Hollow carbon fiber membrane and preparation method therefor, and gas membrane module and use thereof

Abstract

The present invention relates to the technical field of ethane / ethylene separation, and specifically discloses a hollow carbon fiber membrane and a preparation method therefor, and a gas membrane module and the use thereof. The preparation method comprises: carbonizing a hollow fiber membrane so as to obtain a hollow carbon fiber membrane, wherein, during the carbonization process, the inner cavities of the hollow fiber membrane are filled with a first inert atmosphere, and a pressure difference between the inner cavities and a region outside of the hollow fiber membrane is kept at 0.01 MPa to 5 MPa, the temperature of the first inert atmosphere being 100°C or less. The hollow carbon fiber membrane prepared in the present invention exhibits good durability and bending resistance. In addition, the hollow carbon fiber membrane also exhibits good gas permeation and separation properties, including a high ethane / ethylene separation selectivity coefficient and high ethane permeation flux. The hollow carbon fiber membrane of the present invention can be widely used in the field of gas separation.

Description

Hollow carbon fiber membranes, their preparation methods, gas membrane modules and applications

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Chinese Patent Application No. 202411740999.3, filed on November 29, 2024, the contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to the field of ethane / ethylene separation technology, specifically to a hollow carbon fiber membrane, its preparation method, gas membrane module, and applications. Background Technology

[0004] Light hydrocarbons are important chemical raw materials, mainly including alkanes such as methane, ethane, propane, and butane, and olefins such as ethylene, propylene, and butene. These light hydrocarbons have wide applications in petrochemical, natural gas chemical, and coal chemical industries. Currently, the main light hydrocarbon separation process is cryogenic distillation, which separates light hydrocarbons by utilizing the difference in boiling points at different temperatures. However, due to the similar physical properties of alkanes and olefins, cryogenic distillation is very energy-intensive and has high operating costs. Membrane separation technology is a novel separation technology with advantages such as low energy consumption, small footprint, and simple operation. This technology utilizes the selective permeability of membranes to achieve effective separation of different gas components. Therefore, membrane separation technology holds promise for achieving efficient and energy-saving separation of alkanes and olefins.

[0005] Existing hollow fiber membranes mainly use polymers as membrane materials, such as polyimide (PI) and polyether ether ketone (PEEK). Hollow fiber membranes made from these polymer membrane materials are suitable for gas separation. However, when used for the separation of ethane and ethylene, the separation selectivity is insufficient, and effective separation of ethane and ethylene cannot be achieved.

[0006] In gas separation applications, high-partial-pressure ethane gas molecules selectively "dissolve" in hollow fiber membranes. These ethane gas molecules easily alter the polymer chains of the hollow fiber membrane, resulting in a swelling effect, known as the "plasticization effect." The "plasticization effect" leads to a continuous decrease in the gas separation selectivity of the hollow fiber membrane, causing a decline in its durability.

[0007] Hollow fiber membranes can be made into hollow carbon fiber membranes after carbonization. Existing hollow carbon fiber membranes have poor bending resistance. Such hollow carbon fiber membranes are prone to damage or breakage when folded into bundles or bundled for membrane module manufacturing, resulting in poor durability.

[0008] Therefore, how to enable gas separation membranes to have high durability while effectively separating ethane and ethylene gases, thereby achieving commercial-scale application of ethane and ethylene separation, has become an urgent problem to be solved in the field of gas separation membranes. Summary of the Invention

[0009] The purpose of this invention is to overcome the problems of poor durability and poor selectivity for separating ethane and ethylene in existing gas separation membranes, and to provide a hollow carbon fiber membrane, its preparation method, gas membrane assembly and application, which has excellent bending resistance and durability.

[0010] To achieve the above objectives, a first aspect of the present invention provides a method for preparing hollow carbon fiber membranes, wherein the method includes:

[0011] The hollow fiber membrane is carbonized to obtain the hollow carbon fiber membrane;

[0012] During the carbonization process, the internal cavity of the hollow fiber membrane is filled with a first inert atmosphere, and a pressure difference of 0.01 MPa to 5 MPa exists between the internal cavity and the external region of the hollow fiber membrane. The temperature of the first inert atmosphere is below 100°C.

[0013] A second aspect of the present invention provides a hollow carbon fiber membrane prepared by the aforementioned method.

[0014] A third aspect of the present invention provides a gas separation membrane assembly comprising a hollow carbon fiber membrane prepared by the aforementioned method.

[0015] A fourth aspect of the present invention provides an application of the aforementioned hollow carbon fiber membrane or the aforementioned gas separation membrane assembly in ethane / ethylene gas separation.

[0016] The hollow carbon fiber membrane prepared by the above-mentioned technical solution of the present invention has excellent durability, including high bending resistance and high plasticizing resistance. Under high ethane content and high pressure inlet conditions, its gas separation selectivity can still remain stable. In addition, the hollow carbon fiber membrane also has excellent gas permeation and separation performance, including high ethane / ethylene separation selectivity coefficient and ethane permeation flux. Attached Figure Description

[0017] Figure 1 is a cross-sectional schematic diagram of the hollow fiber membrane of the present invention during the carbonization process, wherein the outer surface temperature T1 of the hollow fiber membrane is greater than the inner surface temperature T2 of the hollow fiber membrane; and the internal pressure P2 of the hollow fiber membrane is greater than the external pressure P1 of the hollow fiber membrane.

[0018] Explanation of reference numerals in the attached figures

[0019] 1 - External pressure P1 of the hollow fiber membrane; 2 - Internal pressure P2 of the hollow fiber membrane; 3 - Hollow fiber membrane; 4 - External surface temperature T1 of the hollow fiber membrane; 5 - Internal surface temperature T2 of the hollow fiber membrane; 6 - Hollow portion of the hollow fiber membrane. Detailed Implementation

[0020] 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.

[0021] The first aspect of this invention provides a method for preparing hollow carbon fiber membranes, wherein the method includes:

[0022] The hollow fiber membrane is carbonized to obtain the hollow carbon fiber membrane;

[0023] During the carbonization process, the internal cavity of the hollow fiber membrane is filled with a first inert atmosphere, and a pressure difference of 0.01 MPa to 5 MPa exists between the internal cavity and the external region of the hollow fiber membrane (e.g., 0.01 MPa, 0.1 MPa, 0.2 MPa, 0.5 MPa, 1 MPa, 1.5 MPa, 2 MPa, 2.5 MPa, 3 MPa, 3.5 MPa, 4 MPa, 4.5 MPa, 5 MPa, or any two of the above values). The temperature of the first inert atmosphere is below 100°C (e.g., 10°C, 15°C, 20°C, 25°C, 30°C, 40°C, 60°C, 80°C, 100°C, or any two of the above values).

[0024] When the temperature of the first inert atmosphere is below 100°C, there is a significant temperature difference with the carbonization temperature of the carbonization furnace. This results in a significant temperature difference between the internal cavity of the hollow fiber membrane and the external region of the hollow fiber membrane. In conjunction with the internal and external pressure difference, this helps to control the degree of carbonization of the hollow fiber membrane, thereby improving the performance of the hollow carbon fiber membrane.

[0025] According to one embodiment of the present invention, the pressure in the internal cavity is higher than the pressure in the external region of the membrane. That is, the pressure in the internal cavity is 0.01 MPa to 5 MPa greater than the pressure in the external region of the hollow fiber membrane.

[0026] Figure 1 is a cross-sectional schematic diagram of the hollow fiber membrane of the present invention during the carbonization process, wherein the outer surface temperature T1 of the hollow fiber membrane is greater than the inner surface temperature T2 of the hollow fiber membrane; and the internal pressure P2 of the hollow fiber membrane is greater than the external pressure P1 of the hollow fiber membrane.

[0027] According to one embodiment of the present invention, a method for forming the first inert atmosphere may include introducing an inert gas from both ends of the hollow fiber membrane into the internal cavity of the hollow fiber membrane.

[0028] The inert gas may be nitrogen, argon, or helium.

[0029] The temperature of the inert gas can be 20-30℃.

[0030] The anti-plasticization performance of the present invention refers to the fact that, under high ethane content and high pressure inlet conditions, the hollow carbon fiber membrane of the present invention can effectively reduce the "plasticization effect" of ethane gas molecules on the membrane. Specifically, when the hollow carbon fiber membrane is exposed to high ethane content and high pressure inlet conditions, its ethane / ethylene separation selectivity remains unchanged or decreases slightly, and remains stable overall.

[0031] The inventors of this invention discovered that when the pressure inside the hollow fiber membrane is set higher than the pressure outside the membrane, and the pressure difference between the inside and outside regions of the hollow fiber membrane is set within the range of 0.01 to 5 MPa, the obtained hollow carbon fiber membrane has an ethane / ethylene separation selectivity greater than 10 compared to the hollow fiber membrane, and its ethane permeation performance is also significantly improved. In addition, the obtained hollow carbon fiber membrane has excellent durability, including high bending resistance and anti-plasticization properties.

[0032] The inventors of this invention have discovered that when the temperature of the first inert atmosphere is set at 20-30°C, the obtained hollow carbon fiber membrane has an ethane / ethylene separation selectivity greater than 10 compared to hollow fiber membranes, and its ethane permeation performance is also significantly improved. In addition, the obtained hollow carbon fiber membrane has excellent durability, including high bending resistance and anti-plasticization properties.

[0033] During carbonization, a pressure difference exists between the internal cavity and the external region of the hollow fiber membrane, with the pressure inside the cavity being higher than that outside. Driven by this pressure difference, the low-temperature (typically 20-30°C) inert gas in the internal cavity diffuses from the inside of the hollow fiber membrane to the outside. Because the temperature outside the membrane is higher (typically above 600°C), a gradual temperature change occurs across the cross-section of the hollow fiber membrane from the inside out (lower temperature inside, higher temperature outside), resulting in a gradient in the degree of carbonization from the inside out. Due to the high-temperature environment outside the membrane, the outer surface layer is completely carbonized, forming a dense and extremely thin layer. Extending inward from the outer surface layer, the hollow fiber membrane also has multiple porous layers. These porous layers are affected by the gradual temperature change, with the degree of carbonization decreasing from the outside in. The innermost porous layer is either uncarbonized or incompletely carbonized. Therefore, the hollow carbon fiber membrane obtained by the above carbonization has the above-mentioned asymmetric structure, which makes the hollow carbon fiber membrane have both high ethane permeability and high ethane / ethylene selectivity, as well as high bending resistance and anti-plasticization properties.

[0034] According to one embodiment of the present invention, the preparation of hollow fiber membrane may further include the step of forming a hollow fiber membrane from a casting solution, wherein the steps sequentially include: spinning, curing, solvent exchange and drying.

[0035] According to one embodiment of the present invention, the casting solution used in the preparation of the hollow fiber membrane includes polyimide.

[0036] The polyimide may contain structural units derived from aromatic dianhydrides and aromatic diamines.

[0037] According to one embodiment of the present invention, the aromatic dianhydride may include 4,4'-(hexafluoroisopropylidene) phthalic anhydride (6FDA) and / or 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA).

[0038] According to one embodiment of the present invention, the aromatic diamine may include 2,6-diaminotoluene (2,6-DAT) and / or 4,6-diamino-1,3-benzenediol (DAPI).

[0039] The inventors of this invention conducted screening experiments on various aromatic dianhydrides and aromatic diamines in polyimide and found that when the aromatic dianhydride was selected from 6FDA or BTDA and the aromatic diamine was selected from 2,6-DAT or DAPI, the ethane / ethylene separation selectivity of the obtained hollow carbon fiber membrane could reach more than 10. Moreover, compared with the hollow carbon fiber membranes that had not undergone pre-oxidation and carbonization, the ethane permeation performance of this hollow carbon fiber membrane was significantly improved. In addition, the obtained hollow carbon fiber membrane has excellent durability properties, including high bending resistance and anti-plasticization properties.

[0040] According to a preferred embodiment of the present invention, the polyimide is 6FDA-2,6-DAT or BTDA-DAPI. Wherein, 6FDA-2,6-DAT represents a polyimide formed by the polycondensation reaction of 6FDA (4,4'-(hexafluoroisopropylidene) phthalic anhydride) and 2,6-DAT (2,6-diaminotoluene); "BTDA-DAPI" represents a polyimide formed by the polycondensation reaction of BTDA (3,3',4,4'-benzophenone tetracarboxylic dianhydride) and DAPI (4,6-diamino-1,3-benzenediphenol).

[0041] The 6FDA-2,6-DAT has the following structure:

[0042] The BTDA-DAPI has the following structure:

[0043] In some embodiments, the viscosity of the casting solution is 0.65-0.9 dL / g, for example, 0.65 dL / g, 0.7 dL / g, 0.75 dL / g, 0.8 dL / g, 0.85 dL / g, 0.9 dL / g, or any combination of two of the above values, preferably 0.66-0.68 dL / g.

[0044] The inventors of this invention have discovered that when the viscosity of the 6FDA-2,6-DAT or BTDA-DAPI is in the range of 0.65-0.9 dL / g, the obtained hollow carbon fiber membrane has an ethane / ethylene separation selectivity greater than 10 compared to hollow fiber membranes, and the ethane permeation performance is also significantly improved. In addition, the obtained hollow carbon fiber membrane has excellent durability, including high bending resistance and anti-plasticization properties.

[0045] According to a preferred embodiment of the present invention, the viscosity of the 6FDA-2,6-DAT or BTDA-DAPI may be 0.65-0.9 dL / g, preferably 0.66-0.68 dL / g.

[0046] The inventors of this invention have discovered that, based on the total weight of the casting solution, when the polyimide content is in the range of 20-40% by weight, the obtained hollow carbon fiber membrane has an ethane / ethylene separation selectivity greater than 10 compared to hollow fiber membranes, and the ethane permeation performance is also significantly improved. In addition, the obtained hollow carbon fiber membrane has excellent durability, including high bending resistance and anti-plasticization properties.

[0047] According to a preferred embodiment of the present invention, the polyimide content is 20-40% by weight, based on the total weight of the casting solution, for example, 20% by weight, 22% by weight, 24% by weight, 26% by weight, 28% by weight, 30% by weight, 32% by weight, 34% by weight, 36% by weight, 38% by weight, 40% by weight, or any combination of two of the above values, preferably 25-35% by weight.

[0048] According to a preferred embodiment of the present invention, the casting solution further includes a solvent.

[0049] The solvent may be one or more of N-methylpyrrolidone, tetrahydrofuran, and dichloromethane, and is more preferably N-methylpyrrolidone.

[0050] Based on the total weight of the casting solution, the amount of solvent used can be 60-80% by weight, for example, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, or any two of the above values, and more preferably 65-75% by weight.

[0051] The spinning method can be conventional in the art and may include: co-extruding the casting solution and the core solution through a spinneret.

[0052] Spinning conditions can be adjusted as needed. These conditions may include: a spinning temperature of 20-50℃, such as 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, or any combination of two of these values; a spinning air gap of 1-10cm, such as 1cm, 3cm, 5cm, 7cm, 9cm, 10cm, or any combination of two of these values, preferably 5-8cm; and an outer diameter of 300-500μm, such as 300μm, 350μm, 400μm, 450μm, 500μm, or any combination of two of these values, preferably 40μm. 0-450μm; the ratio of the inner diameter to the outer diameter of the spinneret is (0.35-0.6):1, for example, 0.35:1, 0.4:1, 0.45:1, 0.5:1, 0.6:1, or any two of the above values, preferably (0.4-0.5):1; the core fluid includes N-methylpyrrolidone and water, wherein the weight ratio of N-methylpyrrolidone to water is (4-999):1, for example, 4:1, 10:1, 20:1, 30:1, 40:1, 50:1, 100:1, 500:1, 999:1, or any two of the above values, preferably (10-30):1.

[0053] The curing process can be a conventional curing operation in the art, generally involving immersing the nascent film filaments formed in the spinning step into a coagulation bath.

[0054] The curing conditions can be as follows: the coagulation bath temperature is preferably 20-25℃, for example, 20℃, 21℃, 22℃, 23℃, 24℃, 25℃, or any two of the above values; the solvent of the coagulation bath is preferably water, such as tap water.

[0055] The solvent exchange step may include, in sequence, immersing the cured film filaments obtained after curing in water (e.g., pure water) for 16-48 hours (e.g., 16h, 24h, 36h, 42h, 48h, or any two of the above values), then immersing in methanol 2-5 times (e.g., 3 times), each time for 20-30 minutes, and finally immersing in hexane 2-5 times (e.g., 3 times), each time for 20-30 minutes.

[0056] The drying process can be carried out in a vacuum oven.

[0057] The drying conditions may include: a drying temperature of 70-90℃ (e.g., 70℃, 75℃, 76℃, 78℃, 80℃, 82℃, 84℃, 86℃, 88℃, 90℃, or any two of the above values), preferably 80-85℃, and a drying time of 1-6 hours (e.g., 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or any two of the above values).

[0058] According to one embodiment of the present invention, the hollow fiber membrane is further subjected to pre-oxidation before carbonization.

[0059] According to one embodiment of the present invention, the pre-oxidation method includes heating the hollow fiber membrane.

[0060] The pre-oxidation conditions may include: a temperature of 260-300℃ (e.g., 260℃, 265℃, 270℃, 275℃, 280℃, 290℃, 300℃, or any two of the above values), a heating rate of 1-8℃ / minute (e.g., 1℃ / minute, 2℃ / minute, 3℃ / minute, 4℃ / minute, 5℃ / minute, 6℃ / minute, 7℃ / minute, 8℃ / minute, or any two of the above values), and a holding time of 0.5-2 hours (e.g., 0.5 hours, 1 hour, 1.5 hours, 2 hours, or any two of the above values).

[0061] The pre-oxidation can be carried out in a carbonization furnace.

[0062] The inventors of this invention have discovered that when the pre-oxidation temperature is in the range of 260-320℃ and the pre-oxidation heating rate is in the range of 3-8℃ / min, compared with hollow fiber membranes, the obtained hollow carbon fiber membrane has an ethane / ethylene separation selectivity greater than 10 and a significant improvement in ethane permeation performance; in addition, the obtained hollow carbon fiber membrane has excellent durability, including high bending resistance and anti-plasticization performance.

[0063] According to a preferred embodiment of the present invention, the carbonization method includes: further heating the pre-oxidized hollow fiber membrane.

[0064] According to a preferred embodiment of the present invention, the carbonization is carried out under a second inert atmosphere.

[0065] The carbonization conditions may be as follows: the second inert atmosphere is nitrogen or argon, preferably nitrogen; the carbonization temperature is 550-700℃ (e.g., 550℃, 570℃, 590℃, 610℃, 630℃, 650℃, 670℃, 680℃, 700℃, or any combination of two of the above values); the carbonization heating rate is 5-10℃ / minute (e.g., 5℃ / minute, 5.5℃ / minute, 6℃ / minute, 6.5℃ / minute, 7℃ / minute, 8℃ / minute, 9℃ / minute, 10℃ / minute, or any combination of two of the above values); and the carbonization holding time is 20-120 minutes (e.g., 20 minutes, 30 minutes, 50 minutes, 80 minutes, 100 minutes, 120 minutes, or any combination of two of the above values), preferably 30-60 minutes.

[0066] The inventors of this invention have discovered that when the carbonization temperature is in the range of 610-680℃ and the carbonization heating rate is in the range of 5-7℃ / min, compared with hollow fiber membranes, the obtained hollow carbon fiber membrane has an ethane / ethylene separation selectivity greater than 10 and a significant improvement in ethane permeation performance; in addition, the obtained hollow carbon fiber membrane has excellent durability, including high bending resistance and anti-plasticization performance.

[0067] The pressure inside the carbonization furnace can be atmospheric pressure or slightly positive pressure (e.g., below 50 kPa).

[0068] The carbonization process further includes a step of cooling the hollow carbon fiber membrane obtained after carbonization. Specifically, the cooling process involves naturally cooling the hollow carbon fiber membrane obtained after carbonization to room temperature in an inert atmosphere.

[0069] To ensure the economic feasibility of separating ethane and ethylene gases, the gas separation membrane needs to have a separation selectivity of more than 10 for ethane and ethylene. However, the separation selectivity of traditional gas separation membranes for ethane and ethylene is generally less than 7.

[0070] In this invention, unless otherwise specified, the temperature is room temperature and the pressure is atmospheric pressure.

[0071] Therefore, a second aspect of the present invention provides a hollow carbon fiber membrane prepared according to the method described above.

[0072] In some embodiments, the ethane / ethylene separation selectivity of the hollow carbon fiber membrane is ≥10. The hollow carbon fiber membrane of the present invention can meet the economic feasibility requirements for commercially viable ethane and ethylene gas separation.

[0073] The ethane permeation flux of the hollow carbon fiber membrane is related to the type of polyimide. In some embodiments, the ethane permeation flux of the 6FDA-2,6-DAT-based hollow carbon fiber membrane is 8.5-11.5 GPU.

[0074] In some embodiments, the separation selectivity factor for ethane and ethylene in the hollow carbon fiber membrane is 10 or higher.

[0075] In some embodiments, the minimum radius of curvature of the hollow carbon fiber membrane is 3-8 mm.

[0076] A third aspect of the present invention provides a gas separation membrane assembly, the gas separation membrane assembly comprising the aforementioned hollow carbon fiber membrane.

[0077] The gas separation membrane assembly may include components conventional in the art and may be prepared according to conventional methods in the art.

[0078] A fourth aspect of the present invention provides an application of the aforementioned hollow carbon fiber membrane or gas separation membrane assembly in ethane / ethylene gas separation.

[0079] The separation of ethane / ethylene gases can be carried out in accordance with conventional methods in this field.

[0080] The present invention will be described in detail below through embodiments.

[0081] The analysis and evaluation methods used in the following embodiments are shown below.

[0082] Viscosity measurement methods

[0083] The test solution was filtered through a 0.45 μm PTFE injection filter and added to a 200 μm Ubbelohde viscometer. The viscometer was placed in a 30.0 °C water bath and allowed to equilibrate for 30 minutes. Measurements were recorded until three consecutive differences were within 0.1 seconds. The viscosity was calculated using the average of these three measurements using the following equation:

[0084] η inh (dL / g): Viscosity

[0085] t (seconds): Solution flow time

[0086] t0 (seconds): Solvent flow time

[0087] C(g / dL): solution concentration

[0088] Gas permeation performance test method for hollow (carbon) fiber membranes (before / after carbonization)

[0089] Several hollow fiber membrane filaments (before / after carbonization) were placed in a stainless steel tube, and both ends were sealed with epoxy resin. Pure gas permeation performance was then tested in a gas permeation testing system.

[0090] The testing process is as follows:

[0091] 1. Replace the test system with the gas to be tested;

[0092] 2. Maintain a stable system temperature of 25℃, introduce the gas to be tested, and adjust the gas pressure to 0.1MPa (gauge pressure);

[0093] 3. After stabilizing for 30 minutes, measure the permeate flow rate.

[0094] The gas permeation flux can be calculated using equation (1):

[0095] In the formula: (P / L) represents the permeation flux of the hollow fiber membrane (1 GPU = 1 × 10⁻⁶). -6 cm 3 (STP) / (cm 2 -s-cmHg); Q represents the permeate flow rate (cm). 3 (STP) / s); △P represents the pressure difference across the membrane fiber (since the permeate side is at atmospheric pressure, it is equal to the gas pressure on the feed side) (cmHg); A represents the effective membrane area (cm²). 2 ); n represents the number of membrane filaments; D represents the outer diameter of the hollow fiber membrane filament (cm); l represents the effective length of the membrane filament (cm). 2 ).

[0096] The selectivity coefficient for pure gas separation can be calculated using equation (2):

[0097] In the formula: A and B represent different pure gas components.

[0098] Determination of bending resistance

[0099] Hollow (carbon) fiber membranes are wound around cylinders of various diameters, and it is observed whether they break (break). The cylinder with the largest curvature is identified, and its bending resistance is represented by the value of the smallest radius of curvature.

[0100] Example 1

[0101] This embodiment illustrates the preparation method of 6FDA-2,6-DAT hollow carbon fiber membrane.

[0102] (1) Preparation of hollow fiber membrane

[0103] The dried 6FDA-2,6-DAT was dissolved in NMP with a solid content of 29% by weight. The mixture was stirred thoroughly at room temperature until homogeneous to obtain a casting solution with a viscosity of 0.67 dL / g.

[0104] In hollow fiber spinning equipment, casting solution and core solution are co-extruded and spun through a spinneret according to a set spinning process to prepare nascent fiber membranes. The core solution is a 95% NMP / 5% water (w / w) solution, and the coagulation solution is room temperature tap water. The main process parameters are: temperature 45℃; air gap 4cm; outer diameter 400 micrometers; inner diameter / outer diameter ratio 0.45.

[0105] The nascent membrane fibers were solidified by immersing them in water, then immersed in pure water for 24 hours, then immersed in methanol three times for 30 minutes each time, and finally immersed in hexane three times for 30 minutes each time. The membrane was then dried in a vacuum oven at 75°C for 3 hours to obtain a hollow fiber membrane.

[0106] The ethane permeation flux of the hollow fiber membrane was tested to be 3.8 GPU using the gas permeation performance test method, and the ethane / ethylene separation selectivity was 6.7. The minimum radius of curvature of the hollow carbon fiber membrane was tested to be <1 mm using the bending resistance test method.

[0107] (2) Preparation of hollow carbon fiber membrane

[0108] Hollow fiber membrane filaments were placed in a carbonization device for pre-oxidation treatment at a temperature of 280℃, a heating rate of 5℃ / minute, and a holding time of 1 hour.

[0109] Carbonization was carried out in a high-purity inert atmosphere (nitrogen) by heating to 600°C at a rate of 8°C / min and holding at that temperature for 45 minutes. Heating was then stopped, and the mixture was allowed to cool naturally to room temperature in the same inert atmosphere (nitrogen) to obtain a hollow carbon fiber membrane. During the carbonization process, nitrogen gas was introduced into the internal cavity of the hollow fiber membrane from both ends, filling the internal cavity with a nitrogen atmosphere. The pressure in the internal cavity was set to be 0.5 MPa higher than the pressure in the external region of the membrane. The temperature of the first inert atmosphere was 25°C.

[0110] The ethane permeation flux and ethane / ethylene separation selectivity of the hollow carbon fiber membrane were tested using the gas permeation performance test method, and the minimum radius of curvature of the hollow carbon fiber membrane was tested according to the bending resistance test method. The specific results are shown in Table 1.

[0111] Comparative Example 1

[0112] The operation was carried out according to the method described in Example 1, except that during the carbonization process, the hollow fiber membrane was completely placed in the carbonization furnace so that the temperature and pressure of the internal cavity and the external area of ​​the membrane were the same, and the carbonization temperature was 650°C.

[0113] The ethane permeation flux and ethane / ethylene separation selectivity of the hollow carbon fiber membrane were tested using the gas permeation performance test method, and the minimum radius of curvature of the hollow carbon fiber membrane was tested according to the bending resistance test method. The specific results are shown in Table 1.

[0114] Example 2

[0115] The operation was carried out according to the method described in Example 1, except that the temperature of the nitrogen gas in the internal cavity of the hollow fiber membrane was 80°C during the carbonization process.

[0116] The ethane permeation flux and ethane / ethylene separation selectivity of the hollow carbon fiber membrane were tested using the gas permeation performance test method, and the minimum radius of curvature of the hollow carbon fiber membrane was tested according to the bending resistance test method. The specific results are shown in Table 1.

[0117] Comparative Example 2

[0118] The operation was carried out according to the method described in Example 1, except that the temperature of the nitrogen gas in the internal cavity of the hollow fiber membrane was 200°C during the carbonization process.

[0119] The ethane permeation flux and ethane / ethylene separation selectivity of the hollow carbon fiber membrane were tested using the gas permeation performance test method, and the minimum radius of curvature of the hollow carbon fiber membrane was tested according to the bending resistance test method. The specific results are shown in Table 1.

[0120] Example 3 Group

[0121] Example 3-1: The method described in Example 1 is followed, except that during the carbonization process, the pressure in the internal cavity is 0.2 MPa greater than the pressure in the outer region of the hollow fiber membrane.

[0122] Example 3-2: The method described in Example 1 is followed, except that during the carbonization process, the pressure in the internal cavity is 4.5 MPa greater than the pressure in the outer region of the hollow fiber membrane.

[0123] The ethane permeation flux and ethane / ethylene separation selectivity of the hollow carbon fiber membrane were tested using the gas permeation performance test method, and the minimum radius of curvature of the hollow carbon fiber membrane was tested according to the bending resistance test method. The specific results are shown in Table 1.

[0124] Example 4

[0125] This embodiment illustrates the preparation method of BTDA-DAPI hollow carbon fiber membrane.

[0126] (1) Preparation of hollow fiber membrane

[0127] After drying (BTDA-DAPI) was dissolved in NMP with a solid content of 27% by weight. The solution was stirred thoroughly at room temperature until homogeneous to obtain a casting solution with a viscosity of 0.68 dL / g.

[0128] In hollow fiber spinning equipment, casting solution and core solution are co-extruded and spun through a spinneret according to a set spinning process to prepare nascent fiber membranes. The core solution is a 95% NMP / 5% water (w / w) solution, and the coagulation solution is room temperature tap water. The main process parameters are: temperature 25℃; air gap 4cm; outer diameter 400 micrometers; inner diameter / outer diameter ratio 0.45.

[0129] The nascent membrane fibers were solidified by immersing them in water, then immersed in pure water for 48 hours, then immersed in methanol three times for 30 minutes each time, and finally immersed in hexane three times for 30 minutes each time. The membrane was then dried in a vacuum oven at 75°C for 3 hours to obtain a hollow fiber membrane.

[0130] The ethane permeation flux of the hollow fiber membrane was tested to be 0.56 GPU using the gas permeation performance test method, and the ethane / ethylene separation selectivity was 7.4. The minimum radius of curvature of the hollow carbon fiber membrane was tested to be <1 mm using the bending resistance test method.

[0131] (2) Preparation of hollow carbon fiber membrane

[0132] Hollow fiber membrane filaments were placed in a carbonization device for pre-oxidation treatment at a temperature of 240℃, a heating rate of 2℃ / minute, and a holding time of 1 hour.

[0133] Carbonization was carried out in a high-purity inert atmosphere (nitrogen) by heating to 660°C at a rate of 7°C / min, holding at that temperature for 30 minutes, and then stopping the heating. The mixture was then allowed to cool naturally to room temperature in the high-purity inert atmosphere (nitrogen) to obtain a hollow carbon fiber membrane. During the carbonization process, nitrogen gas was introduced into the internal cavity of the hollow fiber membrane from both ends, filling the internal cavity with a nitrogen atmosphere. The pressure in the internal cavity was set to be 0.5 MPa higher than the pressure in the external region of the hollow fiber membrane. The temperature of the first inert atmosphere was 25°C.

[0134] The ethane permeation flux and ethane / ethylene separation selectivity of the hollow carbon fiber membrane were tested using the gas permeation performance test method, and the minimum radius of curvature of the hollow carbon fiber membrane was tested according to the bending resistance test method. The specific results are shown in Table 1.

[0135] Example 5

[0136] The procedure is performed according to the method described in Example 1, except that 6FDA-2,6-DAT is replaced with an equivalent mass of 6FDA-MDA.

[0137] The ethane permeation flux of the hollow fiber membrane was tested to be 5.4 GPU using the gas permeation performance test method, and the ethane / ethylene separation selectivity was 5.4. The minimum radius of curvature of the hollow carbon fiber membrane was tested to be <1 mm using the bending resistance test method.

[0138] The ethane permeation flux and ethane / ethylene separation selectivity of the hollow carbon fiber membrane were tested using the gas permeation performance test method, and the minimum radius of curvature of the hollow carbon fiber membrane was tested according to the bending resistance test method. The specific results are shown in Table 1.

[0139] Table 1

[0140] The technical solution provided by this invention, where the pressure inside the hollow fiber membrane is higher than the pressure outside the membrane, the pressure difference between the internal cavity and the external region of the hollow fiber membrane is set within the range of 0.01 to 5 MPa, and the temperature of the first inert atmosphere is set below 100°C, results in an ethane / ethylene separation selectivity greater than 10 compared to a traditional hollow fiber membrane, and a significant improvement in ethane permeation performance. Furthermore, the obtained hollow carbon fiber membrane exhibits excellent durability, including high bending resistance and resistance to plasticization. If the hollow fiber membrane is not pre-oxidized and carbonized, the ethane / ethylene separation selectivity and ethane permeation flux of the obtained hollow carbon fiber membrane will be significantly reduced.

[0141] 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 combinations of 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 method for preparing hollow carbon fiber membranes, wherein, The method includes: The hollow fiber membrane is carbonized to obtain the hollow carbon fiber membrane; During the carbonization process, the internal cavity of the hollow fiber membrane is filled with a first inert atmosphere, and a pressure difference of 0.01 MPa to 5 MPa exists between the internal cavity and the external region of the hollow fiber membrane, and the temperature of the first inert atmosphere is below 100°C.

2. The method according to claim 1, wherein, The pressure in the internal cavity is higher than the pressure in the external region; and / or The temperature of the first inert atmosphere is 20-30℃.

3. The method according to claim 1 or 2, wherein, The method for preparing the hollow fiber membrane includes sequentially passing the casting solution through spinning, curing, solvent exchange, and drying.

4. The method according to claim 3, wherein, The casting solution includes polyimide.

5. The method according to claim 4, wherein, The polyimide contains structural units derived from aromatic dianhydrides and aromatic diamines; and / or Based on the total weight of the casting solution, the polyimide content is 20-40% by weight; and / or The viscosity of the casting solution is 0.65-0.9 dL / g.

6. The method according to claim 5, wherein, The aromatic diamine includes 4,4'-(hexafluoroisopropylidene) phthalic anhydride (6FDA) and / or 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), and the aromatic diamine includes 2,6-diaminotoluene (2,6-DAT) and / or 4,6-diamino-1,3-benzenediol (DAPI); The viscosity of the casting solution is 0.66-0.68 dL / g.

7. The method according to any one of claims 4-6, wherein, The polyimide is 6FDA-2,6-DAT or BTDA-DAPI.

8. The method according to any one of claims 3-7, wherein, The casting solution also includes a solvent.

9. The method according to claim 8, wherein, The solvent is one or more of N-methylpyrrolidone, tetrahydrofuran, and dichloromethane.

10. The method according to claim 9, wherein, Based on the total weight of the casting solution, the solvent content is 70-80% by weight.

11. The method according to any one of claims 3-10, wherein, The spinning conditions include: a spinning temperature of 20-50℃; an air gap of 1-10cm; an outer diameter of 300-500μm for the spinneret; and an inner diameter to outer diameter ratio of (0.35-0.6):1 for the spinneret; and / or The core solution used in the spinning process includes N-methylpyrrolidone and water, wherein the weight ratio of N-methylpyrrolidone to water is (4-999):

1.

12. The method according to any one of claims 3-11, wherein, The drying conditions include: a drying temperature of 70-90℃ and a drying time of 1-6 hours.

13. The method according to any one of claims 1-12, wherein, The process before carbonization also includes pre-oxidizing the hollow fiber membrane.

14. The method according to claim 13, wherein, The pre-oxidation conditions include: a temperature of 260-300℃, a heating rate of 1-8℃ / minute, and a holding time of 0.5-2 hours.

15. The method according to any one of claims 1-14, wherein, The carbonization conditions include: the carbonization is carried out under a second inert atmosphere, the carbonization temperature is 550-700℃, the carbonization heating rate is 5-10℃ / minute, and the carbonization holding time is 20-120 minutes.

16. A hollow carbon fiber membrane prepared by the method according to any one of claims 1-15, characterized in that, The ethane / ethylene separation selectivity coefficient of the hollow carbon fiber membrane is ≥10.

17. A gas separation membrane assembly comprising the hollow carbon fiber membrane of claim 16.

18. The application of the hollow carbon fiber membrane of claim 16 or the gas separation membrane assembly of claim 17 in ethane / ethylene gas separation.

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