Dehydrogenation catalyst for regulating carrier pores

Abstract

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

Description

Technical Field

[0001] The present invention relates to a dehydrogenation catalyst and a method for manufacturing the same, and more particularly to a spherical platinum-based catalyst containing tin and potassium components used in the catalytic dehydrogenation reaction of light hydrocarbons in the C3-C5 range such as propane and butane. The catalyst carrier has a pore size and surface area adjusted by heat treatment, and the platinum and tin alloy components exist in an egg-shell form only from the catalyst surface to a specific depth. In the catalyst according to the present invention, the catalyst carrier is a mixture of γ-alumina and θ-alumina, has a pore volume of 0.5-0.65 cc / g, the platinum dispersion of the catalyst is 30-50%, and the average platinum particle size is 3 nm-5 nm. Background Art

[0002] Light olefins are substances used for various commercial purposes such as raw materials for plastics, synthetic rubbers, medical and chemical products, and can be manufactured by the dehydrogenation reaction of the above-mentioned light hydrocarbons.

[0003]

[0004] As a catalyst for catalyzing the dehydrogenation reaction of light hydrocarbons, spherical forming carriers having fine pores such as alumina, zeolite, silica, and spinel-type metal aluminates are mainly used. These substances have good effects in terms of anti-coking performance or selectivity of products. However, as the reaction progresses, the amount of coke accumulated in the catalyst gradually increases and the fine pores are blocked by coke, resulting in the inactivation of the active metal present inside the fine pores and being unable to participate in the reaction. Therefore, a carrier structure that can reduce side reactions such as cracking and coke deposition is required. Therefore, it is necessary to maintain large pores while reducing fine pores inside the catalyst. In view of the above viewpoints, an alumina carrier that can be relatively easily adjusted in pore size only by heat treatment is mainly applied as the catalyst carrier. However, γ-alumina is vulnerable to coke deposition due to its small pore size and can cause side reactions due to the acid centers of the carrier, while α-alumina can induce metal aggregation by hindering metal dispersion. Therefore, although its selectivity is excellent, it has the problem of a decrease in the overall conversion rate. Summary of the Invention

[0005] As a result of the present inventors' research on dehydrogenation catalyst carriers, it was found that a mixed carrier of α-alumina and θ-alumina can remove acid centers by high-temperature heat treatment and thereby suppress side reactions, and can minimize the aggregation between metals due to its excellent binding force with metals, which is beneficial to conversion rate and selectivity.

[0006] The object of the present invention is to provide a catalyst with improved durability by suppressing the inevitable platinum sintering phenomenon in the catalyst used in the dehydrogenation reaction of light hydrocarbons. The object is achieved by treating a porous alumina support to form a mixture of γ-alumina and θ-alumina with appropriate pore size and surface area, and a dehydrogenation catalyst in which platinum and tin alloy components exist in an egg-shell form only from the catalyst surface to a specific depth. Without limitation, the support of the catalyst according to the present invention preferably has a pore volume of 0.5 to 0.65 cc / g, the platinum dispersion of the catalyst is 30 to 50%, and the average platinum particle size is 3 nm to 5 nm.

[0007] In the dehydrogenation catalyst according to the present invention, the platinum-tin alloy is distributed in an egg-shell form in a support with adjusted pore size and surface area, and the dispersion of the active metal is maximized. Therefore, even when operating for a long time in the dehydrogenation process, a high conversion rate and selectivity can be maintained. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 The changes in the conversion rate and selectivity over time are illustrated. DETAILED DESCRIPTION

[0009] For the catalyst with an egg-shell form of active metal according to the present invention, as a porous alumina support, in particular, a mixture of α-alumina and θ-alumina is used as the support, and platinum, tin, and potassium are impregnated into the support. The platinum-tin alloy is distributed in an egg-shell structure from the support surface to a specific depth, and potassium is uniformly distributed throughout the support interior.

[0010] In the present application, the catalyst refers to a spherical catalyst, that is, a structure in which an active component and / or an auxiliary metal component is supported on a spherical support. The active component and / or the active metal and the tin component as an auxiliary metal exist in an egg-shell form, which is a form existing with a specific thickness from the catalyst surface to the catalyst center. In terms of directly forming a thickness from the catalyst surface, it is different from a ring form without the presence of the above components on the surface. In the present application, the active component will be described with platinum as the center, and tin and potassium components are exemplified as auxiliary metals, but it is not limited thereto, and metal components with the same purpose or function understood by those skilled in the art can be easily applied to the present invention. In the catalyst achieved in the present application, the support preferably can have a pore volume of 0.5 to 0.65 cc / g, the dispersion of platinum in the catalyst can be 30 to 50%, and the average particle size of the platinum-tin alloy can be 3 nm to 5 nm, but only examples with representative values within the above numerical ranges are described as embodiments.

[0011] The eggshell-shaped platinum catalyst with the specific structure of the present invention can be generally manufactured through the steps described below.

[0012] 1) Preparation of a platinum-tin mixed solution: Since tin has a high reducibility, precipitation of platinum easily occurs in the air in a composite solution of platinum and tin. Therefore, the selection of the solvent is very important when preparing the composite solution. The present inventors selected a solvent that does not cause the reduction of tin, thereby ensuring that the precursor solution can maintain a stabilized state even over time. First, during the mixing of the precursors of platinum and tin, an organic solvent is added to ensure that the platinum-tin complex does not break, and hydrochloric acid is added to prepare a solution in an acidic environment. The organic solvent for this purpose can be selected from one or two solvents among methanol, ethanol, butanol, acetone, ethyl acetate, acetonitrile, ethylene glycol, triethylene glycol, ethylene glycol ether, glycerol, sorbitol, xylitol, dialkyl ether, and tetrahydrofuran, or can be used sequentially or as a mixed solution.

[0013] 2) Uniform impregnation of the platinum-tin mixed solution into a porous alumina support: To adjust the pore size and pore volume, γ and θ crystalline porous alumina supports heat-treated at 850-1100°C in a calcination furnace are used. The prepared platinum-tin solution is impregnated into the heat-treated support by the spray impregnation method. The heat treatment temperature is closely related to the crystal phase and pore structure of the support. When the heat treatment temperature is below 850°C, the crystal phase of alumina is mainly in the γ phase, and there may be a problem that the diffusion rate of the reactants in the support becomes slow due to the too small pore size of the support. When the heat treatment temperature reaches above 1100°C, the crystal phase of alumina is mainly in the α phase. Although the pore size exists in a state favorable for the reaction, there may be a problem of reduced dispersion of the active metal distributed in the α-alumina phase during the loading of the active metal. Therefore, the heat treatment temperature is set at 850-1100°C to modify it into a mixed state of α and θ alumina.

[0014] 3) Fixing the metal in the support: After impregnation, a drying process is carried out in a dryer at 100-150°C or above for 12 hours or more, and then the metal is fixed in the support by calcination in an air environment within the range of 400-700°C.

[0015] 4) Loading and fixing of an alkali metal: To inhibit side reactions caused by acid centers remaining in the porous alumina support, an alkali metal is loaded. Potassium is loaded into the pores inside the support by the spray impregnation method, and dried in a dryer at 100-150°C for 12 hours or more, and then potassium is fixed in the support by calcination in an air environment within the range of 400-700°C.

[0016] 5) Reduction: After fixing the alkali metal, a reduction process is carried out using hydrogen in the range of 400 to 600 degrees to obtain the final catalyst. When the temperature during the reduction process is below 400 degrees, it may cause the problem that metal oxides cannot be completely reduced, and when the temperature is higher than 600 degrees, it may cause the problem of a decrease in active sites due to the aggregation and sintering of metal particles.

[0017] In order to confirm the dispersion degree of the metal active substance for the catalyst according to the present invention, a carbon monoxide adsorption test is carried out. First, after heating to 400 degrees using helium, it is treated with oxygen and hydrogen to remove the moisture in the catalyst and reduce the unreduced metal oxides. Next, after cooling to 50 degrees, 7% carbon monoxide gas is injected, and then the amount of carbon monoxide gas adsorbed onto the noble metal is analyzed. Assuming that carbon monoxide and platinum are adsorbed in a ratio of 1:1, the dispersion degree and particle size of platinum are finally calculated. In addition, in order to evaluate the dehydrogenation performance, hydrocarbons with 2 to 5 carbon atoms, including alkanes, isoalkanes, and alkyl aromatics, preferably hydrocarbons with 3 to 4 carbon atoms, are diluted with hydrogen, and at 500 to 680 °C, preferably 570 °C, 0 to 2 atmospheres, preferably 1.5 atmospheres, and the liquid hourly space velocity (LHSV) of the alkanes is 1 to 40 h -1 The dehydrogenation reaction is carried out by gas-phase reaction under the following conditions.

[0018] Example 1

[0019] It is used after heat-treating the bead-shaped alumina support at 950 °C. Chloroplatinic acid is used as the platinum precursor, and stannous chloride is used as the tin precursor. Tin chloride equivalent to 0.2 wt% and hydrochloric acid equivalent to 5% of the total solution are mixed compared with the total weight of the catalyst. Next, after preparing a platinum-tin solution by adding chloroplatinic acid equivalent to 0.4 wt% compared with the total weight of the catalyst, it is added to ethanol in an amount equivalent to the total pore volume of the support and dissolved. The platinum-tin solution is impregnated into the prepared alumina support by the incipient wetness impregnation method. After drying the support loaded with the platinum-tin mixed solution at 120 °C for 12 hours, the active metal is fixed by performing a heat treatment process in an air environment and at 550 °C for 3 hours. Next, 0.8 wt% of potassium nitride compared with the total weight of the catalyst is also impregnated into the internal pores of the alumina containing platinum and tin by the incipient wetness impregnation method. After drying the support loaded with the metal at 120 °C for 12 hours, a catalyst loaded with the metal is produced by performing a heat treatment process at 550 °C for 3 hours. As the catalyst reduction process, the catalyst is completed by heating to 550 °C in a stepwise manner in an air environment and then maintaining it in a hydrogen environment for 1 hour. Example 1 is a method for manufacturing a catalyst by the platinum-tin co-impregnation method.

[0020] Comparative Example 1

[0021] Different from Example 1, a comparative catalyst is prepared by sequentially impregnating platinum, tin, and potassium. Alumina heat-treated in the same manner as in Example 1 is used. Chloroplatinic acid is used as the platinum precursor, and a solution obtained by mixing platinum equivalent to 0.4 wt% and hydrochloric acid equivalent to 5 wt% of the total solution compared with the total weight of the catalyst is diluted with deionized water in an amount equivalent to the total pore volume of the support, and then impregnated into the support by the incipient wetness impregnation method. The support loaded with platinum is subjected to drying and heat treatment processes to fix the active metal as shown in Example 1. Next, stannous chloride is used as the tin precursor, and a solution obtained by mixing tin equivalent to 0.2 wt% and the same amount of hydrochloric acid as in the platinum addition step compared with the total weight of the catalyst is loaded in the same manner as the platinum addition step, and then drying and heat treatment processes are performed. Next, a mixture of potassium nitride equivalent to 0.8 wt% and nitric acid equivalent to 1% of the total solution is diluted with deionized water, and then impregnated, dried, and calcined in the same manner. As the catalyst reduction process, a catalyst is produced by heating to 550 °C in a stepwise manner in an air environment and then maintaining it in a hydrogen environment for 1 hour.

[0022] Comparative Example 2

[0023] A catalyst was prepared in the same manner as in Example 1, except that the bead-shaped alumina support was used after heat treatment at 850 °C.

[0024] Comparative Example 3

[0025] A catalyst was prepared in the same manner as in Example 1, except that the bead-shaped alumina support was used after heat treatment at 1050 °C.

[0026] Comparative Example 4

[0027] A catalyst was prepared in the same manner as in Example 1, except that the bead-shaped alumina support was used after heat treatment at 1100 °C.

[0028] Test Example:

[0029] The catalysts according to the Examples and Comparative Examples were filled into a fixed-bed catalytic reactor and propane dehydrogenation reaction was carried out. In the composition of the reaction gas in the reactor, the volume ratio of hydrogen and propane was 0.61, and 95 ppm of the total gas consisted of H2S gas in order to prevent corrosion of the stainless steel (SUS) reactor. After heating to 607 °C at a heating rate of 6 °C per minute in a hydrogen atmosphere, propane dehydrogenation reaction was carried out while introducing propane and hydrogen in the specified ratio. The product gas was analyzed by gas chromatography to calculate the conversion and selectivity.

[0030] Table 1 shows the results of summarizing the platinum dispersion measurement results by carbon monoxide adsorption and the propane dehydrogenation reaction results for the catalysts according to the Examples and Comparative Examples, and Table 2 shows the results of summarizing the changes in the surface area and pore structure of the heat-treated supports. Figure 1 The changes in conversion and selectivity over time were plotted.

[0031]

Table 1

[0032]

[0033]

Table 2

[0034]

[0035] Dispersion evaluation

[0036] It can be confirmed from Table 1 that the platinum dispersion of Example 1 prepared using a platinum-tin mixed solution is higher than that of Comparative Example 1 prepared by sequential impregnation.

[0037] Performance evaluation of the catalyst

[0038] Because the initial conversion rate and selectivity of the alloy catalyst with high dispersion are relatively high, a relatively high propylene yield is presented. After 10 hours of activation of all the tested catalysts, although the propylene yield decreases due to the sintering of platinum and the deposition of carbon, the decrease rate of the yield of the platinum-tin alloy catalyst with a relatively high initial dispersion value is smaller compared with the comparative catalyst prepared by successive impregnation.

[0039] Support structure evaluation

[0040] By comparing the support structures based on the changes in the support calcination temperature in Table 2, it can be confirmed that in Comparative Example 2 with the lowest calcination temperature, although the conversion rate is relatively high, the selectivity is relatively low and the reduction rate of the propylene yield based on time is relatively large. Although not limited to theory, it is predicted that the above-mentioned phenomenon is because acid centers exist in the support due to the relatively low calcination temperature. Therefore, even when the dispersion of platinum is relatively high, the deposited carbon will be accelerated due to the existing acid centers, and the deposited carbon will block the platinum active sites and lead to a decrease in durability. On the contrary, in Comparative Example 4 with the highest support calcination temperature of 1100 degrees, although most of the acid centers of the support can be removed, the surface area will decrease due to the collapse of the pore structure of the support, and further cause a decrease in the dispersion and active area of platinum. Therefore, the final activity and durability both decrease.

Claims

1. A dehydrogenation catalyst, As a spherical dehydrogenation catalyst used in the catalytic dehydrogenation reaction of light hydrocarbons, the alumina support is heat-treated at 950 °C so that the alumina support is composed of a mixture of γ-alumina and θ-alumina, the platinum-tin alloy component exists in an egg-shell form, and potassium is uniformly distributed, and the dispersion of the platinum is 30-50%.

2. The dehydrogenation catalyst according to claim 1, The support has a pore volume of 0.5-0.65 cc / g.

3. The dehydrogenation catalyst according to claim 1, The average particle size of the platinum-tin alloy is 3 nm to 5 nm.

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