A Pt highly dispersed low-carbon alkane dehydrogenation catalyst, its preparation method and application

Abstract

The present invention belongs to the field of high-performance catalysts, and provides a low-carbon alkane dehydrogenation catalyst with highly dispersed Pt, a preparation method and an application thereof. By controlling processes such as the carrier preparation process, the Pt impregnation temperature and pH value, and the catalyst post-treatment, the size of Pt active particles and the metal dispersion degree are synergistically controlled, thereby further improving the stability of the catalyst. After 80 h of reaction evaluation, it is found that the propane conversion rate of the catalyst only decreases by 3.3%. At a reaction temperature of 630 °C, it still has high reaction stability. The catalyst has both high activity and anti-carbon deposition ability in the dehydrogenation of low-carbon alkanes to olefins, and solves the problem of low stability of existing catalysts.

Description

Technical Field

[0001] The present invention belongs to the field of high-performance dehydrogenation catalysts, and discloses a low-carbon alkane dehydrogenation catalyst with highly dispersed Pt, a preparation method thereof, and an application thereof. Background Art

[0002] Alkane dehydrogenation units are favored by refining enterprises due to advantages such as short process flow, low investment, good product quality, high conversion rate, few by-products, and mainly producing low-carbon olefins. Especially after 2020, there has been a blowout development situation in China. It is expected that by 2025, the production capacity of alkane dehydrogenation units will reach its peak, and the speed of newly built units will slow down in the later stage. According to statistics, by 2023, the production capacity of domestic moving-bed alkane dehydrogenation units that have been put into production and under construction has reached 20 million tons / year, and the catalyst demand is about 3,000 tons / year. However, the domestic catalyst demand situation is passive, mainly monopolized by foreign catalysts, and the catalyst price is high. Therefore, in the long run, realizing independent R & D and production of catalysts is the only way to solve this problem.

[0003] The patent application number CN201910595345.9, titled "A platinum-based catalyst for propane dehydrogenation to propylene and a preparation method thereof", discloses a preparation method of a Pt-based propane dehydrogenation catalyst. However, through verification, it is found that the stability of this catalyst is poor and carbon deposition is serious during the reaction process.

[0004] Patent CN103785384 provides a preparation technology for low-carbon alkane to olefin catalysts with alumina as the carrier, Sn and alkali metals as promoters, and Pt as the active component. The main disadvantages of this catalyst are that the active component Pt is prone to uneven dispersion, resulting in low stability and activity repeatability of the catalyst, and lacking the key technology to ensure uniform dispersion of Pt.

[0005] Combined with existing literature reports, Pt-based low-carbon alkane dehydrogenation catalysts are mainly prepared by the impregnation method. However, in existing research, there are no reports on the direct influence rules of carrier calcination temperature, pH value of Pt impregnation solution, impregnation temperature, catalyst post-treatment, etc. on the size of catalyst Pt active particles and metal dispersion, nor on the influence rules of catalyst activity and stability. And the research in this aspect is of great significance to the industrial actual dehydrogenation process of the low-carbon alkane dehydrogenation to olefin system. Summary of the Invention

[0006] In view of many deficiencies in the prior art, the present invention provides a Pt highly dispersed dehydrogenation catalyst for light alkanes and a preparation method thereof. By controlling the carrier preparation process, Pt impregnation temperature and pH value, catalyst post-treatment and other processes, the size of Pt active particles and metal dispersion are synergistically controlled, thereby further improving the stability of the catalyst. After 80 h of reaction evaluation, it is found that the propane conversion rate of the catalyst only decreases by 3.3%. At a reaction temperature of 630 °C, it still has high reaction stability. This catalyst has high activity and anti-coking ability in the dehydrogenation of light alkanes to olefins, solving the problem of low stability of existing catalysts.

[0007] The main inventive concept of the present invention is as follows:

[0008] The inventors found that introducing appropriate amounts of various additives such as Sn, Ti, Zn and alkali metals during the preparation process of the alumina carrier, mixing them evenly with the aluminum sol, and through the -HO bond relationship between the metal components, after drying and calcining for dehydration and condensation, with the help of the connection of -O- (bridging oxygen bond), a stably bonded M-O-M or M-O-T (M, T represent Al, Sn, Ti, Zn and alkali metal components) metal oxide carrier is formed. This carrier is dominated by alumina, and the additive metal components are evenly dispersed in the carrier skeleton, strengthening the interaction between the additive and the carrier, which helps to improve the thermal stability and structural stability of the carrier. At the same time, the alkali metal is beneficial to neutralize the acidity of the catalyst, slow down the coking rate of the catalyst, and improve the reaction stability of the catalyst. At the same time, the dehydrogenation effect of the additives Sn, Zn, Ti helps to improve the reaction activity of the catalyst; secondly, the inventors found in the research that a suitable impregnation temperature during the impregnation process helps to improve the impregnation depth and uniform dispersion of Pt. In the actual moving bed industrial application, it is beneficial to reduce the loss of Pt and extend the catalyst life; the pH value of the Pt impregnation solution directly affects the size of the catalyst active particles and the level of metal dispersion. The larger the active particles, the lower the metal dispersion of the catalyst, and the worse the corresponding catalyst activity and stability. In addition, the high-temperature calcination and oxychlorination processes after impregnating with the Pt solution help to strengthen the connection of the strong -O- (bridging oxygen bond) between the carrier, additive and Pt, prevent the aggregation of Pt active particles, ensure the uniform dispersion of Pt on the carrier, reduce the loss of Pt during the reaction process, and improve the catalyst activity and stability.

[0009] Based on the above inventive concept, the specific technical solutions of the present application are as follows:

[0010] A Pt highly dispersed dehydrogenation catalyst for light alkanes, with alumina as the carrier, Pt as the active component, and additives being Sn, Ti, Zn or alkali metal. The contents of each component based on the total weight of the catalyst are as follows: Pt is 0.1 - 3.0%, Sn is 0.2 - 3.0%, Ti is 0.1 - 3.0%, Zn is 0.1 - 4.0%, alkali metal is 0.5 - 3.0%, and the balance is the carrier;

[0011] Further, the contents of each component are as follows: Pt is preferably 0.2-1.0%, Sn is preferably 0.2-1.0%, Ti is preferably 0.1-1.5%, Zn is preferably 0.5-3.0%, the alkali metal is preferably 0.5-2.0%, and the balance is the carrier.

[0012] The carrier used is θ-alumina or γ-alumina or α-alumina or a mixture thereof.

[0013] In addition, the inventors also provided a method for preparing the above-mentioned Pt highly dispersed low-carbon alkane dehydrogenation catalyst, which specifically includes the following steps:

[0014] (1) Mix pseudoboehmite and metatitanic acid with water evenly, add an appropriate amount of concentrated nitric acid while stirring at 60-90°C, stir for 2-5 hours at the same temperature, then mix evenly with an aqueous solution containing precursors of Sn, Zn, and alkali metal salts, age at 40-70°C for 3-8 hours, drop into oil ammonia for shaping, after drying at 120°C, then calcine at 850-1050°C for 4-8 hours to obtain spherical carriers with a particle size of 1.6-1.8 mm for standby;

[0015] (2) Use chloroplatinic acid as the platinum precursor, add deionized water, hydrochloric acid or ethanolamine to prepare an aqueous chloroplatinic acid solution with a pH value of 1-5 for standby;

[0016] (3) Immerse the carrier pellets into the aqueous chloroplatinic acid solution, keep at 40-65°C for 24 hours, with a rotation speed of 15 r / min, and then slowly evaporate the water at the same rotation speed at a temperature of 65-95°C to completely load Pt on the carrier;

[0017] (4) After drying the catalyst obtained in step (3) at 120°C, calcine it with air containing a small amount of chlorine, then purge and cool with nitrogen, and then reduce it with hydrogen to obtain the target catalyst.

[0018] In the above step (1), the precursors of Sn, Zn, and alkali metal salts are all water-soluble; further, the precursor of Sn is selected from tin tetrachloride or tin acetate; the precursor of the alkali metal salt is selected from sodium hydroxide or sodium nitrate or potassium chloride or potassium nitrate or calcium hydroxide; the precursor of Zn is selected from zinc chloride or zinc acetate.

[0019] The dosages of the above precursors are determined according to the contents of each component based on the total weight of the catalyst as follows: Pt is 0.1-3.0%, Sn is 0.2-3.0%, Ti is 0.1-3.0%, Zn is 0.1-4.0%, and the alkali metal is 0.5-3.0%.

[0020] After high-temperature calcination, the carrier is mainly θ-alumina according to the calcination temperature, and it can also be a mixture of θ-alumina and one or two of γ-alumina or α-alumina.

[0021] Preferably, in step (1), the mass ratio of pseudoboehmite, concentrated nitric acid, and deionized water used is (9-15):1:(40-60); the mass ratio of Sn, Zn, alkali metal salt precursor to deionized water used = 1:(10-15).

[0022] Preferably, in step (2), the pH value of the chloroplatinic acid aqueous solution is 2-3.

[0023] Preferably, in step (3), the volume ratio of the alumina spheres to the chloroplatinic acid aqueous solution is 1:1.2. The impregnation temperature is preferably maintained at 50-60°C for 24 h, the rotation speed is 15 r / min, and then the water is slowly evaporated at 70-80°C while the rotation speed remains unchanged.

[0024] Preferably, in step (4), the drying, calcination, and reduction are specifically as follows: after drying at 120°C for 5-12 h, calcination is carried out at 450-650°C for 4-8 h in an air atmosphere, and the space velocity is 600-1200 h -1 ; and the air contains 0.2-1.0% by volume of chlorine. After the calcination is completed, nitrogen is purged to cool down to 200°C, and then hydrogen is switched for reduction. The hydrogen space velocity is 200-800 h -1 , the temperature is 400-600°C, and the holding time is 4-8 h.

[0025] The inventor found through experimental comparison that the catalyst prepared by introducing appropriate amounts of various promoters such as Sn, Ti, Zn, and alkali metals during the preparation of the alumina support has higher stability than the catalyst obtained by impregnating and loading each promoter on a pure alumina support later. This further verifies that the support preparation technology in this concept helps to strengthen the interaction between the promoter and the support, improve the thermal stability and structural stability of the support, and at the same time, the alkali metal is beneficial to neutralize the acidity of the catalyst and slow down the carbon deposition rate of the catalyst. The dehydrogenation effects of Sn, Zn, and Ti also contribute to improving the reaction activity of the catalyst.

[0026] Controlling the calcination temperature of the support can effectively improve the stability of the catalyst and reduce the occurrence of side reactions. The calcination temperature of the support is 950°C - 1000°C, and the main crystal phase of the support is the θ type. When the calcination temperature of the support is lower than 850°C or higher than 1050°C, under the same impregnation process, problems such as reduced conversion rate, selectivity, or stability of the catalyst occur.

[0027] The inventors further found that when the support is impregnated with an aqueous solution of chloroplatinic acid, it is necessary to strictly control the impregnation temperature and pH value of the support. If the impregnation temperature of the support is too low, it is likely to cause uneven impregnation of Pt and low metal dispersion. Especially when the impregnation solution is below 45 °C, the active component Pt crystal grains of the obtained catalyst are generally larger than 4.5 nm. The relatively large Pt crystal grains are likely to cause the Pt metal dispersion to be lower than 24%, and the stability of the catalyst during the reaction process is relatively poor. If the impregnation temperature of the support is too high, it is likely to cause a decrease in the strength of the support, affecting the long-term operation of the catalyst. When the pH value of the support impregnation solution is too low (pH < 1), the acid strength of the catalyst is still relatively high after treatment, resulting in an increase in by-products during the reaction process, a decrease in the selectivity of the catalyst, and serious carbon deposition, which seriously affects the stability of the catalyst. When the pH value of the impregnation solution is too high (pH > 5), the active component Pt crystal grains are generally larger than 6 nm, and the Pt in the catalyst is likely to be unevenly dispersed, and the Pt metal dispersion (<18%) is relatively low, resulting in a relatively rapid decline in both the activity and stability of the catalyst. Moreover, during the regeneration process of the catalyst, the dispersion of Pt is still relatively low. Therefore, the pH value of the aqueous solution of chloroplatinic acid is further preferably 2 - 3.

[0028] At the same time, the inventors found through repeated verification that a certain amount of chlorine gas is injected during the catalyst calcination process. This oxychlorination process not only helps to correct the problem of uneven dispersion of the active component Pt during the impregnation process, but also helps to prevent the re-aggregation of Pt particles during high-temperature calcination, providing guarantee for the activity and stability of the catalyst. And the inventors finally determined that the corresponding effect is the best when the air contains 0.2 - 1.0% by volume of chlorine gas, thus filling the blank in this field.

[0029] The present invention also discloses the specific application of the above-mentioned low-carbon alkane dehydrogenation catalyst, specifically applied in the low-carbon alkane dehydrogenation process. The low-carbon alkane raw material used is propane, isobutane, or a mixed raw material of both. A fixed-bed reactor is adopted, and the following specific operations are carried out:

[0030] Load the catalyst into the constant-temperature section of the reactor, purge and dry with nitrogen, maintain at 200 °C for 4 h, then turn off the nitrogen and switch to hydrogen. The hydrogen space velocity is 100 h -1 , and increase the temperature to the reaction temperature of 550 - 630 °C at a heating rate of 1 °C / min. After the reaction temperature is stable, introduce the low-carbon alkane. The mass space velocity of the low-carbon alkane is 3 - 4 h -1 , the reaction pressure is 0 - 0.1 Mpa, the hydrogen-hydrocarbon molar ratio is 0.45, and the hydrogen sulfide content in the hydrogen is 100 - 160 ppm.

[0031] It is found through the evaluation results that the catalyst of the present invention has a high alkane conversion rate and reaction stability, and the carbon deposition resistance ability is significantly improved. When propane is used as the raw material, at a reaction temperature of 600 °C, the initial propane conversion rate is 39.5%, and the selectivity is 98.3%. After 80 h of reaction, the propane conversion rate is 36.2%, and the propylene selectivity is 98.6%. The catalyst conversion rate only decreases by 3.3%. When the reaction temperature is increased to 630 °C, within the same reaction time of 80 h, the propane conversion rate of this catalyst decreases from 42.1% to 30.5%, while the propane conversion rate of the commonly used industrial alkane dehydrogenation catalyst decreases from 41.6% to 21.3%. This catalyst shows high reaction stability. When isobutane is used as the raw material, at a reaction temperature of 560 °C, after 80 h of reaction, the isobutane conversion rate decreases from 49.2% to 35.6%, and the isobutene selectivity increases from 92.2% to 93.1%. The isobutane conversion rate of the commonly used industrial alkane dehydrogenation catalyst decreases from 45.5% to 25.7%, and the isobutene selectivity increases from 89.6% to 91.5%. It can be seen that the catalyst effect of this application is significantly better than that of the existing industrial alkane dehydrogenation catalyst.

[0032] In summary, the Pt highly dispersed light alkane dehydrogenation catalyst provided by this application has high reaction activity, stability and carbon deposition resistance ability, and solves the problems of low stability of existing catalysts, low repetition rate of preparation processes, and easy carbon deposition in the reaction process. Specific Embodiments

[0033] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments. The methods are all conventional methods unless otherwise specified. In the following embodiments and experimental examples, unless otherwise specified, various raw materials are obtained commercially. The percentages in the following embodiments are weight percentages unless otherwise specified. The platinum-containing industrial alkane dehydrogenation catalyst used in the comparative example can be a commercially available catalyst of UOP or BASF.

[0034] Example 1

[0035] A Pt highly dispersed light alkane dehydrogenation catalyst and its preparation method are as follows:

[0036] (1) Dissolve 0.71 g of tin tetrachloride, 1.86 g of potassium chloride, and 3.27 g of zinc acetate in 60 g of deionized water for later use; disperse 80 g of pseudo-boehmite and 1.33 g of metatitanic acid in 320 g of water to obtain a pseudo-boehmite slurry. After heating and stirring evenly at 85 °C, add 6.2 g of concentrated nitric acid to the above pseudo-boehmite slurry. At the same time, pour the metal ion aqueous solution containing tin, potassium, and zinc into the above slurry and continue stirring for 3 h. Then, age at 60 °C for 5 h, drop it into an oil-ammonia column for forming. After drying at 120 °C, calcine at 950 °C for 5 h to obtain an alumina support with a particle size of 1.6 - 1.8 mm, containing 0.5% Sn, 1.5% K, 1.0% Ti, and 1.5% Zn for later use.

[0037] (2) At 55 °C, immerse 30 g of the alumina support prepared in step (1) into 56 ml of an aqueous solution of chloroplatinic acid with a pH of 2.5. The mass fraction of Pt in the solution is 0.27%. Immerse at this temperature for 24 h with a rotation speed of 15 r / min. Subsequently, at the same rotation speed, raise the temperature to 80 °C, slowly evaporate the excess water until the catalyst particles are distinct, then dry at 120 °C for 5 h, and continue high-temperature calcination in an air atmosphere with a chlorine content of 0.5% (volume percentage) and an airspeed of 1000 h -1 , calcine at 600 °C for 5 h. After the calcination is completed, purge with nitrogen and cool down to 200 °C. Then, in a hydrogen atmosphere, continue to heat up to 550 °C and hold for 5 h for catalyst reduction with a hydrogen space velocity of 300 h -1 , to obtain a low-carbon alkane dehydrogenation catalyst containing 0.5% Pt, 0.5% Sn, 1.5% K, 1.0% Ti, and 1.5% Zn.

[0038] (3) Application of the above low-carbon alkane dehydrogenation catalyst in propane dehydrogenation, the specific steps are as follows:

[0039] Use a fixed-bed reactor, load the catalyst into the constant-temperature section of the reactor, purge and dry with nitrogen, hold at 200 °C for 4 h. Then, turn off the nitrogen and switch to hydrogen with a hydrogen space velocity of 100 h -1 , increase the temperature to the reaction temperature of 600 °C at a heating rate of 1 °C / min. Using propane as the raw material, the reaction pressure is atmospheric pressure, the hydrogen-hydrocarbon molar ratio is 0.45, and the alkane mass space velocity is 3.5 h -1 , carry out the dehydrogenation reaction under the condition that the hydrogen sulfide content in hydrogen is 120 ppm. The Pt metal dispersion, active particle size of the catalyst active component, and reaction data are shown in Table 1.

[0040] Example 2

[0041] (1) The catalyst preparation is carried out by the method of Example 1;

[0042] (2) Application of the low-carbon alkane dehydrogenation catalyst in propane dehydrogenation, the specific steps are as follows:

[0043] A fixed-bed reactor was used. The catalyst was loaded into the isothermal section of the reactor and purged with nitrogen for drying, maintained at 200 °C for 4 h, then the nitrogen was turned off and hydrogen was switched. The hydrogen space velocity was 100 h -1 , and it was heated to the reaction temperature of 560 °C at a heating rate of 1 °C / min. Using isobutane as the raw material, the reaction pressure was atmospheric pressure, the hydrogen-hydrocarbon molar ratio was 0.45, and the alkane mass space velocity was 3.5 h -1 . The dehydrogenation reaction was carried out under the condition that the hydrogen sulfide content in hydrogen was 120 ppm. The Pt metal dispersion, active particle size of the catalyst active component and reaction data are shown in Table 2.

[0044] Example 3

[0045] The method of Example 1 was used for catalyst preparation and application evaluation. The difference was that the carrier calcination temperature was lowered to 800 °C, and the other conditions remained unchanged. The raw material was propane. The Pt metal dispersion, active particle size of the catalyst active component and reaction data are shown in Table 1.

[0046] Example 4

[0047] The method of Example 1 was used for catalyst preparation and application evaluation. The difference was that the carrier calcination temperature was raised to 1100 °C, and the other conditions remained unchanged. The raw material was propane. The Pt metal dispersion, active particle size of the catalyst active component and reaction data are shown in Table 1.

[0048] Example 5

[0049] The method of Example 1 was used for catalyst preparation and application evaluation. The difference was that the carrier impregnation temperature was lowered to 40 °C, and the other conditions remained unchanged. The raw material was propane. The Pt metal dispersion, active particle size of the catalyst active component and reaction data are shown in Table 1.

[0050] Example 6

[0051] The method of Example 1 was used for catalyst preparation and application evaluation. The difference was that the pH value of the impregnation solution of the active component Pt was = 1, and the other conditions remained unchanged. The raw material was propane. The Pt metal dispersion, active particle size of the catalyst active component and reaction data are shown in Table 1.

[0052] Example 7

[0053] The method of Example 1 was used for catalyst preparation and application evaluation. The difference was that the pH value of the impregnation solution of the active component Pt was = 4, and the other conditions remained unchanged. The raw material was propane. The Pt metal dispersion, active particle size of the catalyst active component and reaction data are shown in Table 1.

[0054] Example 8

[0055] The method of Example 1 was used for catalyst preparation and application evaluation, with the difference that the pH value of the impregnation solution of the active component Pt was 6, and the other conditions remained unchanged. The raw material was propane. The metal dispersion of the active component Pt of the catalyst, the active particle size, and the reaction data are shown in Table 1.

[0056] Example 9

[0057] The method of Example 1 was used for catalyst preparation and application evaluation, with the difference that no chlorine gas was injected during the air calcination of the catalyst. The metal dispersion of the active component Pt of the catalyst, the active particle size, and the reaction data are shown in Table 1.

[0058] Example 10

[0059] The method of Example 1 was used for catalyst preparation and application evaluation, with the difference that the reaction temperature was 630 °C and the raw material was only propane. The metal dispersion of the active component Pt of the catalyst, the active particle size, and the reaction data are shown in Table 1.

[0060] Comparative Example 1

[0061] The method of Example 1 was used for catalyst application evaluation, with the difference that the catalyst in the fixed-bed reactor was selected from existing industrial alkane dehydrogenation catalysts. The metal dispersion of the active component Pt of the catalyst, the active particle size, and the reaction data are shown in Table 1.

[0062] Comparative Example 2

[0063] The method of Comparative Example 1 was used for catalyst application evaluation, with the difference that the reaction temperature was 630 °C. The metal dispersion of the active component Pt of the catalyst, the active particle size, and the reaction data are shown in Table 1.

[0064] Comparative Example 3

[0065] The method of Example 2 was used for catalyst application evaluation, with the difference that the catalyst in the fixed-bed reactor was selected from existing industrial alkane dehydrogenation catalysts. The metal dispersion of the active component Pt of the catalyst, the active particle size, and the reaction data are shown in Table 2.

[0066] The above examples and comparative examples were summarized, and the propane conversion rate and propylene selectivity at the initial 1 h and reaction 80 h were used for comparison. The effects of the carrier calcination temperature, the impregnation solution temperature and pH value, and the presence or absence of chlorine during the catalyst calcination process on the metal dispersion of the active component Pt, the catalyst activity, and the stability were investigated. The specific results are shown in Table 1.

[0067] Table 1

[0068]

[0069] As can be seen from the data comparison in Table 1, the alkane dehydrogenation catalyst prepared by the present invention exhibits high catalytic activity and stability in the dehydrogenation reaction of light alkanes. In Example 1, the propane conversion rate and stability of the dehydrogenating agent are the best.

[0070] By comparing Examples 1, 3, and 4, it is found that too low or too high carrier calcination temperature will affect the catalyst conversion rate, stability, and Pt metal dispersion. When the calcination temperature is too high, the specific surface area and pore volume may decrease, resulting in lower Pt metal dispersion of the active component;

[0071] By comparing Examples 1 and 5, it is found that too low carrier impregnation temperature is likely to lead to low Pt metal dispersion, reducing the selectivity and stability of the catalyst. However, during the actual impregnation process, when the impregnation temperature is higher than 70 °C in part, serious powder dropping of the carrier occurs, reducing the particle strength of the catalyst;

[0072] By comparing Examples 1, 6, 7, and 8, it is found that as the pH value of the carrier impregnation solution increases, the Pt metal dispersion of the active component shows a decreasing trend, the active particle size continuously increases, and the propane conversion rate and stability of the catalyst decrease. However, in actual applications, when the Pt metal dispersion is 28 - 31% and the active particle size is 3 - 4 nm, the catalyst performance is the best;

[0073] By comparing Examples 1 and 9, it is found that no chlorine injection during the catalyst calcination process will lead to a decrease in Pt metal dispersion, an increase in the active particle size, and a decrease in the catalyst stability;

[0074] By comparing Examples 1, 10, Comparative Example 1, and Comparative Example 2, it can be found that as the reaction temperature increases, both the catalyst conversion rate and selectivity decrease. However, at the same reaction temperature, the catalyst of the present invention has higher reaction activity, selectivity, and stability.

[0075] According to the scheme described in Example 2, using isobutane as the raw material, the isobutane conversion rate and isobutene selectivity of the catalyst of the present invention are compared with those of Comparative Example 3 at the initial 1 h and the reaction for 80 h. The specific data are shown in Table 2.

[0076] Table 2

[0077]

[0078] It is found from the data comparison in Table 2 that the catalyst of the present invention has higher catalyst activity and stability than Comparative Example 3, and the catalytic effect is excellent.

[0079] The above description is only an embodiment of the present application and does not impose any form of limitation on the present application. Although the present application is disclosed above with a preferred embodiment, it is not intended to limit the present application. Any person skilled in the relevant art can make some changes or modifications using the disclosed technical content within the scope of the technical solution of the present application, which are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A Pt highly dispersed dehydrogenation catalyst for light alkanes, characterized in that: The carrier is alumina, Pt is the active component, and the promoters are Sn, Ti, Zn and alkali metals. The contents of each component based on the total weight of the catalyst are as follows: Pt is 0.1 - 3.0%, Sn is 0.2 - 3.0%, Ti is 0.1 - 3.0%, Zn is 0.1 - 4.0%, alkali metals are 0.5 - 3.0%, and the balance is the carrier; The specific steps of its preparation method are as follows: (1) Mix pseudo - boehmite and metatitanic acid with water evenly. While stirring at 60 - 90 °C, add an appropriate amount of concentrated nitric acid, stir for 2 - 5 h at the same temperature, then mix evenly with the aqueous solution dissolving the precursors of Sn, Zn and alkali metal salts, age at 40 - 70 °C for 3 - 8 h, drop into oil - ammonia for shaping. After drying at 120 °C, then calcine at 850 - 1050 °C for 4 - 8 h to obtain spherical carriers with a particle size of 1.6 - 1.8 mm for standby; (2) Use chloroplatinic acid as the platinum precursor, add deionized water, hydrochloric acid or ethanolamine to prepare a chloroplatinic acid aqueous solution with a pH value of 2 - 3 for standby; (3) Immerse the carrier pellets into the chloroplatinic acid aqueous solution, keep at the impregnation temperature of 50 - 60 °C for 24 h, with a rotation speed of 15 r / min. Then slowly evaporate the water at 70 - 80 °C while keeping the rotation speed unchanged, so that Pt is completely loaded on the carrier; in step (3), the volume ratio of the alumina pellets to the chloroplatinic acid aqueous solution is 1:1.2; (4) After drying the catalyst obtained in step (3) at 120 °C, calcine it with air containing a small amount of chlorine, then purge with nitrogen to cool down, and then reduce it with hydrogen to obtain the target catalyst; The drying, calcination, and reduction described in step (4) are specifically as follows: After drying at 120°C for 5 - 12 h, under an air atmosphere, calcination is carried out at 450 - 650°C for 4 - 8 h, and the space velocity is 600 - 1200 h -1 ; and the air contains 0.2 - 1.0% by volume of chlorine. After the calcination is completed, nitrogen is used for purging to cool down to 200°C, and then hydrogen is switched for reduction. The hydrogen space velocity is 200 - 800 h -1 , the temperature is 400 - 600°C, and the holding time is 4 - 8 h.

2. The low-carbon alkane dehydrogenation catalyst according to claim 1, wherein: The contents of each component based on the total weight of the catalyst are as follows: Pt is 0.2 - 1.0%, Sn is 0.2 - 1.0%, Ti is 0.1 - 1.5%, Zn is 0.5 - 3.0%, alkali metals are 0.5 - 2.0%, and the balance is the carrier.

3. The low-carbon alkane dehydrogenation catalyst according to claim 1 or 2, characterized in that: The carrier used is θ - alumina or γ - alumina or α - alumina or a mixture thereof.

4. The low-carbon alkane dehydrogenation catalyst according to claim 1, wherein: In step (1), the precursors of Sn, Zn and alkali metal salts are all water - soluble; among them, the precursor of Sn is selected from tin tetrachloride or tin acetate; the precursor of the alkali metal salt is selected from sodium hydroxide or sodium nitrate or potassium chloride or potassium nitrate or calcium hydroxide; the precursor of Zn is selected from zinc chloride or zinc acetate.

5. The low-carbon alkane dehydrogenation catalyst according to claim 1, wherein: In step (1), the mass ratio of pseudo - boehmite, concentrated nitric acid and deionized water used is (9 - 15):1:(40 - 60); the mass ratio of the precursors of Sn, Zn and alkali metal salts to the deionized water used = 1:(10 - 15).

6. Use of the low-carbon alkane dehydrogenation catalyst according to claim 1 in an alkane dehydrogenation process, characterized in that: Specifically applied in the low - carbon alkane dehydrogenation process, the low - carbon alkane raw material used is propane, isobutane or a mixed raw material of both. A fixed - bed reactor is used, and the specific operation is as follows: Load the catalyst into the isothermal section of the reactor, purge and dry it with nitrogen, maintain it at 200 °C for 4 h, then turn off the nitrogen and switch to hydrogen. The hydrogen space velocity is 100 h -1 , and increase the temperature to the reaction temperature of 550 - 630 °C at a heating rate of 1 °C / min. After the reaction temperature is stable, introduce light alkanes. The mass space velocity of light alkanes is 3 - 4 h -1 , the reaction pressure is 0 - 0.1 Mpa, the hydrogen-hydrocarbon molar ratio is 0.45, and the hydrogen sulfide content in hydrogen is 100 - 160 ppm.

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