Nanosheet-shaped mfi-type molecular sieve, and preparation method and application thereof

Abstract

The application belongs to the technical field of molecular sieve, and provides a nanosheet MFI type molecular sieve, a preparation method and application thereof. The method comprises the following steps: mixing tetraethyl orthosilicate, tetrapropylammonium hydroxide and water, and aging to obtain an intermediate solution; mixing the intermediate solution, ammonium fluoride and water, and crystallizing to obtain the nanosheet MFI type molecular sieve. In the application, ammonium fluoride is introduced into a MFI type molecular sieve synthesis solution as a mineralizer, the morphology, b-axis thickness and twin crystal number of the nanosheet MFI type molecular sieve are adjusted by changing the aging time and the crystallization time, and finally, the nanosheet MFI type molecular sieve with uniform particle size, regular structure and almost no twin crystal is prepared, which can meet the customized synthesis demand of nanoscale zeolite materials. The MFI type molecular sieve membrane prepared by using the nanosheet MFI type molecular sieve prepared by the application has good gas separation value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of molecular sieve, in particular to a kind of nanosheet MFI type molecular sieve and its preparation method and application. BACKGROUND

[0002] MFI type molecular sieve has two-dimensional 10-membered ring channel, which is composed of straight channel parallel to b-axis direction and "Z" shape channel parallel to a-axis direction, b-axis channel transmission path is short, and has the pore size (0.53nm×0.56nm) of molecule size, suitable for the selective passage of some gas. Therefore, MFI type molecular sieve has wide application prospect in gas separation field. Nanosheet MFI type molecular sieve has the same channel structure and channel size as traditional molecular sieve, and the b-axis thickness is in nanoscale, its channel is shorter, and the gas transmission path is smaller, which improves the gas permeation rate while ensuring selectivity, and is beneficial to the further application of MFI type molecular sieve in gas separation. Therefore, it is of great significance to prepare a kind of nanosheet MFI type molecular sieve with uniform particle size, regular structure and no twin crystal. SUMMARY

[0003] The present application aims to overcome the problems in the prior art, and provides a kind of nanosheet MFI type molecular sieve and its preparation method and application.

[0004] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical solutions:

[0005] The present application provides a kind of nanosheet MFI type molecular sieve and its preparation method, comprising the following steps:

[0006] (1) mixing tetraethyl orthosilicate, tetrapropylammonium hydroxide and water, and aging to obtain an intermediate solution;

[0007] (2) mixing the intermediate solution, ammonium fluoride and water, and crystallizing to obtain the nanosheet MFI type molecular sieve.

[0008] Preferably, the mass ratio of tetraethyl orthosilicate, tetrapropylammonium hydroxide and water in step (1) is 15-16:5.5-6.5:17-18.

[0009] Preferably, the temperature of aging in step (1) is 80-100℃, and the aging time is 5-9h.

[0010] Preferably, the mass ratio of tetraethyl orthosilicate in step (1) to ammonium fluoride in step (2) is 15-16:1.8-2.5.

[0011] Preferably, the mass ratio of ammonium fluoride to water in step (2) is 1.8-2.5:17.5-18.5.

[0012] As preferred, the temperature of the mixing in step (2) is 80-100℃, and the time of the mixing is 10-14h.

[0013] As preferred, the temperature of the crystallization in step (2) is 80-100℃, and the time of the crystallization is 1-4d.

[0014] The application also provides the nanosheet MFI-type molecular sieve prepared by the preparation method.

[0015] The application also provides the application of the nanosheet MFI-type molecular sieve in the field of gas separation.

[0016] The application has the following beneficial effects:

[0017] The application provides a preparation method of nanosheet MFI-type molecular sieve, which comprises the following steps: mixing tetraethyl orthosilicate, tetrapropylammonium hydroxide and water to obtain an intermediate solution through aging; mixing the intermediate solution, ammonium fluoride and water to obtain nanosheet MFI-type molecular sieve through crystallization. In the application, ammonium fluoride is introduced into the MFI-type molecular sieve synthesis solution as a mineralizer, the morphology, b-axis thickness and twin crystal number of the nanosheet MFI-type molecular sieve are adjusted by changing the aging time and the crystallization time, and finally the nanosheet MFI-type molecular sieve with uniform particle size, regular structure and almost no twin crystal is prepared, which can meet the customized synthesis demand of nanoscale zeolite material. The MFI-type molecular sieve membrane prepared by using the nanosheet MFI-type molecular sieve prepared by the application has good gas separation performance. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is an XRD characterization graph of the nanosheet MFI-type molecular sieve in Example 1 (2Theta (degree) - 2θ (°), Intensity (a.u.) - intensity (a.u.));

[0019] Figure 2 It is an SEM characterization graph of the nanosheet MFI-type molecular sieve in Example 1;

[0020] Figure 3 It is an XRD characterization graph of the sheet MFI-type molecular sieve in Comparative Example 1 (2Theta (degree) - 2θ (°), Intensity (a.u.) - intensity (a.u.));

[0021] Figure 4 It is an SEM characterization graph of the sheet MFI-type molecular sieve in Comparative Example 1;

[0022] Figure 5XRD characterization pattern of the MFI type molecular sieve in Comparative Example 2 (2Theta (degree) - 2Q (°), Intensity (a.u.) - Intensity (a.u.));

[0023] Figure 6 SEM characterization pattern of the MFI type molecular sieve in Comparative Example 2;

[0024] Figure 7 XRD characterization pattern of the MFI type molecular sieve in Comparative Example 3 (2Theta (degree) - 2Q (°), Intensity (a.u.) - Intensity (a.u.));

[0025] Figure 8 SEM characterization pattern of the MFI type molecular sieve in Comparative Example 3;

[0026] Figure 9 XRD characterization pattern of the MFI type molecular sieve in Comparative Example 4 (2Theta (degree) - 2Q (°), Intensity (a.u.) - Intensity (a.u.));

[0027] Figure 10 SEM characterization pattern of the MFI type molecular sieve in Comparative Example 4;

[0028] Figure 11 XRD characterization pattern of the MFI type molecular sieve in Comparative Example 5 (2Theta (degree) - 2Q (°), Intensity (a.u.) - Intensity (a.u.));

[0029] Figure 12 SEM characterization pattern of the MFI type molecular sieve in Comparative Example 5;

[0030] Figure 13 XRD characterization pattern of the MFI type molecular sieve in Comparative Example 6 (2Theta (degree) - 2Q (°), Intensity (a.u.) - Intensity (a.u.));

[0031] Figure 14 SEM characterization pattern of the MFI type molecular sieve in Comparative Example 6;

[0032] Figure 15 XRD characterization pattern of the MFI type molecular sieve in Comparative Example 7 (2Theta (degree) - 2Q (°), Intensity (a.u.) - Intensity (a.u.));

[0033] Figure 16 SEM characterization pattern of the MFI type molecular sieve in Comparative Example 7;

[0034] Figure 17 XRD characterization graph (2Theta (degree) -2θ (°), Intensity (a.u.) -Intensity (a.u.) ) of the MFI type molecular sieve in the form of a sheet in Comparative Example 8;

[0035] Figure 18 SEM characterization graph of the MFI type molecular sieve in the form of a sheet in Comparative Example 8;

[0036] Figure 19 SEM characterization graph of the MFI type molecular sieve membrane in Application Example 1;

[0037] Figure 20 Data graph (Permeance (GPU) -Permeation flux (gas permeation unit), Temperature (℃) -Temperature (℃), Separation factor (separation factor) ) of the MFI type molecular sieve membrane in Application Example 1 for separation of a two-component H2 / CO2 gas at different temperatures. DETAILED DESCRIPTION

[0038] The present application provides a preparation method of a nanosheet MFI type molecular sieve, comprising the following steps:

[0039] (1) mixing tetraethyl orthosilicate, tetrapropylammonium hydroxide and water to obtain an intermediate solution;

[0040] (2) mixing the intermediate solution, ammonium fluoride and water to obtain the nanosheet MFI type molecular sieve.

[0041] In the present application, tetraethyl orthosilicate is used as a silicon source, tetrapropylammonium hydroxide is used as a structure directing agent, and ammonium fluoride is used as a mineralizer.

[0042] In the present application, in step (1), the mixing is preferably carried out by initially mixing tetrapropylammonium hydroxide and water, and then adding tetraethyl orthosilicate dropwise.

[0043] In the present application, the dropwise addition is carried out under stirring, and the stirring speed is preferably 700-800 r / min, further preferably 720-780 r / min, and more preferably 750-760 r / min; and the stirring temperature is preferably 20-30℃, further preferably 22-28℃, and more preferably 23-27℃.

[0044] In the present application, the mass ratio of tetraethyl orthosilicate, tetrapropylammonium hydroxide and water in step (1) is preferably 15-16:5.5-6.5:17-18, further preferably 15.2-15.8:5.7-6.3:17.2-17.8, and more preferably 15.3-15.7:5.9-6.1:17.3-17.7.

[0045] In the present application, the aging in step (1) is carried out under the condition of water bath heating; the temperature of the aging is preferably 80-100℃, further preferably 85-95℃, more preferably 88-92℃; the time of the aging is preferably 5-9h, further preferably 6-8h, more preferably 6.5-7.5h.

[0046] In the present application, the mass ratio of tetraethyl orthosilicate in step (1) to ammonium fluoride in step (2) is preferably 15-16:1.8-2.5, further preferably 15.2-15.8:2.0-2.3, more preferably 15.3-15.7:2.1-2.2.

[0047] In the present application, the mass ratio of ammonium fluoride in step (2) to water is preferably 1.8-2.5:17.5-18.5, further preferably 2.0-2.3:17.7-18.3, more preferably 2.1-2.2:17.8-18.2.

[0048] In the present application, the ammonium fluoride and water are first mixed, and then the obtained system is rapidly added to the intermediate solution, followed by the mixing in step (2).

[0049] In the present application, the mixing in step (2) is carried out under the condition of water bath heating, the rotation speed of the mixing is preferably 700-800r / min, further preferably 720-780r / min, more preferably 750-760r / min; the temperature of the mixing is preferably 80-100℃, further preferably 85-95℃, more preferably 88-92℃; the time of the mixing is preferably 10-14h, further preferably 11-13h, more preferably 11.5-12.5h.

[0050] In the present application, the crystallization in step (2) is preferably carried out in a crystallization kettle, the temperature of the crystallization is preferably 80-100℃, further preferably 85-95℃, more preferably 88-92℃; the time of the crystallization is preferably 1-4d, further preferably 1.2-3d, more preferably 1.3-1.5d.

[0051] In the present application, after the crystallization is completed, the obtained system is sequentially subjected to washing, centrifugation and drying to obtain the nanosheet-like MFI type molecular sieve.

[0052] In the present application, the washing and centrifugation are not subject to specific conditions, and can be completed by the conventional technical means in the art; the temperature of the drying is preferably 30-50℃, further preferably 35-45℃, more preferably 37-43℃.

[0053] The application further provides the nanosheet-shaped MFI type molecular sieve prepared by the preparation method.

[0054] The application further provides application of the nanosheet-shaped MFI type molecular sieve in the field of gas separation.

[0055] The technical solutions provided by the application are described in detail below in combination with examples, but they should not be understood as limiting the protection scope of the application.

[0056] Example 1

[0057] 6.03 g of tetrapropylammonium hydroxide and 17.5 g of water were initially mixed, then 15.6 g of tetraethyl orthosilicate was added dropwise under the condition of a temperature of 25 ℃ and a rotation speed of 750 r / min, the obtained mixed solution was aged in a 90 ℃ water bath for 6 h to obtain an intermediate solution; 2.22 g of ammonium fluoride and 18 g of water were first mixed, then the obtained system was rapidly added to the intermediate solution, and the system was stirred at a rotation speed of 750 r / min for 12 h under a 90 ℃ water bath, then was transferred to a crystallization kettle for crystallization at 90 ℃ for 1 d (1 day), after the end, the obtained system was sequentially washed, centrifuged and dried at 40 ℃ to obtain the nanosheet-shaped MFI type molecular sieve.

[0058] The nanosheet-shaped MFI type molecular sieve obtained in the example was characterized, and the XRD characterization graph of the nanosheet-shaped MFI type molecular sieve in the example was obtained as shown in Figure 1 From Figure 1 it can be obtained that the diffraction peaks at 2θ = 8.0°, 8.9°, 9.1°, 14.8°, 23.2°, 24.0°, 24.8°, 45.2°, 45.5° correspond to the (101), (020), (111), (301), (501), (303), (521), (1000) and (0100) crystal faces of silicalite-1 respectively, indicating that the nanosheet-shaped MFI type molecular sieve has been successfully synthesized; the SEM characterization graph of the nanosheet-shaped MFI type molecular sieve in the example is shown in Figure 2 From Figure 2 it can be obtained that the b-axis thickness of the nanosheet-shaped MFI type molecular sieve prepared in the example is 164.4 nm, the particle size is uniform, the structure is regular, and there is almost no twin crystal.

[0059] Comparative Example 1

[0060] In the control example 1, other conditions were unchanged, the aging time was modified to 12 h, and the crystallization time was modified to 3 d (3 days), and the sheet-shaped MFI type molecular sieve was obtained.

[0061] The sheet-shaped MFI type molecular sieve obtained in the comparative example was characterized, and the XRD characterization graph of the sheet-shaped MFI type molecular sieve in the comparative example was obtained as shown inFigure 3 shown; from Figure 3 It can be obtained that the diffraction peaks at 2θ=8.0°, 8.9°, 9.1°, 14.8°, 23.2°, 24.0°, 24.8°, 45.2°, and 45.5° correspond to the (101), (020), (111), (301), (501), (303), (521), (1000), and (0100) crystal planes of silicalite-1, respectively, indicating that the flake MFI type molecular sieve has been successfully synthesized; the SEM characterization diagram of the flake MFI type molecular sieve in this comparative example is as follows Figure 4 shown; from Figure 4 It can be seen that the flaky MFI molecular sieve prepared in this comparative example is thicker and has more twin crystals.

[0062] Comparative Example 2

[0063] The other conditions in Example 1 were kept unchanged, and the aging time was modified to 12 h and the crystallization time to 2 d to obtain a flaky MFI molecular sieve.

[0064] The flaky MFI molecular sieve obtained in this comparative example was characterized to obtain an XRD pattern of the flaky MFI molecular sieve in this comparative example. Figure 5 shown; from Figure 5 It can be obtained that the diffraction peaks at 2θ=8.0°, 8.9°, 9.1°, 14.8°, 23.2°, 24.0°, 24.8°, 45.2°, and 45.5° correspond to the (101), (020), (111), (301), (501), (303), (521), (1000), and (0100) crystal planes of silicalite-1, respectively, indicating that the flake MFI type molecular sieve has been successfully synthesized; the SEM characterization diagram of the flake MFI type molecular sieve in this comparative example is as follows Figure 6 shown; from Figure 6 It can be seen that the flaky MFI molecular sieve prepared in this comparative example is thicker and has more twin crystals.

[0065] Comparative Example 3

[0066] The other conditions in Example 1 were kept unchanged, and the aging time was modified to 12 h and the crystallization time to 1 d to obtain a flaky MFI molecular sieve.

[0067] The flaky MFI molecular sieve obtained in this comparative example was characterized to obtain an XRD pattern of the flaky MFI molecular sieve in this comparative example. Figure 7 shown; from Figure 7peaks at 2-theta = 8.0°, 8.9°, 9.1°, 14.8°, 23.2°, 24.0°, 24.8°, 45.2°, 45.5°, corresponding to (101), (020), (111), (301), (501), (303), (521), (1000) and (0100) crystal planes of silicalite-1, respectively, indicating that the flaky MFI type molecular sieve has been successfully synthesized; the SEM characterization graph of the flaky MFI type molecular sieve in the present example is shown in Figure 8 From Figure 8 It can be obtained from the above that, compared with Comparative Examples 1 and 2, the twin crystals of the flaky MFI type molecular sieve prepared in the present example are slightly reduced.

[0068] Comparative Example 4

[0069] While other conditions in Control Example 1 remain unchanged, the aging time is modified to 10 h, and the crystallization time is modified to 3 d, to obtain a flaky MFI type molecular sieve.

[0070] The flaky MFI type molecular sieve obtained in the present example is characterized to obtain the XRD characterization graph of the flaky MFI type molecular sieve in the present example, as shown in Figure 9 From Figure 9 It can be obtained from the above that, 2-theta = 8.0°, 8.9°, 9.1°, 14.8°, 23.2°, 24.0°, 24.8°, 45.2°, 45.5°, corresponding to (101), (020), (111), (301), (501), (303), (521), (1000) and (0100) crystal planes of silicalite-1, respectively, indicating that the flaky MFI type molecular sieve has been successfully synthesized; the SEM characterization graph of the flaky MFI type molecular sieve in the present example is shown in Figure 10 From Figure 10 It can be obtained from the above that, the b-axis thickness of the flaky MFI type molecular sieve prepared in the present example is reduced, and the twin crystals are slightly reduced.

[0071] Comparative Example 5

[0072] While other conditions in Control Example 1 remain unchanged, the aging time is modified to 10 h, and the crystallization time is modified to 3 d, to obtain a flaky MFI type molecular sieve.

[0073] The flaky MFI type molecular sieve obtained in the present example is characterized to obtain the XRD characterization graph of the flaky MFI type molecular sieve in the present example, as shown in Figure 11 From Figure 11peaks at 2-theta = 8.0°, 8.9°, 9.1°, 14.8°, 23.2°, 24.0°, 24.8°, 45.2°, 45.5°, corresponding to (101), (020), (111), (301), (501), (303), (521), (1000) and (0100) crystal planes of silicalite-1, respectively, indicating that the flaky MFI type molecular sieve has been successfully synthesized; the SEM characterization graph of the flaky MFI type molecular sieve in the present example is shown in Figure 12 From Figure 12 It can be obtained from the above that, compared with the comparative example 4, the b-axis thickness of the flaky MFI type molecular sieve prepared in the present example is reduced, and the amount of twin crystals is more.

[0074] Comparative example 6

[0075] The other conditions in the control example 1 are unchanged, the aging time is modified to 10h, and the crystallization time is modified to 1d, to obtain a flaky MFI type molecular sieve.

[0076] The flaky MFI type molecular sieve obtained in the present example is characterized, and the XRD characterization graph of the flaky MFI type molecular sieve in the present example is shown in Figure 13 From Figure 13 It can be obtained from the above that, 2-theta = 8.0°, 8.9°, 9.1°, 14.8°, 23.2°, 24.0°, 24.8°, 45.2°, 45.5°, corresponding to (101), (020), (111), (301), (501), (303), (521), (1000) and (0100) crystal planes of silicalite-1, respectively, indicating that the flaky MFI type molecular sieve has been successfully synthesized; the SEM characterization graph of the flaky MFI type molecular sieve in the present example is shown in Figure 14 From Figure 14 It can be obtained from the above that, the b-axis thickness of the flaky MFI type molecular sieve prepared in the present example is about 190nm, and the amount of twin crystals is reduced.

[0077] Comparative example 7

[0078] The other conditions in the control example 1 are unchanged, the aging time is modified to 10h, and the crystallization time is modified to 1d, to obtain a flaky MFI type molecular sieve.

[0079] The flaky MFI type molecular sieve obtained in the present example is characterized, and the XRD characterization graph of the flaky MFI type molecular sieve in the present example is shown in Figure 15 From Figure 15It can be obtained that the diffraction peaks at 2θ=8.0°, 8.9°, 9.1°, 14.8°, 23.2°, 24.0°, 24.8°, 45.2°, and 45.5° correspond to the (101), (020), (111), (301), (501), (303), (521), (1000), and (0100) crystal planes of silicalite-1, respectively, indicating that the flake MFI type molecular sieve has been successfully synthesized; the SEM characterization diagram of the flake MFI type molecular sieve in this comparative example is as follows Figure 16 shown; from Figure 16 It can be seen that the b-axis thickness of the flaky MFI molecular sieve prepared in this comparative example is reduced, and the amount of twins is less than that of the molecular sieves obtained in comparative examples 5 and 6.

[0080] Comparative Example 8

[0081] The other conditions in Example 1 were kept unchanged, and the aging time was modified to 4 h and the crystallization time to 1 d to obtain an MFI molecular sieve.

[0082] The MFI molecular sieve obtained in this comparative example was characterized to obtain an XRD characterization diagram of the MFI molecular sieve in this comparative example. Figure 17 shown; from Figure 17 It can be seen that most diffraction peaks correspond to the standard card, but the diffraction peaks between 11.9°-22.0° and 26.3°-45.5° are not obvious, and the diffraction peaks show low intensity overall, indicating that the crystallization of the MFI molecular sieve is incomplete; the SEM characterization diagram of the MFI molecular sieve in this comparative example is as follows Figure 18 shown; from Figure 18 It can be seen that the b-axis thickness of the MFI molecular sieve prepared in this comparative example is 101 nm, but the number of regular nanosheets in the product is extremely small, and it contains a large amount of amorphous material, which is consistent with the characterization results of XRD, indicating that the flaky MFI molecular sieve could not be successfully synthesized under this condition.

[0083] Application Example 1

[0084] The nano-sheet MFI molecular sieve prepared in Example 1 was hydrothermally crystallized at 180°C for 12 hours to obtain an MFI molecular sieve membrane. The obtained MFI molecular sieve membrane was characterized, and a SEM characterization image of the MFI molecular sieve membrane was obtained, as shown in FIG. Figure 19 shown; from Figure 19 It can be seen that the MFI molecular sieve membrane is densely cross-linked and defect-free, indicating that the MFI molecular sieve membrane is successfully prepared using the nano-sheet MFI molecular sieve in Example 1.

[0085] The MFI type molecular sieve membrane prepared by the application example is used to separate a two-component H2 / CO2 gas, and a data graph of the separation of the two-component H2 / CO2 gas at different temperatures by the MFI type molecular sieve membrane is obtained, as shown in Figure 20 From Figure 20 It can be obtained that the separation factor of the MFI type molecular sieve membrane prepared by the application example for the two-component H2 / CO2 gas is stable at about 7 at 25 DEG C, 50 DEG C, 75 DEG C and 100 DEG C, wherein the permeation flux of H2 increases from 310 GPU to 360 GPU, indicating that the MFI type molecular sieve membrane prepared by the application example has good H2 / CO2 gas separation performance.

[0086] From the above examples, it can be seen that the application provides a preparation method of nanosheet MFI type molecular sieve, ammonium fluoride is introduced as a mineralizer in a MFI type molecular sieve synthesis solution, the morphology, b-axis thickness and twin crystal number of the nanosheet MFI type molecular sieve are adjusted by changing the aging time and crystallization time, and finally the nanosheet MFI type molecular sieve with uniform particle size, regular structure and almost no twin crystal is prepared, which can meet the customized synthesis demand of nanoscale zeolite materials; the MFI type molecular sieve membrane prepared by the nanosheet MFI type molecular sieve prepared by the application has good gas separation value.

[0087] The above only describes the preferred embodiments of the application, and it should be noted that, for those skilled in the art, some improvements and refinements can be made without departing from the principles of the application, and these improvements and refinements should also be considered as the protection scope of the application.

Claims

1. Application of a nano-sheet MFI molecular sieve in the field of gas separation, characterized in that: The nano-sheet MFI molecular sieve is used to separate two-component H2 / CO2 gases; The preparation method of the nano-sheet MFI molecular sieve comprises the following steps: (1) mixing ethyl orthosilicate, tetrapropylammonium hydroxide and water, and aging the mixture to obtain an intermediate solution; (2) mixing the intermediate solution, ammonium fluoride and water, and crystallizing to obtain the nano-sheet-shaped MFI molecular sieve; The aging temperature in step (1) is 80-100° C., and the aging time is 5-9 hours; The crystallization temperature in step (2) is 80-100° C., and the crystallization time is 1-4 days.

2. The use according to claim 1, characterized in that The mass ratio of the tetraethyl orthosilicate, tetrapropylammonium hydroxide and water in step (1) is 15-16:5.5-6.5:17-18.

3. The use according to claim 1, characterized in that The mass ratio of the ethyl orthosilicate in step (1) to the ammonium fluoride in step (2) is 15-16:1.8-2.

5.

4. The use according to claim 1, wherein The mass ratio of ammonium fluoride to water in step (2) is 1.8-2.5:17.5-18.

5.

5. The use according to claim 1, characterized in that The mixing temperature in step (2) is 80-100° C., and the mixing time is 10-14 h.

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