A method for preparing a hydrophobic vocs adsorbent

Abstract

The application discloses a preparation method of a hydrophobic VOCs adsorbent, comprising the following steps: S1, mixing a silicon source, an alkali source and water to form a solution A, adding a tungsten source and a cashew phenol polyoxyethylene ether sulfonate into the solution A to obtain a gel B, then adding ZSM-5 seeds into the gel B, stirring uniformly, performing crystallization, cooling, filtering, washing, drying and calcining after the crystallization is completed, and obtaining a tungsten-doped ZSM-5 molecular sieve; S2, adding a nitrogen-containing solution into the tungsten-doped ZSM-5 molecular sieve to perform exchange, and then performing calcination to obtain the adsorbent. The molecular sieve synthesized by using the method has low synthesis cost, short synthesis time, excellent hydrophobic performance, and excellent VOCs (benzene) adsorption performance under high humidity.

Description

Technical Field

[0001] This invention belongs to the field of VOCs adsorbent technology, specifically relating to a method for preparing a hydrophobic VOCs adsorbent. Background Technology

[0002] VOCs (volatile organic compounds) are toxic, flammable, and explosive. They are precursors to smog formation, severely damaging the ecological environment, endangering human health, and are a major cause of air pollution. In recent years, VOCs treatment has become a key research and development focus. Among various VOCs treatment methods, adsorption has advantages such as simple operation, mature technology, and low cost, and is therefore widely used. Currently, commonly used adsorbents include carbon-based adsorbents, molecular sieve adsorbents, and polymer materials. Molecular sieves are widely used due to their uniform and abundant pore structure, good hydrothermal stability, and strong adsorption performance for oxygen-containing organic compounds. Among them, ZSM-5, compared with other types of molecular sieves, has a high silicon-to-aluminum ratio and a structurally stable five-membered ring, enabling it to treat VOCs at high temperatures. Furthermore, its pore structure is not destroyed during thermal desorption, resulting in stable adsorption performance and recyclability. However, actual industrial organic waste gas often contains a large amount of water vapor, which greatly reduces the adsorption capacity of molecular sieves for VOCs. Therefore, hydrophobic modification of molecular sieves is necessary to improve their adsorption performance under high humidity. Generally, organic template agents are used to dope other transition metal elements from groups IV, V, and VI (such as Zr, V, Nb, Cr, Mo, and W) into the molecular sieve framework to regulate hydrophobicity. A nitrogen solution post-treatment method is then used to treat the molecular sieve. During calcination, nitrogen molecules combine with the surface hydroxyl groups of ZSM-5, altering the silanol groups and other defect sites, ultimately introducing nitrogen-containing functional groups onto the molecular sieve. These nitrogen-containing functional groups enhance the surface alkalinity of the adsorbent, increasing the material's affinity for VOCs (benzene molecules), and further improving adsorption capacity.

[0003] Patent CN114950351A discloses a method and application for enhancing the adsorption of VOCs by doping and modifying ZSM-5 molecular sieve. The method loads metal cations into ZSM-5 molecular sieve via ion exchange to improve its VOCs adsorption performance. However, this method does not embed the metal cations into the molecular sieve framework, making it easier for the metal cations to be lost.

[0004] Patent CN109513458A describes the process of adding a silicon source dropwise to an aqueous solution of a structure-directing agent to form a clear solution A; then adding an aqueous solution of a tungsten source or a tungsten source dropwise to solution A, followed by hydrothermal crystallization at 110℃~150℃ for 48h~120h to obtain an MFI-type molecular sieve catalyst with a framework of tungsten atoms.

[0005] Patent CN104437605A describes the process of stirring a certain proportion of deionized water, alkali source, organic template agent, tungsten source, and silicon source to form an initial gel, which is then hydrothermally crystallized to synthesize W-ZSM-5 molecular sieve. X-ray diffraction patterns have shown that W enters the molecular sieve framework, causing its unit cells to expand and increase in volume.

[0006] The two patents mentioned above use organic template agents to introduce W into the molecular sieve framework, which is expensive and will increase the synthesis cost of zeolite; the nitrogen oxides and carbon oxides produced by the decomposition of organic matter will cause environmental pollution, and the hydrothermal method has a long synthesis time, uneven heating of the gel, and difficulty in rapid nucleation. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a hydrophobic VOCs adsorbent. The molecular sieve synthesized using this method has low synthesis cost, short synthesis time, and excellent hydrophobic properties, and exhibits excellent adsorption performance for high humidity VOCs (benzene).

[0008] To achieve the above objectives, the present invention provides a method for preparing a hydrophobic VOCs adsorbent, comprising the following steps:

[0009] S1, a silicon source, an alkaline source and water are mixed to form a solution A. A tungsten source and cashew phenol polyoxyethylene ether sulfonate are added to the solution A to obtain gel B. Then, ZSM-5 seed crystals are added to the gel B, stirred evenly and crystallized. After crystallization, the solution is cooled, filtered, washed, dried and calcined to obtain tungsten-doped ZSM-5 molecular sieve.

[0010] S2, a nitrogen-containing solution is added to the tungsten-doped ZSM-5 molecular sieve for exchange, and then calcined to obtain the adsorbent.

[0011] The preparation method of the hydrophobic VOCs adsorbent of the present invention, wherein the molar ratio of cashew phenol polyoxyethylene ether sulfonate, silicon source, alkali source, tungsten source and H2O in gel B is 0.005-0.02:1:0.1-1:0.01-0.05:4-8, wherein the silicon source is calculated as SiO2 and the tungsten source is calculated as WO3.

[0012] In step S1 of this invention, the process of forming a gel is a conventional operation in the art. This invention recommends that the gel be formed by uniform stirring at 60℃~90℃ for 15~60 minutes. After adding ZSM-5 seed crystals to the gel, stirring for 1~3 hours can achieve uniform mixing, and then crystallization can be carried out.

[0013] The method for preparing the hydrophobic VOCs adsorbent of this invention uses cashew phenol polyoxyethylene ether sulfonate, which is sodium cashew phenol polyoxyethylene ether sulfonate and / or ammonium cashew phenol polyoxyethylene ether sulfonate. Cashew phenol polyoxyethylene ether sulfonate can be obtained by purchasing or self-preparation, and this invention does not impose specific limitations. The method for preparing cashew phenol polyoxyethylene ether sulfonate can be as follows: Step 1, using cashew phenol as a raw material, cashew phenol polyoxyethylene ether is synthesized with ethylene oxide under alkaline conditions; Step 2, using cashew phenol polyoxyethylene ether as a raw material, tert-butanol base is added, anhydrous ethanol is used as a solvent, the mixture is refluxed, and then the reaction system is cooled to room temperature. 1,3-propanesulfonate lactone or 1,4-butanesulfonate lactone is added dropwise, the mixture is refluxed, and cooled to obtain cashew phenol polyoxyethylene ether sulfonate.

[0014] The method for preparing the hydrophobic VOCs adsorbent of the present invention comprises the following: the silicon source is one or more of silica sol, tetraethyl silicate, methyl orthosilicate and water glass; the alkali source is ethylamine and / or n-butylamine; and the tungsten source is one or more of ammonium metatungstate, ammonium tungstate and sodium tungstate dihydrate.

[0015] The preparation method of the hydrophobic VOCs adsorbent of the present invention uses a mass ratio of ZSM-5 seed crystals to gel B of (1-5):100.

[0016] In the preparation method of the hydrophobic VOCs adsorbent of the present invention, in step S1, crystallization is carried out in a temperature-controlled microwave radiation heating device. The temperature-controlled microwave radiation heating device has a polytetrafluoroethylene bushing, which is a commonly used device in the field, and the present invention does not impose any special limitations on it. The microwave radiation heating power can be selected as 900W.

[0017] In the preparation method of the hydrophobic VOCs adsorbent of the present invention, the crystallization temperature in step S1 is 135℃~170℃ and the crystallization time is 1h~3h.

[0018] In the preparation method of the hydrophobic VOCs adsorbent of the present invention, the drying temperature in step S1 is 100-120℃ and the drying time is 8-12h.

[0019] In the preparation method of the hydrophobic VOCs adsorbent of the present invention, the nitrogen-containing solution in step S2 is one or more of ammonium nitrate, urea and ammonia solution, and the mass ratio of tungsten-doped Na-type ZSM-5 molecular sieve to nitrogen atoms in the nitrogen-containing solution is 1:0.08-1.4.

[0020] The preparation method of the hydrophobic VOCs adsorbent of the present invention includes a calcination condition in step S2 of heating to 500℃~700℃ at a heating rate of 2~5℃ / min and calcination for 4~6h.

[0021] Beneficial effects of this invention:

[0022] (1) Introducing tungsten into the MFI molecular sieve framework can effectively improve the hydrophobicity of the molecular sieve, thereby enhancing its adsorption performance for VOCs under high humidity. After nitrogen modification, nitrogen molecules combine with the surface hydroxyl groups of ZSM-5 during calcination, causing changes in defect sites such as silanol groups and silica nests in the molecular sieve, ultimately introducing nitrogen-containing functional groups onto the molecular sieve. These nitrogen-containing functional groups enhance the surface alkalinity of the adsorbent, increase the affinity of the material for benzene molecules, and reduce the diffusion resistance of benzene in the material channels. As a result, the adsorption capacity and adsorption rate of benzene on the modified molecular sieve are significantly improved, and the adsorption performance is further enhanced.

[0023] (2) The synthesis process does not use organic template agents, which greatly reduces the cost. The method of using seed crystal method combined with microwave radiation heating has a short synthesis time.

[0024] (3) Adding cashew phenol polyoxyethylene ether sulfonate increases the solvent interface during crystal nucleation and growth. Adding a small amount of cashew phenol polyoxyethylene ether sulfonate can effectively reduce the surface tension of the solution, making it easier to nucleate from an energy perspective, and forming micelles in the gel. This effect increases the contact and interaction probability between silicon and tungsten, that is, it improves the crystallization rate by changing the thermodynamic properties of the sol, thereby improving the crystallinity of the sample and successfully introducing tungsten into the molecular sieve framework. Attached Figure Description

[0025] Figure 1 The images show the XRD patterns of the molecular sieves obtained in Comparative Examples 1, 2, and 3 of this invention.

[0026] Figure 2 This refers to the UV-Vis of the molecular sieve obtained in Example 3 of the present invention. Detailed Implementation

[0027] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0028] (1) Mix the silicon source with the alkali source and H2O to form solution A;

[0029] (2) Add the tungsten source dropwise to the above solution A, then add the additive sodium cashew phenol polyoxyethylene ether sulfonate, and stir at a constant speed for 15 to 60 minutes at 60℃~90℃ to hydrolyze and form a mixed gel B.

[0030] (3) Add seed crystal ZSM-5 to the above-mentioned mixed gel B, stir evenly and age to obtain mixture C;

[0031] (4) The mixture C was placed in a temperature-controlled microwave radiation heating device with a polytetrafluoroethylene liner for crystallization. After crystallization, it was cooled to room temperature and then centrifuged, filtered, washed, dried and calcined in sequence to obtain tungsten-doped ZSM-5 molecular sieve.

[0032] (5) The tungsten-doped ZSM-5 molecular sieve was exchanged with a nitrogen solution of a certain concentration, mixed evenly at a certain mass ratio, and then placed in a muffle furnace (SXL-1008, Shanghai Jinghong Experimental Equipment Co., Ltd.) and calcined at a heating rate of 2℃ / min to 550℃ for 6 hours. After cooling, the sample was taken out. According to the above method, the sample was prepared with reference to the specific raw material selection and process conditions in Table 1 below.

[0033] Samples were prepared according to the above method, referring to the specific raw material selection and process conditions in Table 1 below.

[0034] Table 1 shows the selection and proportions of each raw material.

[0035]

[0036] Comparative Example 1 is ZSM-5 (grade: LZS-1) produced by Lanzhou Petrochemical;

[0037] Comparative Example 2: Tungsten-doped Na-type ZSM-5 molecular sieve (grade: LZS-1) produced by Lanzhou Petrochemical was exchanged with 100 ml of urea of ​​a certain concentration. The mass ratio of molecular sieve to nitrogen atoms was 1:1.4. The sieve was then placed in a muffle furnace and heated to 550°C at a rate of 2°C / min and calcined for 6 hours. After cooling, the sieve was removed and the product was obtained.

[0038] Table 2 Crystallinity of Examples and Comparative Examples

[0039] Sample Name Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Crystallinity 91 92 92 89 93 85 87

[0040] As can be seen from Table 2, the crystallinity of the sample synthesized in this invention is higher than that of Comparative Example 1 and Comparative Example 2.

[0041] from Figure 1 It can be seen that the sample exhibits strong diffraction peaks at 2θ = 7.9°, 8.8°, 23.1°, and 23.8°, corresponding to the (101), (200), (501), and (051) crystal planes of the MFI type molecular sieve, respectively. The characteristic peak at 24.3° corresponds to the monoclinic and symmetrical planes. The characteristic diffraction peaks of the molecular sieve modified with urea after W doping did not disappear, nor did any new peaks appear, indicating that the crystal structure of the support was not destroyed. Among them, the characteristic peaks of Comparative Example 2 and Example 3 on the (101) and (200) crystal planes became stronger than those of Comparative Example 1 with the introduction of urea.

[0042] from Figure 2As can be seen from Example 3, a strong absorption peak appears at 220 nm, which is attributed to isolated tetrahedral tungsten species in the molecular sieve framework. This indicates that the prepared molecular sieve is a heteroatom molecular sieve with framework tungsten doping. In addition, the molecular sieve shows weak bands at 270 nm and around 400 nm, indicating the presence of a small amount of oligomeric octahedral WOx species and WO3 crystals, indicating that tungsten atoms were successfully introduced into the molecular sieve framework.

[0043] VOCs adsorption performance test

[0044] Take 1.0g of sample and fill it into the adsorption tube. At 150-350℃, purge the activated carbon with nitrogen and the molecular sieve with pure air. After 3 hours, weigh the adsorption tube and conduct an adsorption evaluation experiment.

[0045] The adsorption bed temperature was room temperature. Once the temperature stabilized at 30℃, a standard gas of benzene / nitrogen at a flow rate of 100 mL / min and a concentration of 0.35 mg / L was introduced. The humidity was 50% (15℃). The outlet gas was continuously detected by a gas chromatograph (GC-7890) to analyze the changes in organic matter content in the VOCs gas before and after adsorption.

[0046] Table 3 Adsorption performance of the examples and comparative examples

[0047] Sample Name Penetration time (min) Saturated adsorption capacity (mg / g) Comparative Example 1 23.66 9.2 Comparative Example 2 105.40 31.76 Example 3 133.21 45.56 Example 4 122.38 42.26 Example 5 107.21 53.99

[0048] Table 3 summarizes the saturated adsorption capacity and breakthrough time of the composite modified ZSM-5 and comparative molecular sieves in Examples 3-5 of this patent under 50% humidity for dynamic adsorption of benzene. The results show that the synthesized samples of this patent have obvious performance advantages in VOCs adsorption under high humidity conditions and exhibit excellent dynamic adsorption capacity.

[0049] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a hydrophobic VOCs adsorbent, characterized in that, Includes the following steps: S1, a silicon source, an alkaline source and water are mixed to form a solution A. A tungsten source and cashew phenol polyoxyethylene ether sulfonate are added to the solution A to obtain gel B. Then, ZSM-5 seed crystals are added to the gel B, stirred evenly and crystallized. After crystallization, the solution is cooled, filtered, washed, dried and calcined to obtain tungsten-doped ZSM-5 molecular sieve. S2, a nitrogen-containing solution is added to the tungsten-doped ZSM-5 molecular sieve for exchange, and then calcined to obtain the adsorbent; The molar ratio of cashew phenol polyoxyethylene ether sulfonate, silicon source, alkali source, tungsten source and H2O in gel B is 0.005~0.02:1:0.1~1:0.01~0.05:4~8, wherein the silicon source is calculated as SiO2 and the tungsten source is calculated as WO3. In step S1, crystallization is carried out in a temperature-controlled microwave radiation heating device; The crystallization temperature in step S1 is 135 ℃~170 ℃, and the crystallization time is 1 h~3 h; In step S2, the nitrogen-containing solution is one or more of ammonium nitrate, urea and ammonia solution, and the mass ratio of tungsten-doped Na-type ZSM-5 molecular sieve to nitrogen atoms in the nitrogen-containing solution is 1:0.08~1.

4.

2. The method for preparing the hydrophobic VOCs adsorbent according to claim 1, characterized in that, The cashew phenol polyoxyethylene ether sulfonate is sodium cashew phenol polyoxyethylene ether sulfonate and / or ammonium cashew phenol polyoxyethylene ether sulfonate.

3. The method for preparing the hydrophobic VOCs adsorbent according to claim 1, characterized in that, The silicon source is one or more of silica sol, tetraethyl silicate, methyl orthosilicate, and water glass; the alkali source is ethylamine and / or n-butylamine; and the tungsten source is one or more of ammonium metatungstate, ammonium tungstate, and sodium tungstate dihydrate.

4. The method for preparing the hydrophobic VOCs adsorbent according to claim 1, characterized in that, The mass ratio of ZSM-5 seed crystals to gel B is (1~5):

100.

5. The method for preparing the hydrophobic VOCs adsorbent according to claim 1, characterized in that, In step S1, the drying temperature is 100~120℃ and the drying time is 8~12 h.

6. The method for preparing the hydrophobic VOCs adsorbent according to claim 1, characterized in that, In step S2, the calcination conditions are to raise the temperature to 500℃~700℃ at a rate of 2~5℃ / min and calcine for 4~6 h.

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