A method for preparing a humidity-responsive co2 composite membrane

Abstract

This invention relates to a method for preparing a humidity-responsive CO2 composite membrane, comprising the following steps: adding anhydrous piperazine to a carboxymethyl chitosan solution and dissolving and mixing it to obtain a CMCs-PiP mixed solution; multi-coating the CMCs-PiP mixed solution onto a polyethersulfone support layer, and drying it to obtain a CMCs-PiP / PES composite membrane; dissolving particles in a mixed solvent of n-propanol and n-butanol, and refluxing and stirring to obtain a solution; multi-coating the solution onto the CMCs-PiP / PES composite membrane, and drying it to obtain the composite membrane. The CO2 separation composite membrane prepared by this invention, by introducing carboxymethyl chitosan as an intermediate layer of the composite membrane, not only helps to improve the compatibility between the support layer and the selective layer, but also, with the assistance of water, effectively reduces the resistance of the intermediate layer to CO2 transfer, thereby facilitating the practical application of CO2 separation and filling the gap in existing technology regarding intermediate layer research.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a method for preparing a humidity-responsive CO2 composite membrane. Background Technology

[0002] The growing prominence of global warming has made reducing greenhouse gas emissions, particularly carbon dioxide (CO2), an urgent need. Flue gas generated during combustion power generation has become a major source of CO2 emissions, making the separation and capture of CO2 from this gas crucial to addressing this challenge. Currently, CO2 separation is mainly achieved through technologies such as pressure swing adsorption (PSA), amine washing, cryogenic distillation, and membrane separation. Among these technologies, membrane separation technology has gained widespread academic and industrial application due to its high efficiency, low cost, and design flexibility.

[0003] Existing gas separation membranes can be mainly divided into dense polymer membranes and ultrathin composite membranes (UTFCs). While dense membranes exhibit good gas selectivity, their gas permeability is relatively poor. In contrast, UTFCs, due to their ultrathin membrane structure, successfully reduce gas permeation resistance. Typically, UTFCs consist of a multilayer structure, including a support layer (providing mechanical strength), an intermediate layer (improving the compatibility between the support layer and the polymer selective layer), and a selective layer (primarily contributing to gas separation). Although research on the selective layer is relatively abundant, research on the intermediate layer is relatively limited. This results in the intermediate layer's inability to further improve its compatibility with the selective layer, leading to insufficient assurance of membrane stability and long-term reliability. Furthermore, the current intermediate layer exhibits significant resistance to CO2 transfer, affecting the practical application of CO2 separation. Therefore, further improvements are needed. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for preparing a humidity-responsive CO2 composite membrane.

[0005] This invention is achieved through the following technical solution:

[0006] A method for preparing a humidity-responsive CO2 composite membrane includes the following steps:

[0007] S1. Add anhydrous piperazine to a carboxymethyl chitosan solution and dissolve and mix to obtain a CMCs-PiP mixed solution;

[0008] S2. The CMCs-PiP mixed solution is coated in multiple layers onto a polyethersulfone support layer and dried to obtain a CMCs-PiP / PES composite film.

[0009] S3. Will 3533 granules were dissolved in a mixed solvent of n-propanol and n-butanol, and after reflux and stirring, the following was obtained: 3533 solution;

[0010] S4. The above A 3533 solution was multilayered and coated onto the CMCs-PiP / PES composite membrane, and after drying, the desired product was obtained. 3533 / CMCs-PiP / PES composite membrane.

[0011] According to the above technical solution, preferably, in step S1, carboxymethyl chitosan is dissolved in water to obtain a 1 wt% carboxymethyl chitosan solution; during stirring, anhydrous piperazine is added, wherein the relative mass of the anhydrous piperazine is 20% of that of the carboxymethyl chitosan, to obtain a CMCs-PiP mixed solution.

[0012] According to the above technical solution, preferably, in step S2, two layers of the CMCs-PiP mixed solution are coated on the polyethersulfone support layer.

[0013] According to the above technical solution, preferably, in step S2, the CMCs-PiP mixed solution is cast onto a polyethersulfone support layer and coated using a micron-sized coater; after drying, the above operation is repeated once, and a CMCs-PiP / PES composite film is obtained after drying.

[0014] According to the above technical solution, preferably, in step S3, the... 3533 particles were dissolved in a mixed solvent of n-propanol and n-butanol in a volume ratio of 3:1, and refluxed and stirred at 80°C for 2 hours to obtain 0.5 wt% of the aforementioned product. 3533 solution.

[0015] According to the above technical solution, preferably, the CMCs-PiP mixed solution or The 3533 solution was filtered using an injector and a 0.45μm filter to remove undissolved small particles, and then air bubbles in the solution were removed by vacuum decompression.

[0016] According to the above technical solution, preferably, in step S4, the... The 3533 solution was cast onto the CMCs-PiP / PES composite membrane and coated using a micron-sized coater; after drying, the above operation was repeated once, and the final product was obtained. 3533 / CMCs-PiP / PES composite membrane.

[0017] According to the above technical solution, preferably, the polyethersulfone support layer is pretreated, the pretreatment including: repeatedly cleaning the polyethersulfone support layer, immersing the polyethersulfone support layer in an aqueous solution of sodium dodecyl sulfate; immersing the polyethersulfone support layer again in n-hexane; wiping off the surface solution and fixing it to the surface of the glass plate.

[0018] According to the above technical solution, preferably, the polyethersulfone support layer is immersed in a 0.5wt% sodium dodecyl sulfate aqueous solution for 24 hours, and then immersed in n-hexane for 2 hours.

[0019] The beneficial effects of this invention are:

[0020] The CO2 separation composite membrane prepared in this invention introduces carboxymethyl chitosan as the intermediate layer of the composite membrane. Carboxymethyl chitosan, as a water-swellable material, exhibits unique advantages in water-promoted carbon dioxide transfer applications. In actual flue gas emissions, the presence of moisture is unavoidable. The properties of carboxymethyl chitosan cause it to swell under the influence of water, effectively increasing the free volume of the membrane layer and providing more space for CO2 transfer. Furthermore, the addition of piperazine as a small molecule additive allows it to entangle with the polymer chains of carboxymethyl chitosan, further enhancing the driving force of CO2 transfer. In water, piperazine precipitates cations, which undergo self-assembly with the anionic polymer carboxymethyl chitosan. This not only strengthens the overall structure of the membrane but also improves its selective CO2 transport efficiency. To further improve the stability and performance of the membrane, a thin intermediate layer is deposited on the support layer. This not only strengthens its structural support but also improves the compatibility between the support layer and the selective layer. Finally, pretreatment of the support layer with hexane effectively fills the pores and hinders the penetration of polar aqueous solutions to a certain extent, thereby further improving the overall system performance and stability. This is beneficial for practical applications of CO2 separation and fills a gap in existing research on intermediate layers. Meanwhile, carboxymethyl chitosan, as a water-soluble substance, reduces the difficulty of preparing the casting solution and improves the unpleasant odor and toxicity of organic solvents, providing a more user-friendly and environmentally friendly option for practical applications. Attached Figure Description

[0021] Figure 1 This is a scanning electron microscope image of the intermediate layer of the CO2 separation composite membrane prepared in this invention.

[0022] Figure 2 This is an atomic force microscope image of the intermediate layer of the CO2 separation composite membrane prepared in this invention.

[0023] Figure 3 This is the Fourier transform infrared spectrum of the intermediate layer of the CO2 separation composite membrane prepared in this invention. Detailed Implementation

[0024] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0025] The reagents used in this invention are:

[0026] Carboxymethyl chitosan: molecular weight 240 kDa, degree of deacetylation greater than 90%, degree of substitution 90%;

[0027]

[0028] Ultrafiltration membrane polyethersulfone (PES) with a molecular weight cutoff of 20,000;

[0029] Anhydrous piperazine (PiP), 99%;

[0030]

[0031] 3533 particles, industrial grade.

[0032]

[0033] This invention includes the following steps:

[0034] Step S1. Add anhydrous piperazine to the carboxymethyl chitosan solution and dissolve and mix to obtain a CMCs-PiP mixed solution.

[0035] Specifically, at room temperature, carboxymethyl chitosan is dissolved in water using a magnetic stirrer to obtain a 1 wt% carboxymethyl chitosan solution; during stirring, anhydrous piperazine is added, with the anhydrous piperazine having a relative mass of 20% of the carboxymethyl chitosan, to obtain a CMCs-PiP mixed solution; the solution is filtered using an injector and a 0.45 μm filter membrane to remove undissolved small particles, and then air bubbles in the solution are removed by vacuum decompression.

[0036] Step S2. The CMCs-PiP mixed solution is coated in multiple layers onto a polyethersulfone support layer and dried to obtain a CMCs-PiP / PES composite film.

[0037] Specifically, the polyethersulfone support layer is pretreated, which includes: repeatedly cleaning the polyethersulfone support layer; immersing the polyethersulfone support layer in a 0.5 wt% sodium dodecyl sulfate aqueous solution for 24 hours to remove surface oil and improve the hydrophilicity of the membrane; immersing the polyethersulfone support layer again in n-hexane for 2 hours to fill the pores of the membrane and slow down the penetration of the solution into the pores; drying the surface and fixing it to the surface of the glass plate.

[0038] In this example, the CMCs-PiP mixed solution is preferably cast onto a polyethersulfone support layer and coated using a micron coater. It is then placed in an artificial climate chamber at 60°C and 40% humidity to allow the solvent to evaporate for 1 hour. After drying, the remaining layers are coated, and the above operation is repeated once. The membrane is then dried in an artificial climate chamber at 60°C and 40% relative humidity for 6 hours. After drying, a two-layer CMCs-PiP / PES composite membrane is obtained.

[0039] S3. Will 3533 granules were dissolved in a mixed solvent of n-propanol and n-butanol, and after reflux and stirring, the following was obtained: 3533 solution.

[0040] Specifically, the aforementioned 3533 particles were dissolved in a mixed solvent of n-propanol and n-butanol in a volume ratio of 3:1, and refluxed and stirred at 80°C for 2 hours to obtain 0.5 wt% of the aforementioned product. The 3533 solution was filtered using an injector and a 0.45 μm filter to remove undissolved small particles, and then air bubbles in the solution were removed by vacuum decompression.

[0041] S4. The above A 3533 solution was multilayered and coated onto the CMCs-PiP / PES composite membrane, and after drying, the desired product was obtained. 3533 / CMCs-PiP / PES composite membrane.

[0042] Specifically, the aforementioned The 3533 solution was cast onto the CMCs-PiP / PES composite membrane and coated using a micron-sized coater. The membrane was then placed in a 40°C oven to evaporate the solvent for 1 hour. After drying, the above process was repeated once, and the membrane was dried in a 40°C oven for 48 hours. The dried membrane was then obtained... 3533 / CMCs-PiP / PES composite membrane.

[0043] like Figure 1 As shown, scanning electron microscopy (SEM) was performed on the top of the prepared composite membrane, and no obvious aggregation was observed. The static contact angle of pure water was 78.29°, indicating good hydrophilicity and improving the compatibility between the hydrophobic support layer and the hydrophilic selective layer.

[0044] The CO2 separation composite membrane prepared by this invention introduces carboxymethyl chitosan as the intermediate layer of the composite membrane, realizing the preparation of a water-assisted CO2 capture material. This not only effectively improves the compatibility between the support layer and the selective layer, but also increases the free volume and provides selectivity with the help of water in the actual CO2 separation process.

[0045] Meanwhile, the preparation process disclosed in this application has the following advantages:

[0046] Carboxymethyl chitosan, as a water-soluble substance, reduces the difficulty of preparing casting solutions and alleviates the unpleasant odor and toxicity problems associated with traditional organic solvent-dependent preparation methods. This not only provides operators with a safer and more comfortable working environment but also reduces dependence on organic solvents, lowers material and processing costs, and mitigates the environmental impact of the preparation process. Furthermore, carboxymethyl chitosan's high degree of substitution and molecular weight, by increasing the solution viscosity, further optimizes the composite membrane preparation process.

[0047] Secondly, this invention improves the filtration and degassing methods by using an injector and a 0.45μm pinhole filter for filtration and vacuum degassing for degassing, effectively avoiding defects that are more likely to occur in low-viscosity solutions during coating. This method abandons the previous centrifugal filtration method, avoiding the viscosity reduction of non-Newtonian pseudoplastic fluids caused by strong shear forces, thereby maintaining the ideal rheological properties of the solution.

[0048] Furthermore, by pretreating the support layer, using surfactants to improve the surface hydrophilicity and remove oil stains of the polysulfone ultrafiltration membrane, and then soaking it in n-hexane to fill the pores, this invention slows down the leakage of the casting solution, creating more ideal conditions for subsequent coating and composite membrane preparation.

[0049] Furthermore, the continuous coating method and carefully designed drying process modify the support layer. Layer-by-layer coating can effectively cover defects, making the gas permeability of the membrane more stable. During the evaporation and drying process, the solvent will also penetrate into the substrate. The membrane liquid with lower viscosity is more likely to penetrate downward and cause defects. The fixed drying process can avoid errors and different structural defects generated during the drying process, thereby ensuring the stability and consistency of the quality of the prepared composite membrane, thus improving the gas separation efficiency and the reliability of the composite membrane.

[0050] In summary, the CO2 separation composite membrane prepared by this invention, by introducing carboxymethyl chitosan as the intermediate layer of the composite membrane, not only helps to improve the compatibility between the support layer and the selective layer, but also increases the free volume within the membrane and provides selectivity with the assistance of water. This is beneficial for the practical application of CO2 separation and fills the gap in the research of low-viscosity water-swellable material intermediate layers in the prior art. At the same time, as a water-soluble substance, carboxymethyl chitosan reduces the difficulty of preparing the casting solution and improves the unpleasant odor and toxicity of organic solvents, providing a more user-friendly and environmentally friendly option for practical applications.

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a humidity-responsive CO2 composite membrane, characterized in that, Includes the following steps: S1. Anhydrous piperazine is added to a carboxymethyl chitosan solution and dissolved and mixed to obtain a CMCs-PiP mixed solution. The anhydrous piperazine is added as a small molecule auxiliary agent to entangle with the polymer chains of carboxymethyl chitosan. In water, the anhydrous piperazine precipitates cations and undergoes self-assembly with the anionic polymers of carboxymethyl chitosan to enhance the driving force of CO2 transfer. S2. The CMCs-PiP mixed solution is coated in multiple layers onto a polyethersulfone support layer and dried to obtain a CMCs-PiP / PES composite film. S3. Dissolve Pebax® 3533 granules in a mixed solvent of n-propanol and n-butanol, and reflux and stir to obtain a Pebax® 3533 solution; S4. The Pebax® 3533 solution is multilayered and coated onto the CMCs-PiP / PES composite membrane. After drying, the Pebax® 3533 / CMCs-PiP / PES composite membrane is obtained. Before coating the polyethersulfone support layer, the polyethersulfone support layer is pretreated. The pretreatment includes: repeatedly washing the polyethersulfone support layer; immersing the polyethersulfone support layer in an aqueous solution of sodium dodecyl sulfate; immersing the polyethersulfone support layer again in n-hexane to fill the pores of the membrane and slow down the penetration of the solution into the pores; drying the surface and fixing it to the surface of the glass plate.

2. The method for preparing a humidity-responsive CO2 composite membrane according to claim 1, characterized in that, In step S1, carboxymethyl chitosan is dissolved in water to obtain a 1 wt% carboxymethyl chitosan solution; during stirring, anhydrous piperazine is added, wherein the relative mass of the anhydrous piperazine is 20% of that of the carboxymethyl chitosan, to obtain a CMCs-PiP mixed solution.

3. The method for preparing a humidity-responsive CO2 composite membrane according to claim 1, characterized in that, In step S2, two layers of the CMCs-PiP mixed solution are coated on the polyethersulfone support layer.

4. The method for preparing a humidity-responsive CO2 composite membrane according to claim 3, characterized in that, In step S2, the CMCs-PiP mixed solution is cast onto a polyethersulfone support layer and coated using a micron-sized coater; after drying, the above operation is repeated once, and a CMCs-PiP / PES composite film is obtained after drying.

5. The method for preparing a humidity-responsive CO2 composite membrane according to claim 2, characterized in that, In step S3, the Pebax® 3533 particles are dissolved in a mixed solvent of n-propanol and n-butanol in a volume ratio of 3:1, and the mixture is refluxed and stirred at 80°C for 2 hours to obtain a 0.5 wt% Pebax® 3533 solution.

6. The method for preparing a humidity-responsive CO2 composite membrane according to claim 5, characterized in that, The CMCs-PiP mixed solution or Pebax® 3533 solution was filtered using an injector and a 0.45 μm filter to remove undissolved small particles, and then air bubbles in the solution were removed by vacuum decompression.

7. The method for preparing a humidity-responsive CO2 composite membrane according to claim 1, characterized in that, In step S4, the Pebax® 3533 solution is cast onto the CMCs-PiP / PES composite membrane and coated using a micron-sized coater; after drying, the above operation is repeated once, and the Pebax® 3533 / CMCs-PiP / PES composite membrane is obtained after drying.

8. The method for preparing a humidity-responsive CO2 composite membrane according to claim 1, characterized in that, The polyethersulfone support layer was immersed in a 0.5 wt% sodium dodecyl sulfate aqueous solution for 24 hours, and then immersed in n-hexane for 2 hours.

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