A chromium-based propane dehydrogenation catalyst and its preparation method and application

Abstract

The present invention belongs to the technical field of catalyst preparation, and specifically relates to a chromium-based propane dehydrogenation catalyst, a preparation method thereof and an application thereof. The chromium-based propane dehydrogenation catalyst of the present invention comprises a Nb2O5-Al2O3 composite carrier, an active component Cr element and metal additives K element, Sb element and V element, and its chemical formula is Cr-K-Sb-V / Nb2O5-Al2O3. The present invention selects a specific surfactant and utilizes the synergistic effect between NN-bis-hydroxyethyl alkylamide and hexadecyltrimethylammonium bromide to significantly improve the propane conversion rate, propylene selectivity and propylene yield of the chromium-based propane dehydrogenation catalyst; by screening the loaded metal component, a chromium-based propane dehydrogenation catalyst is obtained, which is used to catalyze the propane dehydrogenation reaction to produce propylene, and has the advantages of high propane conversion rate, propylene selectivity and propylene yield, and the preparation method is simple, and is suitable for industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst preparation, and specifically relates to a chromium-based propane dehydrogenation catalyst and a preparation method and application thereof. Background Art

[0002] Propane dehydrogenation technology mainly includes oxidative dehydrogenation, inorganic membrane reaction dehydrogenation and catalytic dehydrogenation. The technology of propane catalytic dehydrogenation has been industrially produced. The reaction of propane dehydrogenation to propylene is a strong endothermic process with an increase in the number of molecules. The conversion rate of propane is determined by the thermodynamic equilibrium constant. It can be seen from the reaction that if the propane conversion rate is to be improved, high temperature and low pressure conditions are required. However, high temperature reactions are prone to catalyst sintering, carbon deposition, deactivation, instability, etc., thereby reducing the conversion rate and activity of the catalyst. γ-Al2O3 is often used as a carrier for propane dehydrogenation catalysts because of its good high temperature stability (<800°C) and large specific surface area.

[0003] Chinese invention patent application CN117643875A discloses a preparation method and application of a chromium-based propane dehydrogenation catalyst. The catalyst is prepared by modifying a composite carrier with multiple active components, wherein the composite carrier is composed of an XY-Al compound prepared by a precipitation-impregnation method and γ-Al2O3, η-Al2O3 or δ-Al2O3, wherein X is from a transition metal and Y is from an alkaline earth metal; the multiple active components are composed of Cr, Ga, alkali metals and rare earth metals, and based on the mass of the catalyst itself, the components include the following mass percentages: 10-20% active component Cr2O3, 0.05-5% Ga2O3, 0.1-2.0% alkali metals, 0.1-2.0% rare earth metals, 60-80% of the composite carrier, and the rest is a binder. The contents of X and Y elements in the composite carrier are both 0.01-5.0%, and the sum of the mass percentages of the above components is 100%.

[0004] Another Chinese invention patent application CN104923227A discloses a propane dehydrogenation to propylene catalyst with high stability and a preparation method thereof, which uses a composite oxide alumina-chromium oxide as a composite carrier, metal Pt as an active component, and metal Sn, La and Y as additives. Its chemical formula is Pt-Sn-La-Y / Cr2O3·Al2O3, and the mass ratio of Cr2O3 to Al2O3 in the composite carrier is 2:1. The loading amount of the additives in the catalyst is: Pt is 0.2-1.0wt%, Sn is 0.4-1.5wt%, La is 0-1.4wt%, and Y is 0.2-1.2wt%.

[0005] Another Chinese invention patent application CN104971717A discloses a Pt-modified ZnO / Al2O3 catalyst, a preparation method and an application thereof. The catalyst uses Al2O3 as a carrier, loads an active component ZnO, and uses a small amount of Pt as an auxiliary agent, wherein the mass percentage of Zn is 1-30%, and the mass percentage of Pt is 0.03-0.3%. The catalyst is prepared by a co-impregnation method, wherein the Al2O3 carrier is impregnated in an aqueous solution of zinc nitrate and chloroplatinic acid, and then dried and calcined to obtain a Pt-ZnO / Al2O3 catalyst.

[0006] However, the substrate selectivity and propylene yield of the propane dehydrogenation catalyst prepared in the above patent are not ideal. In view of this, the art urgently needs to develop a chromium-based propane dehydrogenation catalyst with excellent catalytic performance. Summary of the invention

[0007] In view of the problems existing in the prior art, the present invention provides a chromium-based propane dehydrogenation catalyst and a preparation method and application thereof.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] A chromium-based propane dehydrogenation catalyst comprises a Nb2O5-Al2O3 composite carrier, an active component Cr element, and metal additives K element, Sb element and V element, and the chemical formula of the catalyst is Cr-K-Sb-V / Nb2O5-Al2O3.

[0010] Preferably, the chromium-based propane dehydrogenation catalyst comprises, by mass percentage, 15-20% of the active component in terms of metal content, 1-2% of the metal additive in terms of metal content, and a Nb2O5-Al2O3 composite carrier supplemented to 100%.

[0011] More preferably, the chromium-based propane dehydrogenation catalyst comprises, by mass percentage, 18-20% of the active component in terms of metal content, 1.5-1.8% of the metal additive in terms of metal content, and a Nb2O5-Al2O3 composite carrier supplemented to 100%.

[0012] The present invention also provides a method for preparing the chromium-based propane dehydrogenation catalyst, comprising the following steps:

[0013] (1) First, a niobium precursor, a surfactant, a polyol and water are mixed, and then γ-Al2O3 and an acid solution are added in sequence, followed by calcination to obtain a Nb2O5-Al2O3 composite carrier;

[0014] (2) The Nb2O5-Al2O3 composite carrier is then impregnated into a mixed solution containing Cr salt, K salt, Sb salt and V salt, dried and calcined to obtain the composite carrier.

[0015] Preferably, the niobium precursor in step (1) is selected from one or more of niobium oxalate, niobium pentachloride and niobium pentoxide.

[0016] More preferably, the niobium precursor is niobium pentachloride or niobium pentoxide.

[0017] Preferably, the surfactant in step (1) includes NN-bis(hydroxyethyl)alkylamide and hexadecyltrimethylammonium bromide.

[0018] Preferably, the polyol in step (1) is selected from one or more of isopropanol, propylene glycol, ethylene glycol and glycerol.

[0019] More preferably, the polyol is isopropanol or glycerol.

[0020] Preferably, the acid solution in step (1) is a nitric acid or hydrochloric acid solution with a concentration of 0.2-0.4 mol / l.

[0021] Preferably, the molar volume ratio of the niobium precursor, surfactant, polyol, water, γ-Al2O3 and acid solution in step (1) is 0.3-0.5 mol: 0.005-0.01 mol: 0.1 mol: 4-6 ml: 0.5-1.5 mol: 2-3 ml.

[0022] Preferably, after the addition of γ-Al2O3 in step (1), stirring is required at 500-600 rpm for 2-4 h, and after the addition of the acid solution, stirring is required at 1000-2000 rpm for 3-4 h.

[0023] Preferably, the calcination process in step (1) includes first vacuum drying at 80-100°C for 16-20 h, keeping at 200-300°C for 1-2 h; then calcining at 600-700°C for 2-4 h to obtain Nb2O5-Al2O3 powder; finally, mixing the Nb2O5-Al2O3 powder with starch in a mass ratio of 2-3:1, and calcining at 400-600°C for 5-7 h.

[0024] Preferably, after the calcination in step (1), ball milling is further performed to obtain Nb2O5-Al2O3 powder with a particle size of 10-30 μm, and after extrusion molding, a Nb2O5-Al2O3 composite carrier with a length of 5-8 mm is obtained.

[0025] Preferably, the Cr salt in step (2) is selected from one or more of chromium oxide, chromium chloride, chromium bromide, chromium nitrate and chromium phosphate.

[0026] More preferably, the Cr salt is chromium oxide, chromium chloride or chromium nitrate.

[0027] Preferably, the K salt in step (2) is selected from one or more of potassium nitrate, potassium carbonate, potassium sulfate and potassium chloride.

[0028] More preferably, the K salt is potassium nitrate or potassium chloride.

[0029] Preferably, the Sb salt in step (2) is selected from one or more of antimony trichloride, antimony trifluoride, antimony sulfate and antimony nitrate.

[0030] More preferably, the Sb salt is antimony trichloride or antimony nitrate.

[0031] Preferably, the V salt in step (2) is selected from one or more of sodium vanadate, vanadium oxide and vanadium chloride.

[0032] More preferably, the V salt is vanadium oxide or vanadium chloride.

[0033] Preferably, in the mixed solution in step (2), the concentration of Cr salt is 0.6-0.8 g / ml, the concentration of K salt is 0.03-0.06 g / ml, the concentration of Sb salt is 0.01-0.05 g / ml, and the concentration of V salt is 0.003-0.006 g / ml.

[0034] More preferably, in the mixed solution, the concentration of the Cr salt is 0.8 g / ml, the concentration of the K salt is 0.5 g / ml, the concentration of the Sb salt is 0.04 g / ml, and the concentration of the V salt is 0.005 g / ml.

[0035] Preferably, the immersion temperature in step (2) is 30-50° C., and the immersion time is 8-10 h.

[0036] Preferably, the drying temperature in step (2) is 100-140° C., and the drying time is 4-6 h.

[0037] Preferably, the calcination temperature in step (2) is 600-800° C., and the calcination time is 3-5 h.

[0038] The present invention also provides the use of the chromium-based propane dehydrogenation catalyst or the chromium-based propane dehydrogenation catalyst prepared by the preparation method in a propane dehydrogenation reaction.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The present invention selects a specific surfactant and utilizes the synergistic effect between NN-bis(hydroxyethyl)alkylamide and hexadecyltrimethylammonium bromide to significantly improve the propane conversion rate, propylene selectivity and propylene yield of the chromium-based propane dehydrogenation catalyst.

[0041] (2) By screening the loaded metal components, a Cr-K-Sb-V / Nb2O5-Al2O3 catalyst was obtained. The catalyst has high activity and is used to catalyze the dehydrogenation of propane to produce propylene. It has the advantages of high propane conversion rate, propylene selectivity and propylene yield. The preparation method is simple and is suitable for industrial production. DETAILED DESCRIPTION

[0042] It is worth noting that the raw materials used in the present invention are all common commercially available products, among which γ-Al2O3, with a purity of 99.99%, was purchased from Jiangsu Tianxing New Materials Co., Ltd.

[0043] Example 1

[0044] A chromium-based propane dehydrogenation catalyst has a chemical formula of Cr-K-Sb-V / Nb2O5-Al2O3. The composition of the chromium-based propane dehydrogenation catalyst is as follows, calculated by mass percentage: an active component (Cr element) having a metal content of 18.7%, a metal additive (K element, Sb element and V element) having a metal content of 1.5%, and a Nb2O5-Al2O3 composite carrier supplemented to 100%.

[0045] The preparation method of the above chromium-based propane dehydrogenation catalyst is as follows:

[0046] (1) Using niobium oxalate as an organic precursor, niobium oxalate (0.4 mol), surfactant (composed of 0.005 mol NN-bis(hydroxyethyl)alkylamide and 0.005 mol hexadecyltrimethylammonium bromide), isopropanol (0.1 mol) and water (5 ml) were mixed, and then γ-Al2O3 powder (1 mol) was added. The mixture was stirred at 600 rpm for 3 h, and then 2 ml of 0.2 mol / l nitric acid solution was added. The mixture was stirred at 1500 rpm for 3 h to obtain a gel. The gel was then dried in a vacuum oven at 90°C for 20 h. After drying, the gel was placed in a muffle furnace at a heating rate of 5°C / min, first heated to 250°C for 2 h, and then heated to 650°C for calcination for 3 h to obtain Nb2O5-Al2O3 powder. Finally, Nb2O5-Al2O3 powder and starch were mixed in a mass ratio of 2:1 and extruded into a mixture. The mixture was then placed in a muffle furnace and heated to 500°C for calcination at a heating rate of 5°C / min for 6 h. After calcination, the mixture was ball milled to obtain Nb2O5-Al2O3 powder with a particle size of 20 μm. The Nb2O5-Al2O3 composite carrier with a length of 5 mm was obtained by extrusion.

[0047] (2) Weigh a certain amount of chromium oxide, potassium chloride, dysprosium nitrate and vanadium chloride, dissolve them in 100 ml of water to obtain a mixed solution, in which the concentration of Cr salt is 0.8 g / ml, the concentration of K salt is 0.05 g / ml, the concentration of Sb salt is 0.03 g / ml, and the concentration of V salt is 0.004 g / ml. Then, the Nb2O5-Al2O3 composite carrier obtained in step (1) is impregnated in the above mixed solution at a temperature of 40°C for 8 h. After the impregnation, take it out and dry it at 120°C for 5 h. Finally, place it in a muffle furnace, heat it at a heating rate of 5°C / min, heat it to 700°C and calcine it for 4 h to obtain it.

[0048] Example 2

[0049] A chromium-based propane dehydrogenation catalyst has a chemical formula of Cr-K-Sb-V / Nb2O5-Al2O3. The composition of the chromium-based propane dehydrogenation catalyst is as follows, calculated by mass percentage: an active component (Cr element) having a metal content of 15.6%, a metal additive (K element, Sb element and V element) having a metal content of 2.0%, and a Nb2O5-Al2O3 composite carrier supplemented to 100%.

[0050] The preparation method of the above chromium-based propane dehydrogenation catalyst is as follows:

[0051] (1) Using niobium oxalate as an organic precursor, niobium oxalate (0.5 mol), surfactant (composed of 0.003 mol NN-bis(hydroxyethyl)alkylamide and 0.004 mol hexadecyltrimethylammonium bromide), isopropanol (0.1 mol) and water (6 ml) were mixed, and then γ-Al2O3 powder (1.5 mol) was added. The mixture was stirred at 500 rpm for 4 h, and then 3 ml of 0.4 mol / l hydrochloric acid solution was added. The mixture was stirred at 2000 rpm for 4 h to obtain a gel. The gel was then placed in a vacuum drying oven at 100°C for 18 h. After drying, the gel was placed in a muffle furnace at a heating rate of 5°C / min, first heated to 300°C for 1 h, and then heated to 700°C for calcination for 2 h to obtain Nb2O5-Al2O3 powder. Finally, Nb2O5-Al2O3 powder and starch were mixed in a mass ratio of 3:1 and extruded into a mixture. The mixture was then placed in a muffle furnace and heated to 600°C for calcination at a heating rate of 5°C / min for 5 h. After calcination, the mixture was ball milled to obtain Nb2O5-Al2O3 powder with a particle size of 10 μm. The Nb2O5-Al2O3 composite carrier with a length of 8 mm was obtained by extrusion.

[0052] (2) Weigh a certain amount of chromium nitrate, potassium nitrate, antimony trichloride and vanadium oxide, dissolve them in 100 ml of water to obtain a mixed solution, in which the concentration of Cr salt is 0.8 g / ml, the concentration of K salt is 0.06 g / ml, the concentration of Sb salt is 0.05 g / ml, and the concentration of V salt is 0.006 g / ml. Then, the Nb2O5-Al2O3 composite carrier obtained in step (1) is impregnated in the above mixed solution at a temperature of 50°C for 10 h. After the impregnation, take it out and dry it at 140°C for 4 h. Finally, place it in a muffle furnace, heat it at a heating rate of 5°C / min, heat it to 800°C and calcine it for 3 h to obtain it.

[0053] Example 3

[0054] A chromium-based propane dehydrogenation catalyst has a chemical formula of Cr-K-Sb-V / Nb2O5-Al2O3. The composition of the chromium-based propane dehydrogenation catalyst is as follows, calculated by mass percentage: an active component (Cr element) having a metal content of 20.0%, a metal additive (K element, Sb element and V element) having a metal content of 1.2%, and a Nb2O5-Al2O3 composite carrier supplemented to 100%.

[0055] The preparation method of the above-mentioned chromium-based propane dehydrogenation catalyst is as follows:

[0056] (1) With niobium pentachloride as an organic precursor, niobium pentachloride (0.3 mol), surfactant (composed of 0.0025 mol N.N-bis(hydroxyethyl)alkylamide and 0.0025 mol hexadecyltrimethylammonium bromide), hexadecyltrimethylammonium bromide (0.004 mol), isopropanol (0.1 mol) and water (4 ml) were mixed, and then γ-Al2O3 powder (0.5 mol) was added. The mixture was stirred at 600 rpm for 2 h, and then 2 ml of 0.4 mol / l hydrochloric acid solution was added. The mixture was stirred at 1000 rpm for 3 h to obtain a gel. The gel was then dried in a vacuum oven at 80°C for 20 h. After drying, the gel was placed in a muffle furnace at a heating rate of 5°C / min, first heated to 200°C and kept at this temperature for 2 h, and then heated to 600°C and calcined for 4 h to obtain Nb2O5-Al2O3 powder. Finally, Nb2O5-Al2O3 powder and starch were mixed in a mass ratio of 3:1 and extruded into a mixture. The mixture was then placed in a muffle furnace and heated to 400°C at a heating rate of 5°C / min and calcined for 7 h. After calcination, the mixture was ball milled to obtain Nb2O5-Al2O3 powder with a particle size of 30 μm. The Nb2O5-Al2O3 composite carrier with a length of 6 mm was obtained by extrusion.

[0057] (2) Weigh a certain amount of chromium bromide, potassium sulfate, dysprosium nitrate and vanadium chloride, dissolve them in 100 ml of water to obtain a mixed solution, in which the concentration of Cr salt is 0.6 g / ml, the concentration of K salt is 0.03 g / ml, the concentration of Sb salt is 0.01 g / ml, and the concentration of V salt is 0.003 g / ml. Then, the Nb2O5-Al2O3 composite carrier obtained in step (1) is impregnated in the above mixed solution at a temperature of 30°C for 8 h. After the impregnation is completed, it is taken out and dried at 100°C for 6 h. Finally, it is placed in a muffle furnace, and the heating rate is also 5°C / min. It is heated to 600°C and roasted for 5 h to obtain.

[0058] Comparative Example 1

[0059] The same as Example 1, the only difference is that the surfactant in step (1) is NN-bis(hydroxyethyl)alkylamide.

[0060] A chromium-based propane dehydrogenation catalyst, whose chemical formula is Cr-K-Sb-V / Nb2O5-Al2O3, and whose preparation method is as follows:

[0061] (1) Using niobium oxalate as an organic precursor, niobium oxalate (0.4 mol), surfactant (0.01 mol NN-bis(hydroxyethyl)alkylamide), isopropanol (0.1 mol) and water (5 ml) were mixed, and then γ-Al2O3 powder (1 mol) was added. The mixture was stirred at 600 rpm for 3 h, and then 2 ml of 0.2 mol / l nitric acid solution was added. The mixture was stirred at 1500 rpm for 3 h to obtain a gel. The gel was then dried in a 90°C vacuum oven for 20 h. After drying, the gel was placed in a muffle furnace at a heating rate of 5°C / min, first heated to 250°C for 2 h, and then heated to 650°C for calcination for 3 h to obtain Nb2O5-Al2O3 powder. Finally, Nb2O5-Al2O3 powder and starch were mixed in a mass ratio of 2:1 and extruded into a mixture. The mixture was then placed in a muffle furnace and heated to 500°C for calcination at a heating rate of 5°C / min for 6 h. After calcination, the mixture was ball milled to obtain Nb2O5-Al2O3 powder with a particle size of 20 μm. The Nb2O5-Al2O3 composite carrier with a length of 5 mm was obtained by extrusion.

[0062] (2) Weigh a certain amount of chromium oxide, potassium chloride, dysprosium nitrate and vanadium chloride, dissolve them in 100 ml of water to obtain a mixed solution, in which the concentration of Cr salt is 0.8 g / ml, the concentration of K salt is 0.05 g / ml, the concentration of Sb salt is 0.03 g / ml, and the concentration of V salt is 0.004 g / ml. Then, the Nb2O5-Al2O3 composite carrier obtained in step (1) is impregnated in the above mixed solution at a temperature of 40°C for 8 h. After the impregnation, take it out and dry it at 120°C for 5 h. Finally, place it in a muffle furnace, heat it at a heating rate of 5°C / min, heat it to 700°C and calcine it for 4 h to obtain it.

[0063] Comparative Example 2

[0064] The same as Example 1, the only difference is that the surfactant in step (1) is hexadecyltrimethylammonium bromide.

[0065] A chromium-based propane dehydrogenation catalyst, whose chemical formula is Cr-K-Sb-V / Nb2O5-Al2O3, and whose preparation method is as follows:

[0066] (1) Using niobium oxalate as an organic precursor, niobium oxalate (0.4 mol), surfactant (0.01 mol hexadecyltrimethylammonium bromide), isopropanol (0.1 mol) and water (5 ml) were mixed, and then γ-Al2O3 powder (1 mol) was added. The mixture was stirred at 600 rpm for 3 h, and then 2 ml of 0.2 mol / l nitric acid solution was added. The mixture was stirred at 1500 rpm for 3 h to obtain a gel. The gel was then dried in a 90°C vacuum oven for 20 h. After drying, the gel was placed in a muffle furnace at a heating rate of 5°C / min, first heated to 250°C for 2 h, and then heated to 650°C for calcination for 3 h to obtain Nb2O5-Al2O3 powder. Finally, Nb2O5-Al2O3 powder and starch were mixed in a mass ratio of 2:1 and extruded into a mixture. The mixture was then placed in a muffle furnace and heated to 500°C for calcination at a heating rate of 5°C / min for 6 h. After calcination, the mixture was ball milled to obtain Nb2O5-Al2O3 powder with a particle size of 20 μm. The Nb2O5-Al2O3 composite carrier with a length of 5 mm was obtained by extrusion.

[0067] (2) Weigh a certain amount of chromium oxide, potassium chloride, dysprosium nitrate and vanadium chloride, dissolve them in 100 ml of water to obtain a mixed solution, in which the concentration of Cr salt is 0.8 g / ml, the concentration of K salt is 0.05 g / ml, the concentration of Sb salt is 0.03 g / ml, and the concentration of V salt is 0.004 g / ml. Then, the Nb2O5-Al2O3 composite carrier obtained in step (1) is impregnated in the above mixed solution at a temperature of 40°C for 8 h. After the impregnation, take it out and dry it at 120°C for 5 h. Finally, place it in a muffle furnace, heat it at a heating rate of 5°C / min, heat it to 700°C and calcine it for 4 h to obtain it.

[0068] Comparative Example 3

[0069] The same as Example 1, the only difference is that the metal additives are K element, Y element and La element.

[0070] A chromium-based propane dehydrogenation catalyst, whose chemical formula is Cr-KY-La / Nb2O5-Al2O3, and whose preparation method is as follows:

[0071] (1) Using niobium oxalate as an organic precursor, niobium oxalate (0.4 mol), surfactant (composed of 0.005 mol NN-bis(hydroxyethyl)alkylamide and 0.005 mol hexadecyltrimethylammonium bromide), isopropanol (0.1 mol) and water (5 ml) were mixed, and then γ-Al2O3 powder (1 mol) was added. The mixture was stirred at 600 rpm for 3 h, and then 2 ml of 0.2 mol / l nitric acid solution was added. The mixture was stirred at 1500 rpm for 3 h to obtain a gel. The gel was then dried in a vacuum oven at 90°C for 20 h. After drying, the gel was placed in a muffle furnace at a heating rate of 5°C / min, first heated to 250°C for 2 h, and then heated to 650°C for calcination for 3 h to obtain Nb2O5-Al2O3 powder. Finally, Nb2O5-Al2O3 powder and starch were mixed in a mass ratio of 2:1 and extruded into a mixture. The mixture was then placed in a muffle furnace and heated to 500°C for calcination at a heating rate of 5°C / min for 6 h. After calcination, the mixture was ball milled to obtain Nb2O5-Al2O3 powder with a particle size of 20 μm. The Nb2O5-Al2O3 composite carrier with a length of 5 mm was obtained by extrusion.

[0072] (2) Weigh a certain amount of chromium oxide, potassium chloride, yttrium nitrate and lanthanum nitrate, dissolve them in 100 ml of water to obtain a mixed solution, in which the concentration of Cr salt is 0.8 g / ml, the concentration of K salt is 0.05 g / ml, the concentration of Y salt is 0.03 g / ml, and the concentration of La salt is 0.004 g / ml. Then, the Nb2O5-Al2O3 composite carrier obtained in step (1) is impregnated in the above mixed solution at a temperature of 40°C for 8 h. After the impregnation, take it out and dry it at 120°C for 5 h. Finally, place it in a muffle furnace, heat it at a heating rate of 5°C / min, heat it to 700°C and calcine it for 4 h to obtain it.

[0073] Comparative Example 4

[0074] The same as Example 1, the only difference is that the organic precursor is chromium nitrate.

[0075] A chromium-based propane dehydrogenation catalyst, whose chemical formula is Cr-K-Sb-V / Cr2O3-Al2O3, and whose preparation method is as follows:

[0076] (1) Using chromium nitrate as an organic precursor, chromium nitrate (0.4 mol), surfactant (composed of 0.005 mol NN-bis(hydroxyethyl)alkylamide and 0.005 mol hexadecyltrimethylammonium bromide), isopropanol (0.1 mol) and water (5 ml) were mixed, and then γ-Al2O3 powder (1 mol) was added. The mixture was stirred at 600 rpm for 3 h, and then 2 ml of 0.2 mol / l nitric acid solution was added. The mixture was stirred at 1500 rpm for 3 h to obtain a gel. The gel was then dried in a vacuum oven at 90°C for 20 h. After drying, the gel was placed in a muffle furnace at a heating rate of 5°C / min, first heated to 250°C for 2 h, and then heated to 650°C for calcination for 3 h to obtain Nb2O5-Al2O3 powder. Finally, Nb2O5-Al2O3 powder and starch were mixed in a mass ratio of 2:1 and extruded into a mixture. The mixture was then placed in a muffle furnace and heated to 500°C at a heating rate of 5°C / min for 6 h. After calcination, the mixture was ball milled to obtain Cr2O3-Al2O3 powder with a particle size of 20 μm. The Nb2O5-Al2O3 composite carrier with a length of 5 mm was obtained by extrusion.

[0077] (2) Weigh a certain amount of chromium oxide, potassium chloride, dysprosium nitrate and vanadium chloride, dissolve them in 100 ml of water to obtain a mixed solution, in which the concentration of Cr salt is 0.8 g / ml, the concentration of K salt is 0.05 g / ml, the concentration of Sb salt is 0.03 g / ml, and the concentration of V salt is 0.004 g / ml. Then, immerse the Cr2O3-Al2O3 composite carrier obtained in step (1) in the above mixed solution at a temperature of 40°C for 8 h. After immersion, take it out and dry it at 120°C for 5 h. Finally, place it in a muffle furnace, heat it at a heating rate of 5°C / min, heat it to 700°C and calcine it for 4 h to obtain the product.

[0078] Test Case

[0079] The chromium-based propane dehydrogenation catalysts prepared in Examples 1-3 and Comparative Examples 1-4 were respectively characterized by propane dehydrogenation catalytic reaction, and the reaction conditions were as follows:

[0080] In the fixed bed reactor, the catalyst loading was 5 g, the reaction temperature was controlled at 600 °C, the reaction pressure was normal pressure, the reaction gas composition was: C3H8:N2=9:1, and the propane mass space velocity was 800 h -1 , the product was obtained, and the product was analyzed using a GC7900 gas chromatograph to analyze the alkane and olefin contents in the dehydrogenation product online, and the propane conversion rate, propylene selectivity and propylene yield were calculated. The results are shown in Table 1.

[0081] Table 1 Test data

[0082] serial number Propane conversion rate (%) Propylene selectivity (%) Propylene yield (%) Example 1 55.4 94.2 52.2 Example 2 54.7 94.0 51.4 Example 3 55.2 94.1 51.9 Comparative Example 1 43.8 80.5 35.3 Comparative Example 2 44.9 81.4 36.5 Comparative Example 3 35.2 73.9 26.0 Comparative Example 4 38.6 76.8 29.6

[0083] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A chromium-based propane dehydrogenation catalyst, characterized in that: The chromium-based propane dehydrogenation catalyst comprises a Nb2O5-Al2O3 composite carrier, an active component Cr element, and metal additives K element, Sb element, and V element, and its chemical formula is Cr-K-Sb-V / Nb2O5-Al2O3. The preparation method of the chromium-based propane dehydrogenation catalyst comprises the following steps: (1) First, a niobium precursor, a surfactant, a polyol and water are mixed, and then γ-Al2O3 and an acid solution are added in sequence, followed by calcination to obtain a Nb2O5-Al2O3 composite carrier; (2) The Nb2O5-Al2O3 composite carrier is then impregnated into a mixed solution containing Cr salt, K salt, Sb salt and V salt, dried and calcined to obtain: In step (1), the niobium precursor is selected from one or more of niobium oxalate, niobium pentachloride and niobium pentoxide, the surfactant is NN-bis(hydroxyethyl)alkylamide and hexadecyltrimethylammonium bromide, and the calcination process comprises first vacuum drying at 80-100°C for 16-20 h, and keeping at 200-300°C for 1-2 h; then calcining at 600-700°C for 2-4 h to obtain Nb2O5-Al2O3 powder; finally, mixing the Nb2O5-Al2O3 powder with starch in a mass ratio of 2-3:1, calcining at 400-600°C for 5-7 h, and after the calcination, ball milling is performed to obtain Nb2O5-Al2O3 powder with a particle size of 10-30 μm, and extruding to obtain a Nb2O5-Al2O3 composite carrier with a length of 5-8 mm.

2. The chromium-based propane dehydrogenation catalyst according to claim 1, characterized in that: In terms of mass percentage, the chromium-based propane dehydrogenation catalyst includes: an active component with a metal content of 15-20%, a metal additive with a metal content of 1-2%, and a Nb2O5-Al2O3 composite carrier supplemented to 100%.

3. A method for preparing a chromium-based propane dehydrogenation catalyst as claimed in claim 1 or 2, characterized in that: The steps include: (1) First, a niobium precursor, a surfactant, a polyol and water are mixed, and then γ-Al2O3 and an acid solution are added in sequence, followed by calcination to obtain a Nb2O5-Al2O3 composite carrier; (2) The Nb2O5-Al2O3 composite carrier is then impregnated into a mixed solution containing Cr salt, K salt, Sb salt and V salt, dried and calcined to obtain: In step (1), the niobium precursor is selected from one or more of niobium oxalate, niobium pentachloride and niobium pentoxide, the surfactant is NN-bis(hydroxyethyl)alkylamide and hexadecyltrimethylammonium bromide, and the calcination process comprises first vacuum drying at 80-100°C for 16-20 h, and keeping at 200-300°C for 1-2 h; then calcining at 600-700°C for 2-4 h to obtain Nb2O5-Al2O3 powder; finally, mixing the Nb2O5-Al2O3 powder with starch in a mass ratio of 2-3:1, calcining at 400-600°C for 5-7 h, and after the calcination, ball milling is performed to obtain Nb2O5-Al2O3 powder with a particle size of 10-30 μm, and extruding to obtain a Nb2O5-Al2O3 composite carrier with a length of 5-8 mm.

4. The preparation method according to claim 3, characterized in that: In step (1), the polyol is selected from one or more of isopropanol, propylene glycol, ethylene glycol and glycerol, and the acid solution is a nitric acid or hydrochloric acid solution with a concentration of 0.2-0.4 mol / L.

5. The preparation method according to claim 3, characterized in that: The molar volume ratio of the niobium precursor, surfactant, polyol, water, γ-Al2O3 and acid solution in step (1) is 0.3-0.5 mol:0.005-0.01 mol:0.1 mol:4-6 mL:0.5-1.5 mol:2-3 mL. After the addition of γ-Al2O3, the mixture needs to be stirred at 500-600 rpm for 2-4 h. After the addition of the acid solution, the mixture needs to be stirred at 1000-2000 rpm for 3-4 h.

6. The preparation method according to claim 3, characterized in that: In step (2), the Cr salt is selected from one or more of chromium oxide, chromium chloride, chromium bromide, chromium nitrate and chromium phosphate, the K salt is selected from one or more of potassium nitrate, potassium carbonate, potassium sulfate and potassium chloride, the Sb salt is selected from one or more of antimony trichloride, antimony trifluoride, antimony sulfate and antimony nitrate, and the V salt is selected from one or more of sodium vanadate, vanadium oxide and vanadium chloride.

7. The preparation method according to claim 6, characterized in that: In step (2), the concentration of Cr salt in the mixed solution is 0.6-0.8 g / mL, the concentration of K salt is 0.03-0.06 g / mL, the concentration of Sb salt is 0.01-0.05 g / mL, and the concentration of V salt is 0.003-0.006 g / mL. The impregnation temperature is 30-50°C, the impregnation time is 8-10 h, the drying temperature is 100-140°C, the drying time is 4-6 h, the calcination temperature is 600-800°C, and the calcination time is 3-5 h.

8. Use of the chromium-based propane dehydrogenation catalyst according to any one of claims 1 to 2 or the chromium-based propane dehydrogenation catalyst prepared by the preparation method according to any one of claims 3 to 7 in a propane dehydrogenation reaction.