Ultrafine hollow fiber membrane and its preparation method and application

Abstract

The present invention provides an ultrafine hollow fiber membrane and its preparation method and application, the ultrafine hollow fiber membrane is composed of a dense outer skin layer, a foam middle layer and a dense inner skin layer, the dense outer skin layer, the foam middle layer and the dense inner skin layer are prepared by a casting solution of the same composition, the casting solution includes a polymer, a pore former, a thickener and a solvent, and the mass percentage N% of the pore former in the casting solution and the mass percentage G% of the polymer and the mass percentage Z% of the thickener meet: Z=k*G / N, wherein k is a correction coefficient in the range of 0.1-0.8. The present invention prepares a hollow fiber membrane by preparing a certain ratio of casting solution according to specific spinning conditions, while maintaining the membrane with good gas permeability, mechanical strength, pressure resistance and other properties, greatly reducing the diameter of the hollow fiber membrane, thereby effectively improving the packing density in the unit volume component, increasing the membrane area, and improving the efficiency of the component.

Description

Technical Field

[0001] The present invention relates to the technical field of hollow fiber membranes, and in particular to an ultrafine hollow fiber membrane and a preparation method and application thereof. Background Art

[0002] Hollow fiber membrane is a highly efficient gas separation technology that uses special membrane materials and structural designs to achieve selective separation of different gas molecules. This membrane is characterized by a hollow fiber structure that can separate different gases according to the size and properties of gas molecules under a certain pressure difference. Moreover, membrane separation technology has the advantages of no phase change, low energy consumption, and safe operation. It is a green and sustainable development technology with broad application prospects. Therefore, hollow fiber membrane is the main research direction of commercial gas separation membranes.

[0003] Generally, in order to ensure a high packing density per unit volume, the hollow fiber membrane is required to have a small diameter and a certain wall thickness in addition to having properties such as gas permeability, mechanical strength, pressure resistance, and bending resistance.

[0004] Most of the hollow fiber membranes currently available on the market have large diameters and thin walls, making it difficult to take into account the performance of the above-mentioned aspects at the same time, which limits their large-scale commercialization. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides an ultrafine hollow fiber membrane and a preparation method and application thereof.

[0006] In the first aspect, the present invention provides an ultrafine hollow fiber membrane, which is composed of a dense outer skin layer, a foam middle layer and a dense inner skin layer, and the dense outer skin layer, the foam middle layer and the dense inner skin layer are prepared by using a casting liquid with the same composition, and the casting liquid includes a polymer, a pore-forming agent, a thickener and a solvent, and the mass percentage N% of the pore-forming agent in the casting liquid, the mass percentage G% of the polymer and the mass percentage Z% of the thickener satisfy: Z = k*G / N, wherein k is a correction coefficient in the range of 0.1-0.8.

[0007] Furthermore, the value range of N is 2-10, and the value range of G is 15-30.

[0008] The composition of the casting solution of the hollow fiber membrane is a key factor in the preparation process, which directly affects the performance and structure of the final membrane. The casting solution is usually composed of a polymer, a solvent, a pore-forming agent and other optional additives. The selection and proportion of these components are crucial to the formation of the membrane. The present invention has found that in order to ensure that an ultrafine hollow fiber membrane (with an outer diameter of about 0.18 to 0.24 mm) is prepared under the premise of meeting the gas permeability, mechanical strength, pressure resistance and other properties, it is necessary to add a thickener to the casting solution, and keep the amount of the high molecular polymer, pore-forming agent and thickener to meet the above-mentioned specific relationship.

[0009] In some embodiments of the present invention, the high molecular polymer is selected from one or more of polysulfone, polyethersulfone, polyaryletherketone, ethyl cellulose, and polyimide;

[0010] The thickener is selected from one or more of polyvinyl pyrrolidone, water and ethanol.

[0011] Preferably, the high molecular polymer is polysulfone; and the thickener is polyvinyl pyrrolidone.

[0012] Further preferably, the number average molecular weight of the high molecular weight polymer is 50000-80000;

[0013] The K value of the polyvinyl pyrrolidone is 90.

[0014] In some embodiments of the present invention, the pore-forming agent is selected from one or more of polyethylene glycol and polyvinyl alcohol.

[0015] In some embodiments of the present invention, the solvent is a mixture of one or more of N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide and water. Preferably, the mass ratio of one or more of N,N-dimethylacetamide, N,N-dimethylformamide and dimethyl sulfoxide to water is 10 to 20:1.

[0016] In some embodiments of the present invention, the diameter (mm) of the ultrafine hollow fiber membrane satisfies: D=P*M, where P is the spinning pressure (MPa), ranging from 0.2 to 0.5 MPa, and M is the correction coefficient of the diameter, ranging from 0.36 to 1.2.

[0017] It should be noted that the diameter in the present invention refers to the outer diameter. Moreover, when P is smaller, M is preferably a larger value. For example, when P is 0.2 MPa, M is preferably 1.2, and the diameter is 0.24 mm; when P is 0.5 MPa, M is preferably 0.36, and the diameter is 0.18 mm.

[0018] The wall thickness H (mm) of the ultrafine hollow fiber membrane satisfies: H=X*D, wherein X is a correction coefficient of the wall thickness in the range of 0.3 to 0.4.

[0019] In a second aspect, the present invention also provides a method for preparing the ultrafine hollow fiber membrane.

[0020] The preparation method provided by the invention comprises: mixing the components of the casting liquid to obtain the casting liquid, adopting a spinneret high pressure extrusion phase conversion method to prepare a hollow fiber membrane embryo, and then solidifying the membrane.

[0021] Furthermore, during the spinneret high-pressure extrusion phase inversion method, the spinning pressure P (MPa) and the phase inversion air gap L (cm) satisfy: P / L=S, where S is a correction coefficient ranging from 0.1 to 0.2.

[0022] In the preparation process of hollow fiber membrane, the control of spinning conditions is crucial, which directly affects the morphology, structure and performance of fiber membrane. Among them, the spinning pressure determines the speed of polymer solution extrusion, which in turn affects the formation of fiber. The length of the air gap between the spinneret and the coagulation bath will affect the stretching and curing process of the fiber. The present invention has found that when the spinning pressure P (MPa) and the phase inversion air gap L (cm) meet the above relationship, the obtained hollow fiber membrane is more ideal.

[0023] In a third aspect, the present invention provides an application of the ultrafine hollow fiber membrane in gas separation. Specifically, the ultrafine hollow fiber membrane of the present invention can be used for oxygen / nitrogen separation, helium / methane separation, and hydrogen / carbon dioxide separation.

[0024] The present invention provides an ultrafine hollow fiber membrane and a preparation method and application thereof. The hollow fiber membrane is prepared by mixing a certain ratio of casting liquid according to specific spinning conditions. While maintaining the membrane with good gas permeability, mechanical strength, pressure resistance and other properties, the diameter of the hollow fiber membrane is greatly reduced, thereby effectively improving the packing density within the unit volume component, increasing the membrane area, and improving the efficiency of the component. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 This is a physical picture of the ultrafine hollow fiber membrane prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased through regular channels.

[0029] Example 1

[0030] This embodiment provides an ultrafine hollow fiber membrane, and the composition of the membrane casting solution is as follows:

[0031] High molecular weight polymer: polysulfone (number average molecular weight Mw is 50000), mass percentage is 15%;

[0032] Pore-forming agent: polyethylene glycol, mass percentage is 2%;

[0033] Thickener: polyvinyl pyrrolidone (K value is 90), mass percentage is 1.5%;

[0034] Solvent: a mixture of N,N-dimethylacetamide and water in a mass ratio of 10:1, with a mass percentage of 81.5%.

[0035] This embodiment also provides a method for preparing the ultrafine hollow fiber membrane, comprising the following steps:

[0036] After the high molecular polymer, pore-forming agent, thickener and solvent are uniformly mixed, vacuum degassing is performed to obtain a casting solution;

[0037] The casting liquid is ejected from the spinneret at a spinneret pressure of 0.5 MPa, wherein the core liquid is a mixture of water and N,N-dimethylacetamide in a volume ratio of 1:1, the core liquid temperature is 42°C, and the core liquid pressure is 0.06 MPa; after passing through an air layer and a coagulation bath, the hollow fiber membrane is solidified to obtain a phase transition air gap of 5 cm, the coagulation bath is a mixture of water and N,N-dimethylacetamide in a volume ratio of 1:1, the temperature is 68°C, and the coagulation bath depth is 40 cm;

[0038] Then the prepared hollow fiber membrane was immersed in deionized water for 48 hours, during which the deionized water was replaced twice, and dried to obtain an ultrafine hollow fiber membrane.

[0039] The actual picture of the ultrafine hollow fiber membrane prepared in this embodiment is as follows: Figure 1As shown, its outer diameter is 0.18mm and its wall thickness is 0.054mm.

[0040] Example 2

[0041] This embodiment provides an ultrafine hollow fiber membrane, and the composition of the membrane casting solution is as follows:

[0042] High molecular weight polymer: polyethersulfone (number average molecular weight Mw is 60000), mass percentage is 30%;

[0043] Pore-forming agent: polyethylene glycol, mass percentage is 10%;

[0044] Thickener: polyvinyl pyrrolidone (K value is 90), mass percentage is 6%;

[0045] Solvent: a mixture of N,N-dimethylformamide and water in a mass ratio of 10:1, with a mass percentage of 54%.

[0046] This embodiment also provides a method for preparing the ultrafine hollow fiber membrane, comprising the following steps:

[0047] After the high molecular polymer, pore-forming agent, thickener and solvent are uniformly mixed, vacuum degassing is performed to obtain a casting solution;

[0048] The casting liquid is ejected from the spinneret at a spinneret pressure of 0.2 MPa, wherein the core liquid is a mixture of water and N,N-dimethylacetamide in a volume ratio of 1:1, the core liquid temperature is 40°C, and the core liquid pressure is 0.05 MPa; after passing through an air layer and a coagulation bath, the hollow fiber membrane is solidified, wherein the phase inversion air gap is 1 cm, the coagulation bath is a mixture of water and N,N-dimethylacetamide in a volume ratio of 1:1, the temperature is 65°C, and the coagulation bath depth is 20 cm;

[0049] Then the prepared hollow fiber membrane was immersed in deionized water for 48 hours, during which the deionized water was replaced twice, and dried to obtain an ultrafine hollow fiber membrane.

[0050] The ultrafine hollow fiber membrane prepared in this embodiment has an outer diameter of 0.24 mm and a wall thickness of 0.096 mm.

[0051] Example 3

[0052] This embodiment provides an ultrafine hollow fiber membrane, and the composition of the membrane casting solution is as follows:

[0053] High molecular weight polymer: polysulfone (number average molecular weight Mw is 50000) and polyaryletherketone (number average molecular weight Mw is 50000), with a mass percentage of 20%;

[0054] Pore-forming agent: polyvinyl alcohol, mass percentage is 5%;

[0055] Thickener: polyvinyl pyrrolidone (K value is 90), mass percentage is 4%;

[0056] Solvent: a mixture of N,N-dimethylformamide and water in a mass ratio of 20:1, with a mass percentage of 71%.

[0057] This embodiment also provides a method for preparing the ultrafine hollow fiber membrane, comprising the following steps:

[0058] After the high molecular polymer, pore-forming agent, thickener and solvent are uniformly mixed, vacuum degassing is performed to obtain a casting solution;

[0059] The casting liquid is ejected from the spinneret at a spinneret pressure of 0.3 MPa, wherein the core liquid is a mixture of water and N,N-dimethylacetamide in a volume ratio of 1:1, the core liquid temperature is 38°C, and the core liquid pressure is 0.08 MPa; after passing through an air layer and a coagulation bath, the hollow fiber membrane is solidified, wherein the phase inversion air gap is 2 cm, the coagulation bath is a mixture of water and N,N-dimethylacetamide in a volume ratio of 1:1, the temperature is 68°C, and the coagulation bath depth is 30 cm;

[0060] Then the prepared hollow fiber membrane was immersed in deionized water for 48 hours, during which the deionized water was replaced twice, and dried to obtain an ultrafine hollow fiber membrane.

[0061] The ultrafine hollow fiber membrane prepared in this embodiment has an outer diameter of 0.21 mm and a wall thickness of 0.074 mm.

[0062] Example 4

[0063] The difference between this embodiment and embodiment 1 is that the thickener is replaced by ethanol.

[0064] Example 5

[0065] The difference between this embodiment and embodiment 1 is that the thickener is replaced by polyvinyl pyrrolidone (K value is 20).

[0066] Example 6

[0067] The difference between this embodiment and embodiment 1 is that polysulfone is replaced by polyimide having a number average molecular weight Mw of 100,000.

[0068] Comparative Example 1

[0069] This comparative example provides a hollow fiber membrane, and the composition of the membrane casting solution is as follows:

[0070] High molecular weight polymer: polysulfone (number average molecular weight Mw is 50000), mass percentage is 5%;

[0071] Pore-forming agent: polyethylene glycol, mass percentage is 1%;

[0072] Thickener: polyvinyl pyrrolidone (K value is 90), mass percentage is 5%;

[0073] Solvent: a mixture of N,N-dimethylacetamide and water in a mass ratio of 10:1, with a mass percentage of 89%.

[0074] The preparation method is the same as Example 1.

[0075] The outer diameter of the hollow fiber membrane prepared in this comparative example is 0.38 mm, and the wall thickness is 0.08 mm.

[0076] Comparative Example 2

[0077] This comparative example provides a hollow fiber membrane, the composition of its casting solution is the same as that of Example 3, and its preparation method is as follows:

[0078] After the high molecular polymer, pore-forming agent, thickener and solvent are uniformly mixed, vacuum degassing is performed to obtain a casting solution;

[0079] The casting liquid is ejected from the spinneret at a spinneret pressure of 0.1 MPa, wherein the core liquid is a mixture of water and N,N-dimethylacetamide in a volume ratio of 1:1, the core liquid temperature is 38°C, and the core liquid pressure is 0.08 MPa; after passing through an air layer and a coagulation bath, the hollow fiber membrane is solidified, wherein the phase inversion air gap is 10 cm, the coagulation bath is a mixture of water and N,N-dimethylacetamide in a volume ratio of 1:1, the temperature is 68°C, and the coagulation bath depth is 30 cm;

[0080] Then the prepared hollow fiber membrane was immersed in deionized water for 48 hours, during which the deionized water was replaced twice, and dried to obtain an ultrafine hollow fiber membrane.

[0081] The outer diameter of the hollow fiber membrane prepared in this comparative example is 0.19 mm, and the wall thickness is 0.05 mm.

[0082] Performance Testing

[0083] The hollow fiber membranes obtained in the examples and comparative examples were tested for gas permeability, mechanical strength and pressure resistance.

[0084] The test method is as follows:

[0085] Gas separation performance: The prepared hollow fiber membrane was sealed with epoxy resin, and the gas separation performance was tested using gas chromatography.

[0086] Pressure resistance test: seal one end of the prepared hollow fiber membrane and pass high-pressure gas into the other end to test the pressure resistance performance. When the membrane can maintain a certain pressure for 30 minutes without damage, the pressure at this time is determined as the pressure resistance.

[0087] Mechanical strength test: The prepared hollow fiber membrane was cut into a certain length and subjected to a mechanical tensile performance test using a universal testing machine.

[0088] The test results are shown in Table 1.

[0089] Table 1

[0090]

[0091] From the above results, it can be seen that the ultrafine hollow fiber membrane prepared in the embodiment of the present invention has good oxygen / nitrogen selectivity, mechanical strength and pressure resistance.

[0092] It should be noted that the endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this article.

[0093] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "specific implementations", or "some specific implementations" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiment of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An ultrafine hollow fiber membrane, characterized in that: The ultrafine hollow fiber membrane is composed of a dense outer skin layer, a foam middle layer and a dense inner skin layer, and the dense outer skin layer, the foam middle layer and the dense inner skin layer are prepared by using a casting solution of the same composition, the casting solution includes a high molecular polymer, a pore former, a thickener and a solvent, and the mass percentage N% of the pore former in the casting solution, the mass percentage G% of the high molecular polymer and the mass percentage Z% of the thickener satisfy: Z=k*G / N, wherein k is a correction coefficient ranging from 0.1 to 0.8; The value range of N is 2-10, and the value range of G is 15-30.

2. The ultrafine hollow fiber membrane according to claim 1, characterized in that: The high molecular polymer is selected from one or more of polysulfone, polyethersulfone, polyaryletherketone, ethylcellulose and polyimide; The thickener is selected from one or more of polyvinyl pyrrolidone, water and ethanol.

3. The ultrafine hollow fiber membrane according to claim 2, characterized in that: The high molecular polymer is polysulfone; The thickener is polyvinyl pyrrolidone.

4. The ultrafine hollow fiber membrane according to claim 2, characterized in that: The number average molecular weight of the high molecular weight polymer is 50000-80000; The K value of the polyvinyl pyrrolidone is 90.

5. The ultrafine hollow fiber membrane according to any one of claims 1 to 4, characterized in that: The pore-forming agent is selected from one or more of polyethylene glycol and polyvinyl alcohol; The solvent is a mixture of one or more of N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide and water.

6. The ultrafine hollow fiber membrane according to any one of claims 1 to 4, characterized in that: The diameter (mm) of the ultrafine hollow fiber membrane satisfies: D=P*M, where P is the spinning pressure (MPa), ranging from 0.2 to 0.5 MPa, and M is the correction coefficient of the diameter, ranging from 0.36 to 1.2; The wall thickness H (mm) of the ultrafine hollow fiber membrane satisfies: H=X*D, wherein X is a correction coefficient of the wall thickness in the range of 0.3 to 0.

4.

7. The method for preparing the ultrafine hollow fiber membrane according to any one of claims 1 to 6, characterized in that: include: After the components of the casting solution are mixed to obtain the casting solution, a hollow fiber membrane embryo is prepared by a spinneret high pressure extrusion phase conversion method, and then the membrane is solidified; During the spinneret high-pressure extrusion phase inversion method, the spinning pressure P (MPa) and the phase inversion air gap L (cm) satisfy: P / L=S, where S is a correction coefficient in the range of 0.1 to 0.

2.

8. Use of the ultrafine hollow fiber membrane according to any one of claims 1 to 6 in gas separation.

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