A method for preparing in-situ post-oxidized carbon molecular sieve hollow fiber membranes and applications thereof

Abstract

The present application relates to a kind of preparation method and application of carbon molecular sieve hollow fiber membrane in situ post-oxidation, and preparation method includes: in oxidizing atmosphere, positive pressure difference is applied between the shell side and hollow tube side of carbon molecular sieve hollow fiber membrane, and heating treatment is carried out, to obtain carbon molecular sieve hollow fiber membrane in situ post-oxidation treatment.Compared with prior art, the present application provides a kind of in situ oxidation strategy, by forcing oxygen diffusion through CMS hollow fiber membrane layer, oxygen doping and oxidation functionalization are carried out to CMS hollow fiber membrane, to improve the separation performance of CMS hollow fiber membrane, to provide a kind of simple strategy for the structure customization and performance optimization of CMS hollow fiber membrane.After 60min in situ oxidation, CO2 permeability increases from 297.1Barrer to 1369.0Barrer, while CO2 / N2 selectivity remains at 51, CO2 / CH4 selectivity remains at 101.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of gas separation membranes, and relates to a preparation method and application of a carbon molecular sieve hollow fiber membrane, in particular to a preparation method and application of a carbon molecular sieve hollow fiber membrane for realizing efficient CO2 separation through in-situ post-oxidation treatment. BACKGROUND

[0002] For a long time, developing efficient CO2 capture technologies, such as separating CO2 from flue gas and removing CO2 from natural gas (a cleaner alternative to coal or oil), has been attractive to the whole world to reduce CO2 emissions. Compared with traditional heat-driven separation technologies, the method of membrane separation shows exponential improvement in energy efficiency, which can reduce the energy cost of separation. Among various available membrane materials from flexible polymers to rigid molecular sieve inorganic materials, carbon molecular sieve (CMS) membranes, which have excellent separation performance, chemical stability and easy scalability, are one of the most attractive materials for CO2 separation.

[0003] CMS membranes are inorganic molecular sieve membranes obtained by pyrolysis of polymer precursor membranes, thereby combining the advantages of polymer membranes and inorganic membranes. In addition, CMS membranes have a bimodal pore size distribution of micropores and ultramicropores , which provides good gas permeability and molecular sieve performance. This microporous structure feature dominating the gas separation performance can be tailored by different methods, including modification of the polymer precursor, control of carbonization conditions, and adoption of additional post-treatment. Suitable pore sizes are expected to realize the permeation effect on gas molecules, thereby further improving the gas permeability of CMS membranes.

[0004] At present, CMS membranes are used for efficient separation and capture of CO2, but there are still problems of poor CO2 permeability and poor adsorption effect. SUMMARY

[0005] The purpose of the present application is to provide a preparation method and application of a carbon molecular sieve hollow fiber membrane with high CO2 selective permeability.

[0006] The purpose of the present application can be achieved by the following technical solutions.

[0007] A preparation method of a carbon molecular sieve hollow fiber membrane through in-situ post-oxidation, comprising:

[0008] applying a positive pressure difference between the shell side and the hollow tube side of the carbon molecular sieve hollow fiber membrane in an oxidation atmosphere and performing a heating treatment to obtain the carbon molecular sieve hollow fiber membrane through in-situ post-oxidation treatment.

[0009] Further, the oxidation atmosphere is an air atmosphere or an oxygen atmosphere.

[0010] Further, the positive pressure difference is 1-5 bar.

[0011] Further, the gas pressure on the shell side of the carbon molecular sieve hollow fiber membrane is 2-6 bar, and the gas pressure on the hollow tube side of the carbon molecular sieve hollow fiber membrane is 0.8-1.2 bar.

[0012] Further, in the heating treatment, the heating temperature is 280-330 DEG C.

[0013] Further, the preparation method of the carbon molecular sieve hollow fiber membrane comprises the following steps:

[0014] S1: mixing microcrystalline cellulose (MCC), 1-ethyl-3-methyl imidazole acetate (EmimAc), dimethyl sulfoxide (DMSO) to obtain a spinning solution; and preparing a hollow fiber membrane by dry-wet spinning method;

[0015] S2: heating and carbonizing the hollow fiber membrane to obtain a carbon molecular sieve hollow fiber membrane.

[0016] Further, in step S1, the content of microcrystalline cellulose in the spinning solution is 10-14 wt%; and the mass ratio of 1-ethyl-3-methyl imidazole acetate to dimethyl sulfoxide is 1:(2-4).

[0017] Further, in step S2, the carbonization temperature is 550-650 DEG C, and the carbonization time is 6-8 h.

[0018] A carbon molecular sieve hollow fiber membrane subjected to in-situ post-oxidation, which is prepared by the method described above.

[0019] The application of the carbon molecular sieve hollow fiber membrane subjected to in-situ post-oxidation described above, which comprises using the carbon molecular sieve hollow fiber membrane subjected to in-situ post-oxidation for separating carbon dioxide and nitrogen, and / or carbon dioxide and methane.

[0020] In order to improve the CO2 permeability of the existing CMS hollow fiber membrane, the present application proposes an in-situ air post-oxidation treatment method for the purpose of modifying the structure of the CMS hollow fiber membrane, so that air penetrates through the CMS hollow fiber membrane under the action of pressure difference, the structure and surface properties of the CMS hollow fiber membrane are adjusted by changing the treatment time, the in-situ regulation of the CMS hollow fiber membrane is realized, and the separation performance of CO2 is improved. The in-situ post-oxidation treatment method gradually increases the effective separation pore size of the CMS hollow fiber membrane, and enhances the permeability of CO2. At the same time, due to the introduction of oxygen-containing functional groups with high affinity for CO2 by post-oxidation treatment, the solubility and permeability selectivity of CO2 is further improved. Finally, high-efficiency screening of CO2 can be realized, and an engineering optimization strategy for regulating the gas transmission channel of the CMS hollow fiber membrane in the order of angstrom is provided.

[0021] Compared with the prior art, the present application has the following characteristics:

[0022] The present application provides an in-situ oxidation strategy, which improves the separation performance of CMS hollow fiber membranes by forcing oxygen diffusion through the CMS hollow fiber membrane layer to perform oxygen doping and oxidation functionalization on the CMS hollow fiber membrane, customizes gas transport channels penetrating sub-nanometer size within the angstrom size, and provides a simple strategy for structure customization and performance optimization of CMS hollow fiber membranes. After 60 min of in-situ oxidation, the CO2 permeance is increased from 297.1 Barrer to 1369.0 Barrer, while the CO2 / N2 selectivity is maintained at 51 and the CO2 / CH4 selectivity is maintained at 101. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a SEM image of the CMS hollow fiber membrane in Example 1;

[0024] Figure 2 is a schematic diagram of the interlayer spacing change of the CMS hollow fiber membrane in Examples 1-3;

[0025] Figure 3 is a schematic diagram of the pore size change of the CMS hollow fiber membrane in Examples 1-3;

[0026] Figure 4 is a C1s graph of X-ray photoelectron spectroscopy (XPS) analysis of the CMS hollow fiber membrane in Examples 1-3;

[0027] Figure 5 is an O1s graph of X-ray photoelectron spectroscopy (XPS) analysis of the CMS hollow fiber membrane in Examples 1-3;

[0028] Figure 6 is a carbon dioxide adsorption isotherm (298K) of the CMS hollow fiber membrane in Examples 1-3;

[0029] Figure 7 is a schematic diagram of the structure of the membrane module;

[0030] Figure 8 is Figure 7 is a local enlarged view of the hollow fiber membrane at A in FIG. 8. DETAILED DESCRIPTION

[0031] The present application will be described in detail below in conjunction with the accompanying drawings and specific examples.

[0032] A post-in-situ oxidation carbon molecular sieve hollow fiber membrane, the preparation method comprising the following steps:

[0033] 1) Using microcrystalline cellulose as raw material, 1-ethyl-3-methyl imidazole acetate and dimethyl sulfoxide as co-solvents, a spinning solution is prepared; the spinning solution is prepared into a hollow fiber membrane through dry-wet spinning method;

[0034] In the spinning solution, the content of microcrystalline cellulose is 10-14wt%; 1-ethyl-3-methyl imidazole acetate is used to dissolve cellulose, and dimethyl sulfoxide is used to reduce the viscosity of the solution, the mass ratio of 1-ethyl-3-methyl imidazole acetate and dimethyl sulfoxide is 1:(2-4); and preferably, the preparation temperature of the spinning solution is 55-65℃;

[0035] Preferably, the hollow fiber membrane is collected in a deionized water tank, and the deionized water is replaced several times to completely remove the residual co-solvents;

[0036] 2) The hollow fiber membrane is heated and carbonized at 550-650℃ for 6-8h in an inert gas atmosphere to obtain a carbon molecular sieve hollow fiber membrane;

[0037] Wherein, the inert gas is argon or nitrogen; preferably, natural drying is performed before heating and carbonization, the drying temperature is room temperature, and the drying time is 22-26h;

[0038] 3) A positive pressure difference of 1-5bar is applied between the shell side and the hollow tube side of the carbon molecular sieve hollow fiber membrane in an oxidation atmosphere, and heating treatment is performed at 280-330℃ for 0.5-1.5h to obtain an in-situ post-oxidized carbon molecular sieve hollow fiber membrane;

[0039] Wherein, the oxidation atmosphere is preferably air atmosphere or oxygen atmosphere; preferably, the gas pressure of the shell side of the carbon molecular sieve hollow fiber membrane is 2-6bar, and the gas pressure of the hollow tube side of the carbon molecular sieve hollow fiber membrane is 0.8-1.2bar.

[0040] An application of an in-situ post-oxidized carbon molecular sieve hollow fiber membrane, comprising using the in-situ post-oxidized carbon molecular sieve hollow fiber membrane for the separation of carbon dioxide and nitrogen, and / or carbon dioxide and methane.

[0041] Compressed air is introduced into the membrane module, and in-situ post-oxidation treatment is performed by means of pressure difference and heating temperature, by changing the treatment time, the permeation micropore of the Angstrom level is expanded, the pore size and pore volume of the CMS membrane are increased, and the CO2 gas flux is improved. At the same time, the oxygen doping of the post-oxidation treatment can increase the content of oxygen-containing functional groups, improve the CO2 affinity of the carbon molecular sieve hollow fiber membrane, and further improve the CO2 solubility and permeability selectivity, thereby effectively improving the CO2 separation performance. This provides a simple method for structural modification of the carbon molecular sieve hollow fiber membrane, and has the advantages of easy realization of large-scale preparation, etc.

[0042] The following examples are implemented on the basis of the above technical solutions of the application, and give detailed implementation modes and specific operation processes, but the protection scope of the application is not limited to the following examples.

[0043] In the following examples, the used spinning device is a product of DKN-02 model of Dalian Kona Science and Technology Development Co., Ltd., the fiber membrane layer spacing is measured by an X-ray diffractometer (D8 Advance), and the pore size is measured by a specific surface and porosity analyzer (BELSORP-MAX).

[0044] Example 1:

[0045] A carbon molecular sieve hollow fiber membrane CMS-0, a preparation method thereof comprises the following steps:

[0046] 1) Preparation of a hollow fiber membrane with cellulose as a precursor:

[0047] 27.27 g of MCC was added to 150 g of DMSO in batches, and stirring was performed to uniformly disperse the MCC, and then 50 g of 1-ethyl-3-methylimidazole acetate was added to prepare a spinning solution. The spinning solution was placed in a homogenizer, the temperature was set to 60°C, and the solution was placed for 24 h to fully mix and uniformly disperse the solution. The 60°C spinning solution was placed in a spinning tank, and after being cooled to room temperature, a spinning machine and a core liquid pump were used to respectively transport the spinning solution and the core liquid to a spinneret, pass through an air layer, and then enter a coagulation bath. After the solvent was removed and coagulation by water washing at room temperature, the membrane was prepared into a hollow fiber membrane, wherein the core liquid was deionized water, the coagulation bath was water, and the temperature was room temperature. In the spinning process, the air gap between the spinneret and the coagulation bath was set to 2 cm, and the flow rates of the spinning solution and the core liquid were set to 3.5 mL min -1 and 2.5 mL min -1 , respectively. The winding speed of the hollow fiber membrane was kept at 8 m / min, the hollow fiber membrane was cut into 1.5 m, and was collected in a deionized water tank, and the deionized water was replaced several times to completely remove the residual cosolvent.

[0048] 2) Preparation of a CMS hollow fiber membrane:

[0049] The wet hollow fiber membrane was exposed to air for 24 h for drying. Carbonization was performed at a temperature of 600°C for 6.5 h under the condition of argon blowing in a tube furnace to obtain a CMS hollow fiber membrane. In addition, SEM analysis was performed on the CMS hollow fiber membrane, Figure 1 which is a SEM image of the surface and cross section of the CMS hollow fiber membrane, and a smooth membrane surface and uniform membrane thickness can be seen, and the membrane thickness is 28 μm.

[0050] 3) Preparation of a membrane module:

[0051] For example, Figure 7As shown, the two ends of the CMS hollow fiber membrane are respectively sealed in two three-way joints 1 using high-temperature-resistant epoxy resin glue 2 to make a membrane module, so that gas can be introduced to the outside of the shell of the CMS hollow fiber membrane through the upper connecting pipe of the three-way joint 1, and gas can be introduced to the hollow pipe side of the CMS hollow fiber membrane through the outer end of the two three-way joints 1.

[0052] Gas separation performance test

[0053] The CMS hollow fiber membrane gas separation performance test uses a gas permeation instrument to test the gas separation performance of all sample membrane materials by a pressure difference method according to the national standard GB / T 1083, the test pressure is 2 bar, the test temperature is 26℃, and during the test, the downstream of the sample cell is pumped to a vacuum (below 30 Pa), and after a period of stabilization, the test is started (about 2h). Put the carbon molecular sieve membrane module into the test cell to start the test, and after the gas permeation amount is stable for a period of time, end the test and repeat three times, and calculate the permeation coefficient and the selectivity coefficient using the following formula:

[0054]

[0055]

[0056] Wherein, P i , P j are the permeation coefficients of gases i, j, α represents the selectivity coefficient, Q (cm 3 (STP) s -1 ) represents the volume flow rate of the gas at the outlet, l (cm) is the thickness of the membrane, A represents the membrane area (cm 2 ), ΔP (cmHg) represents the pressure difference of gas i on both sides of the membrane. 1Barrer = 10 -10 cm 3 (STP) cm (cm 2 scmHg) -1 .

[0057] Example 2:

[0058] A carbon molecular sieve hollow fiber membrane CMS-30 for realizing high-efficiency CO2 separation through in-situ post-oxidation treatment, the preparation method of which is only different from that of Example 1 in that:

[0059] In step 3), the prepared membrane module is placed in a tubular furnace for heating, the temperature is 305℃, the treatment time is 30 min, and at the same time of heating, compressed air with a pressure of 4 bar is sent to the outside of the shell of the membrane module, while the air inside the hollow pipe of the membrane module is kept at 1 bar, forming a pressure difference. The finally obtained in-situ post-oxidation treated membrane is subjected to gas separation test.

[0060] Example 3:

[0061] A carbon molecular sieve hollow fiber membrane CMS-60 for high-efficiency CO2 separation by in-situ post-oxidation treatment, the preparation method of which is only different from that of Example 2 in that the treatment time is 60 min.

[0062] The gas performance of the obtained membrane is shown in the following table:

[0063] Table 1: Change of gas permeability coefficient and selectivity of CMS hollow fiber membrane after post-oxidation treatment with time

[0064]

[0065] From the above results, it can be seen that the gas permeability coefficients of CO2, N2 and CH4 of the CMS hollow fiber membrane prepared in the above examples are obviously increased, and the selectivity of CO2 / N2 and CO2 / CH4 is good. The CO2 permeability coefficient of the CMS hollow fiber membrane treated for 60 min is increased by 4.6 times.

[0066] In order to further illustrate the structure regulation of the in-situ post-oxidation treatment on the CMS hollow fiber membrane, the changes of the interlayer spacing, pore size distribution and carbon structure of the untreated membrane and the post-oxidation treated membrane are analyzed and tested, as shown in Figures 2 to 4 Figure 2 It can be seen that the interlayer spacing of the untreated CMS hollow fiber membrane is After in-situ oxidation treatment for different times, the interlayer spacing of the CMS hollow fiber membrane is increased to (30 min) and (60 min), which indicates that a more open structure is obtained by in-situ post-oxidation treatment. In addition, as shown in Figure 3 , in the range of , the post-oxidation treated CMS hollow fiber membrane is significantly increased in the distribution of around, which indicates the increase of sub-nanopores. As shown in Figure 4 , the peak area ratio of sp 3 hybrid carbon to sp 2 hybrid carbon gradually decreases, which indicates that the in-situ oxidation treatment reduces the graphitization degree of the carbon structure. The above tests show that the structure regulation of the CMS hollow fiber membrane by in-situ post-oxidation treatment proposed in the application is beneficial to improve the permeability of CO2. In addition, the changes of the surface properties of the CMS hollow fiber membrane are further illustrated by the analysis of the O1s graph of XPS and the CO2 adsorption test, as shown in Figure 5 It can be seen that the -COOH group of the post-oxidation treated membrane is increased, which is beneficial to the adsorption of CO2, and as shown in Figure 6 ​It can be seen that the CO2 adsorption capacity is increased by 2 times. The results reported by the present application will provide a new way for the in-situ structural modification of CMS hollow fiber membranes in the future to obtain high-performance membranes.

[0067] The above description of the embodiments is to enable a person having ordinary skill in the art to understand and use the application. It is obvious that those skilled in the art can easily make various modifications to the embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present application is not limited to the above embodiments, and improvements and modifications made by those skilled in the art without departing from the scope of the present application should be within the scope of protection of the present application.

Claims

1. A method for preparing in situ post-oxidized carbon molecular sieve hollow fiber membranes, characterized by, The application relates to a carbon molecular sieve hollow fiber membrane and a preparation method thereof. A positive pressure difference is applied between the shell side and the hollow tube side of the carbon molecular sieve hollow fiber membrane in an oxidation atmosphere, and a heating treatment is performed to obtain an in-situ post-oxidation carbon molecular sieve hollow fiber membrane.

2. The method for producing in-situ post-oxidation carbon molecular sieve hollow fiber membranes according to claim 1, characterized in that, The oxidation atmosphere is an air atmosphere or an oxygen atmosphere.

3. The method for producing in-situ post-oxidation carbon molecular sieve hollow fiber membranes according to claim 1, characterized in that, The positive pressure difference is 1-5 bar.

4. The method for producing in-situ post-oxidation carbon molecular sieve hollow fiber membranes according to claim 3, characterized in that, The air pressure on the shell side of the carbon molecular sieve hollow fiber membrane is 2-6 bar, and the air pressure on the hollow tube side of the carbon molecular sieve hollow fiber membrane is 0.8-1.2 bar.

5. The method for preparing in-situ post-carbon dioxide molecular sieve hollow fiber membrane according to claim 1, characterized in that, In the heating treatment, the heating temperature is 280-330 DEG C.

6. The method of claim 1, wherein the in-situ post-oxidation of the carbon molecular sieve hollow fiber membrane is performed at a temperature of about 300 °C to about 400 °C. The preparation method of the carbon molecular sieve hollow fiber membrane comprises the following steps: S1: mixing microcrystalline cellulose, 1-ethyl-3-methyl imidazole acetate and dimethyl sulfoxide to obtain a spinning solution; and preparing a hollow fiber membrane through dry-wet spinning method; S2: heating and carbonizing the hollow fiber membrane to obtain a carbon molecular sieve hollow fiber membrane.

7. The method for producing in-situ post-oxidation carbon molecular sieve hollow fiber membranes according to claim 6, characterized in that, In step S1, the content of the microcrystalline cellulose in the spinning solution is 10-14 wt%; and the mass ratio of the 1-ethyl-3-methyl imidazole acetate to the dimethyl sulfoxide is 1:(2-4).

8. The method of claim 6, wherein the in-situ post-oxidation of the carbon molecular sieve hollow fiber membrane is performed at a temperature of about 300 °C to about 400 °C. In step S2, the carbonization temperature is 550-650 DEG C, and the carbonization time is 6-8 h.

9. An in-situ post-oxidized carbon molecular sieve hollow fiber membrane, characterized in that, The carbon molecular sieve hollow fiber membrane is prepared by the method according to any one of claims 1-8.

10. Use of the in-situ post-oxidation of carbon molecular sieve hollow fiber membranes as claimed in claim 9, characterized in that, The in-situ post-oxidation carbon molecular sieve hollow fiber membrane is used for separating carbon dioxide and nitrogen and / or carbon dioxide and methane.

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