Method for preparing open-cell zeolite molecular sieve homogeneous dispersion liquid under mild conditions

Abstract

The invention discloses a method for preparing open-cell zeolite molecular sieve homogeneous dispersion liquid under mild conditions. The method comprises the following steps: dispersing a molecular sieve containing a template agent in a quartz container filled with methyl pyrrolidone and hydrogen peroxide, and carrying out ultraviolet radiation on a solution in a continuous stirring state to obtain the activated open-pore zeolite molecular sieve dispersion liquid. According to the method provided by the invention, the organic template agent in micropores of the zeolite molecular sieve nanosheets or nanoparticles can be effectively removed at a temperature close to room temperature, the operation is simple, the condition is mild and pollution-free, and the problem that the zeolite molecular sieve nanosheets or nanoparticles are seriously agglomerated during traditional high-temperature roasting and pore opening is effectively solved. The highly dispersed open-pore zeolite molecular sieve nanosheet or nanoparticle dispersion liquid has a wide application prospect in construction of a two-dimensional zeolite molecular sieve membrane or a mixed matrix membrane.

Description

Technical Field

[0001] The invention belongs to the field of zeolite molecular sieve materials, and in particular relates to a method for activating zeolite molecular sieve pores under near room temperature conditions and directly obtaining an open-pore zeolite molecular sieve uniform dispersion. Background Art

[0002] Zeolite molecular sieve is an inorganic porous material with a uniformly dispersed angstrom-level pore structure and excellent chemical stability. Therefore, it has a wide range of applications in the fields of catalysis, separation, adsorption, etc. In particular, in the field of membrane separation, zeolite molecular sieve nanosheets and nanoparticles can be used as important basic structural units to construct high-performance two-dimensional zeolite molecular sieve membranes or mixed matrix membranes. Since most zeolite molecular sieve nanosheets or nanoparticles can only be successfully synthesized under the guidance of a template agent, the resulting zeolite molecular sieve microporous channels will be occupied by template agent molecules. This requires decomposing the template agent in the pores to activate the pores of the zeolite molecular sieve nanosheets or nanoparticles before they can be used to construct two-dimensional zeolite molecular sieve membranes or mixed matrix membranes. The activation and opening of existing zeolite molecular sieves is usually achieved by high-temperature calcination. However, the high temperature process will cause serious sintering and agglomeration of zeolite molecular sieve nanosheets and nanoparticles, thereby reducing the orderliness of nanosheet stacking in the two-dimensional zeolite molecular sieve membrane and the dispersibility of nanosheets or nanoparticles in the mixed matrix membrane, seriously affecting the separation performance of the two-dimensional zeolite molecular sieve membrane and the mixed matrix membrane. Therefore, achieving efficient activation of two-dimensional zeolite molecular sieve nanosheets and nanoparticles while preventing them from agglomerating is of great significance for the development of new high-performance two-dimensional zeolite molecular sieve membranes and mixed matrix membranes.

[0003] Patent CN 105271284A discloses that the template agent in mesoporous silica molecular sieves MCM-41, SBA-15, and pure silicon MFI molecular sieve nanosheets can be removed by using piranha solution at 80°C. However, the strongly acidic piranha solution can easily destroy the skeleton structure of the porous material. Patent CN 102774849 A discloses a method for removing the template agent in UZM-5 molecular sieve under neutral conditions at room temperature, but the method introduces Fe 2+ / Fe 3+ Ions and other transition metal ions will cause varying degrees of contamination to the material itself. It is of great significance to remove the organic template in the micropores of zeolite molecular sieve under mild conditions without causing any damage or contamination to the material itself. Summary of the invention

[0004] The purpose of the present invention is to develop a method for preparing a highly dispersed liquid of an open-pore zeolite molecular sieve under mild conditions, and the method does not cause any damage or secondary pollution to the structure of the zeolite molecular sieve.

[0005] The technical solution adopted by the present invention is:

[0006] A method for preparing a uniform dispersion of an open-pore zeolite molecular sieve under mild conditions comprises the following steps:

[0007] (1) mixing a zeolite molecular sieve to be activated with methyl pyrrolidone and a hydrogen peroxide solution to obtain a uniform zeolite molecular sieve dispersion; the zeolite molecular sieve to be activated contains a template;

[0008] (2) The dispersion is continuously irradiated with ultraviolet light under stirring to obtain a uniform dispersion of the open-pore zeolite molecular sieve.

[0009] The above method for preparing a uniform dispersion of open-pore zeolite molecular sieve under mild conditions comprises centrifuging the dispersion obtained in step (2), re-adding methyl pyrrolidone and fresh hydrogen peroxide solution to perform ultraviolet radiation treatment again, and repeating the above radiation process several times to obtain a highly dispersed uniform dispersion of open-pore zeolite molecular sieve.

[0010] The above-mentioned method for preparing a uniform dispersion of open-pore zeolite molecular sieve under mild conditions, the zeolite molecular sieve crystal type includes but is not limited to MFI, MWW, DDR, CHA, STT, LTA, FER, and FAU type molecular sieves.

[0011] The above method for preparing a uniform dispersion of open-pore zeolite molecular sieve under mild conditions, the molecular sieve morphology includes zeolite molecular sieve nanoparticles and zeolite molecular sieve nanosheets.

[0012] In the above method for preparing a uniform dispersion of open-pore zeolite molecular sieve under mild conditions, the mixing container is made of quartz.

[0013] In the above method for preparing a uniform dispersion of open-pore zeolite molecular sieve under mild conditions, the concentration of the hydrogen peroxide solution is 1-28wt%, the concentration of methyl pyrrolidone in the final zeolite molecular sieve dispersion is 0.5-5wt%, and the concentration of the molecular sieve is 0.5-100mg ml -1 .

[0014] In the above method for preparing a uniform dispersion of open-pore zeolite molecular sieve under mild conditions, the wavelength of the ultraviolet light source is 10-400nm.

[0015] In the above method for preparing a uniform dispersion of open-pore zeolite molecular sieve under mild conditions, the distance between the ultraviolet light source and the zeolite molecular sieve dispersion is 0-30 cm.

[0016] The above method for preparing a uniform dispersion of open-pore zeolite molecular sieve under mild conditions, wherein the ultraviolet radiation intensity is 10-25000 μW cm -2, preferably 10000 μW cm -2 -20000μW cm -2 .

[0017] In the above method for activating zeolite molecular sieve pores at room temperature, the temperature of the zeolite molecular sieve dispersion during ultraviolet radiation is less than 100°C, preferably room temperature; the single radiation time is 1-100h, preferably 1-24h, most preferably 12-24h.

[0018] In the above method for preparing a uniform dispersion of open-pore zeolite molecular sieve under mild conditions, the radiation process is repeated 1 to 5 times, preferably 2 to 6 times.

[0019] Compared with the prior art, the present invention has the following advantages and technical effects:

[0020] The present invention can open the microporous molecular sieve at room temperature and neutral conditions without introducing metal ions and other pollutants. The above process has mild reaction conditions, the whole process is green and pollution-free, and a zeolite molecular sieve dispersion liquid with a complete crystal structure, no pollution, and high dispersion can be directly obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a photograph of the prepared open-pore ZSM-5 nanosheets uniform dispersion.

[0022] Figure 2 Thermogravimetric curves of ZSM-5 nanosheets before and after pore opening.

[0023] Figure 3 N2 adsorption-desorption isotherms of ZSM-5 nanosheets before and after pore opening.

[0024] Figure 4 Photo of the prepared open-pore MWW nanosheets uniform dispersion.

[0025] Figure 5 Thermogravimetric curves of MWW nanosheets before and after pore opening.

[0026] Figure 6 N2 adsorption-desorption isotherms of MWW nanosheets before and after pore opening.

[0027] Figure 7 Photograph of the prepared open-pore silicalite-1 zeolite nanoparticle dispersion. DETAILED DESCRIPTION

[0028] The method proposed in the present invention is further described below in conjunction with specific embodiments, but the implementation methods of the present invention are not limited to the following examples.

[0029] Example 1

[0030] ZSM-5 zeolite molecular sieve nanosheets are obtained by exfoliating the synthesized layered ZSM-5 zeolite molecular sieve. ph-ph-10-6 The template was dispersed in deionized water, ultrasonically dispersed for 30 min, and then sodium hydroxide and sodium aluminate solution were added. After stirring for 1 hour, tetraethyl orthosilicate was added and stirred for 4 h to obtain a molar ratio of C ph-ph-10-6 :20SiO2:2.5Na2O:0.2Al2O3:80EtOH:800H2O synthesis solution, wherein EtOH is ethanol, formed by hydrolysis of tetraethyl orthosilicate. The obtained synthesis solution is transferred to a stainless steel autoclave and rotated for crystallization at 150°C for 3 days at a speed of 40rpm. After hydrothermal synthesis, the synthetic product is washed several times to neutrality and dried overnight at 60°C to obtain a layered ZSM-5 zeolite molecular sieve. Take 2.0g of hexadecyltrimethylammonium bromide (CTAB) and dissolve it in 13g of 7.6wt% tetrapropylammonium hydroxide (TPAOH) solution, add 0.4g of layered ZSM-5 zeolite molecular sieve, and stir at room temperature for 24 hours. The stirred molecular sieve is centrifuged, washed, and dried overnight at 60°C. 0.3 g of the dried molecular sieve sample was mixed with 15 g of hydroxyl-terminated polybutadiene (HTPB), and 20 ml of toluene was added. After stirring at room temperature for four days, the ZSM-5 nanosheets were obtained by washing with a large amount of toluene and centrifuging.

[0031] In a quartz container, 0.2 g of an organic template (C Ph-Ph-10-6 ) ZSM-5 molecular sieve nanosheets were mixed with 1g methyl pyrrolidone and 20ml (28wt%) hydrogen peroxide solution, and stirred to obtain a uniform dispersion of ZSM-5 nanosheets. The nanosheet dispersion was irradiated with an ultraviolet lamp under stirring at room temperature for pore opening activation treatment. The radiation distance between the ultraviolet lamp and the dispersion was 1cm, and the radiation intensity was 10000μW cm -2 The single irradiation time was 24 hours, and the irradiation process was repeated 4 times, with a total irradiation treatment time of 96 hours. After each irradiation, the obtained dispersion was centrifuged, and 1g of methyl pyrrolidone and 20ml (28wt%) fresh hydrogen peroxide solution were added again for ultraviolet irradiation treatment. After the reaction was completed, a uniformly dispersed ZSM-5 molecular sieve nanosheet dispersion could be directly obtained.

[0032] Figure 1 This is a photo of the prepared open-pore ZSM-5 nanosheet dispersion, and no obvious particle agglomeration was found. Figure 2 Thermogravimetric curves of ZSM-5 nanosheets before and after opening. Before activation, the nanosheets containing organic templates have a significant weight loss peak in the range of 300-600℃, corresponding to the organic template (C Ph-Ph-10-6 ) after activation; after activation, there is no obvious weight loss within 300-600 °C, indicating that the organic template has been removed. Figure 3 is the N2 adsorption-desorption isotherm of ZSM-5 nanosheets before and after opening. Figure 3 It can be seen that the adsorption amount of ZSM-5 nanosheets at low pressure before activation is very low, which is because the organic template blocks the micropores; the adsorption amount of ZSM-5 nanosheets at low pressure after activation is greatly increased, indicating that the micropore channels of the activated ZSM-5 nanosheets have been opened and the organic template has been effectively removed.

[0033] Example 2

[0034] MWW zeolite molecular sieve nanosheets are obtained by peeling off the layered MWW zeolite molecular sieve. The silica sol solution is added dropwise to the NaOH aqueous solution at room temperature and stirred for 20 hours to obtain a silicon source solution. NaAlO2 is dissolved in water, slowly dripped into the silicon source solution, and stirred for 30 minutes. The template HMI is added and stirred for 30 minutes to obtain a synthetic liquid sol with a molar ratio of 1SiO2:0.041Al2O3:0.21Na2O:0.35HMI. The synthetic liquid sol is loaded into a stainless steel reactor with a polytetrafluoroethylene liner, and a dynamic hydrothermal reaction is carried out in a rotary oven at a speed of 45rpm, a reaction temperature of 143°C, and a reaction time of 2 days. After hydrothermal synthesis, the synthetic product is washed several times to neutrality to obtain a layered MWW zeolite molecular sieve. 0.5g of layered MWW zeolite molecular sieve, 0.56g of hexadecyltrimethylammonium bromide (CTAB) and 0.97g of tetrapropylammonium hydroxide (TPAOH) were mixed, and then 3.01g of deionized water was added, and stirring was maintained at room temperature for 16h. The molecular sieve was washed and centrifuged several times at 8000rpm, and dried at 60°C. 0.5g of the dried molecular sieve was placed in a beaker, 20ml of hydroxyl-terminated polybutadiene (HTPB) was poured in, and 5ml of toluene solution was added. After the solution was stirred for a long time at room temperature until transparent, it was washed with a large amount of toluene, and then centrifuged several times at 10000rpm to obtain MWW molecular sieve nanosheets.

[0035] In a quartz container, 0.06 g of MWW molecular sieve nanosheets containing hexamethyleneimine (HMI) was mixed with 0.8 methylpyrrolidone and 20 ml (25 wt%) hydrogen peroxide solution, and stirred evenly to obtain a MWW zeolite nanosheet dispersion. The dispersion was irradiated with an ultraviolet lamp under stirring at room temperature, with a radiation distance of 1 cm and a radiation intensity of 10000 μW cm -2 The single irradiation time is 24 hours, and the irradiation treatment is only performed once. After the reaction is completed, a uniformly dispersed MWW type molecular sieve nanosheet dispersion is directly obtained.

[0036] Figure 4 This is a photo of the prepared open-pore ZSM-5 nanosheet dispersion, and no obvious particle agglomeration was found. Figure 5The thermogravimetric curves of MWW nanosheets before and after activation. The decomposition of the template agent HMI starts at 350°C. The weight loss of the molecular sieve nanosheets before activation is about 10% in the range of 350-700°C, and there is no weight loss peak in the nanosheets after activation at 350-700°C, indicating that there is no organic template in the nanosheets after activation. Figure 6 The N2 adsorption and desorption isotherms of MWW zeolite nanosheets before and after activation. The adsorption of the nanosheets in the low partial pressure region before activation is very low, mainly because the HMI template blocks the pores of the zeolite. After activation, the adsorption of the zeolite nanosheets in the low pressure region increases, indicating that the micropores are effectively released.

[0037] Example 3

[0038] A certain amount of tetraethyl orthosilicate (TEOS) was slowly added to a tetrapropylammonium hydroxide (TPAOH) aqueous solution, and stirred at room temperature for 10 hours to obtain a synthetic solution with a molar ratio of SiO2:0.35TPAOH:10H2O. The obtained synthetic solution was transferred to a stainless steel autoclave and statically crystallized at 115°C for 40 hours. After hydrothermal synthesis, the obtained product was washed several times to neutrality and then dried at 100°C overnight to obtain silicalite-1 zeolite nanoparticles.

[0039] In a quartz container, 0.03 g of silicalite-1 zeolite particles containing tetrapropylammonium hydroxide template agent were mixed with 0.5 g of methyl pyrrolidone and 30 ml of 28 wt% hydrogen peroxide solution, and stirred evenly to obtain silicalite-1 zeolite nanoparticle dispersion. Under room temperature stirring, the nanoparticle dispersion was irradiated with ultraviolet light for pore activation treatment. The radiation distance between the ultraviolet light and the dispersion was 1 cm, and the radiation intensity was 20000 μW cm -2 The single irradiation time was 12 hours, the number of repetitions was 5 times, and the total irradiation treatment time was 60 hours. After each irradiation, the obtained dispersion was centrifuged and 0.5 methyl pyrrolidone 30 ml (28 wt%) fresh hydrogen peroxide solution was added again for ultraviolet irradiation treatment. After the reaction was completed, the silicalite-1 zeolite nanoparticle dispersion with open pores was directly obtained, such as Figure 7 shown.

[0040] Comparative Example 1

[0041] Except that the ZSM-5 zeolite molecular sieve nanosheet dispersion in the quartz container was not subjected to ultraviolet irradiation, the other experimental conditions were consistent with those in Example 1. The ZSM-5 zeolite molecular sieve nanosheets in the solution were easily agglomerated and sank, and a uniform and stable dispersion could not be obtained. In addition, the ZSM-5 zeolite molecular sieve nanosheets still contained a large amount of organic templates, indicating that the pores were not fully opened.

[0042] Comparative Example 2

[0043] Except that hydrogen peroxide was not added to the ZSM-5 zeolite molecular sieve nanosheets in the quartz container, the other experimental conditions were consistent with Example 1. The ZSM-5 zeolite molecular sieve nanosheets finally obtained were difficult to disperse in water, and a uniform and stable dispersion could not be obtained. In addition, the ZSM-5 zeolite molecular sieve nanosheets still contained a large amount of organic templates, indicating that the pores were not fully opened.

Claims

1. A method for preparing a uniform dispersion of an open-pore zeolite molecular sieve under mild conditions, characterized in that: The following steps are involved: (1) mixing a zeolite molecular sieve to be activated with methyl pyrrolidone and a hydrogen peroxide solution to obtain a uniform zeolite molecular sieve dispersion; the zeolite molecular sieve to be activated contains a template; (2) The dispersion is continuously irradiated with ultraviolet light under stirring to obtain a uniform dispersion of the open-pore zeolite molecular sieve.

2. The method for preparing a uniform dispersion of an open-pore zeolite molecular sieve under mild conditions according to claim 1, characterized in that: The dispersion obtained in step (2) is centrifuged, and methyl pyrrolidone and fresh hydrogen peroxide solution are added again for ultraviolet radiation treatment. After repeating the above radiation process several times, a highly dispersed open-pore zeolite molecular sieve uniform dispersion can be obtained.

3. A method for preparing a uniform dispersion of open-pore zeolite molecular sieve under mild conditions according to claim 1 or 2, characterized in that: The crystal form of the zeolite molecular sieve described in step (1) includes one or more of MFI, MWW, DDR, CHA, STT, LTA, FER, and FAU type molecular sieves.

4. A method for preparing a uniform dispersion of an open-pore zeolite molecular sieve under mild conditions according to claim 1 or 2, characterized in that: The morphology of the zeolite molecular sieve described in step (1) includes zeolite molecular sieve nanoparticles and zeolite molecular sieve nanosheets.

5. A method for preparing a uniform dispersion of open-pore zeolite molecular sieve under mild conditions according to claim 1 or 2, characterized in that: The concentration of the hydrogen peroxide solution in step (1) is 1-28 wt%, the concentration of methyl pyrrolidone in the final dispersion is 0.05-5 wt%, and the concentration of the zeolite molecular sieve is 0.5-100 mg ml -1 .

6. A method for preparing a uniform dispersion of an open-pore zeolite molecular sieve under mild conditions according to claim 1 or 2, characterized in that: The wavelength of the ultraviolet light source in step (2) is 10-400nm.

7. A method for preparing a uniform dispersion of open-pore zeolite molecular sieve under mild conditions according to claim 1 or 2, characterized in that: The distance between the ultraviolet light source described in step (2) and the zeolite molecular sieve dispersion is 0-30 cm.

8. A method for preparing a uniform dispersion of open-pore zeolite molecular sieve under mild conditions according to claim 1 or 2, characterized in that: The ultraviolet radiation intensity described in step (2) is 10-25000 μW cm -2 .

9. A method for preparing a uniform dispersion of an open-pore zeolite molecular sieve under mild conditions according to claim 1 or 2, characterized in that: In step (2), the temperature of the zeolite molecular sieve dispersion during ultraviolet radiation is less than 100° C., preferably room temperature; and the single radiation time is 1-100 hours, preferably 1-24 hours.

10. The method for preparing a uniform dispersion of an open-pore zeolite molecular sieve under mild conditions according to claim 2, characterized in that: The radiation process is repeated 1-10 times, preferably 2-6 times.

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