Method for regulating and controlling acid sites of catalyst and application of method in hydrogen production through plastic pyrolysis

Abstract

The invention belongs to the technical field of solid waste disposal and pyrolysis hydrogen production, and discloses a method for regulating and controlling acid sites of a catalyst and application of the method in plastic pyrolysis hydrogen production. The method comprises the following steps: mixing a template agent with water, adding an aluminum source and a silicon source, stirring to obtain a precursor solution, carrying out a hydrothermal crystallization reaction, collecting a product, and drying and roasting the product to obtain the SSZ-13 molecular sieve catalyst. The preparation method comprises the following steps: on the basis of hydrothermally synthesizing a small-pore molecular sieve SSZ-13 by using an organic template agent, adjusting the number and strength of acid sites by changing the cation concentration of a precursor; different metal salt solutions are selected to optimize acid site properties; and adjusting the distribution and activity of acid sites through acid-base treatment, high-temperature roasting and the like. When the SSZ-13 molecular sieve is applied to enhanced microwave pyrolysis hydrogen production, the SSZ-13 molecular sieve shows excellent hydrogen production rate, and the hydrogen proportion can reach 52% at most and is 4.7 times of the hydrogen production rate of pure plastic. The environment risk of the plastic is reduced, and meanwhile carbon emission reduction is promoted.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of solid waste disposal and hydrogen production by pyrolysis, and particularly relates to a method for regulating acid sites of a catalyst and application of the method in hydrogen production by plastic pyrolysis. BACKGROUND

[0002] It is well known that plastic products are ubiquitous in numerous industrial applications and daily activities. However, a large amount of waste plastics is generated due to the limited service life (mostly disposable products). The current disposal method of waste plastics mainly relies on incineration and landfill. This disposal status leads to the emission of a large amount of greenhouse gases on the one hand, and the exposure of plastics to the environment after aging processes such as radiation, photodegradation, biodegradation, etc. to microplastics, which has a huge negative impact on the human body and the ecological environment. Efficient disposal and high-value conversion of plastics are imminent. In recent years, microwave-assisted catalytic pyrolysis for hydrogen production has been widely used due to its green and efficient nature. However, the core work is to develop efficient catalysts to regulate the proportion and selectivity of gas-liquid-solid three-phase products.

[0003] Currently, many Ni, Al, CuO, FeO, MnO, MgO, etc. are common metal and oxide catalysts that have been developed and applied, but there are some drawbacks. For example, in the study of MOFs-derived Fe-C composite catalyst for microwave-assisted catalytic pyrolysis of high-density polyethylene for hydrogen production (DOI: 10.27724 / d.cnki.gnmgk.2025.000496), the Fe species catalyst has poor stability at high temperatures, is easy to carbonize, and the hydrogen production efficiency after recycling is only 25.3 mmol / g. In the study of Ni-Fe / γ-Al2O3 catalyst preparation and its performance in microwave-assisted high-density polyethylene pyrolysis for hydrogen production (DOI: 10.27724 / d.cnki.gnmgk.2025.000290), the impurities in the reaction system reduce the stability of the catalyst, making it difficult to prepare and costly. Recently, among molecular sieve catalysts, HY, REY (rare earth modified zeolite), HZSM-5, FCC, MCM-41, etc. exhibit good catalytic pyrolysis activity and thermodynamic stability. Influenced by the acidity, pore structure, crystal size, etc. of various molecular sieve catalysts, the light oil yield in the liquid product yield and the yield of gas products are greatly affected. The acid-base degree, specific surface area, pore size distribution, etc. of the catalyst also have a great influence on the catalytic cracking rate, product yield, and component distribution of the liquid product. Currently, researchers improve the pore size and specific surface area of molecular sieves through surface modification, crystallization nucleation conditions, etc. However, there is little research on the regulation of the number and location of acid sites, which is one of the key factors for regulating product selectivity and also an important challenge currently facing.

[0004] In view of the deficiencies and shortcomings of the prior art, a practical and controllable method must be taken to convert plastics with environmental and resource properties into high-value products (green hydrogen energy) in the context of sustainable development, greatly reducing greenhouse gas emissions from traditional incineration, which is of great significance to sustainable development and waste-free city construction. SUMMARY

[0005] In order to overcome the shortcomings and deficiencies of the prior art, the primary purpose of the present application is to provide a method for regulating the acid sites of a catalyst to obtain a series of SSZ-13 molecular sieves with different acid site quantities and distribution behaviors.

[0006] Another purpose of the present application is to provide an SSZ-13 molecular sieve prepared by the above method.

[0007] Another purpose of the present application is to provide the above-mentioned SSZ-13 molecular sieve for use in the application of hydrogen production from plastic pyrolysis.

[0008] The purpose of the present application is achieved by the following technical solutions:

[0009] A method for regulating the acid sites of a catalyst, comprising the following steps:

[0010] Mixing a template agent with water, adding an aluminum source and a silicon source, and stirring to obtain a precursor solution; subjecting the precursor solution to a hydrothermal crystallization reaction, collecting the crystallization product; and drying and calcining the crystallization product to obtain an SSZ-13 molecular sieve catalyst with adjustable acid sites, thereby achieving regulation of the acid sites of the catalyst.

[0011] Preferably, a metal salt is also added to the precursor solution; the metal salt is sodium hydroxide and / or potassium hydroxide, and the molar ratio of the total amount of the metal salt to the aluminum source and the silicon source is 0.1-0.6:1.

[0012] Preferably, the molar ratio of the template agent to the total amount of the aluminum source and the silicon source is 0.2-1:1; and the molar ratio of the template agent to water is 1:40-200.

[0013] Preferably, the template agent is at least one of TMAdaOH, benzyltrimethylammonium, choline, or a copper-amine complex;

[0014] The aluminum source is Al(OH)3 and / or aluminum isopropoxide;

[0015] The silicon source is at least one of silica sol, tetraethyl orthosilicate, sodium silicate, or fumed silica.

[0016] Preferably, the hydrothermal crystallization reaction conditions are a temperature of 150-200°C and a time of 5-10 days.

[0017] Preferably, the calcination condition is: 8-12h of calcination at 1-10℃ / min to 400-600℃;

[0018] The stirring condition is: 100-2000rpm of stirring for at least 1h.

[0019] The collection is suction filtration collection, and a washing treatment is performed before the collection, and the washing is washing until the pH of the supernatant is 3-10.

[0020] An SSZ-13 molecular sieve catalyst is prepared by the above method.

[0021] Preferably, the acid sites of the SSZ-13 molecular sieve catalyst include Lewis acid sites and The molar ratio of the acid sites is 0-0.5:1.

[0022] Preferably, the Si / Al ratio of the SSZ-13 molecular sieve catalyst is 10-40.

[0023] The application of the above-mentioned SSZ-13 molecular sieve catalyst in hydrogen production by plastic pyrolysis.

[0024] Preferably, the application is microwave pyrolysis for hydrogen production, including the following steps:

[0025] The plastic is uniformly mixed with the SSZ-13 molecular sieve catalyst to obtain a mixture, and the mixture is placed in a reactor, and microwave pyrolysis reaction is carried out under an inert atmosphere, and the reaction product is collected.

[0026] The mass ratio of the SSZ-13 molecular sieve catalyst to the plastic is 0.01-2:1.

[0027] The reaction condition is: 200-800℃ for 1-10min, and the power of the microwave is 100-1400W.

[0028] The plastic is one or more of polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC) or polyethylene terephthalate (PET).

[0029] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0030] (1) The molecular sieve prepared in the present application can adjust the number and distance of Al atoms in the framework and the types or number of coexisting extra-framework cations during synthesis, so as to optimize the arrangement and microcoordination environment of the acid sites in the CHA structure.

[0031] (2) The molecular sieve prepared in the application exhibits excellent hydrogen production efficiency in the process of microwave pyrolysis for hydrogen production under the synergistic effect of acid sites, and the hydrogen production rate can reach up to 52%. The technology for regulating the acid sites of the molecular sieve has strong frontiers and excellent performance, and has not been applied in the same field of research.

[0032] (3) The microporous structure of the SSZ-13 molecular sieve prepared in the application can adsorb and concentrate the target product, so that it is highly gathered near the active site, the local reaction concentration is improved, and the activation energy of the hydrogen production reaction is reduced, so that hydrogen gas can be released at a lower temperature. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The XRD graph of the series of SSZ-13 prepared in Examples 1-4 of the application.

[0034] Figure 2 The BET graph of the series of SSZ-13 prepared in Examples 1-4 of the application.

[0035] Figure 3 The NH3-TPD graph for characterizing the acid site distribution of the SSZ-13 prepared in Examples 1 and 3 of the application.

[0036] Figure 4 The NMR graph of the SSZ-13 prepared in Examples 1 and 3 of the application.

[0037] Figure 5 The TG-DSC graph of the plastic PE used in the application.

[0038] Figure 6 The graph of the proportion of each gas phase product under the microwave pyrolysis reaction of the series of SSZ-13 prepared in Examples 1-4 of the application under the same conditions.

[0039] Figure 7 The graph of the proportion of three-phase products under the microwave pyrolysis reaction of the series of SSZ-13 prepared in Examples 1-4 of the application under the same conditions. DETAILED DESCRIPTION

[0040] The application will be further described in detail below in combination with the embodiments and the drawings, but the embodiments of the application are not limited thereto. For the process parameters not specifically mentioned, the conventional technology can be referred to.

[0041] Example 1

[0042] In a 100 mL PARR® autoclave liner, 31.23 g of N,N,N-trimethyl-1-adamantylammonium hydroxide, TMAdaOH (Macklin, 25 wt% in H2O) was dissolved in 28.53 g of deionized water and stirred for 15 min at room temperature. 0.29 g of Al(OH)3(Aladdin, 99.99%) was added to the above solution and stirred for 15 min at room temperature. 11.11 g of silica sol (Sigma Aldrich, Ludox AS-40, 40 wt% in H2O) was added to the above solution and stirred for 2 h at room temperature to a homogeneous precursor solution. The TMAdaOH molar amount in the solution was 0.48 times that of Al(OH)3and silica sol. The precursor solution was transferred to a 100 mL PTFE-lined stainless steel autoclave and crystallized at 160 °C for 6 days in a rotary oven at 35 rpm. The reactor inner surface was washed with deionized water (70 mL / g cat.) to avoid material residue and the sample was washed until the pH of the supernatant was ~7, followed by suction filtration collection and drying at 100 °C for 24 h. The sample was then placed in a flowing dry air at 580 °C (heating rate 5 °C / min) for 10 h. The white material prepared above was labeled as SSZ-13-Z1.

[0043] Example 2

[0044] Different from Example 1, the TMAdaOH molar amount in the solution was adjusted to be 0.24 times that of Al(OH)3and silica sol under the condition of fixed Al(OH)3(Aladdin, 99.99%) and silica sol (Sigma Aldrich, Ludox AS-40, 40 wt% in H2O), and 4.38 g of 5M NaOH solution (Aladdin, 98%) was added to the above solution, the NaOH molar amount was 0.24 times that of Al(OH)3and silica sol. The white material prepared was labeled as SSZ-13-Z2.

[0045] Example 3

[0046] Different from Example 2, the condition of fixed NaOH (Aladdin, 98%), silica sol (Sigma Aldrich, Ludox AS-40, 40 wt% in H2O) and TMAdaOH (Macklin, 25 wt% in H2O), the aluminum hydroxide in the solution was replaced with aluminum isopropoxide, and the aluminum molar amount was unchanged. The white material prepared was labeled as SSZ-13-Z3.

[0047] Example 4

[0048] Unlike Example 2, under the condition of fixing Al(OH)3 (Aladdin, 99.99%) and silica sol (Sigma Aldrich, Ludox AS-40, 40wt% in H2O), the molar amount of TMAdaOH in the solution was adjusted to 0.2 times that of Al(OH)3 and silica sol, the molar amount of NaOH in the solution was adjusted to 0.14 times that of Al(OH)3 and silica sol, and 0.62g of KOH was added to the above solution, with the molar amount of KOH being 0.14 times that of Al(OH)3 and silica sol. The white material prepared was designated as SSZ-13-Z4.

[0049] Figure 1 The XRD patterns of the prepared materials show that all materials have a single CHA structure, indicating that all samples have the same crystal structure.

[0050] Figure 2 The BET plot of the prepared materials shows that the SSZ-13 material prepared in the example exhibits a typical Type I isotherm (without obvious hysteresis loop), which corresponds to the typical isotherm plot of microporous molecular sieves, indicating that the prepared materials all have similar pore structures.

[0051] Figure 3 The NH3-TPD diagram of the prepared material shows that two desorption peaks appear at approximately 150℃ and 450℃, corresponding to the desorption of physically adsorbed NH3 at Lewis acid sites (weak acid sites) and strongly adsorbed NH3 at Brownian acid sites (strong acid sites), respectively. The intensity of SSZ-13-Z3 is significantly higher than that of SSZ-13-Z1, indicating that the composition of the precursor solution can be optimized by using metal salt solution, which synergistically enhances the role of structure-directing small cations and aluminum precursors with special intrinsic properties in the crystallization of molecular sieves, effectively increasing the number of acid sites.

[0052] Figure 4 For the prepared materials 27 The Al NMR spectrum shows that the material mainly contains tetrahedral coordinated framework Al atoms (chemical shift ~60 ppm) and a small portion (<3%) of octahedral coordinated Al atoms (chemical shift ~1 ppm). The intensity of SSZ-13-Z3 is significantly higher than that of SSZ-13-Z1. Figure 3 Analysis shows that the synergistic effect of metal salt solution and aluminum isopropoxide can promote the entry of Al sites into the molecular sieve framework, thereby increasing the number of acid sites.

[0053] Figure 5 The TG-DSC chart for the plastic PE used shows that PE requires temperatures of ~500℃ and above for pyrolysis.

[0054] Comparative Example 1

[0055] Unlike Example 1, SSZ-13 could not be successfully prepared by adjusting the molar amount of TMAdaOH in the solution to 0.15 times that of Al(OH)3 (Aladdin, 99.99%) and silica sol (Sigma Aldrich, Ludox AS-40, 40wt% in H2O) while keeping the Al(OH)3 (Aladdin, 99.99%) and silica sol (Sigma Aldrich, Ludox AS-40, 40wt% in H2O) constant.

[0056] Comparative Example 2

[0057] Unlike Example 2, SSZ-13 could not be successfully prepared when the molar amount of TMAdaOH in the solution was adjusted to 0.08 times that of Al(OH)3 (Aladdin, 99.99%), NaOH and silica sol (SigmaAldrich, Ludox AS-40, 40wt% in H2O) while keeping the Al(OH)3 (Aladdin, 99.99%), NaOH and silica sol (SigmaAldrich, Ludox AS-40, 40wt% in H2O) fixed.

[0058] Example 6

[0059] The materials prepared in Examples 1-4 (Si / Al = 12) were subjected to microwave pyrolysis of plastics to produce H2 with commercially available molecular sieve SSZ-13 (Si / Al = 12.5). The specific steps are as follows:

[0060] First, accurately weigh 1g of PE plastic and 1g of each of the SSZ-13-Z1, SSZ-13-Z2, SSZ-13-Z3, and SSZ-13-Z4 molecular sieve catalysts, and mix them thoroughly in a microwave-absorbing boat. Connect the reaction apparatus and ensure it is well-sealed. Adjust the nitrogen flow rate to 40mL / min and turn on the microwave reactor. Set the power to 300-1000W and the initial reaction temperature to 500℃. Before the reaction begins, purge the reaction tube with nitrogen for 30 minutes to ensure all oxygen is removed. After the reaction starts, when the temperature inside the microwave reactor reaches 500℃, react for 5 minutes and then stop the reaction. Nitrogen gas is continuously introduced throughout the reaction. After the reaction ends, purge with nitrogen for another 10 minutes and then remove the gas bag to end the experiment. Perform gas chromatography analysis on the gas in the gas bag, such as... Figure 6 As shown, SSZ-13-Z3 has the highest hydrogen production rate, with an H2 content of 52%. The H2 content of SSZ-13-Z1, SSZ-13-Z2 and SSZ-13-Z3 can also reach 37%, 43% and 42% respectively, which is higher than 26% of SSZ-13, and the hydrogen production rate is increased by 42.3% to 100%.

[0061] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method of modulating the acid sites of a catalyst, characterized by, The method comprises the following steps: mixing a template agent with water, adding an aluminum source and a silicon source, and stirring to obtain a precursor solution; subjecting the precursor solution to a hydrothermal crystallization reaction, and collecting a crystallization product; subjecting the crystallization product to drying and calcination to obtain an SSZ-13 molecular sieve catalyst, thereby realizing the regulation of acid sites of the catalyst.

2. The method for regulating the acid sites of a catalyst according to claim 1, characterized in that, The precursor solution further comprises a metal salt; the metal salt is sodium hydroxide and / or potassium hydroxide, and the molar ratio of the metal salt to the total amount of the aluminum source and the silicon source is 0.1-0.6:

1.

3. The method of claim 1 or 2, wherein the catalyst is a zeolite. The molar ratio of the template agent to the total amount of the aluminum source and the silicon source is 0.2-1:

1.

4. The method of claim 1, wherein the catalyst is a zeolite. The template agent is at least one of TMAdaOH, benzyltrimethylammonium, choline, or a copper-amine complex; The aluminum source is Al(OH)3 and / or aluminum isopropoxide; The silicon source is at least one of silica sol, tetraethyl orthosilicate, sodium silicate, or fumed silica.

5. The method of claim 1, wherein the catalyst is a zeolite. The hydrothermal crystallization reaction conditions are as follows: the temperature is 150-200 ℃, and the time is 5-10 days.

6. The method of claim 1, wherein the catalyst is a zeolite. The calcination conditions are as follows: the temperature is raised to 400-600 ℃ at a rate of 1-10 ℃ / min, and the calcination time is 8-12 h; The stirring conditions are as follows: the stirring rate is 100-2000 rpm, and the stirring time is at least 1 h; the collection is performed by suction filtration, and the crystallization product is washed before being collected.

7. An SSZ-13 molecular sieve catalyst characterized by, The SSZ-13 molecular sieve catalyst is prepared by the method of any one of claims 1-6.

8. The SSZ-13 molecular sieve catalyst of claim 7, wherein, The acid sites of the SSZ-13 molecular sieve catalyst include Lewis acid sites and acid sites.

9. The SSZ-13 molecular sieve catalyst of claim 7 or 8 is used in the production of hydrogen by plastic pyrolysis.

10. Use according to claim 9, characterized in that, The application is microwave pyrolysis for hydrogen production; The mass ratio of the SSZ-13 molecular sieve catalyst to the plastic is 0.01-2:1.

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