A micro-micro-mesoporous composite pore system ZSM-5 molecular sieve and a synthesis method and VOCs adsorption application thereof

Abstract

The application relates to a micro-micro-mesoporous composite pore system ZSM-5 molecular sieve and a synthesis method and VOCs adsorption application thereof. On the basis of maintaining original micropore structure, a second micropore structure and a mesopore structure are introduced, wherein the original micropore structure can adsorb small molecules such as dichloromethane, the newly introduced second micropore structure can adsorb macromolecules such as m-xylene, the mesopore structure can improve the molecular diffusion rate, reduce the desorption temperature and improve the desorption speed. The application also relates to a preparation method of the material, mainly adopting an inorganic cation or a surfactant-mediated molecular sieve controllable desilication method. The material shows higher adsorption capacity and lower desorption temperature in the adsorption process of VOCs with a relatively wide boiling point distribution.

Description

Technical Field

[0001] This application relates to a micro-micro-mesoporous composite pore system ZSM-5 molecular sieve, its synthesis method and VOCs adsorption application, belonging to the field of inorganic synthesis and environmental adsorption. Background Technology

[0002] Industrial VOC emissions exhibit distinct industry-specific characteristics. For instance, emissions from the petroleum refining industry primarily consist of alkanes, olefins, and aromatics; while industries like pharmaceuticals, in addition to conventional VOCs (containing only C, H, and O), also involve emissions of chlorinated VOCs (CVOCs). The difficulty of catalytic purification varies significantly among different types of VOCs. Therefore, it is necessary to develop VOC adsorption materials that combine broad-spectrum applicability with industry-specific characteristics, taking into account the emission features of each industry. Microporous molecular sieves such as MFI, BEA, and FAU are the most commonly used VOC adsorption materials. Among them, ZSM-5 molecular sieve is mainly used for the adsorption of small molecule VOCs and VOCs such as benzene and toluene, while Beta and FAU molecular sieves can adsorb larger VOC molecules, such as xylene, trimethylbenzene, and styrene, but their ability to capture small molecule VOCs is extremely poor. Furthermore, all three types of molecular sieves mentioned above are microporous materials, and their inherent microporous structure restricts the diffusion of VOC molecules, resulting in low micropore utilization. Additionally, the desorption of adsorbed VOC molecules is difficult, and the desorption process consumes a lot of energy.

[0003] The introduction of secondary porous structures into ZSM-5 molecular sieves has been extensively studied, including methods such as steam treatment followed by acid washing for aluminum removal and alkali treatment for silicon removal. Due to the high humidity of the gases in actual working conditions for VOC adsorption, the adsorbent is typically a high-silica, hydrophobic MFI molecular sieve (SiO2 / Al2O3 > 300). Therefore, the secondary porous structure can only be constructed by selectively clipping silicon atoms from the molecular sieve framework. The optimal SiO2 / Al2O3 ratio for alkali treatment is between 50 and 100. To prevent over-etching, protective agents such as piperidine and hexadecyltrimethylammonium bromide are added. However, this method only introduces a mesoporous structure into the microporous zeolite, without a secondary microporous structure. The main reason for this is the lack of protection in the framework, leading to over-etching. Patent CN111377461A introduces a secondary non-penetrating mesoporous structure by calcining ZSM-5 molecular sieve powder, reacting it with an alkaline solution, then with an acid solution, and finally supplementing with silicon and aluminum sources and organic bases for hydrothermal synthesis. Patent CN109835914A introduces mesoporous structures into ZSM-5 molecular sieves through a combination of thermal dispersion and alkali treatment, and can control the size of the resulting mesopores while maintaining good acidity. Patent CN111099620A primarily addresses the problems of low mesoporous order, low sample solid yield, and low crystallinity in existing alkali treatment methods for preparing mesoporous ZSM-5 molecular sieves, proposing a scheme that pre-contaminates the ZSM-5 molecular sieve with an ordered mesoporous guiding agent solution before alkali treatment, effectively solving these problems. Patent CN109201106A, through the mixed reaction of inorganic and organic alkali solutions, introduces a certain amount of mesoporous structure while retaining a large number of microporous structures in the molecular sieve, combining the advantages of microporous ZSM-5 molecular sieves and mesoporous materials. None of the above patents involve a micro-micro-mesoporous composite pore system for ZSM-5 molecular sieves; they are limited to introducing secondary mesoporous structures, mainly due to excessive etching of the molecular sieve framework. Summary of the Invention

[0004] This application proposes a micro-micro-mesoporous composite pore system, ZSM-5 molecular sieve, which introduces a second microporous structure (0.8 nm to 2.0 nm) and a mesoporous structure (3 nm to 20 nm) while maintaining the original microporous structure (approximately 0.55 nm). The original microporous structure can adsorb small molecules such as dichloromethane, while the newly introduced second microporous structure can adsorb large molecules such as m-xylene. The mesoporous structure can improve the molecular diffusion rate, reduce the desorption temperature, and increase the desorption speed.

[0005] This application develops a controllable editing technology for the framework of high-silicon ZSM-5 molecular sieves. It mainly uses a method of controllable desilication of molecular sieves mediated by nonpolar cations and / or surfactants to precisely control the position and speed of silicon atom removal from the framework, and finally introduces secondary microporous and mesoporous structures.

[0006] This application relates to a micro-micro-mesoporous composite pore system ZSM-5 molecular sieve, its synthesis method, and its application in VOCs adsorption. The ZSM-5 molecular sieve is characterized by the introduction of a second microporous structure and a mesoporous structure while maintaining the original microporous structure of ZSM-5. The VOCs adsorption process is complex in real-world conditions, with VOCs exhibiting a wide boiling point distribution and significant molecular size differences. Commonly used ZSM-5 adsorbents cannot effectively remove large molecular VOCs such as m-xylene and trimethylbenzene; while high-silica Y adsorbents have extremely low adsorption capacity for small molecular VOCs such as dichloromethane and acetone. Furthermore, the inherent microporous structure of the molecular sieve limits the desorption of adsorbed VOC molecules, resulting in high energy consumption during the desorption process. The original microporous structure can adsorb small molecules such as dichloromethane, the newly introduced second microporous structure can adsorb large molecules such as m-xylene, and the mesoporous structure can improve the molecular diffusion rate, lower the desorption temperature, and increase the desorption speed. The preparation method mainly employs inorganic cations or surfactants-mediated controlled desilication methods for molecular sieves. This material exhibits high adsorption capacity and low desorption temperature in the adsorption of VOCs with a wide boiling point distribution.

[0007] According to another aspect of this application, a micro-micro-mesoporous composite pore system ZSM-5 molecular sieve is provided, wherein the micro-micro-mesoporous composite pore system ZSM-5 molecular sieve has a microporous structure I, a microporous structure II and a mesoporous structure;

[0008] The pore size of the microporous structure I is 0.55 nm;

[0009] The pore size of the microporous structure II is 0.8–2 nm;

[0010] Optionally, the pore size of the microporous structure II is 0.8–1.5 nm;

[0011] Optionally, the pore size of the microporous structure II is any value among 0.8nm, 0.9nm, 1nm, 1.1nm, 1.2nm, 1.3nm, 1.4nm, and 1.5nm, or a range between any two.

[0012] The pore size of the mesoporous structure is 3–20 nm.

[0013] Optionally, the pore size of the mesoporous structure is 5–20 nm;

[0014] Optionally, the pore size of the mesoporous structure is any value among 5nm, 10nm, 15nm, and 20nm, or a range between any two.

[0015] The specific pore volume of the microporous structure II is 0.01–0.15 cm³. 3 / g;

[0016] Optionally, the specific pore volume of the microporous structure II is 0.01–0.08 cm³. 3 / g;

[0017] Optionally, the specific pore volume of the microporous structure II is 0.01 cm³. 3 / g, 0.02cm 3 / g, 0.03cm 3 / g, 0.04cm 3 / g, 0.05cm 3 / g, 0.06cm 3 / g, 0.07cm 3 / g, 0.08cm 3 Any value in / g or any range between the two.

[0018] The specific pore volume of the mesoporous structure is 0.03–0.60 cm³. 3 / g;

[0019] Optionally, the specific pore volume of the mesoporous structure is 0.1–0.60 cm³. 3 / g.

[0020] Optionally, the specific pore volume of the mesoporous structure is 0.1 m³. 3 / g, 0.2m 3 / g, 0.3m 3 / g, 0.4m 3 / g, 0.5m 3 / g, 0.6m 3 Any value in / g or any range between the two.

[0021] According to another aspect of this application, a method for preparing the above-mentioned micro-micro-mesoporous composite pore system ZSM-5 molecular sieve is provided, comprising the following steps:

[0022] ZSM-5 molecular sieve powder was mixed with an alkaline solution containing additives, reacted, and dried to obtain the micro-micro-mesocomposite pore system ZSM-5 molecular sieve.

[0023] Furthermore, it includes the following steps:

[0024] The alkaline solution containing the additives is heated, and then ZSM-5 molecular sieve powder is added and stirred. The mixture is then reacted, washed, and dried to obtain the micro-micro-mesocomposite pore system ZSM-5 molecular sieve.

[0025] In the alkaline solution containing the auxiliaries:

[0026] The alkali is selected from at least one of NaOH, Na2CO3, NaHCO3, NaAlO2, NH3·H2O, KOH, K2CO3, and KHCO3;

[0027] The concentration of the alkali is 0.02–0.60 mol / L;

[0028] Optionally, the concentration of the alkali is any value or a range between 0.02 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, and 0.6 mol / L.

[0029] The auxiliary agent is selected from cationic and / or surfactants;

[0030] The cation is selected from Al. 3+ Ga 3+ B 3+ At least one of them;

[0031] The concentration of the cation is 0.06–0.30 mol / L;

[0032] Optionally, the concentration of the cation is any value selected from 0.06 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, or any range between two of them.

[0033] The surfactant is selected from at least one of tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrabutylammonium hydroxide, tetrabutylammonium bromide, and hexadecyltrimethylammonium bromide;

[0034] The concentration of the surfactant is 0.02–0.30 mol / L;

[0035] Optionally, the concentration of the surfactant is any value selected from 0.02 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, or any range between two of these values.

[0036] The liquid-to-solid ratio of the alkaline solution containing the additives to the ZSM-5 molecular sieve powder is 5–60 cm⁻¹. 3 / g.

[0037] Optionally, the solid-liquid ratio of the alkaline solution containing the additive to the ZSM-5 molecular sieve powder is 5 cm⁻¹. 3 / g, 10cm 3 / g, 15cm 3 / g、20cm 3 / g、25cm 3 / g, 30cm 3 / g, 35cm 3 / g、40cm 3 / g、45cm 3 / g, 50cm3 / g、55cm 3 / g、60cm 3 Any value in / g or any range between the two.

[0038] The reaction temperature is 50–95°C;

[0039] Optionally, the temperature of the reaction is any value among 50°C, 60°C, 70°C, 80°C, 90°C, and 95°C, or a range between any two.

[0040] The reaction time is 5 to 240 minutes.

[0041] Optionally, the reaction time is any value among 5 min, 10 min, 50 min, 100 min, 150 min, 200 min, and 240 min, or a range between any two.

[0042] The drying temperature is 80–200°C;

[0043] Optionally, the drying temperature is any value or a range between any two of 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, and 200℃.

[0044] The drying time is 2 to 20 hours;

[0045] Optionally, the drying time is any value among 2h, 5h, 10h, 15h, and 20h, or a range between any two.

[0046] Furthermore, it includes the following steps:

[0047] An alkaline solution containing cationic additives and / or surfactants is heated to the reaction temperature. A certain amount of ZSM-5 molecular sieve powder is added under stirring. Timing begins after the solid is added. After a period of reaction, the mixture is washed, centrifuged, and dried to obtain the micro-micro-mesocomposite pore system ZSM-5 molecular sieve.

[0048] According to another aspect of this application, a VOCs adsorption method is provided, using the micro-micro-mesoporous composite pore system ZSM-5 molecular sieve described above or the micro-micro-mesoporous composite pore system ZSM-5 molecular sieve prepared by the above preparation method.

[0049] The advantages of this application are:

[0050] This application proposes a micro-micro-mesoporous composite pore system, ZSM-5 molecular sieve, which introduces a second microporous structure (0.8 nm to 2.0 nm) and a mesoporous structure (3 nm to 20 nm) while maintaining the original microporous structure (approximately 0.55 nm). The original microporous structure can adsorb small molecules such as dichloromethane, while the newly introduced second microporous structure can adsorb large molecules such as m-xylene. The mesoporous structure can improve the molecular diffusion rate, reduce the desorption temperature, and increase the desorption speed.

[0051] This application develops a controllable editing technology for the framework of high-silicon ZSM-5 molecular sieves. It mainly uses an inorganic cation and / or surfactant-mediated controllable desilication method to precisely control the position and speed of silicon atom removal from the framework, ultimately introducing secondary microporous and mesoporous structures.

[0052] This application relates to a micro-micro-mesoporous composite pore system ZSM-5 molecular sieve, its synthesis method, and its application in VOCs adsorption. The ZSM-5 molecular sieve is characterized by the introduction of a second microporous structure and a mesoporous structure while maintaining the original microporous structure of ZSM-5. The VOCs adsorption process is complex in real-world conditions, with VOCs exhibiting a wide boiling point distribution and significant molecular size differences. Commonly used ZSM-5 adsorbents cannot effectively remove large molecular VOCs such as m-xylene and trimethylbenzene; while high-silica Y adsorbents have extremely low adsorption capacity for small molecular VOCs such as dichloromethane and acetone. Furthermore, the inherent microporous structure of the molecular sieve limits the desorption of adsorbed VOC molecules, resulting in high energy consumption during the desorption process. The original microporous structure can adsorb small molecules such as dichloromethane, the newly introduced second microporous structure can adsorb large molecules such as m-xylene, and the mesoporous structure can improve the molecular diffusion rate, lower the desorption temperature, and increase the desorption speed. The preparation method mainly employs inorganic cations or surfactants-mediated controlled desilication methods for molecular sieves. This material exhibits high adsorption capacity and low desorption temperature in the adsorption of VOCs with a wide boiling point distribution. Attached Figure Description

[0053] Figure 1 This is a transmission electron microscope image of the sample from Example 1.

[0054] Figure 2 The pore size distribution curve is shown for the sample in Example 1.

[0055] Figure 3 The results show the VOCs adsorption performance evaluation of the sample in Example 1. Detailed Implementation

[0056] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0057] Unless otherwise specified, the raw materials and reagents used in the embodiments of this application were all purchased commercially.

[0058] Example 1:

[0059] First, ZSM-5 powder was placed in a solution containing aluminum nitrate, with a liquid-to-solid ratio of 30 cm⁻¹. 3 The solution contained 0.02 mol / L aluminum nitrate. After stirring the solution at 65°C for 1 hour, tetrapropylammonium bromide (TPABr) with a concentration of 0.05 mol / L was added. Stirring continued for another hour, followed by the addition of solid NaOH with a concentration of 0.20 mol / L. Timing was started after the addition of NaOH, and the reaction was terminated after 30 minutes. The sample was then washed, centrifuged, and dried to obtain a solid sample.

[0060] Figure 1 The transmission electron microscope (TEM) results of the sample from Example 1 show that the sample obtained in Example 1 has a distinct mesoporous structure.

[0061] Figure 2 The pore size distribution curve of the sample in Example 1 shows that the sample obtained in Example 1 has obvious pore size distribution in 0.50 nm, 1 nm to 2 nm and 3 nm to 20 nm.

[0062] Figure 1 and Figure 2 The successful acquisition of the micro-micro-mesocomposite pore system ZSM-5 molecular sieve was demonstrated.

[0063] Example 2:

[0064] First, place ZSM-5 powder in a solution containing aluminum sulfate, with a liquid-to-solid ratio of 20 cm⁻¹. 3 The solution contained 0.03 mol / L aluminum sulfate. After stirring the solution at 75°C for 1 hour, tetrabutylammonium hydroxide (TBAOH) with a concentration of 0.10 mol / L was added. Stirring continued for another hour, followed by the addition of solid Na₂CO₃ with a concentration of 0.30 mol / L. Timing was started after the addition of Na₂CO₃, and the reaction was terminated after 20 minutes. The sample was then washed, centrifuged, and dried to obtain a solid sample.

[0065] Example 3

[0066] First, ZSM-5 powder was placed in a solution containing gallium nitrate, with a liquid-to-solid ratio of 10 cm⁻¹. 3 The solution contained 0.01 mol / L gallium nitrate. After stirring the solution at 60°C for 1 hour, 0.20 mol / L hexadecyltrimethylammonium bromide (CTAB) was added. Stirring continued for another hour, followed by the addition of 0.50 mol / L solid NaHCO3. Timing was started after the addition of NaHCO3, and the reaction was terminated after 60 minutes. The sample was then washed, centrifuged, and dried to obtain a solid sample.

[0067] Example 4

[0068] First, place ZSM-5 powder in a solution containing aluminum chloride, with a liquid-to-solid ratio of 30 cm⁻¹. 3 The solution contained 0.02 mol / L aluminum chloride. After stirring the solution at 65°C for 1 hour, ammonia solution with a concentration of 0.20 mol / L was added. Timing was started after the addition of ammonia solution, and the reaction was terminated after 15 minutes. The sample was then washed, centrifuged, and dried to obtain a solid sample.

[0069] Example 5

[0070] First, place ZSM-5 powder in a solution containing boric acid, with a liquid-to-solid ratio of 30 cm⁻¹. 3 The solution contained 0.08 mol / L boric acid. After stirring the solution at 80℃ for 1 h, tetrapropylammonium hydroxide (TPAOH) with a concentration of 0.10 mol / L was added. After stirring until homogeneous, solid Na2CO3 with a concentration of 0.30 mol / L was added. Timing started from the addition of Na2CO3, and the reaction was terminated after 10 min. The sample was then washed, centrifuged, and dried to obtain a solid sample.

[0071] Example 6

[0072] Examples 1-5 were evaluated using a self-made adsorption apparatus in the laboratory. The adsorbates were dichloromethane, acetone, toluene, and m-xylene. The humidity was controlled at 60%, and the VOCs concentration was 1500 mg / m³. 3 The adsorbent content is 1.0 g, and the volume hourly space velocity is 30,000 h⁻¹. -1 The adsorption results of Example 1 are as follows: Figure 3 As shown, it exhibits high adsorption capacity for four different sizes of VOC molecules.

[0073] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing a micro-micro-mesoporous composite pore system ZSM-5 molecular sieve, characterized in that, Includes the following steps: ZSM-5 molecular sieve powder is mixed with a solution containing a first additive, then a second additive is added and reacted with an alkali. The resulting product is washed and dried to obtain the micro-micro-meso composite pore system ZSM-5 molecular sieve. The first auxiliary agent is selected from cationic compounds; The second auxiliary agent is selected from surfactants; in, The alkali is selected from at least one of NaOH, Na2CO3, NaHCO3, NaAlO2, NH3·H2O, KOH, K2CO3, and KHCO3; The concentration of the alkali is 0.02~0.60 mol / L; the cations are selected from at least one of Al 3+ , Ga 3+ , B 3+ ; In the solution containing the first auxiliary agent, the concentration of the cation is 0.06~0.30 mol / L; The surfactant is selected from at least one of tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrabutylammonium hydroxide, tetrabutylammonium bromide, and hexadecyltrimethylammonium bromide; In the alkaline solution containing the second auxiliary agent, the concentration of the surfactant is 0.02~0.30 mol / L; The ZSM-5 molecular sieve obtained by the preparation method has microporous structure I, microporous structure II, and mesoporous structure.

2. The preparation method according to claim 1, characterized in that, The pore size of the microporous structure II is 0.8~1.5 nm; The pore size of the mesoporous structure is 5~20nm; The specific pore volume of the microporous structure II is 0.01 to 0.15 cm3 / g. 3 / g.

3. The preparation method according to claim 1, characterized in that, Preferably, the specific pore volume of the microporous structure II is 0.01 to 0.08 cm3 / g. 3 / g; The specific pore volume of the mesoporous structure is 0.03 ~ 0.60 cm 3 / g; The specific pore volume of the mesoporous structure is 0.1 ~0.60 cm 3 / g.

4. The preparation method according to claim 1, characterized in that, The mixing temperature is 50~95℃; Stirring is required during the reaction process.

5. The preparation method according to claim 1, characterized in that, The reaction temperature is 50~95℃; The reaction time is 5 to 240 minutes.

6. The preparation method according to claim 1, characterized in that, The drying temperature is 80~200℃. o C; The drying time is 2 to 20 hours.

7. A ZSM-5 molecular sieve with a micro-micro-mesoporous composite pore system prepared by the method described in any one of claims 1 to 6, characterized in that, The ZSM-5 molecular sieve, a micro-micro-mesoporous composite pore system, has microporous structure I, microporous structure II, and mesoporous structure. The pore size of the microporous structure I is 0.55 nm; The pore size of the microporous structure II is 0.8~2nm; The pore size of the mesoporous structure is 3~20nm.

8. A method for VOCs adsorption, characterized in that, The ZSM-5 molecular sieve with micro-micro-mesoporous composite pore system prepared by the preparation method according to any one of claims 1 to 6, or the ZSM-5 molecular sieve with micro-micro-mesoporous composite pore system according to claim 7.

Images