Carbon molecular sieve membrane based on argon plasma treatment and preparation method and application thereof

Abstract

The application belongs to the field of membrane separation technology, and particularly relates to a carbon molecular sieve membrane based on argon plasma treatment and a preparation method and application thereof, which is obtained by treating a carbon molecular sieve membrane with argon plasma; argon ions react with functional groups in the carbon molecular sieve membrane to form a connecting structure between carbon chains; the method comprises the following steps: configuring a casting solution in which a polymer precursor is dissolved; removing bubbles in the casting solution and performing spinning; soaking the obtained membrane and then drying; performing high-temperature carbonization on the dried membrane to obtain a carbon molecular sieve membrane; and performing plasma treatment on the prepared carbon molecular sieve membrane in a near-vacuum argon environment to obtain a carbon molecular sieve membrane based on argon plasma treatment. Compared with the prior art, the application solves the defects of the carbon molecular sieve membrane in the prior art, i.e., the carbon molecular sieve membrane does not have the property of resisting aging and has a short service life, and realizes the effective extension of the service life of the carbon molecular sieve membrane while ensuring excellent gas separation performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of membrane separation technology, and particularly relates to a carbon molecular sieve membrane based on argon plasma treatment and a preparation method and application thereof. BACKGROUND

[0002] Hydrogen energy is considered to be the future energy due to its energy density and zero carbon emission advantages. In the process of large-scale hydrogen production such as steam reforming, efficient separation of carbon dioxide is a key step for preparing high-purity blue hydrogen.

[0003] Gas separation process is an essential unit operation in chemical industry. Traditional gas separation technologies include absorption, cryogenic separation, pressure swing adsorption (PSA) and the like. Gas absorption is to separate the component with the largest solubility in a gas mixture by using the different solubilities of components in a certain liquid absorbent, and has a wide application in the separation of CO2. Monoethanolamine or solid absorbent is commonly used, however, solvent recovery is a high energy consumption process. Cryogenic separation process is to separate according to the different boiling points of feed components, which also has the disadvantages of high production cost and energy consumption. PSA process is to separate based on the difference in adsorption amount of adsorbent to each component in the gas mixture at high pressure, which needs to consider the adsorption performance and service life of the adsorbent, and also has the disadvantage of low recovery rate in the production process.

[0004] Gas membrane separation technology is to separate two different gas mixtures by using pressure gradient as the driving force for mass transfer. Compared with traditional separation technologies, it has the advantages of no phase change, high efficiency, low energy consumption and simple operation. Overall, gas separation membranes are mainly divided into polymer membranes and inorganic membranes, and carbon molecular sieve membranes are carbon-based inorganic membranes prepared by high-temperature carbonization of polymer precursors, which have excellent separation performance and structural adjustability. The rigid slit-like pore structure makes it have better plasticization resistance and smaller swelling compared with polymer membranes, and has lower production cost compared with other inorganic membranes. The gas separation performance of carbon molecular sieve membranes exceeds the upper limit of the permeability-selectivity of many gas pairs.

[0005] "Structural aging" is the main challenge in the application of carbon molecular sieve membranes. Due to the collapse of the pore structure caused by the accumulation of disordered carbon chains in the carbon molecular sieve membrane during use, the membrane permeability continuously decreases during use. It is reported that the carbon molecular sieve membrane prepared by using polyimide as the precursor will have a 70% flux loss within 36 days.

[0006] CN116571099A mixes rare earth salt in the precursor to improve gas selectivity; CN112044273A synchronously improves permeability and selectivity by reshaping the polymer chain structure; CN109070009A improves permeability and selectivity by accelerating cooling after pyrolysis. As can be seen from the above, the current research mainly focuses on improving the gas separation performance of carbon molecular sieve membranes, including improvements in the formula, process, etc.; but there is a lack of research on the "anti-aging" performance in the prior art, such as the improved carbon molecular sieve membrane proposed above still has a relatively short service life. Therefore, it is necessary to further improve the "anti-aging" performance, i.e., the service life, on the basis of ensuring the gas separation effect, so that the gas membrane separation technology is more suitable for practical application environments. SUMMARY

[0007] The purpose of the present application is to provide a carbon molecular sieve membrane based on argon plasma treatment and a preparation method and application to solve the defects of the carbon molecular sieve membrane in the prior art, i.e., not having "anti-aging" performance and having a relatively short service life, and to achieve effective extension of the service life of the carbon molecular sieve membrane while ensuring excellent gas separation performance.

[0008] The purpose of the present application is achieved by the following technical solutions:

[0009] The present application discloses a carbon molecular sieve membrane based on argon plasma treatment obtained by treating a carbon molecular sieve membrane with argon plasma;

[0010] The argon ions react with the functional groups in the carbon molecular sieve membrane to form a connecting structure between the carbon chains.

[0011] Preferably, the carbon molecular sieve membrane is prepared from microcrystalline cellulose as a polymer precursor. Cellulose has the advantages of abundant resources and low production cost compared to other polymer precursors of carbon molecular sieve membranes, and can produce more ordered graphite-like structures after high-temperature carbonization, thus having more excellent "anti-aging" performance compared to other carbon molecular sieve membranes.

[0012] The present application discloses a method for preparing a carbon molecular sieve membrane based on argon plasma treatment as described above, comprising the following steps:

[0013] S1: preparing a carbon molecular sieve membrane:

[0014] S11: preparing a casting solution with a polymer precursor dissolved therein;

[0015] S12: removing the gas bubbles in the casting solution prepared in step S1 and performing spinning;

[0016] S13: soaking the membrane obtained by spinning in step S2, followed by drying;

[0017] S14: carbonizing the film dried in step S3 at high temperature to obtain a carbon molecular sieve membrane;

[0018] S2: treating the carbon molecular sieve membrane with argon plasma;

[0019] The carbon molecular sieve membrane prepared in step S1 is treated with argon plasma under a near-vacuum argon environment to obtain an argon plasma-treated carbon molecular sieve membrane.

[0020] Preferably, in step S11, the casting solution is formed by dissolving microcrystalline cellulose in a mixture of DMSO (dimethyl sulfoxide) and EmimAc (1-ethyl-3-methyl-imidazole acetate, a cosolvent), and the casting solution is a homogeneous solution.

[0021] Preferably, in the casting solution, the mass percentage of microcrystalline cellulose is 12%, the mass percentage of DMSO is 66%, and the mass percentage of EmimAc is 22%.

[0022] Preferably, in step S12, the casting solution is vacuumed and heated to 60°C for 12 h to remove air bubbles.

[0023] Preferably, in step S13, deionized water is used as the soaking liquid for soaking to remove residual solvents on the surface of the film; and drying is performed by hanging drying, and a weight is hung at the bottom of the film during drying to prevent curling.

[0024] Preferably, in step S14, high-temperature carbonization is performed in an argon atmosphere by a staged heating method, and the heating program is as follows: heating from 20°C to 200°C at a rate of 5°C / min and maintaining for 2 h; heating from 200°C to 340°C at a rate of 10°C / min and maintaining for 1 h; heating from 340°C to 700°C at a rate of 5°C / min and maintaining for 2 h; during high-temperature carbonization, the flow rate of argon is 60 mL / min; and then naturally cooling to room temperature.

[0025] Preferably, in step S2, the pressure of the near-vacuum is 26 Pa, the flow rate of argon during plasma treatment is 18 mL / min, the power of plasma treatment is 100-200 W, and the time of plasma treatment is 10-25 min.

[0026] More preferably, the power of plasma treatment is 150 W, and the time of plasma treatment is 20 min.

[0027] The plasma treatment uses a radio frequency power source as an argon plasma generator.

[0028] The third aspect of the present application discloses an application of the carbon molecular sieve membrane based on argon plasma treatment in a gas membrane separation process of H2 / CO2.

[0029] The working principle of the present application is as follows:

[0030] By reacting argon ions with functional groups in the carbon molecular sieve membrane, a "lock chain" connection structure can be introduced between carbon chains, which improves the order of carbon chain arrangement in the carbon molecular sieve membrane to a certain extent, i.e., improves the structural stability of the carbon molecular sieve membrane, and finally improves the performance stability of the carbon molecular sieve membrane in use.

[0031] Compared with the prior art, the present application has the following beneficial effects:

[0032] 1. After optimization of the plasma treatment conditions, 150W and 20min are the optimal treatment conditions, the H2 permeation rate is 213 Barrer at room temperature, and the H2 / CO2 selectivity is 90.

[0033] 2. After plasma treatment, the hydrogen-carbon dioxide separation selectivity is significantly improved.

[0034] 3. After plasma treatment, the performance of the carbon molecular sieve membrane can be maintained basically unchanged within 120 days, and only 7% of the hydrogen flux is lost within 180 days.

[0035] 4. After plasma treatment, the performance of the carbon molecular sieve membrane can still be maintained for more than 300h under the condition of 11bar, 130℃ and the presence of water vapor. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 It is a schematic diagram of the structural change of the carbon molecular sieve membrane in the plasma treatment process;

[0037] Figure 2 It is a structural schematic diagram of the continuous dry-wet spinning equipment;

[0038] Figure 3 It is an XRD spectrum of examples 1-3 and untreated carbon molecular sieve membrane;

[0039] Figure 4 It is a pore size distribution curve of examples 1-3 and untreated carbon molecular sieve membrane;

[0040] Figure 5 It is a Raman spectrum of examples 1-3 and untreated carbon molecular sieve membrane;

[0041] Figure 6 It is a performance comparison diagram of examples 1-3 and untreated carbon molecular sieve membrane and the prior art H2 / CO2 separation membrane;

[0042] Figure 7 The single-component gas permeation rate test results of the carbon molecular sieve membrane of Example 3;

[0043] Figure 8 The long-term stability test results of Example 3 and untreated carbon molecular sieve membranes;

[0044] Figure 9 The dynamic stability test results of the carbon molecular sieve membrane of Example 3. DETAILED DESCRIPTION

[0045] The present application will be described in detail below with reference to the accompanying drawings and specific examples.

[0046] In the following description, if not specifically stated, the reagents used can be selected from conventional commercially available products, and the methods used can be known in the art.

[0047] The present application provides a method for preparing and optimizing the performance of a carbon molecular sieve membrane. By reacting argon ions with functional groups in the carbon molecular sieve membrane, a "lock chain" connection structure can be introduced between the carbon chains, as shown in Figure 1 which improves the order of carbon chain arrangement in the carbon molecular sieve membrane to some extent, i.e., improves the structural stability of the carbon molecular sieve membrane, and ultimately improves the performance stability of the carbon molecular sieve membrane during use.

[0048] Example 1

[0049] In this example, the preparation of the carbon molecular sieve membrane includes the following steps:

[0050] Step 1: Prepare the casting solution. Dissolve microcrystalline cellulose in DMSO and EmimAc, wherein the mass fractions of microcrystalline cellulose, DMSO and EmimAc in the mixed solution are 12%, 66% and 22%, respectively. Then place the container containing the mixed solution into a rolling mixer and mix at 60°C for 12h until a uniform transparent golden yellow solution without obvious bubbles is formed, forming a homogeneous solution.

[0051] Step 2: Spinning to prepare the cellulose precursor membrane. Place the prepared casting solution into the spinning machine liquid tank, as shown in Figure 2 vacuumize and set the heating temperature to 60°C for 12h to ensure that the bubbles in the casting solution are completely removed. Then fill the gel tank and water washing tank with water, and set the temperature to 25°C. In addition, control the rotation speed of the metering pump to 3.5r / min, the core liquid flow rate to 2.5mL / min, the core liquid to be deionized water, and the spinning head distance from the liquid surface to be 5cm. Then spin according to the existing process.

[0052] Step 3: Drying. The new membrane after spinning preparation needs to be soaked in deionized water for 3 days to completely remove the residual solvent on the surface, and then the membrane is cut into a size of 1 m each. Hang to dry, while hanging two paper clips at the bottom as weights, which can ensure that the membrane does not curl during the drying process without damaging the structure of the membrane.

[0053] Step 4: High-temperature carbonization. Carbonization was carried out under an argon atmosphere according to the temperature control program, during which the argon flow rate was controlled at 60 mL / min. The carbonization temperature control program was as follows: the temperature was raised from 20°C to 200°C at a rate of 5°C / min, and maintained for 2 h; the temperature was raised from 200°C to 340°C at a rate of 10°C / min, and maintained for 1 h; the temperature was raised from 340°C to 700°C at a rate of 5°C / min, and maintained for 2 h, and then naturally cooled to room temperature. A carbon molecular sieve membrane with microcrystalline cellulose as the precursor was obtained.

[0054] Step 5: Argon plasma treatment. The argon flow rate was 18 mL / min, the vacuum degree was 26 Pa, and the treatment temperature was room temperature. More specifically, it includes the following steps:

[0055] (i) The prepared carbon molecular sieve membrane was placed in the furnace cavity and sealed, and the argon feed flow rate was set to 18 mL / min through the flow controller;

[0056] (ii) The furnace cavity was pumped to about 26 Pa using a vacuum pump;

[0057] (iii) The treatment power and time were adjusted to 150 W and 10 min, respectively, and the radio frequency power was turned on for plasma treatment.

[0058] The carbon molecular sieve membrane based on argon plasma treatment prepared in this example is denoted as: CMS-150 / 10.

[0059] Example 2

[0060] The preparation method of this example is basically the same as that of Example 1, except that the treatment power and time are controlled at 150 W and 15 min, respectively, during the plasma treatment. The carbon molecular sieve membrane based on argon plasma treatment thus prepared is denoted as: CMS-150 / 15.

[0061] Example 3

[0062] The preparation method of this example is basically the same as that of Example 1, except that the treatment power and time are controlled at 150 W and 20 min, respectively, during the plasma treatment. The carbon molecular sieve membrane based on argon plasma treatment thus prepared is denoted as: CMS-150 / 20.

[0063] The carbon molecular sieve membranes based on argon plasma treatment prepared in Examples 1-3 and the untreated carbon molecular sieve membrane (as a comparative sample, denoted as CMS-0) were characterized by XRD, Raman and BET for the pore structure of the carbon molecular sieve membranes, as shown in Figures 3-5 The reduction of the d-spacing in the XRD pattern Figure 3 after plasma treatment and the increase of the pore content of 0.37 nm in the pore size distribution curve Figure 4 based on the CO2 isotherm adsorption curve at 25℃ calculated by the NLDFT model) both indicate that the plasma treatment can reduce the pore structure of the carbon molecular sieve membrane, which is more conducive to the separation of H2 and CO2. The reduction of the I D / I G ratio in the Raman spectrum Figure 5 after plasma treatment indicates that the plasma treatment is conducive to the improvement of the ordered degree of the carbon molecular sieve membrane structure, which is conducive to the improvement of the anti-aging performance of the carbon molecular sieve membrane.

[0064] The carbon molecular sieve membranes based on argon plasma treatment prepared in Examples 1-3 and the untreated carbon molecular sieve membrane were further compared with the membranes for H2 / CO2 separation in the prior art in performance, as shown in Figure 6 It can be seen that the carbon molecular sieve membrane treated at 150W for 20min (Example 3) has a more outstanding upper bound breakthrough compared with the carbon molecular sieve membranes treated under other conditions and other separation membranes recently reported. The membrane of Example 3 has a H2 permeance of 213 Barrer and a H2 / CO2 selectivity of 90 at room temperature, as shown in Figure 7 .

[0065] The carbon molecular sieve membrane based on argon plasma treatment prepared in Example 3 was tested for long-term stability, which was divided into: 1. single gas long-term stability test at room temperature; and 2. mixed gas dynamic stability test.

[0066] As shown in Figure 8 , the carbon molecular sieve membrane based on argon plasma treatment of Example 3 and the untreated carbon molecular sieve membrane were tested for single gas long-term stability at room temperature. It can be seen that the membrane of Example 3 maintains basically unchanged within 120 days, and only has a hydrogen flux loss of 7% within 180 days, while the stability of the untreated membrane experiences a rapid decline and is basically stable at a hydrogen flux loss of 32%.

[0067] As shown in Figure 9The mixed gas dynamic stability test was performed on the carbon molecular sieve membrane based on argon plasma treatment of Example 3, and the test conditions were as follows: 50 mol% H2 / 50 mol% CO2, dry-wet feed switching, test pressure was 11 bar, and temperature was 130 DEG C. It can be seen that the membrane of Example 3 can still maintain performance stability for more than 300 h under harsh conditions of high temperature and high pressure and containing water vapor.

[0068] It can be seen that the carbon molecular sieve membrane based on argon plasma treatment has excellent long-term stability, and can also maintain performance stability under harsh conditions of high temperature and high pressure and containing water vapor, and has great application prospect in the actual application of water vapor reforming hydrogen production.

[0069] The above description of the examples is for facilitating the ordinary skilled person in the art to understand and use the application. The person skilled in the art can obviously easily make various modifications to the examples, and apply the general principles described herein to other examples without creative labor. Therefore, the application is not limited to the above examples, and the improvements and modifications made by the person skilled in the art according to the disclosure of the application without departing from the scope of the application should be within the protection scope of the application.

Claims

1. A carbon molecular sieve membrane based on argon plasma treatment, characterized in that, It is obtained by treating carbon molecular sieve membranes with argon plasma. Argon ions react with functional groups in the carbon molecular sieve membrane to form a linkage structure between carbon chains.

2. The carbon molecular sieve membrane based on argon plasma treatment according to claim 1, characterized in that, The carbon molecular sieve membrane is prepared by using microcrystalline cellulose as a polymer precursor.

3. A method for preparing a carbon molecular sieve membrane based on argon plasma treatment as described in claim 1 or 2, characterized in that, Includes the following steps: S1: Preparation of carbon molecular sieve membranes: S11: Prepare a casting solution containing dissolved polymer precursors; S12: Remove air bubbles from the casting solution prepared in step S1 and perform spinning; S13: Soak the membrane obtained from spinning in step S2, and then dry it; S14: The membrane dried in step S3 is subjected to high-temperature carbonization to obtain a carbon molecular sieve membrane. S2: Treatment of carbon molecular sieve membranes using argon plasma: The carbon molecular sieve membrane prepared in step S1 is subjected to plasma treatment in a near-vacuum argon atmosphere to obtain a carbon molecular sieve membrane based on argon plasma treatment.

4. The method for preparing a carbon molecular sieve membrane based on argon plasma treatment according to claim 3, characterized in that, In step S11, the casting solution is formed by dissolving microcrystalline cellulose in a mixture of DMSO and EmimAc, and the casting solution is a homogeneous solution.

5. The method for preparing a carbon molecular sieve membrane based on argon plasma treatment according to claim 4, characterized in that, In the casting solution, the mass percentage of microcrystalline cellulose is 12%, the mass percentage of DMSO is 66%, and the mass percentage of EmimAc is 22%.

6. The method for preparing a carbon molecular sieve membrane based on argon plasma treatment according to claim 3, characterized in that, In step S12, the casting solution is evacuated and heated to 60°C and kept at that temperature for 12 hours to remove air bubbles.

7. The method for preparing a carbon molecular sieve membrane based on argon plasma treatment according to claim 3, characterized in that, In step S13, deionized water is used as the soaking solution to remove residual solvent from the membrane surface; drying is carried out by hanging and air drying, during which a weight is suspended at the bottom of the membrane to prevent it from curling.

8. The method for preparing a carbon molecular sieve membrane based on argon plasma treatment according to claim 3, characterized in that, In step S14, high-temperature carbonization is carried out in an argon atmosphere by a staged heating process. The heating program is as follows: heating from 20°C to 200°C at a heating rate of 5°C / min and holding for 2 hours; heating from 200°C to 340°C at a heating rate of 10°C / min and holding for 1 hour; heating from 340°C to 700°C at a heating rate of 5°C / min and holding for 2 hours; and then naturally cooling to room temperature.

9. The method for preparing a carbon molecular sieve membrane based on argon plasma treatment according to claim 3, characterized in that, In step S2, the near-vacuum pressure is 26 Pa, the argon flow rate during plasma treatment is 18 mL / min, the plasma treatment power is 100-200 W, and the plasma treatment time is 10-25 min.

10. The application of a carbon molecular sieve membrane based on argon plasma treatment as described in claim 1 or 2 in a gas membrane separation process for H2 / CO2.

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