Bifunctional catalyst for in-situ capture of carbon dioxide and oxidation of ethane to produce ethylene, preparation method and application thereof

Abstract

The present invention belongs to the technical field of oxidative dehydrogenation catalyst preparation, and in particular, relates to a bifunctional catalyst for in-situ capture of carbon dioxide and oxidation of ethane to prepare ethylene, as well as a preparation method and application thereof. The bifunctional catalyst comprises a magnesium-chromium oxide catalyst and a calcium-cerium oxide adsorbent, wherein the magnesium-chromium oxide catalyst is MgCr2O4, and the calcium-cerium oxide adsorbent comprises CaO and CeO2, wherein CaO accounts for more than 60% of the total mass of the calcium-cerium oxide adsorbent. The bifunctional catalyst provided by the present invention has in-situ capture and in-situ catalytic functions, and the carbon dioxide in the reaction gas is captured by the calcium-cerium oxide adsorbent, and then the ethane in the reaction gas reacts with the carbon dioxide released by the adsorbent under the catalytic action of the magnesium-chromium oxide catalyst to generate ethylene in situ, so that the CO2 gas in the low-content CO2 reaction gas can be efficiently captured and in-situ converted and utilized, which greatly improves the catalytic activity and the selectivity of the product ethylene.

Description

Technical Field

[0001] The present invention relates to the technical field of oxidative dehydrogenation catalyst preparation, and in particular to a bifunctional catalyst for preparing ethylene by in-situ capture of carbon dioxide and oxidation of ethane, and a preparation method and application thereof. Background Art

[0002] Ethylene is an important basic organic chemical raw material, which can be used to produce polymer materials such as polyethylene, polystyrene, polyvinyl chloride, and derivatives such as vinyl chloride, vinyl dichloride, ethylene oxide, and ethylene glycol. More than 70% of the products in the petrochemical industry are related to ethylene, and its production output, production technology and application are the indicators of a country's chemical level. The traditional raw materials for the preparation of ethylene are mostly naphtha or light oil, and ethylene is produced by high-temperature cracking of naphtha or light oil. However, the reduction of oil reserves and the increasing tension of energy have made the development of non-petroleum routes for the preparation of ethylene the main trend at present.

[0003] With the breakthrough of shale gas and methane hydrate mining technology, the production of ethylene by replacing oil with natural gas, which has relatively abundant reserves, wide distribution and low price, can avoid the oil route and has good development prospects; ethane, as the main component of natural gas, methane hydrate and shale gas, is cleaner and more abundant in source. Using ethane as a raw material to produce ethylene has become a feasible method to improve the ethylene production process and has attracted widespread attention from researchers. In terms of production technology, ethane steam cracking is a traditional process for producing ethylene. Due to the limitation of thermodynamic equilibrium conversion rate, the process needs to be at a higher temperature to obtain the ideal ethylene yield, which leads to high energy consumption and requires a large amount of water vapor. In addition, a large amount of by-products such as coke, acetylene and C3 components will be produced in the above cracking process. Therefore, ethane catalytic dehydrogenation or catalytic oxidative dehydrogenation (ODH) technology, which is mainly characterized by low reaction temperature and high conversion rate, has become a hot topic. Given the strong oxidizing property of O2, it is easy to cause side reactions to peroxidize ethane, thereby reducing the selectivity of ethylene. Therefore, carbon dioxide (CO2) is often added to the reaction system. CO2 is used as a mild oxidant. Under the premise of ensuring ethane conversion, it can effectively avoid the deep oxidation of reaction intermediates to improve ethylene selectivity. At the same time, it can also react with H2 produced by ethane dehydrogenation to generate H2O and CO, pushing the reaction to move in a direction that is conducive to ethylene production. It can simultaneously improve the selectivity and conversion rate of raw materials and reduce the reaction temperature to reduce energy consumption. Moreover, using CO2 as a raw material can also alleviate the adverse effects of greenhouse gases on the environment, and has a good prospect for industrial application. Therefore, ethane oxidative dehydrogenation to ethylene under a carbon dioxide atmosphere is a green new process with great development potential.

[0004] Conventional industrial catalysts such as precious metal catalysts are not suitable for ethane oxidative dehydrogenation reaction under carbon dioxide atmosphere, and their ability to catalyze and activate CO2 is not strong, which slows down the redox cycle. Studies have found that the current Cr-based catalyst has a variety of valence states of Cr, and it is easy to form a redox cycle between high-valent ions and low-valent ions. It has very good catalytic performance for ethane ODH under carbon dioxide atmosphere, and is currently the most studied transition metal oxide catalyst. Cr-based catalysts often show a high ethane conversion rate in a short period of time, but their lifespan is short. At the same time, the reaction raw material requires high-purity CO2. Therefore, if you want to directly use the low-concentration CO2 in the flue gas (15%-20%), it requires high capture, desorption, storage, and transportation costs. These requirements greatly increase the cost of catalyst application, and also bring strict environmental requirements for the use of catalysts (high temperature, high-concentration raw material atmosphere). Therefore, the development of new, efficient, and high-performance catalysts to reduce the cost of use and broaden the use scenarios is the main problem in the field of ethane carbon dioxide oxidative dehydrogenation to prepare ethylene. Summary of the invention

[0005] In view of the above problems in the prior art, the present invention provides a bifunctional catalyst for in-situ capture of carbon dioxide and oxidation of ethane to produce ethylene and a preparation method thereof, and provides the application of the bifunctional catalyst in the field of ethane oxidative dehydrogenation to solve or at least alleviate some or all of the technical problems in the prior art.

[0006] To achieve the above object, the present invention is specifically implemented through the following technical solutions:

[0007] The first aspect of the present invention provides a bifunctional catalyst for in-situ capture of carbon dioxide and oxidation of ethane to produce ethylene, comprising a magnesium-chromium oxide catalyst and a calcium-cerium oxide adsorbent, wherein the magnesium-chromium oxide catalyst is MgCr2O4, and the calcium-cerium oxide adsorbent comprises CaO and CeO2, wherein CaO accounts for more than 60% of the total mass of the calcium-cerium oxide adsorbent.

[0008] Furthermore, the mass ratio of the magnesium chromium oxide catalyst (MgCr2O4) to the calcium cerium oxide adsorbent is 1:0.5-2.

[0009] Furthermore, the calcium cerium oxide adsorbent comprises 85% by mass of CaO and 15% by mass of CeO2.

[0010] The second aspect of the present invention provides a method for preparing the bifunctional catalyst for in-situ capture of carbon dioxide and oxidation of ethane to produce ethylene, comprising the following steps:

[0011] S1, preparing a magnesium chromium oxide catalyst and a calcium cerium oxide adsorbent respectively;

[0012] S2. Mix the magnesium-chromium oxide catalyst and the calcium-cerium oxide adsorbent in proportion to prepare a powder to obtain a bifunctional catalyst.

[0013] Furthermore, the method for preparing the magnesium chromium oxide catalyst and the calcium cerium oxide adsorbent is selected from one or more of a precipitation method, a hydrothermal method, a solvothermal method and a solid phase thermal decomposition method.

[0014] Furthermore, the preparation of the magnesium chromium oxide catalyst comprises the following steps:

[0015] Magnesium salt, chromium salt and citric acid are added to a solvent and mixed evenly, wherein the molar ratio of magnesium ion to chromium ion in the magnesium salt and the chromium salt is 1:2, and the mixture is heated and stirred to react until the solution is fully converted into a gel, and then aged and calcined in an oxygen-containing atmosphere to obtain a magnesium-chromium oxide catalyst.

[0016] Furthermore, in the preparation of the magnesium chromium oxide catalyst, the temperature of the heating and stirring reaction is 70-100°C, the gel is dried and aged in an oven at 130-170°C, and the aged gel is calcined at 800-1000°C for 3-5h.

[0017] Furthermore, the preparation of the calcium cerium oxide adsorbent comprises the following steps:

[0018] Calcium salt, cerium salt and citric acid are added to a solvent and mixed, heated and stirred to react until the solution is fully converted into a gel, aged, and then calcined in an oxygen-containing atmosphere to obtain a magnesium chromium oxide catalyst. The calcium cerium oxide adsorbent includes CaO and CeO2, wherein CaO accounts for more than 60% of the total mass of the calcium cerium oxide adsorbent.

[0019] Furthermore, in the preparation of the calcium cerium oxide adsorbent, the temperature of the heating and stirring reaction is 70-100° C., the gel is dried and aged in an oven at 100-110° C., and the aged gel is calcined at 800-1000° C. for 1-3 hours.

[0020] Furthermore, the solvent is water.

[0021] The third aspect of the present invention provides the use of the bifunctional catalyst for preparing ethylene by in-situ capture of carbon dioxide and oxidation of ethane as described above in the oxidative dehydrogenation of ethane.

[0022] A fourth aspect of the present invention provides a method for in-situ capture and conversion of carbon dioxide to produce ethylene, comprising the following steps:

[0023] The bifunctional catalyst for preparing ethylene by in-situ capture of carbon dioxide and oxidation of ethane as described above is placed in a fixed bed reactor, and a reaction gas containing carbon dioxide and ethane is introduced, so that the reaction gas contacts the bifunctional catalyst and a catalytic reaction is carried out at 600-700°C.

[0024] Further, the reaction gas is factory waste gas, wherein the volume ratio of the carbon dioxide to the ethane is 5: 1. Further, the reaction gas includes 15% carbon dioxide, 3% ethane and 82% nitrogen.

[0025] Furthermore, the feed space velocity of the reaction gas is 30 mL / min.

[0026] The advantages and positive effects of the present invention are:

[0027] 1. The present invention combines the carbon capture, utilization and storage technology with the carbon dioxide weak oxidizing ethane oxidation technology to form a bifunctional catalyst integrating in-situ capture and in-situ catalysis. The carbon dioxide in the reaction gas is first captured by a calcium cerium oxide adsorbent, and then the ethane in the reaction gas reacts with the carbon dioxide released by the adsorbent under the catalytic action of a magnesium chromium oxide catalyst to generate ethylene in situ, so that the catalyst can efficiently capture and in-situ convert and utilize low-content CO2 reaction gas such as CO2 gas in industrial waste gas at the reaction site, which greatly improves the catalytic activity of the adsorption-catalysis bifunctional catalyst, improves the selectivity of the product ethylene, and reduces or even eliminates the production of by-products.

[0028] 2. The present invention can use industrial waste gas as the source gas of CO2 in the ethylene preparation reaction, providing a solution for treating greenhouse gases in factory waste gas, which is beneficial to alleviating the greenhouse effect. In addition, the in-situ capture of CO2 is beneficial to simplifying multiple reactors into one reactor, reducing reactor energy consumption, and has high environmental and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 The cyclic catalytic curve diagram of the bifunctional catalyst for preparing ethylene by in-situ capture of carbon dioxide and oxidation of ethane according to the embodiment of the present invention; wherein, Figures (a)-(d) respectively represent Ca 0.85 Ce 0.15 Adsorbent + MgCr2O4 catalyst group, Ca 0.85 Ce 0.15 Adsorbent + MgGa2O4 catalyst group, Ca 0.85 Ce 0.15 Adsorbent + MgFe2O4 catalyst group and Ca 0.85 Ce 0.15 Adsorbent + MgAl2O4 catalyst group. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. The embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] Based on the information contained in the present invention, it is easy for those skilled in the art to make various changes to the precise description of the present invention without departing from the spirit and scope of the appended claims. It should be understood that the scope of the present invention is not limited to the defined processes, properties or components, because these embodiments and other descriptions are only for the purpose of illustrating specific aspects of the present invention. In fact, various changes that a person skilled in the art or related fields can obviously make to the embodiments of the present invention are covered within the scope of the appended claims.

[0033] In order to better understand the present invention rather than limit the scope of the present invention, all numerals and other numerical values ​​used in the present invention indicating dosage, percentage, etc., should be understood as modified by the word "approximately" in all cases. Therefore, unless otherwise specified, the numerical parameters listed in the specification and the appended claims are approximate values, which may be changed according to the different ideal properties attempted to be obtained. Each numerical parameter should at least be regarded as being obtained according to the reported significant figures and by conventional rounding methods. In addition, the meaning of the terms "include", "comprise", "contain", "have" and the like is non-restrictive, and other steps and other ingredients that do not affect the results can be added.

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is described in detail below.

[0035] An embodiment of the present invention provides a bifunctional catalyst for in-situ capture of carbon dioxide and oxidation of ethane to prepare ethylene, comprising a magnesium-chromium oxide catalyst and a calcium-cerium oxide adsorbent, wherein the magnesium-chromium oxide catalyst is MgCr2O4, and the calcium-cerium oxide adsorbent comprises CaO and CeO2, wherein CaO accounts for more than 60% of the total mass of the calcium-cerium oxide adsorbent, that is, the mass fraction of CaO in the total mass of the calcium-cerium oxide adsorbent is: 60%≤CaO<100%.

[0036] Cr-based catalyst is a good catalyst for converting carbon dioxide (CO2) to produce ethylene. It has a certain oxidizing property and can retain the CC bond in ethane while breaking the CH bond. The present invention selects magnesium chromite MgCr2O4 as the experimental basis for selecting the catalyst. For the selection of the adsorbent, considering that the performance of the adsorbent should not be affected by the application environment of the catalyst, the adsorbent needs to have a capture temperature similar to that of the catalyst. On this basis, calcium cerium oxide with a capture temperature of 600-700°C, which is close to the application temperature of the catalyst, is added to improve the performance of the catalyst. In combination with economy and reaction activity, calcium (Ca) is selected as an in-situ capture adsorbent to form a bifunctional catalyst integrating in-situ capture and in-situ catalysis. The carbon dioxide in the reaction gas is first captured by the calcium cerium oxide adsorbent, and then the ethane in the reaction gas reacts with the carbon dioxide released by the adsorbent under the catalytic action of the magnesium chromium oxide catalyst to generate ethylene in situ. The catalytic reaction will make the carbon dioxide on the adsorbent always in an unsaturated state and continuously released to the catalyst under a concentration gradient. This can achieve efficient capture and in-situ conversion and utilization of low-content CO2 reaction gases such as CO2 gas in industrial waste gas at the reaction site, thereby improving the selectivity of the product ethylene and reducing or even eliminating the production of by-products. In addition, the present invention combines carbon capture, utilization and storage (CCUS) technology and carbon dioxide weak oxidation ethane oxidation technology, and can use industrial waste gas as the source gas of CO2 in the ethylene preparation reaction. In-situ capture can directly use industrial waste gas as a raw material to participate in the preparation of ethylene, which is conducive to simplifying multiple reactors into one reactor, reducing energy consumption, and also providing a solution for treating greenhouse gases in factory waste gas, which is conducive to alleviating the greenhouse effect and has high environmental and economic benefits. (Specific implementation example data of the present invention can be seen in the data of Example 4 below)

[0037] Optionally, the mass ratio of the magnesium chromium oxide catalyst to the calcium cerium oxide adsorbent is 1:0.5-2, preferably 1:1.

[0038] Optionally, the calcium cerium oxide adsorbent includes 85% CaO and 15% CeO2 by mass. Select bimetallic oxides with different ratios of Ca and Ce to cooperate with magnesium chromium oxide catalysts, and compare the composite materials of MgCr2O4 and 85% CaO+15% CeO2 by mass to obtain the best comprehensive effects on CO2 conversion rate, ethane conversion rate, ethylene selectivity, and ethylene yield in ethylene preparation reaction.

[0039] Another embodiment of the present invention provides a method for preparing the bifunctional catalyst for in-situ capture of carbon dioxide and oxidation of ethane to produce ethylene, comprising the following steps:

[0040] S1, preparing a magnesium chromium oxide catalyst and a calcium cerium oxide adsorbent respectively;

[0041] S2. Mix the magnesium-chromium oxide catalyst and the calcium-cerium oxide adsorbent in proportion to prepare a powder to obtain a bifunctional catalyst.

[0042] The preparation method of the bifunctional catalyst for preparing ethylene by in-situ capture of carbon dioxide and oxidation of ethane has the same advantages as the bifunctional catalyst for preparing ethylene by in-situ capture of carbon dioxide and oxidation of ethane as described above over the prior art, which will not be described in detail here. In addition, the preparation method of the catalyst and adsorbent used in the present invention is simple and has low requirements on the reaction equipment.

[0043] The method for preparing the magnesium chromium oxide catalyst and the calcium cerium oxide adsorbent can adopt a precipitation method, a hydrothermal method, a solvent thermal method or a solid phase thermal decomposition method.

[0044] In some preferred embodiments, the catalyst and adsorbent of the present invention are prepared by a solvothermal method.

[0045] Specifically, the preparation of the magnesium chromium oxide catalyst comprises the following steps:

[0046] Magnesium salt, chromium salt and citric acid are added to a solvent and mixed evenly, wherein the molar ratio of magnesium ion to chromium ion in the magnesium salt and the chromium salt is 1:2, and the mixture is heated and stirred to react until the solution is fully converted into a gel, and then aged and calcined in an oxygen-containing atmosphere to obtain a magnesium-chromium oxide catalyst.

[0047] In the above steps, the temperature of the heating and stirring reaction is 70-100°C, the gel is dried and aged in an oven at 130-170°C, and the aged gel is calcined at 800-1000°C for 3-5 hours. Preferably, the temperature of the heating and stirring reaction is 80°C, the gel is dried and aged in an oven at 150°C, and the aged gel is calcined at 900°C for 4 hours.

[0048] Specifically, the preparation of the calcium cerium oxide adsorbent comprises the following steps:

[0049] Calcium salt, cerium salt and citric acid are added to a solvent and mixed, wherein 0.6≤x<1, and heated and stirred to react until the solution is fully converted into a gel, and then aged, and then calcined in an oxygen-containing atmosphere to obtain a magnesium chromium oxide catalyst. The calcium cerium oxide adsorbent includes CaO and CeO2, wherein CaO accounts for more than 60% of the total mass of the calcium cerium oxide adsorbent.

[0050] In the above steps, the temperature of the heating and stirring reaction is 70-100°C, the gel is dried and aged in an oven at 100-110°C, and the aged gel is calcined at 800-1000°C for 1-3 hours. Preferably, the temperature of the heating and stirring reaction is 80°C, the gel is dried and aged in an oven at 105°C, and the aged gel is calcined at 900°C for 2 hours.

[0051] The solvent described above is a conventional solvent, such as any one or more of water, methanol, ethanol, propanol and acetone, preferably water. The reagents used above have good compatibility in aqueous solution and can be uniformly present in a reaction system.

[0052] The present invention does not specifically limit the types of the magnesium salt, chromium salt, calcium salt and cerium salt described above, as long as they can effectively form corresponding ions such as magnesium. In some embodiments, the magnesium salt is one or more of magnesium bromide, magnesium nitrate and magnesium sulfate; the chromium salt is one or more of chromium chloride, chromium bromide, chromium nitrate and chromium sulfate; the calcium salt is one or more of calcium chloride, calcium bromide, calcium nitrate, calcium sulfate, calcium phosphate and calcium acetate; the cerium salt is one or more of cerium chloride, cerium nitrate and cerium sulfate.

[0053] Another embodiment of the present invention provides the use of the bifunctional catalyst for preparing ethylene by in-situ capture of carbon dioxide and oxidation of ethane as described above or the preparation method of the bifunctional catalyst for preparing ethylene by in-situ capture of carbon dioxide and oxidation of ethane as described above in oxidative dehydrogenation of ethane.

[0054] The advantages of using the bifunctional catalyst for preparing ethylene by in-situ capture of carbon dioxide and oxidation of ethane in ethane oxidative dehydrogenation are the same as the advantages of the bifunctional catalyst for preparing ethylene by in-situ capture of carbon dioxide and oxidation of ethane over the prior art as described above, and will not be repeated here.

[0055] Another embodiment of the present invention also provides a method for in-situ capture and conversion of carbon dioxide to produce ethylene, comprising the following steps:

[0056] The bifunctional catalyst for preparing ethylene by in-situ capture of carbon dioxide and oxidation of ethane as described above is placed in a fixed bed reactor, and a reaction gas containing carbon dioxide and ethane is introduced, so that the reaction gas contacts the bifunctional catalyst and a catalytic reaction is carried out at 600-700°C.

[0057] Optionally, the reaction gas is factory waste gas, wherein the volume ratio of the carbon dioxide to the ethane is 5: 1. Exemplarily, the reaction gas includes 15% carbon dioxide, 3% ethane and 82% nitrogen.

[0058] A suitable gas feed rate is beneficial to improving reactivity. Preferably, the feed space velocity of the reaction gas is 30 mL / min.

[0059] Optionally, the bifunctional catalyst is used in an amount of 0.1-10 g.

[0060] The present invention is further described below in conjunction with specific examples. The experimental methods in the following examples without specifying specific conditions are generally carried out according to the conditions recommended by the manufacturer.

[0061] Example 1

[0062] Combined with the research results at home and abroad, among the various catalytic atoms (Ca, Sr, Cu, Co and Zn) that can catalyze the above reaction, the Cr-based catalyst shows excellent results. During the conversion process at 700°C, the ethane conversion rate, ethylene selectivity, and CO2 conversion rate of the zeolite-loaded Cr are 37.1%, 91.2%, and 56%, respectively. This shows that the Cr-based catalyst is a good catalyst for the in-situ capture and conversion of CO2 to prepare ethylene. This embodiment selects spinel as the experimental basis of the catalyst (MgCr2O4), and on this basis attempts to explore other metal elements (MgGa2O4, MgAl2O4, MgFe2O4) to improve the relevant performance of the catalyst. Typical spinel is simply expressed as AB2X4, in which metal A occupies the tetrahedral interstitial position, metal B occupies the octahedral interstitial position, and the X atom occupies the polyhedral vertex position. Since the tetrahedral interstitial is significantly smaller than the octahedral interstitial, the metal cation with a smaller radius occupies the A site, while the larger cation occupies the B site. In addition, the valence of the metal with A and B is usually +2 and +3, respectively. Therefore, the special composition and structure lead to the excellent redox and acid-base properties of spinel, and it is used as a catalyst or carrier in the fields of catalysis and adsorption.

[0063] This example specifically prepares the following catalyst:

[0064] Preparation of magnesium chromium oxide (MgCr2O4) catalyst: Weigh 53.34 g of magnesium nitrate hexahydrate, 55.47 g of chromium nitrate nonahydrate, and 131.15 g of citric acid monohydrate, dissolve the above substances in 449.34 g of deionized water, add a magnetic stirrer to a beaker, heat and stir in an oil bath at 80°C, and after the solution is fully converted into gel, cover the mouth of the beaker with tin foil, and then place it in a 150°C oven. After the sample is dried and aged, the aged gel is placed in a 900°C muffle furnace and calcined for 4 hours, and then the calcined product is ground into a fine powder below 100 mesh using an agate mortar to obtain about 40 g of gray-black MgCr2O4 powder.

[0065] Preparation of MgGa2O4 catalyst: Weigh 45.04g of magnesium nitrate hexahydrate, 399.40g of gallium nitrate nonahydrate, and 110.73g of citric acid monohydrate, dissolve the above substances in 379.38g of deionized water, add a magnetic stirrer to a beaker, heat and stir in an oil bath at 80°C, and after the solution is fully converted into gel, cover the mouth of the beaker with tin foil, and then place it in a 150°C oven. After the sample is dried and aged, the aged gel is placed in a 900°C muffle furnace and calcined for 4h, and then the calcined product is ground into a fine powder below 100 mesh using an agate mortar to obtain about 40g of gray-black MgGa2O4 powder.

[0066] Preparation of MgFe2O4 catalyst: Weigh 55.55g of magnesium nitrate hexahydrate, 525.13g of ferric nitrate nonahydrate, and 136.57g of citric acid monohydrate, dissolve the above substances in 467.94g of deionized water, add a magnetic stirrer to a beaker, heat and stir in an oil bath at 80°C, and after the solution is fully converted into gel, cover the mouth of the beaker with tin foil, and then place it in a 150°C oven. After the sample is dried and aged, the aged gel is placed in a 900°C muffle furnace and calcined for 4h, and then the calcined product is ground into a fine powder below 100 mesh using an agate mortar to obtain about 40g of gray-black MgFe2O4 powder.

[0067] Preparation of MgAl2O4 catalyst: Weigh 48.40g of magnesium nitrate hexahydrate, 424.69g of aluminum nitrate nonahydrate, and 119.00g of citric acid monohydrate, dissolve the above substances in 407.72g of deionized water, add a magnetic stirrer to a beaker, heat and stir in an oil bath at 80°C, and after the solution is fully converted into gel, cover the mouth of the beaker with tin foil, and then place it in a 150°C oven. After the sample is dried and aged, the aged gel is placed in a 900°C muffle furnace and calcined for 4h, and then the calcined product is ground into a fine powder below 100 mesh using an agate mortar to obtain about 40g of gray-black MgAl2O4 powder.

[0068] Example 2

[0069] The present embodiment aims to prepare a mixture of CaO and CeO2 in different mass ratios by the same preparation method, so as to explore the effect of different mass ratios of CaO and CeO2 on the performance of the calcium cerium oxide adsorbent and the composite material. For the sake of simplicity, the following calcium cerium oxide adsorbent is named as Ca x Ce 1-x , where 0.6≤x<1, x represents the mass proportion of CaO in the total mass of the mixture, and 1-x represents the mass proportion of CeO2 in the total mass of the mixture.

[0070] Ca 1.00 Ce 0.00Preparation of adsorbent: Weigh 21.085g of calcium nitrate tetrahydrate, 0.000g of cerium nitrate hexahydrate, and 37.5250g of citric acid monohydrate, dissolve the above substances in 64.28571429g of deionized water, add a magnetic stirrer to a beaker, heat and stir in an oil bath at 80°C, cover the mouth of the beaker with tin foil after the solution is fully converted into gel, and then place it in a 105°C oven. After the sample is dried and aged, put the aged gel in a 900°C muffle furnace and calcine for 2h, and then use an agate mortar to grind the calcined product into a fine powder below 100 mesh to obtain about 5g of white Ca 1.00 Ce 0.00 powder.

[0071] Ca 0.95 Ce 0.05 Preparation of adsorbent: Weigh 20.031g of calcium nitrate tetrahydrate, 0.631g of cerium nitrate hexahydrate, and 36.2596g of citric acid monohydrate, dissolve the above substances in 62.1179g of deionized water, add a magnetic stirrer to a beaker, heat and stir in an oil bath at 80°C, and after the solution is fully converted into gel, cover the mouth of the beaker with tin foil, and then place it in a 105°C oven. After the sample is dried and aged, put the aged gel in a 900°C muffle furnace and calcine for 2h, and then use an agate mortar to grind the calcined product into a fine powder below 100 mesh to obtain about 5g of white Ca 0.95 Ce 0.05 powder.

[0072] Ca 0.85 Ce 0.15 Preparation of adsorbent: Weigh 17.922g of calcium nitrate tetrahydrate, 1.893g of cerium nitrate hexahydrate, and 33.7289g of citric acid monohydrate, dissolve the above substances in 57.7823g of deionized water, add a magnetic stirrer to a beaker, heat and stir in an oil bath at 80°C, cover the mouth of the beaker with tin foil after the solution is fully converted into gel, and then place it in a 105°C oven. After the sample is dried and aged, put the aged gel in a 900°C muffle furnace and calcine for 2h, and then use an agate mortar to grind the calcined product into a fine powder below 100 mesh to obtain about 5g of white Ca 0.85 Ce 0.15 powder.

[0073] Ca 0.75 Ce 0.25Preparation of adsorbent: Weigh 15.814g of calcium nitrate tetrahydrate, 3.156g of cerium nitrate hexahydrate, and 31.1981g of citric acid monohydrate, dissolve the above substances in 53.4468g of deionized water, add a magnetic stirrer to a beaker, heat and stir in an oil bath at 80°C, and after the solution is fully converted into gel, cover the mouth of the beaker with tin foil, and then place it in a 105°C oven. After the sample is dried and aged, place the aged gel in a 900°C muffle furnace and calcine for 2h, and then use an agate mortar to grind the calcined product into a fine powder below 100 mesh to obtain about 5g of white Ca 0.75 Ce 0.25 powder.

[0074] Example 3

[0075] The different proportions of calcium cerium adsorbent (Ca 1.00 Adsorbent, Ca 0.95 Ce 0.05 Adsorbent, Ca 0.85 Ce 0.15 Adsorbent and Ca 0.75 Ce 0.25 The adsorbent was used to capture CO2. The adsorption performance of mixed adsorbents with different mass ratios of CaO and CeO2 was compared. When the mass ratio of CaO to CeO2 was 0.85:0.15, that is, the mass fraction of CaO was 85% and the mass fraction of CeO2 was 15%, the mixed adsorbent had the best performance in capturing carbon dioxide. It also had the best comprehensive effect on the CO2 conversion rate, ethane conversion rate, ethylene selectivity and ethylene yield of the catalyst-catalyzed ethylene preparation reaction. 0.85 Ce 0.15 The adsorbent and the catalysts obtained in Example 1 (MgCr2O4 catalyst, MgGa2O4 catalyst, MgFe2O4 catalyst and MgAl2O4 catalyst) were mixed into powders in a mass ratio of 1:1 to obtain 4 groups of bifunctional catalysts for the catalytic oxidative dehydrogenation of ethane to produce ethylene. The specific groups are as follows: Ca 0.85 Ce 0.15 Adsorbent + MgCr2O4 catalyst group, Ca 0.85 Ce 0.15 Adsorbent + MgGa2O4 catalyst group, Ca 0.85 Ce 0.15 Adsorbent + MgFe2O4 catalyst group, Ca 0.85 Ce 0.15 Adsorbent + MgAl2O4 catalyst group.

[0076] Example 4

[0077] Take 1g of the above four groups of bifunctional catalysts and add them to a fixed bed reactor. Under the reaction conditions of 650℃, at an air flow rate of 30mL / min, first continuously introduce a mixture of 15% carbon dioxide and 85% nitrogen for 30 minutes to simulate the capture process of carbon dioxide in industrial waste gas. Then, it is converted to a mixture of 3% ethane and 97% nitrogen, and continuously introduced for 30 minutes to simulate the catalytic oxidation reaction of ethane. After the reaction, the generated gas is introduced into a GC-900 gas chromatograph and a HidenHPR-20 mass spectrometer for analysis. The CO2 conversion rate, ethane conversion rate, ethylene selectivity, and ethylene yield of the four bifunctional materials are combined for analysis and comparison to obtain the data shown in Table 1. Comprehensive comparison shows that the MgCr2O4 catalyst and Ca 0.85 Ce 0.15 The bifunctional catalyst group combined with the adsorbent has the best comprehensive effect on the ethylene production reaction.

[0078] Table 1 Comparison of catalytic conversion performance of four groups of bifunctional catalysts

[0079]

[0080] Figure 1 Figure 2 shows different groups of cycling experiments, with (a)-(d) summarizing the Ca 0.85 Ce 0.15 Adsorbent + MgCr2O4 catalyst group, Ca 0.85 Ce 0.15 Adsorbent + MgGa2O4 catalyst group, Ca 0.85 Ce 0.15 Adsorbent + MgFe2O4 catalyst group and Ca 0.85 Ce 0.15 The CO2 in-situ capture conversion performance, ethane conversion rate, ethylene selectivity, and ethylene yield of the bifunctional material composed of the adsorbent + MgAl2O4 catalyst group within 10 cycles. Regarding CO2 capture, it can be found that the CO2 capture performance of the four bifunctional materials is not much different. The initial adsorption capacity is 0.24-0.26g / g, and the adsorption capacity of the 10th cycle is 0.20-0.22g / g. The CO2 capture performance before and after 10 cycles is not much different, proving that the CO2 capture capacity of the bifunctional material is stable. Regarding ethylene selectivity, as the cycle proceeds, the selectivity continues to increase and eventually stabilizes. In industrial applications with multiple cycles, the selectivity can remain stable. The CO2 conversion rate and ethane conversion rate have basically remained stable throughout the cycle experiment.

[0081] When MgCr2O4 is selected as the catalyst, the concentration of the by-reaction product CH4 after ten reaction cycles is 0.0428%, 0.06479%, 0.06317%, 0%, 0.0477%, 0.05443%, 0.05675%, 0.05169%, 0.05343%, 0.04424%, all less than 0.1%. It can be seen that the by-reaction product of this catalyst is very small, and the degree of side reaction can be ignored.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A bifunctional catalyst for in-situ capture of carbon dioxide and oxidation of ethane to produce ethylene, characterized in that: It includes a magnesium chromium oxide catalyst and a calcium cerium oxide adsorbent, wherein the mass ratio of the magnesium chromium oxide catalyst to the calcium cerium oxide adsorbent is 1:0.5-2, the magnesium chromium oxide catalyst is MgCr2O4, and the calcium cerium oxide adsorbent includes CaO and CeO2, wherein CaO accounts for more than 60% of the total mass of the calcium cerium oxide adsorbent.

2. The bifunctional catalyst for preparing ethylene by in-situ capture of carbon dioxide and oxidation of ethane according to claim 1, characterized in that: The calcium cerium oxide adsorbent comprises 85% by mass of CaO and 15% by mass of CeO2.

3. A method for preparing a bifunctional catalyst for in-situ capture of carbon dioxide and oxidation of ethane to produce ethylene, characterized in that: The method for preparing a bifunctional catalyst for preparing ethylene by in-situ capture of carbon dioxide and oxidation of ethane as claimed in any one of claims 1 to 2 comprises the following steps: S1, preparing a magnesium chromium oxide catalyst and a calcium cerium oxide adsorbent respectively; S2. Mix the magnesium-chromium oxide catalyst and the calcium-cerium oxide adsorbent in proportion to prepare a powder to obtain a bifunctional catalyst.

4. The method for preparing a bifunctional catalyst for preparing ethylene by in-situ capture of carbon dioxide and oxidation of ethane according to claim 3, characterized in that: The method for preparing the magnesium chromium oxide catalyst and the calcium cerium oxide adsorbent is selected from one or more of a precipitation method, a hydrothermal method, a solvothermal method and a solid phase thermal decomposition method.

5. The method for preparing a bifunctional catalyst for preparing ethylene by in-situ capture of carbon dioxide and oxidation of ethane according to claim 4, characterized in that: The preparation of the magnesium chromium oxide catalyst comprises the following steps: Magnesium salt, chromium salt and citric acid are added to a solvent and mixed evenly, wherein the molar ratio of magnesium ion to chromium ion in the magnesium salt and the chromium salt is 1:2, and the mixture is heated and stirred to react until the solution is fully converted into a gel, and then aged and calcined in an oxygen-containing atmosphere to obtain a magnesium-chromium oxide catalyst.

6. The method for preparing a bifunctional catalyst for preparing ethylene by in-situ capture of carbon dioxide and oxidation of ethane according to claim 5, characterized in that: In the preparation of the magnesium chromium oxide catalyst, the temperature of the heating and stirring reaction is 70-100° C., the gel is dried and aged in an oven at 130-170° C., and the aged gel is calcined at 800-1000° C. for 3-5 hours.

7. The method for preparing a bifunctional catalyst for preparing ethylene by in-situ capture of carbon dioxide and oxidation of ethane according to claim 4, characterized in that: The preparation of the calcium cerium oxide adsorbent comprises the following steps: Calcium salt, cerium salt and citric acid are added to a solvent and mixed, heated and stirred to react until the solution is fully converted into a gel, aged, and then calcined in an oxygen-containing atmosphere to obtain a magnesium chromium oxide catalyst. The calcium cerium oxide adsorbent includes CaO and CeO2, wherein CaO accounts for more than 60% of the total mass of the calcium cerium oxide adsorbent.

8. The method for preparing a bifunctional catalyst for preparing ethylene by in-situ capture of carbon dioxide and oxidation of ethane according to claim 7, characterized in that: In the preparation of the calcium cerium oxide adsorbent, the temperature of the heating and stirring reaction is 70-100° C., the gel is dried and aged in an oven at 100-110° C., and the aged gel is calcined at 800-1000° C. for 1-3 hours.

9. Use of the bifunctional catalyst for preparing ethylene by in-situ capture of carbon dioxide and oxidation of ethane as claimed in any one of claims 1 to 2 in oxidative dehydrogenation of ethane.

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