ZSM-5 molecular sieve and its preparation method and application

Abstract

The present invention discloses a ZSM-5 molecular sieve and its preparation method and application. The method comprises the following steps: a) mixing ZSM-5 seed crystals, a liquid silicon source, a template A, and water to obtain a mixture; b) mixing the mixture obtained in step a) with a solid silicon source and a template B to obtain a crystallized precursor; c) mixing the crystallized precursor with an organic base, and subjecting the mixture to a crystallization reaction to obtain a ZSM-5 molecular sieve. The ZSM-5 molecular sieve obtained by the method of the present invention can be used as an adsorbent to effectively remove VOCs, is easy to regenerate, and maintains substantially unchanged performance after multiple uses.

Description

Technical Field

[0001] The present invention belongs to the field of adsorbent preparation, and in particular relates to a ZSM-5 molecular sieve and a preparation method and application thereof. Background Art

[0002] Since its development by Mobile in the United States in 1972, ZSM-5 molecular sieve has been widely used in oil refining, fine chemicals, and environmental protection. While activated carbon is currently the most commonly used adsorbent, it is highly hydrophilic and difficult to remove and regenerate after adsorbing substances such as olefins, aldehydes, ketones, and alcohols. The adsorption process also releases heat, posing a process risk. While some studies have used zeolite molecular sieves for adsorption, limited research has focused on mixed gas adsorption.

[0003] CN1105906A discloses a tack-free hydrophobic zeolite adsorbent and its preparation. The method involves first mixing a ZSM-5 hydrophobic zeolite with a silica-containing binder, then subjecting it to hydrothermal treatment with an organic amine or organic base, and finally to high-temperature steam activation to obtain a tack-free, high-silicon zeolite. This method yields a tack-free, hydrophobic, high-silicon zeolite with a low water adsorption capacity. However, the preparation requires the use of an existing ZSM-5 secondary crystallization step and high-temperature steam treatment to remove surface acidity.

[0004] CN111408342A discloses a high-silicon composite molecular sieve adsorption method for VOCs removal and its preparation method. This method uses a high-silicon ZSM-5 molecular sieve as a core, organically embedding a Y-type molecular sieve directing agent on the outer surface of the high-silicon ZSM-5 molecular sieve, and employs ultrasonic and microwave treatments during the aging and crystallization processes, respectively. This method is complex and costly to prepare, and the resulting filter cake still requires acid washing and exchange, further increasing the cost of treating the three wastes.

[0005] CN103787367B discloses a method for preparing a tack-free nano ZSM-5 molecular sieve molded product. This method replaces a liquid silicon source with a solid powdered silicon source, uses tetrapropylammonium as a template to prepare a seed crystal directing agent, extrudes the silicon source, aluminum source, and directing agent into strips or coats them onto a tangible structure, and then undergoes solid-phase crystallization in the presence of an organic amine. The ZSM-5 obtained by this method is primarily coated onto the molded product. The molecular sieve itself has no mechanical strength, and the interaction between the molecular sieve and the coating may cause the molecular sieve to fall off over time.

[0006] CN109437211A discloses a high-specific-surface-area, high-VOC-adsorbing silica and its preparation method. This method involves treating commercially available ZSM-5 zeolite with sulfuric acid and then sodium silicate, followed by crushing, washing, and drying to produce a silica adsorbent. The adsorbent prepared by this method has excellent toluene purification effects and a large pore volume and specific surface area, but the preparation cost is high and the process is complex.

[0007] CN1915820A discloses a method for preparing a binder-free small-grain ZSM-5 zeolite. This method uses silica sol or diatomaceous earth as a binder to bond a solid silicon source into a solid state, and then uses organic amine and water vapor for gas-solid phase conversion. The ZSM-5 zeolite synthesized by this method has a high aluminum content, and the specific surface area of ​​the synthesized small grains is mainly micropores, with a micropore specific surface area of ​​225m 2 / g, generally used in the field of catalysis.

[0008] CN103011194A discloses a small-grain high silicon-aluminum ratio ZSM-5 molecular sieve, which is prepared by distributing two systems and then mixing the gel to prepare a high silicon ZSM-5 molecular sieve with a silicon-aluminum ratio in the range of 100 to 600. However, Na is added during the preparation of the molecular sieve. + , acid exchange is required to obtain H-type ZSM-5 molecular sieve, and the product synthesized by this method requires the addition of a binder to have a certain mechanical strength. Summary of the Invention

[0009] To address the shortcomings of the existing technology, the present invention provides a ZSM-5 molecular sieve, its preparation method, and application. The ZSM-5 molecular sieve obtained by the present invention can effectively remove VOCs as an adsorbent, is easy to regenerate, and maintains substantially unchanged performance after multiple uses.

[0010] The first aspect of the present invention provides a method for preparing a ZSM-5 molecular sieve, the method comprising the following steps:

[0011] a) mixing ZSM-5 seed crystals, a liquid silicon source, a template A, and water to obtain a mixed material;

[0012] b) mixing the mixture obtained in step a) with a solid silicon source and a template B to obtain a crystallized precursor;

[0013] c) mixing the crystallization precursor with an organic base and performing a crystallization reaction to obtain a ZSM-5 molecular sieve.

[0014] Furthermore, the silicon-aluminum ratio of the ZSM-5 seed crystal is ≥25, preferably an H-type ZSM-5 zeolite molecular sieve with a silicon-aluminum ratio of 100-500.

[0015] In the present invention, the silicon-aluminum ratio is calculated as the molar ratio of SiO2 / Al2O3.

[0016] Furthermore, the liquid silicon source is selected from one or more of tetraethyl orthosilicate and silica sol. The template agent A is selected from one or more of tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetramethylammonium bromide.

[0017] Furthermore, in step a), the molar ratio of ZSM-5 seed crystals, liquid silicon source (calculated as SiO2), template A, and water is 0.5-2:1-5:1:10-50.

[0018] Furthermore, the solid silicon source is selected from one or more of silica gel, white carbon black, and diatomaceous earth. The template agent B is selected from one or more of dodecyl to octadecyl trimethylammonium and a silane coupling agent. The silane coupling agent is preferably one or more of vinyl triethoxysilane and vinyl trimethoxysilane. The molar ratio of the solid silicon source to the total silicon source in the system, calculated as SiO2, is 0.85-0.95:1. The molar ratio of the template agent B to the total silicon source in the system, calculated as SiO2, is 0.01-0.03:1.

[0019] Furthermore, the organic base is one or more of triethylamine, n-butylamine, and ethylenediamine. The molar ratio of the organic base to the total silicon source in the system calculated as SiO2 is 0.02 to 0.05:1.

[0020] Furthermore, the conditions of the crystallization reaction are: crystallization temperature is 130-170° C., and crystallization treatment time is 48h-144h.

[0021] Furthermore, in step c), after the crystallization reaction is completed, the ZSM-5 product can be separated from the obtained mixture by any conventionally known separation method. As the separation method, for example, a method of filtering, washing and drying the obtained mixture can be cited. Here, the filtration, washing and drying can be carried out in any conventional manner known in the art. For example, as the filtration, for example, the obtained product mixture can be simply filtered. As the washing, for example, washing with deionized water until the pH is neutral can be cited. As the drying temperature, for example, 40 to 160°C can be cited, and as the drying time, for example, 8 to 30 hours can be cited, preferably 10 to 20 hours. The drying can be carried out under normal pressure or under reduced pressure.

[0022] Furthermore, as needed, the molecular sieve prepared according to the above method can be calcined to remove the template and any moisture. The calcination can be carried out in any manner conventionally known in the art, such as calcination at 500-650°C for 1-12 hours. The calcination is generally carried out in an oxygen-containing atmosphere, such as air or oxygen.

[0023] The second aspect of the present invention provides a ZSM-5 molecular sieve prepared by the first aspect.

[0024] Furthermore, the ZSM-5 molecular sieve has the following properties: a silicon-aluminum ratio greater than 100, preferably ≥200, a specific surface area of ​​320 to 470 m 2 / g, the total pore volume is 0.1mL / g-0.4mL / g, the mesopore volume / total pore volume is 0.5-0.95, the bulk density is 0.35-0.55g / mL, and the relative crystallinity is 100%-115%.

[0025] The third aspect of the present invention provides a use of the ZSM-5 molecular sieve prepared according to the first aspect in adsorbing volatile organic compounds.

[0026] Furthermore, the ZSM-5 molecular sieve is used to adsorb volatile organic compounds (VOCs) such as short-chain alkanes, olefins, esters, alcohols, aldehydes, and ketones. 10 One or more straight-chain hydrocarbons and isomers, alcohols and aldehydes containing C1 to C 10 One or more of straight-chain alcohols, aldehydes and isomers, ketones containing C3~C 10 One or more straight-chain ketones and their isomers.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] The preparation method of the present invention is simple and easy to operate, and the various steps cooperate with each other. When the ZSM-5 molecular sieve finally obtained is used for the adsorption of volatile organic compounds (VOCs), it has strong adsorption capacity and a high VOCs removal rate.

[0029] While common volatile organic compounds contain water, the molecular sieves prepared using the specific method of this invention exhibit excellent hydrophobicity, enabling them to maintain good adsorption performance even in the presence of mixed water vapor. Saturated molecular sieve adsorbents can be regenerated through calcination, steam treatment, hot air purging, and other methods, depending on demand, with their adsorption performance remaining essentially unchanged after regeneration. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The XRD diffraction pattern of the ZSM-5 molecular sieve obtained in Example 1 is shown in FIG.

[0031] Figure 2 This is the SEM spectrum of the ZSM-5 molecular sieve obtained in Example 1. DETAILED DESCRIPTION

[0032] The specific embodiments of the present invention are described in detail below. However, it should be noted that the protection scope of the present invention is not limited by these specific embodiments, but is determined by the claims.

[0033] In the present invention, the specific surface area, pore volume, and average pore diameter of the catalyst are all well-known in the art and can be measured using methods and instruments known in the art. Specifically, a US Micromeritics Instrument ASAP2020M physical and chemical adsorption instrument was used. Before measurement, the sample was evacuated and kept at 300°C for 2 hours to remove impurities adhering to the sample surface. High-purity N₂ was then adsorbed under low-temperature liquid nitrogen to obtain an adsorption / desorption curve for the catalyst powder. The specific surface area was calculated using the BET method, and the pore size distribution was calculated using the BJH method.

[0034] In the present invention, the mechanical strength of the catalyst is well known in the art and can be tested using methods and instruments known in the art. Specifically, the catalyst strength was measured using a DLIII intelligent particle strength tester produced by the Dalian Chemical Industry Research and Design Institute. The catalyst strength was measured 22 times, with the maximum and minimum values ​​removed and the average value calculated.

[0035] In the present invention, XRD was performed using a Bruker D-8Advance X-ray diffractometer with Cu Kα radiation as the ray source. Graphite monochromator, tube voltage 40kV, tube current 40mA, small angle diffraction range is 1~6°.

[0036] In the present invention, the relative crystallinity of the sample % = (peak area of ​​the strongest diffraction peak of the sample / peak area of ​​the strongest diffraction peak of the standard sample) * relative crystallinity of the standard sample. The crystallinity of the ZSM-5 molecular sieve obtained in Comparative Example 4 of the present invention is 100%.

[0037] In the present invention, the dynamic n-hexane adsorption test conditions are as follows: the obtained molecular sieve is loaded into a fixed bed adsorption evaluation device with a loading volume of 100 mL, nitrogen is used as a carrier gas, n-hexane is used as an adsorbent, and the concentration of the adsorbed imported organic matter is 1500000 mg / m 3 The total inlet flow rate was 50 mL / min, the adsorption temperature was 35°C, and the adsorption pressure was atmospheric pressure. The equilibrium adsorption capacity was calculated by the change in adsorbent mass before and after adsorption. Experiments with mixed gases or dynamic water adsorption were conducted by replacing the above-mentioned adsorbents with mixed gases or water.

[0038] In the present invention, outlet VOCs in the adsorption evaluation were tested using online chromatography, with automatic sampling every 10 minutes, using an FID detector built by Shimadzu, Japan, and the test conditions were 50°C, heated to 160°C at a rate of 20°C / min, and maintained for 2.5 minutes.

[0039] Example 1

[0040] Preparation of molecular sieves:

[0041] Raw materials were added according to a molar ratio of 0.3:1.2:1:12 of ZSM-5 seed crystals (silicon-aluminum ratio of 100), tetraethyl orthosilicate calculated as SiO2, tetraethylammonium hydroxide, and water to obtain a mixed material.

[0042] The above-mentioned mixture is mixed with white carbon black and vinyl triethoxysilane to form a mixture, wherein the molar ratio of white carbon black to the total silicon source of the system calculated as SiO2 is 0.90:1, and the molar ratio of the added silane coupling agent to the total silicon source of the system calculated as SiO2 is 0.02:1. After drying at 50°C for 4 hours, it is used as a crystallization precursor.

[0043] Triethylamine was measured according to the molar ratio of triethylamine to the total silicon source of the system at SiO2 of 0.02:1, and the measured triethylamine and crystallization precursor were added to the crystallization kettle, and the mixture was placed in a crystallization kettle at 150°C for crystallization for 3 days.

[0044] After crystallization, the mixture was washed with water until neutral and calcined at 550 ° C for 4 h to obtain ZSM-5 molecular sieve (its XRD pattern is shown in Figure 1 The ZSM-5 molecular sieve has a silicon-aluminum ratio of 932 and a specific surface area of ​​380 m 2 / g, with a total pore volume of 0.25 cm 3 / g, mesopore volume / total pore volume is 0.8, and the bulk density is 0.47cm 3 / g, and the relative crystallinity is 115%.

[0045] Evaluation of molecular sieve adsorption performance:

[0046] The adsorption capacity of n-hexane and water was tested, and the results are shown in Table 1.

[0047] Test its performance on dry mixed gas (methane 50mg / m 3 , ethane 31.2 mg / m 3 , propylene 30.4mg / m 3 , acetone 296mg / m 3 tert-Butanol 402 mg / m 3 ) adsorption, the adsorption results are as follows: volume space velocity 40h -1The VOCs removal efficiency within 24 hours is 95%. 3 , n-heptane 166 mg / m 3 , toluene 0.05mg / m 3 , cyclohexane 0.4 mg / m 3 ) adsorption, the adsorption results are as follows: volume space velocity 40h -1 The removal efficiency of VOCs within 24 hours is 97%.

[0048] Example 2

[0049] The molecular sieve was prepared as in Example 1. The difference was that the sample had been calcined at 500°C and used 6 times. The molecular sieve had a silicon-aluminum ratio of 962 and a specific surface area of ​​378 m 2 / g, of which the specific surface area of ​​mesopores is 262m 2 / g, pore volume is 0.25cm 3 / g, mesopore volume / total pore volume is 0.8, and the bulk density is 0.47cm 3 / g, and a relative crystallinity of 115%. The adsorption capacity of n-hexane and water was tested, and the results are shown in Table 1.

[0050] Example 3

[0051] The preparation method of ZSM-5 molecular sieve in Example 3 is different from that in Example 1 except that the silicon-aluminum ratio of the selected ZSM-5 seed crystal is 25. The XRD pattern of the obtained ZSM-5 molecular sieve is the same as that of Example 1. Figure 1 similar.

[0052] The silicon-aluminum ratio of the obtained ZSM-5 molecular sieve is 298, and the specific surface area is 390m 2 / g, with a total pore volume of 0.24 cm 3 / g, mesopore volume / total pore volume is 0.8, and the bulk density is 0.47cm 3 / g, and a relative crystallinity of 115%. Under dynamic adsorption conditions, the adsorption capacity of n-hexane and water was tested, and the results are shown in Table 1.

[0053] Example 4

[0054] The preparation method of ZSM-5 molecular sieve in Example 4 is different from that in Example 1 except that the template B used is vinyltrimethoxysilane and the organic base used is ethylenediamine. Figure 1 similar.

[0055] The silicon-aluminum ratio of the obtained ZSM-5 molecular sieve is 934, and the specific surface area is 362m 2 / g, mesopore volume / total pore volume is 0.82, and the total pore volume is 0.25cm 3 / g, bulk density is 0.46cm 3 / g, and a relative crystallinity of 115%. Under dynamic adsorption conditions, the adsorption capacity of n-hexane and water was tested, and the results are shown in Table 1.

[0056] Comparative Example 1

[0057] The preparation method of the ZSM-5 molecular sieve in Comparative Example 1 is different from that in Example 1 only in that the organic template B (silane coupling agent) is not added.

[0058] The silicon-aluminum ratio of the obtained ZSM-5 molecular sieve is 924, and the specific surface area is 365m 2 / g, with a total pore volume of 0.15 cm 3 / g, mesopore volume / total pore volume is 0.32, and the bulk density is 0.45cm 3 The adsorption capacity of n-hexane and water was tested, and the results are shown in Table 1.

[0059] Comparative Example 2

[0060] The preparation method of the ZSM-5 molecular sieve in Comparative Example 2 is different from that in Example 1 only in that no organic base (triethylamine) is added.

[0061] The silicon-aluminum ratio of the obtained ZSM-5 molecular sieve is 924, and the specific surface area is 330m 2 / g, with a total pore volume of 0.16 cm 3 / g, mesopore volume / total pore volume is 0.87, and the bulk density is 0.51cm 3 / g, and the relative crystallinity is 100%. The adsorption capacity of n-hexane and water was tested, and the results are shown in Table 1.

[0062] Comparative Example 3

[0063] The preparation method of the ZSM-5 molecular sieve in Comparative Example 3 is different from that in Example 1 only in that when preparing the mixed material for molding, aluminum nitrate is added in a ratio of SiO2 / Al2O3 of 25.

[0064] The obtained ZSM-5 molecular sieve has a silicon to aluminum molar ratio of 25 and a specific surface area of ​​345m 2 / g, with a total pore volume of 0.22 cm 3 / g, mesopore volume / total pore volume is 0.7, and the bulk density is 0.51cm 3 The adsorption capacity of n-hexane and water was tested, and the results are shown in Table 1.

[0065] Comparative Example 4

[0066] Sodium hydroxide, sodium aluminate, silicic acid, and water are prepared according to the ratio of 3.25 Na₂O:Al₂O₃:30 SiO₂:958 H₂O. (1) First, thoroughly mix 1420.6 g of water, 27.6 g of sodium hydroxide, and 234 g of TPAOH solution. Add 317.8 g of silicic acid while stirring. After thorough shaking at room temperature, age at 100°C for 16 h to obtain colloidal seed crystals. (2) Thoroughly mix 1735.6 g of water, 17.6 g of sodium hydroxide, 20.6 g of sodium aluminate, and 226.2 g of silicic acid. (3) Place 50 g of the seed crystals obtained in (1) in (2) and mix thoroughly. (4) After crystallization at 180°C for 40 h, the mixture was washed, filtered, and dried, and then calcined at 550°C to obtain ZSM-5 powder. After preparation, alumina was added according to a mass ratio of ZSM-5 powder to alumina of 7:3 to form an adsorbent with a certain mechanical strength. Under dynamic adsorption conditions, its adsorption capacity for n-hexane and water was tested, and the results are shown in Table 1.

[0067] Table 1

[0068]

Claims

1. A method for preparing a ZSM-5 molecular sieve, the method comprising the following steps: a) mixing ZSM-5 seed crystals, a liquid silicon source, a template A, and water to obtain a mixed material; b) mixing the mixture obtained in step a) with a solid silicon source and a template B to obtain a crystallized precursor; c) mixing the crystallization precursor with an organic base and performing a crystallization reaction to obtain a ZSM-5 molecular sieve; The template A is selected from one or more of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetramethylammonium bromide; The template agent B is selected from one or more of dodecyl to octadecyl trimethyl ammonium and silane coupling agents; In step a), the molar ratio of ZSM-5 seed crystal, liquid silicon source (calculated as SiO2), template A, and water is 0.5-2:1-5:1:10-50.

2. The method according to claim 1, characterized in that: In step a), the silicon-to-aluminum ratio of the ZSM-5 seed crystal is ≥25.

3. The method according to claim 1, wherein: In step a), the ZSM-5 seed crystal is an H-type ZSM-5 molecular sieve with a silicon-aluminum ratio of 100 to 500.

4. The method according to claim 1, wherein: In step a), the liquid silicon source is selected from one or more of tetraethyl orthosilicate and silica sol.

5. The method according to claim 1, characterized in that: In step b), the solid silicon source is selected from one or more of silica gel, white carbon black, and diatomaceous earth; and the silane coupling agent is one or more of vinyltriethoxysilane and vinyltrimethoxysilane.

6. The method according to claim 1, characterized in that: Calculated in terms of SiO2, the molar ratio of the solid silicon source to the total silicon source of the system is 0.85-0.95:1; the molar ratio of the template B to the total silicon source of the system is 0.01-0.03:

1.

7. The method according to claim 1, characterized in that: In step c), the organic base is one or more of triethylamine, n-butylamine, and ethylenediamine; and the molar ratio of the organic base to the total silicon source of the system, calculated as SiO2, is 0.02-0.05:

1.

8. The method according to claim 1, characterized in that: The conditions of the crystallization reaction are: crystallization temperature is 130-170° C., and crystallization time is 48 h-144 h.

9. A ZSM-5 molecular sieve prepared according to the method of any one of claims 1 to 8.

10. The ZSM-5 molecular sieve according to claim 9, characterized in that: The ZSM-5 molecular sieve has the following properties: a silicon-aluminum ratio greater than 100, a specific surface area of ​​320-470 m 2 / g, the total pore volume is 0.1mL / g~0.4mL / g, the mesopore volume / total pore volume is 0.5~0.95, the bulk density is 0.35~0.55g / mL, and the relative crystallinity is 100%~115%.

11. The ZSM-5 molecular sieve according to claim 9, characterized in that: The silicon-aluminum ratio of the ZSM-5 molecular sieve is ≥200.

12. Use of the ZSM-5 molecular sieve according to claim 9 in adsorbing volatile organic compounds.

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