A mixed matrix membrane for gas separation, its preparation method and application

Abstract

The present invention belongs to the field of gas separation, and relates to a mixed matrix membrane for gas separation, a preparation method thereof and an application. The preparation method comprises the following steps: mixing a hydroxide, water, an aluminum source, a template agent and a silicon source to obtain a sol; after stirring and aging the sol, carrying out a crystallization reaction, and drying to obtain a molecular sieve; fully stirring and mixing the molecular sieve with a dispersion solvent and then carrying out ultrasonic treatment to obtain a molecular sieve suspension; dropping the molecular sieve suspension onto a support, drying and then calcining to obtain an oriented layered molecular sieve membrane; immersing the membrane in a 1,2,4,5-benzenetetramine tetrahydrochloride solution, taking it out until there are no obvious liquid drops on the surface, and then dropping a toluene solution of terephthalaldehyde, and drying to obtain a mixed matrix membrane for gas separation. The present invention preferably solves the problem that it is difficult to balance gas permeability and selectivity, and can be used for the separation of hydrogen and nitrogen with high permeability and high selectivity.

Description

Technical Field

[0001] The present invention belongs to the field of gas separation, and relates to a mixed matrix membrane for gas separation, a preparation method thereof, and an application thereof. Background Art

[0002] As a secondary energy source, hydrogen cannot be obtained directly. Steam reforming of fossil fuels and water gas shift reaction are the main ways to produce hydrogen at present. However, the hydrogen produced by this method contains a large amount of by-products such as N2, CO2, and H2O. Therefore, it is necessary to separate and purify hydrogen.

[0003] Traditional gas separation generally uses distillation. Compared with traditional distillation separation, membrane separation has the advantages of simple operation, small floor area, and energy consumption reduction of about 90%. It is an environmentally friendly and efficient alternative to traditional gas separation processes. Membrane materials are mainly divided into organic membranes and inorganic membranes. Organic polymer materials have the advantages of strong plasticity, simple preparation, diverse functions, low cost, and good selectivity. They are the most widely used separation membrane materials at present. However, they have the disadvantages of poor heat resistance, corrosion resistance, mechanical strength, and low permeability. For example, the selectivity of polybenzimidazole membrane for H2 / CO2 can reach 140, but the permeability of H2 is only 3.15×10 -10 mol . m -2. s -1. Pa -1 . Inorganic membranes based on molecular sieve materials have a uniform and well-defined pore structure, which is convenient for gas molecules to pass through, and usually have the characteristics of high flux and thermal stability. However, the selectivity of molecular sieve membranes is generally low. For example, the selectivity of MCM-22 molecular sieve membrane obtained by single vacuum filtration for H2 / N2 is only 2, but the H2 permeation flux exceeds 1.0×10 -6 mol . m -2. s -1. Pa -1 , and it is easy to fall off, making it difficult to prepare a continuous and defect-free membrane.

[0004] In summary, the existing membrane materials for hydrogen / nitrogen separation currently have problems such as low hydrogen permeability and low selectivity of hydrogen and other gases, which greatly limit the development and industrial application of hydrogen separation membranes. Summary of the Invention

[0005] The technical problem to be solved by the present invention is the problem that it is difficult to balance the gas permeation amount and selectivity of existing gas separation membrane materials, and to provide a new molecular sieve mixed matrix membrane for hydrogen / nitrogen separation. This method has the advantage of being able to balance the gas permeability and selectivity of gas separation membrane materials.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] A preparation method of a mixed matrix membrane for gas separation, comprising the following steps: mixing a hydroxide, water, an aluminum source, a templating agent, and a silicon source to obtain a sol; after stirring and aging the sol, performing a crystallization reaction, and drying to obtain a molecular sieve; fully stirring and mixing the molecular sieve with a dispersion solvent and then sonicating to obtain a molecular sieve suspension; dropping the molecular sieve suspension onto a support, drying, and then calcining to obtain an oriented layered molecular sieve membrane; immersing the oriented layered molecular sieve membrane in a 1, 2, 4, 5-benzenetetramine tetrahydrochloride solution, taking it out until there are no obvious liquid drops on the surface, and then dropping a toluene solution of terephthalaldehyde, and drying to obtain a mixed matrix membrane for gas separation.

[0008] Further, the hydroxide is one or more of sodium hydroxide, potassium hydroxide, and cesium hydroxide; the aluminum source is one or two of sodium aluminate and aluminum hydroxide; preferably sodium aluminate; preferably sodium hydroxide; the templating agent is one or more of hexamethyleneimine, dicyclohexylamine, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and N, N, N-trimethyladamantane ammonium hydroxide; preferably hexamethyleneimine and dicyclohexylamine; the silicon source is one or more of silica gel, sodium metasilicate nonahydrate, tetraethyl orthosilicate, and silica white; preferably silica gel.

[0009] Further, the molar ratio of the hydroxide, water, aluminum source, templating agent, and silicon source is 0.1 - 0.2:18:0.01 - 0.066:0.3 - 1:1.

[0010] Further, the stirring and aging temperature is 20 - 40 °C, and the stirring and aging time is 2 - 5 hours; the crystallization reaction temperature is 160 - 200 °C, and the crystallization reaction time is 1 - 7 days; the sonication time is 0.5 - 3 hours.

[0011] Further, the dispersion solvent for preparing the molecular sieve suspension is one of water, ethyl acetate, ethanol, or methanol; the concentration of the molecular sieve suspension is 0.125 - 1 wt%.

[0012] Further, the support is placed on a heating table for heating, and the temperature of the heating table is 80 - 200 °C.

[0013] Further, the calcination temperature is 500 - 600 °C, and the calcination time is 4 - 8 hours.

[0014] Further, the time for immersing the layered molecular sieve membrane in the 1, 2, 4, 5-benzenetetramine tetrahydrochloride solution is 0.5 - 3 hours.

[0015] Further, the synthesized molecular sieve is one of two-dimensional six-membered ring molecular sieves such as MCM-22 and ITQ-2; preferably MCM-22.

[0016] The support is mullite or α-Al2O3 ceramic, preferably α-Al2O3 ceramic.

[0017] The present invention also provides a mixed matrix membrane for gas separation, which is prepared by the above preparation method.

[0018] The present invention also provides the application of the above mixed matrix membrane in hydrogen separation.

[0019] Beneficial effects

[0020] In the present invention, the method of thermal dropping of molecular sieve solution is used to load MCM-22 molecular sieve on the support, so that the orientation of the obtained MCM-22 molecular sieve membrane is much higher than that of the molecular sieve membrane prepared by the conventional hydrothermal method, and thus has a higher hydrogen permeability. In addition, the method of the present invention composes a poly(p-phenylene benzimidazole) membrane on the inorganic oriented MCM-22 molecular sieve layer, which has a higher hydrogen permeability, balances the gas permeation amount and selectivity, and can be used for the separation of hydrogen and nitrogen with high permeability and high selectivity. Description of the drawings

[0021] Figure 1 It is a scanning electron microscope (SEM) image of the surface of the oriented MCM-22 molecular sieve membrane prepared by the method of Example 1.

[0022] Figure 2 It is a scanning electron microscope (SEM) image of the cross section of the oriented MCM-22 molecular sieve membrane prepared by the method of Example 1.

[0023] Figure 3 It is an X-ray diffraction (XRD) pattern of the MCM-22 molecular sieve powder and the oriented MCM-22 molecular sieve membrane prepared by the method of Example 1.

[0024] Figure 4 It is a scanning electron microscope (SEM) image of the surface of the oriented MCM-22 molecular sieve mixed matrix membrane prepared by the method of Example 1. Detailed implementation manners

[0025] Example 1

[0026] A preparation method of a mixed matrix membrane for gas separation, comprising the following steps:

[0027] (1) First, water, sodium hydroxide, and sodium aluminate are added to a beaker and stirred at 30 o °C until clear and transparent. Hexamethyleneimine is added dropwise to the beaker, and then stirred for another 30 minutes until uniformly mixed. Dicyclohexylamine is added and stirred for 30 minutes until uniformly mixed. Silica gel (40%) is slowly added dropwise. After the mixture is stirred and aged at 30 °C for 4 hours, it is transferred to a stainless steel autoclave lined with polytetrafluoroethylene and heated at 170 oThe C was crystallized for 3 days. After the crystallization was completed, it was washed with water until neutral and then dried to obtain MCM-22 molecular sieve. The molar ratio of silica gel: sodium aluminate: sodium hydroxide: hexamethyleneimine: dicyclohexylamine: water in the mixed solution was 1: 0.033: 0.1: 0.3: 0.4: 18;

[0028] (2) The MCM-22 molecular sieve prepared in (1) was diluted with water to obtain a 0.125 wt% MCM-22 molecular sieve suspension. After ultrasonic dispersion for 1 hour, 2.5 mL of the molecular sieve suspension was thermally dropped onto a support placed on a heating stage at 150 °C. The support was an α-Al2O3 ceramic substrate with a pore diameter of 0.22 microns and a diameter of centimeters, and it was cooled to room temperature. After calcination at 550 o °C for 6 hours, a high-permeability oriented layered MCM-22 molecular sieve membrane was obtained;

[0029] (3) The oriented layered MCM-22 molecular sieve membrane prepared in (2) was immersed in a 1.5 wt% solution of 1, 2, 4, 5-benzenetetramine tetrahydrochloride (BTA) for 0.5 hours. After taking it out until there were no obvious liquid drops on the surface, a toluene solution of 1.0 wt% terephthalaldehyde (TPA) was dropped, and after drying, an MCM-22 molecular sieve mixed matrix membrane was obtained. This sample was denoted as M0.125-0.5;

[0030] (4) The MCM-22 molecular sieve mixed matrix membrane prepared in step (3) was subjected to gas separation testing.

[0031] Figure 1 Figure 15 is a scanning electron microscope (SEM) image of the surface of the oriented MCM-22 molecular sieve membrane prepared by the method of Example 1. The results show that the α-Al2O3 ceramic substrate is completely covered by flaky MCM-22 molecular sieve, and the membrane surface is continuous.

[0032] Figure 2 Figure 19 is a scanning electron microscope (SEM) image of the cross-section of the oriented MCM-22 molecular sieve mixed matrix membrane prepared by the method of Example 1. The membrane layer thickness is about 1 micron.

[0033] Figure 3 Figure 23 is the X-ray diffraction (XRD) pattern of the MCM-22 molecular sieve powder and the oriented MCM-22 molecular sieve membrane prepared by the method of Example 1. The results show that obvious (00l) peaks appear in the XRD spectrum, indicating that the prepared MCM-22 molecular sieve membrane has orientation.

[0034] Figure 4 Figure 27 is a scanning electron microscope (SEM) image of the surface of the oriented MCM-22 molecular sieve mixed matrix membrane prepared by the method of Example 1. The results show that the surface of the MCM-22 molecular sieve membrane is completely covered by a poly(p-phenylenebenzimidazole) membrane layer, the surface is continuous, and there are no obvious defects.

[0035] Example 2-3

[0036] According to the method of Example 1, only the soaking time in step (3) was changed, and the adjusted soaking times were 2 hours and 3 hours in sequence, denoted as M0.125-x, where x = 2.0, 3.0.

[0037] Example 4

[0038] According to the method of Example 1, only the concentration of the suspension in step (2) was changed, and the adjusted concentration of the suspension was 0.5 wt%, and this sample was denoted as M0.5-0.5.

[0039] Examples 5-6

[0040] According to the method of Example 4, only the soaking time in step (3) was changed, and the adjusted soaking times were 2 hours and 3 hours in sequence, denoted as M0.5-x, where x = 2.0, 3.0.

[0041] Example 7

[0042] According to the method of Example 1, only the concentration of the suspension in step (2) was changed, and the adjusted concentration of the suspension was 1.0 wt%, and this sample was denoted as M1.0-0.5.

[0043] Examples 8-9

[0044] According to the method of Example 7, only the soaking time in step (3) was changed, and the adjusted soaking times were 2 hours and 3 hours in sequence, denoted as M1.0-x, where x = 2.0, 3.0.

[0045] Comparative Example 1

[0046] A method for preparing a mixed matrix membrane for gas separation, comprising the following steps: (1) First, deposit MCM-22 molecular sieve on an α-Al2O3 ceramic substrate by an ultrasonic-assisted method. (2) Age the silica sol at 50 o °C for 60 hours, and then age at room temperature for about 7 days. The aged silica sol was diluted 256 times (Type A silica sol) and 128 times (Type B silica sol) with ethanol. The α-Al2O3 ceramic substrate was vertically impregnated and contacted with Type A silica sol for 20 seconds, and then dried for 40 seconds. The α-Al2O3 ceramic substrate was vertically impregnated and contacted with Type B silica sol for 20 seconds, and then dried for 40 seconds. This process was repeated 3 times. (3) Dry the MCM-22 molecular sieve membrane prepared in step (2) in an oven at 120 °C to obtain a sample, and this sample was denoted as MS. (4) Perform gas separation tests on the MCM-22 molecular sieve membrane prepared in step (3).

[0047] Comparative Example 2

[0048] A method for preparing a mixed matrix membrane for gas separation, comprising the following steps: (1) First, add water, sodium hydroxide, and sodium aluminate to a beaker, and stir at 30 o °C until clear and transparent to obtain solution A. Dropwise add hexamethylenimine to solution A and continue stirring for 30 minutes until evenly mixed to obtain solution B. Add dicyclohexylamine to solution B and stir for 30 minutes until evenly mixed to obtain solution C. Slowly dropwise add silica gel (40%) to solution C to obtain solution D. After stirring and aging solution D for 4 hours, transfer it to a stainless steel autoclave with a polytetrafluoroethylene lining, and crystallize at 150 o °C for 3 days. After crystallization, wash with water until neutral, and dry to obtain MCM-22 molecular sieve. The molar ratio of silica gel: sodium aluminate: sodium hydroxide: hexamethylenimine: dicyclohexylamine: water in the mixed solution is 1: 0.028: 0.15: 0.5: 0.4: 44. (2) Using absolute ethanol as a solvent, disperse the MCM-22 molecular sieve obtained in step (1) into a solution with a concentration of 5 g / L, denoted as solution E. Slowly place the dried ceramic tube into solution E, immerse it for 30 seconds and then slowly take it out, and then place it in an oven at 110 o °C for drying. Repeat the immersion process after 1 hour. (3) Place solution D and the ceramic tube obtained in step (3) together into a polytetrafluoroethylene stainless steel crystallization autoclave, and crystallize at 150 o °C for 3 days, take it out for washing, drying, and calcination to obtain an MCM-22 molecular sieve membrane, and this sample is denoted as M. (4) Perform gas separation tests on the MCM-22 molecular sieve membrane prepared in step (3).

[0049] Comparative Example 3

[0050] A method for preparing a mixed matrix membrane for gas separation, comprising the following steps: (1) First, stir water and sodium hydroxide at room temperature until clear and transparent to obtain solution A. Add aluminum foil to solution A until evenly mixed to obtain solution B. Mix silica sol and water, and rapidly stir at 60 °C to obtain solution C. Add solution B to solution C and stir overnight at room temperature. The mixed solution is prepared according to the ratio of 50 Na2O: 1 Al2O3: 5 SiO2: 1005 H2O. (2) Transfer the mixed solution to a stainless steel autoclave with a polytetrafluoroethylene lining, vertically place an α-Al2O3 ceramic substrate, and crystallize at 120 o °C for 24 hours. (3) After crystallization, wash with water until neutral, and dry to obtain a primary SOD molecular sieve membrane. (4) Repeat the above steps to obtain a secondary SOD molecular sieve membrane, and this sample is denoted as SOD. (5) Perform gas separation tests on the secondary SOD molecular sieve membrane prepared in step (4).

[0051] Comparative Example 4

[0052] A method for preparing a mixed matrix membrane for gas separation, comprising the following steps: (1) Add 2,3,5,6-tetrafluoroterephthalonitrile (2.00 g), 5,5’,6,6’-tetrahydroxy-3,3’,3’-tetramethyl-1,1’-spirobisindane TTSBI (3.20 g), potassium carbonate (3.45 g) and N,N-dimethylpyrrolidone / toluene (15.0 / 5.00 mL) into a three-necked flask. Nitrogen is passed through the flask and reacted at 155 °C for 3.5 hours to obtain a mixed solution A. The mixed solution A is poured into methanol, washed and dried to obtain PIM-1. (2) Add the PIM-1 (2.00 g) prepared in step (1) and 200 mL of tetrahydrofuran into a three-necked flask, stir in a nitrogen atmosphere at 65 °C for 8 hours to obtain a mixed solution B. Add 20.0 mL of hydroxylamine solution to the mixed solution B at 69 °C and react for 20 hours to obtain a reactant C. The reactant C is poured into ethanol, filtered and dried to obtain AO-PIM. (3) Stir γ-(2,3-epoxypropoxy)propyltrimethoxysilane (0.23 mmol) and polyetheramine M2070 (0.23 mmol) at 50 °C for 5 hours to obtain a mixture D. Add SOD (0.23 mmol) to the mixture D at 30 °C to obtain a reactant E. After dialysis, rotation and drying of the reactant E, SOD(PLs) is obtained. (4) Add SOD(PLs) and AO-PIM into DMF respectively and perform ultrasonic treatment to obtain a solution F and a solution G respectively. Then mix the solution F and the solution G and stir continuously to obtain a mixture H. Cast the mixture H to obtain an AO-PIM film.

[0053] The results of specific examples and comparative examples are shown in the following table:

[0054]

[0055] 1 Suspension concentration; 2 Immersion time; 3 Hydrogen permeability; 4 Hydrogen / nitrogen selectivity.

[0056] From the above results, it can be seen that the MCM-22 molecular sieve membrane obtained in Comparative Example 1 has an H2 / N2 selectivity of 100, which is equivalent to the effect of Example 5 of the present invention. However, due to the multiple depositions of the sol, the preparation process is complex compared with the method of the present invention, and the hydrogen permeability is only 2.0×10 -8 mol . m -2. s -1. Pa -1, which is 13 times lower than the hydrogen permeability of Example 5 of the present invention. The hydrogen permeability of the MCM-22 molecular sieve membrane obtained in Comparative Example 2 reached 1.09×10 -6 mol . m -2. s -1. Pa -1 , which is equivalent to the effect of Example 1 of the present invention. However, since this method uses an inorganic membrane and the surface of the MCM-22 molecular sieve layer is not coated with the poly(p-phenylenebenzimidazole) membrane used in the present invention, the H2 / N2 selectivity is only 3.6, which is about 9 times lower than the H2 / N2 selectivity of Example 1 of the present invention. The hydrogen permeability of the MCM-22 molecular sieve membrane obtained in Comparative Example 3 reached 9.5×10 -6 mol . m -2. s -1. Pa -1 , which is equivalent to the effect of Example 2 of the present invention. However, since the surface of the MCM-22 molecular sieve layer in this method is not coated with the poly(p-phenylenebenzimidazole) membrane used in the present invention, the H2 / N2 selectivity is only 5.46, which is about 14 times lower than the H2 / N2 selectivity of Example 1 of the present invention. Moreover, compared with the method of the present invention, the method described in Comparative Example 3 has a long preparation time and complex operation. The AO-PIM thin film obtained in Comparative Example 4 has an H2 / N2 selectivity of 34.2 and a hydrogen permeability of 7.31×10 -6 mol . m -2. s -1. Pa -1 The permeability of hydrogen is equivalent to the effect of Example 1 of the present invention. However, since this method dopes a small amount of inorganic SOD molecular sieve in the polymer, compared with the method of the present invention, its mechanical properties are poor, and the preparation process is complex, with a long cycle. A large amount of toxic and harmful substances such as tetrahydrofuran are used in the preparation process.

Claims

1. A method for preparing a mixed matrix membrane for hydrogen / nitrogen separation, characterized in that, It includes the following steps: Mix hydroxide, water, aluminum source, template agent and silicon source to obtain a sol; the template agent is hexamethyleneimine and dicyclohexylamine; after stirring and aging the sol, carry out a crystallization reaction, and obtain MCM-22 molecular sieve after drying; fully stir and mix the MCM-22 molecular sieve with a dispersion solvent and then ultrasonicate to obtain a molecular sieve suspension; the concentration of the molecular sieve suspension is 0.5 wt%; drop the molecular sieve suspension onto a support, and the support is placed on a heating table for heating, and the temperature of the heating table is 80-200 °C; after drying, calcine to obtain an oriented layered molecular sieve membrane; immerse the oriented layered molecular sieve membrane in a 1, 2, 4, 5-benzenetetramine tetrahydrochloride solution for 2 hours, take it out until there are no obvious liquid drops on the surface, then drop a toluene solution of terephthalaldehyde, and obtain a mixed matrix membrane for hydrogen / nitrogen separation after drying; the mixed matrix membrane is a poly(p-phenylbenzimidazole) membrane composite on MCM-22 molecular sieve.

2. The preparation method of the mixed matrix membrane for hydrogen / nitrogen separation according to claim 1, characterized in that, The hydroxide is one or more of sodium hydroxide, potassium hydroxide, cesium hydroxide; the aluminum source is one or two of sodium aluminate and aluminum hydroxide; the silicon source is one or more of silica gel, sodium metasilicate nonahydrate, tetraethyl orthosilicate, and fumed silica.

3. The preparation method of the mixed matrix membrane for hydrogen / nitrogen separation according to claim 1, characterized in that, The molar ratio of hydroxide, water, aluminum source, template agent and silicon source is 0.1-0.2:18:0.01-0.066:0.3-1:

1.

4. The preparation method of the mixed matrix membrane for hydrogen / nitrogen separation according to claim 1, wherein The stirring and aging temperature is 20-40 °C, and the stirring and aging time is 2-5 hours; the crystallization reaction temperature is 160-200 °C, and the crystallization reaction time is 1-7 days; the ultrasonication time is 0.5-3 hours.

5. The method for preparing a mixed matrix membrane for hydrogen / nitrogen separation according to claim 1, characterized in that, The dispersion solvent for preparing the molecular sieve suspension is one of water, ethyl acetate, ethanol or methanol.

6. The method for preparing a mixed matrix membrane for hydrogen / nitrogen separation according to claim 1, wherein The calcination temperature is 500-600 °C, and the calcination time is 4-8 hours.

7. A mixed matrix membrane for hydrogen / nitrogen separation, characterized in that, Prepared by the preparation method according to any one of claims 1-6.

8. Application of the mixed matrix membrane according to claim 7 in hydrogen separation.

Images