ES2957010A2 - Dehydrogenation catalyst with controlled carrier pores - Google Patents

Abstract

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

Description

DESCRIPTION

Dehydrogenation catalyst with controlled carrier pores

Technical field

The present disclosure relates to a dehydrogenation catalyst and a method of preparing the same. More particularly, the present disclosure relates to a spherical platinum-based catalyst including tin and potassium components used for the catalytic dehydrogenation reaction of light hydrocarbons in the range of C3 to C5, such as propane, butane, and the like, wherein the catalyst carrier has a pore size and surface area controlled by heat treatment, and wherein the platinum-tin alloy components exist in eggshell form only to a certain depth from the surface of the catalyst. In the catalyst according to the present disclosure, the catalyst carrier is a mixture of gamma alumina and theta alumina and has a pore volume of 0.5 to 0.66 cc/g, the platinum dispersibility of the catalyst is 30 to 50 % and the average particle size of platinum is 3 to 5 nm.

Background of the technique

Light olefins have a wide range of commercial applications, including plastics, synthetic rubber, pharmaceuticals and chemicals, and can be produced by the following light hydrocarbon dehydrogenation reaction.

Paraffin (CnH2n+2) ←→ Olefin (CnH2n) Hydrogen (H2)

Catalysts that promote dehydrogenation reactions of light hydrocarbons are mainly spherical carriers, molded with micropores in materials such as alumina, zeolites, silica and spinel-type metal aluminates. These materials are effective in coke resistance and product selectivity, but as the amount of coke accumulated on the catalyst gradually increases as the reaction progresses, the micropores become blocked by the resulting coke, and the active metals within of the pores eventually become inactive and unable to participate in the reaction, so a carrier structure is required that can reduce secondary reactions such as cracking and coke deposition. Therefore, it is necessary for the interior of the catalyst to maintain macropores while reducing micropores, and from this point of view, an alumina carrier, in which it is relatively easy to control the pore size only by heat treatment, is applied. mainly as a catalyst carrier. However, gamma alumina is vulnerable to coke deposition due to its small pore size, side reactions progress due to the acidic sites of the carrier, and alpha alumina can be selective, but has the disadvantage of reducing the rate of overall conversion because alpha alumina hinders metal dispersibility and causes metal agglomeration.

Divulgation

technical problem

The inventors studied dehydrogenation catalyst carriers and found that a mixed carrier of alpha alumina and theta alumina can inhibit side reactions by eliminating acid sites through high temperature heat treatment and has good metal binding, minimizing intermetallic agglomeration, which It is advantageous to minimize conversion rate and selectivity.

Technical solution

An objective of the present disclosure is to provide a catalyst with enhanced durability by suppressing the platinum sintering phenomenon that inevitably occurs in catalysts used for the dehydrogenation of light hydrocarbons. The above objective is achieved by a dehydrogenation catalyst that includes a porous alumina carrier heat treated to form a mixture of gamma alumina and theta alumina having a suitable pore size and surface area, with platinum and tin alloy components present in eggshell form only to a certain depth from the surface of the catalyst. Preferably, but not limited to, the catalyst carrier is a mixture of gamma alumina and theta alumina and has a pore volume of 0.5 to 0.66 cc/g, the platinum dispersibility of the catalyst is 30% to 50%. %, and the average particle size of platinum is in the range of 3 to 5 nm.

Advantageous effects

The dehydrogenation catalyst, according to the present disclosure, is an eggshell form of platinum-tin alloy distributed over a carrier with controlled pore size and surface area, and the dispersion of the active metal is maximized so that the rate Conversion rate and selectivity can be maintained at a high level even during long-term operation in the dehydrogenation process.

Description of the drawings

Figure 1 shows the change in conversion rate and selectivity over time.

Mode for invention

The active metal eggshell catalyst, according to the present disclosure, is a porous alumina carrier. In particular, a mixture of alpha alumina and theta alumina is applied as a carrier, and platinum, tin and potassium are impregnated into the carrier, but the platinum-tin alloy is distributed in an eggshell-shaped structure from the surface of the carrier to a certain depth, and the potassium is evenly distributed throughout the interior of the carrier.

As used herein, catalyst refers to a spherical catalyst in which the active ingredients and/or auxiliary metal components are supported on a spherical carrier. The presence of the active ingredient and/or the active ingredient and the auxiliary metal, tin, in the form of an eggshell is a form in which a certain thickness is present from the surface of the catalyst towards the center of the catalyst and forms a thickness directly from the surface of the catalyst. In this respect, it is distinguished from the ring form in that these components are not present on the surface of the catalyst. Although the active ingredient is described herein as palladium, and tin and potassium are exemplified as auxiliary metals, other metallic components of the same purpose and function as understood by those skilled in the art can be readily employed in the present disclosure. The catalyst carrier as implemented herein may preferably have a pore volume of 0.5 to 0.65 cc/g, a dispersion of platinum in the catalyst of 30% to 50% and an average particle size of the platinum-tin alloy from 3 nm to 5 nm, but only examples that have representative figures within these figures are described by way of example.

The eggshell-shaped platinum catalyst having a unique structure according to the present disclosure can be prepared schematically through the following steps.

1) Preparation of a mixed platinum-tin solution: Composite solutions of platinum and tin cause the precipitation of platinum easily in the air due to the high reducing capacity of tin. Therefore, the selection of solvent is important in the preparation of a compound solution and therefore the present inventors prepared a precursor solution to maintain a stable state over time using a solvent that does not reduce tin. Firstly, in the mixing process of the platinum and tin precursors, organic solvents were added to the solvent.

platinum-tin complex, and hydrochloric acid was added to prepare a solution in an acid atmosphere. The organic solvent for the above purpose is one or two solvents selected from methanol, ethanol, butanol, acetone, ethyl acetate, acetonitrile, ethylene glycol, triethylene glycol, glycol ether, glycerol, sorbitol, xylitol, dialkyl ether and tetrahydrofuran and can be used sequentially or as a mixed solution.

2) Uniform impregnation of a mixed platinum-tin solution in a porous alumina carrier: To control the pore size and pore volume, an alpha and theta crystalline porous alumina carrier is used heat-treated at 850 °C to 1100 °C in a baking oven. The prepared platinum-tin solution is impregnated onto the heat-treated carrier by a spray support method. The heat treatment temperature is closely related to the crystalline phase and pore structure of the carrier, and when the heat treatment temperature is 850 °C or less, the crystalline phase of alumina is dominated by the gamma phase, and the The pore size of the carrier is small, so the rate of diffusion of reactants into the carrier can be reduced. When the heat treatment temperature is 1100 °C or more, the crystalline phase of alumina is dominated by the alpha phase, and the pore size is favorable for the reaction, but the dispersion of active metals distributed in the alumina phase alpha is reduced during the active metal immersion process, so the heat treatment temperature is set at 850°C to 1100°C to form a mixed state of alpha and theta alumina.

3) Fix the metal on the carrier: After impregnation, after drying in a dryer at 100°C to 150°C or more for 12 hours or more, the porous alumina carrier is calcined in an air atmosphere in the range of 400°C to 700°C to fix the metal on the carrier.

4) Alkali metal support and fixation: An alkali metal is supported to suppress side reactions caused by acid sites left on the porous alumina carrier. Potassium is supported in the pores within the carrier by the spray-support method, dried in a dryer at 100°C to 150°C for 12 hours or more, and calcined in an air atmosphere at 400°C. at 700 °C to fix potassium in the carrier.

5) Reduction: After fixing the alkali metal, a reduction process is carried out using hydrogen gas within the range of 400°C to 600°C to obtain a final catalyst. In the reduction process, when the temperature is 400 °C or less, the oxidizing species of metals may not be completely reduced, and when the temperature is above 600 °C, agglomeration and sintering of metal particles may occur, thereby reducing that way the active sites.

A carbon monoxide adsorption experiment was performed to confirm the degree of dispersion of the metallic active material for the catalyst according to the present disclosure. The catalyst is first heated to 400°C with helium gas and then treated with oxygen and hydrogen to remove moisture from the catalyst and reduce unreduced metal oxides. Subsequently, after cooling to 50 °C, 7% carbon monoxide gas is injected to analyze the amount of carbon monoxide gas adsorbed on the precious metal. Assuming that carbon monoxide and platinum are adsorbed in a ratio of 1:1, the dispersibility and particle size of platinum are finally calculated. On the other hand, to evaluate the dehydrogenation performance, hydrocarbons having 2 to 5 carbon atoms, preferably 3 to 4 carbon atoms, including paraffin, isoparaffin and alkyl aromatics, are diluted with hydrogen, and subjected to a gas phase reaction at 500 °C to 680 °C, preferably 570 °C, 0 to 2 atmospheres, preferably 1.5 atmospheres, and the liquid hourly space velocity (LHSV) of paraffin hydrocarbon is 1-40 h-1, and the dehydrogenation reaction is carried out as a gas phase reaction.

Example 1

A bead-type alumina carrier was used by heat treatment at 950 °C. Platinum chloride was used as a platinum precursor and tin chloride as a tin precursor, and tin chloride at 0.2 wt% of the total weight of the catalyst was mixed with hydrochloric acid at 5% of the total solution. Subsequently, the platinumtin solution was prepared by adding 0.4 wt % platinum chloride based on the weight of the catalyst and dissolved in ethanol in an amount corresponding to the total pore volume of the carrier. The prepared alumina carrier was impregnated with the platinum-tin solution using a spray support method. After drying the supported carrier with the platinum-tin mixture solution at 120 °C for 12 hours, an active metal was fixed through a heat treatment process at 550 °C for 3 hours in an air atmosphere. Potassium nitride was then supported in the internal pores of alumina containing platinum and tin by a spray support method at 0.8 wt% of the total weight of the catalyst, and the supported metal carrier was dried at 120° C for 12 hours and heat treated at 550 °C for 3 hours to prepare the supported metal catalyst. The catalytic reduction process was carried out gradually by raising the temperature to 550 °C in an air atmosphere and maintaining it in a hydrogen atmosphere for 1 hour to complete the catalyst. In Example 1, the catalyst was prepared by a platinum-tin co-impregnation method.

Comparative example 1

Unlike Example 1, the comparison catalyst was prepared by sequentially impregnating platinum, tin and potassium. The same heat-treated alumina was used as in Example 1. A solution obtained by mixing 0.4 wt% platinum based on the total weight of the catalyst with 5 wt% hydrochloric acid was diluted in deionized water corresponding to the pore volume. total of the carrier and was impregnated into the carrier by a spray support method. As in Example 1, the supported platinum carrier was subjected to drying and heat treatment to fix the active metal. Next, a solution containing 0.2% by weight of tin and the same amount of hydrochloric acid as in the platinum input stage, using tin chloride as tin precursor, is then impregnated in the same manner as in the platinum input stage, followed by drying and heat treatment. Next, potassium nitride equivalent to 0.8% by weight of the total weight of the catalyst and nitric acid equivalent to 1% of the total solution are mixed and diluted in deionized water, impregnated in the same way, dried and calcine. The catalytic reduction process was carried out gradually by raising the temperature to 550 °C in an air atmosphere and maintaining it in a hydrogen atmosphere for 1 hour to prepare the catalyst.

Comparative example 2

A catalyst was prepared in the same manner as in Example 1, except that a bead-type alumina carrier was thermally treated at 850°C and used.

Comparative example 3

A catalyst was prepared in the same manner as in Example 1, except that a bead-type alumina carrier was thermally treated at 1050°C.

Comparative example 4

A catalyst was prepared in the same manner as in Example 1, except that a bead-type alumina carrier was thermally treated at 1100°C and used.

Experimental example:

A propane dehydrogenation reaction was carried out by loading the catalyst according to the examples and comparative examples in a fixed bed catalytic reactor. The volume ratio of hydrogen and propane in the composition of the reaction gas in the reactor is 0.61, and 95 ppm of the total 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 rate of 6 °C per minute, the propane dehydrogenation reaction proceeds while adding propane and hydrogen at the above constant ratio. The conversion rate and selectivity are calculated by analyzing the product gas using gas chromatography.

Table 1 summarizes the measurement results of platinum dispersion and the results of the propane dehydrogenation reaction using carbon monoxide adsorption for the catalysts according to the examples and comparative examples, and Table 2 summarizes the changes in the surface area and pore structure of heat-treated carriers. Figure 1 shows the change in conversion rate and selectivity over time.

[Table 1]

[Table 2]

Dispersion evaluation table 1 shows that example 1, prepared using a mixed platinum-tin solution, had higher platinum dispersibility compared to comparative example 1, prepared using the sequential method.

Catalyst performance evaluation

Alloy catalysts with higher dispersibility exhibit higher initial conversion rates and selectivity, resulting in higher propylene yields, and all catalysts tested show a decrease in propylene yields due to platinum sintering and carbon precipitation after 10 hours of activity. However, for the platinum-tin alloy catalysts with higher initial dispersibility, the yield reduction rate was lower compared to the comparison catalysts prepared by sequential impregnation.

Carrier structure evaluation

Comparing the carrier structure as a function of carrier calcination temperature in Table 2, Example 2, which has the lowest calcination temperature, has a high conversion rate but low selectivity and a large decrease in propylene yield. over time. Without being limited to theory, this phenomenon is predicted to be due to the fact that, due to the low calcination temperature, there are many acidic sites on the carrier, and even though the dispersion of platinum is high, the acidic sites accelerate the deposition. of carbon, and the deposited carbon blocks the active sites of platinum, resulting in reduced durability. On the other hand, in the case of example 4, where the calcination temperature of the carrier is the highest at 1100 °C, most of the acid sites on the carrier are removed, but the surface area is reduced due to the collapse of the pore structure of the carrier, so that the dispersion and active area of the platinum are reduced, so that both activity and durability are reduced.

Claims (3)

1. Spherical dehydrogenation catalyst used in the catalytic dehydrogenation reaction of light hydrocarbons, in which a carrier is composed of a mixture of gamma alumina and theta alumina, the alloy components of platinum and tin are present in the form of an eggshell, and potassium is evenly distributed. 2. Dehydrogenation catalyst of claim 1, wherein the carrier has a pore volume of 0.5 to 0.65 cc/g. 3. Dehydrogenation catalyst of claim 1, wherein the platinum has a dispersibility in the range of 30% to 50%, and the average particle size of the platinum-tin alloy is in the range of 3 to 5 nm .