A chromium-based catalyst for dehydrogenation of propane to propylene and a preparation method thereof

Abstract

The application belongs to the technical field of chromium-based propane dehydrogenation catalysts, and specifically provides a chromium-based propane dehydrogenation catalyst for preparing propylene and a preparation method thereof. 1‑ m Zr m The carrier is Al The application has the advantages of high conversion rate and selectivity.

Description

Technical Field

[0001] This application belongs to the technical field of chromium-based propane dehydrogenation catalysts, and in particular relates to a chromium-based propane dehydrogenation catalyst for propylene production and its preparation method. Background Technology

[0002] Propylene is a crucial chemical raw material for the production of polypropylene, propane oxide, and acrylonitrile, and is the second most important petrochemical intermediate after ethylene. With the increasing demand for downstream propylene products, propylene production capacity has continued to grow. Currently, there are three main methods for producing propylene: propylene co-production from naphtha cracking, propylene as a byproduct of catalytic cracking, and propylene production from propane dehydrogenation. In recent years, relying on traditional naphtha cracking and catalytic cracking byproduct propylene production has become insufficient to meet the demands of chemical production. Therefore, the low-cost process of producing high-value-added olefins through alkane dehydrogenation has attracted considerable attention.

[0003] Propane dehydrogenation to propylene not only increases the added value of the product and reduces the dependence of propylene production on naphtha cracking and catalytic cracking processes, but also produces high-value hydrogen as a byproduct. However, this reaction is strongly endothermic with a low chemical equilibrium constant, putting it at a thermodynamic disadvantage. Therefore, catalysts are needed to improve its kinetic advantages, making high-performance catalysts a key research focus in propane dehydrogenation to propylene production. Currently, propane dehydrogenation catalysts include platinum-based catalysts, chromium-based catalysts, and composite metal oxide catalysts. Platinum-based catalysts have good activation performance, but Pt is expensive and requires high purity of reactants. They are also prone to carbon deposition and coking during the reaction, leading to the covering of some active sites. Composite metal oxide catalysts have relatively poor activity and selectivity. Chromium-based catalysts have high catalytic activity and lower requirements for reactant purity, but chromium is prone to contamination.

[0004] To address the aforementioned issues, reducing costs, minimizing environmental pollution, improving the stability and selectivity of chromium-based catalysts, and inhibiting coking reactions are of significant technical importance. Summary of the Invention

[0005] To address the aforementioned issues and further improve the performance of chromium-based catalysts, this application provides a chromium-based propane dehydrogenation catalyst for propylene production and its preparation method.

[0006] This application first provides a chromium-based propane dehydrogenation catalyst for propylene production, comprising a support, a main active component, and a secondary active component; the support is Al. 1-m Zr m The composite carrier has an m = 0.1-0.4; the main active component includes Cr; and the secondary active components are selected from alkaline earth metal elements.

[0007] Furthermore, the loading of the main active component is 15-20 wt% of the carrier mass based on the weight of Cr.

[0008] Furthermore, the loading amount of the secondary active component is 0.5-3 wt% of the carrier mass, calculated by weight of alkaline earth metal elements.

[0009] Furthermore, the specific surface area of ​​the carrier is 150-300 m². 2 / g.

[0010] Furthermore, the alkaline earth metal element is at least one of Ca and Mg.

[0011] A method for preparing a chromium-based propane dehydrogenation catalyst for propylene includes the following steps:

[0012] 1) A ternary composite solution was prepared by dissolving ellagic acid, phytic acid and ethylenediamine in an aprotic solvent; aluminum nitrate and zirconium oxynitrate were added to a glucose solution and mixed evenly to prepare a base solution;

[0013] 2) Mix the base liquid and the ternary composite liquid evenly, then add urea solution and alkaline earth metal phosphate dispersion dropwise, stir evenly and crystallize, wash the resulting precipitate, dry and calcine to obtain the carrier;

[0014] 3) Place the carrier in a chromium nitrate solution, stir and impregnate, evaporate the water, and then dry and calcine to obtain the final product.

[0015] Furthermore, in 1), the mass ratio of ellagic acid, phytic acid, and ethylenediamine is (2.5-3):(1-1.5):1.

[0016] Furthermore, in step 2), the volume ratio of the base liquid to the ternary composite liquid is 1:(0.1-0.15).

[0017] Furthermore, in step 2), the alkaline earth metal phosphate dispersion is prepared as follows: magnesium salt and calcium salt are dissolved in deionized water to prepare a calcium-magnesium ion solution, then carrageenan is added and mixed evenly, and after standing, an equal volume of potassium dihydrogen phosphate solution is added and mixed evenly, and the pH is adjusted to 7 to obtain the final product.

[0018] Furthermore, in step 3), the calcination temperature is 550-650℃.

[0019] Compared with the prior art, this application has the following beneficial effects:

[0020] This application uses ellagic acid, phytic acid, and ethylenediamine as ternary components, which are crystallized with aluminum and zirconium components under hydrothermal conditions to form a composite precursor. After calcination, a support containing N, P, and O heteroatom functional domains is obtained, which can reduce the acidity of the support, have a better chromium ion anchoring effect, and inhibit atomic migration and coking at high temperatures. In addition, alkaline earth metal phosphates can improve the electronic field environment around the chromium active center, which is more conducive to stabilizing the key intermediate state of propane dehydrogenation reaction, while suppressing extreme electronic states that lead to side reactions, thus providing catalyst stability.

[0021] Furthermore, compared to the traditional method of directly adding magnesium oxide and calcium oxide, this application uses carrageenan as a stabilizing component. Utilizing the double-helix molecular structure of carrageenan, a stable amorphous phosphate form is constructed, further uniformly reducing the acidity of the support, enhancing the interaction between CrO3 and the support, and inhibiting some Cr... 6+ The reduction to Cr3+ refines the chromium grains and makes them more uniformly distributed on the support, improving the selectivity of propylene. At the same time, it can also reduce the original Cr loading to a certain extent and reduce pollution. Attached Figure Description

[0022] Figure 1 This is a schematic diagram showing the propylene conversion and selectivity data of the catalyst in Examples 1-2 and the control group of this application.

[0023] Figure 2 This is a schematic diagram of the carrier XRD and EDS of Embodiment 2 of this application. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0026] When using “including,” “having,” and “contains” as described herein, the intention is to cover non-exclusive inclusion, unless an explicit qualifying term such as “only,” “consisting of,” etc., is used, in which case another component may be added.

[0027] The terms "preferred," "more preferably," "better," and "even better" used in this application refer to embodiments of this application that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this application. That is, in this application, "preferred," "more preferably," "better," and "even better" are merely descriptions of implementations or embodiments with better effects, but do not constitute a limitation on the scope of protection of this application.

[0028] In this application, terms such as "further," "even more," and "particularly" are used for descriptive purposes and to indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0029] In this application, "at least one" means one or more, such as one, two, or more. "Multiple" or "several" means at least two, such as two, three, etc., and "multi-layered" means at least two layers, such as two layers, three layers, etc., unless otherwise explicitly specified. In the description of this application, "several" means at least one, such as one, two, etc., unless otherwise explicitly specified.

[0030] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0031] Unless otherwise specified, all steps in this application may be performed sequentially or randomly. For example, the method comprising steps (a) and (b) indicates that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc. Unless otherwise stated, singular terms may include plural forms and should not be construed as having a quantity of one.

[0032] In this application, "above" or "below" includes the stated number. For example, "below 1" includes 1.

[0033] In this application, room temperature refers to 0~40℃, including but not limited to 10~40℃, or further to 20~30℃.

[0034] This application, based on extensive experimental research, provides a chromium-based propane dehydrogenation catalyst for propylene production, comprising a support, a main active component, and a secondary active component; the support is Al. 1-m Zr m The composite carrier has an m = 0.1-0.4; the main active component includes Cr; and the secondary active components are selected from alkaline earth metal elements.

[0035] Furthermore, the loading of the main active component is 15-20 wt% of the carrier mass based on the weight of Cr.

[0036] In some specific embodiments, the loading amount of the main active component, based on the weight of Cr, can be 15 wt%, 15.5 wt%, 16 wt%, 16.5 wt%, 17 wt%, 17.5 wt%, 18 wt%, 18.5 wt%, 19 wt%, 19.5 wt%, or 20 wt% of the carrier mass. Generally, a better technical effect can be achieved when the loading amount of the main active component, based on the weight of Cr, is 19.5 wt% of the carrier mass.

[0037] Furthermore, the loading amount of the secondary active component is 0.5-3 wt% of the carrier mass, calculated by weight of alkaline earth metal elements.

[0038] In some specific embodiments, the loading amount of the secondary active component, based on the weight of alkaline earth metal elements, can be 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt%, or 3wt% of the carrier mass. Generally, when the loading amount of the secondary active component, based on the weight of alkaline earth metal elements, is 2wt% of the carrier mass, better experimental results can be obtained.

[0039] Furthermore, the specific surface area of ​​the carrier is 150-300 m². 2 / g.

[0040] Furthermore, the alkaline earth metal element is at least one of Ca and Mg.

[0041] A method for preparing a chromium-based propane dehydrogenation catalyst for propylene includes the following steps:

[0042] 1) A ternary composite solution was prepared by dissolving ellagic acid, phytic acid and ethylenediamine in an aprotic solvent; aluminum nitrate and zirconium oxynitrate were added to a glucose solution and mixed evenly to prepare a base solution;

[0043] 2) Mix the base liquid and the ternary composite liquid evenly, then add urea solution and alkaline earth metal phosphate dispersion dropwise, stir evenly and crystallize, wash the resulting precipitate, dry and calcine to obtain the carrier;

[0044] 3) Place the carrier in a chromium nitrate solution, stir and impregnate, evaporate the water, and then dry and calcine to obtain the final product.

[0045] Furthermore, in 1), the mass ratio of ellagic acid, phytic acid, and ethylenediamine is (2.5-3):(1-1.5):1.

[0046] In some specific embodiments, in step 1), the mass ratio of ellagic acid, phytic acid, and ethylenediamine can be 2.5:1:1, 2.6:1:1, 2.7:1:1, 2.8:1:1, 2.9:1:1, 3:1:1, 2.5:1.1:1, 2.6:1.2:1, 2.7:1.3:1, 2.8:1.4:1, 2.9:1.5:1, or 3:1.5:1. Generally, a mass ratio of ellagic acid, phytic acid, and ethylenediamine of 2.8:1.2:1 in step 1) yields better technical results.

[0047] Furthermore, in step 2), the volume ratio of the base liquid to the ternary composite liquid is 1:(0.1-0.15).

[0048] In some specific embodiments, in step 2), the volume ratio of the base liquid to the ternary composite liquid can be 1:0.1, 1:0.105, 1:0.11, 1:0.115, 1:0.12, 1:0.125, 1:0.13, 1:0.135, 1:0.14, 1:0.145, or 1:0.15. Generally, in step 2), a volume ratio of 1:0.125 for the base liquid to the ternary composite liquid yields better technical results.

[0049] Furthermore, in step 2), the alkaline earth metal phosphate dispersion is prepared as follows: magnesium salt and calcium salt are dissolved in deionized water to prepare a calcium-magnesium ion solution, then carrageenan is added and mixed evenly, and after standing, an equal volume of potassium dihydrogen phosphate solution is added and mixed evenly, and the pH is adjusted to 7 to obtain the final product.

[0050] Furthermore, in step 3), the calcination temperature is 550-650℃.

[0051] The present application will be further illustrated by the following examples, but these examples do not limit the scope of the present application.

[0052] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in this application, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. All reagents or instruments whose manufacturers are not specified are conventional products that can be purchased commercially. In addition to the specific methods, equipment, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description in this application, any prior art methods, equipment, and materials similar to or equivalent to those described, used, or made by the methods, equipment, and materials in the embodiments of this application may be used to implement this application.

[0053] Example 1

[0054] The preparation method of the chromium-based propane dehydrogenation catalyst for propylene in this embodiment includes the following steps:

[0055] 1) Add 0.01 mol ellagic acid, 1.08 g phytic acid and 1.32 g ethylenediamine to a 250 mL three-necked flask, add 80 mL anhydrous DMSO and mix well. Under nitrogen protection, heat to 80 °C and stir for 5 h, then cool to room temperature to obtain a ternary composite solution; Weigh 0.4954 g glucose and dissolve it in 20 mL deionized water to obtain a glucose solution. Add 3.3762 g aluminum nitrate nonahydrate and 0.2312 g zirconium oxynitrate to the glucose solution and stir for 1.5 h to obtain the base solution;

[0056] 2) Mix 20 mL of base solution with 1.25 mL of ternary composite solution until homogeneous. Then, add 15 mL of a solution containing 1.9219 g of urea and 10 mL of a dispersion containing 0.0646 g of amorphous calcium phosphate and 0.0736 g of amorphous magnesium phosphate dropwise. After stirring until homogeneous, crystallize at 170 °C for 12 h. Cool to room temperature, wash the resulting precipitate with deionized water and anhydrous ethanol, dry at 80 °C for 5 h, and calcine at 700 °C for 4 h in a muffle furnace to obtain the support. The specific surface area of ​​the support was determined to be 230.6 m³ / s using nitrogen physical adsorption. 2 / g, with an average pore size of 11.5nm;

[0057] The preparation method of alkaline earth metal phosphate dispersion is as follows: Dissolve 0.15g magnesium chloride and 0.25g calcium chloride in 50mL of deionized water to prepare a calcium magnesium ion solution, then add 0.05g carrageenan and mix well. After standing, add an equal volume of potassium dihydrogen phosphate solution and mix well. Adjust the pH to 7 to obtain the solution.

[0058] 3) Weigh 3.0013g of chromium nitrate nonahydrate and dissolve it in 15mL of deionized water. Stir until homogeneous to obtain a chromium nitrate solution. Then accurately weigh 2g of the carrier and place it in the prepared chromium nitrate solution. Stir and soak for 5h. Then evaporate the water at 80℃ and continue drying at 80℃ for 5h. Then transfer it to a muffle furnace and calcine at 600℃ for 4h to obtain the final product.

[0059] Example 2

[0060] The preparation method of the chromium-based propane dehydrogenation catalyst for propylene in this embodiment includes the following steps:

[0061] 1) Add 0.01 mol ellagic acid, 1.08 g phytic acid and 1.32 g ethylenediamine to a 250 mL three-necked flask, add 80 mL anhydrous DMSO and mix well. Under nitrogen protection, heat to 80 °C and stir for 5 h, then cool to room temperature to obtain a ternary composite solution; Weigh 0.4954 g glucose and dissolve it in 20 mL deionized water to obtain a glucose solution. Add 3.3762 g aluminum nitrate nonahydrate and 0.2312 g zirconium oxynitrate to the glucose solution and stir for 1.5 h to obtain the base solution;

[0062] 2) Mix 20 mL of base solution with 1.25 mL of ternary composite solution until homogeneous. Then, add 15 mL of a solution containing 1.9219 g of urea and 10 mL of a dispersion containing 0.0646 g of amorphous calcium phosphate and 0.0543 g of amorphous magnesium phosphate dropwise. After stirring until homogeneous, crystallize at 170 °C for 12 h. Cool to room temperature, wash the resulting precipitate with deionized water and anhydrous ethanol, dry at 80 °C for 5 h, and calcine at 700 °C for 4 h in a muffle furnace to obtain the support. The specific surface area of ​​the support was determined to be 236.2 m³ / h using nitrogen physical adsorption. 2 / g, with an average pore size of 12.3nm;

[0063] The preparation method of alkaline earth metal phosphate dispersion is as follows: Dissolve 0.15g magnesium chloride and 0.25g calcium chloride in 50mL of deionized water to prepare a calcium magnesium ion solution, then add 0.05g carrageenan and mix well. After standing, add an equal volume of potassium dihydrogen phosphate solution and mix well. Adjust the pH to 7 to obtain the solution.

[0064] 3) Weigh 3.0013g of chromium nitrate nonahydrate and dissolve it in 15mL of deionized water. Stir until homogeneous to obtain a chromium nitrate solution. Then accurately weigh 2g of the carrier and place it in the prepared chromium nitrate solution. Stir and soak for 5h. Then evaporate the water at 80℃ and continue drying at 80℃ for 5h. Then transfer it to a muffle furnace and calcine at 600℃ for 4h to obtain the final product.

[0065] control group

[0066] The preparation method of the catalyst in this control group includes the following steps:

[0067] 1) Weigh 0.4954g of glucose and dissolve it in 20mL of deionized water to obtain a glucose solution. Add 3.3762g of aluminum nitrate nonahydrate and 0.2312g of zirconium oxynitrate to the glucose solution and stir for 1.5h to obtain the base solution.

[0068] 2) Add 15 mL of a solution containing 1.9219 g of urea and 10 mL of a dispersion containing 0.1 g of calcium carbonate to 20 mL of base solution. After stirring evenly, crystallize at 170 °C for 12 h, cool to room temperature, wash the resulting precipitate with deionized water and anhydrous ethanol, dry at 80 °C for 5 h, and calcine in a muffle furnace at 700 °C for 4 h to obtain the support. The specific surface area of ​​the support was determined to be 208.3 m³ / h using nitrogen physical adsorption. 2 / g, with an average pore size of 7.6nm;

[0069] 3) Weigh 3.0013g of chromium nitrate nonahydrate and dissolve it in 15mL of deionized water. Stir until homogeneous to obtain a chromium nitrate solution. Then accurately weigh 2g of the carrier and place it in the prepared chromium nitrate solution. Stir and soak for 5h. Then evaporate the water at 80℃ and continue drying at 80℃ for 5h. Then transfer it to a muffle furnace and calcine at 600℃ for 4h to obtain the final product.

[0070] Performance testing

[0071] The propane dehydrogenation performance of the catalysts from Examples 1-2 and the control group was evaluated using a quartz tube fixed reactor. The catalyst loading was 0.15 g. Under hydrogen conditions, the temperature was increased to 600 °C at a rate of 5 °C / min, and reduction was carried out for 2 h. Propane was then introduced at a pressure of 0.05 MPa, with a hydrogen to propane molar ratio of 0.5 and a WHSV of 6 h. -1 The gaseous products of the propane dehydrogenation reaction were monitored online using gas chromatography. The reactor outlet gas composition included methane, ethane, ethylene, propane, and propylene. Propane conversion rate = (X...) in -X out ) / X in propylene selectivity = Y out / (X in -X out ), X in X represents the volume fraction of imported propane. out Y represents the volume fraction of propane exported. out This represents the volume fraction of propylene exported. Specific test data are as follows: Figure 1 As shown. The carrier from Example 2 was subjected to X-ray diffraction and EDS analysis; the specific results are as follows. Figure 2 As shown.

[0072] analyze Figure 1 and Figure 2It can be seen that the support of this application has calcium, magnesium, aluminum and zirconium elements uniformly distributed, with strong interaction, good catalyst stability, and higher propylene selectivity and conversion rate compared with traditional catalysts.

[0073] Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a chromium-based propane dehydrogenation catalyst for propylene, characterized in that: Includes the following steps: 1) A ternary composite solution is prepared by dissolving ellagic acid, phytic acid and ethylenediamine in an aprotic solvent, and a base solution is prepared by adding aluminum nitrate and zirconium oxynitrate to a glucose solution and mixing them evenly; the mass ratio of ellagic acid, phytic acid and ethylenediamine is (2.5-3):(1-1.5):1; 2) Mix the base solution and the ternary composite solution evenly, then add urea solution and alkaline earth metal phosphate dispersion dropwise, stir evenly and crystallize, wash the resulting precipitate, dry and calcine to obtain the carrier; the preparation method of alkaline earth metal phosphate dispersion is as follows: dissolve magnesium salt and calcium salt in deionized water to prepare calcium magnesium ion solution, then add carrageenan and mix evenly, let stand, add an equal volume of potassium dihydrogen phosphate solution and mix evenly, adjust the pH value to 7 to obtain the carrier; the volume ratio of the base solution to the ternary composite solution is 1:(0.1-0.15); 3) Place the carrier in a chromium nitrate solution, stir and impregnate, evaporate the water, and then dry and calcine to obtain the final product.

2. The method for preparing the chromium-based propane dehydrogenation catalyst to propylene according to claim 1, characterized in that: In step 3), the calcination temperature is 550-650℃.

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