A beta zeolite molecular sieve and a method for making the same

Abstract

The application discloses a beta zeolite molecular sieve and a preparation method thereof. The preparation method of the beta zeolite molecular sieve comprises the following steps: a) mixing an alkali source, an aluminum source, a tetraalkylammonium and a silicon source, wherein the molar ratio of the tetraalkylammonium / SiO2 in the obtained mixture is 0.11-0.25; b) drying the material obtained in the step a) to obtain a precursor, wherein the molar ratio of H2O / SiO2 in the obtained precursor is 0.1-2; and c) crystallizing the precursor obtained in the step b) to obtain the beta zeolite molecular sieve. According to the method, the high-silicon beta zeolite molecular sieve is synthesized without adding fluorine and seeds, and the obtained beta zeolite molecular sieve has excellent adsorption performance.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieves, specifically relating to a β-zeolite molecular sieve and its preparation method. Background Technology

[0002] High-silica β-zeolite molecular sieves possess certain acidity and hydrophobicity, showing broad application prospects in catalysis and adsorption. High-silica β-zeolites are generally synthesized using dealumination or fluoride ion addition methods. Dealumination is a complex process, while fluoride ion addition requires the treatment of fluoride-containing wastewater, increasing the production cost of zeolite molecular sieves.

[0003] CN1154341A discloses a method for synthesizing β-zeolite. The reaction system of this method has the following molar composition: SiO2 / Al2O3 = 20–600, Na2O / SiO2 = 0.01–0.1, and TEA... + The ratio of H₂O / SiO₂ is 0.03–0.20, and the ratio of H₂O / SiO₂ is 2–10. This method requires multi-stage crystallization. However, in practice, when TEA is present in the reaction system… + When the SiO2 / Al2O3 molar ratio is below 0.15, the SiO2 / Al2O3 molar ratio of the product is generally low, even when TEA + When the molar ratio of SiO2 is high, it is difficult for the SiO2 / Al2O3 molar ratio of the product to reach more than 500.

[0004] CN101863490A discloses a method for synthesizing small-grained all-silica β-zeolite. This method involves preparing a mixture of silicon source, fluoride ion source, tetraethylammonium hydroxide source, and water, followed by a crystallization reaction to obtain all-silica zeolite with grains smaller than 5 micrometers. This method requires a relatively large molar amount of TEAOH. + The SiO2 molar ratio needs to be between 0.3 and 1.0, and a large amount of F is added. - .

[0005] CN101757889A discloses a BEA-type binder-free hydrophobic high-silica zeolite adsorbent and its preparation method. This method uses sodium-type BEA zeolite with a silicon-to-aluminum molar ratio of 5-300 as raw material, adds amorphous silica gel binder, then performs crystal transformation and inorganic acid dealuminization, and finally undergoes high-temperature steam hydrophobic treatment to obtain the BEA-type binder-free hydrophobic high-silica zeolite adsorbent. This method requires steps such as secondary crystal transformation, acid dealuminization, and steam treatment, making the preparation process complex and increasing the preparation cost.

[0006] CN106517233A discloses a fluorine-free and solvent-free method for synthesizing Beta zeolite molecular sieves enriched in the form of B. This method involves first mixing an alkali source, a template agent, and a silicon source in a mortar, then adding an aluminum source, an iron source, and another silicon source for further mixing. Seed crystals are added during the preparation process. Although this method reduces the SiO2 / template agent molar ratio to 0.1, the resulting SiO2 / Al2O3 molar ratio ranges from 1 to 40, indicating a relatively high aluminum content.

[0007] CN108264056A discloses a method for synthesizing all-silica Beta zeolite molecular sieves via a sodium-free and solvent-free route. This method involves placing a silicon source, a quaternary ammonium base, and all-silica seed crystals in a mortar, grinding, crystallizing, filtering, and drying to obtain sodium-free and solvent-free all-silica Beta zeolite molecular sieves. However, this method requires the addition of some seed crystals, and the molar ratio of the quaternary ammonium base to SiO2 must be greater than 0.15. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a β-zeolite molecular sieve and its preparation method. This method synthesizes high-silica β-zeolite molecular sieves without the addition of fluorine or seed crystals, and the resulting β-zeolite molecular sieve exhibits excellent properties.

[0009] This invention provides a method for preparing β-zeolite molecular sieves, comprising:

[0010] a) Mix the alkali source, aluminum source, tetraalkylammonium, and silicon source, and the molar ratio of tetraalkylammonium / SiO2 in the resulting mixture is 0.11 to 0.25;

[0011] b) Dry the material obtained in step a) to obtain a precursor, wherein the molar ratio of H2O / SiO2 in the precursor is 0.1 to 2, preferably 0.1 to 1.5;

[0012] c) Crystallize the precursor obtained in step b) to obtain β-zeolite molecular sieve.

[0013] Furthermore, in step a), the mixture obtained after mixing undergoes a molding step, and the molding can be carried out using conventional methods in the art, such as kneading and extrusion molding, spray drying molding, etc.

[0014] Further, in step a), the tetraalkylammonium is one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrapropylammonium bromide. The alkali source is NaOH and / or KOH. The aluminum source is one or more of aluminum nitrate (e.g., aluminum nitrate nonahydrate), hydrated alumina (e.g., boehmite), and sodium aluminate. The silicon source is one or more of amorphous silica, silica sol, silica gel, and water glass, preferably amorphous silica (e.g., silica fume).

[0015] Furthermore, in the obtained mixture, the molar ratio of alkali source (calculated as hydroxide) is as follows: alkali source / SiO2 = 0.05–0.2:1, SiO2 / Al2O3 = 200–2500, and H2O / SiO2 = 2.5–15.

[0016] Further, in step b), the drying temperature is 40–120°C. After drying, the molar ratio of H2O / SiO2 in the precursor is 0.1–2, preferably 0.1–1.5.

[0017] Further, in step c), the crystallization temperature is 120-160°C, and the crystallization time is 24-288 hours, preferably 24-96 hours.

[0018] Furthermore, in step c), an organic ammonium may be added during crystallization. The organic amine is selected from one or more of ethylenediamine, triethylamine, and n-butylamine, preferably triethylamine. The molar ratio of the organic amine to SiO2 is between 0.02 and 0.2.

[0019] Further, in step c), the crystallization is followed by post-processing to obtain β-zeolite molecular sieves. The post-processing includes washing, drying, and calcination. The washing is performed using an ammonium salt solution until neutral; the ammonium salt solution is one or more of ammonium nitrate aqueous solution, ammonium chloride aqueous solution, and ammonium carbonate aqueous solution. The drying and calcination can be performed using conventional methods in the art.

[0020] A second aspect of the present invention provides a β-zeolite molecular sieve prepared by the above method.

[0021] Furthermore, the β-zeolite molecular sieve has the following properties: a SiO2 / Al2O3 molar ratio of 200 to +∞, preferably 200 to 1000, more preferably 500 to 1000, and a specific surface area of ​​400 m². 2 / g~700m 2 / g, with a total pore volume of 0.1mL / g to 0.25mL / g and a relative crystallinity of 95% to 120%.

[0022] A third aspect of the present invention provides an application of the β-zeolite molecular sieve prepared by the above method as an adsorbent in the gas phase or liquid phase.

[0023] Compared with the prior art, the present invention has the following superior effects:

[0024] The preparation method of the present invention does not require the addition of F element, the treatment of F-containing wastewater, or the addition of seed crystals or subsequent dealumination. With the use of less template agent, gas-solid phase crystallization can yield β-zeolite molecular sieves with high silicon-to-aluminum ratio, high crystallinity, large specific surface area and suitable pore volume. These β-zeolite molecular sieves have strong adsorption capacity.

[0025] The preparation method of the present invention, by adding organic amines during crystallization, can make the prepared β molecular sieve crystals more dispersed, reduce agglomeration, and have a higher specific surface area.

[0026] The inventors discovered that by drying the precursor to control the H2O / SiO2 molar ratio within a suitable range, the precursor obtained before crystallization can be in a shaped state, eliminating the need for subsequent addition of a binder. Furthermore, the β-zeolite molecular sieve obtained under these conditions exhibits better adsorption performance in both gas and liquid phases. Due to its high silica-to-alumina ratio, the presence of water in the liquid phase does not cause competitive adsorption, thus enhancing its adsorption capacity in the liquid phase. Without the preparation method of this invention, it would be impossible to obtain β-zeolite molecular sieves using such a low amount of template agent. Attached Figure Description

[0027] Figure 1 The XRD diffraction pattern of the β-zeolite molecular sieve obtained in Example 1;

[0028] Figure 2 This is a SEM image of the β-zeolite molecular sieve obtained in Example 1. Detailed Implementation

[0029] The specific embodiments of the present invention will be described in detail below. However, it should be noted that the scope of protection of the present invention is not limited by these specific embodiments, but is determined by the claims.

[0030] In this invention, the specific surface area and pore volume of the catalyst are terms known in the art and can be tested using methods and instruments known in the art. Specifically, an ASAP2020M physicochemical adsorption instrument from Micron Instruments (USA) was used. Before measurement, the sample was evacuated and treated at 300°C for 2 hours to remove impurities adhering to the sample surface. Then, high-purity N2 was adsorbed at low temperature using liquid nitrogen to obtain the adsorption / desorption curve of the catalyst powder. The specific surface area was calculated using the BET method, and the pore volume was calculated using the BJH method.

[0031] In this invention, the mechanical strength of the catalyst has a meaning known in the art and can be tested using methods and instruments known in the art. Specifically, the catalyst strength is determined using a DLⅢ type intelligent particle strength testing machine produced by Dalian Chemical Research and Design Institute. The measurement is performed 22 times, and the maximum and minimum values ​​are removed before taking the average value.

[0032] In this invention, XRD was performed using a Bruker D-8 Advance X-ray diffractometer, with Cu K radiation as the X-ray source. The graphite monochromator has a tube voltage of 40kV and a tube current of 40mA, with a small-angle diffraction range of 5–50°.

[0033] In this invention, the analysis of the microstructure, structure, and grain size of the samples was performed using an XL30E scanning electron microscope from FEI Corporation, USA, with a magnification of 40,000x and an accelerating voltage of 50V-30kV.

[0034] In this invention, the chemical composition of the sample, i.e. the silicon-to-aluminum ratio, was determined using an X-ray fluorescence spectrometer, specifically a Bruker S4 Pioneer instrument.

[0035] In this invention, the relative crystallinity % of the sample = (the area of ​​the strongest diffraction peak of the sample / the area of ​​the strongest diffraction peak of the standard) * the relative crystallinity of the standard. In this invention, the product of β molecular sieve prepared by liquid phase with a certain amount of binder is used as the standard, and its relative crystallinity is 100%.

[0036] Example 1

[0037] a) NaOH solid, aluminum nitrate nonahydrate, tetraethylammonium hydroxide solution, and silica were mixed and a 3 mm diameter strip crystallization precursor was prepared by kneading and extrusion. The molar ratio of NaOH to SiO2 in the resulting mixture was 0.1:1, the molar ratio of tetraethylammonium hydroxide to SiO2 was 0.14:1, the molar ratio of SiO2 to Al2O3 was 600:1, and the molar ratio of water to SiO2 was 3:1.

[0038] b) Dry the molding material obtained in step a) at 80°C. After drying, the molar ratio of water to SiO2 in the resulting precursor is 0.1.

[0039] c) Triethylamine was added to the dried precursor, and the mixture was crystallized in a hydrothermal reactor. The molar ratio of triethylamine to SiO2 was 0.05:1, the crystallization temperature was 130℃, and the crystallization time was 48 h. After crystallization, the triethylamine was recovered. The crystallized solid product was washed with ammonium nitrate aqueous solution until neutral, dried at 80℃ for 4 h, and then calcined at 550℃ for 4 h to obtain β-zeolite molecular sieve. Its XRD and SEM spectra are shown below. Figure 1 and Figure 2 As shown in the figure. The characterization results are shown in Table 1.

[0040] Example 2

[0041] Unlike Example 1, in step a), the molar ratio of tetraethylammonium hydroxide to SiO2 is 0.11:1. The characterization results of the obtained β-zeolite molecular sieve are shown in Table 1.

[0042] Example 3

[0043] Unlike Example 1, in step a), the molar ratio of tetraethylammonium hydroxide to SiO2 is 0.21:1. The characterization results of the obtained β-zeolite molecular sieve are shown in Table 1.

[0044] Example 4

[0045] Unlike Example 1, triethylamine was not added in step c). The characterization results of the obtained β-zeolite molecular sieve are shown in Table 1, and it was found that the obtained product exhibited a certain degree of agglomeration.

[0046] Example 5

[0047] Unlike Example 1, in step a), the molar ratio of SiO2:Al2O3 is 1500:1. The characterization results of the obtained β-zeolite molecular sieve are shown in Table 1.

[0048] Example 6

[0049] Unlike Example 1, the molar ratio of water to SiO2 in step b) is 1.3. The characterization results of the obtained β-zeolite molecular sieve are shown in Table 1.

[0050] Comparative Example 1

[0051] a) NaOH solid, aluminum nitrate nonahydrate, tetraethylammonium hydroxide solution, and silica were mixed and a 3 mm diameter strip crystallization precursor was prepared by kneading and extrusion. The molar ratio of NaOH to SiO2 in the resulting mixture was 0.1:1, the molar ratio of tetraethylammonium hydroxide to SiO2 was 0.14:1, the molar ratio of SiO2 to Al2O3 was 600:1, and the molar ratio of water to SiO2 was 3:1.

[0052] b) Triethylamine was added to the obtained shaped material and then crystallized in a hydrothermal reactor. The molar ratio of triethylamine to SiO2 was 0.05:1, the crystallization temperature was 130℃, and the crystallization time was 48 h. After crystallization, the triethylamine was recovered. The crystallized solid product was washed with ammonium nitrate aqueous solution until neutral, dried at 80℃ for 4 h, and then calcined at 550℃ for 4 h. The resulting solid had an amorphous structure and a crystallinity of 0. No shaped β-zeolite molecular sieve product was obtained after crystallization.

[0053] Table 1

[0054]

[0055] Example 7

[0056] The β-zeolite molecular sieve prepared in Example 1 was applied in a gas-phase adsorption experiment. The obtained β-zeolite molecular sieve was loaded into a fixed-bed adsorption evaluation device with a loading volume of 100 mL. Nitrogen was used as the carrier gas, and cyclohexane was used as the adsorbate. The concentration of the inlet organic matter was 400,000–500,000 mg / mL. 3The inlet flow rate was 50 mL / min, the adsorption temperature was 35℃, and the adsorption pressure was atmospheric pressure. Online gas chromatography with an FID detector was used to detect the tail gas after adsorption. The equilibrium time of the adsorbent refers to the time it takes for the tail gas outlet concentration to reach the inlet concentration. The equilibrium adsorption capacity was obtained by the change in the mass of the adsorbent before and after adsorption. The adsorption evaluation results are shown in Table 2.

[0057] Example 8

[0058] The β-zeolite molecular sieve prepared in Example 1 was used to adsorb organic matter in the liquid phase. The obtained β-zeolite molecular sieve was loaded into a fixed-bed adsorption evaluation device, with a mass hourly space velocity of 50 h⁻¹. -1 The adsorption temperature and pressure were both at room temperature and atmospheric pressure. A 1 mg / g phenol aqueous solution was prepared as simulated water, and the concentration of organic matter in the water was measured using a Shimadzu TOC analyzer (TC value). The equilibrium adsorption capacity was calculated based on the breakthrough curve. The adsorption evaluation results are shown in Table 2.

[0059] Comparative Example 2

[0060] Unlike Example 7, the adsorbent used is commercially available activated carbon for adsorbing VOCs, with a total specific surface area of ​​935.2 m². 2 / g, with a microporous specific surface area of ​​510.2m². 2 / g.

[0061] Comparative Example 3

[0062] Unlike Example 8, the adsorbent used is Seplite XDA-based ultra-high cross-linked macroporous adsorption resin (Xi'an Lanxiao Technology).

[0063] Comparative Example 4

[0064] Unlike Example 8, the adsorbent used was a commercially available low-silica β-zeolite molecular sieve with a SiO2:Al2O3 molar ratio of 40.5. This sieve was prepared by adding boehmite and dilute nitric acid solution at a mass ratio of 8:2, followed by kneading, extrusion molding, drying, and calcination. The resulting β-zeolite was a 3mm diameter strip with a specific surface area of ​​486.9 m². 2 / g.

[0065] Table 2

[0066]

Claims

1. A method for preparing β-zeolite molecular sieves, comprising: a) Mix the alkali source, aluminum source, tetraalkylammonium, and silicon source, and the molar ratio of tetraalkylammonium / SiO2 in the resulting mixture is 0.11~0.25; b) Dry the material obtained in step a) to obtain a precursor, wherein the molar ratio of H2O / SiO2 in the precursor is 0.1~2; c) Crystallize the precursor obtained in step b) to obtain β-zeolite molecular sieve; In the resulting mixture, the molar ratios are: alkali source / SiO2 = 0.05~0.2:1, SiO2 / Al2O3 = 200~2500, and H2O / SiO2 = 2.5~15. In step b), the drying temperature is 40~120℃; In step c), an organic ammonium is added during crystallization, wherein the organic amine is selected from one or more of ethylenediamine, triethylamine, and n-butylamine.

2. The method according to claim 1, characterized in that: In step a), the tetraalkylammonium is one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrapropylammonium bromide.

3. The method according to claim 1, characterized in that: In step a), the alkali source is NaOH and / or KOH; the aluminum source is one or more of aluminum nitrate, hydrated alumina, and sodium aluminate; and the silicon source is one or more of amorphous silica, silica sol, silica gel, and water glass.

4. The method according to claim 1, characterized in that: In step b), the molar ratio of H2O / SiO2 in the obtained precursor is 0.1~1.

5.

5. The method according to claim 1, characterized in that: In step c), the crystallization time is 24h~288h, and the crystallization temperature is 120~160℃.

6. The method according to claim 5, characterized in that: In step c), the crystallization time is 24h~96h.

7. The method according to claim 1, characterized in that: In step c), the molar ratio of the organic amine to SiO2 is 0.02 to 0.

2.

8. A β-zeolite molecular sieve prepared according to any one of claims 1-7.

9. The β-zeolite molecular sieve according to claim 8, characterized in that: The β-zeolite molecular sieve has the following properties: a SiO2 / Al2O3 molar ratio of 200 to +∞, and a specific surface area of ​​400 m². 2 / g~700m 2 / g, with a total pore volume of 0.1mL / g to 0.25mL / g and a relative crystallinity of 95% to 120%.

10. The β-zeolite molecular sieve according to claim 9, characterized in that: The β-zeolite molecular sieve has the following properties: the SiO2 / Al2O3 molar ratio is 200~1000.

11. The application of a β-zeolite molecular sieve prepared according to any one of claims 1-7 as an adsorbent in the gas or liquid phase.

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