Catalyst for preparing isobutene through direct dehydrogenation of isobutane as well as preparation method and application of catalyst

Abstract

The invention belongs to the technical field of olefin catalysts prepared through alkane dehydrogenation, and particularly discloses a catalyst for preparing isobutene through direct dehydrogenation of isobutane as well as a preparation method and application of the catalyst. According to the preparation method, polyvinylpyrrolidone, Cr (NO3) 3.9 H2O and Al (NO3) 3.9 H2O are used as raw materials, and the catalyst is obtained through stirring and mixing, liquid nitrogen solidification, vacuum freeze drying and calcination. Wherein the Cr species is CrOx (x = 1-3) which is an active component playing a catalytic role, and the aluminum species is Al2O3 which plays a carrier role and is used for dispersing the active component. A small amount of transition metal or alkali metal can be introduced as an auxiliary agent. The catalyst disclosed by the invention has a relatively high specific surface area, the dispersity of a Cr element can be remarkably improved, and the activity of the catalyst in a catalytic reaction is improved; the interaction between Cr and the carrier is increased, and the stability of the reaction for producing isobutene through dehydrogenation of isobutane is remarkably enhanced; and the reaction temperature range of the reaction suitable for preparing isobutene through isobutane dehydrogenation is wide.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts for preparing olefins by dehydrogenating alkanes, and in particular relates to a catalyst for preparing isobutylene by directly dehydrogenating isobutane, and a preparation method and application thereof. Background Art

[0002] Isobutane dehydrogenation product isobutene, an important chemical intermediate raw material, is widely used in the synthesis of various organic chemicals such as polyisobutene, tert-butyl alcohol, methyl tert-butyl ether, butyl rubber, methacrylonitrile and antioxidants. With the continuous development and use of downstream chemical products, the demand for isobutene at home and abroad is also gradually increasing. my country has abundant C4 resources, among which the isobutane content is relatively large. A large part of isobutane is used to produce civilian fuels, resulting in a waste of resources. The preparation of high-value-added isobutene by isobutane dehydrogenation reaction can improve the chemical utilization rate of isobutane, meet the growing market demand, and bring more economic benefits to the petrochemical industry.

[0003] There are two main types of industrial isobutane dehydrogenation catalysts: one is platinum-based precious metal catalysts, and the other is chromium-based catalysts. Platinum-based catalysts are expensive and have problems such as difficulty in dispersion, sintering and carbon deposition during the reaction. Compared with precious metal catalysts, chromium-based catalysts are relatively cheap and have relatively low requirements for impurities in the raw materials, but they also generally have the problem of poor stability. Therefore, extending the regeneration cycle of chromium-based catalysts is an important means to further improve their economic benefits. Traditional chromium-based isobutane dehydrogenation catalysts are mainly prepared by impregnation, which is prone to uneven dispersion of active components. To this end, Li Li et al. summarized the effects of different carriers and additives on the dehydrogenation reaction and found that smaller pore structures can improve the selectivity of the reaction; the weakly acidic sites on the carrier surface, the high dispersion of active components on the surface, and the alkaline additives are conducive to improving the catalyst's anti-carbon deposition performance and improving its stability. Wang Zongting et al. prepared Cr-K-γCr2O3 / Al2O3 catalyst by microwave method and evaluated its performance. The microwave method can improve the dispersion of active components and reduce the grain size of active components in the catalyst. The activity, stability and wear resistance of the prepared catalyst are improved.

[0004] In order to solve the problem of rapid deactivation rate of chromium-based catalysts, it is necessary to develop a new catalyst preparation method to improve the dispersion of the active components of the catalyst and improve its stability. Summary of the invention

[0005] In view of the problems of uneven distribution of active components and poor stability of chromium-based catalysts in the prior art, the present invention aims to provide a catalyst for dehydrogenating isobutane to isobutylene and a preparation method and application thereof. The preparation method uses PVP as a template agent, introduces Cr ions and Al ions into a solution containing the template agent to obtain a CrO catalyst with a high specific surface area and high active component dispersion. x A mixed oxide catalyst formed by (x=1-3) and Al2O3 is prepared, thereby improving the interaction between the components in the catalyst and increasing the stability of the catalytic reaction; further, a small amount of additives such as transition metals or alkali metals are introduced during the catalyst preparation process to increase the dispersion of the active components in the catalyst and the interaction with the carrier, thereby improving the adsorption of alkane molecules on the active sites and reducing the number of strong acid sites in the carrier, so that the activity or selectivity of the catalyst is further improved.

[0006] The preparation method of the present invention has a wide range of suitable reaction temperatures, has high stability and olefin selectivity at high temperatures, and can maintain a high conversion rate at lower reaction temperatures. The preparation method has easy-to-obtain raw materials, a simple process, good reproducibility, and has important application value.

[0007] The present invention provides a method for preparing a catalyst for preparing isobutylene by direct dehydrogenation of isobutane, comprising the following steps:

[0008] Weigh polyvinyl pyrrolidone and dissolve it in pure water, then add the required amount of Cr(NO3)3·9H2O and Al(NO3)3·9H2O, continue stirring to obtain a uniform mixed solution, then add the obtained mixed solution drop by drop into liquid nitrogen to form a uniformly dispersed solid mixture, then put the obtained solid mixture together with the unvolatile liquid nitrogen into a vacuum freeze dryer for vacuum freeze drying, and finally calcine in a muffle furnace to obtain the catalyst.

[0009] Furthermore, in the mixed solution, the ratio of polyvinyl pyrrolidone to pure water is 1g:20ml to 6g:20ml, and the ratio of polyvinyl pyrrolidone to (the total mass of Cr(NO3)3·9H2O and Al(NO3)3·9H2O) is 1g:7g to 6g:7g, preferably, the ratio of polyvinyl pyrrolidone to pure water to (the 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°C, vacuum degree 0.1Pa, drying time 48h; the calcination temperature is 550-650°C, preferably 600°C, and the time is 4-6h, preferably 5h.

[0010] Furthermore, a soluble transition metal salt, alkali metal salt, transition metal salt hydrate, alkali metal salt hydrate or transition metal hydroxide, alkali metal hydroxide is used as an auxiliary agent to partially replace Al(NO3)3·9H2O, and the total mass of the transition metal salt, alkali metal salt, transition metal salt hydrate, alkali metal salt hydrate or transition metal hydroxide, alkali metal hydroxide 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 the Cr element in the catalyst is 5% to 20% of the total molar amount of the transition metal element or alkali metal element M, the Cr element, and the Al element in the catalyst. Preferably, M = Zr, Ni, Zn, Co, K, Ca.

[0012] Furthermore, the molar amount of the transition metal element or alkali metal element M in the catalyst is 0.1% to 20% of the total molar amount of the M element, Al element and Cr element 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 a carrier used to disperse active components.

[0014] Furthermore, the catalyst also includes an auxiliary agent 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 components and reducing the acidity of the carrier.

[0015] Furthermore, the molar amount of Cr element in the catalyst is 5% to 20% of the total molar amount of Cr element, Al element and auxiliary metal element 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 the auxiliary metal element M, Al element and Cr element in the catalyst.

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

[0018] A method for preparing isobutylene, wherein the catalyst of the present invention is used to catalyze the dehydrogenation of isobutane to obtain isobutylene, and the method specifically comprises the following steps: loading the catalyst into a fixed bed reactor, and reacting in the fixed bed reactor, wherein the reaction conditions are: the amount of the catalyst 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 normal pressure, and the space velocity is 6-18 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 the internal standard.

[0019] Further, the reaction temperature is 500-600°C, preferably 600°C; i-C4H 10 The volume ratio of N2 is 1:6 to 1:1, preferably 1:6; the air velocity is 6 to 12 L·g -1 ·h -1 , more preferably 6 L·g -1 ·h -1 .

[0020] Compared with the catalyst for catalyzing the dehydrogenation of isobutane to prepare isobutene in the prior art, 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 , mainly Cr2O3, which is the active component for catalysis, and the aluminum species is Al2O3, which acts as a carrier for dispersing the active components.

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

[0023] (3) A small amount of transition metal elements or alkaline metal elements introduced into the catalyst of the present invention as an auxiliary agent can improve the dispersion of the active component and the interaction between the active component and the carrier, enhance the adsorption of alkane molecules by the active site, reduce the number of strong acid sites in the carrier, and further improve the activity or selectivity of the catalyst. In the catalytic reaction, transition metal elements also show weak catalytic activity; while alkali metal elements reduce the catalytic activity of the active component and improve the selectivity.

[0024] (4) The catalyst of the present invention can maintain a relatively high activity at a reaction temperature of 500 to 650°C; the reaction temperature range of the isobutane dehydrogenation reaction to produce isobutene is relatively wide. Within the reaction temperature range of 500 to 600°C, the isobutene selectivity can be maintained at a high level, while the selectivity of by-products such as CH4, ethane, propane, propylene, butane, and CO2 is relatively low.

[0025] (5) The preparation method of the catalyst of the present invention is simple, the raw materials are easily available, and the reproducibility is good. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0027] Figure 2 A transmission electron micrograph of a mixed oxide catalyst formed by Cr2O3 and Al2O3 prepared in Example 1;

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

[0029] Figure 4 is a transmission electron microscopy image of the commercial alumina-supported chromium-based catalyst in Comparative Example 1;

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

[0031] The technical solution of the present invention is further described below in conjunction with the embodiments, but the embodiments are not intended to limit the protection scope of the present invention.

[0032] Example 1

[0033] 4 g of polyvinyl pyrrolidone (PVP, Sinopharm Chemical Reagent Co., Ltd., CAS: 9003-39-8, K30, analytical grade, the same below) was weighed and dissolved in 20 ml of pure water, stirred for 0.5 h, and then 0.3735 g of Cr(NO3)3·9H2O (Sinopharm Chemical Reagent Co., Ltd., CAS: 7789-02-8, analytical grade, the same below) and 6.6535 g of Al(NO3)3·9H2O (Sinopharm Chemical Reagent Co., Ltd., CAS: 7784-27-2, analytical grade, the same below) were added, and stirring was continued for 1 h to obtain a uniform mixed solution, and then the obtained mixed solution was added dropwise into liquid nitrogen to form a uniformly dispersed solid mixture, and then the obtained solid mixture was placed in a vacuum freeze dryer together with the unvolatile liquid nitrogen for vacuum freeze drying for 48 h. The vacuum freeze drying conditions were: temperature -85 ° C, vacuum degree 0.1 Pa, and finally calcined at 600 ° C in a muffle furnace for 5 h 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 It means that the molar ratio of Cr element to Al element is 0.5 / 9.5, i.e. 1 / 19 (theoretical calculated value, the same as in the following embodiments).

[0035] The catalyst performance evaluation test was carried out in a fixed bed reactor (TORCH) under the following reaction conditions: the catalyst dosage was 0.2 mg; the reaction temperature was 600 °C; i-C4H 10 :N2 (volume ratio) is 1:6; normal pressure, air velocity is 6L·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 the 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 in an appropriate amount of pure water, stir to dissolve, and then add the solution dropwise onto 2.85 g of Al2O3 (Sinopharm Chemical Reagent Co., Ltd., CAS: 1344-28-1, analytical grade, the same below) carrier, and then put the resulting solid mixture into an oven and dry it at 100°C for 10 h, and finally calcine it at 600°C in a muffle furnace for 5 h to obtain a Cr / Al2O3-1-19 catalyst, recorded as catalyst N-Cat.

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

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

[0040] For 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 by a nitrogen physical adsorption-desorption instrument. The results are listed in Table 1. The nitrogen physical adsorption-desorption isotherms are shown in Table 1. Figure 1 shown.

[0041] Table 1 Nitrogen physical adsorption-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 0.5 Al 9.5 O x The catalyst has a high specific surface area, which is conducive to the dispersion of active components, increases the contact area between active components and reactants, and improves its catalytic reaction activity and stability.

[0044] For Cr in Example 1 0.5 Al 9.5 O x The catalysts were characterized by scanning transmission electron microscopy. Figure 2 and 3 As shown in the figure, it can be seen that Cr 0.5 Al 9.5 O x The catalyst is in the form of thin flakes, and the active components are evenly dispersed. The Cr / Al2O3-1-19 catalyst in Comparative Example 1 was characterized by scanning transmission electron microscopy, and the resulting image is as follows: Figure 4 and 5 As shown in the figure, it can be seen that the dispersion of active components of Cr / Al2O3-1-19 catalyst is lower than that of Cr 0.5 Al 9.5 O x Catalyst. Among them, Figure 3 and Figure 5 It is a high-angle annular dark field image. Figure 3 This indicates that the Cr species are evenly distributed in the catalyst, and no special bright-colored areas appear; Figure 5 There are obvious bright areas in the graph, indicating that Cr species are accumulated and poorly dispersed.

[0045] Example 2

[0046] 4 g of polyvinyl pyrrolidone was dissolved in 20 ml of pure water and stirred for 0.5 h. Then, 0.5955 g of Cr(NO3)3·9H2O and 6.4209 g of Al(NO3)3·9H2O were added and stirred for 1 h to obtain a uniform mixed solution. The obtained mixed solution was then added dropwise into liquid nitrogen to form a uniformly dispersed solid mixture. The obtained solid mixture was then placed in a vacuum freeze dryer together with the unvolatile liquid nitrogen and vacuum freeze-dried for 48 h. The vacuum freeze-drying conditions were: temperature -85 ° C, vacuum degree 0.1 Pa, and finally calcined at 600 ° C in a muffle furnace for 5 h 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 It means that the molar ratio of Cr element to Al element is 0.8 / 9.2.

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

[0049] Example 3

[0050] 4 g of polyvinyl pyrrolidone was weighed and dissolved in 20 ml of pure water, stirred for 0.5 h, then 0.7427 g of Cr(NO3)3·9H2O and 6.2667 g of Al(NO3)3·9H2O were added, and the stirring was continued for 1 h to obtain a uniform mixed solution, and then the obtained mixed solution was added dropwise into liquid nitrogen to form a uniformly dispersed solid mixture, and then the obtained solid mixture was placed in a vacuum freeze dryer together with the unvolatile liquid nitrogen for vacuum freeze drying for 48 h. The vacuum freeze drying conditions were: temperature -85 ° C, vacuum degree 0.1 Pa, and finally calcined at 600 ° C in a muffle furnace for 5 h to obtain Cr1Al9O x Catalyst, denoted as catalyst C-Cat.

[0051] Cr1Al9O x Cr1 and Al9 in the catalyst means that the molar ratio of Cr element to Al element is 1 / 9.

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

[0053] Example 4

[0054] Weigh 4 g of polyvinyl pyrrolidone and dissolve it in 20 ml of pure water, stir for 0.5 h, then add 0.8892 g of Cr(NO3)3·9H2O and 6.1132 g of Al(NO3)3·9H2O, continue stirring for 1 h to obtain a uniform mixed solution, then add the obtained mixed solution drop by drop into liquid nitrogen to form a uniformly dispersed solid mixture, then put the obtained solid mixture together with the unvolatile liquid nitrogen into a vacuum freeze dryer for vacuum freeze drying for 48 h. The vacuum freeze drying conditions are: temperature -85 ° C, vacuum degree 0.1 Pa, and finally calcined at 600 ° C in a muffle furnace for 5 h 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 It means that the molar ratio of Cr element to Al element is 1.2 / 8.8.

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

[0057] Example 5

[0058] Weigh 4 g of polyvinyl pyrrolidone and dissolve it in 20 ml of pure water, stir for 0.5 h, then add 1.1077 g of Cr(NO3)3·9H2O and 5.8844 g of Al(NO3)3·9H2O, continue stirring for 1 h to obtain a uniform mixed solution, then add the obtained mixed solution drop by drop into liquid nitrogen to form a uniformly dispersed solid mixture, then put the obtained solid mixture together with the unvolatile liquid nitrogen into a vacuum freeze dryer for vacuum freeze drying for 48 h. The vacuum freeze drying conditions are: temperature -85 ° C, vacuum degree 0.1 Pa, and finally calcine at 600 ° C in a muffle furnace for 5 h 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 It means that the molar ratio of Cr element to Al element is 1.5 / 8.5.

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

[0061] Example 6

[0062] 4 g of polyvinyl pyrrolidone was weighed and dissolved in 20 ml of pure water, stirred for 0.5 h, then 1.3246 g of Cr(NO3)3·9H2O and 5.6571 g of Al(NO3)3·9H2O were added, and stirring was continued for 1 h to obtain a uniform mixed solution, and then the obtained mixed solution was added dropwise into liquid nitrogen to form a uniformly dispersed solid mixture, and then the obtained solid mixture together with the unvolatile liquid nitrogen was placed in a vacuum freeze dryer for vacuum freeze drying for 48 h. The vacuum freeze drying conditions were: temperature -85 ° C, vacuum degree 0.1 Pa, and finally calcined at 600 ° C in a muffle furnace for 5 h 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 It means that the molar ratio of Cr element to Al element is 1.8 / 8.2.

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

[0065] Example 7

[0066] 4 g of polyvinyl pyrrolidone was weighed and dissolved in 20 ml of pure water, stirred for 0.5 h, then 1.4684 g of Cr(NO3)3·9H2O and 5.5065 g of Al(NO3)3·9H2O were added, and the stirring was continued for 1 h to obtain a uniform mixed solution, and then the obtained mixed solution was added dropwise into liquid nitrogen to form a uniformly dispersed solid mixture, and then the obtained solid mixture together with the unvolatile liquid nitrogen was placed in a vacuum freeze dryer for vacuum freeze drying for 48 h. The vacuum freeze drying conditions were: temperature -85 ° C, vacuum degree 0.1 Pa, and finally calcined at 600 ° C in a muffle furnace for 5 h to obtain Cr2Al8O x Catalyst, denoted as catalyst G-Cat.

[0067] Cr2Al8O x Cr2 and Al8 in the catalyst means that the molar ratio of Cr element to Al element is 2 / 8.

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

[0069] Example 8

[0070] Weigh 4 g of polyvinyl pyrrolidone and dissolve it in 20 ml of water, stir for 0.5 h, then add 0.7384 g of Cr(NO3)3·9H2O, 6.1610 g of Al(NO3)3·9H2O, and 0.0792 g of Zr(NO3)4·5H2O (Sinopharm Chemical Reagent Co., Ltd., CAS: 13986-27-1, analytical grade), continue stirring for 1 h to obtain a uniform mixed solution, then add the obtained mixed solution drop by drop into liquid nitrogen to form a uniformly dispersed solid mixture, then put the obtained solid mixture together with the unvolatile liquid nitrogen into a vacuum freeze dryer for vacuum freeze drying for 48 h, and the vacuum freeze drying conditions are: temperature -85 ° C, vacuum degree 0.1 Pa, and finally calcine at 600 ° C in a muffle furnace for 5 h 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, Zr in catalyst 0.1 and Al 8.9 It means that the molar ratio of Cr element, Zr element and Al element is 1 / 0.1 / 8.9.

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

[0073] Example 9

[0074] 4 g of polyvinyl pyrrolidone was weighed and dissolved in 20 ml of water, stirred for 0.5 h, and then 0.7466 g of Cr(NO3)3·9H2O, 6.2294 g of Al(NO3)3·9H2O, and 0.0188 g of KNO3 (Sinopharm Chemical Reagent Co., Ltd., CAS: 7757-79-1, analytical grade) were added, and stirring was continued for 1 h to obtain a uniform mixed solution, and then the obtained mixed solution was added dropwise into liquid nitrogen to form a uniformly dispersed solid mixture, and then the obtained solid mixture was placed in a vacuum freeze dryer together with the unvolatile liquid nitrogen for vacuum freeze drying for 48 h. The vacuum freeze drying conditions were: temperature -85 ° C, vacuum degree 0.1 Pa, and finally calcined at 600 ° C in a muffle furnace for 5 h 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 8.9It means that the molar ratio of Cr element, K element and Al element is 1 / 0.1 / 8.9.

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

[0077] Example 10

[0078] Weigh 4 g of polyvinyl pyrrolidone and dissolve it in 20 ml of water, stir for 0.5 h, then add 0.7444 g Cr(NO3)3·9H2O, 6.2112 g Al(NO3)3·9H2O, and 0.0439 g Ca(NO3)2·4H2O (Sinopharm Chemical Reagent Co., Ltd., CAS: 13477-34-4, analytical grade), continue stirring for 1 h to obtain a uniform mixed solution, then add the obtained mixed solution drop by drop into liquid nitrogen to form a uniformly dispersed solid mixture, then put the obtained solid mixture together with the unvolatile liquid nitrogen into a vacuum freeze dryer for vacuum freeze drying for 48 h, and the vacuum freeze drying conditions are: temperature -85 ° C, vacuum degree 0.1 Pa, and finally calcine at 600 ° C in a muffle furnace for 5 h 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, Ca in catalyst 0.1 and Al 8.9 It means that the molar ratio of Cr element, Ca element and Al element is 1 / 0.1 / 8.9.

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

[0081] Embodiment 11

[0082] 4 g of polyvinyl pyrrolidone was weighed and dissolved in 20 ml of water, stirred for 0.5 h, and then 0.7437 g of Cr(NO3)3·9H2O, 6.2057 g of Al(NO3)3·9H2O, and 0.0540 g of Co(NO3)2·6H2O (Sinopharm Chemical Reagent Co., Ltd., CAS: 10026-22-9, analytical grade) were added, and stirring was continued for 1 h to obtain a uniform mixed solution, and then the obtained mixed solution was added dropwise into liquid nitrogen to form a uniformly dispersed solid mixture, and then the obtained solid mixture was placed in a vacuum freeze dryer together with the unvolatile liquid nitrogen for vacuum freeze drying for 48 h. The vacuum freeze drying conditions were: temperature -85 ° C, vacuum degree 0.1 Pa, and finally calcined at 600 ° C in a muffle furnace for 5 h 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, Co in catalyst 0.1 and Al 8.9 It means that the molar ratio of Cr element, Co element and Al element is 1 / 0.1 / 8.9.

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

[0085] Example 12

[0086] Weigh 4 g of polyvinyl pyrrolidone and dissolve it in 20 ml of water, stir for 0.5 h, then add 0.7437 g of Cr(NO3)3·9H2O, 6.2058 g of Al(NO3)3·9H2O, and 0.0540 g of Ni(NO3)2·6H2O (Sinopharm Chemical Reagent Co., Ltd., CAS:13478-00-7, analytical grade), continue stirring for 1 h to obtain a uniform mixed solution, then add the obtained mixed solution drop by drop into liquid nitrogen to form a uniformly dispersed solid mixture, then put the obtained solid mixture together with the unvolatile liquid nitrogen into a vacuum freeze dryer for vacuum freeze drying for 48 h, and the vacuum freeze drying conditions are: temperature -85 ° C, vacuum degree 0.1 Pa, and finally calcine at 600 ° C in a muffle furnace for 5 h 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, Ni in catalyst 0.1 and Al 8.9 It means that the molar ratio of Cr element, Ni element and Al element is 1 / 0.1 / 8.9.

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

[0089] Example 13

[0090] Weigh 4 g of polyvinyl pyrrolidone and dissolve it in 20 ml of water, stir for 0.5 h, then add 0.7435 g of Cr(NO3)3·9H2O, 6.2039 g of Al(NO3)3·9H2O, and 0.0552 g of Zn(NO3)2·6H2O (Sinopharm Chemical Reagent Co., Ltd., CAS:10196-18-6, analytical grade), continue stirring for 1 h to obtain a uniform mixed solution, then add the obtained mixed solution drop by drop into liquid nitrogen to form a uniformly dispersed solid mixture, then put the obtained solid mixture together with the unvolatile liquid nitrogen into a vacuum freeze dryer for vacuum freeze drying for 48 h, and the vacuum freeze drying conditions are: temperature -85 ° C, vacuum degree 0.1 Pa, and finally calcine at 600 ° C in a muffle furnace for 5 h 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, Zn in catalyst 0.1 and Al 8.9 It means that the molar ratio of Cr element, Zn element and Al element is 1 / 0.1 / 8.9.

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

[0093] Embodiment 14

[0094] 0.2 mg of the catalyst C-Cat in Example 3 was taken and the reaction performance was tested in a fixed bed reactor (TORCH); the reaction conditions were: reaction temperature 580°C; i-C4H 10 :N2 (volume ratio) is 1:6; normal pressure, air velocity is 6L·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 the internal standard. The initial and final reaction data within 20 hours after the introduction of isobutane are shown in Table 2.

[0095] Embodiment 15

[0096] 0.2 mg of the catalyst C-Cat in Example 3 was taken and the reaction performance was tested in a fixed bed reactor (TORCH); the reaction conditions were: reaction temperature 620°C; i-C4H 10 :N2 (volume ratio) is 1:6; normal pressure, air velocity is 6L·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 the 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 onto 2.7 g of Al2O3 carrier. Then, put the obtained solid mixture into an oven and dry it at 100°C for 10 h. Finally, calcine it at 600°C in a muffle furnace for 5 h to obtain Cr / Al2O3-1-9 catalyst, which is recorded as catalyst O-Cat.

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

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

[0101] Comparative Example 3

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

[0103] Comparative Example 4

[0104] The catalyst OMA-10Cr in the document “Catalytic dehydrogenation of isobutane over ordered mesoporous Cr2O3–Al2O3 composite oxides” (Catalysis Communications, 2013, 35: 76-81) is denoted as catalyst Q-Cat.

[0105] Table 2 Catalyst performance for direct dehydrogenation of isobutane

[0106]

[0107] Comparison of Examples 1 to 7 shows that with the increase of Cr content in the catalyst, the isobutane conversion rate and isobutene selectivity first increase and then decrease. When the Cr to Al ratio is 1 / 9, the conversion rate and selectivity are the highest, which are 61% and 91%, respectively. In addition, the catalyst also maintains a low deactivation rate of only 0.07h in the 20h reaction performance test. -1 .

[0108] Comparing Example 3, Example 9, and Example 10, it can be seen from the data in Table 2 that when a small amount of alkali metal additive is added to the catalyst, the isobutane conversion rate of the catalyst will decrease to a certain extent, while the isobutene selectivity will be greatly improved to 98%-99%.

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

[0110] Comparing Example 3, Example 14, and Example 15, according to the data in Table 2, it can be seen that as the reaction temperature increases, the reaction activity of the catalyst will increase significantly, but when the reaction temperature is too high, the isobutylene selectivity decreases significantly. The catalyst has a high isobutylene selectivity (89-91%) while maintaining a high activity at a reaction temperature of 600°C.

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

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

Claims

1. A method for preparing a catalyst for direct dehydrogenation of isobutane to prepare isobutene, comprising the following steps: Weigh polyvinyl pyrrolidone and dissolve it in pure water, then add the required amount of Cr(NO3)3·9H2O and Al(NO3)3·9H2O, continue stirring to obtain a uniform mixed solution, then add the obtained mixed solution drop by drop into liquid nitrogen to form a uniformly dispersed solid mixture, then put the obtained solid mixture together with the unvolatile liquid nitrogen into a vacuum freeze dryer for vacuum freeze drying, and finally calcine in a muffle furnace to obtain the catalyst.

2. The preparation method according to claim 1, characterized in that: In the mixed solution, the ratio of polyvinyl pyrrolidone to pure water is 1-6 g: 20 ml, and the ratio of polyvinyl pyrrolidone to (the total mass of Cr(NO3)3·9H2O and Al(NO3)3·9H2O) is 1-6 g: 7 g, preferably polyvinyl pyrrolidone to pure water to (the total mass of Cr(NO3)3·9H2O and Al(NO3)3·9H2O) is 4 g: 20 ml: 7 g; the stirring time is 1 hour; the vacuum freeze-drying conditions are: temperature -85°C, vacuum degree 0.1 Pa, and drying time 48 hours; the calcination temperature is 550-650°C, preferably 600°C, and the time is 4-6 hours, preferably 5 hours.

3. The preparation method according to claim 1, characterized in that: A soluble transition metal salt, alkali metal salt, transition metal salt hydrate, alkali metal salt hydrate or transition metal hydroxide, alkali metal hydroxide is used to partially replace Al(NO3)3·9H2O. The total mass of the transition metal salt, alkali metal salt, transition metal salt hydrate, alkali metal salt hydrate or transition metal hydroxide, alkali metal hydroxide and Al(NO3)3·9H2O after the partial replacement is the same as the mass of Al(NO3)3·9H2O before the partial replacement.

4. The preparation method according to claim 3, characterized in that: The molar amount of the Cr element in the catalyst is 5% to 20% of the total molar amount of the transition metal element or alkali metal element M, Al element, and Cr element in the catalyst; preferably, the transition metal element or alkali metal element M is Zr, Ni, Zn, Co, K, or Ca.

5. The preparation method according to claim 4, characterized in that: The molar amount of the transition metal element or alkali metal element M in the catalyst is 0.1% to 20% of the total molar amount of the transition metal element or alkali metal element M, Al element and Cr element in the catalyst.

6. A catalyst prepared by the preparation method according to any one of claims 1 to 5, characterized in that: In the catalyst, the active component is CrO x , where x=1~3 and Al2O3 is the carrier.

7. The catalyst according to claim 6, characterized in that It also includes an auxiliary agent, which is a transition metal element or an alkali metal element; preferably, the transition metal element or the alkali metal element is Zr, Ni, Zn, Co, K, or Ca.

8. The catalyst according to claim 7, characterized in that The molar amount of Cr element in the catalyst is 5% to 20% of the total molar amount of Cr element, Al element and transition metal element or alkali metal element as an auxiliary agent in the catalyst; preferably, the molar amount of transition metal element or alkali metal element as an auxiliary agent in the catalyst is 0.1% to 20% of the total molar amount of transition metal element or alkali metal element, Al element and Cr element as an auxiliary agent in the catalyst.

9. Use of the catalyst prepared by the preparation method according to any one of claims 1 to 5 or the catalyst according to any one of claims 6 to 8 as a catalyst for catalyzing the dehydrogenation of isobutane to prepare isobutene.

10. A method for preparing isobutylene, characterized in that: The preparation method uses the catalyst prepared by the preparation method described in any one of claims 1 to 5 or the catalyst described in any one of claims 6 to 8 to catalyze the dehydrogenation of isobutane to obtain isobutene, and specifically comprises the following steps: loading the catalyst into a fixed bed reactor, and reacting on the fixed bed reactor, and the reaction conditions are: the amount of the catalyst is 0.2 mg; the reaction temperature is 400-800°C; i-C4H 10 The volume ratio of N2 is 1:8~2:1; the reaction pressure is normal pressure, and the space velocity is 6-18 L·g -1 ·h -1 ; Preferably, the reaction temperature is 500-600 °C, more preferably 600 °C; Preferably, i-C4H 10 The volume ratio of N2 is 1:6 to 1:1, more preferably 1:6; preferably, the air velocity is 6 to 12 L·g -1 ·h -1 , more preferably 6 L·g -1 ·h -1 .

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