An on-line purification method and system for an alcohol amine absorbent

Abstract

The present application relates to the field of carbon capture absorbent regeneration, and discloses an online purification method and system for alcohol amine absorbent. The system comprises a nanofiltration unit, an ion exchange unit and a reverse osmosis device, and can be directly connected to a carbon capture system for use, realizing online efficient purification. The method couples nanofiltration process and ion exchange process, and through the dilution-purification-concentration process of desalted water, can comprehensively remove solid suspended matter, molecular impurities and ionic impurities in alcohol amine absorbent after use of the carbon capture system, simplify the purification and regeneration process of the absorbent, and improve the purification efficiency. The purified alcohol amine absorbent can be directly returned to the carbon capture system, and the desalted water produced after concentration can be continuously used for diluting the absorbent to be purified, saving purification cost and being conducive to actual production and use.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of carbon capture absorbent regeneration, in particular to an online purification system method and system of alcohol amine absorbent. BACKGROUND

[0002] Carbon capture technology is an effective technology for reducing carbon dioxide emissions. At present, the chemical absorption method using alcohol amine solution as absorbent is mainly used in large-scale carbon dioxide capture system. In the long-term operation process, alcohol amine will gradually degrade to produce impurities, resulting in performance degradation and even irreversible deactivation. The impurity components are complex, usually mainly three types, respectively are solid suspended matter (fine dust), ionic impurity salt (heat stable salt), molecular impurity (part of degradation, polymerization product), three kinds of impurities need different treatment due to different sources.

[0003] At present, there are mainly three technologies in the purification of alcohol amine absorbent, one is to use activated carbon three-stage filtration device for online purification, which has the defects of difficult to remove heat stable salt and fine dust and easy to block; two is to use ion exchange or electrodialysis technology for online purification of ionic impurities, which can only remove ionic impurities and cannot eliminate solid suspended matter and molecular impurities; three is to use evaporation device to recover organic amine for offline purification, which has the defects of unable to slow down the degradation of organic amine and large amine loss, and needs to be offline, involving complicated steps such as replacing absorbent. Due to the defects of the above three technologies, the existing technology is difficult to realize online efficient purification of alcohol amine absorbent, which is not conducive to the long-term stable operation of carbon capture system, and it is necessary to develop an online purification system and method which is efficient and easy to operate. SUMMARY

[0004] The purpose of the present application is to overcome the problems of poor purification effect and efficiency, offline purification operation and large absorbent loss in the prior art, and provide an online purification method and system of alcohol amine absorbent. The method couples nanofiltration process and ion exchange process, and through the process of desalination water dilution-purification-concentration, the solid suspended matter, molecular impurities and ionic impurities in the alcohol amine absorbent used in carbon capture can be removed comprehensively, the purification and regeneration process of the absorbent is simplified, and the purification efficiency is improved; the regenerated alcohol amine absorbent can be directly returned to the carbon capture system, which is conducive to practical application. The system includes a nanofiltration unit, an ion exchange unit and a reverse osmosis device, which has a simple structure and can be directly connected to the carbon capture system for online purification; the desalination water recovered by the reverse osmosis device can be returned for recycling as dilution water, saving purification cost.

[0005] In order to achieve the above purpose, the online purification method of alcohol amine absorbent comprises the following steps:

[0006] (S1) Dilute the impurity-containing amine absorbent with demineralized water, and then perform nanofiltration on the diluted absorbent.

[0007] (S2) The absorbent after nanofiltration is conditioned with an alkaline substance, and then the conditioned absorbent is subjected to ion exchange with an anion exchange resin.

[0008] (S3) The absorbent after ion exchange is concentrated by reverse osmosis;

[0009] The alkanolamine absorbent is at least one of monoethanolamine, N-methyldiethanolamine, and diethanolamine.

[0010] Preferably, in step (S1), the volume of the impurity-containing alkanolamine absorbent is diluted 2-5 times with the deionized water.

[0011] Preferably, in step (S1), the nanofiltration membrane used in the nanofiltration process allows a molecular weight range of 50-500 to pass through.

[0012] Preferably, in step (S2), the alkaline substance is added for conditioning, so that the pH value of the conditioned absorbent is 9.5-11.5.

[0013] Preferably, in step (S2), the alkaline substance is at least one of NaOH, KOH, and ammonia water.

[0014] Preferably, in step (S2), the anion exchange resin is a strong basic anion exchange resin type I or a strong basic styrene-based anion exchange resin.

[0015] Preferably, in step (S3), after the reverse osmosis concentration, purified absorbent and demineralized water are obtained, and the separated demineralized water is returned to the dilution process in step (S1) for reuse.

[0016] A second aspect of the present invention provides an online purification system for an alcohol amine absorbent, the system comprising a nanofiltration unit, an ion exchange unit, and a reverse osmosis device, wherein the nanofiltration unit comprises a pretreatment tank and a nanofiltration membrane, and the ion exchange unit comprises a conditioning tank and an ion exchange device;

[0017] The pretreatment tank is used to dilute the impurity-containing amine absorbent from the carbon capture system with demineralized water. The nanofiltration membrane is used to perform nanofiltration treatment on the diluted absorbent. The conditioning tank is used to mix the nanofiltration-treated absorbent with an alkaline substance and condition it. The ion exchange device is used to perform ion exchange between the conditioned absorbent and an anion exchange column. The reverse osmosis device is used to concentrate the ion-exchanged absorbent through reverse osmosis and to transport the separated demineralized water to the pretreatment tank for reuse.

[0018] Preferably, the nanofiltration membrane allows the passage of molecules with a weight range of 50-500.

[0019] The third aspect of the present application provides a method for online purification of an alcohol amine absorbent using the aforementioned online purification system, comprising the following steps:

[0020] (S1) diluting the impurity-containing alcohol amine absorbent in a pretreatment tank with desalted water, and then performing nanofiltration treatment on the diluted absorbent through a nanofiltration membrane;

[0021] (S2) conditioning the nanofiltration-treated absorbent in a conditioning tank with an alkaline substance, and then performing ion exchange on the conditioned absorbent through the ion exchange device;

[0022] (S3) performing reverse osmosis concentration on the ion-exchanged absorbent in the reverse osmosis device.

[0023] The online purification method of the alcohol amine absorbent according to the present application couples nanofiltration technology and ion exchange technology, and through the dilution-purification-concentration process of desalted water, can comprehensively remove solid suspensions, molecular impurities and ionic impurities in the alcohol amine absorbent after use in the carbon capture system, simplifies the purification and regeneration process of the absorbent, and improves the purification efficiency; the purified alcohol amine absorbent can be directly returned to the carbon capture system, which is conducive to practical use, and the desalted water produced after concentration can be used for diluting the absorbent to be purified, thereby saving purification costs. The overall process is energy-efficient and can achieve online efficient purification.

[0024] The online purification system of the alcohol amine absorbent according to the present application comprises a nanofiltration unit, an ion exchange unit and a reverse osmosis device, has a simple structure, can be directly connected to the carbon capture system for use, and realizes online purification; the desalted water recovered by the reverse osmosis device can be returned for recycling as dilution water, thereby saving purification costs. The overall system is simple in structure and easy to operate, has continuity of online purification, and is conducive to practical use. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a schematic diagram of the online purification system of the alcohol amine absorbent provided by the present application.

[0026] REFERENCE NUMERALS

[0027] 1, nanofiltration unit; 1-1, pretreatment tank; 1-2, nanofiltration membrane; 2, ion exchange unit; 2-1, conditioning tank; 2-2, ion exchange device; 3, reverse osmosis device. DETAILED DESCRIPTION

[0028] The specific embodiments of the present application are described in detail below. It should be understood that the detailed description and specific examples described herein are intended for purposes of illustration only and are not intended to limit the present application.

[0029] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The ranges or values should be construed to be approximations that allow for significant figure variations. Within ranges given, endpoints are included. Between ranges, other ranges are also intended. Other values that are not expressly listed of enumerated within the body of this disclosure are also intended to be encompassed. Any numerical values include increments of one unit, given the nature of the values or the desired precision of the values. For values that are out of a range, limits, or between the listed values, any intervening value or values, in between, are also intended to be encompassed.

[0030] In the description of the present application, the terms "first", "second", "third", etc., are used only to describe the relative importance of the features, and cannot be understood as indicating the relative importance, or implying the number of the technical features indicated. Therefore, unless otherwise specified, the features defined with "first", "second" can explicitly or implicitly include one or more of the features; the meaning of "multiple" is two or more. The term "include" and any variation thereof means non-exclusive inclusion, and one or more other features, integers, steps, operations, units, components and / or combinations thereof can exist or be added.

[0031] In the description of the present application, the term "include" and any variation thereof means non-exclusive inclusion, and one or more other features, integers, steps, operations, units, components and / or combinations thereof can exist or be added. The terms "center", "transverse", "upper", "lower", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicating the orientation or positional relationship are described based on the orientation or relative position shown in the drawings, and are only for the convenience of the simplified description of the present application, and cannot be understood as indicating that the devices or elements indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0032] In addition, unless otherwise explicitly specified and limited, the terms "mount", "connect", "connection" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integral connection; it can be mechanical connection, or electrical connection; it can be direct connection, or indirect connection through intermediate medium, or internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0033] The present application provides an online purification method of alcohol amine absorbent, comprising the following steps:

[0034] (S1) diluting the alcohol amine absorbent containing impurities with desalted water, and then performing nanofiltration treatment on the diluted absorbent;

[0035] (S2) adjusting the absorbent after nanofiltration with an alkaline substance, and then ion exchanging the adjusted absorbent with an anion exchange resin;

[0036] (S3) concentrating the ion exchanged absorbent by reverse osmosis;

[0037] The alcohol amine absorbent is at least one of monoethanolamine, N-methyl diethanolamine and diethanolamine.

[0038] In the method, preferably, in step (S1), the volume of the alcohol amine absorbent containing impurities is diluted 2-5 times with the desalted water. In specific embodiments, the volume of the alcohol amine absorbent containing impurities can be diluted 2 times, 3 times, 4 times or 5 times with the desalted water. In the present application, diluting the alcohol amine absorbent containing impurities from the carbon capture system with the desalted water can reduce the viscosity of the absorbent, and is conducive to subsequent nanofiltration and ion exchange, and improves the impurity removal efficiency.

[0039] In the method, preferably, in step (S1), the nanofiltration membrane used in the nanofiltration process allows molecules with a molecular weight in the range of 50-500 to pass through. More preferably, the nanofiltration membrane used in the nanofiltration process allows molecules with a molecular weight in the range of 50-450 to pass through. Most preferably, the nanofiltration membrane used in the nanofiltration process allows molecules with a molecular weight in the range of 60-400 to pass through. In the present application, using the nanofiltration membrane in the above range can effectively filter out solid suspensions with a large particle size span (0.5-200 μm) and molecular impurities with a large molecular weight generated by polymerization and degradation of the alcohol amine absorbent, ensuring good impurity removal effect and purification efficiency. In specific embodiments of the present application, commercially available nanofiltration membranes in the above filtration range can be selected, for example, the nanofiltration membrane used can be FilmTec NF270 (Dow Chemical, allowing molecules with a molecular weight in the range of 50-500 to pass through). TM NF270 (Dow Chemical, allowing molecules with a molecular weight in the range of 50-500 to pass through).

[0040] In the method, preferably, in step (S2), the pH value of the adjusted absorbent is 9.5-11.5 by adding the alkaline substance. More preferably, the pH value of the adjusted absorbent is 10-11. Most preferably, the pH value of the adjusted absorbent is 10.2-10.7.

[0041] In the method, preferably, in step (S2), the alkaline substance is at least one of NaOH, KOH and ammonia. More preferably, the alkaline substance is NaOH and / or KOH.

[0042] In the present application, the use of the above-mentioned alkaline substances can make the pH value of the conditioned absorbent within the above-mentioned range, promote the conversion of the carbamate in the alcohol amine absorbent into electrically neutral organic amine molecules, avoid the removal by the anion exchange column in the subsequent ion exchange, reduce the loss of alcohol amine substances, increase the total amount of the recovered absorbent after purification, and prolong the service life of the absorbent as a whole.

[0043] In the method of the present application, preferably, in step (S2), the anion exchange resin is a strong alkaline anion exchange resin type I or a strong alkaline styrene anion exchange resin.

[0044] In the method of the present application, preferably, in step (S3), the desalinated water separated after the reverse osmosis concentration is returned to the dilution process in step (S1) for reuse. In the present application, the use of the desalinated water dilution-purification-concentration process can dilute the concentration of the alcohol amine absorbent, make the diluted absorbent easy to pass through the subsequent purification unit, save the purification time, achieve online purification, and facilitate practical use. The concentrated absorbent reaches the concentration capable of carbon capture and is directly returned to the carbon capture system for use. The desalinated water recovered by concentration can be recycled for diluting the absorbent, save the amount of desalinated water, and reduce the purification cost.

[0045] According to the online purification method of the alcohol amine absorbent of the present application, the nanofiltration process and the ion exchange process are coupled, and the desalinated water dilution-purification-concentration process can comprehensively remove the solid suspended matter, molecular impurities and ionic impurities in the alcohol amine absorbent after use in the carbon capture system, simplify the purification and regeneration process of the absorbent, improve the purification efficiency, and directly return the purified alcohol amine absorbent to the carbon capture system, which is conducive to practical use. The desalinated water produced after concentration can be used for diluting the absorbent to be purified, saving the purification cost. The overall process is energy-efficient and can achieve online efficient purification.

[0046] The present application also provides an online purification system for alcohol amine absorbent, as shown in Figure 1 The system comprises a nanofiltration unit 1, an ion exchange unit 2 and a reverse osmosis device 3. The nanofiltration unit 1 comprises a pretreatment tank 1-1 and a nanofiltration membrane 1-2. The ion exchange unit 2 comprises a conditioning tank 2-1 and an ion exchange device 2-2.

[0047] The pretreatment tank 1-1 is used for diluting the alcohol amine absorbent containing impurities from the carbon capture system with desalted water, the nanofiltration membrane 1-2 is used for nanofiltration treatment of the diluted absorbent, the conditioning tank 2-1 is used for mixing the nanofiltration treated absorbent with alkaline substances and conditioning, the ion exchange device 2-2 is used for ion exchange of the conditioned absorbent with an anion exchange column, and the reverse osmosis device 3 is used for reverse osmosis concentration of the ion exchanged absorbent, and the separated desalted water is transported to the pretreatment tank 1-1 for recycling.

[0048] In the system of the present application, preferably, the nanofiltration membrane 1-2 allows the passage of molecules with a molecular weight range of 50-500. More preferably, the nanofiltration membrane used in the nanofiltration process allows the passage of molecules with a molecular weight range of 50-450. Most preferably, the nanofiltration membrane used in the nanofiltration process allows the passage of molecules with a molecular weight range of 60-400. In the specific embodiments of the present application, various commercially available nanofiltration membranes within the above filtration range can be selected, for example, the nanofiltration membrane used can be FilmTec TM NF270 (DuPont, allowing the passage of molecules with a molecular weight range of 50-500).

[0049] According to the online purification system of the alcohol amine absorbent of the present application, the system comprises a nanofiltration unit, an ion exchange unit and a reverse osmosis device, which is simple in structure, can be directly connected into the carbon capture system for use, realizes online purification, and the desalted water recovered by the reverse osmosis device can be returned for recycling as dilution water, thereby saving purification cost. The overall system is simple in structure and easy to operate, has the continuity of online purification, and is beneficial to practical use.

[0050] The present application also provides a method for online purification of alcohol amine absorbent using the aforementioned online purification system, comprising the following steps:

[0051] (S1) diluting the alcohol amine absorbent containing impurities with desalted water in the pretreatment tank 1-1, and then nanofiltration treating the diluted absorbent through the nanofiltration membrane 1-2;

[0052] (S2) conditioning the nanofiltration treated absorbent with alkaline substances in the conditioning tank 2-1, and then ion exchanging the conditioned absorbent through the ion exchange device 2-2;

[0053] (S3) reverse osmosis concentrating the ion exchanged absorbent in the reverse osmosis device 3.

[0054] In the specific embodiments of the present application, the method for online purification of alcohol amine absorbent using the aforementioned online purification system, as shown in Figure 1 , comprises the following steps:

[0055] (S1) diluting the impurity-containing alcohol amine absorbent from the carbon capture system with desalted water in a pretreatment tank 1-1 to 2-5 times the original volume, and then performing nanofiltration treatment on the diluted absorbent through a nanofiltration membrane 1-2 (molecular weight range of 50-500) to filter out solid suspensions and molecular impurities;

[0056] (S2) adjusting the pH value of the nanofiltration-treated absorbent to 9.5-11.5 in a conditioning tank 2-1 using an alkaline substance, and then performing ion exchange on the conditioned absorbent through the ion exchange device 2-2 to remove ionic impurities;

[0057] (S3) performing reverse osmosis concentration on the ion-exchanged absorbent in a reverse osmosis device 3, and then feeding the alcohol amine absorbent concentrated to the fresh concentration back to the carbon capture system, and feeding the desalted water obtained by concentration to the pretreatment tank 1-1 for recycling.

[0058] In the present application, the fresh concentration refers to the concentration of alcohol amine substances as effective components of the absorbent in the unused alcohol amine absorbent. The purified alcohol amine absorbent is concentrated to the fresh concentration through the aforementioned step (S3), so as to be returned to the carbon capture system for recycling and ensuring the carbon capture effect. In the specific embodiment of the present application, the fresh concentration of the alcohol amine absorbent is 30-40 wt%.

[0059] The online purification system of the alcohol amine absorbent, the method and the application thereof according to the present application will be further illustrated by the following examples. The examples are implemented on the premise of the technical solutions of the present application, and detailed implementation modes and specific operation processes are given, but the protection scope of the present application is not limited to the following examples.

[0060] In the following examples, the experimental methods are the conventional methods in the art unless otherwise specified. The experimental materials used in the following examples are commercially available unless otherwise specified.

[0061] Example 1

[0062] In the present embodiment, the fresh concentration of the alcohol amine absorbent is 30 wt%.

[0063] (S1) diluting the impurity-containing monoethanolamine absorbent (impurity content of 3.51 wt%) from the carbon capture system with desalted water in a pretreatment tank 1-1 to 2 times the original volume, and then performing nanofiltration treatment on the diluted absorbent through a nanofiltration membrane 1-2 (FilmTec TM NF270, DuPont, molecular weight range of 50-500) to filter out solid suspensions and molecular impurities;

[0064] (S2) The absorption agent after nanofiltration is conditioned in conditioning tank 2-1 with NaOH to make the pH value of the absorption agent 10.5, and then the conditioned absorption agent is ion exchanged through ion exchange device 2-2 (the anion exchange column used is a strong alkaline anion exchange resin type I (OH type) exchange column) to remove ionic impurities;

[0065] (S3) The absorption agent after ion exchange is concentrated by reverse osmosis in reverse osmosis device 3, the concentrated alcohol amine absorption agent is fed back to the carbon capture system, and the desalted water obtained by concentration is fed to pretreatment tank 1-1 for recycling.

[0066] Example 2

[0067] In this example, the fresh concentration of the alcohol amine absorption agent is 40wt%.

[0068] (S1) The N-methyldiethanolamine absorption agent containing impurities (impurity content is 5.17wt%) from the carbon capture system is diluted to 4 times the original volume in pretreatment tank 1-1 with desalted water, and then the diluted absorption agent is subjected to nanofiltration treatment through nanofiltration membrane 1-2 (FilmTec TM NF270, DuPont, molecular weight range allowed to pass is 50-500) to filter out solid suspensions and molecular impurities;

[0069] (S2) The absorption agent after nanofiltration is conditioned in conditioning tank 2-1 with KOH to make the pH value of the absorption agent 10, and then the conditioned absorption agent is ion exchanged through ion exchange device 2-2 (the anion exchange column used is a strong alkaline styrene anion exchange resin exchange column) to remove ionic impurities;

[0070] (S3) The absorption agent after ion exchange is concentrated by reverse osmosis in reverse osmosis device 3, the concentrated alcohol amine absorption agent is fed back to the carbon capture system, and the desalted water obtained by concentration is fed to pretreatment tank 1-1 for recycling.

[0071] Example 3

[0072] In this example, the fresh concentration of the alcohol amine absorption agent is 35wt%.

[0073] (S1) The diethanolamine absorption agent containing impurities (diethanolamine, impurity content is 2.78wt%) from the carbon capture system is diluted to 5 times the original volume in pretreatment tank 1-1 with desalted water, and then the diluted absorption agent is subjected to nanofiltration treatment through nanofiltration membrane 1-2 (FilmTec TM NF270, DuPont, molecular weight range allowed to pass is 50-500) to filter out solid suspensions and molecular impurities;

[0074] (S2) The ammonia water is used to adjust the pH value of the absorbent after the nanofiltration treatment in the conditioning tank 2-1, so that the pH value of the absorbent is 11, and then the conditioned absorbent is subjected to ion exchange through the ion exchange device 2-2 (a strong basic styrene anion exchange resin exchange column), so as to remove the ionic impurities;

[0075] (S3) The ion-exchanged absorbent is subjected to reverse osmosis concentration in the reverse osmosis device 3, the concentrated alcohol amine absorbent is transported back to the carbon capture system, and the desalted water obtained by concentration is transported to the pretreatment tank 1-1 for recycling.

[0076] Comparative Example 1

[0077] The method of Example 1 is adopted, except that step (S2) is not performed.

[0078] Test Example

[0079] The concentration of the absorbent and the content of impurities in the alcohol amine absorbent before and after purification are detected by the method of Examples 1-3 and Comparative Example 1, and the results are shown in Table 1:

[0080] Table 1

[0081]

[0082] Therefore, the online purification method and system of the alcohol amine absorbent can effectively remove three types of impurities from different sources, realize online efficient purification of the alcohol amine absorbent used in the carbon capture system, and has good online purification effect, saves the amount of desalted water, and reduces the purification cost through the desalted water dilution-purification-concentration process. The entire online purification system can be directly connected to the carbon capture system, avoiding the transfer of the absorbent, saving the process procedure, reducing the absorbent loss, and being conducive to practical production application.

[0083] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. An online purification method using an alcohol amine absorbent, characterized in that, The method includes the following steps: (S1) Dilute the impurity-containing amine absorbent with demineralized water, and then perform nanofiltration on the diluted absorbent. (S2) The absorbent after nanofiltration is conditioned with an alkaline substance, and then the conditioned absorbent is subjected to ion exchange with an anion exchange resin. (S3) The absorbent after ion exchange is concentrated by reverse osmosis; The alkanolamine absorbent is at least one of monoethanolamine, N-methyldiethanolamine, and diethanolamine.

2. The online purification method according to claim 1, characterized in that, In step (S1), the volume of the impurity-containing alkanolamine absorbent is diluted 2-5 times with the deionized water.

3. The online purification method according to claim 1 or 2, characterized in that, In step (S1), the nanofiltration membrane used in the nanofiltration process allows a molecular weight range of 50-500 to pass through.

4. The online purification method according to claim 1, characterized in that, In step (S2), the alkaline substance is added to condition the absorbent so that the pH value of the conditioned absorbent is 9.5-11.

5.

5. The online purification method according to claim 1 or 4, characterized in that, In step (S2), the alkaline substance is at least one of NaOH, KOH and ammonia water.

6. The online purification method according to claim 1, 4, or 5, characterized in that, In step (S2), the anion exchange resin is a strong basic anion exchange resin type I or a strong basic styrene-based anion exchange resin.

7. The online purification method according to claim 1, characterized in that, In step (S3), after the reverse osmosis concentration, purified absorbent and demineralized water are obtained, and the separated demineralized water is returned to the dilution process in step (S1) for reuse.

8. An online purification system for an alcohol amine absorbent, characterized in that, The system includes a nanofiltration unit (1), an ion exchange unit (2), and a reverse osmosis device (3). The nanofiltration unit (1) includes a pretreatment tank (1-1) and a nanofiltration membrane (1-2). The ion exchange unit (2) includes a conditioning tank (2-1) and an ion exchange device (2-2). The pretreatment tank (1-1) is used to dilute the impurity-containing amine absorbent from the carbon capture system with demineralized water. The nanofiltration membrane (1-2) is used to perform nanofiltration treatment on the diluted absorbent. The conditioning tank (2-1) is used to mix the nanofiltration-treated absorbent with an alkaline substance and condition it. The ion exchange device (2-2) is used to perform ion exchange on the conditioned absorbent with an anion exchange column. The reverse osmosis device (3) is used to concentrate the ion-exchanged absorbent through reverse osmosis and transport the separated demineralized water to the pretreatment tank (1-1) for reuse.

9. The online purification system according to claim 8, characterized in that, The nanofiltration membrane (1-2) allows a molecular weight range of 50-500 to pass through.

10. A method for online purification of alkanolamine absorbents using the online purification system according to claim 8 or 9, characterized in that, The method includes the following steps: (S1) Dilute the impurity-containing amine absorbent with demineralized water in the pretreatment tank (1-1), and then perform nanofiltration treatment through a nanofiltration membrane (1-2); (S2) The absorbent after nanofiltration is conditioned in a conditioning chamber (2-1) with an alkaline substance, and then the conditioned absorbent is subjected to ion exchange through the ion exchange device (2-2). (S3) The absorbent after ion exchange is concentrated by reverse osmosis in the reverse osmosis unit (3).

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