Waste anion exchange membrane recovery method

Abstract

The invention belongs to the field of high polymer materials, and relates to a waste anion exchange membrane recovery method which comprises the following steps: (1) waste AEMs are subjected to a reforming reaction in a protonic acid solution, the concentration of the protonic acid solution is 1-10 M, the reforming reaction time is 4-24 h, and the reaction temperature is 30-80 DEG C; (2) washing the waste AEMs subjected to the reforming reaction with deionized water until the waste AEMs are neutral, and drying to obtain a recycled membrane material; (3) dissolving the recycled membrane material in an organic solvent to obtain a polymer solution; and (4) precipitating, separating and drying the polymer solution in deionized water to obtain the recycled raw material. The method disclosed by the invention has relatively high repeatability, and the obtained recycled AEMs can keep relatively high ion conduction performance. After 50 cycles, compared with the initial AEMs, the retention rate of the conductivity and the mechanical strength of the recycled AEMs are as high as 93% or above.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of high polymer materials, and relates to a recycling method of waste anion exchange membrane. BACKGROUND

[0002] Anion exchange membranes (AEMs) are a class of high polymer functional materials that can conduct and exchange anion groups, and can be used in fuel cells, electrodialysis, bipolar membranes, hydrogen production by water electrolysis, catalytic reduction of carbon dioxide, and high-efficiency separation in chemical industry. During the operation of AEMs, harsh environments such as high temperature, high humidity, high pressure, and strong alkali are usually required to be withstood. Therefore, as the use time of AEMs is prolonged, the performance of the ion membrane will inevitably degrade, which is specifically manifested in the decrease of ion selectivity, the decrease of electrical conductivity and mechanical strength, and the like. These problems will significantly affect the efficient conduction of the ion membrane, and eventually lead to the scrap of the ion membrane.

[0003] The degradation of AEMs mainly comes from the main chain structure and the functional groups of the side chain of the material. Most of the carbon-hydrogen main chain and functional groups will inevitably degrade and fail under alkaline working environment. For example, the widely used polysulfone AEMs are confirmed to have degradation on the main chain under alkaline conditions, resulting in loss of membrane performance (PNAS 2013, 110 (7): 2490-2495). In addition, common functional groups such as quaternary amine groups, imidazole groups, and pyridine groups are easily attacked by OH- or OH radicals, thereby aggravating the degradation of the resin (Energy Environ. Sci., 2014, 7, 3135). The recycling of waste AEMs not only involves the main chain skeleton of the material, but also needs to consider the remodeling of the functional groups, and further needs to combine the feasibility and cost-effectiveness of industrial scale application, which all increase the difficulty and cost of recycling. If these waste AEMs are not effectively treated, not only a large amount of space will be occupied, but also long-term negative effects on the environment will be caused. Therefore, how to effectively recycle and reuse the waste AEMs not only has important theoretical significance, but also has significant economic and social benefits. However, the current recycling technology of waste AEMs still faces great challenges.

[0004] Jianqiu Hou et al. used crosslinking groups on the side chains of polymers to achieve the recovery of ion membranes, but the recovery of degraded ion membrane materials and functional groups still faces great challenges (Journal of Power Sources, 375, (2018), 404); Amaia Lejarazu-Larrañaga et al. used other waste materials to prepare ion membranes to achieve material recovery, but it cannot be applied to the recovery and application of anion resins (Journal of Membrane Science, 593, (2020), 117423). SUMMARY

[0005] The purpose of the present application is to overcome the defects of the prior art, and to provide a method for recycling waste anion exchange membranes. The method has the characteristics of high efficiency, green environmental protection, low cost and simple process. In addition, the method has high repeatability, and the AEMs obtained after multiple recycling can maintain high ion conductivity.

[0006] In order to achieve the above purpose, the present application adopts the following technical scheme: A method for recycling waste anion exchange membranes, comprising the following steps: (1) The waste AEMs are subjected to a reforming reaction in a protonic acid solution, the concentration of the protonic acid solution is 1-10 M, the reforming reaction time is 4-24 h, and the reaction temperature is 30-80°C; (2) The waste AEMs after the reforming reaction are washed to neutral with deionized water, and the recycled membrane material is obtained by drying treatment; (3) The recycled membrane material is subjected to a recycling process to obtain a polymer solution; (4) The polymer solution is precipitated, separated and dried in deionized water to obtain a recycled raw material; (5) The recycled raw material is subjected to a preparation process to obtain a recycled AEM material.

[0007] Preferably, the protonic acid solution in step (1) can be a commonly used strong acid such as nitric acid, sulfuric acid, hydrochloric acid or a mixed solution of strong acids. Preferably, the concentration of the acid solution is 3-8 M.

[0008] Preferably, the waste AEMs in step (1) are aged anion exchange membranes after use. The anion exchange membrane is the anion exchange membrane described in patent CN 116554385 A. The functional groups of the AEMs will undergo chemical degradation (Hofmann reaction or elimination reaction, etc.) under alkaline conditions, thereby removing the functional groups, and then converting to the initial amino active group through the reaction of the protonic acid.

[0009] Preferably, the reforming time is 4-10h, and the reforming temperature is 50-80℃.

[0010] The waste AEMs are defined as follows: after the membrane aging treatment or use, when the ion conductivity of the AEMs is reduced to 50% of the initial value, the ion membrane is referred to as waste AEMs.

[0011] Preferably, the drying in step (2) is drying treatment at 30-60℃ for 4-24h.

[0012] Preferably, the concentration of the polymer solution in step (3) is 2-30 wt%, preferably 2-15 wt%, and further preferably 10-15%.

[0013] Preferably, the recycling process in step (3) is dissolving the recovered membrane material in an organic solvent, and the organic solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, ethanol, ethanol / water mixed solvent, isopropanol / water mixed solvent, n-propanol / water mixed solvent, dimethyl sulfoxide or ethyl acetate.

[0014] Preferably, the drying in step (4) is drying treatment at 30-60℃ for 4-24h.

[0015] The re-preparation process in step (5) is the same as the membrane preparation process, and is specially named for the description of the recycling method.

[0016] The above steps can be recycled, and the recycling refers to the recycling of waste AEMs through the membrane recycling, recycling and membrane re-preparation method to obtain recycled AEMs. In this definition, after one cycle, the recycled AEMs obtained after one cycle of the recycling method from the waste AEMs.

[0017] Advantages of the present application: Compared with the prior art, the present application has at least the following advantages: (1) The recycling and recycling method of the present application does not need complex process and other expensive catalysts, but only uses the catalyst effect of protonic acid to achieve the purpose of reforming, and has the characteristics of high efficiency, green environmental protection, low cost and simple process.

[0018] (2) The method has high repeatability, and the obtained recycled AEMs can maintain high ion conductivity. After 50 cycles, the conductivity retention rate and mechanical strength of the obtained recycled AEMs are as high as 93% or more compared with the initial AEMs.

[0019] (3) The application utilizes the advantage of the main chain structure of AEMs having super strong stability, and retains the structural advantage of the perfluorinated ion membrane after aging. The chemical structures of the recovered raw material, the recovered AEMs, the initial raw material and the initial AEMs obtained by the application are highly consistent. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The infrared spectrum of the initial raw material and the recovered raw material in Example 1.

[0021] Figure 2 The infrared spectrum of the initial AEMs and the recovered AEMs in Example 1.

[0022] Figure 3 The technical roadmap of the waste anion exchange membrane recycling and reusing method of the application. DETAILED DESCRIPTION

[0023] The application will be described in detail below with specific examples, which are only used to illustrate the application and not to limit the protection scope of the application. The application is not limited to the following several embodiments, and other combination schemes derived from the application also belong to the protection scope of the application. The raw materials and reagents involved in the examples are all ordinary commercially available products if not specifically stated, and the experimental methods involved in the examples are all conventional technical means in the field if not specifically stated.

[0024] Anion exchange membrane ion conductivity determination: the resistance R of the sample is tested by a two-electrode method, the instrument is an electrochemical workstation Autolab PGSTA302, the frequency interval is 106Hz-10Hz, and the conductivity is calculated by the following formula: σ=L / RS In the formula: L is the thickness of the membrane (cm), R is the resistance of the membrane (Ω), σ is the conductivity of the sample (S / cm), and S is the test part area of the sample (cm 2 ).

[0025] The application simulates the aging process of the anion membrane by the following method, and uses strong alkali in the alkaline solution during the simulation of the aging process to shorten the decay time.

[0026] The simulated membrane aging process is as follows: the initial AEMs are soaked in an alkaline solution of 6-10M, maintained at 80℃ for a certain period of time, the alkaline solution is replaced every 3h during the period, the product is taken out after the experiment and washed with deionized water for several times, and finally dried at 30-60℃ for 4-24h. In particular, the alkaline solution is a KOH or NaOH aqueous solution.

[0027] The technical roadmap of the waste anion exchange membrane recycling and reusing method of the application is as follows Figure 3The recycling raw material is a polymer material obtained after a recycling process. The re-preparation and re-aging processes are the same as the film preparation and film aging processes. In order to describe the recycling method, the processes are specially named. The cycle refers to the recycling of waste AEMs through the film recycling, recycling, and film re-preparation method. In this definition, the recycled AEMs obtained after one cycle, i.e., one recycling method of waste AEMs.

[0028] Example 1 A method for recycling and recycling of waste anion exchange membranes, the specific steps are as follows: first, according to the raw materials in CN116554385A example 2 to prepare the initial AEMs, then the initial AEMs is soaked in 6M NaOH solution, during the experiment, the alkali solution is replaced every 3h, at 80℃ until the conductivity is reduced to 50% of the initial AEMs, stop the film aging experiment, 50℃ drying treatment for 24h, get waste AEMs.

[0029] The waste AEMs is subjected to film recovery after being subjected to reforming reaction in 4M sulfuric acid (protonic acid) at 80℃ for 4h, and the obtained ion film is washed with deionized water for multiple times, and then dried at 60℃ for 14h to obtain a recycled membrane material. The membrane material is dissolved in ethanol to obtain a 10 wt% polymer solution. Then, the solution is precipitated and separated in deionized water, and then dried at 40℃ for 20h to obtain a recycled raw material, which is denoted as AEMs-Rm-1. Finally, the AEMs is re-prepared according to the film preparation process described in CN116554385A example 2, and the recycled AEMs obtained after one cycle is denoted as AEMs-Re-1. The recycled raw material and the recycled AEMs obtained after repeating the cycle for 50 times are denoted as AEMs-Rm-50 and AEMs-Re-50, respectively.

[0030] NMR test is performed on the target product to confirm the structure and composition, and infrared transmission spectrum is determined, Figure 1 The infrared characterization result graph of the PFSO2NH2 of the initial raw material in the example is shown in the figure. It can be seen from the figure that the characteristic peak of the primary amine on the side chain (-NH2 group) is between 3304~3400 cm -1 and 1548 cm -1 The infrared absorption of the main chain C-F is strong, and the stretching vibration peak at 1050~1350 cm -1 is flat. At the same time, Figure 2 In the infrared spectrum of the prepared initial AEMs, the characteristic peak of the primary amine of PFSO2NH2 at 1548 cm -1 disappears completely, which proves that the primary amine group is completely involved in the reaction; at the same time, the characteristic peak of the primary amine of PFSO2NH2 at 3000~3200 cm -1-CH-, -CH2, -CH3, and 1478cm appeared at this location. -1 The characteristic peaks of the quaternary ammonium group are attributed to the reference Journal of Membrane Science 362 (2010) 97-104; the above results prove that the initial AEMs were successfully prepared according to CN 116554385 A.

[0031] Furthermore, infrared spectroscopy measurements were also performed on the recycled raw materials AEMs-Rm-1 and AEMs-Rm-50. The infrared spectra (...) Figure 1 As can be seen, the spectral structure of the recycled raw material is highly consistent with that of the initial raw material, with the main chain CF structure and the primary amine structure on the side chain, and the COC (989 cm⁻¹) on the side chain. -1 The bonds remained unchanged, and the above results prove that the waste membrane raw materials were effectively recycled.

[0032] Furthermore, infrared spectra were measured on the recovered AEMs-Re-1 and AEMs-Re-50, and the infrared spectra ( Figure 2 It can be seen that the spectral structure of the recovered AEMs is highly consistent with that of the initial AEMs, with similar main chain CF structure and 3000~3200 cm⁻¹ structure on the side chains. -1 -CH-, -CH2, -CH3, and 1478cm -1 The characteristic peaks of the quaternary ammonium group did not change, which proves that the waste membrane material was effectively reused.

[0033] Finally, the conductivity of the recovered AEMs and the initial AEMs (same as Example 2 of CN116554385A) was evaluated. The results showed that the conductivity of AEMs-Re-1 and AEMs-Re-50 in water at 30℃ reached 93.6% and 93.2% of that of the initial AEMs, respectively.

[0034] Example 2 A method for recycling and reusing waste anion exchange membranes differs from Example 1 in that: 3M nitric acid is used as the protic acid for a reforming reaction at 50°C for 8 hours; in addition, the recycled membrane material is dissolved in N,N-dimethylformamide to obtain a 15wt% polymer solution.

[0035] The conductivity of the recovered AEMs and the initial AEMs was evaluated. The results showed that the conductivity of AEMs-Re-1 and AEMs-Re-50 in water at 50℃ reached 93.7% and 93.4% of that of the initial AEMs, respectively.

[0036] Example 3 A method for recycling and reusing waste anion exchange membranes, the only difference is that 5M hydrochloric acid is selected as the proton acid to carry out the reforming reaction at 60℃ for 10h, in addition, the initial AEMs are soaked in 6M KOH solution to carry out membrane aging.

[0037] The conductivity evaluation of the recovered AEMs and the initial AEMs shows that the conductivity of AEMs-Re-1 and AEMs-Re-50 in 50℃ water reaches 93.0% and 93.5% of the initial AEMs respectively.

[0038] Example 4 A method for recycling and reusing waste anion exchange membranes, the only difference with Example 1 is that the raw materials in CN116554385 A Example 6 are selected to prepare the initial AEMs.

[0039] The conductivity evaluation of the recovered AEMs and the initial AEMs shows that the conductivity of AEMs-Re-1 and AEMs-Re-50 in 50℃ water reaches 92.5% and 93.6% of the initial AEMs respectively.

[0040] Example 5 A method for recycling and reusing waste anion exchange membranes, the only difference with Example 1 is that the raw materials in CN116554385 A Example 8 are selected to prepare the initial AEMs, in addition, 5M nitric acid is selected as the proton acid to carry out the reforming reaction.

[0041] The conductivity evaluation of the recovered AEMs and the initial AEMs shows that the conductivity of AEMs-Re-1 and AEMs-Re-50 in 50℃ water reaches 93.4% and 93.4% of the initial AEMs respectively.

[0042] Example 6 A method for recycling and reusing waste anion exchange membranes, the only difference with Example 1 is that the raw materials in CN116554385 A Example 10 are selected to prepare the initial AEMs, in addition, 8M nitric acid is selected as the proton acid to carry out the reforming reaction.

[0043] The conductivity evaluation of the recovered AEMs and the initial AEMs shows that the conductivity of AEMs-Re-1 and AEMs-Re-50 in 50℃ water reaches 94.2% and 94.6% of the initial AEMs respectively.

Claims

1. A method for recovering a waste anion exchange membrane, characterized by, The method comprises the following steps: (1) reforming the waste AEMs in a protonic acid solution, the concentration of the protonic acid solution being 1-10 M, the reforming reaction time being 4-24 h, and the reaction temperature being 30-80℃; (2) washing the waste AEMs after the reforming reaction with deionized water until neutral, and drying to obtain a recycled membrane material; (3) obtaining a polymer solution after recycling the recycled membrane material; (4) precipitating, separating and drying the polymer solution in deionized water to obtain a recycled raw material; (5) obtaining a recycled AEMs material after preparing the recycled raw material.

2. The recycling method according to claim 1, characterized in that, The protonic acid solution in step (1) can be a commonly used strong acid such as nitric acid, sulfuric acid, hydrochloric acid or a mixed solution of strong acids.

3. The recycling method of claim 1, wherein, The concentration of the acid solution in step (1) is 3-8 M.

4. The recycling method of claim 1, wherein, The waste AEMs in step (1) are anion exchange membranes that have aged after use.

5. The recycling method of claim 1, wherein, The waste AEMs in step (1) are ion exchange membranes whose ion conductivity has decreased to 50% of the initial ion conductivity after membrane aging treatment or use.

6. The recycling method of claim 1, wherein, The drying in step (2) is drying treatment at 30-60℃ for 4-24 h.

7. The recycling method of claim 1, wherein, The concentration of the polymer solution in step (3) is 2-30 wt%, preferably 2-15 wt%.

8. The recycling method of claim 1, wherein, The concentration of the polymer solution in step (3) is 10-15 wt%.

9. The recycling method of claim 1, wherein, The organic solvent in step (3) is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, ethanol, an ethanol / water mixed solvent, an isopropyl alcohol / water mixed solvent, a n-propyl alcohol / water mixed solvent, dimethyl sulfoxide or ethyl acetate.

10. The recycling method of claim 1, wherein, The drying in step (4) is drying treatment at 30-60℃ for 4-24 h.

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