KR102523345B1 - Dehydrogenation catalysts with carriers having treated pores - Google Patents

Abstract

The present invention relates to a dehydrogenation catalyst, which is a spherical platinum-based catalyst containing tin and potassium components used for catalyzing the dehydrogenation of light hydrocarbons in the range of C3 to C5, such as propane and butane, wherein the catalyst carrier is controlled by heat treatment. It relates to a dehydrogenation catalyst in which platinum and tin alloy components exist in an egg-shell form only up to a certain depth from the catalyst surface and have a pore size and surface area. 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 to 0.65 cc/g, the platinum dispersion of the catalyst is 30 to 50%, and the platinum average particle size is 3 nm to 5 nm. am.

Description

Dehydrogenation catalysts with carriers having treated pores}

The present invention relates to a dehydrogenation catalyst and a method for preparing the same, and more particularly, to a spherical platinum-based catalyst containing tin and potassium components used for catalytic dehydrogenation of light hydrocarbons in the range of C3 to C5, such as propane and butane. As, the catalyst support has a pore size and surface area controlled by heat treatment, and relates to a dehydrogenation catalyst in which platinum and tin alloy components exist in an egg-shell form only up 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 to 0.65 cc/g, the platinum dispersion of the catalyst is 30 to 50%, and the platinum average particle size is 3 nm to 5 nm. am.

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

Paraffin (C _n H _{2n +2} ) ⇔ Olefin (C _n H _2n ) + Hydrogen (H ₂ )

Catalysts that promote the dehydrogenation reaction of light hydrocarbons are mainly spherical molded carriers with fine pores, such as alumina, zeolite, silica, and spinel-type metal aluminate, and these materials have good effects on coke resistance and product selectivity, but the reaction is As the process progresses, when the amount of coke accumulated in the catalyst gradually increases, the micropores are blocked by coke, and the active metals present inside the pores are deactivated without participating in the reaction. Rescue is required. Therefore, the inside of the catalyst needs to maintain macropores while reducing micropores, and from this point of view, an alumina carrier, which is relatively easy to control the pore size only by heat treatment, is mainly applied as the catalyst carrier. However, gamma alumina is vulnerable to coke deposition due to its small pore size, side reactions proceed due to carrier acid sites, and alpha alumina inhibits the dispersion of metals and causes aggregation of metals, so selectivity may be good, but overall The downside is that the conversion rate is low.

As a result of studying the dehydrogenation catalyst carrier, the present inventors have found that the carrier of a mixture of alpha alumina and theta alumina can suppress side reactions by removing acid sites through high-temperature heat treatment, and has good bonding strength with metals, minimizing aggregation between metals, resulting in conversion rate. and found that it is advantageous for selectivity.

An object of the present invention is to provide a catalyst with enhanced durability by suppressing the platinum sintering phenomenon that inevitably occurs in catalysts used for dehydrogenation of light hydrocarbons. The above object is to heat-treat a porous alumina support to form a mixture of gamma alumina and theta alumina having an appropriate pore size and surface area, and to obtain a dehydrogenation catalyst in which platinum and tin alloy components exist in an egg-shell form only up to a certain depth from the catalyst surface. is achieved Preferably, but not limited to, the carrier of the catalyst according to the present invention has a pore volume of 0.5 ~ 0.65 cc / g, the platinum dispersion of the catalyst is 30 ~ 50%, and the average particle size of platinum may be 3 nm ~ 5 nm. .

In the dehydrogenation catalyst according to the present invention, the platinum-tin alloy is distributed in an egg-shell form on a carrier with controlled pore size and surface area, and the dispersion of the active metal is maximized, resulting in high conversion rate and selectivity even during long-term operation in the dehydrogenation process. can be kept high.

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

The active metal egg-shell catalyst according to the present invention 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, and the platinum-tin alloy is uniform from the surface of the carrier. It is distributed in an egg-shell structure to the depth, and potassium is evenly distributed throughout the inside of the carrier.

The catalyst herein refers to a spherical catalyst, which is a spherical carrier in which active ingredients and/or subsidized ingredients are supported. The presence of the active component and/or the tin component subsidized with the active component in the form of an egg-shell is a form in which they exist in a certain thickness from the catalyst surface toward the center of the catalyst, and form a thickness directly from the catalyst surface, so that they are present on the catalyst surface. It is distinguished from the cyclic form in which the component does not exist. In the present application, the active ingredient is mainly described with platinum, and tin and potassium components are exemplified in subsidy, but it is not limited thereto, and metal components having the same purpose and function understood by those skilled in the art can be easily applied in the present invention, of course. am. The carrier of the catalyst embodied herein may preferably have a pore volume of 0.5 to 0.65 cc/g, the dispersion of platinum in the catalyst is 30 to 50%, and the average particle size of the platinum-tin alloy is 3 nm to 5 nm. However, only examples having representative values within these numerical ranges are described as examples.

The platinum catalyst in the form of an egg-shell having a unique structure according to the present invention can be roughly prepared through the following steps.

1) Preparation of a platinum-tin mixed solution: A composite solution of platinum and tin easily causes precipitation of platinum in the air due to the high reducibility of tin. Therefore, the selection of a solvent is important in preparing a composite solution, and therefore, the present inventors prepared a precursor solution to maintain a stable state over time by using a solvent that does not reduce tin. First, in the process of mixing the platinum and tin precursors, they were added to the organic solvent to prevent breakage of the 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, acenonitrile, ethylene glycol, tri-ethylene glycol, glycol ether, glycerol, sorbitol, xylitol, dialkyl ether, and tetrahydrofuran. It can be selected from, and can be used sequentially or as a mixed solution.

2) Uniformly impregnating the porous alumina carrier with the platinum-tin mixed solution: To control the pore size and pore volume, use a gamma- and theta-crystalline porous alumina carrier heat-treated at 850-1100 degrees in a firing furnace. The prepared platinum-tin solution is impregnated into the heat-treated carrier by a spray-dipping method. The heat treatment temperature is closely related to the crystal phase and pore structure of the carrier, and when the heat treatment temperature is 850 degrees or less, the crystal phase of alumina is mainly gamma phase, and the diffusion rate of reactants in the carrier may be lowered due to the small pore size of the carrier. When the heat treatment temperature is 1100 degrees or more, the alpha phase of the alumina crystal phase is predominant, and the pore size exists in a state favorable to the reaction, but the dispersity of the active metals distributed on the alpha alumina phase in the process of supporting the active metal is high. Since it is lowered, the heat treatment temperature is set to 850-1100 degrees to reform into a mixed state of gamma and theta alumina.

3) Fixing the metal in the carrier: After impregnation, drying in a dryer at 100-150 degrees or more for 12 hours or more, firing in an air atmosphere in the range of 400-700 degrees Celsius fixes the metal in the carrier.

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

5) Reduction: After fixing the alkali metal, a reduction process is performed using hydrogen gas within the range of 400-600 degrees to obtain the final catalyst. In the reduction process, when the temperature is 400 degrees or less, metal oxidizing species may not be completely reduced, and when the temperature is higher than 600 degrees, aggregation and sintering of metal particles may occur, thereby reducing active points.

A carbon monoxide adsorption experiment was conducted to confirm the degree of dispersion of the metal active material for the catalyst according to the present invention. First, after raising the temperature to 400 degrees with helium gas, moisture in the catalyst is removed through oxygen and hydrogen treatment, and unreduced metal oxide is reduced. Subsequently, after cooling to 50 degrees, 7% carbon monoxide gas is injected to analyze the amount of carbon monoxide gas adsorbed to the noble metal. 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. On the other hand, in order 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 heated to 500 to 680 ° C. Preferably 570 ℃, 0-2 atm, preferably 1.5 atm, liquid hourly space velocity (LHSV: Liquid Hourly Space Velocity) 1-40h ^-1 of paraffinic hydrocarbons under conditions of gas phase reaction to perform the dehydrogenation reaction.

Example 1

A bead-type alumina carrier was used by heat treatment at 950 degrees. Chloroplatinic acid as a platinum precursor and tin chloride as a tin precursor were used, and tin chloride corresponding to 0.2 wt% of the total weight of the catalyst and hydrochloric acid corresponding to 5% of the total solution were mixed. Thereafter, chloroplatinic acid corresponding to 0.4wt% of the total weight of the catalyst was added to prepare a platinum-tin solution, and then added to 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-dipping method. After drying the carrier supported 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. Then, 0.8wt% of potassium nitride based on the total weight of the catalyst was also loaded into the internal pores of alumina containing platinum and tin by spray impregnation, and the metal-supported carrier was dried at 120 ° C for 12 hours and then heat-treated at 550 ° C for 3 hours. Through the process, a supported metal catalyst was prepared. In the catalytic reduction process, the catalyst was completed by raising the temperature to 550 ° C in an air atmosphere in a step method and maintaining it in a hydrogen atmosphere for 1 hour. In Example 1, a catalyst was prepared by a platinum-tin co-impregnation method.

Comparative Example 1

Unlike Example 1, a comparative catalyst was prepared by sequentially impregnating platinum, tin, and potassium. Alumina heat-treated in the same manner as in Example 1 was used. Using chloroplatinic acid as a platinum precursor, a solution obtained by mixing platinum corresponding to 0.4wt% of the total weight of the catalyst and hydrochloric acid corresponding to 5wt% of the total solution is diluted in deionized water corresponding to the total pore volume of the carrier and sprayed. The carrier was impregnated by the supporting method. As in Example 1, the platinum-supported carrier was subjected to drying and heat treatment to fix the active metal. Then, using tin chloride as a tin precursor, a solution containing 0.2 wt% of tin and hydrochloric acid of the same amount as in the platinum input step corresponding to 0.2 wt% of the total weight of the catalyst is loaded in the same way as in the platinum input step, followed by drying and heat treatment. go through Thereafter, 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 in deionized water, impregnated in the same way, dried, and calcined. Catalyst reduction was carried out in an air atmosphere up to 550 ° C. in a step manner, and then maintained in a hydrogen atmosphere for 1 hour to prepare a catalyst.

Comparative Example 2

A catalyst was prepared in the same manner as in Example 1, except that a bead-type alumina carrier was heat-treated at 850 degrees.

Comparative Example 3

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

Comparative Example 4

A catalyst was prepared in the same manner as in Example 1, except that a bead-type alumina carrier was heat-treated at 1100 degrees.

Experimental example:

A propane dehydrogenation reaction was performed by charging the catalyst according to Examples and Comparative Examples to 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 H ₂ S gas to prevent corrosion of the SUS reactor. After raising the temperature to 607 degrees in a hydrogen atmosphere at a rate of 6 degrees 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 results of platinum dispersion measurement and propane dehydrogenation reaction using carbon monoxide adsorption for catalysts according to Examples and Comparative Examples, and Table 2 summarizes changes in the surface area and pore structure of the heat-treated carrier. it did Figure 1 shows the change in conversion rate and selectivity over time.

division Active metal distribution pattern carrier
firing temperature
(℃) dispersion
(%) active metal average
particle size
(nm) Conversion rate (%)
C _i /C _f Selectivity (%)
S _i /S _f transference number (%)
Y _i /Y _f transference number
decrease rate
(%) Example 1 egg-shell 950 36.2 3.13 37.0/36.1 90.1/89.9 33.3/32.5 2.65 Comparative Example 1 overall distribution 950 21.2 5.34 36.2/34.5 90.0/89.6 32.6/30.9 5.12 Comparative Example 2 egg-shell 850 42 2.70 39.1/37.9 82.2/77.8 32.1/29.5 8.26 Comparative Example 3 egg-shell 1050 32.8 3.45 36.7/35.5 91.0/90.5 33.4/32.1 3.80 Comparative Example 4 egg-shell 1100 14.4 7.87 35.8/32.3 92.7/91.1 33.2/29.4 11.33

division Carrier heat treatment temperature
(℃) surface area
(m ² /g) mesopore volume
(cm ³ /g) average pore size
(Å) alumina carrier 1 850 132 0.615 139 alumina carrier 2 950 114 0.598 154 alumina carrier 3 1050 91 0.524 170 alumina carrier 4 1100 54 0.367 221

Dispersion evaluation

According to Table 1, Example 1 prepared using the platinum-tin mixed solution had higher dispersion of platinum than Comparative Example 1 prepared through the sequential method.

Catalyst performance evaluation

Alloy catalysts with high dispersion show high propylene yields due to high initial conversion and selectivity. After 10 hours of activation of all catalysts tested, propylene yields decrease due to platinum sintering and carbon deposition, but the initial dispersity values For the high platinum-tin alloy catalyst, the yield reduction rate was low compared to the comparative catalyst prepared by sequential impregnation.

Carrier structure evaluation

Comparing the carrier structure according to the change in the carrier calcination temperature in Table 2, in the case of Comparative Example 2, which has the lowest calcination temperature, the conversion rate is high, but the selectivity is low, and the propylene yield reduction rate with time is large. Although not limited by theory, this phenomenon is due to the presence of many acid sites in the carrier due to the low firing temperature, even if the dispersion of platinum is high, the carbon deposition is accelerated due to the existing acid sites, and the deposited carbons form platinum active sites. It is predicted that this is due to the decrease in durability. On the contrary, in the case of Comparative Example 4, where the carrier firing temperature is the highest at 1100 degrees, most of the acid points of the carrier were removed, but the pore structure of the carrier collapsed and the surface area decreased. You can check.

Claims (3)

As a spherical dehydrogenation catalyst used in the dehydrogenation catalytic reaction of light hydrocarbons, the alumina support is heat-treated at 950 degrees, and the alumina support is composed of a mixture of gamma alumina and theta alumina, and platinum and tin alloy components exist in the form of an egg-shell. And, potassium is uniformly distributed, but the dispersion of the platinum is 30 to 50%, a dehydrogenation catalyst. The dehydrogenation catalyst according to claim 1, wherein the carrier has a pore volume of 0.5 to 0.65 cc/g. The dehydrogenation catalyst according to claim 1, wherein the platinum-tin alloy has an average particle size of 3 nm to 5 nm.

Images