Block polymer gas separation membrane with surface functional layer and preparation method thereof

Abstract

The invention belongs to the field of separation membranes and preparation thereof, and particularly relates to a block polymer gas separation membrane with a surface functional layer and a preparation method of the block polymer gas separation membrane. The separation membrane sequentially comprises a block polymer layer, a modified transition layer and a surface functional layer, the block polymer layer is a main body of the separation membrane, the modified transition layer plays a chemical bridging role, and the surface functional layer is composed of in-situ synthesized nanoscale inorganic particles on the basis of the modified transition layer. The preparation method comprises the following steps: preparing the block polymer layer by utilizing a melt extrusion method or a solution tape casting method based on the block polymer; carrying out chemical modification on the block polymer layer in a dopamine alkaline solution to form a modified transition layer; and placing the modified transition layer in the precursor solution, and synthesizing an inorganic functional layer on the surface of the membrane by using a hydrothermal method to obtain a target product. The invention has the advantages of environmental friendliness, thin thickness, good mechanical strength, strong stability, high gas permeation flux and ideal gas separation selectivity, and is easy to realize large-scale production.

Description

Technical Field

[0001] The invention belongs to the field of separation membranes and preparation thereof, and in particular relates to a block polymer gas separation membrane with a surface functional layer and a preparation method thereof. Background Art

[0002] The main component of natural gas is methane. As a clean and efficient energy source, natural gas occupies an important position in the global energy structure. During the extraction, transportation and utilization of natural gas, a variety of impurity gases such as carbon dioxide, nitrogen and hydrogen sulfide are produced. These impurities not only reduce the combustion calorific value of natural gas, but also cause corrosion to the transmission pipelines and equipment. Therefore, the purification process of natural gas is crucial.

[0003] Traditional natural gas purification methods mainly include adsorption, absorption and cryogenic separation. Although these methods can effectively remove impurities, they have problems such as high energy consumption, high cost and complex equipment. In contrast, membrane separation technology has received extensive attention and application in the field of gas separation due to its advantages such as low energy consumption, simple operation and compact equipment. As the core of membrane separation technology, gas separation membrane plays an important role in the separation of methane and other impurity gases.

[0004] In recent years, block polymer gas separation membranes have become a hot topic of research due to their excellent separation performance and high chemical stability. Simple block polymer membranes may cause the performance of the membrane to decline during use due to the movement of polymer segments. Especially in methane gas separation, how to improve the selectivity and stability of the membrane is an urgent problem to be solved. Current problems include: the trade-off between selectivity and permeability. Traditional membrane materials usually reduce permeability while improving selectivity, resulting in a decrease in overall separation efficiency; the stability of membrane materials. Polymer membranes are prone to aging, deformation or swelling during long-term use, resulting in a decrease in separation performance; mechanical strength and durability. The membrane needs to withstand a certain amount of pressure in actual applications, so the mechanical strength and durability of the membrane material are also key factors. Summary of the invention

[0005] The present invention aims to overcome the shortcomings of the prior art and provide a block polymer gas separation membrane with a surface functional layer which is environmentally friendly, thin, has good mechanical strength, strong stability, high gas permeation flux and ideal gas separation selectivity, and is easy to achieve large-scale production, and a preparation method thereof.

[0006] To solve the above technical problems, the present invention is achieved as follows: A block polymer gas separation membrane with a surface functional layer, the separation membrane comprises a block polymer layer, a modified transition layer and a surface functional layer in sequence, the three membrane layers are organically combined by chemical bonds to form a whole; the block polymer layer is the main body of the separation membrane, the modified transition layer plays a chemical bridging role, and the surface functional layer is composed of nanometer-scale inorganic particles synthesized in situ on the basis of the modified transition layer.

[0007] The method for preparing the block polymer gas separation membrane having a surface functional layer comprises the following steps: (1) Preparation of a block polymer layer: Based on the block polymer, a block polymer layer of a certain thickness is prepared by melt extrusion or solution casting; (2) chemical modification of the surface of the membrane layer, chemically modifying the block polymer layer in step (1) in a dopamine alkaline solution to form a modified transition layer; (3) In situ preparation of the surface functional layer, placing the modified transition layer obtained in step (2) in a precursor solution, and synthesizing an inorganic functional layer on the membrane surface by a hydrothermal method, thereby obtaining the target product, a block polymer gas separation membrane.

[0008] Furthermore, the block polymer layer is composed of styrene-butadiene-styrene triblock polymer, and is prepared by solution casting or melt extrusion, and the layer thickness ranges from 5 to 60 μm.

[0009] Furthermore, the modified transition layer is composed of polydopamine, which is obtained by oxidative self-polymerization of dopamine hydrochloride under alkaline conditions, and has a layer thickness of 0.1 to 0.5 μm.

[0010] Furthermore, the surface functional layer is a membrane layer formed by self-assembly after in-situ growth of inorganic particles, the layer thickness is 0.3-3 μm, and the material is zeolite material or metal organic framework material.

[0011] Furthermore, the block polymer gas separation membrane has an overall thickness of 5 to 100 μm and a mechanical strength of more than 20 MPa.

[0012] Furthermore, in step (1), the melt extrusion method is carried out using a twin-screw extruder, and the extrusion temperature is 80 to 150 o C.

[0013] Furthermore, in step (1), the mass concentration of the solution in the solution casting method is 5-30%, and the solvent is a mixed solvent of ethanol and tetrahydrofuran.

[0014] Furthermore, in step (2), the pH of the dopamine alkaline solution is 6 to 9, and the oxidative self-polymerization time is 1 to 5 hours.

[0015] Furthermore, the block polymer gas separation membrane has a tensile strength of 22 to 29 MPa; when separating a mixed gas of equal volumes of methane and nitrogen, the methane permeation flux of the membrane is 86 to 218 Barrer; and the separation selectivity of methane and nitrogen is 3 to 4.

[0016] The separation membrane prepared by the present invention has a thinner thickness and good mechanical strength. Compared with the pure block polymer membrane prepared by the traditional method, the separation membrane of the present invention has a higher gas permeation flux and a higher gas separation selectivity, and has great application potential in the field of methane gas separation. At the same time, the preparation technology of the present invention is simple and easy to implement, environmentally friendly, and easy to achieve large-scale production. The block polymer gas separation membrane with a surface functional layer obtained according to the above method is thinner in thickness, has a higher mechanical strength, and has no surface defects. It shows a higher gas permeation flux and separation factor, and has a lower material cost, which has a significant promoting effect on promoting the industrial application of methane gas separation composite membranes. The preparation method of the block polymer gas separation membrane of the present invention is simple in process, does not require special equipment, and can also be extended to the preparation of other types of gas separation membranes. DETAILED DESCRIPTION

[0017] The present invention will be described in detail below through specific examples. These examples are provided in order to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art. As mentioned throughout the specification and claims, "including" or "comprising" is an open term, interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present invention, but the description is based on the general principles of the specification and is not intended to limit the scope of the present invention. The scope of protection of the present invention shall be subject to the definition of the attached claims. Unless otherwise specified, the various reagents and materials used in the present invention can be purchased from the market. In the present invention, unless otherwise specified, the percentages involved are all mass percentages.

[0018] Example 1 A method for preparing a block polymer gas separation membrane having a surface functional layer comprises: Preparation of polymer film: SBS triblock polymer was dissolved in a mixed solvent of ethanol and tetrahydrofuran (volume ratio 1:1) to prepare a solution with a mass concentration of 25%. A polymer wet film with a thickness of 150 μm was scraped on a flat glass plate using a solution casting method. o C. After 6 h of drying, a polymer film with a thickness of about 20 μm was obtained.

[0019] Surface chemical modification: The polymer membrane with a size of 10 cm*10 cm was immersed in 500 ml of 2.5% dopamine hydrochloride solution, and the pH was adjusted to 8.5 by Tris buffer, and treated at room temperature for 3 hours. Dopamine self-polymerized on the membrane surface to form a polydopamine modified transition layer with a thickness of 0.1 μm. o C Dry and set aside.

[0020] In-situ preparation of the surface functional layer: 250 mL of deionized water and tetrahydrofuran were measured and mixed. Nickel nitrate hexahydrate (26.3 g) and 2, 5-dihydroxyterephthalic acid (12.2 g) were added thereto and stirred for 2 h to obtain a precursor solution. The chemically modified polymer membrane and 500 mL of the precursor solution were placed in a polytetrafluoroethylene hydrothermal reactor, sealed and reacted in a microwave at 120 ° C for 1.0 h to form a surface functional layer with a thickness of about 2.2 μm. After rinsing with deionized water and drying, a block polymer gas separation membrane with a surface functional layer was obtained.

[0021] Comparative Example 1 The polymer film obtained in step 1 is used as a comparative example, that is, it is not surface chemically modified and composited with a surface functional layer.

[0022] Performance test: The tensile strength of the invention membrane is 28.5 MPa, and the strength of the comparative membrane is 17.2 MPa. For separation of a 1:1 mixed gas of methane and nitrogen, the methane permeation flux of the invention membrane reaches 157.2 Barrer, and the methane / nitrogen separation selectivity is 3.8, while the methane permeation flux of the comparative membrane is 166.3 Barrer, and the methane / nitrogen separation selectivity is 1.2.

[0023] Example 2 A method for preparing a block polymer gas separation membrane having a surface functional layer comprises: Preparation of polymer film: SBS triblock polymer was dissolved in a mixed solvent of ethanol and tetrahydrofuran (volume ratio 1:1) to prepare a solution with a mass concentration of 8%. A polymer wet film with a thickness of 60 μm was scraped on a flat glass plate using a solution casting method and then heated for 120 min. o C. After 4 h of drying, a polymer film with a thickness of about 7 μm was obtained.

[0024] Surface chemical modification: The polymer membrane with a size of 10 cm*10 cm was immersed in 500 ml of 2.0% dopamine hydrochloride solution, and the pH was adjusted to 6.5 with Tris buffer, and treated at room temperature for 5 hours. Dopamine self-polymerized on the membrane surface to form a polydopamine modified transition layer with a thickness of 0.2 μm. o C Dry and set aside.

[0025] In-situ preparation of the surface functional layer: 250 mL of deionized water and tetrahydrofuran were measured and mixed. Nickel nitrate hexahydrate (16.5 g) and 2,5-dihydroxyterephthalic acid (10.7 g) were added thereto and stirred for 2 h to obtain a precursor solution. The chemically modified polymer membrane and 500 mL of the precursor solution were placed in a polytetrafluoroethylene hydrothermal autoclave, sealed and reacted at 100 ° C in a microwave for 6.0 h to form a surface functional layer with a thickness of about 1.5 μm. After rinsing with deionized water and drying, a block polymer gas separation membrane with a surface functional layer was obtained.

[0026] Comparative Example 2 The polymer film obtained in step 1 is used as a comparative example, that is, it is not surface chemically modified and composited with a surface functional layer.

[0027] Performance test: The tensile strength of the invention membrane is 22.1 MPa, and the strength of the comparative membrane is 10.6 MPa. For separation of a 1:1 mixed gas of methane and nitrogen, the methane permeation flux of the invention membrane reaches 217.6 Barrer, and the methane / nitrogen separation selectivity is 3.1, while the methane permeation flux of the comparative membrane is 348.5 Barrer, and the methane / nitrogen separation selectivity is 1.1.

[0028] Example 3 A method for preparing a block polymer gas separation membrane having a surface functional layer comprises: Polymer film preparation: The SBS triblock polymer was heated in a twin-screw extruder at 110°C. The block polymer film with a thickness of 45 μm was directly extruded by melt extrusion.

[0029] Surface chemical modification: The polymer membrane with a size of 10 cm*10 cm was immersed in 500 ml of 3.0% dopamine hydrochloride solution, and the pH was adjusted to 8.5 by Tris buffer, and treated at room temperature for 4 hours. Dopamine self-polymerized on the membrane surface to form a polydopamine modified transition layer with a thickness of 0.3 μm. o C Dry and set aside.

[0030] In-situ preparation of the surface functional layer: 250 mL of deionized water and tetrahydrofuran were measured and mixed. Nickel nitrate hexahydrate (23.5 g) and 2,5-dihydroxyterephthalic acid (12.3 g) were added thereto and stirred for 2 h to obtain a precursor solution. The chemically modified polymer membrane and 500 mL of the precursor solution were placed in a polytetrafluoroethylene hydrothermal autoclave, sealed and reacted in a microwave at 100 ° C for 6.0 h to form a surface functional layer with a thickness of about 3.0 μm. After rinsing with deionized water and drying, a block polymer gas separation membrane with a surface functional layer was obtained.

[0031] Comparative Example 2 The polymer film obtained in step 1 is used as a comparative example, that is, it is not surface chemically modified and composited with a surface functional layer.

[0032] Performance test: The tensile strength of the invention membrane is 25.6 MPa, and the strength of the comparative membrane is 12.5 MPa. For separation of a 1:1 mixed gas of methane and nitrogen, the methane permeation flux of the invention membrane reaches 85.8 Barrer, and the methane / nitrogen separation selectivity is 3.9, while the methane permeation flux of the comparative membrane is 125.2 Barrer, and the methane / nitrogen separation selectivity is 1.6.

[0033] The results of the examples show that the block polymer gas separation membrane with a surface functional layer and the preparation method thereof provided by the present invention overcome the difficulties in the balance between the structure and gas permeability of traditional methane separation composite membrane materials. By introducing the surface functional layer, the present invention can effectively regulate the mechanical properties, surface gas screening properties and free volume in the separation membrane, ensure that the separation membrane has sufficient mechanical strength, and avoid deformation defects of the membrane layer caused by factors such as pressure. In addition, the membrane preparation method of the present invention is simple and suitable for mass production, providing a reliable guarantee for the development of low-concentration methane separation and enrichment technology.

[0034] It is understandable that, for ordinary technicians in this field, various other corresponding changes and extensions can be made based on the technical methods of the present invention, and all these changes and extensions should fall within the protection scope of the claims of the present invention.

Claims

1. A block polymer gas separation membrane having a surface functional layer, characterized in that: The separation membrane includes a block polymer layer, a modified transition layer and a surface functional layer in sequence, and the three membrane layers are organically combined to form a whole; the block polymer layer is the main body of the separation membrane, the modified transition layer plays a chemical bridging role, and the surface functional layer is composed of nano-scale inorganic particles synthesized in situ on the basis of the modified transition layer.

2. The method for preparing a block polymer gas separation membrane having a surface functional layer according to claim 1, characterized in that: The steps include: (1) Preparation of a block polymer layer: Based on the block polymer, a block polymer layer of a certain thickness is prepared by melt extrusion or solution casting; (2) chemical modification of the surface of the membrane layer, chemically modifying the block polymer layer described in step (1) in a dopamine alkaline solution to form a modified transition layer; (3) In situ preparation of the surface functional layer: placing the modified transition layer obtained in step (2) in a precursor solution, and synthesizing an inorganic functional layer on the membrane surface by a hydrothermal method to obtain the target product, a block polymer gas separation membrane.

3. The method for preparing a block polymer gas separation membrane having a surface functional layer according to claim 2, characterized in that: The block polymer layer is composed of styrene-butadiene-styrene triblock polymer and is prepared by solution casting or melt extrusion. The layer thickness ranges from 5 to 60 μm.

4. The method for preparing a block polymer gas separation membrane having a surface functional layer according to claim 3, characterized in that: The modified transition layer is composed of polydopamine and is obtained by oxidative self-polymerization of dopamine hydrochloride under alkaline conditions. The layer thickness is 0.1 to 0.5 μm.

5. The method for preparing a block polymer gas separation membrane having a surface functional layer according to claim 4, characterized in that: The surface functional layer is a membrane layer formed by self-assembly after in-situ growth of inorganic particles, with a layer thickness of 0.3 to 3 μm and made of zeolite material or metal organic framework material.

6. The method for preparing a block polymer gas separation membrane having a surface functional layer according to claim 5, characterized in that: The block polymer gas separation membrane has an overall thickness of 5 to 100 μm and a mechanical strength greater than 20 MPa.

7. The method for preparing a block polymer gas separation membrane having a surface functional layer according to claim 2, characterized in that: In step (1), the melt extrusion method is carried out using a twin-screw extruder, and the extrusion temperature is 80-150 o C.

8. The method for preparing a block polymer gas separation membrane having a surface functional layer according to claim 2, characterized in that: In step (1), the mass concentration of the solution in the solution casting method is 5-30%, and the solvent is a mixed solvent of ethanol and tetrahydrofuran.

9. The method for preparing a block polymer gas separation membrane having a surface functional layer according to claim 2, characterized in that: In step (2), the pH of the dopamine alkaline solution is 6 to 9, and the oxidative self-polymerization time is 1 to 5 hours.

10. The method for preparing a block polymer gas separation membrane having a surface functional layer according to any one of claims 1 to 9, characterized in that: The block polymer gas separation membrane has a tensile strength of 22 to 29 MPa. When separating a mixed gas of equal volumes of methane and nitrogen, the membrane has a methane permeation flux of 86 to 218 Barrers. The separation selectivity of methane and nitrogen is 3 to 4.