A catalyst for preparing isobutene by directly dehydrogenating isobutane and a preparation method and application thereof

Abstract

The application belongs to the technical field of catalysts for preparing olefins by dehydrogenation of alkanes, and specifically discloses a catalyst for preparing isobutene by directly dehydrogenating isobutane and a preparation method and application thereof. x (x=1~3) is an active component for catalysis, and the aluminum species is Al2O3 for acting as a carrier for dispersing the active component. A small amount of transition metal or alkali metal can also be introduced as an additive. The catalyst has a high specific surface area, can significantly improve the dispersity of Cr elements, improve the activity of the catalyst in a catalytic reaction, increase the interaction between Cr and the carrier, and significantly enhance the stability of the reaction of isobutane dehydrogenation to isobutene. The catalyst is suitable for a wide range of reaction temperatures for the reaction of isobutane dehydrogenation to isobutene.

Description

Technical Field

[0001] This invention belongs to the technical field of catalysts for the dehydrogenation of alkane to olefins, and particularly relates to a catalyst for the direct dehydrogenation of isobutane to isobutene, its preparation method and application. Background Technology

[0002] Isobutene, the dehydrogenation product of isobutane, is an important chemical intermediate raw material, widely used in the synthesis of polyisobutene, tert-butanol, methyl tert-butyl ether, butyl rubber, methacrylonitrile, and antioxidants, among other organic chemicals. With the continuous development and use of downstream chemical products, the demand for isobutene is gradually increasing both domestically and internationally. my country has abundant C4 resources, with a significant portion being isobutane. A large portion of isobutane is used in the production of civilian fuels, resulting in resource waste. The dehydrogenation reaction of isobutane to produce high-value-added isobutene can improve the chemical utilization rate of isobutane, meet the growing market demand, and bring greater economic benefits to the petrochemical industry.

[0003] Industrially available isobutane dehydrogenation catalysts mainly fall into two categories: platinum-based noble metal catalysts and chromium-based catalysts. Platinum-based catalysts are expensive and suffer from problems such as poor dispersion, sintering, and carbon deposition during the reaction. Compared to noble metal catalysts, chromium-based catalysts are relatively inexpensive and have lower requirements for impurities in the raw materials, but they generally suffer from poor stability. Therefore, extending the regeneration cycle of chromium-based catalysts is an important means to further improve their economic efficiency. Traditional chromium-based isobutane dehydrogenation catalysts are mainly prepared by impregnation, which easily leads to uneven dispersion of the active components. To address this, Li Li et al. summarized the effects of different supports and promoters on the dehydrogenation reaction, finding that smaller pore structures can improve reaction selectivity; weakly acidic sites on the support surface, high dispersion of the active components on the surface, and basic promoters are beneficial to improving the catalyst's resistance to carbon deposition and its stability. Wang Zongting et al. prepared Cr-K-γCr2O3 / Al2O3 catalysts using a microwave method and evaluated their performance. The microwave method can improve the dispersion of active components and reduce the crystal size of active components in the catalyst. The activity, stability and wear resistance of the prepared catalysts are all improved.

[0004] To address the issue of rapid deactivation rates in chromium-based catalysts, it is necessary to develop a novel catalyst preparation method that improves the dispersion of the active components while simultaneously enhancing their stability. Summary of the Invention

[0005] To address the problems of uneven distribution and poor stability of active components in existing chromium-based catalysts, the present invention aims to provide a catalyst for the dehydrogenation of isobutane to isobutene, its preparation method, and its application. The preparation method uses PVP as a template agent, and introduces Cr and Al ions into a solution containing the template agent to obtain CrO₂ with high specific surface area and highly dispersed active components. x The mixed oxide catalyst formed by (x=1~3) and Al2O3 improves the interaction between the components in the catalyst and increases the stability of the catalytic reaction. Furthermore, a small amount of transition metal or alkali metal promoters are introduced during the catalyst preparation process to increase the dispersion of the active components in the catalyst and their interaction with the support, improve the adsorption of alkane molecules by the active sites, reduce the number of strongly acidic sites in the support, and further enhance the activity or selectivity of the catalyst.

[0006] The preparation method of this invention has a wide suitable reaction temperature range, exhibiting high stability and olefin selectivity at high temperatures, while maintaining a high conversion rate at lower reaction temperatures. The raw materials used in this preparation method are readily available, the process is simple, and it has good reproducibility, making it of significant application value.

[0007] This invention provides a method for preparing a catalyst for the direct dehydrogenation of isobutane to isobutene, comprising the following steps:

[0008] Weigh polyvinylpyrrolidone and dissolve it in pure water. Then add the required amounts of Cr(NO3)3·9H2O and Al(NO3)3·9H2O and continue stirring to obtain a homogeneous mixed solution. Then add the obtained mixed solution dropwise to liquid nitrogen to form a uniformly dispersed solid mixture. Next, put the obtained solid mixture together with the unevaporated liquid nitrogen into a vacuum freeze dryer for vacuum freeze drying. Finally, calcine it in a muffle furnace to obtain the catalyst.

[0009] Further, in the mixed solution, the ratio of polyvinylpyrrolidone:purified water is 1g:20ml to 6g:20ml, and the ratio of polyvinylpyrrolidone:(total mass of Cr(NO3)3·9H2O and Al(NO3)3·9H2O) is 1g:7g to 6g:7g, preferably 4g:20ml:7g; the stirring time is 1h; the vacuum freeze-drying conditions are: temperature -85℃, vacuum degree 0.1Pa, drying time 48h; the calcination temperature is 550~650℃, preferably 600℃, and the time is 4-6h, preferably 5h.

[0010] Furthermore, soluble transition metal salts, alkali metal salts, transition metal hydrates, alkali metal hydrates, or hydroxides of transition metals or alkali metals are used as auxiliaries to partially replace Al(NO3)3·9H2O. The total mass of the transition metal salts, alkali metal salts, transition metal hydrates, alkali metal hydrates, or hydroxides of transition metals or alkali metals and Al(NO3)3·9H2O after partial replacement is the same as the mass of Al(NO3)3·9H2O before partial replacement.

[0011] Furthermore, the molar amount of Cr in the catalyst is 5% to 20% of the total molar amount of transition metal or alkali metal elements M, Cr, and Al in the catalyst. Preferably, M = Zr, Ni, Zn, Co, K, Ca.

[0012] Further, the molar amount of transition metal element or alkali metal element M in the catalyst is 0.1% to 20% of the total molar amount of M, Al and Cr elements in the catalyst. Preferably, M = Zr, Ni, Zn, Co, K, Ca.

[0013] The present invention also provides a catalyst prepared by the above preparation method, wherein the active component of the catalyst is CrO. x (x=1~3), mainly Cr2O3; Al2O3 is used as a carrier to disperse the active components.

[0014] Furthermore, the catalyst also includes an auxiliary agent, which exists in the form of a transition metal oxide or an alkali metal oxide, wherein the transition metal element or the alkali metal element plays the role of dispersing the active component and reducing the acidity of the support.

[0015] Furthermore, the molar amount of Cr in the catalyst is 5% to 20% of the total molar amount of Cr, Al, and auxiliary metal elements M (M = Zr, Ni, Zn, Co, K, Ca, etc.) in the catalyst.

[0016] Furthermore, the molar amount of the auxiliary metal element M (M = Zr, Ni, Zn, Co, K, Ca, etc.) in the catalyst is 0.1% to 20% of the total molar amount of auxiliary metal elements M, Al, and Cr in the catalyst.

[0017] The application of the catalyst of the present invention as a catalyst for the dehydrogenation of isobutane to prepare isobutene.

[0018] A method for preparing isobutylene, comprising the following steps: loading the catalyst into a fixed-bed reactor and carrying out the reaction in the fixed-bed reactor under the following conditions: the amount of catalyst used is 0.2 mg; the reaction temperature is 500–650 °C; i-C4H 10 The volume ratio of N2 is 1:8 to 2:1; the reaction pressure is atmospheric pressure, and the space velocity is 6-18 L·g. -1 ·h -1 The reaction tail gas was analyzed using an Agilent 7890B gas chromatograph, with nitrogen as an internal standard to calculate the conversion rate and product selectivity.

[0019] Furthermore, the reaction temperature is 500–600℃, preferably 600℃; i-C4H 10 The volume ratio of N2 is 1:6 to 1:1, preferably 1:6; the space velocity is 6 to 12 L·g -1 ·h -1 More preferably 6 L·g -1 ·h -1 .

[0020] Compared with existing catalysts for the dehydrogenation of isobutane to isobutene, the catalyst of the present invention has the following beneficial effects and advantages:

[0021] (1) In the catalyst of the present invention, the Cr species is Cr2O x The main component is Cr2O3, which is the active component that plays a catalytic role. The aluminum species is Al2O3, which acts as a carrier to disperse the active component.

[0022] (2) The catalyst of the present invention has a high specific surface area, which can significantly improve the dispersion of Cr element and improve its activity in catalytic reaction; it increases the interaction between Cr and the support, and significantly enhances the stability of the dehydrogenation reaction of isobutane to isobutene.

[0023] (3) The small amount of transition metal elements or alkali metal elements introduced into the catalyst of the present invention as promoters can improve the dispersion of the active components and the interaction between the active components and the support, enhance the adsorption of alkane molecules at the active sites, reduce the number of strongly acidic sites in the support, and further improve the activity or selectivity of the catalyst. In the catalytic reaction, transition metal elements also exhibit weak catalytic activity; while alkali metal elements reduce the catalytic activity of the active components and improve the selectivity.

[0024] (4) At a reaction temperature of 500 to 650°C, the catalyst of the present invention can maintain relatively high activity; it is applicable to a wide range of reaction temperatures for the dehydrogenation of isobutane to isobutene. Within a reaction temperature range of 500 to 600°C, it can maintain high isobutene selectivity, while the selectivity of byproducts such as CH4, ethane, propane, propylene, butane, and CO2 is low.

[0025] (5) The catalyst of the present invention has a simple preparation method, readily available raw materials, and good reproducibility. Attached Figure Description

[0026] Figure 1 The physical adsorption-desorption isotherms of the mixed oxide catalyst formed by Cr2O3 and Al2O3 prepared in Example 1 and the chromium-based catalyst supported on commercial alumina in Comparative Example 1.

[0027] Figure 2 Transmission electron microscope image of the mixed oxide catalyst formed by Cr2O3 and Al2O3 prepared in Example 1;

[0028] Figure 3 This is a high-angle annular dark-field image of the mixed oxide catalyst formed by Cr2O3 and Al2O3 prepared in Example 1;

[0029] Figure 4 Transmission electron microscope image of the chromium-based catalyst supported on commercial alumina in Comparative Example 1.

[0030] Figure 5 This is a high-angle annular dark-field image of the chromium-based catalyst supported on commercial alumina in Comparative Example 1. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to the embodiments. However, the embodiments are not intended to limit the scope of protection of the present invention.

[0032] Example 1

[0033] 4g of polyvinylpyrrolidone (PVP, Sinopharm Chemical Reagent Co., Ltd., CAS: 9003-39-8, K30, analytical grade, the same below) was weighed and dissolved in 20ml of purified water. The mixture was stirred for 0.5h, then 0.3735g of Cr(NO3)3·9H2O (Sinopharm Chemical Reagent Co., Ltd., CAS: 7789-02-8, analytical grade, the same below) and 6.6535g of Al(NO3)3·9H2O (Sinopharm Chemical Reagent Co., Ltd., CAS: 7784-27-2, analytical grade, the same below) were added. The mixture was stirred for another 1h to obtain a homogeneous solution. This solution was then added dropwise to liquid nitrogen to form a uniformly dispersed solid mixture. The resulting solid mixture, along with any remaining liquid nitrogen, was then placed in a vacuum freeze dryer and freeze-dried for 48h under the following conditions: temperature -85℃, vacuum degree 0.1Pa. Finally, the mixture was calcined in a muffle furnace at 600℃ for 5h to obtain Cr. 0.5 Al 9.5 O x Catalyst, denoted as catalyst A-Cat.

[0034] Cr 0.5 Al 9.5 O x Cr in catalyst 0.5 And Al 9.5 This refers to a molar ratio of Cr to Al of 0.5 / 9.5, or 1 / 19 (theoretical calculation value, the same applies to the following examples).

[0035] Catalyst performance evaluation tests were conducted in a fixed-bed reactor (TORCH) under the following conditions: catalyst dosage of 0.2 mg; reaction temperature of 600 °C; i-C4H 10 The N2 (volume ratio) is 1:6; at atmospheric pressure, the space velocity is 6 L·g. -1 ·h -1 The reaction tail gas was analyzed by Agilent 7890B gas chromatography, and the conversion rate and product selectivity were calculated using nitrogen as an internal standard. The initial and final reaction data within 20 hours after the introduction of isobutane are shown in Table 2.

[0036] Comparative Example 1

[0037] Weigh 1.1542 g of Cr(NO3)3·9H2O into an appropriate amount of purified water, stir to dissolve, and then add the solution dropwise onto a 2.85 g Al2O3 (Sinopharm Chemical Reagent Co., Ltd., CAS: 1344-28-1, analytical grade, the same below) support. Then place the resulting solid mixture in an oven and dry at 100 °C for 10 h. Finally, calcine it in a muffle furnace at 600 °C for 5 h to obtain the Cr / Al2O3-1-19 catalyst, denoted as catalyst N-Cat.

[0038] The molar ratio of Cr to Al in the Cr / Al2O3-1-19 catalyst is 1 / 19 (theoretical calculation).

[0039] The catalyst performance evaluation test was the same as in Example 1.

[0040] Regarding Cr in Example 1 0.5 Al 9.5 O x The specific surface area, pore volume, and pore size of the catalyst and the Cr / Al2O3-1-19 catalyst in Comparative Example 1 were characterized using a nitrogen physical adsorption-desorption analyzer. The results are listed in Table 1, and their nitrogen physical adsorption-desorption isotherms are shown below. Figure 1 As shown.

[0041] Table 1. Nitrogen physisorption-desorption data of the catalysts in Example 1 and Comparative Example 1

[0042]

[0043] From the instruction manual Figure 1 As can be seen from Table 1, the Cr in Example 1 0.5 Al 9.5 O x Catalysts have a high specific surface area, which is beneficial to the dispersion of active components, increases the contact area between active components and reactants, and improves their catalytic activity and stability.

[0044] Regarding Cr in Example 1 0.5 Al 9.5 O x The catalyst was characterized using scanning transmission electron microscopy, such as... Figure 2 and 3 As shown in the figure, Cr 0.5 Al 9.5 O x The catalyst exhibits a thin, flake-like structure with uniformly dispersed active components. The Cr / Al₂O₃⁻¹⁹ catalyst in Comparative Example 1 was characterized using scanning transmission electron microscopy, and the resulting images are shown below. Figure 4 and 5 As shown in the figure, the dispersion of the active component in the Cr / Al2O3-1-19 catalyst is lower than that in the Cr catalyst. 0.5 Al 9.5 O x Catalyst. Among them, Figure 3 and Figure 5 It is a high-angle, ring-shaped dark field image. Figure 3 This indicates that the Cr species are distributed relatively evenly in the catalyst, with no particularly bright areas appearing; Figure 5 There are obvious bright areas, indicating that Cr species are accumulated and poorly dispersed.

[0045] Example 2

[0046] 4g of polyvinylpyrrolidone was dissolved in 20ml of purified water and stirred for 0.5h. Then, 0.5955g of Cr(NO3)3·9H2O and 6.4209g of Al(NO3)3·9H2O were added, and stirring was continued for 1h to obtain a homogeneous mixed solution. The resulting mixture was then added dropwise to liquid nitrogen to form a uniformly dispersed solid mixture. The resulting solid mixture, along with the remaining liquid nitrogen, was then placed in a vacuum freeze dryer and freeze-dried for 48h under the following conditions: temperature -85℃, vacuum degree 0.1Pa. Finally, the mixture was calcined in a muffle furnace at 600℃ for 5h to obtain Cr. 0.8 Al 9.2 O x Catalyst, denoted as catalyst B-Cat.

[0047] Cr 0.8 Al 9.2 O x Cr in catalyst 0.8 And Al 9.2 This refers to a molar ratio of Cr to Al of 0.8 / 9.2.

[0048] The catalyst performance evaluation test was the same as in Example 1.

[0049] Example 3

[0050] 4g of polyvinylpyrrolidone was dissolved in 20ml of purified water and stirred for 0.5h. Then, 0.7427g of Cr(NO3)3·9H2O and 6.2667g of Al(NO3)3·9H2O were added, and stirring was continued for 1h to obtain a homogeneous mixed solution. The resulting mixture was then added dropwise to liquid nitrogen to form a uniformly dispersed solid mixture. The resulting solid mixture, along with the remaining liquid nitrogen, was then placed in a vacuum freeze dryer and freeze-dried for 48h under the following conditions: temperature -85℃, vacuum degree 0.1Pa. Finally, the mixture was calcined in a muffle furnace at 600℃ for 5h to obtain Cr1Al9O. x Catalyst, denoted as catalyst C-Cat.

[0051] Cr1Al9O x In the catalyst, Cr1 and Al9 refer to the molar ratio of Cr to Al elements being 1 / 9.

[0052] The catalyst performance evaluation test was the same as in Example 1.

[0053] Example 4

[0054] 4g of polyvinylpyrrolidone was dissolved in 20ml of purified water and stirred for 0.5h. Then, 0.8892g of Cr(NO3)3·9H2O and 6.1132g of Al(NO3)3·9H2O were added, and stirring was continued for 1h to obtain a homogeneous mixed solution. The resulting mixture was then added dropwise to liquid nitrogen to form a uniformly dispersed solid mixture. The resulting solid mixture, along with the remaining liquid nitrogen, was then placed in a vacuum freeze dryer and freeze-dried for 48h under the following conditions: temperature -85℃, vacuum degree 0.1Pa. Finally, the mixture was calcined in a muffle furnace at 600℃ for 5h to obtain Cr. 1.2 Al 8.8 O x Catalyst, denoted as catalyst D-Cat.

[0055] Cr 1.2 Al 8.8 O x Cr in catalyst 1.2 And Al 8.8 This refers to a molar ratio of Cr to Al of 1.2 / 8.8.

[0056] The catalyst performance evaluation test was the same as in Example 1.

[0057] Example 5

[0058] 4g of polyvinylpyrrolidone was dissolved in 20ml of purified water and stirred for 0.5h. Then, 1.1077g of Cr(NO3)3·9H2O and 5.8844g of Al(NO3)3·9H2O were added, and stirring was continued for 1h to obtain a homogeneous mixed solution. The resulting mixture was then added dropwise to liquid nitrogen to form a uniformly dispersed solid mixture. The resulting solid mixture, along with the remaining liquid nitrogen, was then placed in a vacuum freeze dryer and freeze-dried for 48h under the following conditions: temperature -85℃, vacuum degree 0.1Pa. Finally, the mixture was calcined in a muffle furnace at 600℃ for 5h to obtain Cr. 1.5 Al 8.5 O x Catalyst, denoted as catalyst E-Cat.

[0059] Cr 1.5 Al 8.5 O x Cr in catalyst 1.5 And Al 8.5 This refers to a molar ratio of Cr to Al of 1.5 / 8.5.

[0060] The catalyst performance evaluation test was the same as in Example 1.

[0061] Example 6

[0062] 4g of polyvinylpyrrolidone was dissolved in 20ml of purified water and stirred for 0.5h. Then, 1.3246g of Cr(NO3)3·9H2O and 5.6571g of Al(NO3)3·9H2O were added, and stirring was continued for 1h to obtain a homogeneous mixed solution. The resulting mixture was then added dropwise to liquid nitrogen to form a uniformly dispersed solid mixture. The resulting solid mixture, along with the remaining liquid nitrogen, was then placed in a vacuum freeze dryer and freeze-dried for 48h under the following conditions: temperature -85℃, vacuum degree 0.1Pa. Finally, the mixture was calcined in a muffle furnace at 600℃ for 5h to obtain Cr. 1.8 Al 8.2 O x Catalyst, denoted as catalyst F-Cat.

[0063] Cr 1.8 Al 8.2 O x Cr in catalyst 1.8 And Al 8.2 This refers to a molar ratio of Cr to Al of 1.8 / 8.2.

[0064] The catalyst performance evaluation test was the same as in Example 1.

[0065] Example 7

[0066] 4g of polyvinylpyrrolidone was dissolved in 20ml of purified water and stirred for 0.5h. Then, 1.4684g of Cr(NO3)3·9H2O and 5.5065g of Al(NO3)3·9H2O were added, and stirring was continued for 1h to obtain a homogeneous mixed solution. The resulting mixture was then added dropwise to liquid nitrogen to form a uniformly dispersed solid mixture. The resulting solid mixture, along with the remaining liquid nitrogen, was then placed in a vacuum freeze dryer and freeze-dried for 48h under the following conditions: temperature -85℃, vacuum degree 0.1Pa. Finally, the mixture was calcined in a muffle furnace at 600℃ for 5h to obtain Cr2Al8O. x Catalyst, denoted as catalyst G-Cat.

[0067] Cr2Al8O x In the catalyst, Cr2 and Al8 refer to a molar ratio of Cr to Al of 2 / 8.

[0068] The catalyst performance evaluation test was the same as in Example 1.

[0069] Example 8

[0070] 4g of polyvinylpyrrolidone was dissolved in 20ml of water and stirred for 0.5h. Then, 0.7384g of Cr(NO3)3·9H2O, 6.1610g of Al(NO3)3·9H2O, and 0.0792g of Zr(NO3)4·5H2O (Sinopharm Chemical Reagent Co., Ltd., CAS: 13986-27-1, analytical grade) were added and stirred for another 1h to obtain a homogeneous mixed solution. The resulting mixture was then added dropwise to liquid nitrogen to form a uniformly dispersed solid mixture. The resulting solid mixture, along with the remaining liquid nitrogen, was then placed in a vacuum freeze dryer and freeze-dried for 48h under the following conditions: temperature -85℃, vacuum degree 0.1Pa. Finally, the mixture was calcined in a muffle furnace at 600℃ for 5h to obtain Cr1Zr. 0.1 Al 8.9 O x Catalyst, denoted as catalyst H-Cat.

[0071] Cr1Zr 0.1 Al 8.9 O x Cr1 and Zr in the catalyst 0.1 And Al 8.9 This refers to the molar ratio of Cr, Zr, and Al elements being 1 / 0.1 / 8.9.

[0072] The catalyst performance evaluation test was the same as in Example 1.

[0073] Example 9

[0074] 4g of polyvinylpyrrolidone was dissolved in 20ml of water and stirred for 0.5h. Then, 0.7466g of Cr(NO3)3·9H2O, 6.2294g of Al(NO3)3·9H2O, and 0.0188g of KNO3 (Sinopharm Chemical Reagent Co., Ltd., CAS: 7757-79-1, analytical grade) were added and stirred for another 1h to obtain a homogeneous mixed solution. The resulting mixture was then added dropwise to liquid nitrogen to form a uniformly dispersed solid mixture. The resulting solid mixture, along with the remaining liquid nitrogen, was then placed in a vacuum freeze dryer and freeze-dried for 48h under the following conditions: temperature -85℃, vacuum degree 0.1Pa. Finally, the mixture was calcined in a muffle furnace at 600℃ for 5h to obtain Cr1K. 0.1 Al 8.9 O x Catalyst, denoted as Catalyst I-Cat.

[0075] Cr1K 0.1 Al 8.9 O x Cr1, K in catalyst 0.1 And Al 8.9This refers to the molar ratio of Cr, K, and Al elements being 1 / 0.1 / 8.9.

[0076] The catalyst performance evaluation test was the same as in Example 1.

[0077] Example 10

[0078] 4g of polyvinylpyrrolidone was dissolved in 20ml of water and stirred for 0.5h. Then, 0.7444g of Cr(NO3)3·9H2O, 6.2112g of Al(NO3)3·9H2O, and 0.0439g of Ca(NO3)2·4H2O (Sinopharm Chemical Reagent Co., Ltd., CAS: 13477-34-4, analytical grade) were added and stirred for another 1h to obtain a homogeneous mixed solution. The resulting mixture was then added dropwise to liquid nitrogen to form a uniformly dispersed solid mixture. The resulting solid mixture, along with the remaining liquid nitrogen, was then placed in a vacuum freeze dryer and freeze-dried for 48h under the following conditions: temperature -85℃, vacuum degree 0.1Pa. Finally, the mixture was calcined in a muffle furnace at 600℃ for 5h to obtain Cr1Ca 0.1 Al 8.9 O x Catalyst, denoted as catalyst J-Cat.

[0079] Cr1Ca 0.1 Al 8.9 O x Cr1 and Ca in the catalyst 0.1 And Al 8.9 This refers to the molar ratio of Cr, Ca, and Al elements being 1 / 0.1 / 8.9.

[0080] The catalyst performance evaluation test was the same as in Example 1.

[0081] Example 11

[0082] 4g of polyvinylpyrrolidone was dissolved in 20ml of water and stirred for 0.5h. Then, 0.7437g of Cr(NO3)3·9H2O, 6.2057g of Al(NO3)3·9H2O, and 0.0540g of Co(NO3)2·6H2O (Sinopharm Chemical Reagent Co., Ltd., CAS: 10026-22-9, analytical grade) were added and stirred for another 1h to obtain a homogeneous mixed solution. The resulting mixture was then added dropwise to liquid nitrogen to form a uniformly dispersed solid mixture. The resulting solid mixture, along with the remaining liquid nitrogen, was then placed in a vacuum freeze dryer and freeze-dried for 48h under the following conditions: temperature -85℃, vacuum degree 0.1Pa. Finally, the mixture was calcined in a muffle furnace at 600℃ for 5h to obtain Cr1Co. 0.1 Al 8.9 O xCatalyst, denoted as catalyst K-Cat.

[0083] Cr1Co 0.1 Al 8.9 O x Cr1 and Co in catalyst 0.1 And Al 8.9 This refers to the molar ratio of Cr, Co, and Al elements being 1 / 0.1 / 8.9.

[0084] The catalyst performance evaluation test was the same as in Example 1.

[0085] Example 12

[0086] 4g of polyvinylpyrrolidone was dissolved in 20ml of water and stirred for 0.5h. Then, 0.7437g of Cr(NO3)3·9H2O, 6.2058g of Al(NO3)3·9H2O, and 0.0540g of Ni(NO3)2·6H2O (Sinopharm Chemical Reagent Co., Ltd., CAS: 13478-00-7, analytical grade) were added and stirred for another 1h to obtain a homogeneous mixed solution. The resulting mixture was then added dropwise to liquid nitrogen to form a uniformly dispersed solid mixture. The resulting solid mixture, along with the remaining liquid nitrogen, was then placed in a vacuum freeze dryer and freeze-dried for 48h under the following conditions: temperature -85℃, vacuum degree 0.1Pa. Finally, the mixture was calcined in a muffle furnace at 600℃ for 5h to obtain Cr1Ni. 0.1 Al 8.9 O x Catalyst, denoted as catalyst L-Cat.

[0087] Cr1Ni 0.1 Al 8.9 O x Cr1 and Ni in the catalyst 0.1 And Al 8.9 This refers to the molar ratio of Cr, Ni, and Al elements being 1 / 0.1 / 8.9.

[0088] The catalyst performance evaluation test was the same as in Example 1.

[0089] Example 13

[0090] 4g of polyvinylpyrrolidone was dissolved in 20ml of water and stirred for 0.5h. Then, 0.7435g of Cr(NO3)3·9H2O, 6.2039g of Al(NO3)3·9H2O, and 0.0552g of Zn(NO3)2·6H2O (Sinopharm Chemical Reagent Co., Ltd., CAS: 10196-18-6, analytical grade) were added and stirred for another 1h to obtain a homogeneous mixed solution. The resulting mixture was then added dropwise to liquid nitrogen to form a uniformly dispersed solid mixture. The resulting solid mixture, along with the remaining liquid nitrogen, was then placed in a vacuum freeze dryer and freeze-dried for 48h under the following conditions: temperature -85℃, vacuum degree 0.1Pa. Finally, the mixture was calcined in a muffle furnace at 600℃ for 5h to obtain Cr1Zn. 0.1 Al 8.9 O x Catalyst, denoted as catalyst M-Cat.

[0091] Cr1Zn 0.1 Al 8.9 O x Cr1 and Zn in the catalyst 0.1 And Al 8.9 This refers to the molar ratio of Cr, Zn, and Al elements being 1 / 0.1 / 8.9.

[0092] The catalyst performance evaluation test was the same as in Example 1.

[0093] Example 14

[0094] 0.2 mg of the catalyst C-Cat from Example 3 was used to test its reaction performance in a fixed-bed reactor (TORCH); the reaction conditions were: reaction temperature 580 °C; i-C4H 10 The N2 (volume ratio) is 1:6; at atmospheric pressure, the space velocity is 6 L·g. -1 ·h -1 The reaction tail gas was analyzed by Agilent 7890B gas chromatography, and the conversion rate and product selectivity were calculated using nitrogen as an internal standard. The initial and final reaction data within 20 hours after the introduction of isobutane are shown in Table 2.

[0095] Example 15

[0096] 0.2 mg of the catalyst C-Cat from Example 3 was used to test its reaction performance in a fixed-bed reactor (TORCH); the reaction conditions were: reaction temperature 620 °C; i-C4H 10 The N2 (volume ratio) is 1:6; at atmospheric pressure, the space velocity is 6 L·g. -1 ·h -1The reaction tail gas was analyzed by Agilent 7890B gas chromatography, and the conversion rate and product selectivity were calculated using nitrogen as an internal standard. The initial and final reaction data within 20 hours after the introduction of isobutane are shown in Table 2.

[0097] Comparative Example 2

[0098] Weigh 2.3478 g of Cr(NO3)3·9H2O into an appropriate amount of pure water, stir to dissolve, and then add the solution dropwise to 2.7 g of Al2O3 support. Then, put the resulting solid mixture into an oven and dry it at 100 °C for 10 h. Finally, calcine it in a muffle furnace at 600 °C for 5 h to obtain the Cr / Al2O3-1-9 catalyst, denoted as catalyst O-Cat.

[0099] The molar ratio of Cr to Al in the Cr / Al2O3-1-9 catalyst is 1 / 9 (theoretical calculation).

[0100] The catalyst performance evaluation test was the same as in Example 1.

[0101] Comparative Example 3

[0102] The catalyst in Example 1 of the invention patent application CN201510980445.5 (Xiao Junping, Industrial preparation method of chromium series micro spherical fluidized bed isobutane dehydrogenation catalyst, 2016-04-06) is denoted as catalyst P-Cat.

[0103] Comparative Example 4

[0104] In the literature “Catalytic dehydrogenation of isobutane over ordered mesoporousCr2O3–Al2O3 composite oxides” (Catalysis Communications, 2013, 35: 76-81), the catalyst OMA-10Cr is denoted as catalyst Q-Cat.

[0105] Table 2 Performance of the catalyst in the direct dehydrogenation reaction of isobutane

[0106]

[0107] Comparing Examples 1-7, it can be seen that with the increase of Cr content in the catalyst, the isobutane conversion and isobutene selectivity first increase and then decrease. The highest conversion and selectivity are achieved when the Cr to Al ratio is 1 / 9, at 61% and 91%, respectively. Furthermore, this catalyst maintains a low deactivation rate of only 0.07h during the 20h reaction performance test. -1 .

[0108] Comparing Examples 3, 9, and 10, according to the data in Table 2, it can be seen that adding a small amount of alkali metal promoter to the catalyst will cause a certain degree of decrease in the isobutane conversion rate, while the isobutene selectivity will be greatly improved, reaching 98%-99%.

[0109] Comparing Examples 3, 8, 11, 12 and 13, the data in Table 2 show that adding a small amount of transition metal additive to the catalyst can improve the isobutane conversion rate to a certain extent, while the isobutene selectivity does not change much.

[0110] Comparing Examples 3, 14, and 15, the data in Table 2 shows that the catalyst's activity increases significantly with increasing reaction temperature. However, when the reaction temperature is too high, the isobutylene selectivity decreases significantly. The catalyst maintains high activity and high isobutylene selectivity (89-91%) at a reaction temperature of 600°C.

[0111] According to Table 2, as can be seen from Comparative Examples 1 and 2, the catalysts prepared by the PVP template method (catalysts A-Cat and C-Cat in Examples 1 and 3) have higher isobutane conversion and isobutene selectivity than the catalysts P-Cat and O-Cat prepared by the conventional impregnation method, and have better stability and lower deactivation rate during the reaction.

[0112] According to Table 2, the isobutane conversion and isobutene selectivity of the catalyst prepared by the PVP template method (catalyst C-Cat in Example 3) are higher than those of the currently reported chromium-based catalysts (catalysts P-Cat and Q-Cat in Comparative Examples 3 and 4).

Claims

1. The application of a catalyst as a catalyst for the dehydrogenation of isobutane to prepare isobutene, characterized in that, The preparation method of the catalyst includes the following steps: Weigh polyvinylpyrrolidone and dissolve it in pure water. Then add the required amounts of Cr(NO3)3·9H2O and Al(NO3)3·9H2O and continue stirring to obtain a homogeneous mixed solution. Then add the obtained mixed solution dropwise to liquid nitrogen to form a uniformly dispersed solid mixture. Next, put the obtained solid mixture together with the unevaporated liquid nitrogen into a vacuum freeze dryer for vacuum freeze drying. Finally, calcine it in a muffle furnace to obtain the catalyst. In the mixed solution, the ratio of polyvinylpyrrolidone to purified water is 1-6 g: 20 ml, and the total mass of Cr(NO3)3·9H2O and Al(NO3)3·9H2O is 7 g: 1-6 g of polyvinylpyrrolidone; the calcination temperature is 550-600 ℃, and the time is 4-6 h; In the catalyst, the active component is CrO x , where x=1~3, and Al2O3 is the carrier.

2. The application according to claim 1, characterized in that, Polyvinylpyrrolidone: purified water: (total mass of Cr(NO3)3·9H2O and Al(NO3)3·9H2O) is 4g : 20ml : 7g; the stirring time is 1h; the vacuum freeze-drying conditions are: temperature -85℃, vacuum degree 0.1Pa, drying time 48h.

3. The application according to claim 1, characterized in that, Al(NO3)3·9H2O is partially replaced by soluble transition metal salts, alkali metal salts, transition metal salt hydrates, alkali metal salt hydrates, or hydroxides of transition metals or alkali metals. The total mass of the transition metal salts, alkali metal salts, transition metal salt hydrates, alkali metal salt hydrates, or hydroxides of transition metals or alkali metals and Al(NO3)3·9H2O after partial replacement is the same as the mass of Al(NO3)3·9H2O before partial replacement.

4. The application according to claim 3, characterized in that, The molar amount of Cr in the catalyst is 5% to 20% of the total molar amount of transition metal or alkali metal elements M, Al, and Cr in the catalyst.

5. The application according to claim 3, characterized in that, The molar amount of transition metal element or alkali metal element M in the catalyst is 0.1% to 20% of the total molar amount of transition metal element or alkali metal element M, Al element and Cr element in the catalyst.

6. The application according to claim 4 or 5, characterized in that, The transition metal element or alkali metal element M is Zr, Ni, Zn, Co, or K.

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