Polyimide hollow fiber composite gas separation membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of separation membrane materials, and discloses a polyimide hollow fiber composite gas separation membrane as well as a preparation method and application thereof. The polyimide hollow fiber composite gas separation membrane comprises a polyimide hollow fiber gas separation membrane, a protective layer and a connecting layer positioned between the gas separation membrane and the protective layer, wherein the protective layer is a coating formed by silicone rubber; and the connecting layer is made of an amino polymer. According to the composite gas separation membrane, the connecting layer made of the material containing the amino polymer is arranged between the gas separation membrane and the protective layer, so that the cohesiveness between the gas separation membrane and the protective layer is remarkably improved, and the mechanical strength and durability of the composite gas separation membrane are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of separation membrane materials technology, specifically to a polyimide hollow fiber composite gas separation membrane, its preparation method, and its application. Background Technology

[0002] Membrane separation technology utilizes the difference in permeation rates of various gases in different membrane materials to achieve separation. It is an emerging "green technology" that has attracted widespread research interest due to its advantages such as simple equipment, low fixed investment, and low energy consumption. Gas separation membrane technology has developed rapidly in recent decades and has wide applications in fields such as natural gas purification, hydrogen extraction, organic vapor recovery, and air separation.

[0003] Polymer membranes, due to their excellent permeation selectivity and processability, are suitable for large-scale production and are currently the most widely used and researched membrane materials in industry. Polymers currently used for preparing commercial gas separation membranes include cellulose acetate, polysulfone, polyethersulfone, polyphenylene ether, polyamide, and polyimide. From the perspective of membrane morphology, gas separation membranes can be classified into flat sheet membranes and hollow fiber membranes, among others.

[0004] High-performance gas separation membranes not only need to meet high gas permeation and separation performance requirements, but also need to possess sufficient mechanical strength, temperature and pressure resistance, and chemical corrosion resistance. In practical applications, harsh environmental conditions such as high temperature, high pressure, condensable gases, and corrosive gases are often encountered, severely impacting membrane lifespan and increasing the cost of replacing membrane modules. Therefore, adding a protective layer to the membrane surface is a necessary measure for preparing more durable, high-performance gas separation membranes.

[0005] In existing technologies, gas separation membranes with protective layers typically use silicone rubber resins containing siloxane structures, such as polydimethylsiloxane (US20180272291A1), as the protective layer material is usually coated onto the base membrane surface and then dried. However, because silicone rubber often has poor compatibility with the polymer matrix and insufficient adhesion, problems such as uneven coating, defects, and peeling easily occur. The coating struggles to form a good mechanical bond with the membrane surface, ultimately leading to a significant reduction in protective effectiveness. Therefore, there is a need to develop a gas separation membrane with strong adhesion between the protective layer and the base membrane surface, high mechanical strength, and durability. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned problems existing in the prior art and to provide a polyimide hollow fiber composite gas separation membrane, its preparation method and application. The polyimide hollow fiber composite gas separation membrane has a connecting layer made of a material including an amino polymer between the gas separation membrane and the protective layer, which significantly improves the adhesion between the gas separation membrane and the protective layer, and significantly enhances the mechanical strength and durability of the composite gas separation membrane.

[0007] To achieve the above objectives, the present invention provides a polyimide hollow fiber composite gas separation membrane, wherein the polyimide hollow fiber composite gas separation membrane includes a polyimide hollow fiber gas separation membrane, a protective layer, and a connecting layer located between the gas separation membrane and the protective layer;

[0008] The protective layer is a coating formed of silicone rubber;

[0009] The materials constituting the connecting layer include amino polymers.

[0010] A second aspect of the present invention provides a method for preparing a polyimide hollow fiber composite gas separation membrane, wherein the preparation method includes:

[0011] S1. Mix the additive, dopamine, and optionally amino-containing reactants to obtain a mixture;

[0012] S2. The polyimide hollow fiber gas separation membrane is impregnated with the mixture and then subjected to a polymerization reaction.

[0013] S3. The product obtained in step S2 is impregnated with a silicone rubber solution and cured to obtain the polyimide hollow fiber composite gas separation membrane.

[0014] A third aspect of the present invention provides a polyimide hollow fiber composite gas separation membrane prepared by the above-described preparation method.

[0015] A fourth aspect of the present invention provides an application of the above-mentioned polyimide hollow fiber composite gas separation membrane in the separation of He and / or CO2.

[0016] Through the above technical solutions, the polyimide hollow fiber composite gas separation membrane, its preparation method, and its application provided by the present invention achieve the following beneficial effects:

[0017] The polyimide hollow fiber composite gas separation membrane of the present invention has a connecting layer made of a material including an amino polymer between the gas separation membrane and the protective layer, which significantly improves the adhesion between the gas separation membrane and the protective layer, and significantly enhances the mechanical strength and durability of the gas separation membrane.

[0018] Furthermore, by employing a specific polyimide hollow fiber gas separation membrane, which can cooperate with the protective layer formed by silicone rubber and the connecting layer formed by amino polymers, the separation membrane, the protective layer and the connecting layer form an interpenetrating network in pairs, and the boundaries are integrated with each other, which can significantly improve the mechanical strength and durability of the composite gas separation membrane.

[0019] In this invention, a mixture containing additives, dopamine, and optionally amino-containing reactants is used to impregnate a polyimide hollow fiber gas separation membrane. This allows dopamine and optionally amino-containing reactants to polymerize in situ on the surface of the polyimide hollow fiber gas separation membrane, forming a connecting layer containing amino polymers. This connecting layer not only improves the bonding force between the polyimide hollow fiber gas separation membrane and the protective layer formed by silicone rubber, thus improving the resistance to plasticizing aging, chemical corrosion, mechanical strength, and durability of the resulting gas separation membrane, but also promotes the selective transfer of CO2, ensuring that the gas separation membrane maintains a high CO2 / N2 separation coefficient and CO2 flux. Attached Figure Description

[0020] Figure 1 This is a SEM image of the outer surface of the composite gas separation membrane in Example 1.

[0021] Figure 2 This is a SEM image of the composite gas separation membrane of Example 3, taken perpendicular to the axial section. Detailed Implementation

[0022] The endpoints and any values ​​of the ranges disclosed herein 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 the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] The first aspect of the present invention provides a polyimide hollow fiber composite gas separation membrane, wherein the polyimide hollow fiber composite gas separation membrane includes a polyimide hollow fiber gas separation membrane, a protective layer, and a connecting layer located between the gas separation membrane and the protective layer;

[0024] The protective layer is a coating formed of silicone rubber;

[0025] The materials constituting the connecting layer include amino polymers.

[0026] In this invention, a connecting layer made of a material including an amino polymer is provided between the gas separation membrane and the protective layer of the polyimide hollow fiber composite gas separation membrane. This significantly improves the adhesion between the gas separation membrane and the protective layer, thereby significantly enhancing the mechanical strength and durability of the final composite gas separation membrane.

[0027] Specifically, the material constituting the connecting layer includes an amino polymer, which contains unreacted -NH2 and -OH, etc., which interact firmly with the -Si-O-, =O and -O- present in the polyimide hollow fiber gas separation membrane and protective layer through non-covalent bonds such as hydrogen bonding and electrostatic interaction to form a strong bond.

[0028] Furthermore, the amino polymer contained in the connecting layer enables the gas separation membrane to selectively pass gases that have an affinity interaction with amino groups, thereby achieving gas screening and improving gas selectivity. The separation membrane of the present invention can selectively separate CO2 and He gases.

[0029] According to the present invention, the silicone rubber is selected from at least one of polydimethylsiloxane, polydimethylvinylsiloxane, polymethylphenylsiloxane, and polytrifluoropropylmethylsiloxane.

[0030] Furthermore, the silicone rubber is polydimethylsiloxane;

[0031] According to the present invention, the dynamic viscosity of the silicone rubber at 25°C is 15-100,000 cP.

[0032] In this invention, when the dynamic viscosity of the silicone rubber is controlled to meet the above range, it can ensure that the silicone rubber has excellent fluidity, is easy to impregnate and spread on the surface of finer fibers, achieves full impregnation of each fiber, and forms a uniform coating after curing.

[0033] Furthermore, the dynamic viscosity of the silicone rubber at 25°C is 500-7,500 cP.

[0034] According to the present invention, based on the total amount of the amino polymer, the nitrogen content in the amino polymer is 3-45 wt%.

[0035] In this invention, the nitrogen content in the amino polymer is measured by X-ray photoelectron spectroscopy. When the nitrogen content meets the above-mentioned range, it can effectively promote gas transfer and increase CO2 flux.

[0036] Furthermore, based on the total amount of the amino polymer, the nitrogen content in the amino polymer is 6-15 wt%.

[0037] According to the present invention, the theoretical weight-average molecular weight of the amino polymer is 300-50000 Da, preferably 400-10000 Da.

[0038] According to the present invention, the amino polymer is selected from homopolymers and / or copolymers of dopamine.

[0039] In this invention, the homopolymer and / or copolymer of dopamine have a high nitrogen content, which can effectively promote CO2 transport and improve CO2 flux and gas selectivity.

[0040] According to the present invention, the amino polymer is selected from at least one of polydopamine, dopamine-ethylenediamine copolymer, dopamine-propylenediamine copolymer, dopamine-butyldiamine copolymer, dopamine-diethylenetriamine copolymer, dopamine-triethylenetetramine copolymer, dopamine-tetraethylenepentamine copolymer, dopamine-polyethyleneimine copolymer, dopamine-ethylenediamine-polyethyleneimine copolymer, dopamine-propylenediamine-polyethyleneimine copolymer, dopamine-diethylenetriamine-polyethyleneimine copolymer, dopamine-triethylenetetramine-polyethyleneimine copolymer, and dopamine-tetraethylenepentamine-polyethyleneimine copolymer; preferably at least one of polydopamine, dopamine-ethylenediamine copolymer, and dopamine-propylenediamine copolymer.

[0041] According to the present invention, the polyimide hollow fiber gas separation membrane comprises a support layer and a dense layer attached to the outer surface of the support layer, preferably the thickness of the dense layer is less than or equal to 1000 nm and the porosity of the hollow fiber gas separation membrane is 40-80%.

[0042] In this invention, the aforementioned specific polyimide hollow fiber gas separation membrane, with its appropriate porosity and thin dense layer, enables the prepared composite gas separation membrane to possess high mechanical strength while exhibiting excellent gas permeation and separation performance.

[0043] Furthermore, the thickness of the dense layer in the polyimide hollow fiber gas separation membrane is 150-800 nm, and the porosity of the hollow fiber gas separation membrane is 50-70%.

[0044] In this invention, there is no particular limitation on the polyimide used to form the support layer and the dense layer. It can be prepared using conventional types of polyimide in the art. In order to further improve the mechanical strength and separation selectivity of the final composite gas separation membrane, it is preferably prepared using a random copolymer of polyimide shown in Formula I.

[0045]

[0046] In Equation I, m and n are each independent integers from 10 to 2000; X is... Y is Z and Z' are

[0047] In this invention, the outer diameter of the polyimide hollow fiber gas separation membrane is 300-500 μm, and the wall thickness is 70-120 μm.

[0048] According to the present invention, the thickness of the protective layer is 200nm-3000nm.

[0049] According to the present invention, the thickness of the connecting layer is 80-500 nm.

[0050] In this invention, when the thickness of the protective layer and the connecting layer in the composite gas separation membrane meets the above-mentioned range, they can firmly and uniformly cover the surface of the hollow fiber gas separation membrane and form an interpenetrating network, so that the layers can be fused together, and the mechanical strength and durability of the resulting composite gas separation membrane are significantly improved.

[0051] Furthermore, the thickness of the protective layer is 800nm-1600nm, more preferably 900nm-1600nm.

[0052] Furthermore, the thickness of the connecting layer is 200-350nm, more preferably 250nm-300nm.

[0053] According to the present invention, the He permeation rate of the composite gas separation membrane is ≥80 GPU, preferably ≥120 GPU.

[0054] According to the present invention, the CO2 and N2 separation selectivity of the composite gas separation membrane is ≥10, preferably ≥35.

[0055] According to the present invention, the separation selectivity of He and N2 of the composite gas separation membrane is ≥50, preferably ≥90.

[0056] According to the present invention, after 90 days of operation, the retention rate of He permeation rate of the composite gas separation membrane is greater than or equal to 85%, the retention rate of CO2 and N2 separation selectivity of the composite gas separation membrane is greater than or equal to 85%, and the retention rate of He and N2 separation selectivity of the composite gas separation membrane is greater than or equal to 90%.

[0057] A second aspect of the present invention provides a method for preparing a polyimide hollow fiber composite gas separation membrane, wherein the preparation method includes:

[0058] S1. Mix the additive, dopamine, and optionally amino-containing reactants to obtain a mixture;

[0059] S2. The polyimide hollow fiber gas separation membrane is impregnated with the mixture and then subjected to a polymerization reaction.

[0060] S3. The product obtained in step S2 is impregnated with a silicone rubber solution and cured to obtain the polyimide hollow fiber composite gas separation membrane.

[0061] In this invention, a polyimide hollow fiber gas separation membrane is impregnated with a mixture containing additives, dopamine, and optionally amino-containing reactants. This allows dopamine and optionally amino-containing reactants to polymerize in situ on the surface of the polyimide hollow fiber gas separation membrane, forming a connecting layer containing amino polymers. This connecting layer not only improves the bonding force between the polyimide hollow fiber gas separation membrane and the protective layer formed by silicone rubber, thus improving the plasticizing aging resistance, chemical corrosion resistance, mechanical strength, and durability of the resulting gas separation membrane, but also promotes the selective transfer of CO2, ensuring that the composite gas separation membrane still maintains a high CO2 / N2 separation coefficient and CO2 flux.

[0062] Furthermore, by controlling the pH of the polymerization reaction, the concentration of raw materials (dopamine or amino-containing reactants) in the mixture, and the polymerization reaction conditions, a smooth and flat bonding layer is obtained, which has a moderate surface energy (contact angle of pure water 80-100°). Therefore, it has good compatibility with hydrophilic or hydrophobic solutions, providing an excellent environment for the preparation of the second functional layer. This facilitates the uniform coating of the protective layer solution, reduces the defect rate, and ensures that the membrane maintains stable performance during long-term use.

[0063] Furthermore, dopamine contains a large number of amino groups, which can promote CO2 transfer while improving the adhesion between the dopamine and the polyimide hollow fiber gas separation membrane and the protective layer. This results in a separation membrane with high CO2 flux, high mechanical strength, and durability. At the same time, the polymerization reaction of dopamine is mild and the reaction conditions are simple, which is conducive to industrial promotion. When dopamine is polymerized with reactants containing amino groups, the amino content in the connecting layer can be increased, which enhances the CO2 transfer promotion effect of the composite gas separation membrane, thereby improving the CO2 flux and selectivity relative to other gases (such as N2).

[0064] In this invention, the "amino-containing reactant" does not include dopamine.

[0065] According to the present invention, in step S1, the addition of additives makes the pH of the mixture 7.5-10.

[0066] In this invention, adjusting the pH to the above-mentioned range ensures the smooth progress of the preparation reaction of the connecting layer and avoids defects in the obtained connecting layer.

[0067] Furthermore, in step S1, the addition of additives makes the pH of the mixture 8.5-10.

[0068] According to the present invention, the additive includes additive A, or additive A and additive B, wherein additive A is selected from sodium hydroxide, or sodium hydroxide and tris(hydroxymethyl)aminomethane, and additive B is selected from at least one of hydrochloric acid, sodium dihydrogen phosphate and potassium dihydrogen phosphate.

[0069] In this invention, the use of the above-mentioned specific types of additives can achieve stable adjustment of the pH of the polymerization reaction in step (1), so that the reaction environment of the amino monomer (dopamine, or a mixture of dopamine and amino-containing reactants) is always kept in a weakly alkaline to moderately alkaline state, thereby forming a complete amino polymer layer most smoothly.

[0070] In this invention, there are no special requirements for the amount of additive A or additive B, or the amount of sodium hydroxide or tris(hydroxymethyl)aminomethane in additive A, as long as the pH value of the polymerization reaction meets the requirements of this invention.

[0071] According to the present invention, the amino-containing reactants are selected from amino-containing monomers and / or amino-containing polymers.

[0072] According to the present invention, the amino-containing monomer is selected from at least one of ethylenediamine, propylenediamine, butanediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

[0073] According to the present invention, the amino-containing polymer is selected from polyethyleneimine.

[0074] According to the present invention, the weight-average molecular weight of the polyethyleneimine is preferably 500-2000 Da, and more preferably 600-1800 Da.

[0075] In this invention, polyethyleneimine has a relatively small molecular weight, and when it is polymerized with dopamine, the reaction mechanism is similar to that of dopamine with amino-containing monomers.

[0076] According to the present invention, the concentration of dopamine in the mixture is 0.1 wt% to 5 wt%.

[0077] According to the present invention, the concentration of the amino-containing reactant in the mixture is 0-5 wt%.

[0078] In this invention, controlling the concentrations of dopamine and amino-containing reactants in the reaction solution to meet the above-mentioned ranges enables the prepared connecting layer to be thin, smooth, and flat, which helps to prepare a protective layer on it. At the same time, the high amino content in the prepared connecting layer promotes CO2 transfer, so that the composite gas separation membrane has both high CO2 flux and CO2 gas selectivity.

[0079] Furthermore, the concentration of dopamine in the mixture is 0.5wt%-2wt%.

[0080] Furthermore, in the mixture, the concentration of the amino-containing reactant is 0.2 wt%-2 wt%.

[0081] According to the present invention, when dopamine undergoes a polymerization reaction with an amino-containing reactant, the weight ratio of the dopamine to the amino-containing reactant is 1:0.05-10.

[0082] In this invention, controlling the weight ratio of dopamine to the amino-containing reactant to meet the above-mentioned range enables the prepared connecting layer to be thin, smooth, and flat, while improving CO2 flux and CO2 and N2 selectivity.

[0083] Furthermore, when dopamine undergoes a polymerization reaction with an amino-containing reactant, the weight ratio of dopamine to the amino-containing reactant is 1:0.2-1.5.

[0084] According to the present invention, the reaction time of the polymerization reaction is 2-48 h, and the reaction temperature of the polymerization reaction is 0-50 °C.

[0085] In this invention, when the above-mentioned time and temperature conditions for polymerization reaction are met, the resulting connecting layer is thin, smooth and flat, which is beneficial for preparing a protective layer on its surface. At the same time, the reaction conditions are relatively mild, which can be promoted on a large scale for industrial application.

[0086] Furthermore, the polymerization reaction takes 5-24 hours and the polymerization reaction takes 20-35°C.

[0087] In this invention, there is no particular limitation on the mass ratio of the mixture to the polyimide hollow fiber gas separation membrane in step S2, as long as the thickness of the connecting layer in the obtained composite gas separation membrane meets the requirements of this invention. For example, the mass ratio of the mixture to the polyimide hollow fiber gas separation membrane is 25-100 g / g, preferably 40-70 g / g.

[0088] According to the present invention, the solid content of the silicone rubber solution is 0.5-10 wt%.

[0089] In this invention, when the solid content of the silicone rubber solution is controlled to meet the above-mentioned range, the silicone rubber solution has low viscosity and excellent fluidity, making it easy to spread quickly and evenly on the fiber surface and partially penetrate into the connecting layer to form an interpenetrating network.

[0090] Furthermore, the solid content of the silicone rubber solution is 2-4 wt%.

[0091] According to the present invention, the silicone rubber in the silicone rubber solution is selected from at least one of polydimethylsiloxane, polydimethylvinylsiloxane, polymethylphenylsiloxane and polytrifluoropropylmethylsiloxane, preferably polydimethylsiloxane.

[0092] According to the present invention, the dynamic viscosity of the silicone rubber at 25°C is 15-100,000 cP, preferably 500-7,500 cP.

[0093] According to the present invention, the mass ratio of the silicone rubber solution to the mass of the product obtained in step S2 is 20-80:1.

[0094] In this invention, when the ratio of the mass of the silicone rubber solution to the mass of the product obtained in step S2 is controlled to meet the above range, it is possible to ensure that a sufficient amount of silicone rubber can be attached to the surface of each fiber, ensuring that the cured coating is complete and without defects, while not wasting too much silicone rubber solution.

[0095] Furthermore, the mass ratio of the silicone rubber solution to the mass of the product obtained in step S2 is 30-50:1.

[0096] According to the present invention, the curing conditions include: a curing temperature of 15-150℃ and a curing time of 0.5-72h.

[0097] Furthermore, the curing conditions include: a curing temperature of 30-75℃ and a curing time of 5-48h.

[0098] According to the present invention, step S2 further includes washing and drying the product obtained from the polymerization reaction.

[0099] Further, washing is performed using alcohol and / or water. In this invention, the purpose of washing is to remove polymers not adhering to the surface, thereby ensuring a smooth and impurity-free film with the modified bonding layer.

[0100] According to the present invention, step S3 further includes washing the cured product. There are no particular limitations on the solvent used for washing in step S3; for example, water and alcohol can be used.

[0101] A third aspect of the present invention provides a polyimide hollow fiber composite gas separation membrane prepared by the above-described preparation method.

[0102] A fourth aspect of the present invention provides an application of the above-mentioned polyimide hollow fiber composite gas separation membrane in the separation of He and / or CO2.

[0103] The present invention will be described in detail below through embodiments. In the following embodiments,

[0104] He permeation rate was determined by the pressure difference method, specifically according to GB-T 40260-2021 "Test Method for Gas Permeation Performance of Polymer Membrane Materials".

[0105] The formula for calculating the separation coefficient between CO2 and N2 is: CO2 / N2 flux = CO2 flux / N2 flux; where the CO2 flux and N2 flux are measured by the pressure difference method (as above).

[0106] The He / N2 separation coefficient is calculated as He / N2 separation coefficient = He flux / N2 flux.

[0107] The method for detecting the thickness of each layer in the composite gas separation membrane is as follows: the thickness of the polyimide hollow fiber gas separation membrane is (outer diameter - inner diameter) / 2 in the cross-sectional SEM image of the uncoated hollow fiber gas separation membrane perpendicular to the axial direction; the thickness of the connecting layer is the thickness of the outer ring coating in the cross-sectional SEM image of the intermediate product membrane obtained in step S2, and the average value is calculated from 5 points, accurate to 1 nm; the thickness of the protective layer is the thickness of the outermost ring coating in the cross-sectional SEM image of the membrane obtained in step 3, and the average value is calculated from 5 points, accurate to 1 nm.

[0108] The nitrogen content in the amino polymer in the gas separation membrane was determined by X-ray photoelectron spectroscopy.

[0109] The tensile strength and elongation at break of the gas separation membrane were measured using a universal testing machine.

[0110] Dopamine, acquired by Sigma-Aldrich.

[0111] Sodium hydroxide was purchased from Sinopharm Reagent.

[0112] Polydimethylsiloxane, manufactured by Dow Chemical under the brand name SYLGARD TM The product with a viscosity of 184 has a dynamic viscosity of 5100 cP at 25°C.

[0113] All other raw materials used in the examples and comparative examples are commercially available products.

[0114] Preparation Example—Using this example to illustrate the preparation of polyimide hollow fiber gas separation membranes

[0115] Preparation Example 1

[0116] The polyimide random copolymer obtained from Preparation Example 10 of ZL 202210717238.0 was used to prepare a hollow fiber gas separation membrane.

[0117] The specific preparation conditions for the hollow fiber gas separation membrane are as follows:

[0118] (1) 28 wt% of the polyimide random copolymer obtained in Preparation Example 10 above, 52 wt% of NMP, 10 wt% of ethanol (boiling point 78°C), and 10 wt% of THF (boiling point 68.28°C) were added to a vessel equipped with a stirring device. The mixture was heated to 50°C and stirred (600 r / min) for 36 hours under nitrogen protection. After stirring was stopped, the mixture was degassed at 25°C, -0.1 MPa, and 30 r / min for 48 hours. The mixture was then filtered through a filter screen (100 mesh) at 50°C to obtain the casting solution.

[0119] (2) The casting solution and the core solution (NMP: water = 95wt%: 5wt%) were separately delivered to the hollow spinneret using a metering pump. The core solution and the casting solution were extruded together through the spinneret to obtain hollow fibers. The hollow fibers were passed through a 10cm air gap and then placed in water at 30℃ to solidify to obtain a polyimide-based hollow fiber gas separation membrane precursor. The spinneret temperature (extrusion temperature) was 65℃. The flow rates of the casting solution and the core solution entering the hollow spinneret were 6mL / min and 2mL / min, respectively.

[0120] (3) The polyimide hollow fiber gas separation membrane precursor obtained in step (2) is wound up by a winding machine and then extracted twice in water, ethanol, and n-hexane in sequence for 4 hours. After that, the extracted hollow fiber gas separation membrane is placed in a fume hood and naturally dried in air at room temperature for 24 hours to obtain polyimide hollow fiber gas separation membrane A1. The winding speed is 1 m / s.

[0121] The obtained hollow fiber gas separation membrane was characterized by mercury intrusion porosimetry, and the porosity was measured to be 58% and the thickness of the dense layer was 650 nm.

[0122] Mechanical property characterization (characterization method refers to "Determination of tensile properties of plastics GB / T1040.1-2006"): The tensile strength of a single hollow fiber gas separation membrane is 17.45 MPa and the elongation at break is 9%.

[0123] Preparation Example 2

[0124] Hollow fiber gas separation membranes were prepared according to the method described in the preparation example, except that commercially available raw materials were used. 4000TF (produced by Solvay) was used to replace the polyimide random copolymer in Preparation Example 1 to obtain polyimide hollow fiber gas separation membrane A2.

[0125] Tests showed that the hollow fiber gas separation membrane has a porosity of 65% and a dense layer thickness of 420 nm; the tensile strength of a single hollow fiber gas separation membrane is 13.4 MPa and the elongation at break is 1.9%.

[0126] Example 1

[0127] Step 1: At 25℃, add tris(hydroxymethyl)aminomethane aqueous solution, 0.5 mol / L sodium hydroxide aqueous solution and 0.5 mol / L hydrochloric acid aqueous solution and adjust the pH to 8.5 by titration, so that the total mass of the aqueous solution is 200 g. Add 2 g of dopamine and stir until completely dissolved to obtain a mixture. The concentration of dopamine in the mixture is 0.99 wt%.

[0128] Step 2: Immerse 2.09g of the hollow fiber gas separation membrane from the preparation example uniformly in 120g of the mixture from Step 1, and soak for 24 hours. The mass ratio of the mixture to the mass of the polyimide hollow fiber gas separation membrane is 57.4g / g.

[0129] Step 3: Remove the impregnated hollow fiber gas separation membrane, then thoroughly clean it with deionized water and ethanol, and dry it with nitrogen.

[0130] Step 4: 0.576 g of the hollow fiber gas separation membrane obtained in Step 3 was uniformly immersed in 25 g of a 2 wt% polydimethylsiloxane solution. The membrane was first soaked at 25°C for 20 min, then removed with the surface impregnation solution. It was then cured in a ventilated oven at 60°C for 12 h. After the reaction, the residual solvent was thoroughly washed off with water and ethanol to obtain the polyimide hollow fiber composite gas separation membrane M1. The mass ratio of the silicone rubber solution to the product of Step 3 (the dried hollow fiber gas separation membrane) was 43.4:1.

[0131] The gas permeation rate of the composite gas separation membrane M1 was tested and retested after 90 days. The results are shown in Table 2.

[0132] The tensile strength and elongation at break of the composite gas separation membrane M1 were tested and retested after 90 days. The results are shown in Table 3.

[0133] Figure 1 This is a SEM image of the outer surface of the composite gas separation membrane, from... Figure 1 It can be seen that the protective layer is uniformly attached to the surface of the hollow fiber gas separation membrane, without any obvious defects or pits.

[0134] Example 2

[0135] Step 1: At 25℃, add tris(hydroxymethyl)aminomethane aqueous solution, 0.5 mol / L sodium hydroxide aqueous solution and 0.5 mol / L hydrochloric acid aqueous solution and adjust the pH to 10 by titration, so that the total mass of the aqueous solution is 200 g. Add 2 g of dopamine and stir until completely dissolved to obtain a mixture. The concentration of dopamine in the mixture is 0.99 wt%.

[0136] Step 2: Immerse 0.554g of the hollow fiber gas separation membrane from the preparation example uniformly in 30g of the mixture from Step 1, and soak for 4 hours. The mass ratio of the mixture to the polyimide hollow fiber gas separation membrane is 54.2g / g.

[0137] Step 3: Remove the impregnated hollow fiber gas separation membrane, then thoroughly clean it with deionized water and ethanol, and dry it with nitrogen.

[0138] Step 4: Immerse 0.614 g of the hollow fiber gas separation membrane obtained in Step 3 uniformly in 25 g of a 2 wt% polydimethylsiloxane solution. First, soak at 25°C for 20 min. Then, remove the hollow fiber gas separation membrane with the surface impregnation solution and cure it in a 60°C ventilated oven for 12 h. After the reaction, thoroughly wash away the residual solvent with water and ethanol to obtain the polyimide hollow fiber composite gas separation membrane M2. The mass ratio of the silicone rubber solution to the product of Step 3 (the dried hollow fiber gas separation membrane) is 40.7:1.

[0139] The gas permeation rate of the composite gas separation membrane M2 was tested and retested after 90 days. The results are shown in Table 2.

[0140] The tensile strength and elongation at break of the composite gas separation membrane M2 were tested and retested after 90 days. The results are shown in Table 3.

[0141] Example 3

[0142] Step 1: Same as in Example 1.

[0143] Step 2: Same as in Example 1.

[0144] Step 3: Same as in Example 1.

[0145] Step 4: 0.533 g of the hollow fiber gas separation membrane obtained in Step 3 was uniformly immersed in 25 g of a 4 wt% polydimethylsiloxane solution. The membrane was first soaked at 25°C for 20 min, then removed with the surface impregnation solution. It was then cured in a ventilated oven at 60°C for 12 h. After the reaction, the residual solvent was thoroughly washed off with water and ethanol to obtain the polyimide hollow fiber composite gas separation membrane M3. The mass ratio of the silicone rubber solution to the product of Step 3 (the dried hollow fiber gas separation membrane) was 46.9:1.

[0146] The gas permeation rate of the composite gas separation membrane M3 was tested and retested after 90 days. The results are shown in Table 2.

[0147] The tensile strength and elongation at break of the composite gas separation membrane M3 were tested and retested after 90 days. The results are shown in Table 3.

[0148] Figure 2 This is a SEM image of the cross-section of the composite gas separation membrane M3, from... Figure 2 It can be seen that the protective layer of the composite gas separation membrane has a uniform thickness and is firmly connected to the base membrane.

[0149] Example 4

[0150] Step 1: At 25℃, add tris(hydroxymethyl)aminomethane aqueous solution, 0.5 mol / L sodium hydroxide aqueous solution and 0.5 mol / L hydrochloric acid aqueous solution and adjust the pH to 8.5 by titration, so that the total mass of the aqueous solution is 200 g. Add 2 g of dopamine and stir until completely dissolved to obtain a mixture. The concentration of dopamine in the mixture is 0.99 wt%.

[0151] Step 2: Immerse 0.570g of the hollow fiber gas separation membrane from the preparation example uniformly in 20g of the mixture from Step 1, and soak for 24 hours. The mass ratio of the mixture to the mass of the polyimide hollow fiber gas separation membrane is 35.1g / g.

[0152] Step 3: Same as step 3 in the embodiment.

[0153] Step 4: Immerse 0.609 g of the hollow fiber gas separation membrane obtained in Step 3 uniformly in 25 g of a 2 wt% polydimethylsiloxane solution. First, soak at 25°C for 20 min. Then, remove the hollow fiber gas separation membrane with the surface impregnation solution and cure it in a 60°C ventilated oven for 12 h. After the reaction, thoroughly wash away the residual solvent with water and ethanol to obtain the polyimide hollow fiber composite gas separation membrane M4. The mass ratio of the silicone rubber solution to the product of Step 3 (the dried hollow fiber gas separation membrane) is 41.1:1.

[0154] The gas permeation rate of the composite gas separation membrane M4 was tested and retested after 90 days. The results are shown in Table 2.

[0155] The tensile strength and elongation at break of the composite gas separation membrane M4 were tested and retested after 90 days. The results are shown in Table 3.

[0156] Example 5

[0157] Step 1: Same as in Example 1.

[0158] Step 2: Same as in Example 1.

[0159] Step 3: Same as in Example 1.

[0160] Step 4: Immerse 0.545g of the hollow fiber gas separation membrane obtained in Step 3 uniformly in 16g of a 2wt% polydimethylsiloxane solution. First, soak at 25℃ for 20min. Then, remove the hollow fiber gas separation membrane with the surface impregnation solution and cure it in a ventilated oven at 60℃ for 12h. After the reaction, thoroughly wash away the residual solvent with water and ethanol to obtain the polyimide hollow fiber composite gas separation membrane M5. The mass ratio of the silicone rubber solution to the product of Step 3 (the dried hollow fiber gas separation membrane) is 29.4:1.

[0161] The gas permeation rate of the composite gas separation membrane M5 was tested and retested after 90 days. The results are shown in Table 2.

[0162] The tensile strength and elongation at break of the composite gas separation membrane M5 were tested and retested after 90 days. The results are shown in Table 3.

[0163] Example 6

[0164] The composite gas separation membrane M6 was prepared according to the method of Example 1, except that the hollow fiber gas separation membrane prepared in Example 2 was used instead of the hollow fiber gas separation membrane prepared in Example 1.

[0165] The gas permeation rate of the composite gas separation membrane was tested and retested after 90 days. The results are shown in Table 2.

[0166] The tensile strength and elongation at break of the composite gas separation membrane were tested and retested after 90 days. The results are shown in Table 3.

[0167] Comparative Example 1

[0168] The hollow fiber gas separation membrane prepared in Example 1 was used directly.

[0169] The gas permeation rate of the hollow fiber gas separation membrane was tested and retested after 90 days. The results are shown in Table 2.

[0170] The tensile strength and elongation at break of the hollow fiber gas separation membrane were tested and retested after 90 days. The results are shown in Table 3.

[0171] Comparative Example 2

[0172] The composite gas separation membrane was prepared according to the method of Example 1, except that step four was omitted. Composite gas separation membrane D2 was obtained.

[0173] The gas permeation rate of the composite gas separation membrane was tested and retested after 90 days. The results are shown in Table 2.

[0174] The tensile strength and elongation at break of the composite gas separation membrane were tested and retested after 90 days. The results are shown in Table 3.

[0175] Comparative Example 3

[0176] Step 1: Thoroughly clean 0.483 g of the hollow fiber gas separation membrane from Preparation Example 1 with deionized water and ethanol, and then dry it with nitrogen.

[0177] Step 2: The cleaned hollow fiber gas separation membrane was directly and uniformly immersed in 25g of a 2wt% polydimethylsiloxane solution. It was first soaked at 25℃ for 20min, then the hollow fiber gas separation membrane with the surface impregnation solution was removed and cured in a ventilated oven at 60℃ for 12h. After the reaction, the residual solvent was thoroughly washed off with water and ethanol to obtain the composite gas separation membrane D3. The mass ratio of the silicone rubber solution to the product of Step 3 (the dried hollow fiber gas separation membrane) was 51.8:1.

[0178] The gas permeation rate of the composite gas separation membrane was tested and retested after 90 days. The results are shown in Table 2.

[0179] The tensile strength and elongation at break of the composite gas separation membrane were tested and retested after 90 days. The results are shown in Table 3.

[0180] Comparative Example 4

[0181] Step 1: At 25°C, add 1g of 3-aminopropyltriethoxysilane to 99g of n-hexane and stir thoroughly to dissolve.

[0182] Step 2: Immerse the hollow fiber gas separation membrane of Preparation Example 1 uniformly in the solution of Step 1, remove it, and wait 10 minutes for the solvent to evaporate.

[0183] Step 3: 0.578 g of the hollow fiber gas separation membrane from Step 2 was uniformly immersed in 25 g of a 2 wt% polydimethylsiloxane solution. The membrane was first soaked at 25°C for 20 min, then removed with the surface impregnation solution. It was then cured in a ventilated oven at 60°C for 12 h. After the reaction, the residual solvent was thoroughly washed with water and ethanol to obtain the composite gas separation membrane D4. The mass ratio of the silicone rubber solution to the product from Step 2 was 43.3:1.

[0184] The gas permeation rate of the composite gas separation membrane was tested and retested after 90 days. The results are shown in Table 2.

[0185] The tensile strength and elongation at break of the composite gas separation membrane were tested and retested after 90 days. The results are shown in Table 3.

[0186] The thickness of each layer in the polyimide hollow fiber gas separation membrane and the nitrogen content in the amino polymer of the connecting layer were tested, and the results are shown in Table 1.

[0187] Table 1

[0188]

[0189] *Silane coupling agent connects the hollow fiber gas separation membrane to the protective layer, with a theoretical thickness of approximately 0.

[0190] The He permeation rate, He / N2 separation coefficient, and CO2 / N2 separation coefficient of the composite gas separation membranes prepared in the examples and comparative examples were tested, and the results are shown in Table 2. After operating the gas separation membranes of the examples and comparative examples at 0.2 MPa pressure for 90 days under intermittent CO2 / N2 / He alternating or mixed gas flow conditions, the He permeation rate, He / N2 separation coefficient, and CO2 / N2 separation coefficient of the gas separation membranes after operation were tested, and the results are shown in Table 2. The permeation rate retention rate, the CO2 / N2 separation selectivity retention rate, and the He / N2 separation selectivity retention rate were calculated using the following formulas:

[0191] Permeability retention rate, % = Permeability rate after 90 days of operation / Initial permeability rate × 100% (if the value is greater than 100%, take 100% as the upper limit).

[0192] The rate of change in the selectivity of CO2 to N2 separation, % = |(initial CO2 / N2 separation coefficient - CO2 / N2 separation coefficient after 90 days of operation) / initial CO2 / N2 separation coefficient| × 100%.

[0193] The rate of change in the selectivity of He / N2 separation, % = |(initial He / N2 separation coefficient - He / N2 separation coefficient after 90 days of operation) / initial He / N2 separation coefficient| × 100%.

[0194] As the operating time increases, the composite gas separation membrane becomes denser, which leads to an increase in the separation coefficient.

[0195] Table 2

[0196]

[0197]

[0198] Table 2 (continued)

[0199]

[0200] As shown in Table 2, compared with Comparative Examples 1-3, the polyimide hollow fiber composite gas separation membrane provided by the present invention maintains a more stable gas permeation flux and separation coefficient after 90 days. Compared with Comparative Example 4, the method provided by the present invention can obtain a significantly higher gas permeation flux. Compared with Example 6, Example 1 shows that when the method provided by the present invention is applied to non-preferred polyimide membranes other than the polyimide random copolymer shown in Formula I, the gas separation performance of the membrane is slightly worse, but stable permeation flux and separation coefficient can still be obtained.

[0201] The tensile strength and elongation at break of the composite gas separation membranes prepared in the examples and comparative examples were tested, and the results are shown in Table 3. After storing the gas separation membranes of the examples and comparative examples at room temperature and pressure and under natural light for 90 days, the tensile strength and elongation at break of the gas separation membranes after operation were tested, and the results are shown in Table 3.

[0202] Table 3

[0203]

[0204]

[0205] As can be seen from Table 3, compared with the comparative example, the polyimide hollow fiber composite gas separation membrane provided by the present invention has higher tensile strength and still maintains high tensile strength after 90 days of operation.

[0206] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A polyimide hollow fiber composite gas separation membrane, characterized by, The polyimide hollow fiber composite gas separation membrane includes a polyimide hollow fiber gas separation membrane, a protective layer, and a connecting layer located between the gas separation membrane and the protective layer. The protective layer is a coating formed of silicone rubber; The materials constituting the connecting layer include amino polymers.

2. The composite gas separation membrane of claim 1, wherein, The silicone rubber is selected from at least one of polydimethylsiloxane, polydimethylvinylsiloxane, polymethylphenylsiloxane, and polytrifluoropropylmethylsiloxane, preferably polydimethylsiloxane; Preferably, the silicone rubber has a dynamic viscosity of 15-100,000 cP at 25°C, and more preferably 500-7,500 cP.

3. The composite gas separation membrane according to claim 1 or 2, wherein, Based on the total amount of the amino polymer, the nitrogen content in the amino polymer is 3-45 wt%, preferably 6-15 wt%. Preferably, the theoretical weight-average molecular weight of the amino polymer is 300-50000 Da, more preferably 400-10000 Da; Preferably, the amino polymer is selected from homopolymers and / or copolymers of dopamine; Preferably, the amino polymer is selected from at least one of polydopamine, dopamine-ethylenediamine copolymer, dopamine-propylenediamine copolymer, dopamine-butyldiamine copolymer, dopamine-diethylenetriamine copolymer, dopamine-triethylenetetramine copolymer, dopamine-tetraethylenepentamine copolymer, dopamine-polyethyleneimine copolymer, dopamine-ethylenediamine-polyethyleneimine copolymer, dopamine-propylenediamine-polyethyleneimine copolymer, dopamine-diethylenetriamine-polyethyleneimine copolymer, dopamine-triethylenetetramine-polyethyleneimine copolymer, and dopamine-tetraethylenepentamine-polyethyleneimine copolymer; more preferably, at least one of polydopamine, dopamine-ethylenediamine copolymer, and dopamine-propylenediamine copolymer.

4. The composite gas separation membrane according to any one of claims 1 to 3, wherein, The polyimide hollow fiber gas separation membrane includes a support layer and a dense layer attached to the outer surface of the support layer. Preferably, the thickness of the dense layer is less than or equal to 1000 nm and the porosity of the hollow fiber gas separation membrane is 40-80%. More preferably, the thickness of the dense layer is 150-800 nm and the porosity of the hollow fiber gas separation membrane is 50-70%. And / or, the thickness of the protective layer is 200nm-3000nm, preferably 800nm-1600nm; And / or, the thickness of the connecting layer is 80nm-500nm, preferably 200nm-350nm.

5. The composite gas separation membrane according to any one of claims 1-4, wherein, The He permeation rate of the composite gas separation membrane is ≥80 GPU, preferably ≥120 GPU; Preferably, the CO2 and N2 separation selectivity of the composite gas separation membrane is ≥10, more preferably ≥35; Preferably, the separation selectivity of the composite gas separation membrane for He and N2 is ≥50, more preferably ≥90; Preferably, after 90 days of operation, the retention rate of He permeation rate of the composite gas separation membrane is greater than or equal to 85%, the retention rate of CO2 and N2 separation selectivity of the composite gas separation membrane is greater than or equal to 85%, and the retention rate of He and N2 separation selectivity of the composite gas separation membrane is greater than or equal to 90%.

6. A method for preparing a polyimide hollow fiber composite gas separation membrane, characterized in that, The preparation method includes: S1. Mix the additive, dopamine, and optionally amino-containing reactants to obtain a mixture; S2. The polyimide hollow fiber gas separation membrane is impregnated with the mixture and then subjected to a polymerization reaction. S3. The product obtained in step S2 is impregnated with a silicone rubber solution and cured to obtain the polyimide hollow fiber composite gas separation membrane.

7. The preparation method according to claim 6, wherein, In step S1, the addition of additives makes the pH of the mixture 7.5-10, preferably 8.5-10; Preferably, the additive includes additive A, or additive A and additive B, wherein additive A is selected from sodium hydroxide, or sodium hydroxide and tris(hydroxymethyl)aminomethane, and additive B is selected from at least one of hydrochloric acid, sodium dihydrogen phosphate and potassium dihydrogen phosphate; Preferably, the amino-containing reactants are selected from amino-containing monomers and / or amino-containing polymers; Preferably, the amino-containing monomer is selected from at least one of ethylenediamine, propylenediamine, butanediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine; Preferably, the amino-containing polymer is selected from polyethyleneimine; Preferably, the weight-average molecular weight of the polyethyleneimine is 500-2000 Da, and more preferably 600-1800 Da; Preferably, the concentration of dopamine in the mixture is 0.1wt%-5wt%, more preferably 0.5wt%-2wt%. Preferably, the concentration of the amino-containing reactant in the mixture is 0-5 wt%, more preferably 0.2 wt%-2 wt%. Preferably, when dopamine undergoes a polymerization reaction with an amino-containing reactant, the weight ratio of dopamine to the amino-containing reactant is 1:0.05-10, more preferably 1:0.2-1.5; Preferably, the polymerization reaction time is 2-48 hours, more preferably 5-24 hours; the polymerization reaction temperature is 0-50°C, more preferably 20-35°C.

8. The preparation method according to claim 6 or 7, wherein, The solid content of the silicone rubber solution is 0.5-10 wt%, preferably 2-4 wt%. Preferably, the silicone rubber in the silicone rubber solution is selected from at least one of polydimethylsiloxane, polydimethylvinylsiloxane, polymethylphenylsiloxane, and polytrifluoropropylmethylsiloxane, and is preferably polydimethylsiloxane; Preferably, the silicone rubber has a dynamic viscosity of 15-100,000 cP at 25°C, and more preferably 500-7,500 cP. Preferably, the mass ratio of the silicone rubber solution to the mass of the product obtained in step S2 is 20-80:1, more preferably 30-50:1; Preferably, the curing conditions include: a curing temperature of 15-150℃ and a curing time of 0.5-72h.

9. The preparation method according to any one of claims 6-8, wherein, Step S2 also includes washing and drying the product obtained from the polymerization reaction; preferably, washing is performed using alcohol and / or water. Preferably, step S2 further includes washing the cured product.

10. A polyimide hollow fiber composite gas separation membrane prepared by the preparation method according to any one of claims 6-9.

11. The application of the polyimide hollow fiber composite gas separation membrane according to any one of claims 1-5 and 10 in the separation of He and / or CO2.

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