio of the relatively high-valence cations of the multivalent metal M added to the feed to the cathode chamber to the relatively low-valence cations of the multivalent metal M added to the anode chamber is at least 10:

1.

3. The electrodialysis method according to claim 1, wherein the anions of different valence salts of the multivalent metal M are also the same.

4. The electrodialysis method according to claim 1, wherein aqueous solutions of salts of different valence states of the multivalent metal M are added from a buffer tank to the cathode chamber and the anode chamber.

5. The electrodialysis method according to any one of claims 1 to 4, wherein the method further comprises: (3) The feed stream from the cathode chamber and the feed stream from the anode chamber are mixed in a circulation loop, and the resulting mixture is split and added to the cathode chamber and anode chamber of the electrodialysis apparatus as feed for step (2), wherein the molar ratio of the relatively high valence state cations of polyvalent metal M to the relatively low valence state cations of polyvalent metal M in the mixture is at least 1:

10.

6. The electrodialysis method according to claim 5, wherein the molar ratio of the relatively high-valence cations of the polyvalent metal M to the relatively low-valence cations of the polyvalent metal M in the mixture is at least 10:

1.

7. The electrodialysis method according to claim 5, wherein the circulation loop includes a buffer tank, and the resulting mixture is diverted from the buffer tank and added as feed to the cathode chamber and anode chamber of the electrodialysis apparatus, respectively, in step (2).

8. The electrodialysis method according to any one of claims 1 to 4, 6, and 7, wherein, by weight, the feed flow rate to the anode chamber in step (2) is at least three times the feed flow rate to the cathode chamber.

9. The electrodialysis method according to claim 8, wherein, by weight, the feed flow rate to the anode chamber in step (2) is at least 5 times the feed flow rate to the cathode chamber.

10. The electrodialysis method according to any one of claims 1 to 4, 6, 7, and 9, wherein the pH value at the outlet of the anode chamber is controlled to be 10 or higher.

11. The electrodialysis method according to any one of claims 1 to 4, 6, 7, and 9, wherein the pH value at the outlet of the cathode chamber is controlled within the range of 2.5 to 6.

12. The electrodialysis method according to claim 11, wherein the pH value at the cathode chamber outlet is controlled within the range of 3.5 to 5.

13. The electrodialysis method according to any one of claims 1 to 4, 6, 7, 9, and 12, wherein the different valence salts of the polyvalent metal M are Fe. 3+ salt and Fe 2+ The salts of different valence states have corresponding anions that are monovalent or divalent anions.

14. The electrodialysis method according to any one of claims 1 to 4, 6, 7, 9, 12, wherein the raw material aqueous solution added in step (1) is an aqueous solution of Na2SO4, and the different valence salts of the polyvalent metal M added in step (2) are Fe2(SO4)3 and FeSO4.

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