Preparation method of hydrophobic VOCs adsorbent

Abstract

The invention discloses a preparation method of a hydrophobic VOCs adsorbent, which comprises the following steps: S1, mixing a silicon source, an alkali source and water to form a solution A, adding a tungsten source and cardanol polyoxyethylene ether sulfonate into the solution A to obtain a gel B, then adding ZSM-5 seed crystal into the gel B, uniformly stirring, and crystallizing to obtain the hydrophobic VOCs adsorbent. After the crystallization is finished, cooling, filtering, washing, drying and calcining to obtain the tungsten-doped ZSM-5 molecular sieve; and S2, adding a nitrogen-containing solution into the tungsten-doped ZSM-5 molecular sieve for exchange, and then calcining to obtain the adsorbent. The molecular sieve synthesized by the method is low in synthesis cost, short in synthesis time, excellent in hydrophobic performance and excellent in adsorption performance when applied to high-humidity VOCs (benzene).

Description

Technical Field

[0001] The invention belongs to the technical field of VOCs adsorbents, and particularly relates to a method for preparing a hydrophobic VOCs adsorbent. Background Art

[0002] VOCs (volatile organic compounds) are toxic, flammable and explosive, and are precursors to the formation of haze. They will seriously damage the ecological environment, endanger human health, and are also an important cause of air pollution. In recent years, the treatment of VOCs has become a key direction of research and development. Among various VOCs treatment methods, the adsorption method has the advantages of simple operation, mature technology, and low cost, so it has been widely used. Currently, commonly used adsorbents include carbon-based adsorbents, molecular sieve adsorbents, polymer materials, etc. Molecular sieves are widely used because of their uniform and rich pore structure, good hydrothermal stability, and strong adsorption performance for oxygen-containing organic matter. Among them, ZSM-5 has a high silicon-aluminum ratio and a stable five-membered ring structure compared to other types of molecular sieves. It can treat VOCs at high temperatures, and the pore structure is not destroyed during thermal desorption, the adsorption performance is stable, and it can be recycled. However, actual industrial organic waste gas often contains a lot of water vapor, which will greatly reduce the adsorption of VOCs by molecular sieves. Therefore, it is necessary to modify the molecular sieve to be hydrophobic to improve its adsorption performance under high humidity. Generally, organic templates are used to dope other transition metal elements of groups IV, V, and VI (such as Zr, V, Nb, Cr, Mo, and W) into the molecular sieve framework to regulate the hydrophobicity of the molecular sieve. The molecular sieve is treated with nitrogen solution post-treatment. Nitrogen molecules combine with the surface hydroxyl groups of ZSM-5 during calcination, causing the defect sites such as the molecular sieve silicon hydroxyl groups and silicon nests to change, and finally nitrogen-containing functional groups are introduced into the molecular sieve. The nitrogen-containing functional groups enhance the surface alkalinity of the adsorbent, improve the affinity of the material to VOCs (benzene molecules), and the adsorption can be further improved.

[0003] Patent CN114950351A discloses a method and application of doping and modifying ZSM-5 molecular sieve to enhance the adsorption of VOCs. Metal cations are exchanged and loaded into ZSM-5 molecular sieve to improve its VOCs adsorption performance. This method does not embed metal cations into the molecular sieve framework, and metal cations are more easily lost.

[0004] Patent CN109513458A adds a silicon source dropwise to an aqueous solution of a structure directing agent to form a clear solution A; adds an aqueous solution of a tungsten source or a tungsten source dropwise to solution A, and then hydrothermally crystallizes at 110°C to 150°C for 48h to 120h to obtain an MFI-type molecular sieve catalyst having a skeleton of tungsten atoms.

[0005] Patent CN104437605A stirs a certain proportion of deionized water, an alkali source, an organic template, a tungsten source, and a silicon source to form an initial gel, and synthesizes the W-ZSM-5 molecular sieve through hydrothermal crystallization. The X-ray diffraction pattern proves that W enters the molecular sieve framework to expand its unit cell and increase the unit cell volume.

[0006] The above two patents use organic templates 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 takes a long time to synthesize, the gel is heated unevenly, and it is difficult to nucleate quickly. Summary of the invention

[0007] The object of the present invention is to provide a method for preparing a hydrophobic VOCs adsorbent. The molecular sieve synthesized by the method has low synthesis cost, short synthesis time, excellent hydrophobic performance, and excellent adsorption performance for high-humidity VOCs (benzene).

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

[0009] S1, mixing a silicon source, an alkali source and water to form a solution A, adding a tungsten source and cardanol polyoxyethylene ether sulfonate to the solution A to obtain a gel B, then adding ZSM-5 seed crystals to the gel B, stirring evenly and then crystallizing, cooling, filtering, washing, drying and calcining after the crystallization to obtain a tungsten-doped ZSM-5 molecular sieve;

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

[0011] The preparation method of the hydrophobic VOCs adsorbent described in the present invention, the molar ratio of cardanol polyoxyethylene ether sulfonate, silicon source, alkali source, tungsten source and H2O in the 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 the present invention, the process of forming a gel is a conventional operation in the art. The present invention recommends uniform stirring at 60°C to 90°C for 15 to 60 minutes to form a gel, adding ZSM-5 seed crystals to the gel and stirring for 1 to 3 hours to mix evenly, and then crystallizing.

[0013] The preparation method of the hydrophobic VOCs adsorbent of the present invention, the cardanol polyoxyethylene ether sulfonate is cardanol polyoxyethylene ether sulfonate sodium and / or cardanol polyoxyethylene ether sulfonate ammonium. Cardanol polyoxyethylene ether sulfonate can be obtained by purchase or homemade, and the present invention is not specifically limited. The method for preparing cardanol polyoxyethylene ether sulfonate can refer to: step 1, using cardanol as a raw material, and synthesizing cardanol polyoxyethylene ether with ethylene oxide under alkaline conditions; step 2, using cardanol polyoxyethylene ether as a raw material, adding tert-butanol base, anhydrous ethanol as a solvent, reflux, and then cooling the reaction system to room temperature, adding 1,3-propane sultone or 1,4-butane sultone dropwise, reflux, cool, and obtain cardanol polyoxyethylene ether sulfonate.

[0014] The preparation method of the hydrophobic VOCs adsorbent described in the present invention, 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] In the method for preparing the hydrophobic VOCs adsorbent of the present invention, the mass ratio of ZSM-5 seed crystals to gel B is (1-5):100.

[0016] In the preparation method of the hydrophobic VOCs adsorbent of the present invention, in step S1, crystallization is performed in a temperature-controlled microwave radiation heating device. The temperature-controlled microwave radiation heating device has a polytetrafluoroethylene liner and is a commonly used device in the art. The present invention does not make any special restrictions, and the microwave radiation heating power can be selected to be 900W.

[0017] In the method for preparing the hydrophobic VOCs adsorbent of the present invention, the crystallization temperature in step S1 is 135° C. to 170° C., and the crystallization time is 1 h to 3 h.

[0018] In the method for preparing the hydrophobic VOCs adsorbent of the present invention, the drying temperature in step S1 is 100 to 120° C. and the drying time is 8 to 12 hours.

[0019] In the method for preparing a hydrophobic VOCs adsorbent described in 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] In the method for preparing the hydrophobic VOCs adsorbent of the present invention, the calcination conditions in step S2 are to increase the temperature to 500° C. to 700° C. at a heating rate of 2 to 5° C. / min and calcine for 4 to 6 hours.

[0021] Beneficial effects of the present invention:

[0022] (1) Introducing tungsten into the MFI molecular sieve framework can effectively improve the hydrophobicity of the molecular sieve, thereby improving its adsorption performance for VOCs under high humidity. After nitrogen modification, nitrogen molecules combine with the surface hydroxyl groups of ZSM-5 during the calcination process, causing the molecular sieve's silanols and silicon pits to change, and finally introducing nitrogen-containing functional groups on the molecular sieve. The nitrogen-containing functional groups enhance the surface alkalinity of the adsorbent, increase the material's affinity for benzene molecules, and reduce the diffusion resistance of benzene in the material's pores. 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 improved.

[0023] (2) The synthesis process does not use an organic template, which greatly reduces the cost. The seed crystal method is combined with microwave radiation heating, and the synthesis time is short.

[0024] (3) When adding cardanol polyoxyethylene ether sulfonate, the solvent interface increases during crystal nucleation and growth. The addition of a small amount of cardanol polyoxyethylene ether sulfonate can effectively reduce the surface tension of the solution, making it easier to nucleate from an energy perspective and form micelles in the gel. This effect increases the contact and interaction probability between silicon and tungsten, that is, by changing the thermodynamic properties of the sol, the crystallization rate is increased, thereby increasing the crystallinity of the sample and successfully introducing tungsten into the molecular sieve framework. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The XRD diagrams of the molecular sieves obtained in Comparative Example 1, Comparative Example 2 and Example 3 of the present invention are shown.

[0026] Figure 2 This is the UV-Vis of the molecular sieve obtained in Example 3 of the present invention. DETAILED DESCRIPTION

[0027] The present invention is described in detail below by way of examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art in this field can make some non-essential improvements and adjustments to the present invention based on the above content of the present invention.

[0028] (1) mixing a silicon source, an alkali source and H2O to form a solution A;

[0029] (2) adding a tungsten source dropwise to the above solution A, and then adding an additive, sodium polyoxyethylene cardanol ether sulfonate, and stirring at a constant speed at 60° C. to 90° C. for 15 to 60 minutes for hydrolysis to form a mixed gel B;

[0030] (3) adding the seed crystal ZSM-5 to the mixed gel B, stirring evenly and aging to obtain a mixture C;

[0031] (4) placing the mixture C in a temperature-controlled microwave radiation heating device with a polytetrafluoroethylene liner for crystallization, cooling to room temperature after crystallization, and then centrifugally filtering, washing, drying and calcining in sequence to obtain a 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 uniformly according to a certain mass ratio, and then placed in a muffle furnace (SXL-1008, Shanghai Jinghong Experimental Equipment Co., Ltd.) at a heating rate of 2°C / min to 550°C and calcined for 6 hours, and then taken out after cooling. According to the above method, the samples were prepared with reference to the selection of specific raw materials and the implementation process conditions in Table 1 below.

[0033] According to the above method, samples were prepared with reference to the selection of specific raw materials and implementation process conditions in Table 1 below.

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

[0035]

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

[0037] Comparative Example 2 is a ZSM-5 (grade: LZS-1) produced by Lanzhou Petrochemical. 100 ml of urea of ​​a certain concentration is used to exchange the tungsten-doped Na-type ZSM-5 molecular sieve, and the molecular sieve and nitrogen atomic mass ratio is 1:1.4. Then it is placed in a muffle furnace at a heating rate of 2°C / min to 550°C and calcined for 6 hours, and then taken out after cooling.

[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] It can be seen from Table 2 that the crystallinity of the sample synthesized in the embodiment of the present invention is higher than that of Comparative Example 1 and Comparative Example 2.

[0041] from Figure 1 It can be seen that the sample has strong diffraction peaks at 2θ=7.9°, 8.8°, 23.1°, and 23.8°, which correspond to the MFI type molecular sieve (101), (200), (501), and (051) crystal planes. The characteristic peak at 24.3° corresponds to the monoclinic and symmetrical plane. The characteristic diffraction peaks of the molecular sieve of Example 3 modified by urea after W doping did not disappear, and no new peaks appeared, indicating that the carrier crystal structure was not destroyed. Among them, the characteristic peaks of Comparative Example 2 and Example 3 on the (101) and (200) crystal planes became stronger with the introduction of urea compared with Comparative Example 1.

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

[0043] VOCs adsorption performance test

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

[0045] The adsorption bed temperature is room temperature. When the temperature stabilizes at 30°C, 100mL / min, 0.35mg / L benzene / nitrogen standard gas is introduced. The humidity is 50% (15°C). The outlet gas is continuously detected by gas chromatography (GC-7890) to instantly analyze the changes in the organic matter content in the VOCs gas before and after adsorption.

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

[0047] Sample name Breakthrough 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 amount and penetration time of dynamic adsorption of benzene by the composite modified ZSM-5 and comparative molecular sieves of Examples 3 to 5 of this patent at 50% humidity. The results show that the synthetic samples of this patent have obvious performance advantages in the adsorption of VOCs under high humidity conditions and show excellent dynamic adsorption capacity.

[0049] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, technicians familiar with the field may make various corresponding changes and deformations based on the present invention, but these corresponding changes and deformations should all fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a hydrophobic VOCs adsorbent, characterized in that: The following steps are involved: S1, mixing a silicon source, an alkali source and water to form a solution A, adding a tungsten source and cardanol polyoxyethylene ether sulfonate to the solution A to obtain a gel B, then adding ZSM-5 seed crystals to the gel B, stirring evenly and then crystallizing, cooling, filtering, washing, drying and calcining after the crystallization to obtain a tungsten-doped ZSM-5 molecular sieve; S2, adding a nitrogen-containing solution to the tungsten-doped ZSM-5 molecular sieve for exchange, and then calcining to obtain the adsorbent.

2. The method for preparing a hydrophobic VOCs adsorbent according to claim 1, characterized in that: The molar ratio of cardanol polyoxyethylene ether sulfonate, silicon source, alkali source, tungsten source and H2O in the 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.

3. The method for preparing a hydrophobic VOCs adsorbent according to claim 1, characterized in that: The cardanol polyoxyethylene ether sulfonate is cardanol polyoxyethylene ether sulfonate sodium and / or cardanol polyoxyethylene ether sulfonate ammonium.

4. The method for preparing a 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.

5. The method for preparing a 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.

6. The method for preparing a hydrophobic VOCs adsorbent according to claim 1, characterized in that: In step S1, crystallization is performed in a temperature-controlled microwave radiation heating device.

7. The method for preparing a hydrophobic VOCs adsorbent according to claim 1, characterized in that: The crystallization temperature in step S1 is 135° C. to 170° C., and the crystallization time is 1 h to 3 h.

8. The method for preparing a hydrophobic VOCs adsorbent according to claim 1, characterized in that: In step S1, the drying temperature is 100-120° C., and the drying time is 8-12 hours.

9. The method for preparing a hydrophobic VOCs adsorbent according to claim 1, characterized in that: 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.

10. The method for preparing a hydrophobic VOCs adsorbent according to claim 1, characterized in that: The calcination conditions in step S2 are to increase the temperature to 500° C. to 700° C. at a heating rate of 2 to 5° C. / min and calcine for 4 to 6 hours.

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