KFI molecular sieve membrane as well as preparation method and application thereof

Abstract

The invention discloses a KFI molecular sieve membrane as well as a preparation method and application thereof, relates to the field of molecular sieve membranes, and particularly relates to the preparation of the KFI molecular sieve membrane at a certain temperature by coating seed crystals on a porous support body by adopting a secondary hydrothermal growth method and putting the porous support body into synthetic sol. The molar ratio of the synthesized sol is as follows: 1 Al2O3: 2.3 K2O: 0.1 SrO: 10 SiO2: 100-500 H2O. The KFI molecular sieve membrane prepared by the method grows compactly and continuously, and the thickness of a crystal layer is 10 microns. At the temperature of 75 DEG C, the KFI molecular sieve membrane has the separation performance on a 10wt% water / ethanol system as follows: the flux of the membrane is 0.93 kg.m <-2 >. H <-1 >, and the separation factor reaches 219. The KFI molecular sieve membrane is prepared for the first time, is successfully applied to separation of water and alcohols, and has the advantages of being environmentally friendly, simple in membrane separation device, easy and convenient to operate, capable of achieving continuous production and the like.

Description

Technical Field

[0001] The invention relates to the field of molecular sieve membranes, and in particular to a KFI molecular sieve membrane and a preparation method and application thereof. Background Art

[0002] The separation process is an important part of chemical production. Compared with traditional separation processes such as chemical adsorption, physical adsorption and distillation, membrane separation technology has the advantages of low energy consumption, simple operation and continuous production. Molecular sieve membrane has an adjustable skeleton structure and excellent adsorption and separation performance, and is regarded as an ideal membrane separation material. Molecular sieve membrane not only has advantages in the application of catalysis, gas separation and other fields, but also has broad application prospects in separation fields such as alcohol dehydration.

[0003] KFI molecular sieve has 0.39×0.39nm octahedral pores, which allow molecules with smaller kinetic diameters such as H2O (0.27nm), NH3 (0.29nm), and H2 (0.289nm) to pass through, and can adsorb and separate gases such as CO2 and CH4, or separate them from molecules with larger kinetic diameters (such as alcohols, macromolecular alkanes, etc.). Remy et al. synthesized metal ion-exchanged KFI molecular sieves for separation of CO2 / CH4 and CO2 / N2, among which Li-KFI showed the highest selectivity. Kencana et al. from Pohang University in South Korea used KFI molecular sieves to separate CH4 / N2 at room temperature, with a separation factor of 11.8.

[0004] Studies have shown that the use of molecular sieves depends on particle size and dosage, which leads to problems such as difficulty in separation and recovery and low reuse rate, limiting the application of molecular sieves. In order to solve this problem, many researchers have tried to prepare molecular sieve membranes using technologies such as hydrothermal synthesis. This not only overcomes the difficulty of separating molecular sieves from products, but also the prepared molecular sieve membranes are conducive to improving the distribution area and dispersion of molecular sieve particles, and controlling the material separation efficiency of the membrane by controlling the rate at which the material flows through the membrane. Compared with molecular sieve powder, the separation operation flux using molecular sieve membranes is larger, which greatly speeds up the separation and adsorption operation. The process of separation and adsorption using molecular sieve membranes is simple, and liquid and gas molecules can be separated continuously. This is a major advantage of the application of molecular sieve membranes over the application of molecular sieve powders.

[0005] At present, researchers mainly study the optimization method of KFI molecular sieve powder synthesis technology, such as patent CN112479225A uses cyclodextrin as a template to synthesize nano KFI molecular sieve particles; patent CN 114735717A uses FAU molecular sieve crystallization method to quickly synthesize KFI molecular sieve particles. After a large number of literature surveys, no relevant reports on KFI molecular sieve membranes were found. In summary, based on the characteristics of KFI molecular sieve adsorption of substances and the advantages of molecular sieve membranes in the separation process, the present invention proposes a method for preparing KFI molecular sieve membranes. Summary of the invention

[0006] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art and to provide a KFI molecular sieve membrane and a preparation method thereof.

[0007] The technical solution of the present invention is as follows:

[0008] A method for preparing a KFI molecular sieve membrane uses pure phase KFI type molecular sieve crystals as seed crystals, silicon source, aluminum source, strontium source, alkali source and ultrapure water as raw materials, and prepares the KFI molecular sieve membrane on a support through a secondary hydrothermal growth method.

[0009] As a preferred embodiment of the present invention, the following steps are included:

[0010] S1: Mix silicon source, aluminum source, strontium source, alkali source and ultrapure water in a certain proportion and stir to form a uniform initial sol; continue stirring, then transfer to a stainless steel reactor with a polytetrafluoroethylene liner and place in an oven for crystallization; after the crystallization, wash the product with boiling ultrapure water until it is neutral, and dry it to obtain KFI molecular sieve seed powder;

[0011] S2: evenly coating the KFI molecular sieve seed powder on the surface of the support, drying, and obtaining a support coated with the seed powder;

[0012] S3: Mix silicon source, aluminum source, strontium source, alkali source and ultrapure water in a certain proportion and stir to form a uniform synthetic sol; continue stirring, and then transfer to a stainless steel reactor with a polytetrafluoroethylene lining; insert the support coated with seed crystals vertically into the synthetic sol and place it in an oven for crystallization; after the crystallization is completed, wash the product with boiling ultrapure water until it is neutral, and dry it for 8-12 hours to obtain a KFI molecular sieve membrane.

[0013] As a preferred solution of the present invention, step S1 at least includes the following technical features:

[0014] The molar ratio of the initial sol is 1Al2O3:2.3K2O:0.1SrO:10SiO2:100-500H2O;

[0015] Continue stirring for 1-3 hours;

[0016] The crystallization temperature is 140-160°C and the crystallization time is 3-5 days;

[0017] The drying temperature is 70-90°C and the drying time is 8-12 hours.

[0018] As a preferred solution of the present invention, step S3 at least includes the following technical features:

[0019] The molar ratio of the synthetic sol is 1Al2O3:2.3K2O:0.1SrO:10SiO2:100-500H2O;

[0020] Continue stirring for 1-3 hours;

[0021] The crystallization temperature is 100-200°C and the crystallization time is 2-6 days;

[0022] The drying temperature is 70-90°C and the drying time is 8-12 hours.

[0023] As a preferred solution of the present invention, steps S1 and S3 include at least one of the following technical features:

[0025] The silicon source is at least one of silica sol, water glass, tetraethyl orthosilicate, white carbon black, and silicon powder;

[0026] The aluminum source is at least one of aluminum hydroxide, aluminum nitrate, aluminum sulfate, and sodium aluminate;

[0027] The strontium source is at least one of strontium nitrate, strontium chloride and strontium carbonate;

[0028] The alkali source is potassium hydroxide and / or potassium carbonate.

[0029] As a preferred embodiment of the present invention, in step S2, the support material is at least one of α-alumina, mullite, and stainless steel; and / or;

[0030] The support body is in the shape of at least one of a tube, a flat plate, and a hollow fiber.

[0031] The invention also discloses a KFI molecular sieve membrane, which is prepared by any of the above preparation methods.

[0032] The invention also discloses an application of any of the above-mentioned KFI molecular sieve membranes in the dehydration of alcohol substances.

[0033] As a preferred embodiment of the present invention, the alcohol substance includes at least one of methanol, ethanol and isopropanol.

[0034] As a preferred embodiment of the present invention, the separation performance of the KFI molecular sieve membrane for a 10 wt% water / ethanol system is shown as a membrane flux of 0.93 kg·m -2 ·h -1 , the separation factor reaches 219.

[0035] The invention has the following beneficial effects: the invention adopts a secondary hydrothermal growth method to coat a seed crystal on a porous support, puts the seed crystal into a synthetic sol, and prepares a well-grown and dense KFI molecular sieve membrane at a certain temperature. The KFI molecular sieve membrane prepared by the invention has a crystal layer thickness of about 10 microns. The membrane preparation has strong reproducibility and high separation efficiency. It not only has good separation performance, but also can be used as a catalyst for catalytic alcohol-ether conversion, NH3-SCR and other reactions, has the advantages of being green and environmentally friendly, simple membrane separation device, easy operation, continuous production, etc., so the KFI molecular sieve membrane has great application potential in chemical separation, automobile and power plant tail gas treatment, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the X-ray diffraction pattern of KFI molecular sieve membrane.

[0037] Figure 2 This is a field emission scanning electron microscope photo of KFI molecular sieve membrane.

[0038] Figure 3 This is the X-ray diffraction pattern of KFI seed powder.

[0039] Figure 4 This is a field emission scanning electron microscope photo of KFI seed powder.

[0040] Figure 5 This is a schematic diagram of the pervaporation experimental device for alcohol dehydration using KFI molecular sieve membrane, where 1-KFI molecular sieve membrane; 2-constant temperature water tank; 3-raw material bottle; 4-liquid nitrogen tank; 5-cold trap; 6-vacuum pump. DETAILED DESCRIPTION

[0041] The technical solution of the present invention:

[0042] A method for preparing a KFI molecular sieve membrane uses pure phase KFI type molecular sieve crystals as seed crystals, silicon source, aluminum source, strontium source, alkali source and ultrapure water as raw materials, and prepares the KFI molecular sieve membrane on a support through a secondary hydrothermal growth method.

[0043] Specifically, the steps include:

[0044] S1: Mix silicon source, aluminum source, strontium source, alkali source and ultrapure water in a certain proportion and stir to form a uniform initial sol; continue stirring, then transfer to a stainless steel reactor with a polytetrafluoroethylene liner and place in an oven for crystallization; after the crystallization, wash the product with boiling ultrapure water until it is neutral, and dry it to obtain KFI molecular sieve seed powder;

[0045] S2: evenly coating the KFI molecular sieve seed powder on the surface of the support, drying, and obtaining a support coated with the seed powder;

[0046] S3: Mix silicon source, aluminum source, strontium source, alkali source and ultrapure water in a certain proportion and stir to form a uniform synthetic sol; continue stirring, and then transfer to a stainless steel reactor with a polytetrafluoroethylene lining; insert the support coated with seed crystals vertically into the synthetic sol and place it in an oven for crystallization; after the crystallization is completed, wash the product with boiling ultrapure water until it is neutral, and dry it to obtain a KFI molecular sieve membrane.

[0047] As a preferred solution of the present invention, step S1 at least includes the following technical features:

[0048] The molar ratio of the initial sol is 1Al2O3:2.3K2O:0.1SrO:10SiO2:220H2O;

[0049] The stirring time is continued for 1-3 hours, and the specific time can be 1, 2 or 3 hours;

[0050] The crystallization temperature is 140-160° C., specifically 140° C., 150° C., or 160° C., and the crystallization time is 3-5 days, specifically 3 days, 4 days, or 5 days;

[0051] The drying temperature is 70-90°C, which can be 70°C, 80°C, or 90°C, and the drying time is 8-12h, which can be 8, 10, or 12 hours.

[0052] As a preferred solution of the present invention, step S3 at least includes the following technical features:

[0053] The molar ratio of the synthetic sol is 1Al2O3:2.3K2O:0.1SrO:10SiO2:100-300H2O;

[0054] The stirring time is continued for 1-3 hours, and when applied, it can be 1, 2, or 3 hours;

[0055] The crystallization temperature is 100-200°C, and can be 100°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 190°C, or 200°C;

[0056] The drying temperature is 70-90°C, which can be 70°C, 80°C, or 90°C, and the drying time is 8-12h, which can be 8, 10, or 12 hours.

[0057] In some other specific embodiments, steps S1 and S3 include at least one of the following technical features:

[0058] The silicon source is at least one of silica sol, water glass, tetraethyl orthosilicate, white carbon black, and silicon powder;

[0059] The aluminum source is at least one of aluminum hydroxide, aluminum nitrate, aluminum sulfate, and sodium aluminate;

[0060] The strontium source is at least one of strontium nitrate, strontium chloride and strontium carbonate;

[0061] The alkali source is potassium hydroxide and / or potassium carbonate.

[0062] In some specific embodiments, in step S2, the support material is at least one of α-alumina, mullite, and stainless steel; and / or;

[0063] The support body is in the shape of at least one of a tube, a flat plate, and a hollow fiber.

[0064] A KFI molecular sieve membrane is prepared by any of the above preparation methods.

[0065] The present invention also discloses an application of any of the above-mentioned KFI molecular sieve membranes in dehydration of alcohol substances, wherein the alcohol substances include at least one of methanol, ethanol and isopropanol.

[0066] Specifically, the separation performance of the KFI molecular sieve membrane for the 10 wt% water / ethanol system is shown as a membrane flux of 0.93 kg·m -2 ·h -1 , the separation factor reaches 219.

[0067] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. If no specific techniques or conditions are specified in the embodiments, the techniques or conditions described in the literature in this area or the product instructions are used. The reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0068] In the following examples, KFI molecular sieve membranes were used for alcohol dehydration (such as aqueous solutions of methanol, ethanol, and isopropanol) to measure the separation performance of KFI molecular sieve membranes for methanol, ethanol, and isopropanol aqueous solutions. The flux and separation factor of the membrane can be calculated by formula I and formula II.

[0069]

[0070] In Formula I, J i It represents the mass i passing through the molecular sieve membrane per unit time and per unit membrane area, in kg·m -2 ·h -1 ; i is the substance that preferentially permeates the molecular sieve membrane relative to j; m is the mass of the substance collected by the cold trap within △t time; S is the effective area of ​​the membrane;

[0071]

[0072] In formula II, α i / j is the separation factor, X i and Y i Represent the content of substance i on the feed side and the permeate side respectively.

[0073] In the following implementation cases, Figure 5 The pervaporation device was used to test the separation performance of the KFI molecular sieve membrane. The specific steps are as follows:

[0074] The raw material bottle 3 containing the alcohol to be separated (10wt% water / 90wt% alcohol) is placed in a constant temperature water tank 2, and the raw material liquid is stirred with a magnetic stirrer to make it uniformly mixed. The tubular molecular sieve membrane, i.e., the KFI molecular sieve membrane 1, has a tube length of 10 cm and an outer diameter of 1.2 cm. After being packaged into a membrane module, the effective separation area of ​​the membrane is about 20 cm 2 . The membrane assembly is placed on a glass tube connected to the raw material bottle 3. Turn on the water bath power supply, maintain the separation system temperature at 75°C, and turn on the vacuum pump after heating for half an hour. The inside of the test system pipeline is evacuated by the vacuum pump 6 until the vacuum degree is maintained below 0.4MPa. The resulting pressure difference pushes the liquid through the KFI molecular sieve membrane, and after vaporization, it enters the cold trap 5 cooled in the liquid nitrogen tank 4 along the glass pipe and is collected. The components on the feed liquid side and the permeate side are determined by gas chromatography.

[0075] Example 1

[0076] The in-situ hydrothermal preparation method of KFI type molecular sieve membrane includes the following steps:

[0077] Silica sol, strontium nitrate, potassium hydroxide, aluminum hydroxide and ultrapure water are mixed in a certain proportion and stirred into a uniform synthetic sol. The molar ratio of the synthetic sol is 1Al2O3:2.3K2O:0.1SrO:10SiO2:220H2O. The synthetic sol is stirred at room temperature for 2 hours and transferred to a stainless steel reactor with a polytetrafluoroethylene liner. The untreated mullite support, i.e., without seed coating, is vertically inserted into the synthetic sol, placed in an oven, and crystallized at 150°C for 4 days. The product after the crystallization is washed with hot ultrapure water until neutral, and then dried at 80°C to obtain a molecular sieve membrane.

[0078] The molecular sieve membrane prepared by in-situ hydrothermal method was subjected to X-ray diffraction. The X-ray diffraction results are as follows: Figure 1 As shown in the M1 spectrum. It can be seen from the figure that the prepared molecular sieve membrane has a weak KFI characteristic peak, while cracks appear on the surface of the membrane and the KFI crystal layer grows discontinuously. Therefore, the in-situ hydrothermal method is not suitable for preparing a continuous and dense KFI molecular sieve membrane.

[0079] Example 2

[0080] The method of Example 1 is improved, and a secondary hydrothermal preparation method is used to prepare a KFI type molecular sieve membrane, which includes the following steps:

[0081] S1: Mix silica sol HS-40, strontium nitrate, potassium hydroxide, aluminum hydroxide and ultrapure water in a certain proportion and stir to form a uniform initial sol. The molar ratio of the initial sol is 1Al2O3:2.3K2O:0.1SrO:10SiO2:220H2O. The initial sol is stirred at room temperature for 2 hours, transferred to a stainless steel reactor with a polytetrafluoroethylene liner, placed in an oven, and crystallized at 150°C for 5 days. The product after crystallization is washed with hot ultrapure water until neutral, and then dried at 80°C to obtain KFI molecular sieve seed crystals. Figure 3 and Figure 4 They are the X-ray diffraction pattern and field emission scanning electron microscope photograph of KFI seed crystals, and it can be seen that the prepared molecular sieve seed crystals are micron-sized crystals with KFI characteristic structure and no impurity crystals appear.

[0082] S2: manually coating the KFI molecular sieve seed powder obtained in step S1 onto the surface of a pre-moistened tubular mullite support, rubbing evenly, and drying at 80° C. for 2 hours to obtain a support coated with seed powder.

[0083] S3: Preparation process of secondary hydrothermal growth method: Silica sol, strontium nitrate, potassium hydroxide, aluminum hydroxide and ultrapure water are mixed in a certain proportion and stirred into a uniform synthetic sol. The molar ratio of the synthetic sol is 1Al2O3:2.3K2O:0.1SrO:10SiO2:220H2O. The synthetic sol is stirred at room temperature for 2 hours and transferred to a stainless steel reactor with a polytetrafluoroethylene liner. The mullite support coated with KFI seed crystals is vertically inserted into the synthetic sol, placed in an oven, and crystallized at 150°C for 4 days. The product after crystallization is washed with hot ultrapure water until neutral, and then dried at 80°C to obtain a KFI molecular sieve membrane.

[0084] The prepared KFI molecular sieve membrane was subjected to X-ray diffraction, and the X-ray diffraction results were as follows: Figure 1 As shown in the M2 spectrum. It can be seen from the figure that the prepared molecular sieve membrane has a KFI structure and has no impurity peaks. Compared with the XRD diffraction peaks of the support, the crystallinity of the molecular sieve membrane crystal layer is higher.

[0085] The field emission scanning electron microscopy results of the KFI molecular sieve membrane prepared by the secondary hydrothermal growth method are as follows Figure 2 As shown. Figure 2 It can be seen that the molecular sieve crystals on the support form a dense film; the cross-sectional SEM image shows that a continuous crystal layer is formed, and the thickness of the crystal layer is about 10 microns.

[0086] Example 3

[0087] 500 ml of 10 wt% water / 90 wt% methanol, 10 wt% water / 90 wt% ethanol, and 10 wt% water / 90 wt% isopropanol were prepared as raw material solutions and placed in raw material bottles, respectively, and the separation performance of the KFI molecular sieve membrane was tested at 75° C. The results are shown in Table 1.

[0088] Table 1 Separation performance of KFI molecular sieve membrane for 10 wt% water / alcohol at test temperature 75°C

[0089]

[0090] From the table above, we can see that at 75°C, the separation performance of the KFI molecular sieve membrane for the 10 wt% water / ethanol system is shown as a membrane flux of 0.93 kg·m -2 ·h -1 The separation factor reaches 219 and is successfully applied to the separation of water and alcohols. It has the advantages of being green and environmentally friendly, simple membrane separation equipment, easy operation, and continuous production.

[0091] Under the premise that no conflict occurs, those skilled in the art may freely combine and superimpose the above-mentioned additional technical features.

[0092] The above-mentioned embodiments only express the preferred implementation modes of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, various other corresponding changes and deformations can be made according to the technical solutions and concepts described above, and all these changes and deformations should fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a KFI molecular sieve membrane, characterized in that: Pure phase KFI type molecular sieve crystals are used as seed crystals, silicon source, aluminum source, strontium source, alkali source and ultrapure water are used as raw materials, and a KFI molecular sieve membrane is prepared on a support through a secondary hydrothermal growth method.

2. The method for preparing a KFI molecular sieve membrane according to claim 1, characterized in that: The following steps are involved: S1: Mix silicon source, aluminum source, strontium source, alkali source and ultrapure water in a certain proportion and stir to form a uniform initial sol; Continue stirring, then transfer to a stainless steel reactor with a polytetrafluoroethylene liner and place in an oven for crystallization; after the crystallization, the product is washed with boiled ultrapure water until neutral, and dried for 8-12 hours to obtain KFI molecular sieve seed powder; S2: evenly coating the KFI molecular sieve seed powder on the surface of the support, drying, and obtaining a support coated with the seed powder; S3: Mix silicon source, aluminum source, strontium source, alkali source and ultrapure water in a certain proportion and stir to form a uniform synthetic sol; continue stirring, and then transfer to a stainless steel reactor with a polytetrafluoroethylene lining; insert the support coated with seed crystals vertically into the synthetic sol and place it in an oven for crystallization; after the crystallization is completed, the product is washed with boiling ultrapure water until it is neutral, and then dried to obtain a KFI molecular sieve membrane.

3. The method for preparing a KFI molecular sieve membrane according to claim 2, characterized in that: In step S1, at least the following technical features are included: The molar ratio of the initial sol is 1Al2O3:2.3K2O:0.1SrO:10SiO2:100-500H2O; Continue stirring for 1-3 hours; The crystallization temperature is 140-160°C and the crystallization time is 3-5 days; The drying temperature is 70-90°C and the drying time is 1-3 hours.

4. The method for preparing a KFI molecular sieve membrane according to claim 2, characterized in that: In step S3, at least the following technical features are included: The molar ratio of the synthetic sol is 1Al2O3:2.3K2O:0.1SrO:10SiO2:100-500H2O; Continue stirring for 1-3 hours; The crystallization temperature is 100-200°C and the crystallization time is 2-6 days; The drying temperature is 70-90°C and the drying time is 8-12 hours.

5. The method for preparing a KFI molecular sieve membrane according to claim 2, characterized in that: Steps S1 and S3 include at least one of the following technical features: The silicon source is at least one of silica sol, water glass, tetraethyl orthosilicate, white carbon black, and silicon powder; The aluminum source is at least one of aluminum hydroxide, aluminum nitrate, aluminum sulfate, and sodium aluminate; The strontium source is at least one of strontium nitrate, strontium chloride and strontium carbonate; The alkali source is potassium hydroxide and / or potassium carbonate.

6. The method for preparing a KFI molecular sieve membrane according to claim 2, characterized in that: In step S2, the support body is made of at least one of α-alumina, mullite, and stainless steel; and / or; The support body is in the shape of at least one of a tube, a flat plate, and a hollow fiber.

7. A KFI molecular sieve membrane, characterized in that: The method is prepared by any one of claims 1 to 6.

8. Use of the KFI molecular sieve membrane as claimed in claim 7 in the dehydration of alcohols.

9. The use according to claim 8, wherein the alcohol substance comprises at least one of methanol, ethanol and isopropanol.

10. The use as claimed in claim 8, wherein the separation performance of the KFI molecular sieve membrane for a 10 wt% water / ethanol system is shown as a membrane flux of 0.93 kg·m -2 ·h -1 , the separation factor reaches 219.

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