Method and device for removing thermally stable salt through electrodialysis

Abstract

The invention relates to a method for removing thermally stable salt by electrodialysis, which comprises the following steps: i) providing an electrochemical reaction membrane stack which comprises a cathode plate, an anode plate and at least one repeatable unit arranged between the two polar plates, an electric field exists between the cathode plate and the anode plate, each repeatable unit comprises a pure water channel, a desalination channel and an alkali liquor channel in the direction from the cathode plate to the anode plate, the pure water channel is limited by an anion exchange membrane and a cation exchange membrane, the desalination channel is limited by the cation exchange membrane and the anion exchange membrane, and the alkali liquor channel is limited by the anion exchange membrane and the anion exchange membrane; ii) introducing pure water into the pure water channel, introducing raw water into the desalination channel, introducing alkali liquor into the alkali liquor channel, and iii) withdrawing a product stream from the desalination channel; wherein the raw water contains an organic amine compound and a heat-stable salt. The method provided by the invention realizes removal of thermally stable salts by using an electrochemical reaction membrane stack.

Description

Technical Field

[0001] The present application relates to a method and device for removing heat-stable salts by electrodialysis. Background Art

[0002] In the field of thermal power generation, carbon capture, utilization and storage (CCUS) of CO2 produced by combustion is an effective measure to mitigate the greenhouse effect. There are several main methods for capturing CO2: chemical absorption, physical adsorption, membrane separation, etc. Among these methods, chemical absorption using organic amine liquid as absorbent is currently the largest method used in industry.

[0003] In the process of recycling organic amine liquid by chemical absorption, the organic amine liquid that absorbs CO2 undergoes degradation reaction with the components in the flue gas in the regeneration tower to generate a series of heat stable salts (HSS). Heat stable salts are not easy to decompose in organic amine liquid, and will cause corrosion of pipelines and equipment and reduce the absorption capacity of organic amine liquid for CO2. Therefore, the removal of heat stable salts in organic amine liquid is the current research focus of chemical absorption method. At present, the main methods for removing heat stable salts in organic amine liquid are distillation, ion exchange and electrodialysis. Among them, the distillation method has the disadvantage of high energy consumption. The ion exchange method requires a large amount of reagents to regenerate the resin column, which is cumbersome and costly. The operation of electrodialysis is relatively simple and is currently a relatively acceptable method.

[0004] The traditional electrodialysis method removes the heat-stable salt by allowing the anions and cations of the heat-stable salt to move in a directional manner through an ion-selective membrane under the action of an electric field. This method has a low efficiency in removing the heat-stable salt and a low recovery rate for the organic amine solution.

[0005] In recent years, there has been an improved electrodialysis method, which introduces hydroxide ions into the organic amine solution through the action of an electric field during the electrodialysis process, causing a chemical reaction between the thermostable salt and the hydroxide ions, converting the bound amine in the thermostable salt into an organic amine compound, thereby achieving the removal of the thermostable salt.

[0006] CN112495189A discloses a method for removing HSS in a DETA carbon capture process by three-compartment electrodialysis, which uses a membrane pool unit containing anion exchange membrane-anion exchange membrane-cation exchange membrane to be repeatedly arranged, thereby forming a corresponding alkali chamber-feed chamber and salt chamber. Its reaction process is that the protonated amine of the heat-stable salt in the feed chamber reacts with the hydroxide ions migrated from the alkali chamber to neutralize the bound amine to convert it into an organic amine compound. The efficiency of removing heat-stable salts by this method is low, the recovery rate of organic amine liquid is low, and the large amount of hydroxide ions migrating to the feed chamber during the reaction process will cause the pH value of the recovered organic amine liquid to increase, which may cause new precipitation corrosion.

[0007] CN109758918A discloses a method for removing heat-stable salts from an organic amine solution for capturing carbon dioxide by bipolar membrane electrodialysis, wherein the reaction process is that the protonated amine of the heat-stable salt combines with the hydroxide ions generated by the bipolar membrane to form an organic amine compound. The method has a low efficiency in removing heat-stable salts, a low recovery rate for the organic amine solution, and a large amount of hydroxide ions entering the material chamber during the reaction process will cause the pH value of the recovered organic amine solution to increase, which may cause new precipitation corrosion.

[0008] In summary, the electrodialysis methods used in the prior art for removing heat-stable salts each have their own disadvantages.

[0009] Therefore, there is a need in the art for an electrodialysis method for removing heat-stable salts that can improve or overcome the above-mentioned disadvantages. Summary of the invention

[0010] In view of the above problems existing in the art, the present invention provides a method and device for removing heat-stable salts by electrodialysis.

[0011] The first aspect of the present application provides a method for removing heat-stable salts by electrodialysis, comprising the following steps: i) providing an electrochemical reaction membrane stack, the electrochemical reaction membrane stack comprising a cathode plate, an anode plate and at least one repeatable unit disposed between the two electrode plates, an electric field being present between the cathode plate and the anode plate, the repeatable unit comprising a "pure water channel-desalting channel-alkali solution channel" from the cathode plate to the anode plate, the pure water channel being defined by an anion exchange membrane and a cation exchange membrane, the desalting channel being defined by a cation exchange membrane and an anion exchange membrane, and the alkali solution channel being defined by an anion exchange membrane and an anion exchange membrane; ii) introducing pure water into the pure water channel, introducing raw water into the desalination channel, introducing alkali solution into the alkali solution channel, and iii) withdrawing a product stream from the desalination channel; in, The raw water contains an organic amine compound and a heat-stable salt.

[0012] A second aspect of the present application provides a device for removing heat-stable salts by electrodialysis, comprising: - An electrochemical reaction membrane stack, comprising a cathode plate, an anode plate and at least one repeatable unit disposed between the two plates, wherein an electric field exists between the cathode plate and the anode plate, wherein the repeatable unit comprises a "pure water channel-desalting channel-alkali solution channel" from the cathode plate to the anode plate, wherein the pure water channel is defined by an anion exchange membrane and a cation exchange membrane, the desalting channel is defined by a cation exchange membrane and an anion exchange membrane, and the alkali solution channel is defined by an anion exchange membrane and an anion exchange membrane; - a flow unit configured to introduce pure water into the pure water channel, introduce raw water into the desalination channel, introduce alkali solution into the alkali solution channel, and draw out a product stream from the desalination channel, wherein the raw water contains an organic amine compound and a heat-stable salt.

[0013] The method and device of the present invention utilize an electrochemical reaction membrane stack to respectively and directionally migrate cations and anions of a heat-stable salt to different channels, thereby achieving the removal of the heat-stable salt from an organic amine solution. The method and device of the present invention have high efficiency in removing the heat-stable salt and high recovery rate of the organic amine solution, and because the removal process limits the migration of hydroxide ions to the organic amine solution, the increase in the pH value of the recovered organic amine solution can be reduced or even avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A schematic diagram showing a repeatable unit according to one embodiment of the present invention; Figure 2 A schematic diagram showing a repeatable unit constructed from sub-repeatable units in one embodiment of the present invention; Figure 3 A schematic diagram showing ion migration in a repeatable unit according to one embodiment of the present invention; Figure 4 A schematic diagram showing ion migration in a repeatable unit according to one embodiment of the present invention; Figure 5 A schematic diagram showing ion migration in a repeatable unit according to one embodiment of the present invention; Figure 6 A schematic diagram showing ion migration in an example of one embodiment of the present invention is shown; Figure 7 A schematic diagram showing ion migration in a comparative example according to one embodiment of the present invention is shown. DETAILED DESCRIPTION

[0015] In order to make the invention objectives, technical solutions and beneficial technical effects of this application clearer, this application will be described in detail below.

[0016] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0017] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0018] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0019] If there is no special explanation, all steps of the present application can be performed sequentially, randomly, or simultaneously. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially, or steps (a) and (b) performed simultaneously. For example, the method may also include step (c), which means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or steps (a), (c), (b), etc.

[0020] Unless otherwise specified, the terms used in this application have the same meanings as those generally understood by those skilled in the art.

[0021] Unless otherwise specified, the operations mentioned in this application are carried out at room temperature and normal pressure.

[0022] If not specifically stated, the operations mentioned in this application can be implemented by methods known to those skilled in the art.

[0023] Unless otherwise specified, the equipment, devices, instruments, parts, materials, agents, etc. mentioned in this application can be obtained by methods known to those skilled in the art.

[0024] If not otherwise specified, the indicators mentioned in this application, such as concentration, flow rate, current density, etc., can be measured by methods known to those skilled in the art. Definition of terms

[0025] Herein, the term "organic amine solution" refers to a solution containing an organic amine compound. In this article, the organic amine compound may also be referred to as an organic amine molecule, represented by Amin, which has a reaction activity with a target substance (e.g., an acidic gas). The organic amine compound may be of a type known to those skilled in the art, such as monoamines and polyamines, or such as primary amines, secondary amines, tertiary amines, or such as linear amines, cyclic amines, and sterically hindered amines.

[0026] In this article, the term "organic amine ion" refers to an organic amine molecule and a proton (H + ) form a positively charged ion or group, which can be AminH in this article + Indicates that it has no reaction activity with the target substance (such as acidic gas). Organic amine ions are positively charged and have a tendency to move in a directional manner in an electric field. Organic amine ions can exist in a bound state as a component of a stable substance (referred to as "bound amine" in this article), or in a free state as a free ion.

[0027] Herein, the term "heat stable salt (HSS)" or "heat stable salt" refers to a salt that is not easily decomposed by heat and is formed by the combination of an organic amine compound and an absorbed acidic gas (such as CO2, etc.). The cation constituting the heat stable salt is usually a protonated organic amine (i.e., bound amine) formed by an organic amine compound, and the anion constituting the heat stable salt can be of various types depending on the absorbed acidic gas, which is not limited here.

[0028] Herein, the term "channel" refers to the space formed between the electrode plate and the adjacent ion exchange membrane and between two adjacent ion exchange membranes in the electrochemical reaction membrane stack. It is understood that in the electrochemical reaction membrane stack, the electrode plate and the adjacent membrane, and the space between the two adjacent membranes are not close together, but there can be space. There are many ways to name the channel. For example, the channel name can be set according to the substance intended to be contained in the channel during the operation of the membrane stack. For example, "pure water channel" refers to the channel designed to contain pure water in the membrane stack; "alkali channel" refers to the channel designed to contain alkali in the membrane stack; "polar liquid channel" refers to the channel designed to contain polar liquid in the membrane stack. Alternatively, the channel name can be set according to the function intended to be achieved in the channel during the operation of the membrane stack. For example, "desalting channel" refers to the channel designed to achieve the function of removing thermally stable salt in the membrane stack. It is understood that the naming set according to the contained substance or the naming set according to the realized function does not constitute a unique limitation on the channel itself, that is, a channel can be set with multiple names, and multiple channels can also be set with the same name.

[0029] The present invention provides a method for removing heat-stable salt by electrodialysis, comprising the following steps: i) providing an electrochemical reaction membrane stack, the electrochemical reaction membrane stack comprising a cathode plate, an anode plate and at least one repeatable unit arranged between the two electrode plates, an electric field being present between the cathode plate and the anode plate, the repeatable unit comprising a "pure water channel-desalting channel-alkali solution channel" from the cathode plate to the anode plate, the pure water channel being defined by an anion exchange membrane and a cation exchange membrane, the desalting channel being defined by a cation exchange membrane and an anion exchange membrane, and the alkali solution channel being defined by an anion exchange membrane and an anion exchange membrane; ii) introducing pure water into the pure water channel, introducing raw water into the desalination channel, introducing alkali solution into the alkali solution channel, and iii) withdrawing a product stream from the desalination channel; in, The raw water contains an organic amine compound and a heat-stable salt.

[0030] In a preferred embodiment of the present invention, the electrochemical reaction membrane stack may include a plurality of repeatable units disposed between two electrode plates, and the plurality of repeatable units are arranged in sequence.

[0031] In the present invention, the desalination channel is defined by a cation exchange membrane for the pure water channel and an anion exchange membrane for the alkaline solution channel.

[0032] In a preferred embodiment of the present invention, the repeatable unit consists of "pure water channel-desalting channel-alkali solution channel", in other words, the repeatable unit only includes "pure water channel-desalting channel-alkali solution channel".

[0033] In a preferred embodiment of the present invention, the repeatable unit comprises "anion exchange membrane-cation exchange membrane-anion exchange membrane-anion exchange membrane" from the cathode plate to the anode plate.

[0034] In a preferred embodiment of the present invention, the membrane separating each channel in the repeatable unit is composed of "anion exchange membrane-cation exchange membrane-anion exchange membrane-anion exchange membrane". In other words, the membrane separating each channel in the repeatable unit only includes "anion exchange membrane-cation exchange membrane-anion exchange membrane-anion exchange membrane" arranged in sequence.

[0035] In one embodiment of the present invention, the anion and cation exchange membranes included in the electrochemical reaction membrane stack of the present invention may be one or more anion and cation exchange membranes known to those skilled in the art, and may be obtained or prepared in a manner known to those skilled in the art.

[0036] There are many types of ion exchange membranes. The matrix of the membrane is mostly styrene-divinylbenzene copolymer, and there are also polyethylene, fluorinated polymers, polyvinyl pyridine, etc. In terms of functional groups, the membrane of the cation exchange membrane contains negatively charged acidic active groups, so it can selectively pass cations and block anions. The membrane of the anion exchange membrane contains positively charged alkaline active groups, so it can selectively pass anions and block cations. The ion exchange functional groups of the cation exchange membrane are mainly: sulfonic acid group, phosphoric acid group, carboxylic acid group, phenol group, arsenic acid group and selenic acid group; the ion exchange functional groups of the anion exchange membrane are mainly amino group and aromatic amino group.

[0037] Common preparation methods for ion exchange membranes include impregnation, casting, and scraping. Among them, the scraping method is the most important method for producing ion exchange membranes. This method is to dissolve or disperse linear polymers without ion exchange functional groups in a mixture of olefin monomers that can introduce ion exchange groups and cross-linking agents, prepare them into a paste, and apply them on a supporting mesh for reinforcement. The base membrane is polymerized to obtain the base membrane, and then the ion exchange groups are introduced through polymer chemical reactions to make ion exchange membranes.

[0038] In one or more embodiments, the anion exchange membrane comprises an anion exchange resin and a support mesh, and the cation exchange membrane comprises a cation exchange resin and a support mesh.

[0039] There is no particular limitation on the anion exchange resin used for the anion exchange membrane in principle, and those skilled in the art can select a suitable anion exchange resin according to actual needs. In one or more embodiments, the anion exchange resin can be selected from amino- or arylamino-modified styrene-divinylbenzene copolymers and derivatives thereof. Preferably, the anion exchange resin can be divinylbenzene-trimethylaminomethylstyrene chloride copolymer.

[0040] There is no particular limitation on the cation exchange resin used for the cation exchange membrane in principle, and those skilled in the art can select suitable cation exchange resins according to actual needs. In one or more embodiments, the cation exchange resin can be selected from styrene-divinylbenzene copolymers and derivatives thereof modified by sulfonic acid groups, phosphoric acid groups, carboxylic acid groups, phenolic groups, arsenic acid groups or selenoic acid groups. Preferably, the cation exchange resin can be a sodium salt of a sulfonated divinylbenzene-styrene polymer.

[0041] In one or more embodiments, the support mesh for the ion exchange membrane may include one or more selected from the group consisting of polyolefins, fluoropolymers, and polyesters.

[0042] In a preferred embodiment, the support scrim for the anion exchange membrane comprises a polyolefin and the support scrim for the cation exchange membrane comprises a fluoropolymer.

[0043] When the support mesh for anion exchange membranes includes polyolefins and the support mesh for cation exchange membranes includes fluoropolymers, better thermally stable salt removal effects can be achieved compared to using ion exchange membranes including support meshes made of other materials.

[0044] In one or more embodiments, the polyolefin is selected from one or more of polyethylene and polypropylene. Preferably, the polyolefin may be polyethylene.

[0045] In one or more embodiments, the fluorine-containing polymer is selected from one or more homopolymers and copolymers of fluorine-containing olefins. More preferably, the fluorine-containing polymer can be selected from one or more of polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer and ethylene-tetrafluoroethylene copolymer. Further preferably, the fluorine-containing polymer can be an ethylene-tetrafluoroethylene copolymer.

[0046] In a particularly preferred embodiment, the support mesh for the anion exchange membrane comprises polyethylene, and the support mesh for the cation exchange membrane comprises ethylene-tetrafluoroethylene copolymer. More preferably, the support mesh for the anion exchange membrane may be composed of polyethylene, and the support mesh for the cation exchange membrane may be composed of ethylene-tetrafluoroethylene copolymer.

[0047] The anion and cation exchange membranes included in the electrochemical reaction membrane stack of the present invention can be commercially available products. Examples of anion exchange membranes include Selemion AMVN produced by Asahi Glass Co., Ltd., ASE produced by Astom Co., Ltd., Japan, AR103 produced by Veolia of France, FAS produced by Fumatech of Germany, and AME-Type12 produced by Fujifilm of Japan. Preferably, the anion exchange membrane can be an anion exchange membrane (AMVN) of Asahi Glass Co., Ltd., Japan. Examples of cation exchange membranes include Selemion CMVN produced by Asahi Glass Co., Ltd., CSE produced by Astom Co., Ltd., Japan, CR61 produced by Veolia of France, FKS produced by Fumatech of Germany, and CME-Type12 produced by Fujifilm of Japan. Preferably, the cation exchange membrane can be a cation exchange membrane (CMVN) of Asahi Glass Co., Ltd., Japan.

[0048] The cathode and anode plates included in the electrochemical reaction membrane stack of the present invention may be one or more cathode and anode plates known to those skilled in the art, and may be obtained or prepared in a manner known to those skilled in the art.

[0049] In one embodiment of the present invention, Figure 1 As shown, the electrochemical reaction membrane stack may include anode and cathode plates and a plurality of anion exchange membranes (denoted as A membrane) and cation exchange membranes (denoted as C membrane) disposed between the two plates. In the figure, "..." indicates other ion exchange membranes that may exist. The anion exchange membranes and cation exchange membranes are parallel to the cathode and cathode plates and are arranged in the following order from the cathode plate to the anode plate, forming a repeatable unit: A film-C film-A film-A film.

[0050] For ease of description, within a repeatable unit, it can also be written as: First A film-C film-second A film-third A film.

[0051] Among them, the pure water channel is defined by the first A membrane and the C membrane, that is, the space between the first A membrane and the C membrane constitutes the pure water channel; the desalination channel is defined by the C membrane and the second A membrane, that is, the space between the C membrane and the second A membrane constitutes the desalination channel; the alkali solution channel is defined by the second A membrane and the third A membrane, that is, the space between the second A membrane and the third A membrane constitutes the alkali solution channel.

[0052] In the case of describing the repeatable unit with the above structure, when multiple repeatable units are arranged in sequence, adjacent repeatable units can share the same anion exchange membrane. In other words, the A membrane that participates in forming the alkaline solution channel of the previous repeatable unit can also be used as the A membrane that participates in forming the pure water channel of the next repeatable unit. Taking two adjacent repeatable units as an example, the arrangement of their ion exchange membranes can be: First A film-C film-second A film-third A film-C film-fourth A film-fifth A film.

[0053] Among them, "first A film-C film-second A film-third A film" constitutes the first repeatable unit, and "third A film-C film-fourth A film-fifth A film" constitutes the second repeatable unit.

[0054] The electrochemical reaction membrane stack of the above embodiment can also be described in other ways, for example, Figure 2 As shown, the electrochemical reaction membrane stack may include anode and cathode plates and a plurality of anion exchange membranes (denoted as A membranes) and cation exchange membranes (denoted as C membranes) disposed between the two plates. In the figure, "..." indicates other ion exchange membranes that may exist. The repeatable unit may be constructed using the following sub-repeatable units: A film-C film-A film.

[0055] For ease of description, within a sub-repeatable unit, it can also be written as: First A film-C film-second A film.

[0056] In the case of describing the sub-repeatable unit with the above structure, when multiple sub-repeatable units are arranged in sequence, adjacent sub-repeatable units do not share the same anion exchange membrane. Therefore, two adjacent sub-repeatable units can contain a repeatable unit. Taking two adjacent sub-repeatable units as an example, the arrangement of their ion exchange membranes can be: First A film-C film-second A film-third A film-C film-fourth A film.

[0057] Among them, "first A membrane-C membrane-second A membrane" constitutes the previous sub-repeatable unit, and "third A membrane-C membrane-fourth A membrane" constitutes the next sub-repeatable unit. In these two adjacent sub-repeatable units, there is a repeatable unit consisting of "first A membrane-C membrane-second A membrane-third A membrane". In other words, in this repeatable unit, the pure water channel is composed of the space between the "first A membrane-C membrane" of the previous sub-repeatable unit, the desalination channel is composed of the space between the "C membrane and the second A membrane" of the previous sub-repeatable unit, and the alkali solution channel is composed of the space between the second A membrane of the previous sub-repeatable unit and the third A membrane of the next sub-repeatable unit.

[0058] It can be understood that the repeatable unit including "pure water channel-desalting channel-alkaline solution channel" and the repeatable unit including "A membrane-C membrane-A membrane-A membrane" can be equivalent. The focus of the description of the former is on the spatial structure of the repeatable unit, and the focus of the description of the latter is on the framework structure of the repeatable unit.

[0059] It can be understood that the description that the repeatable unit is composed of "pure water channel-desalting channel-alkali solution channel" or the repeatable unit is composed of "A membrane-C membrane-A membrane-A membrane" or similar descriptions do not exclude additional structures in the repeatable unit, that is, the repeatable unit can be additionally provided with other structures, such as other channels, in addition to the structure of "pure water channel-desalting channel-alkali solution channel" or "A membrane-C membrane-A membrane-A membrane", provided that the additional other structures do not affect the realization of the concept of the present invention. Specifically, as long as the migration and removal of the heat-stable salt in the organic amine solution under the action of the electric field is achieved through the structure of "pure water channel-desalting channel-alkali solution channel" or "A membrane-C membrane-A membrane-A membrane", the additional constituent elements and their combinations are all included in the scope of the present invention.

[0060] In the electrochemical reaction membrane stack, a polar liquid channel is formed between the pole plate and the adjacent ion exchange membrane. In one embodiment of the present invention, a salt solution (also referred to as a polar liquid) for providing an operating environment for the core components of the device when the device is running can be introduced into the cathode and anode liquid channels. The polar liquid can be, for example, a sodium chloride solution or a sodium sulfate solution, preferably a sodium sulfate solution. The concentration of the polar liquid can be routinely determined by a person skilled in the art. For example, a sodium sulfate solution with a concentration of 3% based on the total weight of the sodium sulfate solution can be used. The polar liquid preferably circulates between its corresponding supply unit and the polar liquid channel.

[0061] In one embodiment of the present invention, the ion exchange membranes adjacent to the cathode and anode plates in the electrochemical reaction membrane stack can all be cation exchange membranes. Such a configuration can reduce or even prevent the entry of foreign ions (for example, brought by the polar liquid) into the system, thereby improving the purity of the product. To achieve this purpose, other channels can be added to both sides of the repeatable unit in the electrochemical reaction membrane stack. For example, Figure 6 As shown in the example, a desalination channel and an alkali solution channel are added between the cathode plate and the repeatable unit, and a pure water channel is added between the anode plate and the repeatable unit. In this way, the two ends of the electrochemical reaction membrane stack are the desalination channel and the pure water channel respectively, so that the ion exchange membrane adjacent to the cathode and anode plates in the electrochemical reaction membrane stack is a cation exchange membrane.

[0062] In one embodiment of the present invention, the organic amine compound of the present invention is selected from one or more of the following substances: monoethanolamine (MEA), N-methyldiethanolamine (MDEA), diethanolamine (DEA), piperazine (PZ), diethylenetriamine (DETA), triethylenetetramine (TETA), 2-amino-2-methyl-1-propanol (AMP), N-aminoethylpiperazine and 3-diethylaminopropylamine (DEAPA), etc., preferably monoethanolamine, diethanolamine, 2-amino-2-methyl-1-propanol and N-aminoethylpiperazine.

[0063] In one embodiment of the present invention, the cation of the heat-stable salt is selected from one or more of the following substances: protonated monoethanolamine (MEA), N-methyldiethanolamine (MDEA), diethanolamine (DEA), piperazine (PZ), diethylenetriamine (DETA), triethylenetetramine (TETA), 2-amino-2-methyl-1-propanol (AMP), N-aminoethylpiperazine and 3-diethylaminopropylamine (DEAPA), preferably protonated monoethanolamine, diethanolamine, 2-amino-2-methyl-1-propanol and N-aminoethylpiperazine; the anion of the heat-stable salt is selected from one or more of the following ions: formate, acetate, propionate, glycolate, chloride, sulfate, thiocyanate, thiosulfate, nitrate, nitrite and oxalate; preferably formate, acetate, glycolate, sulfate, oxalate and chloride.

[0064] In one embodiment of the present invention, the raw water is an organic amine solution containing a heat-stable salt.

[0065] In a preferred embodiment of the present invention, the initial content of heat-stable salts in the raw water is 5000 to 20000 weight ppm, preferably 5000 to 19000 weight ppm, more preferably 6000 to 19000 weight ppm, more preferably 7000 to 19000 weight ppm, more preferably 7000 to 18000 weight ppm, more preferably 8000 to 18000 weight ppm, more preferably 8000 to 17000 weight ppm, more preferably 8000 to 16000 weight ppm, more preferably 8000 to 15000 weight ppm, more preferably 8000 to 14000 weight ppm, more preferably 8000 to 13000 weight ppm, more preferably 8000 to 12000 weight ppm, more preferably 9000 to 12000 weight ppm, more preferably 10000 to 12000 weight ppm, more preferably 10000 to 11000 weight ppm, based on the total weight of the raw water, so that better heat-stable salt removal effect can be achieved.

[0066] In a preferred embodiment of the present invention, the initial molar concentration of the heat stable salt in the raw water is C S(HSS)It is 0.25 to 1.05 mol / L, preferably 0.25 to 0.95 mol / L, more preferably 0.35 to 0.95 mol / L, more preferably 0.45 to 0.95 mol / L, more preferably 0.45 to 0.85 mol / L, more preferably 0.45 to 0.75 mol / L, more preferably 0.55 to 0.75 mol / L, more preferably 0.65 to 0.75 mol / L, based on the total volume of raw water, so that better heat-stable salt removal effect can be achieved.

[0067] In a preferred embodiment of the present invention, the raw water generally does not contain calcium ions, magnesium ions and barium ions unless these ions are present as impurities. In the case where these ions are present as impurities in the raw water, their concentration is below 20 ppm by weight.

[0068] In a preferred embodiment of the present invention, the raw water generally does not contain iron ions and aluminum ions unless these ions are present as impurities. In the case where iron ions are present in the raw water as impurities, their concentration is below 0.3 mg / L. In the case where aluminum ions are present in the raw water as impurities, their concentration is below 1 mg / L.

[0069] In a preferred embodiment of the present invention, the raw water is pretreated before entering the electrochemical reaction membrane stack of the present invention to remove unwanted impurity ions or limit the content of heat-stable salts to a desired range. The pretreatment can be a means known to those skilled in the art and is implemented in a manner known to those skilled in the art without particular limitation. For example, the pretreatment can be multi-stage filtration or concentration, etc.

[0070] In one embodiment of the present invention, pure water is synonymous with deionized water.

[0071] In one embodiment of the present invention, the alkali solution comprises sodium hydroxide and / or potassium hydroxide, preferably sodium hydroxide. In a preferred embodiment of the present invention, the alkali solution is sodium hydroxide solution.

[0072] In a preferred embodiment of the present invention, the alkali solution is a sodium hydroxide solution, and its initial concentration is 0.80% to 3.2%, preferably 1.0% to 3.2%, more preferably 1.2% to 3.2%, more preferably 1.4% to 3.2%, more preferably 1.6% to 3.2%, more preferably 1.6% to 3.0%, more preferably 1.6% to 2.8%, more preferably 1.6% to 2.6%, more preferably 1.6% to 2.4%, more preferably 1.8% to 2.4%, more preferably 1.8% to 2.2%, more preferably 2%, by mass concentration, so that better heat-stable salt removal effect can be achieved.

[0073] In a preferred embodiment of the present invention, the alkali solution is a sodium hydroxide solution. During the electrochemical reaction, the alkali concentration in the alkali solution channel is no more than 3.2%, more preferably 3.1%, more preferably 3.0%, more preferably 2.9%, more preferably 2.8%, more preferably 2.7%, more preferably 2.6%, more preferably 2.5%, more preferably 2.4%, calculated by mass concentration; the minimum is not less than 0.30%, preferably 0.35%, more preferably 0.40%, more preferably 0.45%, more preferably 0.50%, calculated by mass concentration; thereby achieving a better thermally stable salt removal effect.

[0074] In a preferred embodiment of the present invention, the initial molar concentration of hydroxide ions in the alkali solution is C S(OH-) It is 0.20 to 0.80 mol / L, preferably 0.25 to 0.80 mol / L, more preferably 0.30 to 0.80 mol / L, more preferably 0.35 to 0.80 mol / L, more preferably 0.40 to 0.80 mol / L, more preferably 0.40 to 0.75 mol / L, more preferably 0.40 to 0.70 mol / L, more preferably 0.40 to 0.65 mol / L, more preferably 0.40 to 0.60 mol / L, more preferably 0.45 to 0.60 mol / L, more preferably 0.45 to 0.55 mol / L, more preferably 0.5 mol / L, based on the total volume of the alkali solution, so that better heat-stable salt removal effect can be achieved.

[0075] In a preferred embodiment of the present invention, the ratio of the initial molar concentration of hydroxide ions in the alkali solution to the initial molar concentration of the heat-stable salt in the raw water is C S(OH-) / C S(HSS) It is 0.25 to 1.75, preferably 0.25 to 1.65, more preferably 0.25 to 1.65, more preferably 0.25 to 1.55, more preferably 0.25 to 1.45, more preferably 0.25 to 1.35, more preferably 0.25 to 1.25, more preferably 0.25 to 1.15, more preferably 0.35 to 1.15, more preferably 0.45 to 1.15, more preferably 0.45 to 1.05, more preferably 0.45 to 0.95, more preferably 0.45 to 0.85, more preferably 0.55 to 0.85, more preferably 0.65 to 0.85, more preferably 0.65 to 0.75.

[0076] In a preferred embodiment of the present invention, during the electrochemical reaction, the maximum molar concentration of hydroxide ions in the alkali solution channel is C H(OH-)No more than 0.80 mol / L, more preferably 0.775 mol / L, more preferably 0.75 mol / L, more preferably 0.725 mol / L, more preferably 0.70 mol / L, more preferably 0.675 mol / L, more preferably 0.65 mol / L, more preferably 0.625 mol / L, more preferably 0.60 mol / L, based on the total volume of the liquid in the alkali solution channel; the minimum molar concentration C L(OH-) Not less than 0.075 mol / L, preferably 0.0875 mol / L, more preferably 0.1 mol / L, more preferably 0.1125 mol / L, more preferably 0.125 mol / L, based on the total volume of the liquid in the alkali solution channel; thereby achieving better thermally stable salt removal effect.

[0077] In a preferred embodiment of the present invention, the method of the present invention further comprises, during the electrochemical reaction, when the molar concentration of hydroxide ions in the alkali solution channel decreases to not more than 0.25 mol / L, preferably 0.20 mol / L, more preferably 0.15 mol / L, based on the total volume of the liquid in the alkali solution channel, adding alkali (preferably sodium hydroxide) at least once to increase the hydroxide ion concentration to not less than 0.25 mol / L, more preferably 0.30 mol / L, more preferably 0.35 mol / L, more preferably 0.40 mol / L, more preferably 0.45 mol / L, more preferably 0.50 mol / L, more preferably 0.55 mol / L, based on the total volume of the liquid in the alkali solution channel, thereby achieving better thermally stable salt removal effect.

[0078] In one embodiment of the present invention, the expected technical effect of the present invention can be achieved in the case of a repeatable unit. Select a repeatable unit to illustrate the basic reaction process, such as Figure 3 As shown in the example, the electrochemical reaction membrane stack may include anode and cathode plates and a plurality of anion exchange membranes (denoted as A membrane) and cation exchange membranes (denoted as C membrane) disposed between the two plates. In the figure, "..." indicates other ion exchange membranes that may exist. Pure water is introduced into the pure water channel, raw water is introduced into the desalination channel, and alkali solution is introduced into the alkali solution channel. The anions of the heat-stable salt in the raw water (denoted as [HSS] - )) migrates to the anode through the anion exchange membrane under the action of the electric field; the cation of the heat-stable salt (i.e., the organic amine ion (expressed as AminH + ), which may also be referred to as bound amines when they are components of heat-stable salts, migrate toward the cathode through the cation exchange membrane under the action of an electric field. Thus, the method according to the present invention can remove heat-stable salts through the ion exchange membrane under the action of an electric field.

[0079] In a preferred embodiment of the present invention, when multiple repeatable units are arranged in sequence, further preferred technical effects can be achieved. Three repeatable units arranged in sequence are selected to illustrate the further reaction process, such as Figure 4 As shown in the example, the electrochemical reaction membrane stack may include anode and cathode plates and a plurality of anion exchange membranes (denoted as A membrane) and cation exchange membranes (denoted as C membrane) disposed between the two plates. In the figure, "..." indicates other ion exchange membranes that may exist. Pure water is introduced into the pure water channel, raw water is introduced into the desalination channel (i.e., the raw water channel), and alkali is introduced into the alkali channel. The alkali is, for example, a sodium hydroxide solution. Under the action of the electric field, the cations (organic amine ions (AminH + ), sodium ion (Na + )) migrate to the cathode, and anions (anions of heat stable salts ([HSS] - ) and hydroxide (OH - )) migrate to the anode. Taking into account the effect of the electric field and the limiting effect of the ion exchange membrane in each channel, the ion flow direction of each channel is summarized as follows: Pure water channel: migration of AminH + and OH - ; Raw water channel: Migration of AminH + and [HSS] - ; Alkali channel: OH migration - , move in [HSS] - .

[0080] Without being bound by any particular theory, it is believed that the method of the present invention produces the following reaction: AminH + [HSS - ]+Na + OH - →Amin+H2O+Na + [HSS - ] Without being bound by any particular theory, it can be assumed that in the pure water channel, the OH - The migration of AminH + Migrate from the original water channel to the pure water channel, while AminH in the original water channel + The migration of the raw water channel is beneficial to the [HSS] - The migration of heat-stable salt can achieve better removal effect.

[0081] Without being bound by any particular theory, it can be assumed that the OH - The concentration of OH has multiple effects on the removal of heat-stable salts, which are as follows: ① As mentioned above, OH- Migration into the pure water channel is beneficial to [HSS] - Migrate from the raw water channel, the higher OH in the alkali solution - concentration is conducive to promoting this process; ② On the other hand, the OH - With the [HSS] to be relocated - As negatively charged anions, the excessive OH - Concentration will inhibit [HSS] to a certain extent - Migration of OH in alkali solution; - The concentration of OH is positively correlated with the solution conductivity. - The concentration will lead to too low solution conductivity and too high system resistance, which will increase the energy consumption of the electrodialysis process and reduce the desalination efficiency. The inventors unexpectedly found that the reasonable control of OH in the alkali solution channel during the electrochemical reaction (for example, the early and late stages of the reaction) - The concentration is conducive to achieving better heat-stable salt removal effect.

[0082] Without being bound by any particular theory, it can be assumed that in the alkali solution channel, the [HSS] from the adjacent raw water channel - It can react with Na in the alkali channel + Coordination occurs, thereby alleviating the migration of [HSS] into the alkali channel - AminH migrated into the adjacent pure water channel + The attraction of AminH can reduce or even avoid the migration of AminH from the adjacent pure water channel. + Break through the restriction of anion exchange membrane and migrate further into the alkaline solution channel. + Try to keep it in the pure water channel and separate it from the OH - Reaction to generate Amin and H2O. - The migration rate is greater than that of AminH + The migration rate of OH in the pure water channel - will be relative to AminH + Excess, eventually forming a mixture containing Amin and OH - The solution can be recycled as a by-product stream to further reduce the loss of organic amines.

[0083] It can be understood that, in summary, when there is only one repeatable unit and no other structures are added, the present invention can achieve the expected technical effect; when there are multiple repeatable units, the present invention can achieve further preferred technical effects. Of course, when there is only one repeatable unit, by adding other structures, the above-mentioned further preferred technical effects can also be achieved. For example, Figure 5 As exemplified, the electrochemical reaction membrane stack may include anode and cathode plates and a plurality of anion exchange membranes (denoted as A membranes) and cation exchange membranes (denoted as C membranes) disposed between the two plates, and "..." in the figure indicates other ion exchange membranes that may exist. An adjacent alkali solution channel is disposed next to the pure water channel of the repeatable unit, and an adjacent pure water channel is disposed next to the alkali solution channel of the repeatable unit. In this way, the attached adjacent alkali solution channel and pure water channel can help the repeatable unit achieve a further preferred technical effect (the principle of achieving the further preferred technical effect is described above).

[0084] Compared with the existing three-chamber electrodialysis technology (refer to CN112495189A, which is incorporated herein by reference), the method of the present invention has better technical effects. The existing three-chamber electrodialysis (refer to CN112495189A) adopts a membrane structure of "cation exchange membrane-anion exchange membrane-anion exchange membrane-cation exchange membrane", which defines a membrane pool unit of "alkali chamber-feed chamber-salt chamber" (wherein the alkali chamber is used to hold alkali solution; the feed chamber is used to hold feed solution and realize desalination function; the salt chamber is used to hold deionized water and form a salt solution). Without being limited to any specific theory, it can be considered that in the electrodialysis process of this prior art, hydroxide ions migrate from the alkali chamber into the feed chamber and react with heat-stable salt to generate organic amine compounds, water and heat-stable salt anions, and the heat-stable salt anions migrate from the feed chamber into the salt chamber, thereby realizing the removal of heat-stable salt. In this process, there are two problems: (1) As the reaction proceeds, too much hydroxide ion may migrate into the feed chamber, resulting in an unwanted increase in the pH value of the product stream; (2) Due to the electric field, the following processes actually exist simultaneously in the system: ①OH - Migrate from the alkali chamber to the material chamber; ② OH migrated to the material chamber - Further migrate to the salt chamber; ③ The heat-stable salt anions migrate from the material chamber to the salt chamber. In the same material chamber, the existence of process ② will weaken the progress of process ③, that is, weaken the removal efficiency of heat-stable salt anions.

[0085] Compared with the above-mentioned prior art, the method of the present invention even inhibits OH - Entering into the raw water (or feed liquid), the above-mentioned shortcomings of the prior art are avoided, thereby being able to maintain the pH stability of the feed liquid and improve the removal efficiency of heat-stable salts.

[0086] In one embodiment of the present invention, the pH value of the product stream obtained by the method of the present invention is not higher than that of untreated raw water. In one embodiment of the present invention, the pH value of the product stream obtained by the method of the present invention is lower than that of untreated raw water.

[0087] In one embodiment of the present invention, the method of the present invention further comprises drawing out a byproduct stream from the pure water channel, the byproduct stream comprising an organic amine compound and hydroxide ions, the organic amine compound contained in the byproduct stream being selected from the organic amine compound contained in the raw water. In this way, the organic amine compound in the byproduct stream can be recycled, thereby further reducing the loss of organic amine.

[0088] In a preferred embodiment of the present invention, the method of the present invention further comprises introducing the by-product stream into the desalting channel after optionally concentrating it. The concentration step in the present invention can be carried out by conventional concentration methods and equipment known to those skilled in the art. Concentration can improve the efficiency of processing the by-product stream and secondary recycling of the organic amine compounds therein. In some cases, a small amount of [HSS] may be present in the by-product stream. - , therefore, the byproduct stream can be introduced into the desalination channel to [HSS] - Removal and further purification are performed to utilize the by-product stream.

[0089] In one embodiment of the present invention, the method of the present invention can be carried out continuously or intermittently. In one embodiment of the present invention, the method of the present invention further comprises providing a pure water supply unit, a raw water supply unit and an alkali solution supply unit. Further, the method of the present invention further comprises circulating pure water between the pure water channel and the pure water supply unit, circulating raw water between the desalination channel and the raw water supply unit, and circulating alkali solution between the alkali solution channel and the alkali solution supply unit. Specifically, pure water from the pure water supply unit is introduced from one end of the pure water channel and flows along the channel, then drawn out through the other end, and then circulated back to the pure water supply unit; raw water from the raw water supply unit is introduced from one end of the desalination channel and flows along the channel, then drawn out through the other end, and then circulated back to the raw water supply unit; alkali solution from the alkali solution supply unit is introduced from one end of the alkali solution channel and flows along the channel, then drawn out through the other end, and then circulated back to the alkali solution supply unit.

[0090] In one embodiment of the present invention, the method of the present invention further comprises applying voltage to the cathode and anode plates to generate an electric field. The cathode and anode plates of the electrochemical reaction membrane stack are connected to an external power source, thereby providing an electric field for the membrane stack during the operation of the device, so that the anions and cations move in a directional manner in the membrane stack.

[0091] In one embodiment of the present invention, the initial current density of the electrochemical reaction membrane stack during the method of the present invention is 55-130 A / m 2 , preferably 60-130 A / m 2 , more preferably 60-120 A / m 2 , more preferably 70-120 A / m 2 , more preferably 80-120 A / m 2, more preferably 90-120 A / m 2 , more preferably 100-120 A / m 2 Carrying out the reaction within this initial current density range is beneficial to improving the desalination efficiency.

[0092] In one embodiment of the present invention, the method of the present invention further comprises maintaining the solution conductivity in the alkali solution channel at 20-115 mS / cm, preferably 25-115 mS / cm, more preferably 25-110 mS / cm, more preferably 25-105 mS / cm, more preferably 30-105 mS / cm, more preferably 30-100 mS / cm, more preferably 30-95 mS / cm. Maintaining the solution conductivity in the alkali solution channel within this range is beneficial to the ion migration rate, and thus is beneficial to improving the desalination efficiency.

[0093] In one embodiment of the present invention, the method of the present invention further comprises maintaining the operating temperature of the electrochemical reaction membrane stack at 5-35° C., preferably 10-35° C., more preferably 20-35° C., more preferably 20-30° C., more preferably 25-30° C. Carrying out the reaction at this temperature is beneficial to balancing the ion migration rate and the equipment life, thereby improving the desalination efficiency and reducing the equipment loss.

[0094] In one embodiment of the present invention, the flow rate of each channel of the electrochemical reaction membrane stack can be set in a manner known to those skilled in the art and is not particularly limited herein.

[0095] In one embodiment of the present invention, when the concentration of the heat-stable salt of the solution in the desalting channel is lower than 5000 wt ppm, preferably 4500 wt ppm, the product stream is drawn out from the desalting channel, which is beneficial to balance the removal effect of the heat-stable salt and the loss of the organic amine.

[0096] The present application also provides a device for removing heat-stable salts by electrodialysis, comprising: An electrochemical reaction membrane stack, comprising a cathode plate, an anode plate and at least one repeatable unit arranged between the two plates, an electric field being present between the cathode plate and the anode plate, the repeatable unit comprising a "pure water channel-desalting channel-alkali solution channel" from the cathode plate to the anode plate, the pure water channel being defined by an anion exchange membrane and a cation exchange membrane, the desalting channel being defined by a cation exchange membrane and an anion exchange membrane, and the alkali solution channel being defined by an anion exchange membrane and an anion exchange membrane; The drainage unit is configured to introduce pure water into the pure water channel, introduce raw water into the desalination channel, introduce alkali solution into the alkali solution channel, and draw out a product stream from the desalination channel, wherein the raw water contains an organic amine compound and a heat-stable salt.

[0097] Corresponding to the purpose of the present invention, the device of the present invention utilizes an electrochemical reaction membrane stack to respectively and directionally migrate the cations and anions of the heat-stable salt to different channels, thereby achieving the removal of the heat-stable salt from the organic amine solution. The device of the present invention has high efficiency in removing the heat-stable salt and high recovery rate of the organic amine solution, and because the removal process limits the migration of hydroxide ions to the organic amine solution, the increase in the pH value of the recovered organic amine solution can be reduced or even avoided.

[0098] The descriptions of the apparatus or device in the above method are applicable to the corresponding descriptions of the apparatus of the present invention.

[0099] In one embodiment of the present invention, the electrochemical reaction membrane stack may include a plurality of repeatable units disposed between two electrode plates, and the plurality of repeatable units may be arranged in sequence.

[0100] In one embodiment of the present invention, the drainage unit can also be configured to draw out a by-product stream from the pure water channel, wherein the by-product stream contains organic amine compounds and hydroxide ions. In this way, the organic amine compounds in the by-product stream can be recycled, thereby further reducing the loss of organic amine compounds.

[0101] In one embodiment of the present invention, the flow unit can also be configured to introduce the by-product stream into the desalination channel after optionally being concentrated. In this way, the by-product stream can be introduced into the desalination channel to [HSS] - Removal and further purification are performed to utilize the by-product stream and reduce the loss of organic amine compounds.

[0102] In one embodiment of the present invention, the device of the present invention may further include a concentration unit. The concentration unit includes but is not limited to electrodialysis, forward osmosis, and high pressure membrane. The concentration unit may be configured to concentrate the by-product stream. In this way, the efficiency of processing the by-product stream and reusing the organic amine therein may be improved.

[0103] In one embodiment of the present invention, the device of the present invention may further include a pure water supply unit, a raw water supply unit and an alkaline solution supply unit. The drainage unit may also be configured to circulate the pure water between the pure water channel and the pure water supply unit, circulate the raw water between the desalination channel and the raw water supply unit, and circulate the alkaline solution between the alkaline solution channel and the alkaline solution supply unit.

[0104] In one embodiment of the present invention, the device of the present invention may further include an external power source configured to apply voltage to the cathode and anode plates to generate an electric field.

[0105] In one embodiment of the present invention, the drainage unit can also be configured to draw out the product stream from the desalination channel when the concentration of the heat-stable salt of the organic amine ion in the solution in the desalination channel is lower than 5000 wt ppm, preferably 4500 wt ppm. In this way, it is beneficial to balance the removal effect of the heat-stable salt and the loss of the organic amine.

[0106] In one embodiment of the present invention, the drainage unit of the present invention may further include a pump, preferably a metering pump, for introducing each material flow into the corresponding channel and keeping each material flow circulating between the corresponding channel and the supply unit. Example

[0107] The initial content is 11000 ppm by weight (initial molar concentration is about 0.7 mol / L). The pH of the raw water is 9.45. 2L of NaOH solution (initial mass concentration is 2%) is introduced into each alkali solution channel from the alkali solution supply unit, and the alkali solution is circulated between each alkali solution channel and the alkali solution supply unit. 2L of pure water is introduced into each pure water channel from the pure water supply unit, and the pure water is circulated between each pure water channel and the pure water supply unit. 3L of sodium sulfate solution (mass concentration is 3%) is introduced into the extreme liquid channel.

[0108] The operating temperature of the electrochemical reaction membrane stack was maintained at 25°C; the inter-membrane voltage of the electrochemical reaction membrane stack was set to 6V, and the initial current density of the electrochemical reaction membrane stack was 120A / m at this inter-membrane voltage. 2 .

[0109] Turn on the external power supply and run the device for 180 minutes.

[0110] Monitor the conductivity of the NaOH solution in the alkali solution channel. Before the reaction started, the conductivity of the 2% NaOH solution was 93 mS / cm. When the device was running for 90 minutes, 35 grams of NaOH solid was added. At this time, the mass concentration of the NaOH solution in the alkali solution channel increased from 0.6% to 2.35%, and the conductivity of the solution increased from 28.69 mS / cm to 104.3 mS / cm. After the reaction was completed, the conductivity of the NaOH solution in the alkali solution channel was 49.3 mS / cm.

[0111] During the operation of the device, as the reaction proceeds, the conductivity of the solution in the alkali solution channel changes, resulting in a change in current density. The initial current density at the beginning of the experiment and the current density at the end of the experiment are recorded. The pH value of the product stream is detected. The content of each organic amine compound, heat-stable salt cation (i.e., the ion of each organic amine compound) and anion in the product stream is detected by ion chromatography. It should be noted that in ion chromatography, each organic amine compound and its ion are represented as peaks of the same type. For example, 2-amino-2-methyl-1-propanol and its ion (i.e., protonated 2-amino-2-methyl-1-propanol) are jointly expressed as a peak a in the spectrum, while monoethanolamine and its ion (i.e., protonated monoethanolamine) are jointly expressed as another peak b in the spectrum. The mass concentrations of each organic amine compound and heat-stable salt cation (i.e., the ion of each organic amine compound) are added together to be calculated as the total mass concentration of the organic amine in the product stream, and the content of each heat-stable salt anion is added together to be calculated as the heat-stable salt content of the product stream. The mass of the organic amine is calculated according to the mass concentration of the organic amine in the raw water and the product stream, and the amine recovery rate is further calculated according to the mass of the organic amine in the raw water before the experiment and the mass of the organic amine in the product stream after the experiment. The calculation formula is as follows: η = (m aA / m bA ）×100% m aA : The mass of organic amine in the raw water (i.e., product stream) after the experiment; m bA : The mass of organic amines in raw water before the experiment.

[0112] Example 2 The operation was carried out according to Example 1, except that a NaOH solution with a mass concentration of 1% was used. Before the reaction started, the conductivity of the NaOH solution with a mass concentration of 1% was 48 mS / cm. When the device was running for 40 minutes, 80 minutes, 120 minutes and 160 minutes, NaOH solid was added, and 15 grams of NaOH solid was added each time. During the first addition, the mass concentration of NaOH solution in the alkali channel increased from 0.5% to 1.25%, and the solution conductivity increased from 27.87 mS / cm to 41.76 mS / cm; during the second addition, the mass concentration of NaOH solution in the alkali channel increased from 0.6% to 1.35%, and the solution conductivity increased from 29.93 mS / cm to 42.18 mS / cm; during the third addition, the mass concentration of NaOH solution in the alkali channel increased from 0.6% to 1.35%, and the solution conductivity increased from 28.55 mS / cm to 41.55 mS / cm; during the fourth addition, the mass concentration of NaOH solution in the alkali channel increased from 0.5% to 1.25%, and the solution conductivity increased from 31.21 mS / cm to 45.38 mS / cm. After the reaction, the conductivity of NaOH solution in the alkali channel was 41 mS / cm.

[0113] Example 3 The operation was carried out according to Example 1, except that a NaOH solution with a mass concentration of 3% was used. Before the reaction started, the conductivity of the NaOH solution with a mass concentration of 3% was 138 mS / cm. When the device was running to the 130th minute, 10 grams of NaOH solid was added, at which time the mass concentration of the NaOH solution in the alkali solution channel increased from 0.6% to 1.1%, and the solution conductivity increased from 30.32 mS / cm to 47.63 mS / cm. After the reaction was completed, the conductivity of the NaOH solution in the alkali solution channel was 39 mS / cm.

[0114] Example 4 The operation was carried out according to Example 1, except that the inter-membrane voltage was set to 4.5 V, at which the initial current density of the electrochemical reaction membrane stack was 60 A / m 2 .

[0115] Example 5 The operation was carried out according to Example 1, except that the inter-membrane voltage was set to 5 V, at which the initial current density of the electrochemical reaction membrane stack was 80 A / m 2 .

[0116] Example 6 The operation was carried out according to Example 1, except that the operating temperature of the electrochemical reaction membrane stack was maintained at 5°C.

[0117] Example 7 The operation was carried out according to Example 1, except that the operating temperature of the electrochemical reaction membrane stack was maintained at 15°C.

[0118] Example 8 The operation was carried out according to Example 1, except that the initial content of the heat-stable salt in the raw water used was 5697 ppm by weight (initial molar concentration was about 0.3 mol / L), and the pH of the raw water was 9.91.

[0119] Example 9 The operation was carried out according to Example 1, except that the initial content of the heat-stable salt in the raw water used was 9218 ppm by weight (initial molar concentration was about 0.5 mol / L), and the pH of the raw water was 10.05.

[0120] Example 10 The operation was carried out according to Example 1, except that the initial content of the heat-stable salt in the raw water used was 19105 ppm by weight (initial molar concentration was about 1.0 mol / L), and the pH of the raw water was 9.54.

[0121] The parameters and effect data of Examples 1-7 (amine recovery rate, heat stable salt (HSS) content of the product stream, and pH of the product stream) are summarized in Table 1 below.

[0122] Table 1:

[0123] * C S(NaOH) (%): represents the initial mass concentration of NaOH, in mass %; The ratio of the initial molar concentration of hydroxide ions in the alkali solution of Examples 1-3 and 8-10 to the initial molar concentration of the heat-stable salt in the raw water and the effect data are summarized in Table 2 below.

[0124] Table 2:

[0125] * C S(NaOH) (%): represents the initial mass concentration of NaOH, in mass %; * C S(OH-) (mol / L): indicates OH - The initial molar concentration of , in mol / L; * C S(HSS) (mol / L): represents the initial molar concentration of the heat stable salt, in mol / L.

[0126] The initial molar concentration of hydroxide ions in the alkali solution and the change in molar concentration in the alkali solution channel and the effect data of Examples 1-3 are summarized in Table 3 below.

[0127] Table 3:

[0128] * C S(NaOH) (%): represents the initial mass concentration of NaOH, in mass %; * C NaOH (%): represents the real-time mass concentration of NaOH, that is, the mass concentration of alkali in the alkali solution channel, in mass %; * C S(OH-) (mol / L): indicates OH - The initial molar concentration of , in mol / L; * C OH- (mol / L): indicates OH - The real-time molar concentration, i.e., the molar concentration of hydroxide ions in the alkali solution channel, is expressed in mol / L; The higher the amine recovery rate, the smaller the loss of organic amines. The lower the content of heat-stable salts, the higher the efficiency of heat-stable salt removal and the better the effect of heat-stable salt removal.

[0129] Without being bound by any particular theory, it can be considered that the hydrolysis or conjugation of the heat-stable salt anions present in the solution with water results in a relative increase in the concentration of hydroxide ions, resulting in a relative increase in the pH value. After the experiment, the heat-stable salt anions contained in the product stream decreased relative to the raw water, so that the hydrolysis or conjugation that caused the pH value to increase was weakened, resulting in a slight decrease in the pH value of the product stream relative to the raw water. Comparative Example

[0130] Using the same materials and substances as in Example 1, the comparative example adopts the electrochemical reaction membrane stack configuration of the prior art, and its structure is as follows: Figure 7 In the example, the anion exchange membrane is represented as membrane A, the cation exchange membrane is represented as membrane C; the desalination channel is represented as channel 1, the alkali channel is represented as channel 2, the pure water channel is represented as channel 3, and the polar liquid channel is represented as channel 4. In the figure, "..." indicates other ion exchange membranes. The repeatable unit of the comparative example is composed of "alkali channel-desalination channel-pure water channel" from the cathode plate to the anode plate, and the electrochemical reaction membrane stack of the comparative example includes 10 such repeatable units.

[0131] The operation was carried out according to Example 1. It should be noted that when the inter-membrane voltage of the comparative example was 6 V, its initial current density was 210 A / m 2 .

[0132] The parameters and effect data (amine recovery rate, heat-stable salt content and product stream pH) of Example 1 and the comparative example are summarized in Table 4 below.

[0133] Table 4:

[0134] * C S(NaOH) (%): represents the initial mass concentration of NaOH, in mass %.

[0135] It can be seen that, compared with the comparative example, the loss of organic amine in Example 1 of the present invention is less; the efficiency of heat-stable salt removal is higher and the effect is better; the pH of the comparative example increases, while the pH of the product stream remains basically stable without any unexpected increase.

Claims

1. A method for removing heat-stable salts by electrodialysis, comprising the following steps: i) providing an electrochemical reaction membrane stack, the electrochemical reaction membrane stack comprising a cathode plate, an anode plate and at least one repeatable unit arranged between the two plates, an electric field being present between the cathode plate and the anode plate, the repeatable unit comprising a "pure water channel-desalting channel-alkali solution channel" from the cathode plate to the anode plate, the pure water channel being defined by an anion exchange membrane and a cation exchange membrane, the desalting channel being defined by a cation exchange membrane and an anion exchange membrane, and the alkali solution channel being defined by an anion exchange membrane and an anion exchange membrane; ii) introducing pure water into the pure water channel, introducing raw water into the desalination channel, introducing alkali solution into the alkali solution channel, and iii) withdrawing a product stream from the desalination channel; in, The raw water contains an organic amine compound and a heat-stable salt.

2. The method according to claim 1, wherein the organic amine compound is selected from one or more of monoethanolamine, diethanolamine, 2-amino-2-methyl-1-propanol and N-aminoethylpiperazine and derivatives thereof, and the heat-stable salt is composed of the following anions and cations: The cation of the heat stable salt is selected from one or more of protonated monoethanolamine, diethanolamine, 2-amino-2-methyl-1-propanol and N-aminoethylpiperazine; The anion of the heat stable salt is selected from one or more of formate, acetate, glycolate, sulfate, oxalate and chloride. 3 . The method according to claim 1 , wherein the desalination channel is defined by a cation exchange membrane of the pure water channel and an anion exchange membrane of the alkali solution channel.

4. The method according to claim 1 or 2, wherein the initial molar concentration of the heat-stable salt in the raw water is 0.25 to 1.05 mol / L, preferably 0.45 to 0.75 mol / L.

5. The method according to claim 1 or 2, wherein the initial molar concentration of hydroxide ions in the alkali solution is 0.20 to 0.80 mol / L, preferably 0.40 to 0.80 mol / L.

6. The method according to claim 1 or 2, wherein the alkali solution is a sodium hydroxide solution.

7. The method according to claim 1 or 2, wherein the ratio of the initial molar concentration of hydroxide ions in the alkali solution to the initial molar concentration of the heat-stable salt in the raw water is 0.25 to 1.15, preferably 0.45 to 1.15, and more preferably 0.55 to 0.

85.

8. The method according to claim 1 or 2, wherein the initial current density of the electrochemical reaction membrane stack during the method is 55-130 A / m 2 .

9. The method according to claim 1 or 2, further comprising maintaining the solution conductivity in the alkali solution channel between 20-115 mS / cm.

10. A device for removing heat-stable salts by electrodialysis, comprising: - an electrochemical reaction membrane stack, comprising a cathode plate, an anode plate and at least one repeatable unit disposed between the two plates, an electric field being present between the cathode plate and the anode plate, the repeatable unit comprising a "pure water channel-desalting channel-alkali solution channel" from the cathode plate to the anode plate, the pure water channel being defined by an anion exchange membrane and a cation exchange membrane, the desalting channel being defined by a cation exchange membrane and an anion exchange membrane, and the alkali solution channel being defined by an anion exchange membrane and an anion exchange membrane; - a drainage unit configured to introduce pure water into the pure water channel, introduce raw water into the desalination channel, introduce alkali solution into the alkali solution channel, and draw out a product stream from the desalination channel, wherein the raw water contains an organic amine compound and a heat-stable salt.

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