CN116547073A

CN116547073A - Dehydrogenation catalyst with regulation of support pores

Info

Publication number: CN116547073A
Application number: CN202180081472.2A
Authority: CN
Inventors: 崔贤雅; 金浩东; 姜东君; 徐正民; 刘英山
Original assignee: Heesung Catalysts Corp
Current assignee: Heesung Catalysts Corp
Priority date: 2020-12-04
Filing date: 2021-11-18
Publication date: 2023-08-04
Also published as: KR20220078856A; WO2022119191A1; ES2957010A2; KR102523345B1; ES2957010R1

Abstract

The present invention relates to a dehydrogenation catalyst, and more particularly, to a spherical platinum-based catalyst containing tin and potassium components, which is used for catalytic dehydrogenation of light hydrocarbons in the C3 to C5 range such as propane and butane, wherein the catalyst support has a pore size and a surface area adjusted by heat treatment, and the platinum and tin alloy components are present in an egg-shell state from the surface of the catalyst to a specific depth. In the catalyst according to the present invention, the catalyst carrier is a mixture of gamma alumina and theta alumina, has a pore volume of 0.5 to 0.65cc/g, a platinum dispersity of the catalyst of 30 to 50%, and a platinum average particle size of 3nm to 5nm.

Description

Dehydrogenation catalyst with regulation of support pores

Technical Field

The present invention relates to a dehydrogenation catalyst and a method for producing the same, and more particularly, to a spherical platinum catalyst containing tin and potassium components, which is used for catalytic dehydrogenation of light hydrocarbons in the C3 to C5 range such as propane and butane, wherein the catalyst support has a pore size and a surface area adjusted by heat treatment, and the platinum and tin alloy components are present in an egg-shell state only from the surface of the catalyst to a specific depth. In the catalyst according to the present invention, the catalyst carrier is a mixture of gamma alumina and theta alumina, has a pore volume of 0.5 to 0.65cc/g, a platinum dispersity of the catalyst of 30 to 50%, and a platinum average particle size of 3nm to 5nm.

Background

Light olefins are materials used for various commercial purposes such as plastics, synthetic rubbers, medical and chemical materials, and can be produced by dehydrogenation of light hydrocarbons as described above.

As a catalyst for catalyzing the dehydrogenation reaction of light hydrocarbons, spherical shaped carriers having fine pores such as alumina, zeolite, silica, spinel-type metal aluminates, etc. are mainly used, and these have good effects in terms of anti-carbon deposition performance or selectivity of products, but as the reaction proceeds, the amount of carbon deposition accumulated in the catalyst gradually increases and the fine pores are blocked by carbon deposition, thereby eventually causing the active metal existing inside the fine pores to fail to participate in the reaction, i.e., to be deactivated. Thus, there is a need for a support structure that reduces side reactions such as cracking and carbon deposition. Therefore, it is necessary to reduce the number of micropores and to maintain the number of huge micropores in the catalyst, and in view of the above, an alumina carrier which can relatively easily adjust the pore size by heat treatment alone is mainly used as a catalyst carrier. However, gamma alumina is vulnerable in terms of carbon deposition due to its small pore size, and side reactions occur due to the acid center of the support, whereas alpha alumina induces a metal agglomeration phenomenon by blocking the dispersity of metals, so that it has a problem that the overall conversion rate is lowered while its selectivity is excellent.

Disclosure of Invention

As a result of the studies of the present inventors on a dehydrogenation catalyst support, it was found that a mixture support of α alumina and θ alumina can remove acid centers by high temperature heat treatment and thereby inhibit side reactions, and can minimize agglomeration between metals because of excellent binding force with metals, thus contributing to conversion rate and selectivity.

The purpose of the present invention is to provide a catalyst which has improved durability by suppressing the platinum sintering (sintering) phenomenon that inevitably occurs in catalysts used in the dehydrogenation of light hydrocarbons. The object is achieved by a dehydrogenation catalyst comprising a porous alumina carrier, a mixture of gamma alumina and theta alumina having an appropriate pore size and surface area, and platinum and tin alloy components present in an egg-shell form only from the surface of the catalyst to a specific depth. The support of the catalyst according to the invention has, without limitation, a pore volume of 0.5 to 0.65cc/g, a platinum dispersity of 30 to 50% and a platinum average particle size of 3 to 5nm.

In the dehydrogenation catalyst according to the present invention, the platinum-tin alloy is distributed in an egg-shell form in the carrier having the pore size and surface area adjusted and the dispersion degree of the active metal is maximized, so that a high conversion rate and selectivity can be maintained even in the case of long-term operation in the dehydrogenation process.

Drawings

Fig. 1 illustrates a change in the conversion rate and the selection map with the lapse of time.

Detailed Description

The catalyst of the active metal egg-shell morphology according to the present invention is suitably used as a porous alumina carrier, particularly, a mixture of alpha alumina and theta alumina is used as a carrier and platinum, tin and potassium are impregnated into the carrier, the platinum-tin alloy is distributed in an egg-shell structure from the surface of the carrier to a specific depth, and the potassium is uniformly distributed throughout the inside of the carrier.

In the present application, the catalyst refers to a spherical catalyst, i.e., a structure in which an active ingredient and/or an auxiliary metal ingredient are supported on a spherical support. The active component and/or the active metal and the tin component as the auxiliary metal are present in an egg-shell form, and are present in a specific thickness from the catalyst surface to the catalyst center, and are different from a ring form in which the component is not present in the surface, in terms of forming the thickness directly from the catalyst surface. In the present application, the active ingredient will be described mainly with palladium, and tin and potassium are exemplified as auxiliary metals, but the present invention is not limited thereto, and metal components having the same purpose or function as understood by the relevant practitioner can be easily applied thereto. In the catalyst realized in the present application, the carrier may preferably have a pore volume of 0.5 to 0.65cc/g, the dispersity of platinum in the catalyst may be 30 to 50%, and the average particle size of the platinum-tin alloy may be 3nm to 5nm, but illustrations having representative values within the numerical ranges are described as examples only.

The eggshell-shaped platinum catalyst having the specific structure according to the present invention can be produced by the steps described below.

1) Preparation of platinum-tin mixed solution: since tin has high reducibility, platinum and tin complex solutions are prone to platinum precipitation in air. Therefore, the choice of solvent is very important in the production of the composite solution, and therefore the inventors have chosen a solvent that does not cause tin reduction, thereby ensuring that the precursor solution can maintain a stable state even with the passage of time. First, in the process of mixing platinum and tin precursors, an organic solvent is added to ensure that the platinum-tin complex is not broken, and hydrochloric acid is added to produce a solution in an acid environment. The organic solvent for the purpose may be one or two solvents selected from methanol, ethanol, butanol, acetone, ethyl acetate, acetonitrile, ethylene glycol, triethylene glycol, glycol ether, glycerin, sorbitol, xylitol, dialkyl ether and tetrahydrofuran, or may be used sequentially or as a mixed solution.

2) Uniformly impregnating the platinum-tin mixed solution into a porous alumina carrier: in order to adjust the pore size and pore volume, an α and θ crystalline porous alumina support heat-treated in a baking furnace at 850 to 1100 degrees is used. The prepared platinum-tin solution was impregnated into the heat-treated support by a spray impregnation method. The heat treatment temperature is closely related to the crystal phase and pore structure of the support, and in the case where the heat treatment temperature is 850 degrees or less, the crystal phase of alumina is mainly in the form of gamma phase, which may cause a problem that the diffusion rate of the reactant in the support becomes slow due to the too small pore size of the support, whereas in the case where the heat treatment temperature is 110 degrees or more, the crystal phase of alumina is mainly in the form of alpha phase, and the pore size is present in a state favorable for the reaction, but in the process of supporting the active metal, there is a problem that the dispersion degree of the active metal distributed to the alpha alumina phase is lowered, and therefore, the mixed state of alpha and theta alumina is modified by setting the heat treatment temperature to 850 to 1100 degrees.

3) Fixing the metal into the carrier: the drying process is performed in a drier of 100 to 150 degrees or more for 12 hours or more after impregnation, and then the metal is fixed into the support by firing in an air atmosphere and in a range of 400 to 700 degrees.

4) Supporting and fixing alkali metal: in order to suppress side reactions occurring due to acid centers remaining in the porous alumina carrier, alkali metals are supported. The potassium is supported in pores inside the carrier by a spray leaching method, and dried in a drier of 100 to 150 degrees for 12 hours or more, and then the potassium is fixed in the carrier by roasting in an air atmosphere and in a range of 400 to 700 degrees.

5) And (3) reduction: the reduction process is performed using hydrogen in the range of 400 to 600 degrees after the alkali metal is fixed, thereby obtaining a final catalyst. In the case where the temperature during the reduction is 400 degrees or less, there is a possibility that the metal oxide is not completely reduced, whereas in the case where the temperature is higher than 600 degrees, there is a possibility that the active sites are reduced due to agglomeration and sintering of the metal particles.

The carbon monoxide adsorption test was performed in order to confirm the dispersity of the metal active material with respect to the catalyst according to the present invention. First, after the temperature is raised to 400 degrees by helium gas, the moisture in the catalyst is removed by treatment with oxygen and hydrogen, and the metal oxide that is not reduced is reduced. Next, 7% of carbon monoxide gas was injected after cooling to 50 degrees, and the amount of carbon monoxide gas adsorbed to the noble metal was analyzed. It was assumed that carbon monoxide and platinum were adsorbed in a 1:1 ratio, and finally the dispersity and particle size of platinum were calculated. In addition, in order to evaluate dehydrogenation performance, hydrocarbons having a carbon number of 2 to 5, including paraffins, isoparaffins and alkylaromatics, preferably having a carbon number of 3 to 4, are diluted with hydrogen and at 500 to 680 ℃, preferably 570 ℃, 0 to 2 atmospheres, preferably 1.5 atmospheres, the liquid hourly space velocity (LHSV: liquid Hourly Space Velocity) of the paraffins is 1 to 40 hours ^-1 Is carried out by a gas phase reaction.

Example 1

The bead-type alumina carrier was used after being heat-treated at 950 ℃. Chloroplatinic acid was used as a platinum precursor, tin chloride was used as a tin precursor, and tin chloride corresponding to 0.2wt% of the total weight of the catalyst and 5% of hydrochloric acid corresponding to the total solution were mixed. Next, after a platinum-tin solution was produced by adding chloroplatinic acid in an amount equivalent to 0.4wt% based on the total weight of the catalyst, the solution was dissolved in ethanol in an amount equivalent to the total pore volume of the carrier. The platinum-tin solution was impregnated into the prepared alumina support by spray impregnation. After the carrier carrying the platinum-tin mixed solution was dried at 120 ℃ for 12 hours, the active metal was fixed by performing a heat treatment process in an air atmosphere at 550 ℃ for 3 hours. Next, 0.8wt% of potassium nitride, which is compared with the total weight of the catalyst, was similarly supported in the internal pores of alumina containing platinum and tin by a spray dipping method, and after drying the metal-supported carrier at 120 ℃ for 12 hours, the metal-supported catalyst was produced by performing a heat treatment process at 550 ℃ for 3 hours. As the catalyst reduction process, the catalyst was completed by raising the temperature to 550 ℃ in a stepwise (step) manner in an air atmosphere and then maintaining the temperature in a hydrogen atmosphere for 1 hour. Example 1 is a method of preparing a catalyst by platinum-tin simultaneous impregnation.

Comparative example 1

Unlike example 1, a comparative catalyst was prepared by impregnating platinum, tin and potassium in this order. Alumina subjected to heat treatment in the same manner as in example 1 was used. Chloroplatinic acid was used as a platinum precursor, and a solution obtained by mixing platinum in an amount of 0.4wt% based on the total weight of the catalyst and hydrochloric acid in an amount of 5wt% based on the total weight of the solution was diluted into deionized water having a total pore volume corresponding to the carrier, and impregnated into the carrier by a spray impregnation method. The platinum-carrying carrier was subjected to the drying and heat treatment processes as shown in example 1 to fix the active metal. Next, tin chloride was used as a tin precursor, and a solution obtained by mixing tin in an amount equivalent to 0.2wt% based on the total weight of the catalyst and hydrochloric acid in an amount equivalent to that in the platinum addition step was carried out in the same manner as in the platinum addition step, followed by drying and heat treatment. Next, potassium nitride corresponding to 0.8wt% of the total weight of the catalyst and nitric acid corresponding to 1% of the total solution were mixed, diluted with deionized water, impregnated in the same manner, dried and calcined. As a catalyst reduction process, a catalyst was produced by raising the temperature to 550 ℃ in a stepwise (step) manner in an air atmosphere and then maintaining the temperature in a hydrogen atmosphere for 1 hour.

Comparative example 2

A catalyst was produced in the same manner as in example 1, except that the bead-type alumina carrier was used after performing heat treatment at 850 degrees.

Comparative example 3

A catalyst was produced in the same manner as in example 1, except that the bead-type alumina carrier was used after performing heat treatment at 1050 degrees.

Comparative example 4

A catalyst was produced in the same manner as in example 1, except that the bead-type alumina carrier was used after performing heat treatment at 1100 degrees.

Test example:

the catalysts according to examples and comparative examples were packed into a fixed bed catalytic reactor and propane dehydrogenation reaction was performed. In the composition of the reaction gas in the reactor, the volume ratio of hydrogen to propane was 0.61, and in order to prevent corrosion of the stainless steel (SUS) reactor, 95ppm of the whole gas was composed of H2S gas. After the temperature was raised to 607 degrees at a temperature raising rate of 6 degrees per minute in a hydrogen atmosphere, propane dehydrogenation reaction was performed while propane and hydrogen were fed in the specific ratio. The generated gas was analyzed by gas chromatography (Gas chromatography), and the conversion rate and selectivity were calculated.

Table 1 is a result of finishing the results of the dispersity measurement of platinum adsorbed with carbon monoxide and the results of the propane dehydrogenation reaction with respect to the catalysts according to examples and comparative examples, and table 2 is a result of finishing the surface area of the heat-treated support and the change of the pore structure. Fig. 1 illustrates a change in the conversion rate and the selection map with the lapse of time.

[ Table 1 ]

[ Table 2 ]

Evaluation of dispersity

From table 1, it was confirmed that example 1 produced using the platinum-tin mixed solution had a higher dispersivity of platinum than comparative example 1 produced by sequential impregnation.

Evaluation of catalyst Performance

The alloy catalyst having a high degree of dispersion exhibited a higher propylene yield because of its higher initial conversion and selectivity, and after all the test object catalysts had been activated for 10 hours, the platinum-tin alloy catalyst having a higher initial degree of dispersion had a smaller yield reduction rate than the comparative catalyst produced by sequential impregnation, although the propylene yield was reduced due to sintering of platinum and deposition of carbon.

Carrier structure assessment

By comparing the support structure based on the change in the support firing temperature in table 2, it was confirmed that in comparative example 2 where the firing temperature was the lowest, the conversion was high, but the selectivity was low and the reduction rate of propylene yield based on time was large. Although not limited to theory, it is predicted that the phenomenon described above is due to the presence of acid centers in the carrier caused by the low firing temperature, and therefore, even in the case of high dispersion of platinum, carbon deposition is accelerated by the presence of acid centers, and the deposited carbon will clog the platinum active sites and cause a decrease in durability. In contrast, in comparative example 4 in which the calcination temperature of the support was highest, i.e., 1100 degrees, most of the acid centers of the support could be removed, but the pore structure of the support collapsed, resulting in a decrease in the surface area and further in the dispersity and active area of platinum, and thus the final activity and durability were reduced.

Claims

1. A catalyst for the dehydrogenation of a hydrocarbon,

as a spherical dehydrogenation catalyst used in catalytic dehydrogenation of light hydrocarbons, a carrier is composed of a mixture of gamma alumina and theta alumina, platinum and tin alloy components are present in an egg-shell form, and potassium is uniformly distributed.

2. The dehydrogenation catalyst according to claim 1,

the support has a pore volume of 0.5 to 0.65 cc/g.

3. The dehydrogenation catalyst according to claim 1,

the dispersity of the platinum is 30-50%, and the average particle size of the platinum-tin alloy is 3-5 nm.