A low-Pt-loading propane dehydrogenation catalyst and its application

Abstract

The present invention relates to a low-Pt-loading propane dehydrogenation catalyst and its application. The catalyst comprises: an alumina support, a main active component Pt, a first promoter Sn, a second promoter, and a third promoter. The second promoter is at least one element in Group IIIA, and the third promoter is at least one of alkali metals or alkaline earth metals. It is prepared by the following method: S1, pretreating the alumina support under vacuum conditions; S2, impregnating the pretreated alumina support into an impregnation solution comprising a Pt precursor, an Sn precursor, a second promoter precursor, a third promoter precursor, and hydrochloric acid; S3, after the impregnation is completed, drying and calcining to obtain a catalyst precursor; S4, pre-reducing the catalyst precursor under H2 conditions to obtain a propane dehydrogenation catalyst. The catalyst provided by the present invention selects appropriate promoters and loadings, improves the utilization rate of the active component Pt, and while reducing the Pt loading, maintains excellent propane dehydrogenation activity and propylene selectivity.

Description

Technical Field

[0001] The present invention relates to a catalyst, and particularly to a catalyst for catalytic dehydrogenation of propane to propylene with a low Pt loading and its application. Background Art

[0002] Propylene is a very important basic chemical raw material and is widely used in the production of chemical products such as polypropylene, acrylonitrile, propylene oxide, isopropyl alcohol, and acrylic acid. In recent years, with the rapid development of the national economy, the market demand for propylene has been steadily increasing, and the traditional propylene production methods can no longer meet the demand. With the large-scale commercialization of shale gas, the method of preparing propylene from inexpensive propane has become one of the important technical means to meet the increase in propylene production.

[0003] The propane catalytic dehydrogenation reaction is restricted by the thermodynamic equilibrium and needs to be carried out under harsh conditions of high temperature and low pressure. However, a higher reaction temperature will cause side reactions such as cracking and isomerization of propane, reducing the selectivity of propylene. At the same time, the deposition of coke makes the catalyst extremely easy to deactivate. Therefore, developing a propane dehydrogenation catalyst with high activity, selectivity, and stability is the key to the propane dehydrogenation to propylene technology. Currently, the most widely used propane dehydrogenation process is UOP's Oleflex technology, which uses alumina-supported Pt as the propane dehydrogenation catalyst. Although the Pt-based propane dehydrogenation catalyst has high activity, a series of additives still need to be added to improve the propylene selectivity and catalyst stability. The PtSnK / Al2O3 catalyst is the Pt-based catalyst system that has been studied and applied more currently. The addition of the additive Sn can not only improve the dispersion of the active metal Pt, enhance the catalytic activity and stability, but also weaken the adsorption of propylene on the Pt surface through the electronic effect, improving the reaction selectivity; the additive K mainly inhibits the formation of coke by neutralizing the acidity of the carrier, thereby improving the stability of the catalyst. The addition of other additives can further improve the propane dehydrogenation performance of the catalyst.

[0004] The dehydrogenation catalysts disclosed in US Patent Nos. US13742439 and US10340282 mention the use of Ga and In in the additive components to improve the dehydrogenation performance of the catalyst.

[0005] Chinese Patent CN106582629A discloses a propane dehydrogenation catalyst, which uses alumina as the carrier, Pt-group metals as the active components, and Sn, Group IIIA elements, and C as additives. When using this catalyst for the propane dehydrogenation to propylene reaction, a relatively high propane conversion rate and propylene selectivity can be obtained.

[0006] Chinese Patent CN106607019 discloses a propane dehydrogenation catalyst. This catalyst uses multi-walled carbon nanotubes as a support and loads Pt and B components. This catalyst shows a certain stability in the propane dehydrogenation reaction, but the propane conversion rate (6.5%) and propylene selectivity (76%) are not high.

[0007] Chinese Patent CN104588007A discloses a saturated alkane dehydrogenation catalyst and its preparation method. This catalyst uses boron-containing alumina as a support, Pt as the active component, and contains two kinds of promoters at the same time. The first promoter is Sn, and the second promoter is one or several of K, Na, and Mg. However, the stability of this catalyst is poor, and it is necessary to improve the catalyst stability by injecting sulfur into the raw materials.

[0008] However, as a precious metal, Pt is expensive. Improving the utilization rate of the active component Pt and preparing a propane dehydrogenation catalyst with a low Pt loading and excellent performance are of great significance for reducing the industrial application cost. Chinese Patent CN108325523A discloses a propane dehydrogenation catalyst supported by magnesium aluminate spinel and loaded with Pt, B, and K. The Pt loading of this catalyst is relatively low, being 0.05 - 0.29% (the Pt loading of the catalyst in most current studies is generally 0.3 - 0.6%). Pt shows a highly dispersed state in one or two dimensions on the surface of the support, and Pt atoms exist in the form of single atoms or sub-nanometer clusters. This catalyst shows high selectivity and good stability in the propane dehydrogenation reaction, but its activity is not high, and the initial conversion rate can only reach 18%. Summary of the Invention

[0009] The purpose of the present invention is to provide a propane dehydrogenation catalyst with a low Pt loading to solve the problem in the prior art that while reducing the Pt loading, the propane dehydrogenation activity and propylene selectivity decrease.

[0010] The purpose of the present invention also lies in providing an application of the propane dehydrogenation catalyst with a low Pt loading.

[0011] To achieve the above purpose, the present invention provides a propane dehydrogenation catalyst with a low Pt loading, including: an alumina support, a main active component Pt, a first promoter Sn, a second promoter, and a third promoter. The second promoter is at least one of the elements in Group IIIA, and the third promoter is at least one of an alkali metal or an alkaline earth metal;

[0012] The catalyst is prepared by the following method:

[0013] S1, pretreat the alumina support under vacuum conditions;

[0014] S2, immerse the pretreated alumina support into an impregnation solution including a Pt precursor, an Sn precursor, a second promoter precursor, a third promoter precursor, and hydrochloric acid;

[0015] S3. After impregnation, dry and calcine to obtain a catalyst precursor;

[0016] S4. Pre - reduce the catalyst precursor under H2 conditions to obtain a propane dehydrogenation catalyst.

[0017] For the low - Pt - loading propane dehydrogenation catalyst of the present invention, the second promoter is selected from at least one of B, Ga, and In, and preferably B.

[0018] For the low - Pt - loading propane dehydrogenation catalyst of the present invention, the alkali metal is selected from at least one of Li, Na, and K, and the alkaline earth metal is selected from at least one of Mg and Ca.

[0019] For the low - Pt - loading propane dehydrogenation catalyst of the present invention, by elemental mass fraction, it contains 0.01% - 0.25% of the main active component Pt, 0.01% - 1.5% of the first promoter Sn, 0.03% - 1% of the second promoter, 0.1% - 1% of the third promoter, and the rest is an alumina support.

[0020] For the low - Pt - loading propane dehydrogenation catalyst of the present invention, the mass ratio of Sn to Pt is 0.1:1 - 6:1, and preferably 0.2:1 - 4:1.

[0021] For the low - Pt - loading propane dehydrogenation catalyst of the present invention, the mass ratio of the second promoter element to Pt is 0.1:1 - 10:1, and preferably 0.2:1 - 5:1.

[0022] For the low - Pt - loading propane dehydrogenation catalyst of the present invention, the mass ratio of the third promoter element to Pt is 0.5:1 - 50:1, and preferably 2:1 - 10:1.

[0023] For the preparation method of the low - Pt - loading propane dehydrogenation catalyst of the present invention, in step S1, the pretreatment time is 0.2 - 1 h, in step S2, the hydrochloric acid concentration is 36 - 38%, the addition amount is 5% - 20% of the total mass of the catalyst, and the impregnation time is 0.5 - 5 h.

[0024] For the preparation method of the low - Pt - loading propane dehydrogenation catalyst of the present invention, the drying conditions are drying at 80 - 130 °C for 2 - 10 h, the calcination conditions are calcining at 400 - 750 °C for 2 - 8 h, and the pre - reduction conditions are pre - reducing at 450 - 600 °C for 1 - 4 h.

[0025] For the low - Pt - loading propane dehydrogenation catalyst of the present invention, in step S2, equal - volume impregnation is used for impregnation.

[0026] To achieve the above object, the present invention also provides an application of a propane dehydrogenation catalyst with a low Pt loading. Among them, the reaction temperature is 500°C to 650°C, the reaction pressure is 0 to 0.5 MPa, and the liquid hourly space velocity of propane is 1 to 10 h -1 , and the hydrogen-hydrocarbon molar ratio is 0.25:1 to 4:1.

[0027] The beneficial effects of the present invention are as follows:

[0028] The propane dehydrogenation catalyst provided by the technology of the present invention improves the utilization rate of the active component Pt by selecting appropriate additives and loadings. While reducing the Pt loading, it can still maintain excellent propane dehydrogenation activity and propylene selectivity, which is of great significance for reducing the production cost of the catalyst and has broad industrial application prospects. At the same time, the catalyst preparation method provided by the present invention is simple, the process is mature, and it is easy to realize the industrial production of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a graph showing the change of propane conversion rate with time for the propane dehydrogenation reaction catalyzed by catalysts Cat-1, Cat-G, Cat-D1, and Cat-D2;

[0030] Figure 2 It is a graph showing the change of propylene selectivity with time for the propane dehydrogenation reaction catalyzed by catalysts Cat-1, Cat-G, Cat-D1, and Cat-D2. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention will be specifically described below by way of examples. It is necessary to point out here that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention according to the above content of the present invention.

[0032] Example 1

[0033] Weigh 3.0 g of alumina support and place it in a vacuum impregnator. Evacuate to vacuum and perform vacuum treatment for 0.5 h. Then immerse it isovolumetrically in 2.7 mL of an aqueous solution containing 0.0126 g of chloroplatinic acid, 0.0192 g of stannous chloride, 0.0858 g of boric acid, 0.0286 g of potassium chloride, and 0.2750 g of concentrated hydrochloric acid with a mass concentration of 38%. After impregnation for 30 min, dry it by evacuating in a water bath at 85°C for 2 h, and calcine it in a muffle furnace at 600°C for 4 h, and pre-reduce it in a hydrogen atmosphere at 520°C for 2 h. The content of each component in the obtained catalyst is 0.2% Pt, 0.4% Sn, 0.5% B, and 0.5% K in terms of elemental mass, denoted as Cat-1.

[0034] Example 2

[0035] Weigh 3.0 g of alumina support and place it in a vacuum impregnator. Evacuate to vacuum and perform vacuum treatment for 0.2 h. Then, immerse it isovolumetrically in 2.7 mL of an aqueous solution containing 0.0126 g of chloroplatinic acid, 0.0192 g of stannous chloride, 0.0298 g of indium chloride, 0.0286 g of potassium chloride, and 0.2750 g of concentrated hydrochloric acid with a mass concentration of 38%. After impregnation for 2 h, carry out vacuum drying in a water bath at 85 °C for 5 h, calcine in a muffle furnace at 400 °C for 2 h, and pre-reduce in a hydrogen atmosphere at 600 °C for 1 h. The content of each component in the obtained catalyst is 0.2% Pt, 0.4% Sn, 0.5% In, and 0.5% K in terms of elemental mass, denoted as Cat-2.

[0036] Example 3

[0037] Weigh 3.0 g of alumina support and place it in a vacuum impregnator. Evacuate to vacuum and perform vacuum treatment for 1 h. Then, immerse it isovolumetrically in 2.7 mL of an aqueous solution containing 0.0126 g of chloroplatinic acid, 0.0192 g of stannous chloride, 0.0550 g of gallium nitrate, 0.0286 g of potassium chloride, and 0.2750 g of concentrated hydrochloric acid with a mass concentration of 38%. After impregnation for 5 h, carry out vacuum drying in a water bath at 85 °C for 10 h, calcine in a muffle furnace at 750 °C for 8 h, and pre-reduce in a hydrogen atmosphere at 450 °C for 4 h. The content of each component in the obtained catalyst is 0.2% Pt, 0.4% Sn, 0.5% Ga, and 0.5% K in terms of elemental mass, denoted as Cat-3.

[0038] Example 4

[0039] Catalysts Cat-4 and Cat-5 are prepared by the same method as in Example 1, except that the content of each component of the catalyst is changed, and the specific composition is listed in Table 1.

[0040] Example 5

[0041] Catalysts Cat-6 and Cat-7 are prepared by the same method as in Example 2, except that the content of each component of the catalyst is changed, and the specific composition is listed in Table 1.

[0042] Example 6

[0043] Catalyst Cat-8 is prepared by the same method as in Example 3, except that the content of each component of the catalyst is changed, and the specific composition is listed in Table 1.

[0044] Example 7

[0045] Catalysts Cat-9 to Cat-12 are prepared by the same method as in Example 1, except that calcium chloride, magnesium chloride, lithium chloride, and sodium chloride are used instead of potassium chloride, and the content of each component of the catalyst is changed, and the specific composition is listed in Table 1.

[0046] Comparative Example 1

[0047] Similar to the method of Example 1, except that boric acid is not added during the catalyst preparation process, and the remaining methods are exactly the same as those of Example 1. The content of each component in the obtained catalyst is 0.2% Pt, 0.4% Sn, and 0.5% K by elemental mass, denoted as Cat-D1.

[0048] Comparative Example 2

[0049] Preparation of B-containing basic solution: At a constant temperature of 30 °C, take 400 g of deionized water, add 30 mL of ammonia water with a concentration of 2.94 mol / L, then add 35.13 g of boric acid, and make up the volume to 500 mL with deionized water in a 500 mL volumetric flask. The final pH value of the solution is 8.7, and its composition is 39.77 g / L of B2O3 (mass percentage content calculated as B2O3 is 4%) and 3 g / L of NH3. The solution is placed in a closed system at room temperature for 24 h without obvious change.

[0050] Weigh 30.0 g of alumina support, measure an appropriate amount of the above B-containing basic solution, add it to the alumina support, stir until uniform, age at room temperature for 10 hours, dry at 100 °C for 4 hours, and calcine at 350 °C for 4 hours. Weigh an appropriate amount of stannic chloride and dissolve it in deionized water, and make up the volume to 27 mL. Add the prepared Sn-containing solution to the B-containing alumina support, mix evenly, and age for 2 h. Dry at 80 °C for 8 hours, and then calcine at 600 °C for 4 hours. Weigh an appropriate amount of chloroplatinic acid and dissolve it in deionized water, and make up the volume to 27 mL. Add it to the above calcined sample, age for 3 hours, dry at 80 °C for 8 hours, and calcine at 600 °C for 4 hours. Weigh an appropriate amount of potassium nitrate to prepare an aqueous solution, impregnate at 70 °C for 2 h, and dry and calcine under the same conditions as after Pt impregnation. The content of each component in the obtained catalyst is 0.2% Pt, 0.4% Sn, 0.5% B, and 0.5% K by elemental mass, denoted as Cat-D2.

[0051] Table 1 Catalyst Component Content Table of Examples and Comparative Examples

[0052] Catalyst Number Content of Each Component of the Catalyst Cat-1 0.2% Pt 0.4% Sn 0.5% B 0.5% K Cat-2 0.2% Pt 0.4% Sn 0.5% In 0.5% K Cat-3 0.2% Pt 0.4% Sn 0.5% Ga 0.5% K Cat-4 0.15% Pt 0.4% Sn 0.5% B 0.5% K Cat-5 0.05% Pt 0.1% Sn 0.03% B 0.8% K Cat-6 0.01% Pt 0.01% Sn 0.1% In 0.5% K Cat-7 0.25% Pt 1.5% Sn 0.7% In 0.5% K Cat-8 0.2% Pt 0.05% Sn 1% Ga 0.1% K Cat-9 0.2% Pt 0.6% Sn 0.5% B 1% Ca Cat-10 0.2% Pt 0.6% Sn 0.5% B 1% Mg Cat-11 0.2% Pt 0.4% Sn 0.7% B 1% Li Cat-12 0.2% Pt 0.4% Sn 0.7% B 1% Na Cat-D1 0.2% Pt 0.4% Sn 0.5% K Cat-D2 0.2% Pt 0.4% Sn 0.5% B 0.5% K

[0053] Reaction Performance Evaluation of Propane Dehydrogenation Catalyst

[0054] Take 1.0 g of the catalysts Cat-1 to Cat-12, Cat-D1, Cat-D2 prepared in the above examples and comparative examples, and the fresh imported industrial catalyst DEH-16 (denoted as Cat-G, the Pt loading of this catalyst is 0.3%), and load them into a quartz tubular fixed-bed reactor with an inner diameter of 15 mm. In a hydrogen atmosphere, heat up to 600 °C at a heating rate of 6 °C / min. After the temperature is stable, introduce propane, and the reaction evaluation time is 72 h. The reaction conditions are: temperature 600 °C, pressure is atmospheric pressure, and the liquid hourly space velocity of propane is 3.4 h -1 , and the hydrogen / propane molar ratio is 0.5:1. The propane dehydrogenation performance of the catalysts is listed in Table 2.

[0055] Table 2 Data table of propane dehydrogenation performance of catalysts

[0056]

[0057] Among them, the variation relationships of propane conversion rates of the catalysts Cat-1, Cat-G, Cat-D1, and Cat-D2 in the propane dehydrogenation reaction with time are shown in Figure 1 , and the variation relationships of propylene selectivities of the catalysts Cat-1, Cat-G, Cat-D1, and Cat-D2 in the propane dehydrogenation reaction with time are shown in Figure 2 . It can be seen from the figures that the catalyst Cat-1 provided by the present invention exhibits significantly better propane conversion rate and propylene selectivity than Cat-D1. Compared with Cat-G, Cat-1 has similar initial activity. After reacting for 50 h, the activity of Cat-1 begins to show an advantage. From the perspective of propylene selectivity, Cat-1 is better than Cat-G, indicating that Cat-1 has better propane dehydrogenation performance than the imported foreign industrial catalyst. In addition, the propane dehydrogenation performance of the catalyst Cat-D2 is poor, which is quite different from that of Cat-1, indicating that the preparation method described in Comparative Example 2 cannot prepare the propane dehydrogenation catalyst with low Pt loading and excellent performance described in this application.

[0058] It can be known from the experimental results that the low-Pt-loading propane dehydrogenation catalyst provided by this application has high propane dehydrogenation activity, propylene selectivity, and catalyst stability, and the relatively low noble metal Pt loading can greatly reduce the production cost of the catalyst, having broad industrial application prospects.

[0059] Of course, the present invention can also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations should all fall within the protection scope of the claims of the present invention.

Claims

1. A low-Pt-loading propane dehydrogenation catalyst, characterized in that, Comprising: An alumina support, a main active component Pt, a first promoter Sn, a second promoter, and a third promoter, wherein the second promoter is at least one element from Group IIIA, and the third promoter is at least one of an alkali metal or an alkaline earth metal; the mass ratio of Sn to Pt is 0.1:1 to 6:1; the mass ratio of the second promoter element to Pt is 0.1:1 to 10:1; the mass ratio of the third promoter element to Pt is 0.5:1 to 50:1; the second promoter is selected from at least one of B, Ga, and In; The catalyst is prepared by the following method: S1, pretreating the alumina support under vacuum conditions; S2, impregnating the pretreated alumina support into an impregnation solution comprising a Pt precursor, an Sn precursor, a second promoter precursor, a third promoter precursor, and hydrochloric acid; S3, after the impregnation is completed, drying and calcining to obtain a catalyst precursor; S4, pre-reducing the catalyst precursor under H2 conditions to obtain a propane dehydrogenation catalyst.

2. The low-Pt loading propane dehydrogenation catalyst according to claim 1, wherein The second promoter is B.

3. The low-Pt-loading propane dehydrogenation catalyst according to claim 1, wherein The alkali metal is selected from at least one of Li, Na, and K, and the alkaline earth metal is selected from at least one of Mg and Ca.

4. The low-Pt-loading propane dehydrogenation catalyst according to claim 1, wherein, By elemental mass fraction, it contains 0.01% - 0.25% of the main active component Pt, 0.01% - 1.5% of the first promoter Sn, 0.03% - 1% of the second promoter, 0.1% - 1% of the third promoter, and the rest is the alumina support.

5. The low-Pt-loading propane dehydrogenation catalyst according to claim 1, wherein The mass ratio of Sn to Pt is 0.2:1 to 4:

1.

6. The low-Pt loading propane dehydrogenation catalyst according to claim 1, wherein The mass ratio of the second promoter element to Pt is 0.2:1 to 5:

1.

7. The low-Pt loading propane dehydrogenation catalyst according to claim 1, characterized in that, The mass ratio of the third promoter element to Pt is 2:1 to 10:

1.

8. The low-Pt-loading propane dehydrogenation catalyst according to claim 1, wherein, In step S1, the pretreatment time is 0.2 - 1 h, in step S2, the hydrochloric acid concentration is 36 - 38%, the addition amount is 5% - 20% of the total mass of the catalyst, and the impregnation time is 0.5 - 5 h.

9. The low-Pt loading propane dehydrogenation catalyst according to claim 1, wherein The drying conditions are drying at 80 - 130 °C for 2 - 10 h, the calcining conditions are calcining at 400 - 750 °C for 2 - 8 h, and the pre-reduction conditions are pre-reducing at 450 - 600 °C for 1 - 4 h.

10. The low-Pt loading propane dehydrogenation catalyst according to claim 1, wherein In step S2, equal-volume impregnation is used for impregnation.

11. Use of the low-Pt-loading propane dehydrogenation catalyst according to any one of claims 1 to 10, characterized in that, The reaction temperature is 500 °C to 650 °C, the reaction pressure is 0 to 0.5 MPa, the liquid hourly space velocity of propane is 1 to 10 h -1 , and the hydrogen-hydrocarbon molar ratio is 0.25:1 to 4:1.

Images