Online purification method and system for alcohol amine absorbent

Abstract

The invention relates to the field of regeneration of carbon capture absorbents, and discloses an online purification method and system of an alcohol amine absorbent. The system comprises a nanofiltration unit, an ion exchange unit and a reverse osmosis device, and can be directly connected into a carbon capture system for use to realize online efficient purification. According to the method, a nanofiltration process and an ion exchange process are coupled, and suspended solids, molecular state impurities and ionic state impurities in the alcohol amine absorbent used by a carbon capture system can be comprehensively removed through a desalting water dilution-purification-concentration process, so that the purification and regeneration process of the absorbent is simplified, and the purification efficiency is improved; the purified alcohol amine absorbent can be directly returned to a carbon capture system, and demineralized water generated after concentration can be continuously used for diluting the absorbent to be purified, so that the purification cost is saved, and the practical production and application are facilitated.

Description

Technical Field

[0001] The invention relates to the field of carbon capture absorbent regeneration, and in particular to an online purification system method and system for alcohol amine absorbents. Background Art

[0002] Carbon capture technology is an effective technology for reducing carbon dioxide emissions. At present, large-scale carbon dioxide capture systems mainly use chemical absorption methods with alcohol amine solution as absorbent. During long-term operation, alcohol amines will gradually degrade and produce impurities, resulting in performance degradation and even irreversible inactivation. The impurity components are complex and usually fall into three main categories, namely, suspended solids (fine dust), ionic salts (thermally stable salts), and molecular impurities (partial degradation, polymerization products). The three impurities require different treatment methods due to their different sources.

[0003] At present, there are three main technologies for purifying alcohol amine absorbents. The first is to use an activated carbon three-stage filtration device for online purification, which has the disadvantages of being difficult to remove heat-stable salts and fine dust and easy to clog; the second is to use ion exchange or electrodialysis technology to purify ionic impurities online, which can only remove ionic impurities, and cannot eliminate solid suspended matter and molecular impurities; the third is to use an evaporation device to recover organic amines for offline purification, which has the disadvantages of being unable to slow down the degradation of organic amines and causing large amine losses, and needs to be carried out offline, involving cumbersome steps such as replacing absorbents. Due to the defects of the above three technologies, it is difficult for the existing technology to achieve online and efficient purification of alcohol amine absorbents, which is not conducive to the long-term stable operation of the carbon capture system. It is necessary to develop an efficient and easy-to-operate online purification system and method. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems of poor purification effect and efficiency, cumbersome offline purification operation and high absorbent loss in the prior art, and to provide an online purification method and system for alcoholamine absorbents. The method couples the nanofiltration process and the ion exchange process, and through the process of desalted water dilution-purification-concentration, can completely remove the suspended solids, molecular impurities and ionic impurities in the alcoholamine absorbent used for carbon capture, simplify the purification and regeneration process of the absorbent, and improve the purification efficiency; the regenerated alcoholamine 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, 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 as dilution water for recycling, saving purification costs.

[0005] In order to achieve the above object, the present invention provides an online purification method of an alcohol amine absorbent, comprising the following steps:

[0006] (S1) diluting the impurity-containing alcohol amine absorbent with deionized water, and then subjecting the diluted absorbent to nanofiltration treatment;

[0007] (S2) conditioning the absorbent after the nanofiltration treatment with an alkaline substance, and then performing ion exchange between the conditioned absorbent and an anion exchange resin;

[0008] (S3) concentrating the absorbent after ion exchange by reverse osmosis;

[0009] Wherein, the alcohol amine absorbent is at least one of monoethanolamine, N-methyldiethanolamine and diethanolamine.

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

[0011] Preferably, in step (S1), the nanofiltration membrane used in the nanofiltration treatment process allows the passage of molecular weights in the range of 50-500.

[0012] Preferably, in step (S2), the absorbent is conditioned by adding the alkaline substance 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 strongly basic anion exchange resin type I or a strongly basic styrene-based anion exchange resin.

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

[0016] The second aspect of the present invention provides an online purification system for an alcoholamine absorbent, the system comprising a nanofiltration unit, an ion exchange unit and a reverse osmosis device, the nanofiltration unit comprising a pretreatment box and a nanofiltration membrane, the ion exchange unit comprising a conditioning box and an ion exchange device;

[0017] Among them, the pretreatment box is used to dilute the impure alcohol amine absorbent from the carbon capture system with deionized water, the nanofiltration membrane is used to perform nanofiltration treatment on the diluted absorbent, the conditioning box is used to mix the absorbent after nanofiltration treatment with an alkaline substance and condition it, the ion exchange device is used to perform ion exchange on the conditioned absorbent with an anion exchange column, the reverse osmosis device is used to perform reverse osmosis concentration on the absorbent after ion exchange, and the separated deionized water is transported to the pretreatment box for reuse.

[0018] Preferably, the nanofiltration membrane allows the passage of molecular weights in the range of 50-500.

[0019] The third aspect of the present invention provides a method for online purification of an alcoholamine absorbent using the above-mentioned online purification system, comprising the following steps:

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

[0021] (S2) conditioning the absorbent after the nanofiltration treatment with an alkaline substance in a conditioning box, and then passing the conditioned absorbent through the ion exchange device for ion exchange;

[0022] (S3) The absorbent after ion exchange is concentrated by reverse osmosis in a reverse osmosis device.

[0023] According to the online purification method of the alcoholamine absorbent described in the present invention, the nanofiltration process and the ion exchange process are coupled, and the solid suspended matter, molecular impurities and ionic impurities in the alcoholamine absorbent after use in the carbon capture system can be completely removed through the process of deionized water dilution-purification-concentration, simplifying the purification and regeneration process of the absorbent and improving the purification efficiency; the purified alcoholamine absorbent can be directly returned to the carbon capture system, which is conducive to practical application, and the deionized water generated after concentration can continue to be used to dilute the absorbent to be purified, saving purification costs. The overall process is efficient and energy-saving, and can achieve online and efficient purification.

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

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

[0026] Description of Reference Numerals

[0027] 1. Nanofiltration unit; 1-1. Pretreatment box; 1-2. Nanofiltration membrane; 2. Ion exchange unit; 2-1. Conditioning box; 2-2. Ion exchange device; 3. Reverse osmosis device. DETAILED DESCRIPTION

[0028] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0029] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0030] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating relative importance or implicitly indicating the number of technical features indicated. Therefore, unless otherwise specified, features defined as "first" and "second" may explicitly or implicitly include one or more of the features; "plurality" means two or more. The term "including" and any variation thereof means non-exclusive inclusion, and one or more other features, integers, steps, operations, units, components and / or combinations thereof may 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 may exist or be added. Terms indicating orientation or positional relationships such as "center", "lateral", "upper", "lower", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. are described based on the orientation or relative positional relationships shown in the drawings, and are only simplified descriptions for the convenience of describing the present application, rather than indicating that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present application.

[0032] In addition, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be internally connected between two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0033] The present invention provides an online purification method for an alcoholamine absorbent, comprising the following steps:

[0034] (S1) diluting the impurity-containing alcohol amine absorbent with deionized water, and then subjecting the diluted absorbent to nanofiltration treatment;

[0035] (S2) conditioning the absorbent after the nanofiltration treatment with an alkaline substance, and then performing ion exchange between the conditioned absorbent and an anion exchange resin;

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

[0037] Wherein, the alcohol amine absorbent is at least one of monoethanolamine, N-methyldiethanolamine and diethanolamine.

[0038] In the method of the present invention, preferably, in step (S1), the volume of the alcohol amine absorbent containing impurities is diluted by 2-5 times with the deionized water. In a specific embodiment, the volume of the alcohol amine absorbent containing impurities can be diluted by 2 times, 3 times, 4 times or 5 times with the deionized water. In the present invention, the use of deionized water to dilute the alcohol amine absorbent containing impurities from the carbon capture system can reduce the viscosity of the absorbent, and is beneficial to subsequent nanofiltration treatment and ion exchange, thereby improving the impurity removal efficiency.

[0039] In the method described in the present invention, preferably, in step (S1), the nanofiltration membrane used in the nanofiltration treatment process allows a molecular weight range of 50-500 to pass. More preferably, the nanofiltration membrane used in the nanofiltration treatment process allows a molecular weight range of 50-450 to pass. Most preferably, the nanofiltration membrane used in the nanofiltration treatment process allows a molecular weight range of 60-400 to pass. In the present invention, the use of a nanofiltration membrane in the above range can effectively filter out suspended solids with a larger particle size span (0.5-200μm) and larger molecular weight molecular impurities produced by the polymerization and degradation of alcoholamine absorbents, thereby ensuring better impurity removal effect and purification efficiency. In a specific embodiment of the present invention, various types of commercially available nanofiltration membranes within the above filtration range can be selected. For example, the nanofiltration membrane model used can be FilmTec TM NF270 (DuPont, the allowed molecular weight range is 50-500).

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

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

[0042] In the present invention, the above-mentioned types of alkaline substances are used to make the pH value of the absorbent after conditioning within the aforementioned range, which can promote the conversion of carbamate in the alcoholamine absorbent into electrically neutral organic amine molecules, avoid being removed by anion exchange columns in subsequent ion exchange, reduce the loss of alcoholamine substances, increase the total amount of absorbent recovered after purification, and extend the overall service life of the absorbent.

[0043] In the method of the present invention, preferably, in step (S2), the anion exchange resin is a strongly basic anion exchange resin type I or a strongly basic styrene anion exchange resin. More preferably, the anion exchange resin is a strongly basic anion exchange resin type I (OH type) or a strongly basic styrene anion exchange resin.

[0044] In the method of the present invention, preferably, in step (S3), after the reverse osmosis concentration, the purified absorbent and deionized water are obtained, and the separated deionized water is returned to the dilution process of step (S1) for reuse. In the present invention, the process of deionized water dilution-purification-concentration can dilute the concentration of the alcohol amine absorbent, so that the diluted absorbent can easily pass through the subsequent purification unit, saving purification time; the concentrated absorbent reaches a concentration that can be used for carbon capture and is directly returned to the carbon capture system for use, achieving online purification and facilitating practical use; the concentrated and recovered deionized water can be recycled for diluting the absorbent, saving the amount of deionized water and reducing the purification cost.

[0045] According to the online purification method of the alcoholamine absorbent described in the present invention, the nanofiltration process and the ion exchange process are coupled, and the solid suspended matter, molecular impurities and ionic impurities in the alcoholamine absorbent after use in the carbon capture system can be completely removed through the process of deionized water dilution-purification-concentration, simplifying the purification and regeneration process of the absorbent and improving the purification efficiency; the purified alcoholamine absorbent can be directly returned to the carbon capture system, which is conducive to practical application, and the deionized water generated after concentration can continue to be used to dilute the absorbent to be purified, saving purification costs. The overall process is efficient and energy-saving, and can achieve online and efficient purification.

[0046] The present invention also provides an online purification system for an alcoholamine absorbent, such as Figure 1 As shown, the system includes a nanofiltration unit 1, an ion exchange unit 2 and a reverse osmosis device 3, wherein the nanofiltration unit 1 includes a pretreatment box 1-1 and a nanofiltration membrane 1-2, and the ion exchange unit 2 includes a conditioning box 2-1 and an ion exchange device 2-2;

[0047] Among them, the pretreatment box 1-1 is used to dilute the impure alcohol amine absorbent from the carbon capture system with deionized water, the nanofiltration membrane 1-2 is used to perform nanofiltration treatment on the diluted absorbent, the conditioning box 2-1 is used to mix the absorbent after nanofiltration treatment 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 perform reverse osmosis concentration on the absorbent after ion exchange, and the separated deionized water is transported to the pretreatment box 1-1 for reuse.

[0048] In the system described in the present invention, preferably, the molecular weight range allowed by the nanofiltration membrane 1-2 is 50-500. More preferably, the molecular weight range allowed by the nanofiltration membrane used in the nanofiltration treatment process is 50-450. Most preferably, the molecular weight range allowed by the nanofiltration membrane used in the nanofiltration treatment process is 60-400. In a specific embodiment of the present invention, various commercially available nanofiltration membranes within the above-mentioned filtration range can be selected. For example, the nanofiltration membrane model used can be FilmTec TM NF270 (DuPont, the allowed molecular weight range is 50-500).

[0049] According to the online purification system of the alcoholamine absorbent of the present invention, the system includes a nanofiltration unit, an ion exchange unit and a reverse osmosis device, has a simple structure, can be directly connected to a carbon capture system for use, and realizes online purification; the demineralized water recovered by the reverse osmosis device can be returned as dilution water for recycling, saving purification costs. The overall system is simple in structure and easy to operate, has the continuity of online purification, and is conducive to practical use.

[0050] The present invention also provides a method for online purification of alcoholamine absorbent using the above-mentioned online purification system, comprising the following steps:

[0051] (S1) diluting the impurity-containing alcohol amine absorbent in the pretreatment tank 1-1 with deionized water, and then performing nanofiltration treatment on the diluted absorbent through the nanofiltration membrane 1-2;

[0052] (S2) conditioning the absorbent after the nanofiltration treatment with an alkaline substance in a conditioning box 2-1, and then passing the conditioned absorbent through the ion exchange device 2-2 for ion exchange;

[0053] (S3) The absorbent after ion exchange is concentrated by reverse osmosis in the reverse osmosis device 3.

[0054] In a specific embodiment of the present invention, a method for online purification of alcohol amine absorbent using the above-mentioned online purification system formulation is as follows: Figure 1 As shown, the method comprises the following steps:

[0055] (S1) diluting the impurity-containing alcohol amine absorbent from the carbon capture system in the pretreatment box 1-1 to 2-5 times of the original volume with deionized water, and then passing the diluted absorbent through a nanofiltration membrane 1-2 (the molecular weight allowed to pass is 50-500) for nanofiltration treatment to filter out solid suspended matter and molecular impurities;

[0056] (S2) using an alkaline substance to condition the absorbent after the nanofiltration treatment in a conditioning box 2-1 to adjust the pH value of the absorbent to 9.5-11.5, and then passing the conditioned absorbent through the ion exchange device 2-2 to perform ion exchange to remove ionic impurities;

[0057] (S3) The absorbent after ion exchange is reverse osmosis concentrated in the reverse osmosis device 3, the alcohol amine absorbent reaching a fresh concentration after concentration is transported back to the carbon capture system, and the concentrated deionized water is transported to the pretreatment box 1-1 for recycling.

[0058] In the present invention, the fresh concentration refers to the concentration of the alcoholamine substance as the effective component of the absorbent in the unused alcoholamine absorbent. The purified alcoholamine absorbent is concentrated to the fresh concentration through the aforementioned step (S3), and can be returned to the carbon capture system for continuous recycling and to ensure the carbon capture effect. In a specific embodiment of the present invention, the fresh concentration of the alcoholamine absorbent is 30-40wt%.

[0059] The online purification system and method and application of the alcoholamine absorbent of the present invention are further illustrated by examples. The examples are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the following examples.

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

[0061] Example 1

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

[0063] (S1) Dilute the impurity-containing monoethanolamine absorbent (impurity content of 3.51 wt%) from the carbon capture system in the pretreatment tank 1-1 to twice its original volume with deionized water, and then pass the diluted absorbent through the nanofiltration membrane 1-2 (FilmTec TM NF270, DuPont, the molecular weight range allowed is 50-500) for nanofiltration treatment to remove suspended solids and molecular impurities;

[0064] (S2) conditioning the absorbent after the nanofiltration treatment with NaOH in the conditioning box 2-1 to make the pH value of the absorbent 10.5, and then passing the conditioned absorbent through the ion exchange device 2-2 (the anion exchange column used is a strong basic anion exchange resin type I (OH type) exchange column) to perform ion exchange to remove ionic impurities;

[0065] (S3) The absorbent after ion exchange is reverse osmosis concentrated in the reverse osmosis device 3, the concentrated alcohol amine absorbent is transported back to the carbon capture system, and the concentrated deionized water is transported to the pretreatment box 1-1 for recycling.

[0066] Example 2

[0067] In this embodiment, the fresh concentration of the alcohol amine absorbent is 40 wt %.

[0068] (S1) Dilute the impure N-methyldiethanolamine absorbent (impurity content 5.17 wt%) from the carbon capture system in the pretreatment tank 1-1 to 4 times the original volume with deionized water, and then pass the diluted absorbent through the nanofiltration membrane 1-2 (FilmTec TM NF270, DuPont, the molecular weight range allowed is 50-500) for nanofiltration treatment to remove suspended solids and molecular impurities;

[0069] (S2) conditioning the absorbent after the nanofiltration treatment with KOH in the conditioning box 2-1 to make the pH value of the absorbent 10, and then passing the conditioned absorbent through the ion exchange device 2-2 (the anion exchange column used is a strong alkaline styrene-based anion exchange resin exchange column) to perform ion exchange to remove ionic impurities;

[0070] (S3) The absorbent after ion exchange is reverse osmosis concentrated in the reverse osmosis device 3, the concentrated alcohol amine absorbent is transported back to the carbon capture system, and the concentrated deionized water is transported to the pretreatment box 1-1 for recycling.

[0071] Example 3

[0072] In this embodiment, the fresh concentration of the alcohol amine absorbent is 35 wt %.

[0073] (S1) Diethanolamine absorbent (diethanolamine, impurity content 2.78 wt%) from the carbon capture system is diluted to 5 times its original volume in the pretreatment tank 1-1 with deionized water, and the diluted absorbent is passed through the nanofiltration membrane 1-2 (FilmTec TM NF270, DuPont, the molecular weight range allowed is 50-500) for nanofiltration treatment to remove suspended solids and molecular impurities;

[0074] (S2) conditioning the absorbent after the nanofiltration treatment with ammonia water in the conditioning box 2-1 to make the pH value of the absorbent 11, and then passing the conditioned absorbent through the ion exchange device 2-2 (strong basic styrene anion exchange resin exchange column) to perform ion exchange to remove ionic impurities;

[0075] (S3) The absorbent after ion exchange is reverse osmosis concentrated in the reverse osmosis device 3, the concentrated alcohol amine absorbent is transported back to the carbon capture system, and the concentrated deionized water is transported to the pretreatment box 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 Case

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

[0080] Table 1

[0081]

[0082] It can be seen that the online purification method and system of the alcoholamine absorbent described in the present invention can effectively remove three types of impurities from different sources, and realize online and efficient purification of the alcoholamine absorbent used in the carbon capture system; through the process of desalted water dilution-purification-concentration, it has a good online purification effect, while saving the amount of desalted water and reducing the purification cost; the entire online purification system can be directly connected to the carbon capture system, avoiding the transportation of the absorbent, saving process procedures, reducing the absorbent loss, and is conducive to actual production application.

[0083] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. An online purification method for an alcoholamine absorbent, characterized in that: The method comprises the following steps: (S1) diluting the impurity-containing alcohol amine absorbent with deionized water, and then subjecting the diluted absorbent to nanofiltration treatment; (S2) conditioning the absorbent after the nanofiltration treatment with an alkaline substance, and then performing ion exchange between the conditioned absorbent and an anion exchange resin; (S3) performing reverse osmosis concentration on the absorbent after ion exchange; Wherein, the alcohol amine 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 alcohol amine absorbent containing impurities is diluted 2-5 times with the demineralized 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 treatment process allows the passage of molecular weights in the range of 50-500.

4. The online purification method according to claim 1, characterized in that: In step (S2), the absorbent is conditioned by adding the alkaline substance 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 strongly basic anion exchange resin type I or a strongly basic styrene anion exchange resin.

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

8. An online purification system for an alcoholamine absorbent, characterized in that: 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 box (1-1) and a nanofiltration membrane (1-2); the ion exchange unit (2) comprises a conditioning box (2-1) and an ion exchange device (2-2); The pretreatment box (1-1) is used to dilute the alcohol amine absorbent containing impurities from the carbon capture system with deionized water, the nanofiltration membrane (1-2) is used to perform nanofiltration treatment on the diluted absorbent, the conditioning box (2-1) is used to mix the absorbent after nanofiltration treatment 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 perform reverse osmosis concentration on the absorbent after ion exchange, and the separated deionized water is transported to the pretreatment box (1-1) for reuse.

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

10. A method for online purification of alcoholamine absorbent using the online purification system according to claim 8 or 9, characterized in that: The method comprises the following steps: (S1) diluting the impurity-containing alcohol amine absorbent in the pretreatment tank (1-1) with deionized water, and then passing the diluted absorbent through a nanofiltration membrane (1-2) for nanofiltration treatment; (S2) conditioning the absorbent after the nanofiltration treatment with an alkaline substance in a conditioning box (2-1), and then passing the conditioned absorbent through the ion exchange device (2-2) for ion exchange; (S3) The absorbent after ion exchange is concentrated by reverse osmosis in a reverse osmosis device (3).

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