Method for regulating metal site by low-temperature plasma-activated ammonium type ZSM-5 molecular sieve and application thereof

Abstract

The application provides a method for activating ammonium type ZSM-5 molecular sieves by using low-temperature plasma, and mainly solves the problem that the traditional high-temperature calcination activation process easily leads to collapse of the molecular sieve framework, reduction of the acidity and influence on the activity. The synthesized ammonium type molecular sieves are placed in low-temperature plasma for treatment, collision and bombardment between high-energy particles generated by the plasma and the molecular sieves are utilized to convert the ammonium type ZSM-5 molecular sieves into hydrogen type molecular sieves with catalytic activity, so that the activation temperature is reduced, the damage to the framework structure of the molecular sieves is reduced, more framework Al is reserved, the acidity of the molecular sieves is improved, and the catalytic activity and the target product selectivity of the molecular sieves for cracking light alkanes to prepare low-carbon olefins can be improved. The method for activating the molecular sieves has high efficiency, mild conditions, low energy consumption, simple operation, more B acid sites, and significantly improved performance for cracking C4-C10 light alkanes to prepare low-carbon olefins.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of chemical industry, and particularly relates to a new method for low-temperature, high-efficiency, low-energy-consumption and rapid ammonium type ZSM-5 molecular sieve ammonium removal and activation into hydrogen type ZSM-5 molecular sieve with catalytic activity. BACKGROUND

[0002] With the continuous development of renewable energy technology, the demand for low-carbon olefins (especially ethylene and propylene) in the battery and electronic material industries is growing. Naphtha catalytic cracking, as an efficient low-carbon olefin production technology, significantly reduces energy consumption and carbon emissions compared to the steam cracking process. In addition, by adjusting the properties of the catalyst, the product distribution of the catalytic cracking process can be flexibly regulated, thereby better meeting market demand. The development and optimization of the catalyst are the core of this process, directly determining the selectivity, yield of the products and the overall efficiency of the process.

[0003] ZSM-5 molecular sieve, which contains abundant acid sites, is one of the most widely used catalytic materials in catalytic cracking. The unique sinusoidal channel and straight channel intersection ten-membered ring system of ZSM-5 molecular sieve enables it to have the ability of "shape-selective catalysis", which can improve the selectivity of low-carbon olefins (C2-C4). During the synthesis of ZSM-5 molecular sieve, after ion exchange to obtain ammonium type molecular sieve, it needs to be treated by high-temperature calcination (>500 ℃) to convert it into hydrogen type ZSM-5 molecular sieve with acid catalytic activity. However, high temperature will damage the framework structure of the molecular sieve, thereby affecting its stability and acid properties, and reducing the catalytic cracking activity.

[0004] Plasma is a kind of high activity substance composed of high energy particles such as high energy electrons, ions, atoms, molecules and free radicals, which has unique physical and chemical properties and is called the fourth state of matter. According to the relationship between the energy state of its system, electron temperature and bulk temperature, it can be divided into hot plasma and cold plasma. Hot plasma is often used in high energy physical processes such as nuclear fusion and space engine, while cold plasma is widely used in research and production processes. In cold plasma, dielectric barrier discharge (DBD) is a form of non-equilibrium gas discharge, which inserts an insulating medium in the discharge space. When a high alternating voltage is applied, the gas between the electrodes will be broken down to produce discharge and form dielectric barrier discharge. The temperature of high energy particles in the discharge process can reach tens of thousands of degrees, but the system temperature is maintained at room temperature to 200 ℃. The unique physical and chemical properties of DBD make it play a unique role in catalyst synthesis and surface modification, such as plasma etching treatment of nickel-based electrolytic water catalytic material to improve its electrocatalytic oxygen evolution performance (CN118326434A), and plasma modification of iron-doped nickel sulfide to improve its degradation ability to acid lake blue A (CN115520938B). The process of DBD plasma treatment of catalytic materials has the advantages of low temperature, low energy consumption, simple operation, high efficiency, etc., and is a very potential molecular sieve activation method. SUMMARY

[0005] The purpose of the present application is to provide a method for mild activation of ammonium type ZSM-5 molecular sieve, to solve the problems of easy destruction of molecular sieve framework structure, reduction of acid content, high energy consumption and long time in the calcination activation process, and to improve the performance of ZSM-5 molecular sieve in catalyzing light alkane cracking.

[0006] To solve the above problems, the present application uses dielectric barrier discharge plasma treatment instead of calcination process to activate ammonium type ZSM-5 molecular sieve under certain conditions to obtain hydrogen type ZSM-5 molecular sieve. The specific technical solutions are as follows:

[0007] 1) Put the ammonium type ZSM-5 molecular sieve into a dielectric barrier discharge plasma reactor;

[0008] 2) Perform plasma discharge treatment under certain preset conditions

[0009] Preferably, the silicon-aluminum ratio of the ammonium type ZSM-5 molecular sieve is 50, 100, 200 or 300.

[0010] The specific conditions of the dielectric barrier discharge plasma include:

[0011] The plasma discharge mode is dielectric barrier discharge;

[0012] The atmosphere of the plasma treatment is air;

[0013] Preferably, the input voltage of the plasma power supply is 100-200 V;

[0014] Preferably, the input current of the plasma power supply is 1-2 A;

[0015] Preferably, the time of the plasma treatment is 20-80 min;

[0016] The beneficial effects that can be produced by the present application include:

[0017] 1) The activation method of the ammonium-type ZSM-5 molecular sieve provided by the present application uses dielectric barrier discharge plasma and takes air as the discharge atmosphere to activate the ammonium-type ZSM-5 molecular sieve into a hydrogen-type molecular sieve, which retains the molecular sieve framework structure and framework Al and significantly improves the acid properties and B / L acid ratio of the hydrogen-type ZSM-5 molecular sieve.

[0018] 2) The activation method of the ammonium-type ZSM-5 molecular sieve provided by the present application significantly improves the performance of the activated hydrogen-type ZSM-5 molecular sieve in catalyzing the cracking of light alkanes to produce low-carbon olefins. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the present application, the plasma activation process of the present application and part of the characterization results in the examples are introduced by means of the drawings.

[0020] Figure 1 The figure is a schematic diagram of the plasma activation process of the present application.

[0021] EXPLANATION OF REFERENCE NUMBERS

[0022] 1-plasma high-voltage power supply 2-high-voltage electrode 3-ground electrode

[0023] 4-quartz barrier medium 5-plasma 6-ammonium-type ZSM-5 molecular sieve

[0024] Figure 2 The figure is a Fourier infrared spectrum of the hydrogen-type ZSM-5 molecular sieve obtained in Examples 1-3.

[0025] Figure 3 The figure is a Fourier infrared spectrum of the hydrogen-type ZSM-5 molecular sieve obtained in Examples 3 and 7-9.

[0026] Figure 4 The figure is an Al NMR spectrum of the hydrogen-type ZSM-5 molecular sieve obtained in Example 3 and Comparative Example 1. 27

[0027] Figure 5 ​Pyridine infrared spectra of the hydrogen form ZSM-5 molecular sieves obtained in Example 3 and Comparative Example 1. DETAILED DESCRIPTION

[0028] The application will be described in detail below by specific examples, but the application is not limited to the specific examples listed.

[0029] The ammonium form ZSM-5 molecular sieves with different Si / Al ratios in the examples and comparative examples in the present application were synthesized by a hydrothermal method, and the specific synthesis steps were as follows:

[0030] Step one: tetraethyl orthosilicate (TEOS, 25 g), tetrapropylammonium hydroxide (TPAOH, 40 wt% aqueous solution, 15 g) were weighed and added to deionized water (H2O, 47.8 g), and stirred at 80 ℃ for 24 h to form a uniform mixed solution A.

[0031] Step two: aluminum nitrate nonahydrate (Al(NO3)3·9H2O, 0.1125 g, 0.225 g, 0.45 g, 0.9 g were added to the mixed solution A obtained in step one to synthesize ZSM-5 molecular sieves with different Si / Al ratios), sodium hydroxide (NaOH, 0.48 g), deionized water (H2O, 8 g) were added and stirred uniformly to form a uniform mixed solution B.

[0032] Step three: the mixed solution B obtained in step two was transferred to a stainless steel hydrothermal kettle with a polytetrafluoroethylene liner, and crystallized at 170 ℃ for 24 h. The solid product was collected by centrifugation and washing, dried at 110 ℃ for 10 h, and then transferred to a muffle furnace for calcination at 550 ℃ for 3 h to obtain Na form ZSM-5 molecular sieves.

[0033] Step four: the Na form ZSM-5 molecular sieves obtained in step three were transferred to a flask, and ammonium chloride solution (1M, solid-liquid ratio of 1:10) was used for ammonium ion exchange for 4 h, and the process was repeated twice. The solid product was collected by centrifugation and washing, and dried at 110 ℃ for 10 h to obtain ammonium form ZSM-5 molecular sieves.

[0034] In the context of the present specification, including all examples and comparative examples, the crystallinity of the molecular sieves was measured by an X-ray diffractometer of Japan Rigaku Company. Cu-Kα ray was used, the operating voltage was 40 KV, the current was 20 mA, the scanning speed was 10° / min, the scanning range was 2θ = 5~80°, and the step was 0.01°. The relative crystallinity was calculated with reference to the ammonium form ZSM-5 molecular sieves with a Si / Al ratio of 300.

[0035] In the context of the present specification, including all examples and comparative examples, the ammonium removal effect of the molecular sieve is detected by a Fourier infrared spectrometer of Nicolet-380 model of Thermo Fisher Scientific. The scanning resolution is 4 cm -1 , and the scanning range is 4000-400 cm -1 .

[0036] In the context of the present specification, including all examples and comparative examples, the framework aluminum content and non-framework aluminum content of the molecular sieve are determined by a nuclear magnetic resonance spectrometer of AVANCE III HD 500MHz model of Bruker 27 Al NMR.

[0037] In the context of the present specification, including all examples and comparative examples, the acid type of the molecular sieve is detected by in-situ pyridine infrared (Py-IR) by a Fourier infrared spectrometer of Nicolet-710 model of Thermo Fisher Scientific. 20 mg of the sample to be detected is pressed into a tablet and fixed in an in-situ infrared reactor, vacuum pretreated at 400 ℃ for 1 h, adsorbed with pyridine vapor for 3 min after cooling to room temperature, and then the infrared spectrum is recorded by heating to 150 ℃ and 300 ℃, the scanning resolution is 4 cm -1 , the scanning times are 64, and the scanning range is 4000-400 cm -1 .

[0038] Example 1

[0039] 1 g of ammonium-type ZSM-5 molecular sieve with a silicon-aluminum ratio of 50 is uniformly placed in a dielectric barrier discharge plasma reactor, the plasma input voltage is set to 120 V, the input current is 1.5 A, and the treatment is performed for 30 min to obtain a hydrogen-type ZSM-5 molecular sieve. The ammonium removal effect of the molecular sieve is investigated, and the performance of cracking n-hexane is evaluated.

[0040] Example 2

[0041] 1 g of ammonium-type ZSM-5 molecular sieve with a silicon-aluminum ratio of 50 is uniformly placed in a dielectric barrier discharge plasma reactor, the plasma input voltage is 120 V, the input current is 1.5 A, and the treatment is performed for 45 min to obtain a hydrogen-type ZSM-5 molecular sieve. The ammonium removal effect of the molecular sieve is investigated, and the performance of cracking n-hexane is evaluated.

[0042] Example 3

[0043] Take 1 g of ammonium type ZSM-5 molecular sieve with a silicon aluminum ratio of 50 and place it uniformly in a dielectric barrier discharge plasma reactor, the plasma input voltage is 120 V, the input current is 1.5 A, and the treatment time is 60 min, to obtain a hydrogen type ZSM-5 molecular sieve. The ammonium removal effect, crystallinity, framework aluminum content, and acid properties of the molecular sieve are investigated, and its performance in cracking n-hexane is evaluated.

[0044] [Example 4]

[0045] Take 1 g of ammonium type ZSM-5 molecular sieve with a silicon aluminum ratio of 100 and place it uniformly in a dielectric barrier discharge plasma reactor, the plasma input voltage is 120 V, the input current is 1.5 A, and the treatment time is 60 min, to obtain a hydrogen type ZSM-5 molecular sieve. The crystallinity, framework content, and acid properties of the molecular sieve are investigated, and its performance in cracking n-hexane is evaluated.

[0046] [Example 5]

[0047] Take 1 g of ammonium type ZSM-5 molecular sieve with a silicon aluminum ratio of 200 and place it uniformly in a dielectric barrier discharge plasma reactor, the plasma input voltage is 120 V, the input current is 1.5 A, and the treatment time is 60 min, to obtain a hydrogen type ZSM-5 molecular sieve. The crystallinity, framework aluminum content, and acid properties of the molecular sieve are investigated, and its performance in cracking n-hexane is evaluated.

[0048] [Example 6]

[0049] Take 1 g of ammonium type ZSM-5 molecular sieve with a silicon aluminum ratio of 300 and place it uniformly in a dielectric barrier discharge plasma reactor, the plasma input voltage is 120 V, the input current is 1.5 A, and the treatment time is 60 min, to obtain a hydrogen type ZSM-5 molecular sieve. The crystallinity, framework aluminum content, and acid properties of the molecular sieve are investigated, and its performance in cracking n-hexane is evaluated.

[0050] [Example 7]

[0051] Take 1 g of ammonium type ZSM-5 molecular sieve with a silicon aluminum ratio of 50 and place it uniformly in a dielectric barrier discharge plasma reactor, the plasma input voltage is 100 V, the input current is 1.5 A, and the treatment time is 60 min, to obtain a hydrogen type ZSM-5 molecular sieve. The ammonium removal effect of the molecular sieve is investigated, and its performance in cracking n-hexane is evaluated.

[0052] [Example 8]

[0053] Take 1 g of ammonium type ZSM-5 molecular sieve with a silicon aluminum ratio of 50 and place it evenly in a dielectric barrier discharge plasma reactor. The plasma input voltage is 80 V, the input current is 1.5 A, and the treatment time is 60 min. Hydrogen type ZSM-5 molecular sieve is obtained. The ammonium removal effect of the molecular sieve is investigated, and its performance in cracking n-hexane is evaluated.

[0054] [Example 9]

[0055] Take 1 g of ammonium type ZSM-5 molecular sieve with a silicon aluminum ratio of 50 and place it evenly in a dielectric barrier discharge plasma reactor. The plasma input voltage is 60 V, the input current is 1.5 A, and the treatment time is 60 min. Hydrogen type ZSM-5 molecular sieve is obtained. The ammonium removal effect of the molecular sieve is investigated, and its performance in cracking n-hexane is evaluated.

[0056] [Example 10]

[0057] Take 1 g of ammonium type ZSM-5 molecular sieve with a silicon aluminum ratio of 50 and place it evenly in a dielectric barrier discharge plasma reactor. The plasma input voltage is 120 V, the input current is 1.5 A, and the treatment time is 60 min. Hydrogen type ZSM-5 molecular sieve is obtained. The ammonium removal effect of the molecular sieve is investigated, and its performance in cracking n-butane is evaluated.

[0058] [Example 11]

[0059] Take 1 g of ammonium type ZSM-5 molecular sieve with a silicon aluminum ratio of 50 and place it evenly in a dielectric barrier discharge plasma reactor. The plasma input voltage is 120 V, the input current is 1.5 A, and the treatment time is 60 min. Hydrogen type ZSM-5 molecular sieve is obtained. The ammonium removal effect of the molecular sieve is investigated, and its performance in cracking n-decane is evaluated.

[0060] [Comparative Example 1]

[0061] Take 1 g of ammonium type ZSM-5 molecular sieve with a silicon aluminum ratio of 50 and place it in a muffle furnace. The temperature is kept at 550 ℃ for 3 h in an air atmosphere. The crystallinity, framework aluminum content, and acid properties of the molecular sieve are investigated, and its performance in cracking n-hexane is evaluated.

[0062] [Comparative Example 2]

[0063] Take 1 g of ammonium type ZSM-5 molecular sieve with a silicon aluminum ratio of 50 and place it in a muffle furnace. The temperature is kept at 550 ℃ for 3 h in an air atmosphere. The crystallinity, framework aluminum content, and acid properties of the molecular sieve are investigated, and its performance in cracking n-hexane is evaluated.

[0064] [Comparative Example 3]

[0065] Take 1 g of ammonium type ZSM-5 molecular sieve with a silicon aluminum ratio of 200 and place it in a muffle furnace, and calcine it at 550 DEG C for 3 hours under an air atmosphere. The crystallinity, framework aluminum content, and acid properties of the molecular sieve are investigated, and the performance of the molecular sieve in cracking n-hexane is evaluated.

[0066] Comparative Example 4

[0067] Take 1 g of ammonium type ZSM-5 molecular sieve with a silicon aluminum ratio of 300 and place it in a muffle furnace, and calcine it at 550 DEG C for 3 hours under an air atmosphere. The crystallinity, framework aluminum content, and acid properties of the molecular sieve are investigated, and the performance of the molecular sieve in cracking n-hexane is evaluated.

[0068] Comparative Example 5

[0069] Take 1 g of ammonium type ZSM-5 molecular sieve with a silicon aluminum ratio of 50 and place it in a muffle furnace, and calcine it at 550 DEG C for 3 hours under an air atmosphere. The crystallinity, framework aluminum content, and acid properties of the molecular sieve are investigated, and the performance of the molecular sieve in cracking n-butane is evaluated.

[0070] Comparative Example 6

[0071] Take 1 g of ammonium type ZSM-5 molecular sieve with a silicon aluminum ratio of 50 and place it in a muffle furnace, and calcine it at 550 DEG C for 3 hours under an air atmosphere. The crystallinity, framework aluminum content, and acid properties of the molecular sieve are investigated, and the performance of the molecular sieve in cracking n-decane is evaluated.

[0072] Table 1. Characterization results of the activated hydrogen type ZSM-5 molecular sieves of Examples 3-6, 10-11 and Comparative Examples 1-6 and catalytic light hydrocarbon cracking performance

[0073]

[0074] As can be seen from Table 1, by comparing Example 3 with Comparative Example 1, Example 4 with Comparative Example 2, Example 5 with Comparative Example 3, and Example 6 with Comparative Example 4, it can be seen that the method of plasma activation of the molecular sieve of the present application can effectively reduce the damage to the structure of the molecular sieve and improve the relative crystallinity of the hydrogen type ZSM-5 molecular sieve.

[0075] As can be seen from Table 1 and Figure 4 , Figure 5 it can be seen that the method of the present application can regulate the positioning of the metal aluminum and significantly improve the framework aluminum content, B acid amount, and total acid amount of the hydrogen type ZSM-5 molecular sieve, as compared with the conventional calcination activation.

[0076] As can be seen from Table 1, the hydrogen type ZSM-5 molecular sieve activated by the method of the present application has better catalytic activity in the application of catalytic cracking of light alkanes, and improves the conversion rate of light alkanes and the yield of low-carbon olefins, as compared with the conventional calcination method.

Claims

1. A method for regulating metal placement in a low-temperature plasma-activated ammonium-type ZSM-5 molecular sieve, characterized in that... The synthesized ammonium-type molecular sieve was placed in a low-temperature plasma reactor and activated under certain conditions to obtain a hydrogen-type ZSM-5 molecular sieve with metallic Al distributed in the framework and exhibiting catalytic activity. The input voltage of the plasma power supply was 100-200V and the input current was 1-2A.

2. The method for regulating metal placement using low-temperature plasma-activated ammonium-type ZSM-5 molecular sieve according to claim 1, characterized in that, The molecular sieve framework contains silicon and aluminum elements, and is an ammonium-type ZSM-5 microporous or mesoporous molecular sieve that has undergone ion exchange.

3. The method for regulating metal placement using low-temperature plasma-activated ammonium-type ZSM-5 molecular sieve according to claim 1, characterized in that, The silica-to-alumina ratio of the molecular sieve is 50-300.

4. The method for regulating metal placement using low-temperature plasma-activated ammonium-type ZSM-5 molecular sieve according to claim 1, characterized in that, The low-temperature plasma is generated by dielectric barrier discharge.

5. The method for regulating metal placement using low-temperature plasma-activated ammonium-type ZSM-5 molecular sieve according to claim 1, characterized in that, The atmosphere for plasma activation is air.

6. The method for regulating metal placement using low-temperature plasma-activated ammonium-type ZSM-5 molecular sieve according to claim 1, characterized in that, The dielectric barrier discharge gap of the plasma reactor is 8 mm.

7. The method for regulating metal placement in ZSM-5 molecular sieve by low-temperature plasma activation according to claim 1, characterized in that, The plasma treatment time is 20-80 min.

8. A hydrogen-type ZSM-5 molecular sieve obtained by activation according to claim 1.

9. The application of the hydrogen-form ZSM-5 molecular sieve as described in claim 8 in the catalytic cracking of light alkane, characterized in that, The light alkane is one of C4-C10 alkanes, and the catalytic cracking reaction conditions for the light alkane are: reaction temperature 500~700 ℃, and mass hourly space velocity 1~2 h⁻¹. -1 .

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