A method for producing olefins by catalytic dehydrogenation of alkanes

Abstract

The application discloses a method for preparing olefins by catalytic dehydrogenation of alkanes. It relates to the technical field of olefin production, and comprises the following steps: activating a catalyst in a reactor under an air atmosphere, wherein the catalyst is a zinc-containing silicate with a crystal structure; introducing inert gas into the reactor to discharge residual air in the reactor; introducing the inert gas and alkane raw material gas into the reactor, and controlling the reaction temperature to be 500-700 DEG C and the space-time flow rate to be 1-100 L / (kg.min); and under the catalysis of the activated catalyst, the alkane raw material gas is dehydrogenated and converted into olefins. The method can effectively improve the stability and production continuity of the production of olefins by dehydrogenation of alkanes.

Description

Technical Field

[0001] This invention relates to a method for the catalytic dehydrogenation of alkanes to prepare olefins. Background Technology

[0002] Olefins are important chemical raw materials used to prepare industrial chemicals such as polymers, nitrs, organic acids, and alcohols. For example, propylene can be used to prepare polypropylene, acrylonitrile, acrylic acid, and isopropanol. Among these, catalytic dehydrogenation of alkanes under anaerobic conditions is a technology for the industrialized production of olefins.

[0003] Currently, the catalysts used for the catalytic dehydrogenation of alkanes to produce olefins are generally catalysts containing precious metals or toxic catalysts such as platinum-based catalysts and chromium-based catalysts. Among them, chromium-based catalysts are inherently toxic and cause environmental pollution, while platinum-based catalysts are not only expensive, but also require the use of chlorine-containing compounds to address the problems of carbon deposition and active component aggregation and sintering during high-temperature reactions, which also brings environmental problems. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide a method for the catalytic dehydrogenation of alkanes to produce olefins. By controlling the reaction temperature and space-time flow rate, and using a crystalline zinc silicate as a catalyst, the method catalyzes the dehydrogenation of alkane feedstock gas into olefins. By selecting a non-toxic and inexpensive crystalline zinc silicate as a catalyst, the production cost of olefins is effectively reduced, and the environmental harm caused by olefin production is also reduced. Furthermore, the solution provided by the present invention can effectively improve the stability and sustainability of olefin production through alkane dehydrogenation.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] In a first aspect, the present invention provides a method for the catalytic dehydrogenation of alkanes to prepare olefins, comprising:

[0007] Step S1: Activate the catalyst in the reactor under an air atmosphere, wherein the catalyst is a zinc silicate with a crystalline structure;

[0008] Step S2: Inert gas is introduced into the reactor to remove residual air from the reactor;

[0009] In step S3, inert gas and alkane feed gas are introduced into the reactor, and the reaction temperature is controlled at 500-700°C and the space-time flow rate is controlled at 1-100 L / (kg·min). Under the catalytic action of the activated catalyst, the alkane feed gas is dehydrogenated and converted into olefins.

[0010] Optionally, the above method further includes:

[0011] Catalysts deactivated due to zinc loss can be regenerated through surface etching.

[0012] Optionally, step S3 above further includes:

[0013] A gaseous weak oxidant is introduced into the reactor to improve the catalytic stability of the catalyst.

[0014] Optionally, step S1 above further includes controlling the activation temperature to 500–650°C.

[0015] Optionally, step S1 above further includes: controlling the activation time to be 30 to 60 minutes.

[0016] Optionally, the duration of introducing the inert gas in step S2 is 5 to 20 minutes.

[0017] Optionally, the space-time flow rate of the inert gas in step S2 above is 10 to 100 L / (kg·min).

[0018] Optionally, in step S3 above, the volume ratio of inert gas to alkane feed gas is 9:1 to 0:1.

[0019] Optionally, the surface etching method is physical etching or chemical etching.

[0020] Optionally, the etching reagents used for the physical etching or chemical etching described above include: fluorine-containing compounds, chloride-containing compounds, and alkaline compounds.

[0021] Optionally, the space-time flow rate of the gaseous weak oxidant is 0.15–0.8 L / (kg·min).

[0022] Optionally, the gaseous weak oxidant includes any one or more of CO2, NO2, and water vapor.

[0023] Optionally, the alkane feed gas is any one of ethane, propane, and butane.

[0024] Optionally, the size of the zinc silicate in the crystal structure is 0.02 μm to 10 μm.

[0025] The technical solution of the first aspect of the above invention has the following advantages or beneficial effects:

[0026] The method for catalytic dehydrogenation of alkanes to prepare olefins provided by this invention can effectively reduce the production cost of olefins and reduce the environmental harm caused by olefin production by using non-toxic and low-cost zinc silicate with a crystalline structure as a catalyst.

[0027] In addition, by designing catalyst activation in an air atmosphere, removing residual air from the reactor with an inert gas, and controlling the reaction temperature to 500–700 °C and the space-time flow rate of 1–100 L / (kg·min) during the catalytic reaction, the zinc silicate catalyst with a crystalline structure can maintain its activity, catalytic selectivity, and catalytic stability for a relatively long time, thereby effectively improving the stability, production continuity, and yield of alkane dehydrogenation to olefins. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the main process of the method for preparing olefins by catalytic dehydrogenation of alkanes according to an embodiment of the present invention;

[0029] Figure 2 These are SEM images of zinc silicate (Zn2SiO4) with three different crystal structures and morphologies provided in the embodiments of the present invention.

[0030] Figure 3 This is a comparison diagram of X-ray powder diffraction patterns of zinc silicate with three different crystal structures according to embodiments of the present invention and standard X-ray powder diffraction patterns.

[0031] Figure 4 This is a schematic diagram illustrating the catalytic effect of the new catalyst provided according to embodiments of the present invention and the catalyst deactivated due to zinc loss after chemical etching with ammonium fluoride.

[0032] Figure 5 This is a schematic diagram illustrating the catalytic effect of zinc silicate with a crystal structure when a small amount of CO2 is introduced during the catalytic reaction, according to an embodiment of the present invention. Detailed Implementation

[0033] Currently, although research on propane dehydrogenation to propylene has found that supported catalysts with cluster structures composed of zinc and oxygen atoms (the size of which is between single atoms and nanoparticles, and the size of the cluster structures used for propane dehydrogenation to propylene is generally controlled to be a few atoms or tens of atoms) as active sites (i.e., the supports for these supported catalysts are generally molecular sieves, amorphous silica, or zirconium dioxide) exhibit good catalytic effects, these supported catalysts with cluster structures composed of zinc and oxygen atoms as active sites have the following problems.

[0034] (1) Due to the weak bonding between the cluster structure of zinc oxygen atoms supported on the support and the support, and the low boiling point of zinc (Zn), the supported catalyst is easily reduced in the propane dehydrogenation reaction and lost with the atmosphere. A large number of active sites on the supported catalyst disappear, resulting in rapid deactivation of the supported catalyst. Therefore, the service life of the supported catalyst with zinc oxide as the active site is short and difficult to regenerate (generally less than 100 hours), that is, the stability of the supported catalyst with zinc oxide as the active site is poor.

[0035] (2) It is quite difficult to precisely control the structure of clusters during the preparation of supported catalysts;

[0036] (3) Supported catalysts require the preparation of supports and active sites. In addition, the conditions for preparing supports and active sites are quite demanding. Therefore, the preparation process of supported catalysts is complex.

[0037] (4) As mentioned above, in order to improve the dispersibility of the supported catalyst with cluster structure composed of zinc oxygen atoms as active sites, porous molecular sieve materials are used as supports. Since template agents are used in the preparation of porous molecular sieves, the production cost of supported catalysts is increased.

[0038] (5) Although some studies have proposed using a composite magnesium oxide / copper oxide method to stabilize zinc oxide on supported catalysts to solve the problem of zinc atoms leaving the catalyst surface, this composite method not only increases the production cost of supported catalysts, but also achieves limited results (catalyst lifetime is still below 100 hours). In addition, although the method of continuously replenishing zinc oxide to the support can enable continuous catalytic production, this method consumes a large amount of zinc oxide, and the lost zinc will redeposit, affecting the reactor and pipelines.

[0039] Therefore, finding a green method for the catalytic dehydrogenation of alkanes to olefins with efficient conversion and selectivity remains a problem that needs to be solved.

[0040] Figure 1 This invention illustrates a novel method for the catalytic dehydrogenation of alkanes to prepare olefins, provided by an embodiment of the present invention. For example... Figure 1 As shown, the method for catalytic dehydrogenation of alkanes to prepare olefins may include the following steps:

[0041] Step S101: Activate the catalyst in the reactor under an air atmosphere, wherein the catalyst is a zinc-containing silicate with a crystalline structure;

[0042] Step S102: Inert gas is introduced into the reactor to remove residual air from the reactor;

[0043] In step S103, inert gas and alkane feed gas are introduced into the reactor, and the reaction temperature is controlled at 500-700℃ and the space-time flow rate is controlled at 1-100 L / (kg·min). Under the catalytic action of the activated catalyst, the alkane feed gas is dehydrogenated and converted into olefins.

[0044] In step S101, activating the catalyst in the reactor under an air atmosphere removes impurities adsorbed on the catalyst surface, exposing the active sites Zn-O in the catalyst (a zinc-containing silicate with a crystalline structure), thereby effectively improving the catalytic activity of the catalyst.

[0045] The zinc-containing silicate with a crystalline structure can be zinc silicate with a crystalline structure, or it can be a zinc-containing silicate containing other metal ions or other non-metals, such as magnesium zinc silicate with a crystalline structure, copper zinc silicate with a crystalline structure, or zinc-silicon molecular sieves. In a preferred embodiment, the zinc-containing silicate with a crystalline structure is readily available and inexpensive zinc silicate with a crystalline structure. Compared with other zinc-containing silicates and supported catalysts, this zinc silicate with a crystalline structure has better catalytic performance and catalytic selectivity.

[0046] The zinc-containing silicate with this crystal structure is fundamentally different from existing supported catalysts with cluster structures composed of zinc and oxygen atoms as active sites.

[0047] First, the zinc-containing silicate with a crystal structure provided in this application has a completely different structure from the supported catalyst with a cluster structure composed of zinc and oxygen atoms as active sites. Specifically, the zinc-containing silicate with a crystal structure proposed in this application, such as zinc silicate, has a crystal structure obtained by the periodic and regular arrangement of zinc (Zn), oxygen (O), and silicon (Si), wherein silicon and zinc atoms exist in the tetrahedral coordination forms of SiO4 and ZnO4, respectively. Unlike the zinc-containing silicate with a crystal structure proposed in this application, the existing supported catalysts with a cluster structure composed of zinc and oxygen atoms as active sites are supported by porous molecular sieves or amorphous silica and cluster structures composed of Zn and O on the surface of the support. This structural difference will directly affect the catalytic principle and catalytic performance of the catalyst. That is, the existing supported catalysts with a cluster structure composed of zinc and oxygen atoms as active sites use a support to support the cluster structure or disperse the cluster structure, with dispersed active sites as the core, while this application utilizes the crystal structure surface to directly expose active sites and highly selective crystal facets to directly achieve catalytic dehydrogenation of alkanes.

[0048] Secondly, the size range of the zinc-containing silicate with crystal structure provided in this application is 0.02 μm to 10 μm. That is, the size of the catalyst particles (zinc-containing silicate with crystal structure) for the catalytic dehydrogenation of alkanes to olefins provided in this application can be any value from 0.02 μm to 10 μm. For example, the size of the zinc-containing silicate with crystal structure can be 0.02 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.5 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 2 μm, 2.5 μm, 2.7 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 4.8 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 6.8 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 10 μm, etc. It is worth noting that when the catalyst particles are irregularly shaped or cuboid in shape, the aforementioned dimensions generally refer to the length of the long side of the catalyst particle or the distance between the two furthest points on the edge of the catalyst particle. Compared to supported catalysts with zinc-oxygen atom clusters as active sites (the size of these clusters is between single atoms and nanoparticles; currently, the size of clusters used for propane dehydrogenation to propylene is generally controlled to be a few atoms or tens of atoms), the catalyst particles in this application are much larger than these clusters. This means that this application can use relatively large-sized zinc-containing silicates, such as zinc silicate, to catalyze alkane dehydrogenation and achieve better catalytic performance and selectivity. This breakthrough overcomes the size limitations of existing cluster structures and eliminates the need for a support, reducing the technical difficulty, complexity, and production cost of using Zn-O as an active site for catalytic dehydrogenation of alkanes to produce olefins. Furthermore, the increased size leads to a higher number of active sites in the catalyst particles. Through subsequent protection of these active sites and / or further regeneration of the catalyst particles, the catalyst has a longer lifespan for catalytic dehydrogenation of alkanes, maintaining good catalytic performance and effectively improving the stability and sustainability of olefin production from alkane dehydrogenation.

[0049] Finally, compared with supported catalysts with cluster structures composed of zinc and oxygen atoms as active sites, the zinc silicate with crystal structure of this application has a simple preparation process, is easy to obtain, and does not have strict requirements on the morphology of the zinc silicate with crystal structure, which can effectively reduce the cost of catalytic dehydrogenation of alkanes to produce olefins.

[0050] It is worth noting that the zinc-containing silicates with crystal structures selected in the embodiments of the present invention can be zinc-containing silicates with crystal structures of arbitrary morphology prepared by existing technologies, such as zinc silicates with crystal structures of arbitrary morphology prepared by existing technologies. For example, this application prepares zinc silicates with crystal structures of arbitrary morphology according to the preparation process of zinc silicates with crystal structures reported in Mater. Lett. 2013, 100, 89-92; and J. Phys. Chem. Solids 2009, 70, 1146-1149, etc., and prepares zinc silicates (Zn2SiO4) with crystal structures of three different morphologies (the three different morphologies are labeled as Zn2SiO4-#1; Zn2SiO4-#2; Zn2SiO4-#3, respectively). Figure 2 The following are scanning electron microscope (SEM) images of the three morphologies prepared. Specifically, Figure 2 In the middle, A is Zn2SiO4-#1, which has a spherical structure. Figure 2 In the middle, B is Zn2SiO4-#2, which has a rod-like structure. Figure 2 The morphology of Zn2SiO4-#3, represented by C, is needle-like. Further analysis was conducted by comparing the X-ray powder diffraction (XRD) patterns of the three different morphologies (labeled Zn2SiO4-#1, Zn2SiO4-#2, and Zn2SiO4-#3) of zinc silicate with the standard X-ray powder diffraction pattern of the crystalline zinc silicate (PDF37-1485 card). The comparison diagram of the XRD patterns is shown below. Figure 3 As shown. (Through) Figure 3 It can be seen that the three different morphologies of zinc silicate (labeled as Zn2SiO4-#1; Zn2SiO4-#2; Zn2SiO4-#3 respectively) prepared are completely consistent with the standard, proving that the material we used is crystalline zinc silicate.

[0051] The reactor can be a fixed-bed reactor or a fluidized-bed reactor, etc.

[0052] Furthermore, during the catalyst activation process in step S101 above, the activation temperature generally needs to be controlled within the range of 500–650℃. For example, the activation temperature can be 500℃, 525℃, 540℃, 550℃, 570℃, 600℃, 620℃, 630℃, 640℃, 650℃, etc. By controlling the activation temperature within the range of 500–650℃, impurities adsorbed on the catalyst surface can be effectively removed, while preventing the loss of Zn from the active sites on the catalyst surface, thus ensuring that the catalyst has relatively good activity.

[0053] Furthermore, research revealed that, compared to existing cluster structures, the catalysts used in this application are generally larger than micrometers in size. If the activation time is less than 30 minutes, the catalyst cannot be fully activated. If the time is too long, it wastes energy and may damage active sites, leading to a decrease in catalytic performance. Therefore, in step S101, the activation time can be controlled between 30 and 60 minutes, for example, 30, 35, 40, 50, or 60 minutes, to ensure catalytic performance while effectively controlling energy consumption during activation.

[0054] In step S102, residual air in the reactor can be removed using an inert gas to prevent its influence on the catalytic reaction performance. This inert gas typically refers to a gas that does not participate in the catalytic reaction of alkane, such as nitrogen, argon, or helium.

[0055] In step S102, the duration of introducing the inert gas is 5 to 20 minutes. For example, the duration of introducing the inert gas can be 5 minutes, 7 minutes, 8 minutes, 10 minutes, 12 minutes, 15 minutes, 17 minutes, 19 minutes, 20 minutes, etc.

[0056] In step S102, the space-time flow rate of the inert gas is 10–100 L / (kg·min). That is, 10–100 L of inert gas passes through each kilogram of catalyst per minute. For example, the space-time flow rate of the inert gas can be 10 L / (kg·min), 15 L / (kg·min), 20 L / (kg·min), 30 L / (kg·min), 35 L / (kg·min), 50 L / (kg·min), 60 L / (kg·min), 80 L / (kg·min), 85 L / (kg·min), 90 L / (kg·min), 95 L / (kg·min), 100 L / (kg·min), etc. Adjusting the space-time flow rate of the inert gas in step S102 helps to expel air while minimizing inert gas loss.

[0057] In step S103, controlling the reaction temperature to 500–700°C means controlling the temperature inside the reactor to any value within the range of 500–700°C during the catalytic reaction, such as 500°C, 525°C, 550°C, 570°C, 590°C, 600°C, 640°C, 670°C, 685°C, or 700°C. By controlling the reaction temperature within this range, the requirements for the dehydrogenation of alkane feed gas into olefins can be met. At the same time, the loss of zinc in the zinc-containing silicate crystal structure can be reduced during the reduction process, thereby effectively improving catalytic stability.

[0058] The space-time velocity can refer to the ratio between the mass of the alkane feed gas and other gases introduced into the reactor together with the alkane feed gas, such as inert gases and weak oxidizing gases (i.e., the total mass of the gases introduced in step S103) and the mass of the catalyst, or it can refer to the ratio between the total mass of the alkane feed gas and the inert gases introduced into the reactor together with the alkane feed gas and the mass of the catalyst. By controlling the space-time flow rate to 1–100 L / (kg·min), such as 1 L / (kg·min), 2 L / (kg·min), 5 L / (kg·min), 10 L / (kg·min), 15 L / (kg·min), 20 L / (kg·min), 30 L / (kg·min), 50 L / (kg·min), 55 L / (kg·min), 60 L / (kg·min), 65 L / (kg·min), 70 L / (kg·min), 75 L / (kg·min), 80 L / (kg·min), 86 L / (kg·min), 90 L / (kg·min), 95 L / (kg·min), and 100 L / (kg·min), the catalytic performance can be ensured while effectively increasing the yield of the target product.

[0059] Further, the volume ratio of the inert gas to the alkane feed gas in step S103 is 9:1 to 0:1. For example, the volume ratio of the inert gas to the alkane feed gas can be 9:1, 8:1, 7.5:1, 7:1, 6:1, 5:1, 4:1, 3:1, 2:1, 1:1, 0:1, etc. In a preferred embodiment, the volume ratio of the inert gas to the alkane feed gas in step S103 is 9:1 to 2:1. Since the olefin conversion rate is affected by the reaction equilibrium, introducing an inert gas in step S103 can reduce the partial pressure of the alkane feed gas, thereby promoting the reaction towards the formation of olefins.

[0060] Alternatively, in step S103 above, inert gas can be omitted, and only alkane feed gas can be introduced into the reactor, i.e., pure alkane feed gas can be used for the reaction. However, the conversion rate is affected by the reaction equilibrium.

[0061] Furthermore, taking the catalytic dehydrogenation of propane to propylene using zinc silicate with three different crystal structures (labeled Zn2SiO4-#1, Zn2SiO4-#2, and Zn2SiO4-#3, respectively) as an example, the yield and selectivity of propylene were tested at different reaction temperatures and space-time flows. The test results are shown in Table 1 below.

[0062] Table 1

[0063]

[0064]

[0065] In Table 1, a represents the space-time flow rate, which is adjusted by controlling the flow rate of N2 and C3H8 to 3 mL N2: 2 mL C3H8 and the amount of catalyst to 30-300 mg to obtain the different space-time flow rates shown in Table 1; b in Table 1 represents the propane conversion rate obtained under the reaction conditions.

[0066] As can be seen from Table 1, under the premise of a fixed reaction temperature, a lower space flow rate can help improve the conversion and selectivity of the target product propylene. In addition, under the same space flow rate, a higher reaction temperature can help improve the conversion and yield of the target product propylene.

[0067] Generally, catalysts become deactivated during use due to the covering of active sites caused by carbon buildup. To address this deactivation, high-temperature air calcination is typically used (e.g., calcination at 500–700°C for about 1 hour to convert the carbon into carbon dioxide). However, with continuous use (i.e., air calcination for decarbonization / catalyst activation – alkane dehydrogenation to olefins reaction – catalyst deactivation due to carbon buildup – air calcination for decarbonization / catalyst activation), the zinc on the catalyst surface is reduced and volatilized by the reducing atmosphere (such as hydrocarbon gases and generated hydrogen) during the reaction, resulting in the loss of active sites and preventing the catalyst from achieving its initial catalytic performance. This invention regenerates the deactivated catalyst due to zinc loss through surface etching. Because the catalyst used in this application is relatively large, surface etching can remove inactive components from the catalyst surface, exposing more active surfaces. Therefore, surface etching allows the regenerated catalyst to maintain reactivity, catalytic stability, and persistence comparable to a newly prepared catalyst.

[0068] The surface etching method can be either physical etching or chemical etching.

[0069] Furthermore, the etching reagents used in physical or chemical etching include fluorinated compounds and / or basic compounds. This effectively ensures the etching effect on the catalyst, exposing more of its active surface. It is worth noting that, in addition to the aforementioned fluorinated and / or basic compounds, the etching reagent further includes chlorinated compounds to better control the etching effect.

[0070] Specifically, the basic principle of physical etching for catalyst etching is as follows: Glow discharge of gas in the plasma reaction chamber generates plasma containing active substances such as ions, electrons, and free radicals. This plasma diffuses and adsorbs onto the surface of the sample to be etched, reacting chemically with the surface atoms to form volatile substances, thus achieving the purpose of etching the sample surface. Simultaneously, the generated plasma, under a certain working pressure, is directed towards the sample surface, physically bombarding and etching to remove redeposited reaction products or polymers. The volatile substances produced by the chemical reaction and the byproducts of the physical bombardment are all removed through a vacuum system. The gases in the plasma reaction chamber mainly include one or more of the following: carbon tetrafluoride, trifluoromethane, sulfur hexafluoride, nitrogen trifluoride, boron trichloride, and chlorine. During plasma etching of deactivated zinc silicate, fluorine or chlorine atoms decomposed in the glow discharge react with surface silicon atoms to generate gaseous products, achieving the purpose of etching and regenerating catalyst activity.

[0071] Specific example 1 for physical etching: A certain amount of deactivated zinc silicate is placed on the sample stage of the etching machine, and etching is performed using carbon tetrafluoride and oxygen. The radio frequency power is 400W, the gas flow ratio is 30mL / min to 1-50mL / min (carbon tetrafluoride : 0.2-10mL / min oxygen), the gas pressure is 5Pa, and the etching time is 30 seconds at a temperature of 10℃-50℃.

[0072] Specific example 2 for physical etching: A certain amount of deactivated zinc silicate is placed on the etching machine sample stage, and etching is performed using carbon tetrafluoride, nitrogen trifluoride and helium. The radio frequency power is 200W, the gas flow ratio is 1-50mL / min carbon tetrafluoride: 0.5-20mL / min nitrogen trifluoride: 2-100mL / min helium, the gas pressure is 5 Pa, and the etching time is 20 seconds at a temperature of 10℃-50℃.

[0073] Specifically, the basic principle of chemical etching for catalyst etching is to use chemical substances that can react with the silicon on the zinc silicate surface and carry it into the solution, thus achieving wet chemical etching. The etchants used include chemical reagents that can react with silicon dioxide, such as hydrogen fluoride, ammonium fluoride, and sodium hydroxide.

[0074] Specific example 1 for chemical etching: A certain amount of deactivated zinc silicate is placed in a reaction vessel, a set amount of water is added, and then a set amount of ammonium fluoride is added for stirring and etching. The reaction is carried out at room temperature of 10℃-50℃ for 5min-12h. Then, the zinc silicate is separated and removed by centrifugation or filtration. The mass of deactivated zinc silicate: the mass of water: the mass of ammonium fluoride = 1:(2-200):(0.1-1).

[0075] Specific example 2 for chemical etching: A certain amount of deactivated zinc silicate is placed in a reactor, a set amount of water is added, and then a set amount of hydrogen fluoride is added for stirring and etching. The reaction is carried out at room temperature of 10℃-50℃ for 5min-12h. Then, the zinc silicate is separated and removed by centrifugation or filtration. The mass of deactivated zinc silicate: the mass of water: the mass of hydrogen fluoride = 1:(2-200):(0.1-1).

[0076] Specific example 3 for chemical etching: A certain amount of deactivated zinc silicate is placed in a reactor, a set amount of water is added, and then a set amount of sodium hydroxide is added for stirring and etching. The reaction is carried out at room temperature of 10℃-50℃ for 5min-12 hours. Then, the zinc silicate is separated and removed by centrifugation or filtration. The mass of deactivated zinc silicate: the mass of water: the mass of sodium hydroxide = 1:(2-200):(0.1-1).

[0077] Understandably, regarding the relationship between temperature, reagent dosage, and etching time involved in the above chemical etching: when the temperature is low and the dosage of etching reagents (ammonium fluoride, hydrogen fluoride, sodium hydroxide, etc.) is small, the etching time can be appropriately extended; when the temperature is high and the dosage of etching reagents (ammonium fluoride, hydrogen fluoride, sodium hydroxide, etc.) is high, the etching time can be appropriately shortened.

[0078] The following example, using the catalytic dehydrogenation of propane to produce propylene, demonstrates the catalytic performance of both the new catalyst and the etched catalyst. Figure 4 The catalytic effects of the new catalyst and the catalyst chemically etched with ammonium fluoride are given by way of example. Figure 4 The catalytic effect is measured by the propane conversion rate during continuous use of the catalyst. Additionally, Figure 4 The catalytic effect was obtained under the following conditions: reaction temperature 550°C, reaction gas flow rate 3 mL N2:2 mL C3H8, and catalyst Zn2SiO4-#1 dosage 300 mg (where propylene selectivity remained at approximately 96%). Figure 4As shown, after continuous use for more than 200 hours, the propane conversion rate of the new catalyst decreased (from 39% initially to below 35%). After etching the catalyst using the process described in Example 1 of the above-mentioned chemical etching, the catalyst only lost a small amount of surface area, and its initial propane conversion rate returned to the effect of the new catalyst (reaching about 39%). It could also continue to be used for more than 200 hours, indicating that the catalytic performance, catalytic stability, and sustainability of the regenerated catalyst remained unchanged.

[0079] In this embodiment of the invention, step S103 may further include: introducing a gaseous weak oxidant into the reactor to improve the catalytic stability of the catalyst. That is, the gaseous weak oxidant is introduced into the reactor simultaneously with the inert gas and the alkane feed gas.

[0080] The space-time flow rate of the aforementioned gaseous weak oxidant is 0.15–0.8 L / (kg·min). That is, the space-time flow rate of the gaseous weak oxidant is 0.15–0.8 L of gaseous weak oxidant passing through each kilogram of catalyst per minute. For example, the space-time flow rate of this gaseous weak oxidant can be 0.15 L / (kg·min), 0.18 L / (kg·min), 0.2 L / (kg·min), 0.25 L / (kg·min), 0.28 L / (kg·min), 0.3 L / (kg·min), 0.35 L / (kg·min), 0.38 L / (kg·min), 0.4 L / (kg·min), 0.47 L / (kg·min), 0.5 L / (kg·min), 0.65 L / (kg·min), 0.68 L / (kg·min), 0.7 L / (kg·min), 0.72 L / (kg·min), 0.75 L / (kg·min), 0.78 L / (kg·min), 0.8 L / (kg·min), etc. The gaseous weak oxidant can prevent the reduction of Zn on the catalyst surface, that is, it stabilizes the zinc active sites on the zinc silicate surface, thus further extending its service life. By controlling the space-time flow rate of this gaseous weak oxidant, the catalyst can be protected, while avoiding excessive waste and consumption of the gaseous weak oxidant.

[0081] In addition to introducing the weak oxidant, inert gas, and alkane feed gas into the reactor so that the catalytic reaction process is completed under the mixture of the weak oxidant, inert gas, and alkane feed gas, step S103 can also be replaced by introducing the weak oxidant and alkane feed gas into the reactor so that the catalytic reaction process is completed under the mixture of the weak oxidant and alkane feed gas. The space-time flow rate of the weak oxidant is generally 0.15 to 0.8 L / (kg·min), and the space-time flow rate of the alkane feed gas is generally 1 to 100 L / (kg·min).

[0082] Specifically, the gaseous weak oxidant selected in this application may include any one or more of CO2, NO2, and water vapor. That is, by selecting a relatively inexpensive and readily available gaseous weak oxidant, the zinc active sites on the zinc silicate surface can be stabilized. Taking the catalytic dehydrogenation of propane to propylene by crystalline zinc silicate as an example, when a small amount of CO2 is introduced during the catalytic reaction, the catalytic effect of crystalline zinc silicate is as follows: Figure 5 As shown (the Figure 5 The catalytic effect is measured by the propane conversion rate during continuous use of the catalyst. Additionally, Figure 5 The catalytic effect was observed under the following conditions: reaction temperature 550°C, reaction gas flow rate of 3 mL / min (N2:2 mL / min C3H8:0.074 mL / min), catalyst dosage of 300 mg Zn2SiO4-#1, and propylene selectivity maintained at approximately 96%. Figure 5 It can be seen that when a small amount of carbon dioxide is introduced during the catalytic reaction, the propane conversion rate decreases slightly (36%), but its service life can reach over 400 hours, and when the carbon dioxide is stopped, a propane conversion rate of over 36% can be obtained. And through... Figure 5 and Figure 4 The initial conversion of propane shown was around 36% at approximately 100 hours, indicating that the catalyst lifetime can be increased by more than four times again under conditions of a small amount of weak oxidant carbon dioxide.

[0083] Furthermore, the combination of gaseous weak oxidants and surface etching can extend the service life of crystalline zinc silicate catalysts in alkane dehydrogenation reactions to several months or even a year, thereby further improving catalytic stability and production sustainability.

[0084] The above-mentioned alkane feed gas is any one of ethane, propane, and butane; to obtain ethylene, propylene, and butadiene.

[0085] The method for preparing olefins by catalytic dehydrogenation of alkanes is described in detail below with several specific examples.

[0086] Example 1:

[0087] Zinc silicate catalyst (Zn2SiO4-#1) was packed into a fixed bed, and the temperature inside the fixed bed was raised to 550℃ under air with a space velocity of 66.7 L / (kg·min) for 1 hour of activation. Afterwards, the fixed bed was purged with nitrogen gas at a space velocity of 66.7 L / (kg·min) for 10 minutes. Then, a reaction gas was introduced with a space velocity of 10 L / (kg·min) N2:6.7 L / (kg·min) C3H8, resulting in a propane conversion of approximately 39% and a propylene selectivity of approximately 96%. As the reaction proceeded (6–8 hours), the catalyst deactivated due to carbon deposition. At this point, the reaction gas was switched back to air at a space velocity of 66.7 L / (kg·min), and the catalyst was activated for 1 hour. This process was repeated to achieve continuous use of the catalyst. After multiple continuous cycles of reaction, the catalytic performance of the catalyst gradually decreased (e.g., Figure 4 (As shown). At this point, after removing carbon deposits, the catalyst is removed and etched using the etching method mentioned above. For example, the used catalyst is dispersed in a certain amount of water (6g of catalyst per liter of water), and ammonium fluoride is added (where the mass ratio of catalyst to ammonium fluoride is 10:1). The mixture is stirred and etched at room temperature (25°C) for 1 hour. Afterward, the catalyst is separated, cleaned, and dried for reuse. This etching process occurs only on the surface of the catalyst, and by controlling the etching process, the mass loss of the catalyst is less than 10%.

[0088] Example 2:

[0089] Zinc silicate catalyst (Zn₂SiO₄-#1) was packed into a fixed bed, and the temperature inside the fixed bed was raised to 600℃ under air with a space-time flow rate of 334 L / (kg·min) for 1 hour for activation. Afterwards, the fixed bed was purged with nitrogen gas at a space-time flow rate of 334 L / (kg·min) for 10 minutes. Then, a reaction gas was introduced with a space-time flow rate of 50 L / (kg·min) N₂: 33.4 L / (kg·min) C₃H₈, resulting in a propane conversion of approximately 40% and a propylene selectivity of approximately 88%. As the reaction proceeded (6–8 hours), the catalyst became deactivated due to carbon deposition. At this point, the reaction gas was switched to air with a space-time flow rate of 334 L / (kg·min), and the catalyst was activated for 1 hour. This process was repeated to achieve continuous use of the catalyst. After multiple continuous cycles of reaction, the catalytic performance of the catalyst gradually decreased. At this point, the catalyst was removed, calcined to remove the carbon deposits, and then etched using the etching method mentioned above. If the used catalyst is dispersed in a certain amount of water (30g of catalyst per liter of water), ammonium fluoride is added (the mass ratio of catalyst to ammonium fluoride is 2:1), and the mixture is stirred and etched at 15°C for 0.5 hours, the catalyst can be separated, cleaned, and dried for reuse.

[0090] Example 3:

[0091] Zinc silicate catalyst (Zn₂SiO₄-#2) was packed in a fixed bed, and the reaction temperature was raised to 500℃ under air at a flow rate of 66.7 L / (kg·min) for 1 hour. Afterward, the fixed bed was purged with nitrogen at a flow rate of 66.7 L / (kg·min) for 10 minutes. Then, a reaction gas was introduced with a flow rate of 10 L / (kg·min) N₂: 6.7 L / (kg·min) C₃H₈: 0.28 L / (kg·min) CO₂, resulting in a propane conversion of approximately 22% and a propylene selectivity of approximately 96%. As the reaction proceeded (6–8 hours), the catalyst deactivated due to carbon deposition. At this point, the reaction gas was switched back to air at a flow rate of 66.7 L / (kg·min), and the catalyst was reactivated for 1 hour. This process was repeated to achieve continuous use of the catalyst. After multiple continuous cycles, the catalytic performance of the catalyst gradually decreased. After prolonged use, zinc loss occurred in the catalyst. After removing the carbon deposits from the catalyst, it is etched using the etching method mentioned above. For example, the used catalyst can be dispersed in water (15g of catalyst per liter of water), hydrogen fluoride can be added (where the mass ratio of catalyst to hydrogen fluoride is 10:1), and the catalyst can be stirred and etched at 45°C for 15 minutes. After that, the catalyst can be separated, cleaned, and dried for reuse.

[0092] Example 4:

[0093] Zinc silicate catalyst (Zn₂SiO₄-#2) was packed into a fixed bed and activated for 1 hour at 670°C with air at a space velocity of 66.7 L / (kg·min). The fixed bed was then purged with nitrogen at a space velocity of 66.7 L / (kg·min) for 10 minutes. Then, a reaction gas was introduced at a space velocity of 10 L / (kg·min) N₂: 6.7 L / (kg·min) C₂H₆, resulting in an ethane conversion of approximately 63% and an ethylene selectivity of approximately 88%. As the reaction proceeded (6–8 hours), the catalyst became deactivated due to carbon buildup. At this point, the reaction gas was switched back to air at a space velocity of 66.7 L / (kg·min), and the catalyst was activated for 1 hour. This process was repeated to achieve continuous use of the catalyst. After multiple continuous cycles, the catalytic performance of the catalyst gradually decreased. At this point, the catalyst was removed after removing carbon buildup and etched using the etching method mentioned above. The used catalyst can be dispersed in water (30g of catalyst per liter of water), and sodium hydroxide can be added (the mass ratio of catalyst to sodium hydroxide is 5:1). The mixture is then stirred and etched at 40°C for 15 minutes. Afterward, the catalyst is separated, cleaned, and dried for reuse. This etching process occurs only on the surface of the catalyst, and by controlling the etching process, the mass loss of the catalyst is kept to less than 10%.

[0094] Example 5:

[0095] Zinc silicate catalyst (Zn₂SiO₄-#2) was packed into a fixed bed. The reaction temperature was raised to 630℃ under air with a space velocity of 33.3 L / (kg·min), and the activation time was 1 h. Afterward, the fixed bed was purged with nitrogen gas at a space velocity of 33.3 L / (kg·min) for 10 min. Then, a reaction gas was introduced with a space velocity of 10 L / (kg·min) N₂: 6.7 L / (kg·min) C₄H₈, resulting in a butane conversion of approximately 58% and a butene selectivity of approximately 82%. As the reaction proceeded (6–8 hours), the catalyst deactivated due to carbon deposition. At this point, the reaction gas was switched to air with a space velocity of 30 L / (kg·min), and the catalyst was activated for 1 h. This process was repeated to achieve continuous use of the catalyst. After multiple continuous cycles, the catalytic performance of the catalyst gradually decreased. At this point, the catalyst was removed, the carbon deposits were removed, and the catalyst was etched using the aforementioned etching method. The used catalyst can be dispersed in water (10g of catalyst per liter of water), and ammonium fluoride can be added (the mass ratio of catalyst to ammonium fluoride is 8:1). The mixture is stirred and etched at room temperature (25°C) for 1.5 hours. Afterward, the catalyst is separated, cleaned, and dried for reuse. This etching process only occurs on the surface of the catalyst, and by controlling the etching process, the mass loss of the catalyst is minimized.

[0096] Example 6:

[0097] Zinc silicate catalyst (Zn₂SiO₄-#3) was packed into a fixed bed and activated for 1 hour at 525°C with air at a space velocity of 66.7 L / (kg·min). The fixed bed was then purged with nitrogen at a space velocity of 66.7 L / (kg·min) for 10 minutes. Subsequently, a reaction gas was introduced with a space velocity of 10 L / (kg·min) N₂: 6.7 L / (kg·min) C₃H₈: 0.28 L / (kg·min) CO₂, resulting in a propane conversion of approximately 29% and a propylene selectivity of approximately 98%. As the reaction proceeded (6–8 hours), the catalyst deactivated due to carbon deposition. At this point, the reaction gas was switched back to air at a space velocity of 66.7 L / (kg·min), and the catalyst was activated for 1 hour. This process was repeated to achieve continuous use of the catalyst. After multiple continuous cycles, the catalytic performance of the catalyst gradually decreased. After prolonged use, zinc loss occurred in the catalyst. After removing the carbon deposits from the catalyst, remove it and etch it using the etching method mentioned above. For example, disperse the used catalyst in water (50g of catalyst per liter of water), add sodium hydroxide (where the mass ratio of catalyst to ammonium fluoride is 5:1), stir and etch at 35°C for 0.5 hours. After that, separate and clean the catalyst, and dry it for reuse.

[0098] Example 7:

[0099] Zinc silicate catalyst (Zn₂SiO₄-#1) was packed in a fixed bed and activated for 1 hour at 575°C with air at a space velocity of 150 L / (kg·min). The fixed bed was then purged with nitrogen at a space velocity of 66.7 L / (kg·min) for 10 minutes. A reaction gas was then introduced with a space velocity of 10 L / (kg·min) N₂: 6.7 L / (kg·min) C₃H₈: 0.5 L / (kg·min) CO₂, resulting in a propane conversion of approximately 30% and a propylene selectivity of approximately 90%. As the reaction proceeded (6–8 hours), the catalyst deactivated due to carbon deposition. At this point, the reaction gas was switched back to air at a space velocity of 66.7 L / (kg·min), and the catalyst was activated for 1 hour. This process was repeated to achieve continuous use of the catalyst. After multiple continuous cycles, the catalytic performance of the catalyst gradually decreased. After prolonged use, zinc loss occurred in the catalyst. After removing carbon deposits from the catalyst, it is etched using the etching method mentioned above. For example, the used catalyst can be dispersed in water (50g of catalyst per liter of water), ammonium fluoride added (the mass ratio of catalyst to ammonium fluoride is 10:1), and etched by stirring at 15°C for 5 hours. Afterward, the catalyst is separated, cleaned, and dried for reuse. This etching process occurs only on the surface of the catalyst, and by controlling the etching process, the mass loss of the catalyst is kept to less than 10%.

[0100] Example 8:

[0101] Zinc silicate catalyst (Zn₂SiO₄-#3) was packed into a fixed bed and activated for 1 hour at 650°C with air at a space velocity of 150 L / (kg·min). The fixed bed was then purged with nitrogen at a space velocity of 50 L / (kg·min) for 10 minutes. Subsequently, a reaction gas was introduced with a space velocity of 10 L / (kg·min) N₂: 6.7 L / (kg·min) C₃H₈: 0.55 L / (kg·min) CO₂, resulting in a propane conversion of approximately 45% and a propylene selectivity of approximately 96%. As the reaction proceeded (6–8 hours), the catalyst deactivated due to carbon deposition. At this point, the reaction gas was switched to air at a space velocity of 150 L / (kg·min), and the catalyst was activated for 1 hour. This process was repeated to achieve continuous use of the catalyst. After multiple continuous cycles, the catalytic performance of the catalyst gradually decreased. After prolonged use, zinc loss occurred in the catalyst. After removing carbon deposits from the catalyst, it is etched using the etching method mentioned above. For example, the used catalyst can be dispersed in water (20g of catalyst per liter of water), and hydrogen fluoride can be added (the mass ratio of catalyst to hydrogen fluoride is 5:1). The mixture is then stirred and etched at 25°C for 20 minutes. Afterward, the catalyst is separated, cleaned, and dried for reuse. This etching process occurs only on the surface of the catalyst, and by controlling the etching process, the mass loss of the catalyst is minimal.

[0102] Example 9:

[0103] Zinc silicate catalyst (Zn₂SiO₄-#3) was packed in a fixed bed and activated for 1 h at 580 °C with air at a space-time flow rate of 50 L / (kg·min). Afterward, the fixed bed was purged with nitrogen at a space-time flow rate of 30 L / (kg·min) for 10 min. Then, a reaction gas was introduced at a space-time flow rate of 20 L / (kg·min) N₂: 13 L / (kg·min) C₄H₂. 10With 0.75 L / (kg·min) CO2, the butane conversion rate is approximately 43%, and the butene selectivity is approximately 92%. As the reaction proceeds (6-8 hours), the catalyst deactivates due to carbon buildup. At this point, the reaction gas is switched to air at a space velocity of 60 L / (kg·min), and the catalyst is activated for 2 hours. This process is repeated to achieve continuous use of the catalyst. After multiple continuous cycles, the catalyst's catalytic performance gradually decreases. After prolonged use, zinc loss occurs in the catalyst. The catalyst is removed after removing carbon buildup and etched using the aforementioned etching method. For example, the used catalyst can be dispersed in water (30 g of catalyst per liter of water), ammonium fluoride is added (the mass ratio of catalyst to ammonium fluoride is 10:1), and the mixture is stirred and etched at 15°C for 3 hours. Afterward, the catalyst is separated, cleaned, and dried for reuse. This etching process occurs only on the surface of the catalyst, and by controlling the etching process, the mass loss of the catalyst is minimal.

Claims

1. A process for the catalytic dehydrogenation of an alkane to produce an alkene, characterized in that, The method comprises: Step S1, activating a catalyst in a reactor under an air atmosphere, wherein the catalyst is a crystal structure zinc silicate; Step S2, introducing an inert gas into the reactor to discharge residual air in the reactor; Step S3, inert gas and alkane raw material gas are introduced into the reactor, and the reaction temperature is controlled at 500-700℃ and the space-time flow rate is controlled at 1-100 L / (kg · min, under the catalysis of the activated catalyst, the alkane raw material gas is dehydrogenated and converted into olefins. Step S3 further comprises: introducing a gaseous weak oxidant into the reactor to improve catalytic stability of the catalyst, wherein the gaseous weak oxidant comprises any one or more of CO2, NO2 and water vapor; The method further comprises: regenerating the deactivated catalyst due to surface zinc loss by surface etching.

2. The method of claim 1, wherein, Step S1 further comprises: controlling the activation temperature to be 500-650℃; and / or, controlling the activation time to be 30-60min.

3. The method according to claim 1, wherein: the inert gas is introduced in step S2 for 5-20min; and / or, The space-time flow rate of the inert gas in step S2 is 10-100 L / (kg · min).

4. The method according to claim 1, wherein: the volume ratio of the inert gas to the alkane raw material gas in step S3 is 9:1-0:

1.

5. The method according to claim 1, wherein: the surface etching is physical etching or chemical etching.

6. The method according to claim 5, wherein: the etching reagent used in the physical etching or the chemical etching comprises a fluorine-containing compound and / or an alkaline compound.

7. The method according to claim 1, wherein: The space-time flow rate of the gaseous weak oxidizing agent is 0.15 to 0.8 L / (kg · min).

8. The method according to any one of claims 1, 2-6, wherein: the alkane raw material gas is any one of ethane, propane and butane; and / or, the size of the crystal structure zinc silicate ranges from 0.02μm to 10μm.

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