ES2957057B2 - Dehydrogenation catalyst having a ring-type metal distribution - Google Patents

Description

DESCRIPTION

Dehydrogenation catalyst having a ring-type metal distribution

Technical field

The present disclosure relates to a dehydrogenation catalyst and, more specifically, to a spherical platinum catalyst containing tin and potassium components used for the catalytic dehydrogenation of C3 to C5 light hydrocarbons, such as propane, butane, and the like. The catalyst has a ring-shaped metal distribution where a platinum component is not present on the surface of the catalyst but is present within the catalyst, in the form of a ring with a predetermined thickness at a predetermined depth from the surface of the catalyst. In the catalyst according to the present disclosure, the tin component is present in an eggshell shape where the tin component is present in a region from the surface to a predetermined depth, and the potassium component is evenly distributed throughout the catalyst.

Background of the technique

Light olefins are materials used for various commercial purposes related to raw materials for plastics, synthetic rubber, medicines, chemicals, and the like and can be produced by the following dehydrogenation of light hydrocarbons.

Paraffin (CnH2n+2) -or- Olefin (CnH2n) Hydrogen (H2)

For catalysts catalyzing the dehydrogenation of light hydrocarbons, spherical-shaped carriers having micropores, such as gamma/theta/alpha alumina, zeolite, silica, spinel-type metal aluminate, and the like, are mainly used. These materials have a satisfactory effect on coke resistance or product selectivity. However, when the amount of coke accumulated on the catalyst gradually increases as the reaction progresses, the micropores become clogged with coke. In addition, the active metals present in the pores eventually cannot participate in the reaction and become inactive. Therefore, a carrier structure capable of reducing side reactions such as cracking and the like and coke deposition is required. On the other hand, the loss of active metals is also an important factor in the decrease of the conversion rate. In particular, in the case of using a fluidized reactor, the loss of active metals may cause the catalyst surface to crack or wear due to the abrasion occurring between the catalyst and the catalyst while the catalyst is flowing, or the abrasion occurring between the catalyst and the reactor. In addition, as illustrated in Figure 1, when the amount of the active metal on the catalyst surface is high, the catalyst surface may be clogged with coke generated by a successively occurring cracking reaction. Therefore, a ring-shaped catalytic structure having a shape in which no active metal is present on the surface can solve such deficiencies.

Disclosure

Technical problem

An objective of the present disclosure is to prevent a decrease in mass transfer by suppressing surface coke deposition that inevitably occurs on a catalyst used for the dehydrogenation of light hydrocarbons, as well as to reduce the loss of platinum active sites due to abrasion resulting from a fluidized bed reactor.

Technical solution

The above object may be achieved by a catalyst used for dehydrogenation of light hydrocarbons, the catalyst having a shape in which platinum is distributed within a ring-shaped spherical carrier with a thickness in a range of 200 um to 500 um at a depth in a range of 30 um to 200 um from the surface of the carrier. Without limitation, in the catalyst of the present disclosure, an eggshell-shaped tin component may be present where the tin component is present in a region from the surface of the catalyst to a predetermined depth, and a potassium component may be uniformly supported on the inside of the carrier.

The present disclosure is characterized by providing a spherical platinum catalyst containing tin and potassium components used for the catalytic dehydrogenation of light hydrocarbons. The platinum component is not present on the surface of the catalyst, but is present within the catalyst, in the form of a ring with a predetermined thickness at a predetermined depth from the catalyst surface. Without limitation, the tin component may be present in an eggshell form where the tin component is present in a region from the catalyst surface to a predetermined depth, and the potassium component may be evenly distributed throughout the catalyst. Preferably, to form a ring-shaped structure, the predetermined depth may be set in a range of 30 um to 200 um, and the predetermined thickness may be set in a range of 200 um to 500 um.

Beneficial effects

In the dehydrogenation catalyst according to the present disclosure, the platinum active component is not present on the surface of the catalyst, but is present within the catalyst, in the form of a ring with a predetermined thickness while separating inward from the surface. When dehydrogenation is performed using such a ring-type catalyst, the deactivation rate of the catalyst is reduced in a durability test while obtaining the same level of activity, compared to that of existing catalysts containing an active component present in a non-ring form. Therefore, even after 24 hours of an abrasion test, an equal or higher level of activity is shown.

Description of the drawings

Figure 1 is a schematic diagram illustrating pore clogging by coke in catalysts where an active component is present or not present on the surface;

Figure 2 is a diagram of EPMA images showing the distribution of active components in a catalyst; and

Figure 3 is a graph showing changes in conversion rate over time.

Best way

A ring-type active metal catalyst according to the present disclosure is a catalyst to which a porous alumina carrier is applied. The catalyst has a shape in which platinum, tin and potassium are introduced. The platinum is distributed in a thickness in the range of 200 um to 500 um at a depth in the range of 30 um to 200 um from the surface of the carrier. In addition, potassium is evenly distributed throughout the interior of the carrier.

The catalyst herein refers to a spherical catalyst, which has a shape in which an active component and/or an auxiliary metal is supported on a spherical carrier. The active component present in a ring-shaped or ring-like form means that the active component is present in a predetermined thickness while separating inward from the catalyst surface, which is distinguished from the tin component present in an eggshell-like form. The eggshell-like form is distinguished from the ring-like form by the fact that the eggshell-like form with a predetermined thickness is present in a region from the catalyst surface to the center of the catalyst, and the thickness thereof is formed directly from the catalyst surface. As used herein, platinum is mainly described as the active component, and the auxiliary metal is exemplified by tin and potassium components. However, the present disclosure is not limited thereto, and metal components having the same purpose and function understood by those skilled in the art can be easily applied to the present disclosure.

The ring-type platinum catalyst having a unique structure according to the present disclosure can be prepared approximately by the following steps.

1) Preparation of platinum-tin mixed solution: While preparing a platinum-tin mixed solution by mixing a platinum precursor solution and a tin precursor, platinum is easily precipitated in the air due to the high reducing ability of tin. To prevent the precipitation of platinum, hydrochloric acid, an inorganic acid, is added in an amount in the range of 10% by weight to 20% by weight to the platinum-tin mixed solution. In addition, to prepare a stable mixed solution, alcohol, for example, ethylene glycol, which is dihydric alcohol, is added in an amount in the range of 5% by weight to 10% by weight to the prepared catalyst, and deionized water is used as a solvent.

2) Uniform impregnation of porous alumina carrier with platinum-tin mixed solution: A heat-treated porous alumina carrier at a temperature in the range of 900 °C to 1060 °C in a baking furnace is used to control the pore size and pore volume. The heat-treated carrier was impregnated with the prepared platinum-tin mixed solution using a spray-support method.

3) Metal immobilization on carrier: After impregnation, a drying process is carried out in a dryer at a temperature of 120 °C or higher for 12 hours or more, followed by baking in an air atmosphere at a temperature in the range of 400 °C to 700 °C to immobilize the metals on the carrier.

4) Alkali metal support and immobilization: An alkali metal is supported to prevent side reactions from occurring due to acidic sites remaining in the porous alumina carrier. Potassium is supported in pores within the carrier using a spray-support method, dried in a dryer at a temperature of 120 °C or higher for 12 hours or more, and baked in an air atmosphere at a temperature in the range of 400 °C to 700 °C to immobilize potassium on the carrier.

5) Reduction: After the alkali metal is immobilized, a reduction process is carried out using hydrogen gas at a temperature in the range of 400 °C to 600 °C to obtain the final catalyst. During the reduction process, when the temperature is 400 °C or lower, the metal oxidation species may not be completely reduced. When the temperature is higher than 600 °C, aggregation and sintering of metal particles may occur, thereby reducing the number of active sites.

Analysis is performed using an electron probe X-ray microanalyzer (hereinafter referred to as EPMA) to confirm the distribution of the metallic active material on the catalyst according to the present disclosure. In addition, to perform abrasion occurring between the catalyst and the catalyst in a fluidized reactor, or abrasion occurring between the catalyst and the reactor, an abrasion test is performed by introducing and rotating the catalyst and SUS type balls in a plastic bottle. On the other hand, to evaluate the dehydrogenation performance, a hydrocarbon having 2 to 5 carbon atoms, including paraffin, isoparaffin and alkyl aromatic compounds, is diluted with hydrogen, the hydrocarbon preferably having 3 to 4 carbon atoms, to perform dehydrogenation with a gas phase reaction under the conditions: a temperature in the range of 500 °C to 680 °C, preferably at 570 °C, a pressure in the range of 0 atm to 2 atm, preferably at 1.5 atm, and a liquid hourly space velocity (LHSV) of paraffinic hydrocarbons in the range of 1 h-1 to 40 h-1.

Example 1

A bead-type alumina carrier was heat treated at a temperature of 1050 °C for use. The heat-treated alumina has the following physical properties: a specific surface area of 95 m2/g, a pore volume of 0.4 cm3/g, and an average pore size of 12 nm. Chloroplatinic acid was used as a platinum precursor, and tin chloride was used as a tin precursor. 0.2% by weight of tin chloride and 6% by weight of ethylene glycol, relative to the total weight of the catalyst, and hydrochloric acid were mixed in an amount corresponding to 10% of the total solution. Then, 0.4% by weight of chloroplatinic acid, relative to the total weight of the catalyst, was added to prepare a platinum-tin mixed solution, which was added to and dissolved in deionized water in an amount corresponding to the total pore volume of the carrier. Next, the heat-treated alumina carrier was impregnated with the platinum-tin mixed solution prepared using a spray-support method. The supported platinum-tin composition was dried at a temperature of 120 °C for 12 hours and then subjected to a heat treatment process at a temperature of 550 °C for 3 hours in an air atmosphere to immobilize the active metal. Subsequently, 0.8% by weight of potassium nitride, relative to the total weight of the catalyst, was once again supported in the internal pores of alumina containing platinum and tin, using a spray-support method. Furthermore, the supported metal composition was dried at a temperature of 120 °C for 12 hours and then subjected to a heat treatment process at a temperature of 550 °C for 3 hours to prepare a supported metal catalyst. A catalytic reduction process was performed to raise the temperature to 550 °C gradually in an air atmosphere, and the elevated temperature was then maintained in a hydrogen atmosphere for 1 hour to prepare the catalyst.

Comparative example 1

While heat-treated alumina was used in the same manner as in Example 1 as a carrier, a comparative catalyst was prepared by a method of sequentially introducing platinum, tin and potassium. Using chloroplatinic acid as a platinum precursor, a solution in which 0.4% by weight of platinum, relative to the total weight of the catalyst, and hydrochloric acid in an amount corresponding to 10% by weight of the total solution were mixed was diluted with deionized water in an amount corresponding to the total pore volume of the carrier, and then introduced into the carrier using a spray-supporting method. The supported platinum composition was subjected to the drying and heat treatment processes in the same manner as in Example 1 to immobilize the active metal. Next, using tin chloride as the tin precursor once again, a solution in which 0.2% by weight of tin, relative to the total weight of the catalyst, and the same amount of hydrochloric acid as in the platinum introduction step were mixed was supported in the same manner. The solution was then subjected to drying and heat treatment processes. Next, 0.8% by weight of potassium nitride, relative to the total weight of the catalyst, and nitric acid in an amount corresponding to 1% of the total solution were mixed and diluted with deionized water to be introduced in the same manner, followed by being subjected to drying and firing. The catalyst reduction was performed by raising the temperature to 550 °C gradually in an air atmosphere, and the elevated temperature was then maintained in a hydrogen atmosphere for one hour to prepare the catalyst.

Experimental example

The distribution of the metallic active material confirmed by EPMA is shown in Figure 2. In the case of Example 1, platinum is not distributed in a region from the surface to a distance of about 100 um, but is observed to have a shape with a predetermined thickness of 300 um at a depth of 100 um from the surface. In contrast, tin was confirmed to be distributed in an eggshell shape in which the tin component is distributed in a region with a predetermined thickness varying directly from the surface. In the case of the comparative example, platinum and tin were evenly distributed in a region running directly from the surface to the interior. Depending on the reagent and concentration, the platinum component may be present in a ring shape with a thickness in a range of 200 um to 500 um at a depth in a range of 30 um to 200 um from the carrier surface.

The propane dehydrogenation was performed by charging a fixed bed catalytic reactor with the catalyst according to the present disclosure. The reaction gas composition in the reactor has a volume ratio of hydrogen and propane of 0.61, and 95 ppm of the entire gas is composed of H2S gas to prevent corrosion of the SUS reactor. After raising the temperature to 607 °C in a hydrogen atmosphere at a heating rate of 6 °C per minute, the propane dehydrogenation proceeds while adding propane and hydrogen at the predetermined ratio described above. The conversion rate and selectivity are calculated by analyzing the product gas using gas chromatography.

Table 1 summarizes the results of the analysis of propane dehydrogenation at an initial stage and after 12 hours.

[Table 1]

The initial conversion rates of the catalysts in the example and comparative example were 36.5 and 36.2, respectively, which were at the same level, but were 35.1 and 34.5, respectively, after 12 hours, causing the separation to widen. In the case of propylene selectivity, the initial values were 88.9% and 89.2%, respectively, and even after 12 hours of reaction, a similar level of difference was observed. In the case of the comparative example, after 12 hours of reaction, a reduction in propylene yield is noticeably shown, which is determined to be due to coke depositing on platinum distributed directly from the surface, thereby clogging the active sites and blocking the reaction gas from reaching the interior. In contrast, in the example case, it is confirmed that the platinum active sites are not exposed to the outside, so the reduction in activity due to coke deposition is small. Figure 3 is a graph showing the changes in the conversion rate over time. It is observed that the catalyst in the example allows achieving a high conversion rate and maintaining the high conversion rate for 12 hours.

In order to evaluate the post-abrasion activity of the Example and the Comparative Example prepared according to the present disclosure, an abrasion test was performed. 50 g of each catalyst was collected and introduced into an empty vessel together with 50 g of SUS type balls. The vessel was then placed on a rotating tool so that the vessel continued to rotate while the surface of the catalyst was damaged. This operation lasted for 10 days. As a result, it was confirmed that the average size of the catalyst was reduced by 7% to 8% in both the Example and the Comparative Example. Propane dehydrogenation was performed using the catalyst subjected to the abrasion test, as described above, for 12 hours, and the results were compared with those before being subjected to the abrasion test. The results are shown in Table 2.

[Table 2]

There was no difference in the activity of the catalyst according to the example, but it was confirmed that the conversion rate in the case of the catalyst according to the comparative example was significantly decreased. In the case of the example, platinum loss caused by the abrasion test is avoided because platinum is present at a predetermined depth of at least 100 um from the surface. However, in the case of the comparative example, it can be inferred that such results were obtained due to the damaged surface as well as the reduced number of platinum active sites.

Claims (4)

1. Dehydrogenation catalyst which is a spherical platinum catalyst comprising tin and potassium components used for the catalytic dehydrogenation of light hydrocarbons, the catalyst having a ring-shaped metal distribution where the platinum component is not present on the surface of the catalyst but is present within the catalyst, in the form of a ring with a predetermined thickness at a predetermined depth from the catalyst surface. 2. The catalyst of claim 1, wherein the tin component is present in an eggshell form wherein the tin component is present in a region from the surface to a predetermined depth. 3. The catalyst of claim 1, wherein the potassium component is evenly distributed throughout the catalyst. 4. The catalyst of any one of claims 1 to 3, wherein the predetermined depth is in a range of 30 um to 200 um, and the predetermined thickness is in a range of 200 um to 500 um.