Preparation method and application of catalyst for preparing olefin through dehydrogenation of high-activity low-carbon alkane

Abstract

The invention belongs to the technical field of catalyst preparation, and discloses a preparation method and application of a catalyst for preparing olefin through dehydrogenation of high-activity low-carbon alkane. The preparation method comprises the following steps: synthesizing an NS-1 molecular sieve catalyst carrier containing auxiliary active metal N (N = Zn, Sn, Y, Co and Cu) and having an MFI structure by a hydrothermal method, and introducing main active metal M (M = Pt, Pd, Ru, Rh and Ir) into a pore channel of the NS-1 molecular sieve catalyst carrier by an ion exchange method. The M-NS-1 catalyst provided by the invention can provide stable propylene space-time yield which is more than three times higher than a literature value at the same temperature.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst preparation, and in particular relates to a preparation method and application of a catalyst for the reaction of dehydrogenating low-carbon alkanes to produce olefins. Background Art

[0002] Ethylene and propylene are important raw materials for the production of a variety of high-value chemical products such as high-molecular polymers. In recent years, the global demand for ethylene and propylene has become increasingly strong. Therefore, the development of practical technologies for directly dehydrogenating these olefins from the corresponding low-carbon alkanes (ethane, propane) has received increasing attention.

[0003] De Cola et al. (Appl. Catal. A, 2006, 306, 85) published a method for converting Zn into 2+ The invention discloses a method for preparing a Pt / Zn-molecular sieve propane dehydrogenation catalyst by introducing a molecular sieve to prepare a carrier, and then using a simple impregnation method to impregnate the carrier with a H2PtCl6 solution.

[0004] Cheng Kang et al. (CN116116453 A) disclosed a catalyst preparation technology in which a silicon-aluminum molecular sieve is treated with acid to dealuminate to obtain a catalyst carrier, and then a first metal (Zn, Sn, Ga, Cu, In, Na, K, Cs, Sr) and a second metal (Pt, Pd, Rh, Ir) are loaded on the carrier by an impregnation method. 0.5 @Y catalyst is used for direct dehydrogenation of propane to propylene. At a reaction temperature of 550℃, the initial space-time yield of propylene is 3.7mmol·g Pt -1 ·h -1 After 6 hours, the propylene space-time yield decreased by about 5%.

[0005] Zhu Haibo et al. (CN 117019207A) disclosed a method of first introducing a secondary active metal component (Sn, Ga or Zn) into a molecular sieve framework, and then preparing a Pt / Zn@zeolite catalyst by an impregnation method. The catalyst was used for the direct dehydrogenation of propane to propylene. The space-time yield of propylene was 21.6 mol·g at a reaction temperature of 600°C. Pt -1 ·h -1 ; In CN114570415A, CN 117019206A and CN 117019208A, Zhu Haibo et al. disclosed a method for synthesizing PtM@ molecular sieve (M=Cu, Ga, Zn, Sn, Ge) as a catalyst for direct dehydrogenation of propane to propylene using a one-pot process.

[0006] Xu Zhikang et al. (CN 117983279A) disclosed a method for preparing a propane dehydrogenation catalyst by introducing Pt and secondary active metals (Sn, Cu, Zn, Ga) into S-1 molecular sieve in one step (simultaneously). At a reaction temperature of 600°C, the obtained PtZnS 1.5 The initial propane conversion rate over the @S-1 catalyst was 44.7%, and after 72 hours, the propane conversion rate decreased by 12%.

[0007] Ji Hongbing et al. (CN 117482981 A) disclosed a method for preparing a Pt / Zn-S-1 propane dehydrogenation catalyst using a Zn-S-1 molecular sieve containing Na (or K) as a carrier. The Zn-S-1 molecular sieve containing Na (or K) was synthesized using dipotassium ethylenediaminetetraacetate or disodium ethylenediaminetetraacetate as a protective agent for Zn. The space-time yield of propylene on the PtZnNa3000 catalyst was 39.2 mol·g Pt -1 ·h -1 , while the PtZn3000 catalyst containing neither Na nor K was almost completely deactivated within 10 hours.

[0008] Zhang et al. (Chinese Journal of Catalysis 2023, 55, 241) published a method to prepare a PtZn@Beta propane dehydrogenation catalyst by encapsulating Zn in Beta molecular sieve with ethylenediamine and NH4F, and then impregnating the carrier with H2PtCl6 solution using a simple impregnation method. -1 Under the condition of -1 Pt -1 .h -1 .

[0009] The catalyst for the dehydrogenation of low-carbon alkanes to olefins prepared by the above method has a low olefin production rate and a fast deactivation rate per unit amount of precious metal M. In order to improve the catalytic efficiency and catalytic stability of the precious metal M, a preparation method for a precious metal M-based catalyst that can give a high olefin production rate and a low deactivation rate needs to be proposed. Summary of the invention

[0010] The present invention provides a preparation technology of a M-NS-1 (wherein M=Pt, Pd, Ru, Rh, Ir; N=Zn, Sn, Y, Co, Cu) catalyst which can provide high activity and high stability and is used for the dehydrogenation of low-carbon alkanes to produce olefins, so that the space-time yield of propane dehydrogenation to produce propylene reaches more than three times the value in existing literature at a reaction temperature of 550°C.

[0011] The above-mentioned object of the present invention is achieved through the following technical solutions.

[0012] 1. Synthesize NS-1 molecular sieve containing secondary active metal N and having MFI topological structure. Mix silicon source, secondary metal N source, tetrapropylammonium hydroxide, alkali metal source and deionized water in a molar ratio of 1SiO2: 0.002-0.08N: 0.2-0.8TPAOH: 0-0.20Na2O (or K2O): 5-100H2O, stir, place the obtained mixture in a hydrothermal kettle at 105-230°C for hydrothermal crystallization for 4-192h, then separate and dry the obtained solid; calcine in air or H2 at 450-650°C for 1-8h to obtain NS-1 molecular sieve.

[0013] 2. Introduce the main active metal M into the above-mentioned NS-1 molecular sieve by ion exchange method to obtain the M-NS-1 catalyst of the present invention. Add the NS-1 molecular sieve to the salt solution containing the main active metal M at a liquid / solid ratio of 2 to 100 mL / g, treat it at 50 to 100 ° C under reflux stirring or ultrasonic conditions for more than 1 hour, then separate the solid by centrifugation or filtration, dry it, and calcine it in air at 500 to 600 ° C for 1 to 8 hours to obtain the M-NS-1 catalyst. The ion exchange process can be completed once or multiple times. The number of exchanges required depends on the concentration of the main active metal M contained in the liquid used in the exchange process, the liquid / solid ratio used, and the content of M in the M-NS-1 catalyst to be prepared.

[0014] When synthesizing NS-1 molecular sieve in step 1, if the obtained NS-1 molecular sieve contains alkali metal due to the use of strong base, it is necessary to use NH4 before implementing step 2. + Ion exchange method is used to remove alkali metals in NS-1 molecular sieve. The specific removal method is as follows: add the above-obtained NS-1 molecular sieve to NH4NO3 aqueous solution at a liquid / solid ratio of 2-50 mL / g, stir under reflux at 50-100°C or under ultrasonic conditions for more than 1 hour, then dry the solid obtained by centrifugation and calcine at 450-600°C for 1-6 hours. + The ion exchange process can be performed once or multiple times.

[0015] The side active metal N is one or more of Zn, Sn, Y, Co, and Cu, and the side active metal source is one or more of nitrates, chlorides, hydroxides, oxides, oxyacid salts, and organic acid salts of the corresponding metals.

[0016] For the M-NS-1 catalyst of the present invention, when it contains multiple secondary active metals N such as N1 and N2, the second secondary active metal N2 can be introduced simultaneously with the first secondary active metal N1 and the main active metal M using the same ion exchange method.

[0017] The silicon source may be one or more of tetraethyl orthosilicate, white carbon black, silica sol, and water glass.

[0018] When synthesizing the NS-1 molecular sieve in step 1, an organic ligand such as ethylenediamine, sodium ethylenediaminetetraacetate or ethylenediaminetetraacetic acid may also be added.

[0019] The main active metal M is one or more of Pt, Pd, Rh, and Ir, and the main active metal source is one or more of amino nitrates, nitrates, and chlorides of the corresponding metals.

[0020] Another object of the present invention is to claim for the use of the above catalyst for the dehydrogenation of light alkanes to olefins.

[0021] In a further preferred embodiment of the present invention, the low carbon alkane in the above application is ethane or propane, and the olefin is ethylene or propylene.

[0022] The method of preparing MN-Beta catalyst by introducing the main active metal M into NS-1 molecular sieve without alkali metal ions by ion exchange method proposed in the present invention can effectively avoid the adverse effects of alkali metal on catalytic performance and greatly improve the catalytic stability of the catalyst, compared with the method of preparing the catalyst by directly introducing the noble metal M into the molecular sieve containing alkali metal by ion exchange method (see Table 1 for a comparison of the catalytic effects of the catalyst obtained in Example 4 and the catalyst obtained in Comparative Example 1).

[0023] The method for preparing the M-NS-1 catalyst by introducing the main active metal M into the NS-1 molecular sieve without alkali metal ions by the ion exchange method proposed by the present invention is different from the existing impregnation method in the preparation procedure in that the preparation process of the catalyst includes a separation process of the obtained solid from the liquid containing the main active metal M, while the existing impregnation method in the literature finally heats the liquid-solid mixture and directly evaporates it to dryness, so there is no such separation process. The above-mentioned catalyst preparation method for introducing M by the ion exchange method proposed by the present invention can separate and recover the M ions that have not entered the molecular sieve pores (adsorbed on the secondary active metal N) because the solid-liquid separation process can avoid the impregnation method heating the liquid containing the main active metal M to dry and disperse unevenly, resulting in a low generation rate of light olefins, and the impregnation method due to the excessive concentration of some main active metal M sites causing excessive dehydrogenation and carbon deposition of light alkanes and rapid deactivation. Therefore, the above-mentioned catalyst preparation method of introducing M by ion exchange method proposed in the present invention can greatly improve the activity and stability of the catalyst and maximize the utilization of the precious metal M (see Table 1 for a comparison of the catalytic effects of the catalyst obtained in Example 1 and the catalyst obtained in Comparative Example 2).

[0024] The present invention proposes the method of preparing M-NS-1 catalyst by introducing the main active metal M into NS-1 molecular sieve without alkali metal ions by ion exchange method. The total mass percentage of the main active metal in the catalyst is between 0.02% and 0.5%, and the total mass percentage of the secondary active metal is between 0.2% and 8%. Since all the main active metals M can be spontaneously adsorbed on the secondary active metal N sites of the NS-1 molecular sieve to obtain high dispersion and finally form an MN active structure, the obtained catalyst is far superior to any MN@zeolite catalyst prepared by a one-pot method in terms of catalytic activity and stability (see Table 1 for a comparison of the catalytic effects of the catalyst obtained in Example 1 and the catalyst obtained in Comparative Example 3). DETAILED DESCRIPTION

[0025] The present invention is described in detail below by specific examples, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0026] Example 1

[0027] 13g of 25wt.% TPAOH solution was mixed with 5g of deionized water, and then 9g of ethyl orthosilicate was added thereto and stirred for 2h, and then 2.5g of an aqueous solution containing 0.4g of zinc gluconate was added and stirred for 2h, and the resulting mixture was crystallized under hydrothermal conditions at 170°C for 72h. The resulting solid was centrifuged, dried, and calcined in air at 550°C for 4h to obtain a ZnS-1 molecular sieve with Zn incorporated into the molecular sieve framework.

[0028] 0.5 g of the ZnS-1 molecular sieve was added to 10 g of a Pt source aqueous solution containing 0.75 mg of Pt(NH3)4(NO3)2, and the mixture was uniformly mixed by ultrasonication, and then refluxed at 80°C for 8 h and centrifuged. The obtained solid was dried at 120°C and calcined in air at 500°C for 2 h to obtain a Pt-ZnS-1 catalyst.

[0029] Example 2

[0030] The ZnYS-1 molecular sieve was synthesized by the method described in Example 1 using step 1, but 2.5 g of a mixed aqueous solution containing 0.4 g of zinc gluconate and 1.5 mg of Y(NO3)3 was used instead of 2.5 g of an aqueous solution containing only 0.4 g of zinc gluconate in Example 1. The preparation of the Pt-ZnYS-1 catalyst in step 2 was exactly the same as the preparation of the Pt-ZnS-1 catalyst in Example 1.

[0031] Example 3

[0032] The ZnS-1 molecular sieve was synthesized by the method described in Example 1, but when preparing the catalyst in Step 2, 10 g of a mixed aqueous solution containing 1.5 mg of Y(NO3)3 and 0.75 mg of Pt(NH3)4(NO3)2 was used instead of the 10 g of aqueous solution containing only 0.75 mg of Pt(NH3)4(NO3)2 in Example 1.

[0033] Example 4

[0034] The ZnS-1 molecular sieve was synthesized by the method described in step 1 of Example 1, but 2.6 g of white carbon black was used instead of 9 g of ethyl orthosilicate in Example 1, and 0.1 g of KOH was added to assist in dissolving the white carbon black. 0.7 g of the obtained ZnS-1 molecular sieve was added to 14 ml of 1 M NH4NO3 aqueous solution, and refluxed at 80°C for 8 h. The solid was then separated and dried, and calcined at 550°C for 4 h. The NH4 + The step 2 of introducing Pt is exactly the same as the method described in Example 1.

[0035] Example 5

[0036] The ZnS-1 molecular sieve and Pt-ZnS-1 catalyst were synthesized by the method described in Example 1, except that 0.4 g of zinc gluconate in Example 1 was replaced by 0.3 g of Zn(NO3)2·6H2O.

[0037] Example 6

[0038] Example 1 was repeated, but in step 1, when synthesizing the ZnS-1 molecular sieve, 0.4 g of zinc gluconate was first dissolved in an aqueous solution containing 0.11 g of ethylenediamine. The colloid used to synthesize the ZnS-1 molecular sieve had the same proportions of components as in Example 1, except for the addition of the above-mentioned ethylenediamine. Step 2 for introducing Pt was also exactly the same as the method described in Example 1.

[0039] Example 7

[0040] The Pd-ZnS-1 catalyst was synthesized by the method described in Example 1, i.e., in the second step, the Pt(NH3)4(NO3)2 aqueous solution was replaced with a PdCl2 aqueous solution of the same mass and molar concentration as the Pt(NH3)4(NO3)2 aqueous solution to exchange the ZnS-1 molecular sieve, and the conditions of the other steps were the same as those in Example 1.

[0041] Example 8

[0042] The catalyst was synthesized by the method described in Example 1, but the molecular sieve synthesized in the first step was CoS-1. In the first step of synthesizing the CoS-1 molecular sieve in this example, the zinc gluconate crystals used in Example 1 were replaced with cobalt nitrate crystals with the same molar number as the zinc gluconate in Example 1, and 0.11 g of ethylenediamine was added to the mixed solution of cobalt nitrate to be dissolved. The other steps and conditions of this example were the same as those in Example 1.

[0043] Comparative Example 1

[0044] The Pt-ZnS-1 catalyst was synthesized by the method described in Example 4, but the NH4 used therein was omitted. + Ion exchange step.

[0045] Comparative Example 2

[0046] The ZnS-1 molecular sieve was synthesized by the method described in Example 1, but Pt was introduced into it by impregnation. The specific implementation process is to take 0.5g of ZnS-1 molecular sieve and add it to 0.5g of Pt source aqueous solution dissolved with 0.75mg Pt(NH3)4(NO3)2, mix it evenly by ultrasonic, impregnate it at room temperature for 12h, and then stir it at 80℃ until dry. Then the obtained solid was dried at 120℃ and calcined in air at 500℃ for 2h to obtain Pt / ZnS-1 catalyst.

[0047] Comparative Example 3

[0048] Pt-ZnS-1 catalyst was synthesized by one-pot method. 13g of 25wt.% TPAOH solution was mixed with 5g of deionized water, and then 9g of ethyl orthosilicate was added and stirred for 2h. Then, a mixed aqueous solution of 2.1g of distilled water, 0.4g of zinc gluconate, 0.75mg of Pt(NH3)4(NO3)2 and 0.4g of ethylenediamine was added and stirred for 2h. Finally, the obtained mixture was crystallized under hydrothermal conditions at 170℃ for 72h, centrifuged, and the obtained solid was dried and calcined in air at 550℃ for 4h.

[0049] Table 1 Catalytic performance of each catalyst using propane dehydrogenation as a model reaction for the dehydrogenation of light alkanes to olefins

[0050] (Catalytic reaction conditions: catalyst loading 25 mg, 550°C, reaction gas flow ratio and flow rate C3H8:H2:N2=5:5:20

[0051] mL / min)

[0052]

[0053] The above-described embodiments are only preferred embodiments of the present invention, but not all feasible embodiments of the present invention. For those skilled in the art, any obvious changes made thereto without departing from the principles and spirit of the present invention should be considered to be included in the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a catalyst for the dehydrogenation of light alkanes to olefins, characterized in that: The following steps are included: S1: Hydrothermal synthesis of NS-1 molecular sieve with MFI structure containing secondary active metal N (N = Zn, Sn, Y, Co, Cu); S2: The main active metal M (M = Pt, Pd, Ru, Rh, Ir) is introduced into the NS-1 molecular sieve carrier by ion exchange method to obtain an M-NS-1 catalyst containing both the main and secondary active metals M and N.

2. The method for preparing a catalyst for the dehydrogenation of light alkanes to olefins according to claim 1, characterized in that: Step S2 is not limited to the introduction of the main active metal, but can also be used to introduce the main active metal and the second secondary active metal simultaneously by ion exchange.

3. The method for preparing a catalyst for the dehydrogenation of light alkanes to olefins according to claim 1, characterized in that: Step S1 is not limited to preparing NS-1 containing only one secondary active metal.

4. The method for preparing a catalyst for the dehydrogenation of light alkanes to olefins according to claim 1, characterized in that: Step S2 is not limited to preparing the M-NS-1 catalyst containing only one main active metal.

5. The method for preparing a catalyst for the dehydrogenation of light alkanes to olefins according to claim 1, characterized in that: Step S1 also includes when NS-1 contains alkali metal, it is necessary to add a NH4 + The case of the alkali metal removal step by the exchange method.

6. The method for preparing a catalyst for the dehydrogenation of light alkanes to olefins according to claim 1, characterized in that: The total mass percentage of the main active metal in the catalyst is between 0.02% and 0.5%, and the total mass percentage of the secondary active metal is between 0.2% and 8%.

7. The method for preparing a catalyst for the dehydrogenation of light alkanes to olefins according to claim 1, characterized in that: The secondary metal N source is one or more of the nitrate, chloride, hydroxide, oxide, oxygen-containing acid salt and organic acid salt of the corresponding metal.

8. The method for preparing a catalyst for the dehydrogenation of light alkanes to olefins according to claim 1, characterized in that: Step S2 specifically comprises: adding NS-1 molecular sieve to a salt solution containing the main active metal M, treating it under reflux stirring or ultrasonic conditions, and then separating the solid by centrifugation or filtration, drying it, and calcining it in air to obtain an M-NS-1 catalyst. The ion exchange process can be completed once or multiple times.

9. The method for preparing a catalyst for the dehydrogenation of light alkanes to olefins according to claim 8, characterized in that: The salt of the main active metal M is one or more of the amino nitrate, nitrate and chloride of the corresponding metal.

10. The method for preparing a catalyst for the dehydrogenation of light alkanes to olefins according to claim 5, characterized in that: The step of removing the alkali metal is to add the NS-1 molecular sieve containing the alkali metal to the NH4NO3 aqueous solution and stir under reflux or ultrasonic conditions, and then dry and calcine the solid obtained by centrifugation. The step of removing the alkali metal includes once NH4 + Exchange or multiple NH4 + exchange.

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