A catalyst for dehydrogenating isobutane to produce isobutene, and its preparation method and application

Abstract

The present invention discloses a catalyst for dehydrogenating isobutane to produce isobutene, comprising a support, an active metal Pt, and a promoter metal Sn supported on the support. The support is zinc-loaded γ-Al2O3, expressed as Zn-γ-Al2O3, and the Pt, Sn, and Zn loadings, as a percentage by mass of γ-Al2O3, are as follows: Pt 0.1-3%, Sn 0.1-2%, and Zn 0.1-1%. The present invention also discloses a preparation method and application of the catalyst. The catalyst has high catalytic activity, low carbon deposition during operation, and good stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of isobutene preparation, and particularly relates to a catalyst for preparing isobutene by dehydrogenating isobutane, and a preparation method and application thereof. Background Art

[0002] Isobutylene has a wide range of applications. It is the primary raw material for the production of methyl tert-butyl ether (MTBE). It is also used in the production of fine chemicals such as tert-butyl alcohol, butyl rubber, and methacrylic acid. With the development of the chemical industry, isobutylene has become considered the most important basic chemical raw material, alongside ethylene and propylene. Its primary sources are the C4 fraction produced as a byproduct of naphtha cracking to ethylene plants, the C4 fraction produced as a byproduct of refinery fluid catalytic cracking (FCC) units, and the C4 component of natural gas.

[0003] In recent years, with the development and utilization of isobutene downstream products, isobutene has been in short supply. Using isobutane dehydrogenation to produce isobutene not only addresses the current isobutene shortage but also fully utilizes isobutane resources. There are two main types of isobutane dehydrogenation catalysts: Pt-based and Cr-based, with Al2O3 as the support. Pt-based catalysts offer advantages over Cr-based catalysts, such as higher reactivity and lower toxicity. Therefore, Pt-based catalysts developed by UOP are still the predominant catalysts in China and abroad. However, Pt-based catalysts suffer from poor stability due to carbon deposition and deactivation during the reaction.

[0004] To further improve the performance of isobutane dehydrogenation to isobutene catalysts, researchers have conducted extensive research. A reference (Industrial Catalysis, 2016, 4:48-54) reported a Pt-Sn-K / Fe(x)-γ-Al2O3 catalyst prepared by vacuum impregnation using Fe-modified γ-Al2O3 as a coprecipitation method. A reference (Industrial Catalysis, 2014, 4:293-296) improved the performance of an existing Pt-Sn catalyst by loading it with nano-Au. A Chinese patent (CN114984951A) utilizes a specially modified zinc aluminate support modified with rare earth elements, employs a noble metal as the active component, and introduces a promoter metal to prepare a dehydrogenation catalyst. A Chinese patent (CN109126788B) reports a Pt-alumina composite catalyst prepared using a batch autoclave process using a γ-Al2O3 support loaded with the active component Pt and promoters Sn, Li, and Yb. Although the above methods have improved the performance of the catalyst to a certain extent, there are still problems that need to be improved, such as the complicated catalyst preparation process, high cost, and weak catalyst resistance to carbon deposition. Summary of the Invention

[0005] In view of the defects of the prior art, the present invention provides a catalyst for dehydrogenating isobutane to produce isobutene, and a preparation method and application thereof. The catalyst has high catalytic activity, less carbon deposition during operation, and good stability.

[0006] A catalyst for dehydrogenating isobutane to produce isobutene comprises a carrier, and an active metal Pt and a promoter metal Sn supported on the carrier. The carrier is zinc-loaded γ-Al2O3, expressed as Zn-γ-Al2O3. The loading amounts of Pt, Sn, and Zn, expressed as a mass percentage of the γ-Al2O3, are as follows: Pt 0.1-3%, Sn 0.1-2%, and Zn 0.1-1%.

[0007] Preferably, the specific surface area of the carrier is 80-120m 2 / g, pore size is 10-20nm, and particle size is 1.8-2mm.

[0008] The preparation method of the catalyst comprises the following steps:

[0009] (1) mixing low sodium pseudo-boehmite with an acid solution, stirring at 60-80°C for 2-3 hours to obtain a crude aluminum sol; adding a non-polar solvent to the crude aluminum sol, stirring at room temperature for 0.5-2 hours, standing at 2-5°C for 3-4 hours, then heating to 40-45°C at a heating rate of 1-3°C / min, stirring at a constant temperature for 30-50 minutes, standing overnight, filtering to obtain an aluminum sol, and drying at room temperature to obtain an aluminum sol powder;

[0010] (2) At room temperature, aluminum sol powder is dissolved in deionized water to prepare aluminum sol with a solid content of 25%. After stirring evenly, a gelling agent is added thereto and stirring is continued for 0.5-1h. Then, a Zn precursor aqueous solution is added thereto and stirring is continued for 1.5-2h. The pH is adjusted to 3-4 to obtain Zn-modified aluminum sol. The Zn-γ-Al2O3 carrier is obtained by the oil column molding method through ball dropping, aging, water washing, drying, and roasting.

[0011] (3) adding a Pt precursor and a Sn precursor to an impregnation solvent in sequence, mixing them uniformly to obtain an impregnation solution, adding the Zn-γ-Al2O3 carrier to the impregnation solution, impregnating, removing the impregnation solvent, drying, and calcining;

[0012] (4) Reducing under a hydrogen atmosphere to obtain the catalyst.

[0013] Preferably, the sodium content in the low-sodium pseudo-boehmite is less than 0.01 wt%.

[0014] Preferably, the volume ratio of the crude aluminum sol to the non-polar solvent in step (1) is 1:(1-3); the non-polar solvent is toluene, carbon tetrachloride or n-heptane; the acid solution is at least one of hydrochloric acid, nitric acid, acetic acid and chloroacetic acid, and the mass concentration of the acid solution is 8%-15%.

[0015] Preferably, the gelling agent is at least one of hexamethylenetetramine, urea, polyethylene glycol 2000, and sodium carboxymethyl cellulose.

[0016] Preferably, the mass ratio of the gelling agent to the aluminum sol with a solid content of 25% is (5-10):100.

[0017] Preferably, the aging is carried out in a nitrogen atmosphere, at 2-2.5 MPa and 140-170° C. for 24-48 hours.

[0018] Preferably, the precursor of Zn is at least one of zinc chloride, zinc nitrate, and zinc acetate; the precursor of Pt is chloroplatinic acid; and the precursor of Sn is at least one of anhydrous tin chloride, anhydrous stannous chloride, and stannous sulfate.

[0019] Preferably, the immersion in step (3) is carried out at room temperature for 6-12 hours; the immersion solvent is water, methanol or ethanol.

[0020] Preferably, the reduction is carried out at 300-450° C. for 2-5 h; the drying is carried out at 80-120° C.; and the calcination is carried out at 500-600° C. for 4-6 h.

[0021] A method for preparing isobutylene by dehydrogenation of isobutane is as follows: a catalyst is loaded in a reaction device, isobutane is used as a raw material, and hydrogen is introduced to react; wherein the reaction temperature is 550-650°C, the reaction pressure is 0-0.1 MPa, and the mass space velocity of isobutane is 0.5-10 h -1 , the molar ratio of isobutane to hydrogen is 1:(0.5-1); the reaction device is a fixed bed, a fluidized bed or a moving bed; the catalyst is the catalyst of the present invention.

[0022] Advantages of the present invention:

[0023] (1) The catalyst of the present invention does not contain Cr element and is environmentally friendly;

[0024] (2) The additive Zn is introduced into the process of preparing the alumina support. On the one hand, the introduction of Zn does not affect the structure of alumina. On the other hand, the strong interaction between Pt clusters and Zn makes Pt less likely to migrate at high temperatures.

[0025] (3) The additives Sn and Zn can weaken the strong interaction between the active component Pt and the support, and improve the dispersion of Pt on the support surface; the addition of Sn and Pt weakens the acidity of the overall catalyst and reduces the formation of carbon deposits;

[0026] (4) Due to the introduction of the Zn additive in the catalyst of the present invention, the mass ratio of Sn / Pt in the catalyst is reduced, thereby reducing the reduction and precipitation of Sn in the catalyst during the high-temperature reaction process, which affects the activity and selectivity of the catalyst;

[0027] (5) The catalyst prepared by the method provided by the present invention is used in the isobutane dehydrogenation reaction to produce isobutene. It has high catalytic activity, little carbon deposition, no obvious deactivation after running for more than 72 hours, and the butene selectivity is always maintained at more than 95%. DETAILED DESCRIPTION

[0028] The sodium content of the low-sodium pseudo-boehmite used in the embodiment of the present invention is less than 0.01 wt %.

[0029] Example 1

[0030] A catalyst for dehydrogenating isobutane to produce isobutene, comprising a carrier, an active metal Pt and a promoter metal Sn supported on the carrier, wherein the carrier is zinc-loaded γ-Al2O3, expressed as Zn-γ-Al2O3, and the loading amounts of Pt, Sn, and Zn, calculated as a mass percentage of the γ-Al2O3, are as follows: Pt 0.5%, Sn 0.5%, and Zn 0.5%; wherein the specific surface area of the carrier is 80-120 m 2 / g, pore size of 10-20nm, particle size of 1.8-2mm; the catalyst is marked as Pt 0.5 -Sn 0.5 / Zn 0.5 -γ-Al2O3;

[0031] Preparation method of the catalyst:

[0032] (1) 135 g of low-sodium pseudo-boehmite prepared by the alcohol aluminum method was mixed with 200 g of a 10 wt% hydrochloric acid solution, and stirred in a water bath at 80 ° C for 2 h at a stirring speed of 200 r / min to obtain a crude aluminum sol; a non-polar solvent n-heptane was added to the crude aluminum sol according to a volume ratio of 1:2 to the non-polar solvent in the crude aluminum sol, and stirred at room temperature for 1 h, and allowed to stand at 2 ° C for 4 h, and then heated to 45 ° C at a heating rate of 3 ° C / min and stirred at a constant temperature for 30 min. After standing overnight, the mixture was filtered to obtain an aluminum sol, which was dried at room temperature to obtain an aluminum sol powder;

[0033] (2) At room temperature, aluminum sol powder was dissolved in deionized water to prepare aluminum sol with a solid content of 25%. After stirring evenly, hexamethylenetetramine and polyethylene glycol 2000 were added and stirring was continued for 0.5 h. Then, zinc nitrate aqueous solution was added and stirring was continued for 1.5 h. The pH of the solution was adjusted to 3.5 with dilute hydrochloric acid solution to obtain Zn-modified aluminum sol. The Zn-modified aluminum sol was dripped into a hot oil column at 120°C to form the aluminum sol using the oil column molding method. Obtain alumina pellets, transfer the pellets to an autoclave, age them at 150°C for 48 h under a nitrogen atmosphere at 2 MPa, wash them with water, dry them at 80°C to constant weight, and calcine them at 550°C for 5 h to obtain a Zn-γ-Al2O3 carrier; wherein the mass ratio of the total mass of hexamethylenetetramine and polyethylene glycol 2000 to the aluminum sol having a solid content of 25% is 10:100, and the mass ratio of hexamethylenetetramine to polyethylene glycol 2000 is 4:1;

[0034] (3) Chloroplatinic acid and anhydrous tin chloride were added to water in sequence and mixed evenly to obtain an impregnation solution. The Zn-γ-Al2O3 carrier was added to the impregnation solution and impregnated at room temperature for 8 h. The solvent water in the system was evaporated using a rotary evaporator, and the mixture was dried at 100°C to constant weight and calcined at 550°C for 5 h.

[0035] (4) Reducing the reaction mixture at 350° C. for 2 h under a hydrogen atmosphere to obtain the catalyst.

[0036] Example 2

[0037] A catalyst for dehydrogenating isobutane to isobutene, wherein the loading amounts of Pt, Sn, and Zn are as follows: Pt 0.5%, Sn 0.5%, and Zn 0.25%; the catalyst is labeled Pt 0.5 -Sn 0.5 / Zn 0.25 -γ-Al2O3; other contents are the same as those in Example 1.

[0038] Example 3

[0039] A catalyst for dehydrogenating isobutane to isobutene, wherein the loading amounts of Pt, Sn, and Zn are as follows: Pt 0.5%, Sn 0.5%, and Zn 0.75%; the catalyst is labeled Pt 0.5 -Sn 0.5 / Zn 0.75 -γ-Al2O3; other contents are the same as those in Example 1.

[0040] Example 4

[0041] A catalyst for dehydrogenating isobutane to isobutene, wherein the loading amounts of Pt, Sn, and Zn are as follows: Pt 0.5%, Sn 0.5%, and Zn 1%; the catalyst is labeled Pt 0.5 -Sn 0.5 / Zn-γ-Al2O3; other details are the same as in Example 1.

[0042] Example 5

[0043] A catalyst for dehydrogenating isobutane to isobutene, wherein the loading amounts of Pt, Sn, and Zn are as follows: Pt 0.5%, Sn 0.25%, and Zn 0.25%; the catalyst is labeled Pt 0.5 -Sn 0.25 / Zn 0.25 -γ-Al2O3; other contents are the same as those in Example 1.

[0044] Example 6

[0045] A catalyst for dehydrogenating isobutane to isobutene, wherein the loading amounts of Pt, Sn, and Zn are as follows: Pt 0.5%, Sn 0.75%, and Zn 0.5%; the catalyst is labeled Pt 0.5 -Sn 0.75 / Zn 0.5 -γ-Al2O3; other contents are the same as those in Example 1.

[0046] Example 7

[0047] A catalyst for dehydrogenating isobutane to isobutene, wherein the loading amounts of Pt, Sn, and Zn are as follows: Pt 0.5%, Sn 1%, and Zn 0.5%; the catalyst is labeled Pt 0.5 -Sn / Zn 0.5 -γ-Al2O3; other contents are the same as those in Example 1.

[0048] Example 8

[0049] A catalyst for dehydrogenating isobutane to isobutene, wherein the loading amounts of Pt, Sn, and Zn are as follows: Pt 0.5%, Sn 0.75%, and Zn 0.75%; the catalyst is labeled Pt 0.5 -Sn 0.75 / Zn 0.75 -γ-Al2O3; other contents are the same as those in Example 1.

[0050] Example 9

[0051] A catalyst for isobutane dehydrogenation to isobutene, comprising a carrier, an active metal Pt and a promoter metal Sn supported on the carrier, wherein the carrier is zinc-loaded γ-Al2O3, expressed as Zn-γ-Al2O3, and the Pt, Sn, and Zn loadings are as follows, calculated as a mass percentage of the γ-Al2O3: Pt 3%, Sn 2%, and Zn 0.1%; wherein the specific surface area of the carrier is 60-120 m 2 / g, pore size of 10-20nm, particle size of 1.8-2mm; the catalyst is marked as Pt3-Sn2 / Zn0.1 -γ-Al2O3;

[0052] Preparation method of the catalyst:

[0053] (1) 135 g of low-sodium pseudo-boehmite prepared by the alcohol aluminum method was mixed with 200 g of 8 wt% nitric acid solution, and stirred in a water bath at 60 ° C for 3 h at a stirring speed of 200 r / min to obtain a crude aluminum sol; a non-polar solvent toluene was added to the crude aluminum sol according to a volume ratio of 1:3 between the crude aluminum sol and the non-polar solvent, and the mixture was stirred at room temperature for 0.5 h, allowed to stand at 5 ° C for 3 h, and then heated to 40 ° C at a heating rate of 1 ° C / min and stirred at a constant temperature for 35 min. After standing overnight, the mixture was filtered to obtain an aluminum sol, which was dried at room temperature to obtain an aluminum sol powder;

[0054] (2) At room temperature, the obtained aluminum sol powder was dissolved in deionized water to prepare an aluminum sol with a solid content of 25%. After stirring evenly, urea was added and the stirring was continued for 1 hour. Then, a zinc chloride aqueous solution was added and the stirring was continued for 2 hours. The pH was adjusted to 3 with dilute hydrochloric acid to obtain a Zn-modified aluminum sol. The Zn-modified aluminum sol was dripped into a hot oil column at 120°C using an oil column molding method to obtain alumina pellets. The pellets were transferred to a high-pressure aging autoclave and aged for 48 hours at 140°C under a nitrogen atmosphere at 2.5 MPa. The pellets were washed with water, dried at 80°C to constant weight, and calcined at 500°C for 6 hours to obtain a Zn-γ-Al2O3 carrier. The mass ratio of the urea to the aluminum sol with a solid content of 25% was 10:100.

[0055] (3) Chloroplatinic acid and anhydrous stannous chloride were added to methanol in sequence and mixed evenly to obtain an impregnation solution. The Zn-γ-Al2O3 carrier was added to the impregnation solution and impregnated at room temperature for 6 h. The solvent methanol in the system was evaporated using a rotary evaporator, dried at 100°C to constant weight, and calcined at 500°C for 6 h.

[0056] (4) Reducing the reaction mixture at 300° C. for 5 h under a hydrogen atmosphere to obtain the catalyst.

[0057] Example 10

[0058] A catalyst for isobutane dehydrogenation to isobutene, comprising a carrier, an active metal Pt and a promoter metal Sn supported on the carrier, wherein the carrier is zinc-loaded γ-Al2O3, expressed as Zn-γ-Al2O3, and the loading amounts of Pt, Sn, and Zn, calculated as a mass percentage of the γ-Al2O3, are as follows: Pt 0.1%, Sn 0.1%, and Zn 0.1%; wherein the specific surface area of the carrier is 60-120 m 2 / g, pore size of 10-20nm, particle size of 1.8-2mm; the catalyst is marked as Pt 0.1-Sn 0.1 / Zn 0.1 -γ-Al2O3;

[0059] Preparation method of the catalyst:

[0060] (1) 135 g of low-sodium pseudo-boehmite prepared by the alcohol aluminum method was mixed with 200 g of 15 wt% acetic acid solution, and stirred in a water bath at 70 ° C for 3 h at a stirring speed of 200 r / min to obtain a crude aluminum sol; a non-polar solvent, carbon tetrachloride, was added to the crude aluminum sol according to a volume ratio of 1:3 between the crude aluminum sol and the non-polar solvent, and stirred at room temperature for 2 h, allowed to stand at 3 ° C for 3 h, and then heated to 40 ° C at a heating rate of 2 ° C / min and stirred at a constant temperature for 35 min. After standing overnight, the mixture was filtered to obtain an aluminum sol, which was dried at room temperature to obtain an aluminum sol powder;

[0061] (2) At room temperature, the obtained aluminum sol powder was dissolved in water to prepare an aluminum sol with a solid content of 25%. After stirring evenly, sodium carboxymethyl cellulose was added and the stirring was continued for 1 hour. Then, an aqueous solution of zinc acetate was added and the stirring was continued for 2 hours. The pH was adjusted to 3 with dilute hydrochloric acid to obtain a Zn-modified aluminum sol. The Zn-modified aluminum sol was dripped into a hot oil column at 120°C using an oil column molding method to obtain alumina pellets. The pellets were transferred to a high-pressure aging autoclave and aged for 24 hours at 2.5 MPa and 170°C under a nitrogen atmosphere. The pellets were washed with water, dried at 120°C to constant weight, and calcined at 600°C for 5 hours to obtain a Zn-γ-Al2O3 carrier. The mass ratio of the sodium carboxymethyl cellulose to the aluminum sol with a solid content of 25% was 5:100.

[0062] (3) Chloroplatinic acid and stannous sulfate were added to ethanol in sequence and mixed evenly to obtain an impregnation solution. The Zn-γ-Al2O3 carrier was added to the impregnation solution and impregnated at room temperature for 12 h. The solvent ethanol in the system was evaporated using a rotary evaporator, and the mixture was dried at 120°C to constant weight and calcined at 600°C for 5 h.

[0063] (4) Reducing the reaction mixture at 450° C. for 2 h under a hydrogen atmosphere to obtain the catalyst.

[0064] Comparative Example 1

[0065] The catalyst comprises a carrier γ-Al2O3 and an active metal Pt supported on the carrier, wherein the Pt loading is 0.5% by mass of the γ-Al2O3; wherein the specific surface area of the carrier is 60-120m 2 / g, pore size of 10-20nm, particle size of 1.8-2mm; the catalyst is marked as Pt 0.5 / γ-Al2O3;

[0066] The preparation method of the catalyst is as follows:

[0067] (1) 135 g of low-sodium pseudo-boehmite prepared by the alcohol aluminum method was mixed with 200 g of a 10 wt% hydrochloric acid solution, and stirred in an 80°C water bath for 2 h at a stirring speed of 200 r / min to obtain a crude aluminum sol;

[0068] (2) At room temperature, hexamethylenetetramine and polyethylene glycol 2000 were added to the crude aluminum sol and stirred for 0.5 h to obtain aluminum sol. The aluminum sol was dripped into a hot oil column at 120°C by an oil column molding method to obtain alumina pellets. The pellets were transferred to a high-pressure aging autoclave, aged for 48 h at 150°C under a nitrogen atmosphere at 2 MPa, washed with water, dried at 80°C to constant weight, and calcined at 550°C for 5 h to obtain a γ-Al2O3 carrier; wherein the total mass of hexamethylenetetramine and polyethylene glycol 2000 was 10% of the mass of the crude aluminum sol, and the mass ratio of hexamethylenetetramine to polyethylene glycol 2000 was 4:1;

[0069] (3) Add chloroplatinic acid to water and mix well to obtain an impregnation solution, add the γ-Al2O3 carrier to the impregnation solution, impregnate at room temperature for 8 hours, evaporate the solvent water in the system using a rotary evaporator, dry at 100°C to constant weight, and calcine at 550°C for 5 hours;

[0070] (4) Reducing the reaction mixture at 350° C. for 2 h under a hydrogen atmosphere to obtain the catalyst.

[0071] Comparative Example 2

[0072] The catalyst comprises a carrier γ-Al2O3, and an active metal Pt and an auxiliary metal Sn supported on the carrier, wherein the Pt loading is 0.5% and the Sn loading is 1% based on the mass percentage of the γ-Al2O3; wherein the specific surface area of the carrier is 60-120m 2 / g, pore size of 10-20nm, particle size of 1.8-2mm; the catalyst is marked as Pt 0.5 -Sn1 / γ-Al2O3;

[0073] The preparation method of the catalyst is as follows:

[0074] (1) 135 g of low-sodium pseudo-boehmite prepared by the alcohol aluminum method was mixed with 200 g of a 10 wt% hydrochloric acid solution, and stirred in an 80°C water bath for 2 h at a stirring speed of 200 r / min to obtain a crude aluminum sol;

[0075] (2) At room temperature, hexamethylenetetramine and polyethylene glycol 2000 were added to the crude aluminum sol and stirred for 0.5 h to obtain aluminum sol. The aluminum sol was dripped into a hot oil column at 120°C by an oil column molding method to obtain alumina pellets. The pellets were transferred to a high-pressure aging autoclave, aged for 48 h at 150°C under a nitrogen atmosphere at 2 MPa, washed with water, dried at 80°C to constant weight, and calcined at 550°C for 5 h to obtain a γ-Al2O3 carrier; wherein the total mass of hexamethylenetetramine and polyethylene glycol 2000 was 10% of the mass of the crude aluminum sol, and the mass ratio of hexamethylenetetramine to polyethylene glycol 2000 was 4:1;

[0076] (3) Add chloroplatinic acid and anhydrous tin chloride to water and mix well to obtain an impregnation solution. Add the γ-Al2O3 carrier to the impregnation solution and impregnate at room temperature for 8 hours. Use a rotary evaporator to evaporate the solvent water in the system, dry at 100°C to constant weight, and calcine at 550°C for 5 hours.

[0077] (4) Reducing the reaction mixture at 350° C. for 2 h under a hydrogen atmosphere to obtain the catalyst.

[0078] Comparative Example 3

[0079] The catalyst includes a carrier and an active metal Pt supported on the carrier, wherein the carrier is γ-Al2O3 loaded with zinc, expressed as Zn-γ-Al2O3, and the loading amount of Pt is 0.5% and the loading amount of Zn is 0.5% by mass percentage of γ-Al2O3; wherein the specific surface area of the carrier is 60-120m 2 / g, pore size of 10-20nm, particle size of 1.8-2mm; the catalyst is marked as Pt 0.5 / Zn 0.5 -γ-Al2O3;

[0080] The preparation method of the catalyst is as follows:

[0081] (1) 135 g of low-sodium pseudo-boehmite prepared by the alcohol aluminum method was mixed with 200 g of a 10 wt% hydrochloric acid solution, and stirred in a water bath at 80 ° C for 2 h at a stirring speed of 200 r / min to obtain a crude aluminum sol; a non-polar solvent n-heptane was added to the crude aluminum sol according to a volume ratio of 1:2 to the non-polar solvent in the crude aluminum sol, and stirred at room temperature for 1 h, and allowed to stand at 2 ° C for 4 h, and then heated to 45 ° C at a heating rate of 3 ° C / min and stirred at a constant temperature for 30 min. After standing overnight, the mixture was filtered to obtain an aluminum sol, which was dried at room temperature to obtain an aluminum sol powder;

[0082] (2) At room temperature, the obtained aluminum sol powder was dissolved in water to prepare an aluminum sol with a solid content of 25%. After stirring evenly, hexamethylenetetramine and polyethylene glycol 2000 were added and stirring was continued for 0.5 h. Then, an aqueous zinc nitrate solution was added and stirring was continued for 1.5 h. The pH was adjusted to 3.5 with dilute hydrochloric acid to obtain a Zn-modified aluminum sol. The Zn-modified aluminum sol was dripped into a hot oil column at 120°C using an oil column molding method to obtain alumina pellets. The pellets were transferred to a high-pressure aging autoclave, aged for 48 h at 150°C under a nitrogen atmosphere at 2 MPa, washed with water, dried at 80°C to constant weight, and calcined at 550°C for 5 h to obtain a Zn-γ-Al2O3 carrier; wherein the mass ratio of the total mass of hexamethylenetetramine and polyethylene glycol 2000 to the aluminum sol with a solid content of 25% was 10:100, and the mass ratio of hexamethylenetetramine and polyethylene glycol 2000 was 4:1;

[0083] (3) Add chloroplatinic acid to water and mix well to obtain an impregnation solution, add the γ-Al2O3 carrier to the impregnation solution, impregnate at room temperature for 8 hours, evaporate the solvent water in the system using a rotary evaporator, dry at 100°C to constant weight, and calcine at 550°C for 5 hours;

[0084] (4) Reducing the reaction mixture at 350° C. for 2 h under a hydrogen atmosphere to obtain the catalyst.

[0085] Comparative Example 4

[0086] The catalyst comprises a carrier γ-Al2O3, and active metal Pt, auxiliary metal Sn and Zn supported on the carrier, wherein the Pt loading is 0.5%, the Sn loading is 1%, and the Zn loading is 0.5% based on the mass percentage of the γ-Al2O3; wherein the specific surface area of the carrier is 60-120m 2 / g, pore size of 10-20nm, particle size of 1.8-2mm; the catalyst is marked as Pt 0.5 -Sn 1- Zn 0.5 / γ-Al2O 3；

[0087] The preparation method of the catalyst is as follows:

[0088] (1) 135 g of low-sodium pseudo-boehmite prepared by the alcohol aluminum method was mixed with 200 g of a 10 wt% hydrochloric acid solution, and stirred in an 80°C water bath for 2 h at a stirring speed of 200 r / min to obtain a crude aluminum sol;

[0089] (2) At room temperature, hexamethylenetetramine and polyethylene glycol 2000 were added to the crude aluminum sol and stirred for 0.5 h to obtain aluminum sol. The aluminum sol was dripped into a hot oil column at 120°C by an oil column molding method to obtain alumina pellets. The pellets were transferred to a high-pressure aging autoclave, aged for 48 h at 150°C under a nitrogen atmosphere at 2 MPa, washed with water, dried at 80°C to constant weight, and calcined at 550°C for 5 h to obtain a γ-Al2O3 carrier; wherein the total mass of hexamethylenetetramine and polyethylene glycol 2000 was 10% of the mass of the crude aluminum sol, and the mass ratio of hexamethylenetetramine to polyethylene glycol 2000 was 4:1;

[0090] (3) Chloroplatinic acid, anhydrous tin chloride, and zinc nitrate were added to water and mixed evenly to obtain an impregnation solution. The γ-Al2O3 carrier was added to the impregnation solution and impregnated at room temperature for 8 h. The solvent water in the system was evaporated using a rotary evaporator, and the system was dried at 100°C to constant weight and calcined at 550°C for 5 h.

[0091] (4) Reducing the reaction mixture at 350° C. for 2 h under a hydrogen atmosphere to obtain the catalyst.

[0092] Comparative Example 5

[0093] A catalyst for isobutane dehydrogenation to isobutene, comprising a carrier, an active metal Pt and a promoter metal Sn supported on the carrier, wherein the carrier is zinc-loaded γ-Al2O3, expressed as Zn-γ-Al2O3, and the Pt, Sn, and Zn loadings are as follows, calculated as a mass percentage of the γ-Al2O3: Pt 0.5%, Sn 1%, and Zn 0.5%; wherein the specific surface area of the carrier is 60-120 m 2 / g, pore size of 10-20nm, particle size of 1.8-2mm; the catalyst is marked as Pt 0.5 -Sn1 / Zn 0.5 -γ-Al2O3(Ⅰ);

[0094] Preparation method of the catalyst:

[0095] (1) 135 g of low-sodium pseudo-boehmite prepared by the alcohol aluminum method was mixed with 200 g of a 10 wt% hydrochloric acid solution, and stirred in a water bath at 80° C. for 2 h at a stirring speed of 200 r / min to obtain a crude aluminum sol; a non-polar solvent, n-heptane, was added to the crude aluminum sol in a volume ratio of 1:2 to the non-polar solvent in the crude aluminum sol, and stirred at room temperature for 1 h, and then heated to 45° C. at a heating rate of 3° C. / min and stirred at a constant temperature for 30 min. After standing overnight, the mixture was filtered to obtain an aluminum sol, which was dried at room temperature to obtain an aluminum sol powder;

[0096] (2) At room temperature, the obtained aluminum sol powder was dissolved in water to prepare an aluminum sol with a solid content of 25%. After stirring evenly, hexamethylenetetramine and polyethylene glycol 2000 were added and stirring was continued for 0.5 h. Then, an aqueous zinc nitrate solution was added thereto and stirring was continued for 1.5 h. The pH was adjusted to 3.5 with a dilute hydrochloric acid solution to obtain a Zn-modified aluminum sol. The Zn-modified aluminum sol was dripped into a hot oil column at 120°C using an oil column molding method to obtain alumina pellets. The pellets were transferred to a high-pressure aging autoclave and aged at 150°C for 48 h under a nitrogen atmosphere at 2 MPa. The pellets were washed with water, dried at 80°C to constant weight, and calcined at 550°C for 5 h to obtain a Zn-γ-Al2O3 carrier. The mass ratio of the total mass of hexamethylenetetramine and polyethylene glycol 2000 to the aluminum sol with a solid content of 25% was 10:100, and the mass ratio of hexamethylenetetramine and polyethylene glycol 2000 was 4:1.

[0097] (3) Chloroplatinic acid and anhydrous tin chloride were added to water in sequence and mixed evenly to obtain an impregnation solution. The Zn-γ-Al2O3 carrier was added to the impregnation solution and impregnated at room temperature for 8 h. The solvent water in the system was evaporated using a rotary evaporator, and the mixture was dried at 100°C to constant weight and calcined at 550°C for 5 h.

[0098] (4) Reducing the reaction mixture at 350° C. for 2 h under a hydrogen atmosphere to obtain the catalyst.

[0099] Comparative Example 6

[0100] A catalyst for dehydrogenating isobutane to produce isobutene, comprising a carrier, an active metal Pt and a promoter metal Sn supported on the carrier, wherein the carrier is zinc-loaded γ-Al2O3, expressed as Zn-γ-Al2O3, and the loading amounts of Pt, Sn, and Zn, calculated as a mass percentage of the γ-Al2O3, are as follows: Pt 0.5%, Sn 1%, and Zn 0.5%; wherein the specific surface area of the carrier is 80-120 m 2 / g, pore size of 10-20nm, particle size of 1.8-2mm; the catalyst is marked as Pt 0.5 -Sn1 / Zn 0.5 -γ-Al2O3(Ⅱ);

[0101] Preparation method of the catalyst:

[0102] (1) 135 g of low-sodium pseudo-boehmite prepared by the alcohol aluminum method was mixed with 200 g of a 10 wt% hydrochloric acid solution, and stirred in an 80° C. water bath for 2 h at a stirring speed of 200 r / min to obtain a crude aluminum sol; a non-polar solvent, n-heptane, was added to the crude aluminum sol in a volume ratio of 1:2 to the non-polar solvent, and the mixture was stirred at room temperature for 1 h, allowed to stand at 2° C. for 4 h, allowed to stand overnight, and then filtered to obtain an aluminum sol, which was dried at room temperature to obtain an aluminum sol powder;

[0103] (2) At room temperature, the obtained aluminum sol powder was dissolved in water to prepare an aluminum sol with a solid content of 25%. After stirring evenly, hexamethylenetetramine and polyethylene glycol 2000 were added and stirring was continued for 0.5 h. Then, an aqueous zinc nitrate solution was added thereto and stirring was continued for 1.5 h. The pH was adjusted to 3.5 with a dilute hydrochloric acid solution to obtain a Zn-modified aluminum sol. The Zn-modified aluminum sol was dripped into a hot oil column at 120°C using an oil column molding method to obtain alumina pellets. The pellets were transferred to a high-pressure aging autoclave and aged at 150°C for 48 h under a nitrogen atmosphere at 2 MPa. The pellets were washed with water, dried at 80°C to constant weight, and calcined at 550°C for 5 h to obtain a Zn-γ-Al2O3 carrier. The mass ratio of the total mass of hexamethylenetetramine and polyethylene glycol 2000 to the aluminum sol with a solid content of 25% was 10:100, and the mass ratio of hexamethylenetetramine and polyethylene glycol 2000 was 4:1.

[0104] (3) Chloroplatinic acid and anhydrous tin chloride were added to water in sequence and mixed evenly to obtain an impregnation solution. The Zn-γ-Al2O3 carrier was added to the impregnation solution and impregnated at room temperature for 8 h. The solvent water in the system was evaporated using a rotary evaporator, and the mixture was dried at 100°C to constant weight and calcined at 550°C for 5 h.

[0105] (4) Reducing the reaction mixture at 350° C. for 2 h under a hydrogen atmosphere to obtain the catalyst.

[0106] Comparative Example 7

[0107] A catalyst for dehydrogenating isobutane to produce isobutene, comprising a carrier, an active metal Pt and a promoter metal Sn supported on the carrier, wherein the carrier is zinc-loaded γ-Al2O3, expressed as Zn-γ-Al2O3, and the loading amounts of Pt, Sn, and Zn, calculated as a mass percentage of the γ-Al2O3, are as follows: Pt 0.5%, Sn 1%, and Zn 0.5%; wherein the specific surface area of the carrier is 80-120 m 2 / g, pore size of 10-20nm, particle size of 1.8-2mm; the catalyst is marked as Pt 0.5 -Sn1 / Zn 0.5 -γ-Al2O3(Ⅲ);

[0108] Preparation method of the catalyst:

[0109] (1) 135 g of low-sodium pseudo-boehmite prepared by the alcohol aluminum method was mixed with 200 g of a 10 wt% hydrochloric acid solution, and stirred in an 80° C. water bath for 2 h at a stirring speed of 200 r / min to obtain a crude aluminum sol; a non-polar solvent, n-heptane, was added to the crude aluminum sol in a volume ratio of 1:2 to the non-polar solvent, and the mixture was stirred at room temperature for 1 h. After standing overnight, the mixture was filtered to obtain an aluminum sol, which was dried at room temperature to obtain an aluminum sol powder;

[0110] (2) At room temperature, the obtained aluminum sol powder was dissolved in water to prepare an aluminum sol with a solid content of 25%. After stirring evenly, hexamethylenetetramine and polyethylene glycol 2000 were added and stirring was continued for 0.5 h. Then, an aqueous zinc nitrate solution was added thereto and stirring was continued for 1.5 h. The pH was adjusted to 3.5 with a dilute hydrochloric acid solution to obtain a Zn-modified aluminum sol. The Zn-modified aluminum sol was dripped into a hot oil column at 120°C using an oil column molding method to obtain alumina pellets. The pellets were transferred to a high-pressure aging autoclave and aged at 150°C for 48 h under a nitrogen atmosphere at 2 MPa. The pellets were washed with water, dried at 80°C to constant weight, and calcined at 550°C for 5 h to obtain a Zn-γ-Al2O3 carrier. The mass ratio of the total mass of hexamethylenetetramine and polyethylene glycol 2000 to the aluminum sol with a solid content of 25% was 10:100, and the mass ratio of hexamethylenetetramine and polyethylene glycol 2000 was 4:1.

[0111] (3) Chloroplatinic acid and anhydrous tin chloride were added to water in sequence and mixed evenly to obtain an impregnation solution. The Zn-γ-Al2O3 carrier was added to the impregnation solution and impregnated at room temperature for 8 h. The solvent water in the system was evaporated using a rotary evaporator, and the mixture was dried at 100°C to constant weight and calcined at 550°C for 5 h.

[0112] (4) Reducing the reaction mixture at 350° C. for 2 h under a hydrogen atmosphere to obtain the catalyst.

[0113] 1. Catalytic Performance Evaluation

[0114] The method for preparing isobutylene using the catalyst provided by the present invention comprises the following steps: loading the catalyst into a fixed-bed quartz reaction tube in a reaction device, using isobutane as a raw material, and introducing hydrogen to react; wherein the reaction temperature is 600°C, the reaction pressure is 0.1 MPa, and the mass space velocity of isobutane is 5 h -1 The molar ratio of isobutane to hydrogen was 1:1, and the separated reaction products were directly analyzed online by an Agilent 7890A gas chromatograph equipped with a hydrogen flame detector (FID).

[0115] Table 1 Reaction conditions and results

[0116]

[0117] As can be seen from Table 1, the catalyst prepared by the present invention has a significantly improved dispersion of active metal Pt compared to conventional Pt / Al2O3 catalysts. The strong interaction between Pt and the additives Sn and Zn makes Pt more evenly dispersed, effectively improving the catalytic activity of the catalyst in the application of isobutane dehydrogenation to isobutene. When the catalyst of the present invention is used for the isobutane dehydrogenation to isobutene reaction, the catalytic performance decreases less than that of the comparative example after 72 hours of evaluation, indicating that the catalyst has good stability. The presence of the two additives Sn and Zn weakens the acidity of the overall catalyst, significantly reduces the formation of catalyst carbon deposits, and enhances the stability and life of the catalyst. By modifying the carrier alumina with Zn, the amount of carbon deposits on the catalyst is significantly reduced. By comparing the performance of the catalyst prepared by Example 7 with that of Comparative Example 4, the catalyst prepared by first modifying the carrier γ-Al2O3 with Zn and then impregnating the active metal Pt and the additive Sn is far superior to the catalyst prepared by conventional mixed impregnation in terms of both the dispersion of Pt metal and the performance of the catalyst. Comparative Examples 5-7 demonstrate that, when preparing the carrier Zn-γ-Al2O3, first performing low-temperature treatment and then performing temperature treatment in step (1) can synergistically improve the catalytic performance of the catalyst.

Claims

1. A method for preparing a catalyst for dehydrogenating isobutane to isobutene, characterized in that: The catalyst includes a carrier, and an active metal Pt and a promoter metal Sn supported on the carrier. The carrier is γ-Al2O3 loaded with zinc, expressed as Zn-γ-Al2O3. The loading amounts of Pt, Sn, and Zn are as follows, calculated as a mass percentage of γ-Al2O3: Pt 0.1-3%, Sn 0.1-2%, and Zn 0.1-1%. The preparation method comprises the following steps: (1) mixing low sodium pseudo-boehmite with an acid solution, stirring at 60-80°C for 2-3 hours to obtain a crude aluminum sol; adding a non-polar solvent to the crude aluminum sol, stirring at room temperature for 0.5-2 hours, standing at 2-5°C for 3-4 hours, then heating to 40-45°C at a heating rate of 1-3°C / min, stirring at a constant temperature for 30-50 minutes, standing overnight, filtering to obtain an aluminum sol, and drying at room temperature to obtain an aluminum sol powder; (2) At room temperature, aluminum sol powder is dissolved in deionized water to prepare aluminum sol with a solid content of 25%. After stirring evenly, a gelling agent is added thereto and stirring is continued for 0.5-1h. Then, a Zn precursor aqueous solution is added thereto and stirring is continued for 1.5-2h. The pH is adjusted to 3-4 to obtain Zn-modified aluminum sol. The Zn-γ-Al2O3 carrier is obtained by the oil column molding method through ball dropping, aging, water washing, drying, and roasting. (3) adding a Pt precursor and a Sn precursor to an impregnation solvent in sequence, mixing them uniformly to obtain an impregnation solution, adding the Zn-γ-Al2O3 carrier to the impregnation solution, impregnating, removing the impregnation solvent, drying, and calcining; (4) Reducing under a hydrogen atmosphere to obtain the catalyst.

2. The method for preparing the catalyst according to claim 1, wherein: The specific surface area of the carrier is 80-120m 2 / g, pore size is 10-20nm, and particle size is 1.8-2mm.

3. The method for preparing the catalyst according to claim 1, wherein: In step (1), the volume ratio of the crude aluminum sol to the non-polar solvent is 1:(1-3); the non-polar solvent is toluene, carbon tetrachloride or n-heptane; the acid solution is at least one of hydrochloric acid, nitric acid, acetic acid and chloroacetic acid, and the mass concentration of the acid solution is 8%-15%.

4. The method for preparing the catalyst according to claim 3, wherein: The gelling agent is at least one of hexamethylenetetramine, urea, polyethylene glycol 2000, and sodium carboxymethyl cellulose; the mass ratio of the gelling agent to the aluminum sol with a solid content of 25% is (5-10):

100.

5. The method for preparing the catalyst according to claim 4, wherein: The aging is carried out in a nitrogen atmosphere, at 2-2.5 MPa and 140-170° C. for 24-48 hours.

6. The method for preparing the catalyst according to claim 5, characterized in that: The precursor of Zn is at least one of zinc chloride, zinc nitrate, and zinc acetate; the precursor of Pt is chloroplatinic acid; and the precursor of Sn is at least one of anhydrous tin chloride, anhydrous stannous chloride, and stannous sulfate.

7. The method for preparing the catalyst according to claim 6, wherein: The immersion in step (3) is carried out at room temperature for 6-12 hours; the immersion solvent is water, methanol or ethanol.

8. The method for preparing the catalyst according to claim 7, characterized in that: The reduction conditions are as follows: reduction at 300-450° C. for 2-5 hours; the drying temperature is 80-120° C.; and the calcination is performed at 500-600° C. for 4-6 hours.

9. A method for preparing isobutylene by dehydrogenating isobutane, characterized in that: The catalyst is loaded into the reaction device, and isobutane is used as the raw material, and hydrogen is introduced to react at the same time; wherein the reaction temperature is 550-650℃, the reaction pressure is 0-0.1Mpa, and the mass space velocity of isobutane is 0.5-10h -1 The molar ratio of isobutane to hydrogen is 1:(0.5-1); the reaction device is a fixed bed, a fluidized bed or a moving bed; the catalyst is a catalyst prepared by the preparation method according to claim 1.

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