Carbon capture membrane with high hydrothermal stability, high temperature resistance and high gas flux as well as preparation method and application of carbon capture membrane

Abstract

The invention belongs to the technical field of gas separation membranes, and particularly relates to a high-hydrothermal-stability, high-temperature-resistant and high-gas-flux carbon capture membrane as well as a preparation method and application of the high-hydrothermal-stability, high-temperature-resistant and high-gas-flux carbon capture membrane. The method comprises the following steps: coating and spreading a polydimethylsiloxane (PDMS) membrane casting solution on a porous support membrane, and heating to cure and crosslink the porous support membrane to obtain a PDMS composite membrane; and carrying out surface treatment on the PDMS composite film by adopting ultraviolet ozone or atmospheric plasma, so that the surface of the PDMS is converted into an organic SiO2 (POSi) layer through oxidation reaction, and the carbon capture film is obtained. The preparation process of the carbon capture membrane provided by the invention is simple and easy to implement and relatively low in cost, the preparation process can be completed under normal pressure, and the prepared carbon capture membrane has the characteristics of high hydrothermal stability, high temperature resistance and high gas flux and selectivity when being used for gas separation.

Description

Technical Field

[0001] This application belongs to the technical field of gas separation membranes. More specifically, it relates to a carbon capture membrane with high hydrothermal stability, high temperature resistance, and high gas flux, and its preparation method and application. Background Art

[0002] As the world's largest coal-consuming country, China currently mainly relies on coal-fired power generation. Coal-fired power plants are the main sources of greenhouse gas emissions in China. Therefore, capturing and sequestering CO 2 from coal-fired power plants is an important technical means to address climate change and reduce greenhouse gas emissions. Developing efficient and low-energy-consuming CO 2 capture technologies has important practical significance.

[0003] CO 2 capture technologies in coal-fired power plants mainly include three technical routes: pre-combustion capture, post-combustion capture, and oxy-fuel combustion. Among them, pre-combustion capture is mainly applied to the integrated gasification combined cycle (IGCC) power generation technology. IGCC power generation technology is a new type of clean coal power generation method that can reduce environmental pollution while improving power generation efficiency, effectively contributing to the realization of carbon emission reduction goals. During the IGCC power generation process, it is necessary to separate and purify H 2 from the gas (H 2 、CO 2 mixed gas) generated after coal gasification and shift, and then use clean energy H 2 to replace coal for combustion power generation. Currently, the technologies used for H 2 / CO 2 separation mainly include absorption method, adsorption method, low-temperature condensation method, and membrane separation method. Membrane separation method has been widely used in H 2 / CO 2 separation due to its high separation efficiency, low energy consumption, small carbon footprint, and easy industrial scale-up.

[0004] Industrial gas separation membranes are mainly made of polymers with good processability and scalability. However, polymers are limited by their inherent trade-off effect, and it is difficult to simultaneously consider the permeability and selectivity of thin films. In addition, when the temperature of the gas is above 150 °C, most polymer membranes will lose their gas separation ability at this temperature. Inorganic membranes can be applied to separate H 2 / CO 2 at high temperatures due to their high temperature resistance, strong chemical inertness, ultra-micropores, and molecular sieving ability. Existing materials include: MOF, two-dimensional MXene, g-C 3 N 4 、GO、SiO 2 、carbon molecular sieve, zeolite, etc.

[0005] Among various inorganic membrane materials, SiO 2 membrane has a unique porous structure, excellent separation performance, and high-temperature resistance, and is expected to be applied to the efficient separation of CO from gas 2 to obtain purified H 2 . However, when water vapor exists in the high-temperature raw gas, the network structure of the SiO 2 membrane is prone to hydrolysis and collapse, thereby reducing gas permeability and selectivity. Currently, relevant literature reports have been made on methods such as metal doping, surface modification, and introduction of organic functional groups to improve the problem of hydrophilic nanopore collapse of the SiO 2 membrane during actual application.

[0006] However, whether it is a traditional inorganic SiO 2 membrane or a SiO 2 membrane obtained by doping metal ions and organic functional groups to improve hydrothermal stability, it ultimately needs to be calcined at high temperature for preparation, requires expensive inorganic ceramic membranes as the support layer, and it is difficult to mass-produce defect-free membranes. There has been research dedicated to treating PDMS with oxygen plasma at room temperature, and an organic SiO 2 membrane can be obtained in a short time. This method combines the simple preparation of polymer membranes and the efficient H 2 / CO 2 separation performance of inorganic membranes, reduces the high energy consumption generated during the preparation process of traditional SiO 2 membranes, and at the same time, a part of organic groups such as methyl groups are retained inside the SiO 2 network structure during the oxidation process, enhancing the hydrothermal stability of the membrane. This method of oxidizing and modifying polymers can greatly simplify the preparation process of the SiO 2 membrane. However, during the modification process of oxygen plasma, a strict vacuum environment needs to be controlled, the preparation process conditions are harsh, and it is difficult to scale up for industrial applications. Therefore, a preparation method for a high-throughput SiO 2 membrane with high hydrothermal stability and easy industrial scale-up is required. Summary of the Invention

[0007] Aiming at the deficiencies of the prior art, the purpose of this application is to provide a carbon capture membrane with high hydrothermal stability, high temperature resistance, and high gas flux, and its preparation method and application, aiming to solve the technical problems that the POSi membranes prepared by existing methods are difficult to scale up for industrial production and have poor hydrothermal stability.

[0008] To achieve the above purpose, in the first aspect, this application provides a preparation method for a carbon capture membrane with hydrothermal stability, including the following steps: (1) Coat and spread the PDMS (polydimethylsiloxane) casting solution on the porous support layer. The PDMS adheres to the porous support layer and is then heated to cure and crosslink to obtain a PDMS composite membrane. (2) Use ultraviolet ozone or atmospheric plasma to perform surface treatment on the PDMS composite membrane obtained in step (1), so that the surface of the PDMS is converted into an organic SiO 2 layer through an oxidation reaction, that is, the carbon capture membrane is obtained; the Si-O-Si network structure of the organic SiO 2 layer contains organic groups, and the organic SiO 2 layer serves as the selective layer of this carbon capture membrane.

[0009] Preferably, in step (2), ultraviolet ozone treatment is used, specifically carried out in an ultraviolet ozone treatment chamber. The distance between the PDMS composite membrane and the ultraviolet lamp in the ultraviolet ozone treatment chamber is 2 - 10 mm. Oxygen is introduced into the ultraviolet ozone treatment chamber, and the flow rate of oxygen is controlled to be 100 - 150 mL / min, and the treatment time is 30 - 60 min.

[0010] Preferably, in step (2), atmospheric plasma treatment is used, specifically, the PDMS composite membrane is treated with an atmospheric plasma cleaner. The working distance is 10 - 30 mm, the moving speed of the robotic arm is 20 - 30 mm / s, the system power is 0.8 - 1 kW, and the number of treatment times is 8 - 12 times.

[0011] According to another aspect of the present invention, there is provided a carbon capture membrane prepared by the described preparation method.

[0012] Preferably, the carbon capture membrane includes a three-layer structure. The bottom layer is a porous support membrane, the middle layer is a PDMS membrane, and the top layer is an organic SiO 2 layer, that is, a POSi selective layer. The carbon capture membrane of the present invention does not require an additional preparation of a selective layer.

[0013] Further preferably, the C / Si atomic ratio in the POSi selective layer is 0.3 - 0.5, and the O / Si atomic ratio is 1.9 - 2.3.

[0014] According to another aspect of the present invention, there is provided the application of the described carbon capture membrane in gas separation.

[0015] Generally speaking, compared with the prior art through the above technical solutions conceived by the present application, the following beneficial effects are obtained: (1) The present invention uses ultraviolet ozone or atmospheric plasma to perform surface oxidation modification on the PDMS membrane, converting the surface of the PDMS membrane into a POSi membrane through an oxidation reaction to obtain the carbon capture membrane, also known as the POSi composite membrane. And the directly oxidized POSi layer after the modification treatment is used as the selective layer of the composite membrane without the need to additionally prepare a selective layer, obtaining a high gas flux POSi carbon capture membrane with high hydrothermal stability. The preparation process of the high gas flux POSi composite membrane of the present invention is simple and feasible, and the cost is relatively low; the oxidation modification method in the present invention can be completed under normal pressure, which is easy to scale up for large-scale industrial production.

[0016] (2) The prior art requires sintering at a high temperature (>600 °C) to prepare an inorganic SiO 2 membrane, which has strict requirements for the support membrane and requires expensive inorganic ceramic membranes. The present invention uses ultraviolet ozone treatment on the PDMS intermediate layer, and by controlling appropriate oxidation process parameters, its surface layer is converted into a POSi structure, without the need to select expensive support layer materials, and the oxidation process can be completed under normal pressure, and the energy consumption in the process of preparing the high gas flux POSi composite membrane is low.

[0017] (3) The present invention uses atmospheric plasma to treat the PDMS intermediate layer to convert its surface into a POSi membrane, and a high gas flux POSi composite membrane can be rapidly prepared at normal temperature and pressure. The spray gun for releasing plasma can move back and forth, and the membrane area that can be processed is large.

[0018] (4) For the POSi composite membrane obtained by treating the PDMS intermediate layer with atmospheric plasma in the present invention, at a test temperature of 150 °C, the H 2 flux of the prepared POSi composite membrane is 159 GPU, and the selectivity of the H 2 / CO 2 mixed gas is 17; for the POSi composite membrane obtained by treating the PDMS intermediate layer with ultraviolet ozone in the present invention, under a high temperature test of 200 °C, the H 2 flux of the prepared POSi composite membrane is as high as 930 GPU, and the selectivity of the H 2 / CO 2 mixed gas is as high as 37, which is higher than that of the vast majority of polymer membrane materials.

[0019] (5) The high gas flux POSi composite membrane in the present invention is obtained by oxidizing the PDMS intermediate layer. While oxidizing into a SiO 2 network structure, a part of organic groups such as -CH 3 etc. are retained, making it have better hydrothermal stability than traditional inorganic SiO 2 membranes, and the presence of water vapor during the test will not affect its gas separation performance. Brief Description of the Drawings

[0020] Figure 1 Schematic diagram of the POSi composite film prepared in Example 1 of the present invention.

[0021] Figure 2 Content (a) is the scanning electron microscope photograph of the surface of the AAO support layer in Example 1, Figure 2 Content (b) is the scanning electron microscope photograph of the surface of the PDMS / AAO composite film prepared in Example 1; Figure 2 Content (c) and content (d) are the cross-sections of AAO and the PDMS / AAO composite film respectively.

[0022] Figure 3 Content (a) is the whole process of preparing the POSi composite film from the AAO film to the PDMS intermediate layer and then through oxidation treatment in Example 1, Figure 3 Content (b) is the schematic diagram of the ultraviolet ozone oxidation treatment process in Example 1 and the schematic diagrams of each layer of the finally obtained POSi composite film, Figure 3 Content (c) is the schematic diagram of the conversion of the PDMS surface layer to the POSi layer during the ultraviolet ozone oxidation treatment process in Example 1.

[0023] Figure 4 It is the performance characterization diagram of the POSi composite film prepared in Example 1. Among them, Figure 4 Content (a) is the graph of the change of the water contact angle on the PDMS surface with the ultraviolet ozone treatment time, Figure 4 Content (b) is the graph of the recovery of the water contact angle on the surface of the POSi30 film that has been treated for 30 minutes after being placed in the air for a period of time, Figure 4 Content (c) is the graph of the change of C, O, and Si elements on the PDMS surface with the ultraviolet ozone treatment time, Figure 4 Content (d) is the surface XPS fine spectra of PDMS and POSi samples obtained at different treatment times.

[0024] Figure 5 It is the gas permeation test diagram of the POSi composite film prepared in Example 1. Among them, Figure 5 Content (a) is the change of the gas separation performance of the POSi30 film with the test temperature, Figure 5 Content (b) is the hydrothermal stability test diagram of the POSi30 film, Figure 5 Content (c) is the long-term stability test diagram of the POSi30 film under high temperature and high pressure, Figure 5 Content (d) is the performance comparison diagram of the POSi30 film and other excellent membrane materials.

[0025] Figure 6 It is the gas flux and separation performance test diagram of the POSi9 composite film prepared in Example 2. Detailed implementation manners

[0026] In order to make the objectives, technical solutions and advantages of the present application more clear and understandable, the present application will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0027] The embodiments of the present invention are implemented on the premise of the technical solution of the present invention, and the detailed implementation manners and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. For the process parameters without specific conditions noted in the following embodiments, they are usually in accordance with conventional conditions.

[0028] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they 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 the present invention.

[0029] A carbon capture membrane with high hydrothermal stability, high temperature resistance and high gas flux provided by the present invention (also referred to as POSi composite membrane in the present invention) includes a porous support layer, a PDMS intermediate layer, and a POSi layer obtained by surface modification of the PDMS intermediate layer; the preparation method of the carbon capture composite membrane includes the following steps: (1) Coating and spreading the PDMS casting solution on the porous support membrane, the PDMS adheres to the porous support membrane, and then heating it to cure and crosslink to obtain a PDMS composite membrane; (2) Using ultraviolet ozone or atmospheric plasma to perform surface treatment on the PDMS composite membrane in step (1), so that the surface of the PDMS membrane is converted into a POSi layer through an oxidation reaction, that is, the carbon capture membrane is obtained; the Si-O-Si network structure of the POSi layer contains organic groups, so it is also called organic SiO 2 layer; and the POSi layer serves as the selective layer of the carbon capture membrane to improve the gas separation performance of the carbon capture membrane.

[0030] The organic SiO 2 layer mentioned in the present invention, also called the POSi layer, is a type of SiO 3 membrane layer whose Si-O-Si network structure contains organic groups such as -CH 2 and -CH 2 OH. The traditional SiO 2 membrane needs to be calcined at high temperature, while the organic SiO 2 membrane layer in the present invention can be prepared under normal temperature and pressure.

[0031] In some embodiments, the preparation of the PDMS casting solution includes the following steps: S1: Mix and stir PDMS monomer, crosslinking agent, catalyst and organic solvent to obtain a prepolymer solution; S2: Stir the prepolymer solution obtained in step S1 at 25 - 35 °C to cause hydrolysis and polycondensation reaction to obtain the PDMS casting solution.

[0032] In some embodiments, the crosslinking agent is tetraethyl orthosilicate (TEOS); the catalyst is dibutyltin dilaurate (DBTDL), and the organic solvent is n - heptane or n - hexane.

[0033] In some embodiments, the concentration of the PDMS prepolymer solution in step S1 is 0.2 wt% - 1.5 wt%; experiments have found that this concentration should not be too low. When the concentration of the prepolymer solution is too low, the solution viscosity is low, and it is extremely easy to penetrate into the porous support layer, making it difficult to form a complete and defect - free PDMS intermediate layer on it for subsequent oxidation modification treatment. The mass ratio of the PDMS monomer to the crosslinking agent and the catalyst is 10:(1 - 7):(1 - 7); the molecular weight of the PDMS monomer is 15 - 90 KDa, preferably 50 - 90 KDa.

[0034] In some embodiments, during the stirring process of step S2, the viscosity of the PDMS prepolymer solution is monitored simultaneously, and when its viscosity reaches 6 - 10 cp, the reaction is stopped.

[0035] In some embodiments, the coating methods include spin - coating, blade - coating, dip - coating, etc.

[0036] In some embodiments, use a pipette to aspirate 200 - 300 μL of the PDMS casting solution with a viscosity of 6 - 10 cp onto the porous support layer, and use a spin coater to completely spread out the solution.

[0037] In some embodiments, when step (2) is treated with ultraviolet ozone, the porous support membrane in step (1) can be anodic aluminum oxide film (AAO), polytetrafluoroethylene membrane (PTFE), polybenzimidazole membrane (PBI), etc. Considering that subsequent tests need to be carried out at a high temperature (200 °C) and taking economic factors into comprehensive consideration, the porous support membrane in step (1) is preferably an AAO membrane. The AAO membrane has regularly arranged straight through - holes, a high porosity, and a high gas flux; the pore diameter of the preferred AAO membrane is 110 - 150 nm.

[0038] When treating the PDMS membrane with oxygen plasma, the preparation process needs to be completed under vacuum conditions, and the volume of the vacuum chamber is small, making it difficult for large-scale industrial production. The present invention uses atmospheric plasma oxidation to prepare the POSi composite membrane, which is not limited by the size of the vacuum chamber and vacuum conditions, and can prepare the POSi composite membrane in a large area. In some embodiments, when treating with atmospheric plasma, the porous support membrane can be polysulfone ultrafiltration membrane (PSF), PBI membrane, PTFE membrane, etc., to meet the requirements of preparing the POSi composite membrane by large-area treatment with atmospheric plasma.

[0039] When the present invention uses atmospheric plasma to treat the PDMS membrane, it is found in the experiment that since strong airflows will be generated when the plasma is released, if the AAO membrane is used as the support layer, it may cause damage to the AAO membrane, and the area of the commercial AAO membrane is small, and a large-area PDMS layer cannot be prepared thereon. Therefore, through a large number of attempts, materials such as PSF, PBI or PTFE are finally used as the support layer, which can be applied to the preparation of the POSi composite membrane by atmospheric plasma treatment.

[0040] In some embodiments, to prevent the PDMS casting solution from infiltrating into the pores of the support membrane, before spin coating, the surface of the porous support layer is wetted with organic solvents such as n-heptane and n-hexane to block its straight-through pores.

[0041] In some embodiments, the surface of the porous support layer is wetted with n-heptane for 2 - 3 min to block its straight-through pores.

[0042] In some embodiments, in step (1), heating to cure and crosslink, the heating temperature is 60 - 80 °C, and the heating time is 1 - 2 hours.

[0043] In some embodiments, step (2) is treated with ultraviolet ozone, specifically in an ultraviolet ozone treatment chamber. The ultraviolet ozone treatment chamber includes but is not limited to an ultraviolet ozone cleaning chamber / machine, an ultraviolet ozone disinfection chamber, etc.; the distance between the PDMS composite membrane and the ultraviolet lamp at the top of the ultraviolet ozone treatment chamber is 2 - 10 mm, and oxygen is introduced into the ultraviolet ozone treatment chamber, and the flow rate of oxygen is 100 - 150 sccm, and the treatment time is 30 - 60 min. Appropriate parameters ensure an appropriate degree of surface modification, so that the prepared composite membrane has a high gas flux and excellent gas separation performance. The present invention utilizes the synergistic effect of ultraviolet light, O 3 and O 3 decomposition to generate O atoms to jointly oxidize the PDMS surface layer and perform surface modification on it.

[0044] When preparing the POSi composite membrane by treating the PDMS intermediate layer with oxygen plasma oxidation, the oxidation intensity is usually high, and appropriate process parameters need to be controlled. Otherwise, over-treatment is likely to occur, resulting in too low gas flux of the composite membrane. The principles of ultraviolet ozone, atmospheric plasma, and oxygen plasma are different when treating the PDMS membrane. It is speculated that during the ultraviolet ozone treatment, the active oxygen atoms generated by the decomposition of ozone under ultraviolet light irradiation are used for oxidation. During the oxygen plasma treatment, oxygen plasma is used for oxidation, while during the atmospheric plasma treatment, both oxygen plasma and nitrogen plasma in the atmosphere are used. In particular, when using atmospheric plasma treatment, it is not clear what kind of influence the nitrogen plasma has on the formation of the POSi membrane.

[0045] The principle of ultraviolet ozone treatment is as follows: Through the irradiation of ultraviolet light with wavelengths of 185 nm and 254 nm, the ultraviolet light with a wavelength of 185 nm causes the oxygen in the air to undergo a photochemical reaction and be converted into ozone, while the ultraviolet light with a wavelength of 254 nm causes the ozone to decompose to generate active oxygen atoms. It is speculated that these active oxygen atoms have strong oxidation ability, and the photon energies of these two specific wavelengths can directly open and cut the covalent bonds in organic molecules, activate the organic molecules, and decompose them into ions and free atoms. Under the synergistic action of oxygen atoms and ultraviolet light irradiation, the PDMS intermediate layer of the present invention is converted into a POSi layer.

[0046] In some embodiments, step (2) is carried out by using atmospheric plasma, specifically, the PDMS intermediate layer is treated with an atmospheric plasma cleaner, the working distance is 30 - 40 mm, the moving speed of the robotic arm is 20 - 30 mm / s, the system power is 0.8 - 1 kW, and the number of treatment times is 8 - 12 times.

[0047] In the present invention, the surface of the PDMS intermediate layer is oxidized and modified by ultraviolet ozone or atmospheric plasma, so that the surface layer of the PDMS layer is converted into a POSi layer through an oxidation reaction. It is found in the experiment that in the preferred embodiment, the C / Si atomic ratio in the modified POSi selective layer is 0.3 - 0.5, and the O / Si atomic ratio is 1.9 - 2.3. When the prepared carbon capture membrane is used for gas separation, it has high hydrothermal stability, relatively high gas flux, and excellent gas separation performance.

[0048] The principle of atmospheric plasma treatment is as follows: Air is introduced into the instrument. After the gas enters the high-voltage electric field, it is ionized into a plasma state, and then the subsequent gas blows the plasma to the surface to be treated for activation treatment.

[0049] Atmospheric plasma treatment method: Place the prepared PDMS composite membrane on the workbench, set the relevant parameters, turn on the operating mode of the robotic arm, and eject plasma from the plasma spray gun below the robotic arm onto the surface of the thin film to in-situ prepare a POSi film on the surface of the PDMS thin film (the surface layer PDMS is transformed into POSi). Advantages of atmospheric plasma: The preparation of the POSi film can be achieved within half a minute, and the thin film modification is carried out by moving the robotic arm back and forth, with a large treatment area, and the efficient preparation of the composite film can be realized under normal temperature and pressure.

[0050] During the process of gas molecules passing through the composite membrane, most of the mass transfer resistance occurs in the selective layer at the top of the composite membrane. In the preferred embodiment of the present invention, the POSi composite membrane obtained by ultraviolet ozone oxidation has higher gas flux and gas separation performance compared to the inorganic SiO 2 membrane prepared in previous studies.

[0051] The carbon capture membrane prepared by the present invention consists of a three-layer structure, with a porous support membrane at the bottom layer, a PDMS membrane in the middle layer, and an organic SiO 2 layer obtained by surface modification of the PDMS middle layer with ultraviolet ozone or atmospheric plasma in the present invention, that is, a POSi selective layer. The carbon capture membrane of the present invention does not require an additional preparation of a selective layer.

[0052] The present invention discloses a preparation method of a high-throughput POSi composite membrane with high hydrothermal stability. The preparation process of the method of the present invention is simple, easy to operate, low-cost, and low-energy-consuming. The prior art needs to be processed in a vacuum or sintered at a high temperature (>600 °C), while the POSi membrane obtained by the present invention can be quickly obtained under normal pressure. The H 2 flux of the POSi30 composite membrane prepared in the preferred embodiment of the present invention is as high as 930 GPU, and the separation performance for H 2 / CO 2 is as high as 37. The molecular structure of the POSi composite membrane obtained by the method of the present invention retains a part of organic groups such as methyl, so that it can still maintain good hydrothermal stability in the presence of water vapor.

[0053] For the process parameters without specific conditions noted in the following examples, they are usually in accordance with conventional conditions.

[0054] The materials, reagents, etc. used in the following examples can be obtained from commercial sources without special instructions.

[0055] The H 2 and CO 2The gas permeation data was measured by a gas permeation meter. Under the test conditions of 2 - 6 bar and 150 - 200 °C, the component distribution in the binary gas mixture was analyzed using a gas chromatograph. In the experiment, water vapor was injected into the feed gas through a bubbler to make the water vapor content in the inlet gas reach 1.5 mol%. During the permeation measurement, CH 4 was used as the purge gas, and the flow rate control range was 25 - 150 sccm.

[0056] The PDMS used in the following examples had a molecular weight of 90 KDa, a concentration of 100%, was in a viscous state, and had a viscosity of 200 Wcst. To facilitate its mixing with the crosslinking agent and catalyst, it was pre-diluted with n-heptane to 5 wt% in advance to make it liquid.

[0057] The embodiments of the present application will be described below with reference to the accompanying drawings in the embodiments of the present application.

[0058] Example 1 UV / O 3 Oxidation to prepare the POSi composite membrane 1. Preparation of the PDMS casting solution: 1.1 Control the mass ratio of 5 wt% PDMS (molecular weight 90 KDa), TEOS, DBTDL, and n-heptane to be 1.5:0.0375:0.0375:3.425. After mixing, a 1.5 wt% PDMS prepolymer raw material with a total mass of 5 g, namely the PDMS prepolymer solution, was obtained.

[0059] 1.2 Place the prepolymer solution in a water bath at 30 °C and stir while heating to further crosslink it. The viscosity of the solution was monitored using a digital rotational viscometer to prevent overreaction and crosslinking into a gel-like substance.

[0060] 1.3 When the viscosity of the prepolymer solution reached 6 - 7 cp, stop stirring and heating in the water bath at this time, and the PDMS casting solution can be obtained.

[0061] 2. Preparation of the PDMS intermediate layer: 2.1 Drop n-heptane onto the AAO and soak it for 3 min. The solution fills the straight through holes of the AAO to prevent possible pore penetration during the spin coating process.

[0062] 2.2 Take 200 μL of the PDMS casting solution and spin coat it onto the AAO substrate film at a speed of 3000 rpm.

[0063] 2.3 Cure in an oven at 80 °C for more than 2 hours to obtain the PDMS / AAO composite membrane.

[0064] 3. Preparation of the POSi composite membrane: 3.1 Place the PDMS composite membrane, i.e., the PDMS / AAO composite membrane, into an ultraviolet ozone cleaning machine, and control the distance between the composite membrane and the ultraviolet lamp tube to be 5 mm.

[0065] 3.2 Introduce oxygen into the ultraviolet ozone cleaning machine, and control its flow rate at 150 sccm.

[0066] 3.3 Treat the sample for 30 min to obtain a POSi composite membrane with a dense selective layer.

[0067] The schematic diagram of the POSi composite membrane prepared in this example is as Figure 1 shown. It consists of a three-layer structure: the bottom layer is the AAO support layer (substrate membrane), and the material of this layer has high mechanical strength and a large pore size, and occupies the largest thickness in the membrane structure; the middle layer is the PDMS membrane, which is relatively thin and has a moderate gas permeation resistance, used to fill the possible defects on the surface of the support layer and provide a smooth surface for the preparation of the selective layer; the top layer is the selective layer obtained by surface modification of the PDMS middle layer with ultraviolet ozone in this example. Its thickness is extremely thin and the gas permeation resistance is large, playing a role in screening different gas molecules. This composite membrane can be directly used for separating mixed gases without the need to additionally prepare a selective layer.

[0068] The surface scanning electron microscope image of the AAO substrate membrane is as Figure 2 shown in content (a). The surface scanning electron microscope photograph of the PDMS / AAO composite membrane prepared in this example is as Figure 2 shown in content (b). It can be seen from this figure that PDMS is uniformly loaded on the AAO substrate membrane through the method of the present invention, completely covering the honeycomb-shaped pores on the AAO substrate membrane. Figure 2 Contents (c) and (d) are respectively the cross-sectional images of AAO and the PDMS / AAO composite membrane. It can be seen that a PDMS thin film with a thickness of about 350 nm is successfully prepared on the AAO substrate membrane by spin coating.

[0069] The N 2 flux of the PDMS / AAO composite membrane prepared in this example is 338 GPU, and the CO 2 flux is 3375 GPU. The separation performance of CO 2 / N 2 is 10.1.

[0070] Figure 3 Content (a) shows the preparation flow chart of the POSi composite membrane in this example, including the spin coating preparation of the PDMS middle layer and the preparation of the POSi composite membrane by ultraviolet ozone modification. Figure 3 Content (b) shows the situation of each layer of the composite membrane. Figure 3Content (c) shows a schematic diagram of the mechanism of ultraviolet ozone modification of the PDMS membrane. The O atoms generated after ozone is irradiated by an ultraviolet lamp convert Si-CH 3 to Si-OH, and then a part of Si-OH dehydrates to form a dense Si-O-Si network structure.

[0071] Figure 4 As shown in Content (a), with the increase of the treatment time, the surface of PDMS gradually changes from hydrophobic to hydrophilic; however, after the POSi sample is exposed to air for a long time, due to the movement of the short chains of the underlying PDMS to the surface, its surface contact angle will gradually recover, but it is always lower than the contact angle of the PDMS sample before treatment, as Figure 4 shown in Content (b). Figure 4 Contents (c) and (d) are the XPS characterizations of the samples. Figure 4 Content (c) shows that with the increase of the ultraviolet ozone treatment time, the content of C element on the surface of the POSi sample gradually decreases, and the content of O element increases, which confirms the transformation of Si-CH 3 to the Si-O-Si structure. When the treatment times are 0, 15, and 30 minutes respectively, the C / Si atomic ratios are 2.35, 0.92, and 0.43 in turn; the corresponding O / Si atomic ratios are 0.91, 1.93, and 2.20 respectively. Within the first 30 minutes of treatment time, the O / Si atomic ratio shows a rapid upward trend. However, when the treatment time is further extended to 90 minutes, the C / Si atomic ratio only decreases by 0.10, and the O / Si atomic ratio only increases by 0.11. This result indicates that with the extension of the treatment time, the diffusion of O atoms into the deep structure of PDMS is restricted. Figure 4 It can also be seen from Content (d) that with the increase of the treatment time, the peak amplitude of Si(-O) 2 of the POSi sample decreases, and a typical Si(-O) 2 peak of SiO 4 appears, and the C-O peak also appears from nothing to something, which confirms the transformation of the PDMS surface layer to the SiO 2 structure.

[0072] Figure 5 shows the gas permeation test results of the POSi30 membrane (indicating the POSi composite membrane obtained after treating the PDMS intermediate layer with ultraviolet ozone for 30 min), Figure 5 Content (a) is about the relationship between the test temperature and the gas flux and separation performance. With the increase of the test temperature, both the gas flux and the gas separation performance increase. To confirm that POSi30 has high hydrothermal stability, 1.5 mol% of water vapor is introduced into the feed gas. As Figure 5 shown in Content (b), the gas permeation performance still remains stable. To confirm the industrial application prospect of the composite membrane, its long-term stability test is carried out under high temperature and high pressure.Figure 5 As shown in content (c), the performance of the composite membrane remained stable under the test conditions of 200 °C and 6 bar. Figure 5 In content (d), the prepared POSi30 in this example was compared with the current research work, which proved that the prepared composite membrane had excellent performance and exhibited H 2 The permeability (flux) was 930 GPU, and the CO 2 permeability was 25 GPU. The H 2 / CO 2 separation performance was as high as 37, where 1 GPU = 10 -6 cm 3 (STP)cm -2 s -1 cmHg -1 . The " " corresponding to the red number 1 in the figure corresponds to the test result of the prepared POSi30 in this example at a test temperature of 150 °C, and the " " corresponding to the red number 2 corresponds to the test result of the prepared POSi30 in this example at a test temperature of 200 °C.

[0073] Comparative Example 1 Other conditions were the same as in Example 1, except that when the viscosity of the casting solution in step 1.3 was <5 cp, the water bath heating and stirring were stopped at this time to obtain the PDMS casting solution. However, at this time, the solution viscosity was low. After spin-coating and curing, the prepared PDMS membrane was subjected to gas permeation testing. The measured N 2 permeability was 268 GPU, and the CO 2 permeability was 674 GPU. The CO 2 / N 2 separation performance was 2.5 (the separation performance of the existing PDMS membrane for CO 2 / N 2 usually reached 12). It can be found that the fluxes of both CO 2 and N 2 decreased, but no selectivity was shown. This may be because the solution viscosity was too low and penetrated into the pores of the base membrane during the spin-coating process, resulting in a relatively serious pore penetration phenomenon, blocking the pores of the base membrane and causing the gas flux to decrease.

[0074] Comparative Example 2 Other conditions were the same as in Example 1, except that in step 1.3, the viscosity of the casting solution reached 12 cp.

[0075] Experiments found that when the viscosity of the casting solution was 12 cp, the solution was already very viscous at this time. After spin-coating and curing, the prepared PDMS membrane was subjected to gas permeation testing. The measured N 2 permeability was 183 GPU, and the CO 2The permeability is 1417 GPU, CO 2 / N 2 The separation performance is 7.7. Comparing with the previous data, when the solution viscosity is too high, the gas flux drops by 2 / 3, CO 2 / N 2 The selectivity is also low. This may be because too high viscosity will lead to poor fluidity of the casting solution, affecting its diffusion on the surface of the substrate membrane, and ultimately resulting in uneven film thickness and local defects.

[0076] When the performance of the PDMS membrane is significantly lower than its intrinsic performance, no further treatment is carried out on it, because a complete and defect-free PDMS membrane is the basis for preparing the POSi selective layer by modification.

[0077] Comparative Example 3 The others are the same as in Example 1, except that in step 3.1, the PDMS composite membrane is placed in an ultraviolet ozone cleaning machine, and the distance between the composite membrane and the ultraviolet lamp tube is 15 mm. It is experimentally measured that the surface of the PDMS composite membrane is still in a hydrophobic state.

[0078] Example 2 Preparation of POSi composite membrane by atmospheric plasma 1 cleaning: 1. Preparation of PDMS casting solution: Weigh 0.04 g of a PDMS solution with a concentration of 10 wt%, 7.92 g of n-heptane solution, 0.02 g of TEOS and 0.02 g of DBTDL, and then mix and stir at room temperature for more than 3.5 h to obtain a PDMS casting solution with a concentration of 0.5 wt%. The molecular weight of the used PDMS is 90 KDa.

[0079] 2. Preparation of PDMS intermediate layer: 2.1 Immerse the PSF substrate membrane (with a molecular weight cut-off of 63000 Da) in deionized water to remove the pore-forming agent in it.

[0080] 2.2 Take 5 mL of the prepared PDMS casting solution and drop it onto the PSF substrate membrane, and prepare the PDMS intermediate layer by scraping, with the thickness of the used scraper being 150 μm.

[0081] 2.3 Cure in an oven at 80 °C for more than 2 hours.

[0082] 3. Preparation of POSi composite membrane: 3.1 Place the PDMS composite membrane on the workbench, adjust the working distance to 13 mm, set the moving speed of the robotic arm to 25 mm / s, and the system power to 1.0 kW. After processing 9 times, the POSi9 composite membrane can be obtained.

[0083] The N of the PDMS / PSF composite membrane prepared in this example2 The flux is 183 GPUs, CO 2 The flux is 1662 GPUs, CO 2 / N 2 The separation performance of / N is 9.1. It is proved that PDMS with good performance has been successfully prepared on the PSF for subsequent oxidative modification to prepare the POSi composite membrane.

[0084] Under the test conditions of 150 °C and 2 bar, the mixed gas permeation test was carried out on the prepared POSi9 composite membrane. H 2 、CO 2 The feed ratio is 50:50. CH 4 is used as the purge gas, and its flow rate is controlled at 25 sccm. The gas components in the permeation test are analyzed by a gas chromatograph.

[0085] Figure 6 The gas permeation performance data of the three membrane materials in this example are shown. Among them, PSF is the base membrane of the composite membrane; PDMS / PSF represents a PDMS / PSF composite membrane formed by scraping a layer of PDMS membrane on the PSF base membrane; POSi9 represents the POSi composite membrane obtained by treating with atmospheric plasma oxidation 9 times in this example. The H 2 permeability of the POSi9 composite membrane under the test condition of 150 °C is 159 GPUs, and CO 2 permeability is 9.4 GPUs. The H 2 / CO 2 separation performance is 17, corresponding to the position of the purple " Figure 5 " in content (d). For the untreated PDMS / PSF composite membrane, the H / CO 2 / CO 2 separation performance is only 0.31.

[0086] Comparative Example 4 Other conditions are the same as in Example 1, except that 3 mol / L of FeSO 4 and 6 mol / L of H 2 O 2 are prepared to obtain the Fenton reagent, which replaces the ultraviolet ozone oxidation in Example 1. The Fenton method is used to oxidize the PDMS thin film, which belongs to wet oxidation. The oxidized composite membrane needs to be dried first. The water contact angle before and after oxidation hardly changes and remains at 105°, indicating that the substances on the PDMS surface have not changed.

[0087] Comparative Example 5 Other conditions are the same as in Example 1, except that 2.1 mol / L sodium persulfate is used to wet-oxidize the pure PDMS film. The water contact angle remains almost unchanged before and after oxidation, staying at 105°, indicating that the substances on the PDMS surface have not changed.

[0088] In Example 1 and Example 2, ultraviolet ozone and atmospheric plasma were used to surface-oxidize PDMS. The water contact angle on the film surface changed from 105° to 0° (superhydrophilic) before and after measurement, indicating the feasibility of the modification method.

[0089] Table 1 compares the gas permeation performance test results of the POSi composite membranes prepared in Example 1 and Example 2 of the present invention with the composite membranes prepared in existing studies (the project numbers correspond to Figure 5 the sample numbers in content (d)). When testing pure gases, the fluxes of hydrogen and carbon dioxide are first measured separately, and then the ratio of the two is the H 2 / CO 2 ideal selectivity data.

[0090] Table 1 Comparison of the performance of the composite membranes prepared in the examples of the present invention with the composite membranes of the prior art

[0091] Continued Table 1 Comparison of the performance of the composite membranes prepared in the examples of the present invention with the composite membranes of the prior art

[0092] As can be seen from Table 1, compared with the polysiloxane (POSi) membrane (H 2 flux is 144 GPU) derived from PDMS under oxygen plasma treatment, the POSi membrane obtained by UV / O 3 treatment in Example 1 has a higher H 2 permeability (379 GPU), and the H 2 / CO 2 selectivity is slightly lower. The H 2 permeability of the POSi membrane obtained by atmospheric plasma treatment in Example 2 is 159 GPU, and the H 2 / CO 2 selectivity is 17. Under vacuum conditions, the oxidation performance of oxygen plasma is significantly enhanced, and its oxidation activity is higher, which can promote the rapid conversion of PDMS into a dense SiO 2 layer. This structure endows the material with higher sieving ability, but at the same time, it also leads to a decrease in the pore size on the composite membrane surface and a significant decrease in gas flux. In addition, due to the vacuum conditions restricting the ability to prepare composite membranes on a large scale, it makes this process difficult to achieve industrial scale-up, thus limiting its application potential in large-scale industrial preparation.

[0093] Example 1 obtains the POSi film through UV / O 3 The H of the POSi film processed 2 / CO 2 separation performance is superior to most polymer films, such as PBI films, polyamide thin-film composite (PA TFC) membranes, etc. Compared with traditional silica membranes calcined using 1,2-bis(triethoxysilyl)ethane (BTESE) as the precursor, the POSi film exhibits higher gas separation performance.

[0094] Some inorganic membranes, such as graphene oxide (GO) membranes, carbon molecular sieve (CMS) membranes, and two-dimensional metal-organic framework Zn 2 (Bim) 4 membranes, etc., exhibit excellent H 2 / CO 2 separation performance, but they are difficult to scale up in industrial production.

[0095] The POSi film prepared in the embodiment of the present invention can achieve excellent H 2 / CO 2 separation performance while having a simpler preparation process, mild preparation conditions, which can be completed under normal pressure, with a lower preparation cost, and is easy to scale up in industrial production.

[0096] As described above, it is only the specific implementation manner of this application, but the protection scope of this application is not limited thereto. Any person skilled in the art within the technical scope disclosed in this application can easily think of changes or substitutions, which should all be covered by the protection scope of this application. Therefore, the protection scope of this application should be subject to the protection scope of the claimed rights.

Claims

1. A method for preparing a carbon capture membrane having hydrothermal stability, characterized in that: The steps include: (1) Spreading the PDMS casting solution on the porous support membrane and heating it to solidify and cross-link it to obtain a PDMS composite membrane; (2) The PDMS composite membrane of step (1) is surface treated by ultraviolet ozone or atmospheric plasma, so that the surface of the PDMS is converted into an organic SiO2 layer through an oxidation reaction, thereby obtaining the carbon capture membrane; the organic SiO2 layer contains organic groups in its Si-O-Si network structure, and the organic SiO2 layer serves as a selective layer of the carbon capture membrane.

2. The preparation method according to claim 1, characterized in that The preparation of the PDMS casting solution comprises the following steps: S1: mixing and stirring PDMS monomer, cross-linking agent, catalyst and organic solvent to obtain a prepolymerization solution; S2: Stirring the prepolymer solution in step S1 at 25-35° C. to cause hydrolysis and polycondensation to occur, thereby obtaining the PDMS casting solution.

3. The preparation method according to claim 2, characterized in that: In step S1, the concentration of the PDMS monomer in the PDMS prepolymer solution is 0.2 wt%-1.5 wt%; the mass ratio of the PDMS monomer, the cross-linking agent and the catalyst is 10:(1-7):(1-7); and the molecular weight of the PDMS monomer is 15 KDa-90 KDa.

4. The preparation method according to claim 1, characterized in that: Step S2: During the stirring process, the viscosity of the PDMS prepolymer solution is monitored. When the viscosity reaches 6-10 cp, the stirring is stopped and the coating is prepared.

5. The preparation method according to claim 1, characterized in that: When step (2) is treated with ultraviolet ozone, the porous support membrane in step (1) is an aluminum oxide film, a polytetrafluoroethylene film or a polybenzimidazole film; When step (2) is treated with atmospheric plasma, the porous support membrane in step (1) is a polysulfone ultrafiltration membrane, a polybenzimidazole membrane or a polytetrafluoroethylene membrane.

6. The preparation method according to claim 1, characterized in that: The heating in step (1) is used to cure and crosslink the mixture, and the heating temperature is 60-80° C. and the heating time is 1-2 hours.

7. The preparation method according to claim 1, characterized in that: Step (2) is treated with ultraviolet ozone, specifically in an ultraviolet ozone treatment box, the distance between the PDMS composite membrane and the ultraviolet lamp in the ultraviolet ozone treatment box is 2-10 mm, oxygen is introduced into the ultraviolet ozone treatment box, the oxygen flow rate is controlled to be 100-150 mL / min, and the treatment time is 30-60 min.

8. The preparation method according to claim 1, characterized in that: Step (2) uses atmospheric plasma for treatment, specifically, uses an atmospheric plasma cleaning machine to treat the PDMS composite film, with a working distance of 10-30 mm, a robot arm moving speed of 20-30 mm / s, a system power of 0.8-1 kW, and a treatment number of 8-12 times.

9. The carbon capture membrane prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the carbon capture membrane according to claim 9 in gas separation.

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