CN114634188A - A kind of preparation method of oriented SAPO-34 molecular sieve membrane - Google Patents

Abstract

The invention relates to a preparation method of an oriented SAPO-34 molecular sieve membrane. The preparation method comprises the following steps: 1) preparation of SAPO-34 molecular sieve; 2) pretreatment of support body; 3) preparation of SAPO-34 molecular sieve membrane; 4) molecular sieve Calcination of membranes. Compared with the conventional sol route synthesis process, the Gel-less synthesis method only adds a small amount of synthetic sol or organic template agent in the reactor, which effectively avoids the complicated mass transfer and heat transfer during the synthesis process, which is beneficial to the batch synthesis of membranes. The SAPO‑34 molecular sieve membrane prepared by this method can be used for gas sieving, such as the removal of CO ₂ and N ₂ in the natural gas purification process. The preparation process is economical, safe and environmentally friendly, and can be used for industrial scale-up preparation of molecular sieve membranes.

Description

A kind of preparation method of oriented SAPO-34 molecular sieve membrane

technical field

The invention provides a preparation method of an oriented SAPO-34 molecular sieve membrane, which belongs to the application field of molecular sieve membrane material separation.

Background technique

The membrane separation process has the advantages of low energy consumption, small footprint and economical cost. As a representative of the eight-membered ring gas separation molecular sieve membrane, SAPO-34 molecular sieve membrane exhibits superior gas permeability, with higher CO ₂ / The separation performance of _CH4 and _CO2 / _N2 , and the construction of SAPO-34 molecular sieve membrane with oriented pore system can greatly improve the separation performance of the membrane, showing potential application prospects in the application of _CO2 removal from natural gas and biogas.

Most of the existing SAPO-34 molecular sieve membranes are synthesized by conventional hydrothermal synthesis methods, such as the SAPO-34 molecular sieve membrane synthesized on silica support by IGBN _{Makertihartha} et al. (Microporous and Mesoporous Materials, 2020, 298, 110068). The N separation factor is 53, the separation factor for _CO2 / _CH4 of the SAPO-34 molecular sieve membrane prepared on the tubular porous alumina support by Yibing Mu et al. (Journal of Membrane Science, 2019, 575, 80-88 ₎ is 160, Yang Chen et al. (Journal of CO ₂ Utilization, 2017, 18, 30-40) Separation selection of equimolar CO ₂ /CH ₄ mixed gas by SAPO-34 molecular sieve membrane prepared on α-Al ₂ O ₃ four-channel hollow fiber support Sex is 160. The high-quality SAPO-34 molecular sieve membrane prepared by Ye Zhang et al. (Journal of Membrane Science, 2020, 612, 118451) has a CO ₂ /CH ₄ selectivity of 150, Rehman et al. (Chemical Engineering Research and Design, 2020, 153, 37- 48) The CO ₂ /CH ₄ selectivity of the SAPO-34 molecular sieve membrane prepared on the tubular support is 68. Meanwhile, the existing published invention patents CN107840351A and CN201410423061.9 both report the preparation method of SAPO-34 molecular sieve membrane. The above-mentioned journal papers and patent reports all use the conventional sol route to synthesize SAPO-34 molecular sieve membrane: the synthetic sol must submerge the carrier, and hydrothermally synthesize it in a closed high temperature and high pressure. The conventional sol route has the following drawbacks: a large amount of raw materials are consumed, and the reaction waste needs to be treated harmlessly; the surface of the carrier, the interior of the carrier pores and the sol body can be nucleated, which makes it difficult to ensure the repeatability of the synthesis; reaction pressure and reaction temperature and sol filling degree Proportional to lead to accidents and so on. Many of the above unfavorable factors hinder the industrialization process of molecular sieve membranes.

The present invention develops the Gel-less synthesis method of SAPO-34 molecular sieve membrane, and compared with the conventional sol route, the above three drawbacks are solved. This method only needs to add a small amount of sol in the reaction kettle, which avoids waste of reactants while ensuring the compactness of the film layer, and can greatly reduce the reaction waste; the steam environment effectively avoids the complex mass transfer and heat transfer in the synthesis process. , which is beneficial to the batch synthesis of membranes; the pressure drop in the kettle is 1/20-1/3 of the conventional sol route, which improves the safety of the reaction.

SUMMARY OF THE INVENTION

The purpose of the present invention is to improve the preparation method of SAPO-34 molecular sieve membrane, greatly reduce the waste of sol, improve the repeatability of membrane synthesis, achieve intrinsic safety, and reduce its industrial production cost. The SAPO-34 molecular sieve membrane prepared by this method has wide application prospects for the separation of gases such as CO ₂ /CH ₄ , N ₂ /CH ₄ , CO ₂ /N ₂ and the like.

For realizing the above-mentioned purpose of the invention, the present invention adopts following technical scheme:

A preparation method of oriented SAPO-34 molecular sieve membrane, the steps are as follows:

(1) Preparation of SAPO-34 molecular sieve seeds:

Add water, structure directing agent (SDA) and aluminum source to the beaker in turn, add silicon source dropwise after stirring for 5h, slowly add phosphoric acid after stirring for 3h, and age at room temperature for 2-24h. The final sol molar composition ratio is H ₂ O/Al ₂ O ₃ =100-900, SDA/Al ₂ O ₃ =0.7-4.5, P ₂ O ₅ /Al ₂ O ₃ =1-5, SiO ₂ /Al ₂ O ₃ = 0.4-1.6. Put the prepared synthetic sol into a PTFE reactor, and use microwave heating to react under the condition of 433-493K for 1-8h. The product obtained from the reaction is washed, centrifuged and dried to obtain SAPO-34 molecular sieve seed crystals.

(2) Pretreatment of porous support carrier:

The SAPO-34 molecular sieve seed crystals prepared in step (1) are dispersed in an ethanol solution, ultrasonicated and vigorously stirred to prepare a seed crystal suspension with a mass fraction of 0.025-0.2%. The α-Al ₂ O ₃ tube was covered with a heat shrinkable tube and placed in a 353K oven for 1 h. After taking it out, quickly put it into the SAPO-34 molecular sieve seed crystal suspension. After standing for 30-60s, pull it out at a constant speed with a pulling machine, and place it vertically for 10 minutes at room temperature. After the surface ethanol evaporates, put it in a 333K oven to dry overnight. , namely, the SAPO-34 nano-seed layer was prepared on the inner wall of the α-Al ₂ O ₃ tube. The seed layer density is 1-300 μg/cm ² .

(3) Preparation of SAPO-34 molecular sieve membrane:

Mix water, phosphoric acid and aluminum isopropoxide, stir vigorously for 3h to form a uniform sol, add silicon source and continue stirring for 2h. Finally, structure directing agent (SDA) was slowly added and aged at 600 rpm for 2-24 h to obtain a membrane synthesis sol. The final sol molar composition ratio is H ₂ O/Al ₂ O ₃ =100-900, SDA/Al ₂ O ₃ =0.7-4.5, P ₂ O ₅ /Al ₂ O ₃ =1-5, SiO ₂ /Al ₂ O ₃ = 0.4-1.6. Dip-coating the support coated with the seed layer in step (2) in a synthetic sol diluted 2.5-20 times for 5-30 s, adding 0.1-5% of the above-mentioned sol by volume to the reactor, and placing the carrier on the stainless steel In the reaction kettle and not in contact with the sol, the reaction 4-13d was heated under the condition of 443-473K. After the reaction, the membrane tube was washed and soaked for 1 hour, dried at 333K, and the SAPO-34 molecular sieve membrane was prepared by calcination in air atmosphere, calcination in oxygen atmosphere or low temperature ozone oxidation to remove the structure directing agent.

The porous support material selected in step (2) of the present invention is alumina, mullite, cordierite, silicon oxide, titanium oxide, silicon carbide or stainless steel; the shape of the support body is tubular, sheet and hollow fiber.

The aluminum source is aluminum hydroxide, sodium metaaluminate, aluminum flake, aluminum isopropoxide, aluminum n-butoxide, aluminum foil, aluminum powder or aluminum oxide.

The silicon source is silica sol, tetraethyl orthosilicate, tetramethyl orthosilicate, sodium silicate, water glass or silicon powder.

The structure directing agent (SDA) is N,N,N-trimethyladamantyl ammonium hydroxide, N,N,N-trimethyladamantyl ammonium bromide, N,N,N-trimethyl ammonium bromide. Adamantyl ammonium iodide, N,N,N-trimethylbenzylammonium hydroxide, N,N,N-trimethylbenzylammonium bromide, N,N,N-trimethylbenzylammonium iodide One or more combinations of ammonium hydroxide, tetraethylammonium hydroxide or dipropylamine.

The removal of the structure directing agent (SDA) was carried out in an oxygen atmosphere with an oxygen flow rate of 200ml min ^-1 , and calcined at 743K for 6h with a heating and cooling rate of 0.5K min ^-1 . The calcined SAPO-34 molecular sieve membrane was stored in a 383K oven for later use.

Effective effect of the present invention:

(1) The present invention adopts the Gel-less method to prepare the SAPO-34 molecular sieve membrane. Compared with the conventional sol route, it can save more than 98% of the reaction sol, reduce the water consumption for membrane rinsing, and avoid the waste liquid treatment step at the same time. The cost of industrial production, the autogenous pressure of the reaction kettle is greatly reduced, and the safety of the reaction is improved.

(2) The present invention adopts the Gel-less method to prepare the SAPO-34 molecular sieve membrane, only a very small amount of synthetic sol is added in the reaction kettle, and the crystallization of the membrane is strictly controlled on the surface of the carrier, which effectively avoids the complicated mass transfer and heat transfer in the synthesis process. , reducing the generation of defects and improving the repetition rate of film preparation.

(3) The present invention adopts the Gel-less method to prepare the SAPO-34 molecular sieve membrane, the orientation of the molecular sieve membrane is related to the orientation of the molecular sieve seed layer, and the orientation of the membrane can be directly controlled by changing the orientation of the seed layer, and the prepared height ( 100) Oriented SAPO-34 molecular sieve membrane exhibits excellent gas separation performance.

Description of drawings

FIG. 1 is the SEM image (FIG. 1a) and the XRD image (FIG. 1b) of the SAPO-34 seed crystal synthesized in Example 1. FIG.

Figure 2 is the SEM image of the surface of the seed layer dip-coated with 0.025wt% SAPO-34 molecular sieve nanosheet suspension (Figure 2a) and the SEM image of the cross-section of the seed layer dip-coated with different concentrations of SAPO-34 molecular sieve nanosheet suspension: 0.025 wt % (2b), 0.05 wt % (2c), 0.1 wt % (2d), 0.25 wt % (2e), 0.5 wt % (2f).

Figure 3 shows the XRD patterns of the seed layer dip-coated with SAPO-34 molecular sieve nanosheet suspensions with different concentrations: SAPO-34 standard peaks (3a), 0.025wt% (3b), 0.05wt% (3c), 0.1wt% ( 3d), 0.25wt% (3e), 0.5wt% (3f), * are characteristic peaks of α-Al ₂ O ₃ carrier.

4 is the SEM images of the surface and cross-section of the SAPO-34 molecular sieve membranes synthesized in Examples 2, 3, 4 and 5: 4a is the surface of the membrane M2 of Example 2, 4b is the section of the membrane M2 of Example 2, and 4c is an example 3 is the surface of the film M3 of Example 3, 4d is the cross-section of the film M3 of Example 3, 4e is the surface of the film M4 of Example 4, 4f is the cross-section of the film M4 of Example 4, 4g is the surface of the film M5 of Example 5, and 4h is the example 5 of the film M5 section.

5 is the SEM images of the surface and cross-section of the SAPO-34 molecular sieve membranes synthesized in Examples 6 and 7: 5a is the surface of the membrane M6 of Example 6, 5b is the section of the membrane M6 of Example 6, and 5c is the membrane M7 of Example 7 The surface and 5d are the section of the film M7 of Example 7.

6 is the SEM images of the surface and cross-section of the SAPO-34 molecular sieve membranes synthesized in Examples 11, 12, 13 and 14: 6a is the surface of the membrane M11 of Example 11, 6b is the section of the membrane M11 of Example 11, and 6c is an example 12 is the surface of the film M12, 6d is the cross section of the film M12 of Example 12, 6e is the surface of the film M13 of Example 13, 6f is the cross section of the film M13 of Example 13, 6g is the surface of the film M14 of Example 14, and 6h is the example 14 of the film M14 section.

Detailed ways

In order to further describe the present invention, specific embodiments for implementing the present invention are given below, but the claimed scope of the present invention is not limited to the embodiments.

Example 1

The preparation method of SAPO-34 molecular sieve membrane is as follows:

Step 1: Preparation of SAPO-34 molecular sieve seeds. Tetraethylammonium hydroxide (TEAOH, 35 wt%) and water _were mixed, and aluminum _isopropoxide powder ( _C9H21AlO3 , 98%) was added. After stirring for 5 h to form a clear solution, silicon source (AS-40, 40%) was added dropwise. After stirring was continued for ₃ h, phosphoric acid (H3PO4, 85% ₎ was slowly added, and the addition rate was controlled to prevent the formation of a precipitate. After addition, the mixture was aged at room temperature for 2 hours to form a clear synthetic sol. The final molar composition ratio of the sol was H ₂ O/Al ₂ O ₃ =140, TEAOH/Al ₂ O ₃ =4, P ₂ O ₅ /Al ₂ O ₃ =2, and SiO ₂ /Al ₂ O ₃ =0.6. The prepared synthetic sol was placed in a PTFE reactor, heated by microwave, and crystallized at 453K for 1 h. After the reaction was completed, the product was collected by centrifugation at 10,000 rpm, washed until neutral, and freeze-dried for use.

Step 2: Pretreatment of the porous support. The SAPO-34 molecular sieve seed crystals prepared in step (1) were dispersed in an ethanol solution, ultrasonicated and vigorously stirred to prepare a seed crystal suspension with a mass fraction of 0.025%. The α-Al ₂ O ₃ tube was covered with a heat shrinkable tube and placed in a 353K oven for 1 h. After taking it out, quickly put it into the SAPO-34 molecular sieve seed suspension, and after standing for 30s, pull it out at a constant speed with a pulling machine, and place it vertically for 10min at room temperature. The SAPO-34 nano-seed layer was prepared on the inner wall of the α-Al ₂ O ₃ tube, and the thickness of the seed layer was 50 nm.

Step 3: Preparation of SAPO-34 molecular sieve membrane. Mix water, phosphoric acid (H ₃ PO ₄ .85%) and aluminum isopropoxide (C9H ₂₁ AlO ₃ , 98%), stir vigorously for 3h to form a uniform sol, add silicon source (AS-40, 40%) and continue stirring for 2h . Finally, tetraethylammonium hydroxide (TEAOH, 35wt%) was slowly added and aged at 600rpm for 6h to prepare a membrane synthesis sol. The final molar composition ratio of the sol was H ₂ O/Al ₂ O ₃ =140, TEAOH/Al ₂ O ₃ =4, P ₂ O ₅ /Al ₂ O ₃ =2, and SiO ₂ /Al ₂ O ₃ =0.6. In the step (2), the support for coating the seed layer is dip-coated in the synthetic sol diluted 5 times for 30 s, and the above-mentioned sol of 5% of the volume of the reactor is added to the reactor, and the carrier is placed in the stainless steel reactor and does not mix with The sol was contacted, and the reaction was heated at 453K for 9d. After the reaction, the membrane was washed and soaked in deionized water for 1 h, and dried at 333K. Labeled as M1. The templating agent was removed under an oxygen atmosphere.

Step 4: Removal of organic structure directing agent. The TEAOH template was removed by calcination in an oxygen (99.99%) atmosphere. The flow rate of the oxygen gas flow was about 200 ml min ^-1 . The molecular sieve membrane was calcined for 6 h by passing oxygen into the tube furnace at a temperature of 743 K. min ^-1 . The calcined SAPO-34 molecular sieve membrane was stored in a 383K oven for later use.

The seed crystals shown in Fig. 1(a) have typical nanoplatelet morphology with uniform size, platelet diameters of 400–500 nm, crystal thicknesses of ~20 nm, and aspect ratios >20. The crystals are highly dispersed and have no agglomeration phenomenon, and are suitable for coating on 200nm alumina porous supports. The method of dip coating is used to make the seeds evenly distributed on the surface of the support. The XRD pattern of the seeds shows a pure phase CHA structure.

Example 2

The preparation method of SAPO-34 molecular sieve is the same as that in Example 1, and the difference in the membrane preparation process is that the synthesis time is 4 days. Marked as M2.

Example 3

The preparation method of SAPO-34 molecular sieve is the same as that in Example 1, and the difference in the membrane preparation process is that the synthesis time is 6 days. Marked as M3.

Example 4

The preparation method of SAPO-34 molecular sieve is the same as that in Example 1, and the difference in the membrane preparation process is that the synthesis time is 11 days. Marked as M4.

Example 5

The preparation method of SAPO-34 molecular sieve is the same as that in Example 1, and the difference in the membrane preparation process is that the synthesis time is 13 days. Marked as M5.

Example 6

The preparation method of SAPO-34 molecular sieve is the same as that in Example 1, and the difference in the membrane preparation process is that the synthesis time is 4 days and the synthesis temperature is 473K. Marked as M6.

Example 7

The preparation method of SAPO-34 molecular sieve is the same as that in Example 1, and the difference in the membrane preparation process is that the synthesis time is 4 days and the synthesis temperature is 493K. Marked as M7.

Example 8

The preparation method of SAPO-34 molecular sieve is the same as that in Example 1. The difference in the preparation process of membrane and seed crystal is that the mass fraction of the seed crystal suspension used for dip coating is 0.1%, the thickness of the seed crystal layer is 400 nm, and the membrane synthesis time is 4 days. . Marked as M8.

Example 9

The preparation method of SAPO-34 molecular sieve is the same as that of Example 1. The difference in the preparation process of membrane and seed crystal is that the mass fraction of the seed crystal suspension used for dip coating is 0.15%, the thickness of the seed crystal layer is 500 nm, and the membrane synthesis time is 4 days . Marked as M9.

Example 10

The preparation method of SAPO-34 molecular sieve is the same as that in Example 1. The difference in the preparation process of membrane and seed crystal is that the mass fraction of the seed crystal suspension used for dip coating is 0.2%, the thickness of the seed crystal layer is 800 nm, and the membrane synthesis time is 4 days. . Marked as M10.

Example 11

The preparation method of SAPO-34 molecular sieve is the same as that of Example 1. The difference in the preparation process of membrane and seed crystal is that the mass fraction of the seed crystal suspension used for dip coating is 0.05%, the thickness of the seed crystal layer is 200 nm, and the membrane synthesis time is 6 days. . Marked as M11.

Example 12

The preparation method of SAPO-34 molecular sieve is the same as that of Example 1. The difference in the preparation process of membrane and seed crystal is that the mass fraction of the seed crystal suspension used for dip coating is 0.1%, the thickness of the seed crystal layer is 400 nm, and the membrane synthesis time is 6 days. . Marked as M12.

Example 13

The preparation method of SAPO-34 molecular sieve is the same as that in Example 1. The difference in the preparation process of membrane and seed crystal is that the mass fraction of the seed crystal suspension used for dip coating is 0.15%, the thickness of the seed crystal layer is 500 nm, and the membrane synthesis time is 6 days. . Marked as M13.

Example 14

The preparation method of SAPO-34 molecular sieve is the same as that in Example 1. The difference in the preparation process of membrane and seed crystal is that the mass fraction of the seed crystal suspension used for dip coating is 0.2%, the thickness of the seed crystal layer is 800 nm, and the membrane synthesis time is 6 days. . Marked as M14.

Example 15

The preparation method of SAPO-34 molecular sieve is the same as that of Example 1. The difference in the preparation process of membrane and seed crystal is that the mass fraction of the seed crystal suspension used for dip coating is 0.1%, and the thickness of the seed crystal layer is 400 nm. Marked as M15.

Example 16

The preparation method of SAPO-34 molecular sieve is the same as that in Example 1. The difference in the preparation process of membrane and seed crystal is that the mass fraction of the seed crystal suspension used for dip coating is 0.15%, the thickness of the seed crystal layer is 500 nm, and the membrane synthesis time is 6 days. . Marked as M16.

Example 17

The preparation method of SAPO-34 molecular sieve is the same as that in Example 1. The difference in the preparation process of membrane and seed crystal is that the mass fraction of the seed crystal suspension used for dip coating is 0.2%, and the thickness of the seed crystal layer is 800 nm. Marked as M17.

The CO ₂ /CH ₄ gas separation performance test was carried out on the prepared SAPO-34 molecular sieve membrane. The test results are shown in Table 1. The test conditions are: the temperature is 25 °C, the transmembrane pressure drop is 0.2 MPa, and the permeate end pressure is maintained at 0.103 MPa , the molar composition is 50/50%, and the feed gas flow is 4000 ml min ^-1 . The gas flow rate on the permeate side was measured with a soap bubble flowmeter; the gas composition on the permeate side was analyzed with a gas chromatograph.

Table 1 Separation performance of SAPO-34 molecular sieve membrane for CO ₂ /CH ₄ mixed gas

Claims (7)

1. a preparation method of orientation SAPO-34 molecular sieve membrane, is characterized in that, prepared method at least comprises the following steps: (1) Preparation of SAPO-34 molecular sieve seed crystals: add water, structure directing agent (SDA), aluminum source, silicon source and phosphoric acid to a beaker in turn, and age at room temperature for 2-24 hours. The final sol molar composition ratio is H ₂ O/A1 ₂ O ₃ =100-900, SDA/Al ₂ O ₃ =0.7-4.5, P ₂ O ₅ /Al ₂ O ₃ =1-5, SiO ₂ /Al ₂ O ₃ = 0.4 to 1.6. Put the prepared synthetic sol into a PTFE reactor, and use microwave heating to react at 433 to 493 K for 1 to 8 hours. The product obtained from the reaction is washed, centrifuged and dried to obtain SAPO-34 molecular sieve seed crystals. (2) Pretreatment of the porous support: the porous support is coated with a layer of molecular sieve crystal seeds in step (1) by dipping-pulling method, vacuum suction method or wiping method, and the density of the seed layer is 1- 300 μg/cm ² . (3) Preparation of SAPO-34 molecular sieve membrane: water, phosphoric acid and aluminum source, silicon source and structure directing agent (SDA) were added to the beaker in turn, and aged at room temperature for 2-24 h. The final gel molar composition ratio is H ₂ O/Al ₂ O ₃ =100-900, SDA/Al ₂ O ₃ =0.7-4.5, P ₂ O ₅ /Al ₂ O ₃ =1-5, SiO ₂ /Al ₂ O ₃ =0.4 to 1.6. In step (2), the support coated with the seed layer is dip-coated in the synthetic sol diluted 2.5 to 20 times for 5 to 30 s, and the above-mentioned sol of 0.1 to 5% of the volume of the reactor is added to the reaction kettle, and the carrier is placed in stainless steel. In the reaction kettle and not in contact with the sol, the reaction is heated under the conditions of 443-473K for 4-13d. After the reaction, the membrane was washed and soaked in ionized water for 1 hour, dried at 333K, and the SAPO-34 molecular sieve membrane was prepared by removing the structure directing agent by air atmosphere calcination method, oxygen atmosphere calcination method or low temperature ozone oxidation method. 2. the preparation method of SAPO-34 molecular sieve membrane according to claim 1, is characterized in that, in step (1) and (3), the proportion of sol is: H ₂ O/Al ₂ O ₃ =100～ 900, SDA/Al ₂ O ₃ =0.7-4.5, P ₂ O ₅ /Al ₂ O ₃ =1-5, SiO ₂ /Al ₂ O ₃ =0.4-1.6. 3. the preparation method of SAPO-34 molecular sieve membrane according to claim 1, is characterized in that, in step (1), prepared SAPO-34 molecular sieve crystal seed is typical nano-flaky morphology, and size is uniform, The sheet diameter is 400-500 nm, the crystal thickness is ˜20 nm, and the aspect ratio is >20. 4. The preparation method of SAPO-34 molecular sieve membrane according to claim 1, characterized in that, the preparation method of the seed layer in step (2) is preferably a dip-pulling method. 5 . The preparation method of SAPO-34 molecular sieve membrane according to claim 1 , wherein in step (2), a 50-800 nm thick oriented SAPO-34 molecular sieve nanoplatelet seed layer is prepared. 6 . 6. the preparation method of SAPO-34 molecular sieve membrane according to claim 1, is characterized in that, in step (2) and (3), carrier material is ceramics or metal, and shape is sheet type or tubular type or hollow fiber or multi-channel vectors. 7. The preparation method of SAPO-34 molecular sieve membrane according to claim 1, characterized in that, in step (3), the amount of sol added is 0.5-5% of the volume of the reactor.

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