Al-based catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of catalyst preparation processes, and particularly discloses an Al-based catalyst as well as a preparation method and application thereof. The preparation method at least comprises the following steps: S1, in supergravity reaction equipment, inputting a dopant precursor, an aluminum salt precursor, a dispersing agent and a precipitating agent to realize co-precipitation and obtain precursor slurry, and then aging, washing and drying to obtain a precursor; s2, performing two-step roasting on the precursor slurry to obtain a roasted product; and S3, carrying out fluorination treatment on the roasted product to obtain the catalyst. The rotating speed of the supergravity reaction equipment in the S1 is 1000-3000 rpm; the pH value of a precipitate obtained by co-precipitating the divalent dopant precursor and the aluminum salt precursor is 6-12. The catalyst prepared by the method has moderate and weak Lewis acid centers, and the proportion of strong Lewis acid sites is lower than 15%, so that the catalyst can have excellent catalytic activity and relatively high stability at the same time.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, specifically to a catalyst used in the production process of vinyl fluoride, a method for preparing the catalyst, and its application. Background Technology

[0002] Polyvinyl fluoride (PVF) products are mainly thin film products, possessing advantages such as weather resistance, high mechanical strength, chemical inertness, low permeability, and high light transmittance. Therefore, they have wide applications in packaging, glass, electrical, and aircraft manufacturing, and have a promising market prospect. Currently, PVF is mainly prepared through vinyl fluoride (VF), and the main methods for synthesizing VF are the acetylene fluorination method and the HF removal method of 1,1-difluoroethane (hereinafter referred to as R152a). Among them, the R152a HF removal method has been widely used due to its simple and safe process and high product selectivity. In this method, the catalyst is a key component.

[0003] In the common R152a HF removal process, Al-based catalysts exhibit excellent catalytic activity due to their strong Lewis acidity, and are therefore widely used. However, these catalysts also suffer from poor stability due to deactivation caused by the formation of large amounts of carbon deposits. In existing technologies, the acidity of the catalyst is often modulated by adjusting the addition method of promoters during catalyst preparation, ultimately improving stability. However, this preparation method easily leads to localized accumulation of promoters within the catalyst, ultimately resulting in new problems such as a broad range of Lewis acid strength in the catalyst.

[0004] Therefore, there is an urgent need for a method to prepare Al-based catalysts that can produce Al-based catalysts with better stability and meet higher application requirements. Summary of the Invention

[0005] One of the objectives of this invention is to provide a method for preparing an Al-based catalyst to obtain a highly stable Al-based catalyst.

[0006] The second objective of this invention is to provide an Al-based catalyst with high stability prepared by the above-described method.

[0007] A third objective of this invention is to provide an application of the above-mentioned Al-based catalyst in the preparation of fluoroethylene.

[0008] This invention is achieved through the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing an Al-based catalyst, comprising at least the following steps: S1. In a hypergravity reaction apparatus, a dopant precursor, an aluminum salt precursor, a dispersant, and a precipitant are introduced to achieve co-precipitation and obtain a precursor slurry; the precursor slurry is aged, washed, and dried to obtain a precursor; S2. The precursor slurry is subjected to two-step calcination to obtain a calcined product; S3. The calcined product is subjected to fluorination treatment under a fluorine-containing gas atmosphere to process it into an Al-based catalyst; wherein, in S1, the rotation speed of the hypergravity reaction apparatus is 1000~3000 rpm; the pH value of the precipitate obtained by co-precipitation of the divalent dopant precursor and the aluminum salt precursor is 6~12.

[0010] One important means to improve the stability of Al-based catalysts is to precisely control the Lewis acid strength within the catalyst. In this invention, by improving the preparation method, the electronic structure and coordination environment of Lewis acid sites in the catalyst lattice are controlled in situ. This allows for precise control of the Lewis acid strength of the Al-based catalyst, thereby achieving dynamic optimization of the balance between catalytic activity and carbon deposition deactivation.

[0011] Specifically, in this invention, a hypergravity reaction device is introduced into the preparation method of the Al-based catalyst. By controlling and adjusting some processing parameters, the dopant precursor and the aluminum salt precursor can be uniformly mixed at the nanoscale. Subsequently, two calcination steps are taken to form an Al-OMO-Al structure in the calcination product (where M refers to divalent metal M atoms, derived from the dopant precursor). Finally, by using fluorine-containing gas treatment, the oxygen coordination environment in the catalyst lattice is directionally transformed into an F coordination environment, allowing the divalent metal M atoms to be stably anchored in the AlF3 lattice in a monodisperse form, thus forming the desired Al-FMF-Al structure. Under this structure, the catalyst has medium-to-weak Lewis acid centers, and the proportion of strong Lewis acid sites in the catalyst obtained through the above processing steps is guaranteed to be less than 15%. These characteristics enable the catalyst prepared by the method of this invention to possess both excellent catalytic activity and high stability.

[0012] As a further improvement of the present invention, in S1, the dopant precursor is a metal salt, the aluminum salt precursor is an aluminum salt, and the molar ratio of the dopant precursor to the aluminum salt precursor is 1:(1~3).

[0013] As a further improvement of the present invention, in S1, the dopant precursor is selected from any one of Mg(NO3)2, Co(NO3)2, Ni(NO3)2, Cu(NO3)2, Zn(NO3)2 and Sr(NO3)2, thereby providing the divalent metal M atoms required in the catalyst.

[0014] As a further improvement of the present invention, in S1, the amount of dispersant is 0.5 to 0.6% of the mass of the dopant precursor.

[0015] As a further improvement of the present invention, in S1, the reaction temperature is controlled at 30~90°C.

[0016] As a further improvement of the present invention, in S2, the two-step calcination includes the following steps: A. After the programmed temperature is raised to 300~500℃, calcination is continued for 3~4 hours; B. After the programmed temperature is raised to 600~1200℃, calcination is continued for 5~8 hours.

[0017] As a further improvement of the present invention, in step A of S2, calcination is carried out in an air atmosphere; in step B of S2, calcination is carried out in a nitrogen atmosphere or a protective atmosphere.

[0018] As a further improvement of the present invention, a pretreatment step is provided between S2 and S3, which includes the steps of: placing the calcined product under a protective atmosphere or a nitrogen atmosphere and pretreating it at 300~400°C for 1~2 hours, wherein the heating rate before reaching the pretreatment temperature is 3~5°C / min.

[0019] As a further improvement of the present invention, in S3, the fluorination treatment temperature is 200~400℃, the heating rate used to reach the fluorination treatment temperature is 1~5℃ / min, and the fluorination treatment duration is 4~12h.

[0020] As a further improvement of the present invention, in S3, the gas used to form the fluorine-containing gas atmosphere is any one of 1,1-difluoroethane, trifluoromethane, or difluorochloromethane.

[0021] Secondly, the present invention provides an Al-based catalyst, which is prepared by any of the above-described methods for preparing an Al-based catalyst.

[0022] Thirdly, this invention provides the application of the above-mentioned Al-based catalyst in the preparation of ethylene fluoride. Specifically, the above-mentioned Al-based catalyst is used in the conventional R152a deHF removal process.

[0023] The beneficial effect of this invention is that the catalyst prepared by the method of this invention achieves atomic-level dispersion of divalent metal M atoms in the Al-based catalyst lattice, thereby enabling M atoms to be firmly bonded to the AlF3 lattice in a doped form, rather than simply physically adsorbed or surface modified. This effectively avoids problems such as metal agglomeration and uneven distribution that are prone to occur in traditional impregnation methods and other preparation processes.

[0024] Meanwhile, atomic-level doping of M atoms successfully modulates the surface electronic structure of Al-based catalysts, forming a sufficient number of Lewis acid centers with moderate strength. When catalysts possessing these characteristics are used in the R152a defluorination process, the moderately strong Lewis acid centers effectively activate the CH and CF bonds in the R152a molecule, thereby promoting the defluorination reaction; at the same time, they avoid side reactions such as deep defluorination, carbon deposition, and catalyst deactivation caused by strong acid centers. In summary, the processed catalyst achieves an optimal balance between catalytic activity and stability.

[0025] Furthermore, the preparation method presented in this invention has a simple overall process flow, and the processing parameters involved are easy to control, which is conducive to its promotion and large-scale industrial production. Attached Figure Description

[0026] The accompanying drawings are provided below to illustrate the preferred embodiments of the invention and to aid in understanding the objectives and advantages of the invention, wherein:

[0027] Figure 1 The XRD patterns of the catalysts in Example 1 and Comparative Examples 12-14 are shown below.

[0028] Figure 2 The NH3-TPD spectra of the catalysts in Examples 1 and Comparative Examples 12-14 are shown. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0031] Example 1:

[0032] This embodiment provides an Al-based catalyst, which is prepared by the following method:

[0033] S1. Dissolve 0.09 mol of magnesium nitrate hexahydrate (Mg(NO3)2·6H2O) and 0.18 mol of aluminum salt precursor aluminum nitrate nonahydrate (Al(NO3)3·9H2O) in 500 mL of deionized water, and add citric acid as a dispersant at an amount of 0.5% of the mass of the dopant precursor. Finally, stir the raw materials in a constant temperature oil bath at 70℃ for 30 min until they are completely dissolved to achieve preliminary mixing and obtain the first mixture.

[0034] A 14 mol / L NaOH precipitant solution was heat-pretreated in a 70℃ constant temperature oil bath for later use.

[0035] The first mixture was fed into the hypergravity reactor at a rate of 40 mL / min using a peristaltic pump, while the NaOH solution was fed into the hypergravity reactor at a rate of 5 mL / min using a peristaltic pump to carry out a co-precipitation reaction. The hypergravity reactor was rotated at 3000 rpm, and a precursor slurry with a pH maintained at 8 was finally obtained.

[0036] The precursor slurry was aged for 6 hours by stirring at 300 rpm in a constant temperature oil bath at 70℃. Then, it was washed 5 times by centrifugation with deionized water until neutral. Finally, the precipitate obtained after centrifugation was placed in an oven and dried at 110℃ for 12 hours to obtain the precursor.

[0037] S2. The precursor was heated to 400°C in air and calcined for 4 hours, and then heated to 1000°C in nitrogen and calcined for 8 hours to obtain the calcined product.

[0038] S3. The calcined product is subjected to fluorination treatment under a fluorine-containing gas atmosphere. The fluorination treatment temperature is 350℃, the heating rate is 3℃ / min, the fluorination treatment duration is 8h, and the fluorine-containing gas used is R152a gas, finally obtaining an Al-based catalyst.

[0039] Preferably, in S3 of this embodiment, before fluorination, the calcined product is pretreated in a nitrogen atmosphere, during which the reaction temperature is 300°C, the heating rate is 3°C / min, and the pretreatment time lasts for 1 hour.

[0040] Example 2:

[0041] This embodiment provides an Al-based catalyst, the preparation method of which differs from that in Example 1 in that the rotation speed of the hypergravity reactor in S1 is 1000 rpm.

[0042] Example 3:

[0043] This embodiment provides an Al-based catalyst, the preparation method of which differs from that in Example 1 in that: in S1, the rotation speed of the hypergravity reactor is 2000 rpm.

[0044] Example 4:

[0045] This embodiment provides an Al-based catalyst, the preparation method of which differs from that in Example 1 in that: in S1, the mixing of raw materials, pretreatment of precipitant, co-precipitation reaction and slurry aging are all carried out under constant temperature oil bath conditions at 30°C.

[0046] Example 5:

[0047] This embodiment provides an Al-based catalyst, the preparation method of which differs from that in Example 1 in that: in S1, the mixing of raw materials, pretreatment of precipitant, co-precipitation reaction and slurry aging are all carried out under constant temperature oil bath conditions of 50°C.

[0048] Example 6:

[0049] This embodiment provides an Al-based catalyst, the preparation method of which differs from that in Example 1 in that: in S1, the mixing of raw materials, pretreatment of precipitant, co-precipitation reaction and slurry aging are all carried out under constant temperature oil bath conditions of 90°C.

[0050] Example 7:

[0051] This embodiment provides an Al-based catalyst, the preparation method of which differs from that in Example 1 in that: in S3, during the nitrogen pretreatment stage before fluorination, the heating rate is 1℃ / min.

[0052] Example 8:

[0053] This embodiment provides an Al-based catalyst, the preparation method of which differs from that in Example 1 in that: in S3, during the nitrogen pretreatment stage before fluorination, the heating rate is 5℃ / min.

[0054] Example 9:

[0055] This embodiment provides an Al-based catalyst, the preparation method of which differs from that in Example 1 in that the temperature required for the second calcination in S2 is 600°C.

[0056] Example 10:

[0057] This embodiment provides an Al-based catalyst, the preparation method of which differs from that in Example 1 in that the temperature required for the second calcination in S2 is 800°C.

[0058] Example 11:

[0059] This embodiment provides an Al-based catalyst, the preparation method of which differs from that in Example 1 in that the temperature required for the second calcination in S2 is 1200℃.

[0060] Comparative Example 12:

[0061] This comparative example provides a catalyst prepared by the following method:

[0062] S1. Dissolve 0.09 mol of the dopant precursor magnesium nitrate hexahydrate (Mg(NO3)2·6H2O) in 500 mL of deionized water, and add 0.5% of the dispersant citric acid by weight of the precursor. Stir in a constant temperature oil bath at 70 °C for 30 min until completely dissolved to obtain a mixture.

[0063] A 14 mol / L NaOH precipitant solution was heat-pretreated in a 70℃ constant temperature oil bath for later use.

[0064] The mixture was fed into the hypergravity reactor at a rate of 40 mL / min using a peristaltic pump, and NaOH solution was fed into the hypergravity reactor at a rate of 5 mL / min using a peristaltic pump to carry out the precipitation reaction. The hypergravity reactor was rotated at 3000 rpm, and a slurry with pH maintained at 8 was finally obtained.

[0065] The slurry was aged for 6 hours by stirring at 300 rpm in a constant temperature oil bath at 70℃. Then, it was washed 5 times by centrifugation with deionized water until neutral. Finally, the precipitate obtained after centrifugation was placed in an oven and dried at 110℃ for 12 hours to obtain the precursor.

[0066] S2. The precursor was heated to 400°C in air and calcined for 4 hours, and then heated to 1000°C in nitrogen and calcined for 8 hours to obtain the calcined product.

[0067] S3. The calcined product was subjected to fluorination treatment under a fluorine-containing gas atmosphere. The fluorination treatment temperature was 350℃, the heating rate was 3℃ / min, the fluorination treatment duration was 8h, and the fluorine-containing gas used was 1,1-difluoroethane. Finally, a single-component Mg-based catalyst was obtained.

[0068] Preferably, in S3, before fluorination, the calcined product is pretreated under a nitrogen atmosphere, during which the reaction temperature is 300°C, the heating rate is 3°C / min, and the pretreatment time lasts for 1 hour.

[0069] Comparative Example 13:

[0070] This comparative example provides a single-component Al-based catalyst, the preparation method of which differs from that in Comparative Example 12 in that: in S1, 0.18 mol of aluminum salt precursor aluminum nitrate nonahydrate (Al(NO3)3·9H2O) is used as the sole metal source to finally obtain the single-component Al-based catalyst.

[0071] Comparative Example 14:

[0072] This comparative example provides a two-component Mg / Al mechanically mixed catalyst, which is prepared by the following method:

[0073] S1. Prepare magnesium hydroxide precursor and aluminum hydroxide precursor separately:

[0074] Preparation of magnesium hydroxide precursor: 0.09 mol magnesium nitrate hexahydrate (Mg(NO3)2·6H2O) was dissolved in 500 mL of deionized water, and citric acid dispersant at 0.5% of the precursor mass was added. The mixture was stirred in a 70°C constant temperature oil bath for 30 min until completely dissolved to obtain a first mixture. A 14 mol / L precipitant NaOH solution was heat-pretreated in a 70°C constant temperature oil bath. The first mixture and NaOH solution were fed into a high-gravity reactor at a flow rate of 3000 rpm using a peristaltic pump at the same rate as in Example 1 for precipitation to obtain a slurry with a pH of 8. The magnesium hydroxide precursor was then obtained after the same aging, washing, and drying steps as in Example 1.

[0075] Preparation of aluminum hydroxide precursor: 0.18 mol of aluminum nitrate nonahydrate (Al(NO3)3·9H2O) was dissolved in 500 mL of deionized water. The subsequent steps were the same as those for the preparation of magnesium hydroxide precursor to obtain aluminum hydroxide precursor.

[0076] The obtained magnesium hydroxide precursor and aluminum hydroxide precursor were ball-milled in a ball mill at a molar ratio of 1:2 for 4 hours to obtain a mixed precursor.

[0077] S2. The mixed precursors were heated to 400°C in air and calcined for 4 hours, and then heated to 1000°C in nitrogen and calcined for 8 hours to obtain the calcined product.

[0078] S3. The calcined product is subjected to fluorination treatment under a fluorine-containing gas atmosphere. The fluorination treatment temperature is 350℃, the heating rate is 3℃ / min, the fluorination treatment duration is 8h, and the fluorine-containing gas used is 1,1-difluoroethane. Finally, a two-component mechanically mixed catalyst is obtained.

[0079] Preferably, in S3, before fluorination, the calcined product is pretreated under a nitrogen atmosphere, during which the reaction temperature is 300°C, the heating rate is 3°C / min, and the pretreatment time lasts for 1 hour.

[0080] Performance testing:

[0081] In the first aspect, the catalysts in Example 1 and Comparative Examples 12-14 were tested in this embodiment to obtain XRD patterns and NH3-TPD patterns.

[0082] Among them, such as Figure 1 As shown in the figure, the XRD spectra of the catalyst in Example 1 and the catalysts in Comparative Examples 12-14 are mainly summarized and displayed. It can be seen that the catalyst prepared in Example 1 can detect the AlF3 phase, indicating that the metal M atom can be well doped under this preparation method. In contrast, as can be seen from the detection results of the catalyst prepared in Comparative Example 14, the catalyst only has a simple AlF3 and MgF2 complex superposition, that is, the effective doping of divalent metal M is not achieved, and thus the required effective modification of the catalyst is not achieved.

[0083] like Figure 2 As shown in the figure, the NH3-TPD spectra of the catalyst in Example 1 and the catalysts in Comparative Examples 12-14 are summarized and displayed. It can be seen that, compared with the catalysts in Comparative Examples 12-14, the catalyst prepared in Example 1 has more Lewis weak acid sites, which greatly neutralizes the amount of strong Lewis acid sites, successfully modulates the surface electronic structure of the AlF3 catalyst, and forms a sufficient number of Lewis acid centers with moderate strength in the catalyst. The Lewis weak acid sites on the catalyst can maintain suitable activity and increase stability in the R152a deHF removal reaction, which makes the catalyst prepared in Example 1 have better overall performance.

[0084] Secondly, in this embodiment, the catalysts from Examples 1-11 and Comparative Examples 12-14 were used in the R152a deHF removal reaction process, and the conversion rate and selectivity of the catalysts were detected to assess their catalytic activity and stability. The reaction conditions were as follows: 1 ml of 20-40 mesh catalyst was loaded into a fixed-bed reaction tube, and the space velocity of the R152a gas was controlled at 750 h⁻¹ during the reaction. -1 The reaction temperature was set to 340℃.

[0085] The test results are summarized in Table 1:

[0086] Table 1. Summary of conversion and selectivity data of catalysts at different time periods in the examples and comparative examples. catalyst 50-hour conversion rate / selectivity 150h conversion rate / selectivity 300h conversion rate / selectivity Example 1 79.3% / >99% 78.1% / >99% 75.1% / >99% Example 2 79.4% / >99% 77.8% / >99% 74.6% / >99% Example 3 79.2% / >99% 78.0% / >99% 74.8% / >99% Example 4 76.7% / >99% 71.1% / >99% 64.6% / >99% Example 5 79.8% / >99% 75.6% / >99% 69.6% / >99% Example 6 79.1% / >99% 78.2% / >99% 74.8% / >99% Example 7 78.9% / >99% 77.2% / >99% 74.5% / >99% Example 8 79.0% / >99% 76.6% / >99% 72.9% / >99% Example 9 78.5% / >99% 77.3% / >99% 73.7% / >99% Example 10 78.6% / >99% 77.5% / >99% 74.2% / >99% Example 11 78.1% / >99% 76.7% / >99% 71.5% / >99% Comparative Example 12 58.3% / >98% 53.4% / >96% 42.3% / >94% Comparative Example 13 78.8% / >99% 65.2% / >95% 43.7% / >91% Comparative Example 14 78.3% / >98% 61.6% / >94% 40.3% / >91% .

[0087] As shown in Table 1, within a short reaction time, the catalysts in each group of examples exhibited similar conversion rates and selectivity compared to the catalysts in the comparative groups. However, as the reaction time gradually increased, the conversion rates and selectivity of the catalysts in the comparative groups decreased significantly, with the conversion rate decreasing more drastically. While the conversion rates of the catalysts in each group of examples also decreased, the decrease was relatively smaller, and the selectivity remained consistently >99%. These data indicate that the catalysts prepared using the methods described in each group of examples achieved improved performance, possessing both better catalytic activity and improved stability, demonstrating broad application prospects.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an Al-based catalyst, characterized in that, It includes at least the following steps: S1. In a supergravity reaction device, a dopant precursor, an aluminum salt precursor, a dispersant and a precipitant are input to achieve co-precipitation and obtain a precursor slurry. The precursor slurry is aged, washed and dried to obtain the precursor. S2. The precursor is subjected to two-step calcination to obtain the calcined product; S3. The calcined product is subjected to fluorination treatment under a fluorine-containing gas atmosphere to obtain an Al-based catalyst; Within S1, the rotational speed of the hypergravity reaction device is 1000~3000 rpm; the pH value of the precipitate obtained by co-precipitation of the divalent dopant precursor and the aluminum salt precursor is 6~12.

2. The method for preparing an Al-based catalyst according to claim 1, characterized in that, In S1, the dopant precursor is a metal salt, and the molar ratio of the dopant precursor to the aluminum salt precursor is 1:(1~3).

3. The method for preparing an Al-based catalyst according to claim 2, characterized in that, In S1, the dopant precursor is selected from any one of Mg(NO3)2, Co(NO3)2, Ni(NO3)2, Cu(NO3)2, Zn(NO3)2 and Sr(NO3)2.

4. The method for preparing an Al-based catalyst according to claim 1, characterized in that, In S1, the amount of dispersant used is 0.5 to 0.6% of the mass of the dopant precursor.

5. The method for preparing an Al-based catalyst according to claim 1, characterized in that, In S1, the reaction temperature is controlled at 30~90℃.

6. The method for preparing an Al-based catalyst according to claim 1, characterized in that, In S2, the two-step calcination includes the following steps: A. After the temperature is raised to 300~500℃, continue calcining for 3~4 hours; B. After the temperature is raised to 600~1200℃, continue roasting for 5~8 hours.

7. The method for preparing an Al-based catalyst according to claim 1, characterized in that, In S3, the fluorination treatment temperature is 200~400℃, the heating rate to reach the fluorination treatment temperature is 1~5℃ / min, and the fluorination treatment duration is 4~12h.

8. The method for preparing an Al-based catalyst according to claim 1, characterized in that, In S3, the gas used to form the fluorine-containing gas atmosphere is any one of 1,1-difluoroethane, trifluoromethane, or difluorochloromethane.

9. An Al-based catalyst, characterized in that, It is prepared by the method of any one of claims 1 to 8.

10. The application of the Al-based catalyst as described in claim 9 in the preparation of fluoroethylene.

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