Method for preparing dehydrogenation catalyst for straight chain-type light hydrocarbon using stabilized active material complex

Abstract

The present invention relates to a catalyst having improved selectivity and reactivity and applied to preparing olefins by dehydrogenating C9 to C13 paraffin, and particularly to a technique for preparing a catalyst, which uses a heat-treated support having controlled pores, and most of metal components contained therein are distributed evenly in a support in the form of an alloy rather than in the form of each separate metal, thereby exhibiting high a conversion rate and selectivity when used in dehydrogenation.

Claims

1. A dehydrogenation catalyst for use in dehydrogenation of a hydrocarbon gas containing 9 to 13 carbon atoms, configured such that platinum, tin, and an alkali metal are supported to an alumina having controlled pores, wherein the platinum and the tin are in the form of an alloy at a consistent platinum/tin molar ratio at a thickness in an egg-shell shape from the outer surface of the alumina from 110 μm to 250 μm, and wherein the alkali metal is uniformly distributed within the alumina.

2. The dehydrogenation catalyst of claim 1, wherein the platinum/tin molar ratio is 2.0-4.0.

3. The dehydrogenation catalyst of claim 1, wherein the alumina is spherical.

4. The dehydrogenation catalyst of claim 1, wherein the catalyst is configured such that, based on a total weight of the catalyst, 0.1-1.0 wt % of the platinum, 0.2-4.0 wt % of the tin, and 0.1-3.0 wt % of the alkali metal are supported to the alumina.

5. The dehydrogenation catalyst of claim 1, wherein the alkali metal is at least one selected from the group consisting of potassium, sodium, and lithium.

6. A method of dehydrogenating a hydrocarbon, comprising bringing a hydrocarbon gas into contact with the catalyst of claim 1 under dehydrogenation conditions.

7. The method of claim 6, wherein the hydrocarbon gas includes a hydrocarbon gas containing 9 to 13 carbon atoms suitable for dehydrogenation.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows the key process of the present invention compared to a conventional technique;

(2) FIG. 2 is a flowchart showing the processing steps of the present invention;

(3) FIG. 3 shows video microscopy images of catalysts prepared by adjusting the thickness of active metal in Example 2 according to the present invention and Comparative Example 1;

(4) FIG. 4 shows a video microscopy image (a) of the catalyst prepared using a thermally treated support in Example 2 according to the present invention and electron probe microanalysis (EPMA) images (b) thereof; and

(5) FIG. 5 shows the state of alloying of active metals using H2-TPR (Hydrogen Temperature-Programmed Reduction) of the catalysts of Example 1 and Comparative Examples 1 and 2.

BEST MODE

(6) The present invention relates to a catalyst exhibiting improved selectivity and reactivity, suitable for use in the preparation of olefin by dehydrogenating C9-C13 paraffin, and the present inventors have ascertained that the use of a catalyst prepared by intensively supporting active metals only to the outer surface of a support may suppress the dehydrogenation side reaction and may also improve the conversion rate and selectivity upon the catalytic reaction. Particularly, it has been confirmed that when mono-olefin as the target product is prepared from a C9 or higher hydrocarbon having a large molecular size, high selectivity may be expected due to the active material distribution on the outer surface of the support. FIG. 1 shows the key process of the present invention compared to the conventional technique, and FIG. 2 shows the flowchart of the process of the present invention. The method of the present invention as shown in FIG. 2 is comprehensively described below.

(7) 1) Preparation of Stabilized Platinum-Tin Complex Solution

(8) A platinum-tin complex solution enables the easy precipitation of platinum in air due to the high reducibility of tin. In the preparation of a complex solution, the selection of a solvent is very important. When water is used as the solvent, platinum is reduced by tin and thus the platinum-tin precursor solution becomes very unstable, and consequently platinum particles may precipitate, and thus the use thereof as the precursor is impossible. In the present invention, the precursor solution is made stable over time using a solvent that may prevent tin reduction. Specifically, during the mixing of platinum and tin precursors, these precursors are added to an organic solvent so as not to break a platinum-tin complex, and a dispersion stabilizer is added to thus prepare a solution in which the particles are not aggregated. As the organic solvent and dispersion stabilizer, any one or two selected from among water, methanol, ethanol, butanol, acetone, ethyl acetate, acetonitrile, ethylene glycol, triethylene glycol, glycol ether, glycerol, sorbitol, xylitol, dialkyl ether, and tetrahydrofuran may be sequentially used, or may be used in combination. During the preparation of the platinum-tin complex solution, aging in an inert gas atmosphere is performed to thus suppress decomposition by oxygen and realize stabilization. Here, the inert gas may include nitrogen, argon, and helium, and preferably nitrogen gas.

(9) 2) Preparation of Catalyst Using Stabilized Platinum-Tin Complex Solution and Alkali Metal

(10) A PtSn complex solution in an amount corresponding to the total pore volume of the support is prepared, and is used to impregnate the support using a spraying process. After the impregnation process, the catalyst is homogenized while the catalyst is allowed to flow in a nitrogen atmosphere, whereby the active metal concentrations on the surface of the catalyst are made the same, followed by drying at 100 to 150° C. for 24 hr. After the drying, the organic material is removed at 200 to 400° C. in a nitrogen atmosphere, followed by firing at 400 to 700° C. in air. If thermal treatment is carried out at a temperature of less than 400° C., the supported metal may not change into metal oxide species. On the other hand, if thermal treatment is carried out at a temperature of higher than 700° C., intermetallic aggregation may occur, and the activity of the catalyst is not high relative to the amount thereof. After the firing, in order to suppress side reactions of the catalyst, the loading of an alkali metal is carried out. Specifically, lithium is loaded to the pores in the support using the same spraying process as in the platinum-tin complex solution, dried at 100 to 150° C. for 24 hr, and then fired at 400 to 700° C. in air. Finally, after the firing, a reduction process is carried out at 400 to 600° C. using a hydrogen/nitrogen mixed gas (4%/96% 100%/0%), thereby yielding a catalyst. During the reduction process, if the reduction temperature is lower than 400° C., metal oxide species cannot be completely reduced, and two or more kinds of metal particles may be individually present, rather than in the form of an alloy. On the other hand, if the reduction temperature is higher than 600° C., aggregation and sintering of two or more kinds of metal particles may occur, whereby the incidence of active sites may decrease and catalytic activity may be lowered. The reduction process is carried out not in a heating reduction manner with hydrogen gas from a heating step, but in a high-temperature reduction manner in which a nitrogen atmosphere is maintained until the temperature reaches the corresponding temperature, after which hydrogen gas is introduced at the corresponding temperature.

(11) 3) Evaluation of Catalyst Performance

(12) A method of converting a paraffin hydrocarbon into an olefin may be conducted in a manner in which the dehydrogenation catalyst according to the present invention is used, and a hydrocarbon having 2 to 20 carbon atoms, and preferably 9 to 13 carbon atoms, including paraffin, iso-paraffin, and alkyl aromatic material, is diluted with hydrogen, and may then be subjected to a gaseous reaction at 400˜600° C., preferably 470° C., 0˜2 atm, preferably 1.6 atm, and a LHSV (Liquid Hourly Space Velocity) of a paraffin hydrocarbon of 1˜30 h.sup.−1, and preferably 20˜30 h.sup.−1. The reactor for producing olefin through dehydrogenation is not particularly limited, and a fixed-bed catalytic reactor in which the catalyst is packed may be used. Also, since the dehydrogenation reaction is endothermic, it is important that the catalytic reactor be maintained adiabatic at all times. The dehydrogenation reaction of the present invention should be carried out under conditions in which the reaction temperature, pressure and liquid space velocity are maintained within appropriate ranges. If the reaction temperature is low, the reaction does not occur, and if the reaction temperature is too high, the reaction pressure increases in proportion thereto, and moreover, side reactions, such as coke production, isomerization, and the like, may occur.

Example 1

(13) The support of Example 1 was used after pore control of a gamma-alumina support (made by BASF, Germany, specific surface area: 210 m.sup.2/g, pore volume: 0.7 cm.sup.3/g, average pore size: 8.5 nm) through firing at 800° C. for 5 hr. The thermally treated alumina had physical properties including a specific surface area of 150 m.sup.2/g, a pore volume of 0.6 cm.sup.3/g, and an average pore size of 10 nm, and had a dual pore structure comprising mesopores of 10 nm or less and macropores of 50 μm or more. A platinum precursor, chloroplatinic acid (H.sub.2PtCl.sub.6), and a tin precursor, tin chloride (SnCl.sub.2), were used, and chloroplatinic acid in an amount of 0.2 wt % based on the total weight of the catalyst and tin chloride at a tin/platinum molar ratio of 1.0 were mixed in a nitrogen atmosphere. Next, the platinum-tin mixture was added to a solvent in an amount corresponding to the total pore volume of the support and thus dissolved. The solvent comprising ethanol/ethylene glycol/hydrochloric acid at a weight ratio of 100:20:1.5 was used. The support was impregnated with the prepared platinum-tin complex solution using an incipient wetness process. The platinum-tin-supported composition was thermally treated at 600° C. in air for 4 hr to thus immobilize active metals. Thereafter, 0.6 wt % of lithium nitride (Li(NO.sub.3).sub.2) based on the total weight of the catalyst was supported to the pores in the support using an incipient wetness process, and the metal-supported composition was thermally treated at 400° C. in air, thereby preparing a metal-supported catalyst. The catalyst was reduced stepwise in a manner in which the temperature was elevated to 400° C. in a nitrogen atmosphere and then maintained for 4 hr using a hydrogen/nitrogen mixed gas (4%/96%), thereby preparing a catalyst. This catalyst was configured such that platinum and tin were distributed at a thickness of 120 μm on the outer surface of the support and lithium was uniformly distributed in the support.

Example 2

(14) The catalyst of Example 2 was prepared in the same manner as in Example 1, with the exception that the tin/platinum molar ratio was changed to 2.0 upon the preparation of the tin-platinum complex solution. This catalyst was configured such that platinum and tin were distributed at a thickness of 120 μm on the outer surface of the support and lithium was uniformly distributed in the support.

Example 3

(15) The catalyst of Example 3 was prepared in the same manner as in Example 1, with the exception that the tin/platinum molar ratio was changed to 3.0 upon the preparation of the tin-platinum complex solution. This catalyst was configured such that platinum and tin were distributed at a thickness of 120 μm on the outer surface of the support and lithium was uniformly distributed in the support.

Example 4

(16) The catalyst of Example 4 was prepared in the same manner as in Example 1, with the exception that the tin/platinum molar ratio was changed to 4.0 upon the preparation of the tin-platinum complex solution. This catalyst was configured such that platinum and tin were distributed at a thickness of 120 μm on the outer surface of the support and lithium was uniformly distributed in the support.

Example 5

(17) The catalyst of Example 5 was prepared in the same manner as in Example 2, with the exception that the solvent comprising ethanol/ethylene glycol/hydrochloric acid at a weight ratio of 100:20:1.0 was used upon the preparation of the platinum-tin complex solution. This catalyst was configured such that platinum and tin were distributed at a thickness of 60 μm on the outer surface of the support and lithium was uniformly distributed in the support.

Example 6

(18) The catalyst of Example 6 was prepared in the same manner as in Example 2, with the exception that the solvent comprising ethanol/ethylene glycol/hydrochloric acid at a weight ratio of 100:20:2.5 was used upon the preparation of the platinum-tin complex solution. This catalyst was configured such that platinum and tin were distributed at a thickness of 250 μm on the outer surface of the support and lithium was uniformly distributed in the support.

Comparative Example 1

(19) In accordance with the method disclosed in U.S. Pat. No. 4,786,625, a catalyst was prepared. A tin-containing gamma-alumina (made by SASOL, Germany) support was impregnated through an incipient wetness process after dilution of 0.2 wt % of chloroplatinic acid and 0.6 wt % of lithium nitride and thiomalic acid, based on the total weight of the catalyst, with deionized water in an amount corresponding to the total pore volume of the alumina support. Thereafter, the solvent was evaporated at 80° C. using an evaporation dryer, followed by thermal treatment at 540° C. for 4 hr to thus immobilize active metals. Thereafter, a reduction reaction was carried out in a hydrogen atmosphere at 540° C. for 4 hr, thus preparing a catalyst. This catalyst was configured such that platinum was mostly distributed at a thickness of 60 μm on the outer surface of the support but some of the platinum was present up to 150 μm in the support, and tin was distributed at a thickness of 200 μm on the outer surface of the support, and tin and lithium were uniformly distributed in the support.

Comparative Example 2

(20) In accordance with the method disclosed in U.S. Pat. No. 4,716,143, a catalyst was prepared. A thermally treated gamma-alumina support (having a specific surface area of 150 m.sup.2/g, a pore volume of 0.6 cm.sup.3/g, and an average pore size of 10 nm) was impregnated through an incipient wetness process after dilution of chloroplatinic acid in an amount of 0.2 wt % based on the total weight of the catalyst, tin chloride at a tin/platinum molar ratio of 2.0 and hydrochloric acid in an amount of 0.5 wt % based on the total weight of the catalyst with deionized water in an amount corresponding to the total pore volume of the alumina support. The support was impregnated with the prepared platinum-tin complex solution using an incipient wetness process. The platinum-tin-supported composition was dried at 150° C. for 24 hr and then thermally treated at 540° C. in air for 4 hr to thus immobilize active metals. Thereafter, 0.6 wt % of lithium nitride based on the total weight of the catalyst was supported to the pores in the support through an incipient wetness process, and the metal-supported composition was thermally treated at 540° C. in air, thereby preparing a metal-supported catalyst. The catalyst was reduced at 540° C. in a hydrogen atmosphere for 4 hr, thus obtaining a catalyst. This catalyst was configured such that platinum was mostly distributed at a thickness of 180 μm on the outer surface of the support but some of the platinum was present up to 400 μm in the support, and tin was distributed at a thickness of 200 μm on the outer surface of the support, and lithium was uniformly distributed in the support.

Comparative Example 3

(21) The catalyst of Comparative Example 3 was prepared in the same manner as in Comparative Example 2, with the exception that, upon the supporting of platinum and tin, the solvent was added with hydrochloric acid in an amount of 2.0 wt % based on the total weight of the catalyst. This catalyst was configured such that platinum, tin and lithium were uniformly distributed in the support.

(22) The active metal distribution properties in the catalysts of Examples and Comparative Examples are shown in Table 1 below.

Test Examples 1 to 9: Evaluation of Catalyst Performance

(23) In order to measure the activity of the catalyst, a dehydrogenation reaction was carried out, and a fixed-bed reaction system was used as a reactor. Specifically, 1.16 g of the catalyst was placed in a tube-shaped reactor, and hydrogen gas was allowed to uniformly flow at a rate of 235 cc/min so that the catalyst was reduced at 470° C. for 1 hr. Subsequently, the temperature of the reactor was uniformly maintained at 470° C., after which a paraffin hydrocarbon feed having 9 to 13 carbon atoms was continuously supplied into the reactor at a constant rate of 0.7 ml/min using an HPLC pump, and the liquid space velocity was set to 21 h.sup.−1. The reaction pressure was maintained at 1.6 atm using a pressure regulator. The material produced after the reaction was cooled to a temperature of 4° C. or less and stored, and the product taken out of the reactor was transferred to a gas chromatograph through a line wound with a thermal line, and quantitative analysis was performed using an FID (Flame Ionization Detector) and a TCD (Thermal Conductivity Detector). The paraffin conversion rate and olefin selectivity of the product were calculated based on the following equations. The properties of the products using the above catalysts are summarized in Table 2 below.
Paraffin conversion rate=[paraffin mol before reaction−paraffin mol after reaction]/[paraffin mol before reaction]×100
Olefin selectivity=[olefin mol in product]/[product mol]×100%.

(24) FIG. 3 shows video microscopy images of the catalysts prepared by adjusting the thickness of the active metal in Example 2 according to the present invention and in Comparative Example 1. Specifically, the image of (a) shows the catalyst of Example 2 using the tin-platinum alloy solution, and the image of (b) shows the catalyst of Comparative Example 1 using individual platinum and tin solutions. FIG. 4 shows a video microscopy image (a) of the catalyst prepared using the thermally treated support in Example 2 according to the present invention and the electron probe microanalysis (EPMA) images (b) thereof. As shown in the images of (b), platinum and tin of the cross-section of the catalyst were distributed at a uniform thickness in the catalyst. FIG. 5 shows the state of alloying of the active metals using H2-TPR (Hydrogen Temperature-Programmed Reduction) in the catalysts of Example 1 and Comparative Examples 1 and 2. In Example 1, Pt and Sn were not present alone, and only the peak of a PtSn alloy was observed, unlike Comparative Examples 1 and 2.

(25) TABLE-US-00001 TABLE 1 Thickness of metal layer from outer Pt- Sn/Pt Metal surface of Sn molar distribution support (μm) dispersibility No. ratio in support Pt Sn (%) Example 1 1 Uniform  120 120 60 Example 2 2 Uniform  120 120 58 Example 3 3 Uniform  120 120 57 Example 4 4 Uniform  120 120 52 Example 5 2 Uniform  60 60 53 Example 6 2 Uniform  250 250 55 Comparative 2 Non-uniform 60-100 1400 48 Example 1 Comparative 2 Non-uniform 180, 400 200 50 Example 2 Comparative 2 Uniform 1400 1400 55 Example 3

(26) TABLE-US-00002 TABLE 2 Paraffin conversion Mono-olefin Di-olefin Olefin rate selectivity selectivity yield (%) (%) (%) (%) No. Catalyst 4 h/24 h 4 h/24 h 4 h/24 h 4 h/24 h Test Example 1 19.0/18.1 88.5/87.8 7.9/7.8 18.3/17.3 Example 1 Test Example 2 19.1/18.9 89.8/89.9 8.1/8.2 18.7/18.5 Example 2 Test Example 3 18.7/18.6 89.8/89.8 8.0/8.0 18.3/18.2 Example 3 Test Example 4 18.4/18.3 90.1/90.1 8.1/8.2 18.1/18.0 Example 4 Test Example 5 18.6/18.4 89.9/89.9 8.3/8.2 18.3/18.1 Example 5 Test Example 6 19.1/18.7 82.7/82.1 8.4/7.9 17.4/16.8 Example 6 Test Comparative 18.9/18.2 88.8/88.5 7.9/7.8 18.3/17.5 Example 7 Example 1 Test Comparative 18.5/17.9 81.0/79.8 8.0/7.8 16.5/15.7 Example 8 Example 2 Test Comparative 19.6/18.9 78.4/74.1 7.7/6.9 16.8/15.3 Example 9 Example 3

CONCLUSION

(27) When the tin/platinum molar ratio is equal to or less than a predetermined level, the amount of tin preventing deactivation due to coke is small around platinum and thus initial reaction activity may increase but rapid deactivation occurs, undesirably deteriorating durability. On the other hand, when the tin/platinum molar ratio is equal to or greater than a predetermined level, some of the platinum active sites are covered with tin to thus increase selectivity, but the total activity may decrease, ultimately lowering the olefin yield. When the metal layer is thin, a TOF (Turn-Over Frequency) with which the reactant passes through the catalyst is lowered and thus the overall paraffin conversion rate is slightly decreased, but the produced olefin compounds have short retention time in the catalyst and thus pass through the catalyst without side reactions, thereby increasing the olefin yield. In contrast, when the metal layer is thick, the retention time of the reactant in the catalyst active layer is increased, thus raising the conversion rate. However, while the reactant passes through the catalyst, primary dehydrogenation occurs, after which re-adsorption in the catalyst, secondary dehydrogenation, isomerization, cracking, and polymerization take place sequentially, thus decreasing the olefin selectivity, resulting in lowered olefin yield. In Comparative Examples 1 and 2, platinum is not uniformly distributed in the support, and thus an overall non-uniform reaction is carried out, and because of platinum particles present alone and particles having a low tin-platinum alloy ratio in the catalyst, the paraffin conversion rate is increased upon catalytic reaction, but side reactions such as cracking occur, undesirably decreasing olefin selectivity. The product is transferred to platinum particles alone or platinum containing a small amount of tin due to side reactions to thus block active sites, thus causing rapid deactivation of the catalyst, resulting in low durability. Based on the reaction results of Examples and Comparative Examples, the catalyst exhibiting the optimal conversion rate, selectivity and durability is determined to be the catalyst of Example 2, in which the molar ratio of uniform tin-platinum alloy is 2 and the thickness of the metal layer is about 110 to 130 μm.