A mesoporous catalyst for the synthesis of low-carbon olefins from syngas and its preparation method.

Abstract

This invention relates to a mesoporous catalyst for the synthesis of low-carbon olefins from syngas and its preparation method. The catalyst comprises an active component, an auxiliary agent, and a support. The active component is Fe, and the auxiliary agent is one or more of Mn, Ce, Zr, La, K, and Na. The support is a worm-like mesoporous molecular sieve. This invention uses a worm-like mesoporous molecular sieve as the catalyst support, which can increase the contact area between the reactants and the catalyst, effectively preventing pore blockage and catalyst deactivation. Simultaneously, the catalyst is prepared using a vacuum freeze-drying impregnation method, which reduces the agglomeration of the active component on the catalyst surface during preparation, improves the dispersion of the active component, and is beneficial to improving its activity and stability. Compared with traditional catalysts, the catalyst of this invention has a high CO conversion rate and good stability, and has potential for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to a mesoporous catalyst, and more particularly to a mesoporous catalyst for the synthesis of low-carbon olefins from syngas and its preparation method. Background Technology

[0002] The production of low-carbon olefins from syngas is a highly challenging research area in C1 chemistry and chemical engineering. Catalysts are a crucial factor in this process, and iron-based catalysts are currently the most studied. However, these catalysts are prone to wear and agglomeration and deactivation during use. Therefore, supports are needed to improve catalyst stability and increase the dispersion of the active metal components. As an important component of Fischer-Tropsch synthesis catalysts, supports enable better dispersion of metal particles, facilitating timely heat and mass transfer during the reaction and thus influencing catalyst performance. Common supports used in the direct syngas-to-olefins process include Al₂O₃, TiO₂, SiO₂, activated carbon, and molecular sieves. Among these, molecular sieves, with their shape-selective effect, large specific surface area, and regular pore structure, can improve the dispersion of active components and are a highly regarded type of support for syngas-to-olefins reactions.

[0003] There are various methods for preparing catalysts for the direct synthesis of low-carbon olefins from syngas. The preparation method directly affects the particle size of the active component and its distribution within the catalyst. Commonly used methods include impregnation, melting, precipitation, and sol-gel methods. Among these, impregnation is a commonly used method for preparing supported catalysts. Selecting a support with suitable shape and size can improve the dispersion of the supported component, making it suitable for the preparation of supported catalysts. In the impregnation process, drying after impregnation is an essential step. Different drying methods significantly affect the dispersion of the active component and the structure of the support, thus impacting the catalyst's performance. Therefore, there is an urgent need to provide a method for preparing mesoporous catalysts suitable for the direct synthesis of low-carbon olefins from syngas, in order to improve their activity and stability. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a mesoporous catalyst for the synthesis of low-carbon olefins from syngas. This catalyst has high CO conversion rate and good stability, and has potential for industrial application.

[0005] The present invention also provides a method for preparing the above-mentioned mesoporous catalyst for syngas to produce low-carbon olefins.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A mesoporous catalyst for the synthesis of low-carbon olefins from syngas, the catalyst comprising an active component, an auxiliary agent, and a support, wherein the active component is Fe, the auxiliary agent is one or more of Mn, Ce, Zr, La, K, and Na, and the support is a worm-like mesoporous molecular sieve.

[0008] Furthermore, the mesoporous catalyst described above, by weight percentage, comprises: 5-30% Fe, 5-20% additives, and the balance being a support.

[0009] A method for preparing the above-mentioned mesoporous catalyst for the synthesis of low-carbon olefins from syngas includes the following steps:

[0010] 1) Preparation of mesoporous molecular sieve supports

[0011] After dissolving the calculated amounts of water, aluminum sulfate, hexadecyltrimethylammonium bromide (CTAB), and tetraethylammonium hydroxide (TEAOH), silica sol was added, and then the mixture was transferred to a reaction vessel and placed in an oven for a period of time. After filtration, drying, and calcination, a mesoporous molecular sieve support was obtained.

[0012] 2) Vacuum freeze-drying method for impregnating active components

[0013] The active component was impregnated by vacuum freeze-drying. A mixed solution of nitrate containing the active component and additives was mixed with the mesoporous molecular sieve support prepared in step 1). After stirring for a period of time, the mixture was placed in a petri dish and frozen in a refrigerator. After being freeze-dried in a vacuum freeze dryer, the mixture was calcined to obtain the catalyst.

[0014] Specifically, in step 1), aluminum sulfate is calculated as Al, silica sol is calculated as Si, and the molar ratio of Al, Si, hexadecyltrimethylammonium bromide, tetraethylammonium hydroxide, and water is 1:20-30:2-7:10-20:1000-1500.

[0015] Further, in step 1), the solution is placed in an oven at 100~140℃ for 24~72 hours; after the placement is completed, the solution is filtered, dried, and calcined at 400~600℃ for 4~6 hours.

[0016] Specifically, in step 2), after stirring for 6 to 15 hours, the mixture is placed in a petri dish and frozen at -5 to -15°C for 12 to 48 hours. After being freeze-dried in a vacuum freeze dryer at -45 to -55°C and 10 to 100 Pa for 24 to 72 hours, it is calcined at 400 to 600°C for 4 to 6 hours to obtain the catalyst.

[0017] This invention provides the application of the above-mentioned mesoporous catalyst in the catalytic synthesis of low-carbon olefins from syngas.

[0018] In the above application, the catalyst is further reduced in hydrogen before use: the reduction pressure is atmospheric pressure, the reduction temperature is 350~450℃, the reduction time is 4~24 h, and the space velocity is 500~3000 h⁻¹. -1 .

[0019] Further applications, such as the synthesis of low-carbon olefins from syngas, include reactions with pressures of 1–3 MPa, temperatures of 200–500 °C, and gas hourly space velocities of 500–3000 h⁻¹. -1 The molar ratio of H2 to CO in the feed gas is 1~3:1.

[0020] The catalyst described in this invention is used in the one-step conversion of syngas to low-carbon olefins. The specific steps for its application are as follows:

[0021] In a fixed-bed reactor, the catalyst is used for one-step conversion of syngas to low-carbon olefins. The catalyst is first reduced at atmospheric pressure under a H2 atmosphere at a reduction temperature of 350℃ for 4-12 h at a space velocity of 2000 h⁻¹. -1 Then, the reaction was carried out at a pressure of 2 MPa, a temperature of 350 °C, and a space velocity of 1500 h⁻¹. -1 The reaction is carried out under the following conditions: direct conversion of syngas to low-carbon olefins. The molar percentage of each component in the feedstock is: H2:CO = 2.

[0022] This invention employs a worm-like mesoporous molecular sieve as a catalyst support, which increases the contact area between the reactants and the catalyst, effectively preventing catalyst deactivation due to pore blockage. Simultaneously, the catalyst is prepared using a vacuum freeze-drying impregnation method, reducing the agglomeration of active components on the catalyst surface during preparation and improving the dispersion of active components, thus enhancing its activity and stability. Compared with traditional catalysts, the catalyst of this invention exhibits high CO conversion rate and good stability, demonstrating potential for industrial application.

[0023] Vacuum freeze-drying technology involves freezing wet materials or solutions into a solid state at low temperatures (-10℃ to -50℃), and then sublimating the water in the solid state directly into a gaseous state under vacuum, ultimately dehydrating the material. Compared to conventional drying techniques, this method is gentler, sublimating the water in the frozen material directly from the ice solid to vapor without melting the ice, causing minimal damage to the internal structure of the material being dried. Applying vacuum drying to the drying process of catalysts prepared by impregnation has many advantages. First, this drying method operates at low temperatures, minimizing the loss of volatile components. Furthermore, because drying occurs in a frozen state, the volume remains almost unchanged, preserving the original structure and preventing concentration. Additionally, since the water in the material exists as ice crystals after pre-freezing, dissolved substances such as inorganic salts are evenly distributed throughout the material. During sublimation, these dissolved substances precipitate in situ, avoiding the aggregation of surface-active components caused by the migration of water from the material's interior to the surface, which is common in conventional drying methods.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1) The catalyst prepared according to the present invention has a three-dimensional network skeleton worm-like mesoporous channels, which effectively increases the contact area between the reactants and the catalyst, improves the raw material conversion rate, and the CO conversion rate is above 85%. At the same time, it can reduce catalyst deactivation caused by channel blockage.

[0026] 2) The catalyst prepared by vacuum freeze-drying impregnation method reduces the agglomeration of active components on the catalyst surface during the general impregnation drying process, better maintains the pore structure of the support, improves the dispersion of active components, and is conducive to improving its activity and stability. Attached Figure Description

[0027] Figure 1 This is a transmission electron microscope (TEM) image of the mesoporous catalyst of the present invention, illustrating that the catalyst has a uniformly distributed three-dimensional network framework of worm-like mesoporous channels. Detailed Implementation

[0028] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0029] In the following examples, all raw materials used are ordinary commercially available products that can be purchased directly.

[0030] Example 1

[0031] The mesoporous catalyst for the synthesis of low-carbon olefins from syngas provided in this embodiment is prepared through the following steps:

[0032] (1) Preparation of mesoporous molecular sieve support

[0033] After dissolving calculated amounts of water, aluminum sulfate, hexadecyltrimethylammonium bromide (CTAB), and tetraethylammonium hydroxide (TEAOH), silica sol was added; aluminum sulfate was calculated as Al, and silica sol as Si, with a molar ratio of Al:Si:CTAB:TEAOH:H₂O = 1:25:5:15:1200; the mixture was then placed in a reaction vessel and incubated at 120°C for 48 hours; after incubation, the solution was filtered, dried at 110°C for 12 hours, and then calcined at 500°C for 5 hours to obtain a mesoporous molecular sieve support. This support has a three-dimensional network framework and worm-like mesoporous channels (see...). Figure 1 The specific surface area of ​​the catalyst support obtained by testing was 739.2 m². 2 / g, pore volume is 0.755cm³ 3 / g;

[0034] (2) Vacuum freeze-drying method for impregnating active components

[0035] The mixed solution of nitrate containing active components and additives was mixed with the mesoporous molecular sieve support prepared in step (1). Specifically, the support was 30g, the mixed solution volume was 150mL, the iron nitrate mass concentration was 10%, the manganese nitrate mass concentration was 3%, the lanthanum nitrate mass concentration was 1%, and the potassium nitrate mass concentration was 0.5%. After stirring for 8 hours, the mixture was placed in a watch glass and frozen at -10℃ for 24 hours. After being freeze-dried at -50℃ and 50Pa for 48 hours using a vacuum freeze dryer, the mixture was calcined at 550℃ for 4 hours in an air atmosphere in a muffle furnace to obtain the catalyst.

[0036] Figure 1 Transmission electron microscopy (TEM) images of the mesoporous catalyst in this embodiment are provided. Figure 1 As can be seen from the image, the white areas represent mesoporous channels. This type of TEM image is generally considered to represent worm-like materials, indicating that the catalyst possesses a uniformly distributed three-dimensional network framework of worm-like mesoporous channels.

[0037] The catalyst prepared in this embodiment is used in the synthesis of low-carbon olefins from syngas, as follows:

[0038] The catalyst was placed in a fixed-bed reactor and first reduced under a normal pressure in a H2 atmosphere at a reduction temperature of 350℃ for 12 hours at a space velocity of 2000 h⁻¹. -1 Then, the reaction was carried out at a pressure of 2.0 MPa, a temperature of 350 °C, and a space velocity of 1500 h⁻¹. -1 The synthesis of low-carbon olefins was carried out under the following reaction conditions: the molar ratio of H2 to CO in the feedstock was 2:1. The experimental results of the obtained catalyst after 24 hours of synthesis reaction are listed in Table 1.

[0039] Example 2

[0040] The mesoporous catalyst for syngas-to-low-carbon olefins provided in this embodiment is prepared using the same method as in Example 1, with only some parameters adjusted as follows:

[0041] In step (2), the carrier is 30g, the volume of the mixed solution is 150mL, the mass concentration of ferric nitrate is 10%, the mass concentration of manganese nitrate is 3%, and the mass concentration of potassium nitrate is 0.5% (equivalent to the absence of lanthanum nitrate compared to Example 1).

[0042] The catalyst prepared in this example was used in the synthesis of low-carbon olefins from syngas. The reaction process, material types, material ratios, and reaction parameters were the same as in Example 1. The experimental results of the obtained catalyst after 24 hours of synthesis reaction are listed in Table 1.

[0043] Example 3

[0044] The mesoporous catalyst for syngas-to-low-carbon olefins provided in this embodiment is prepared using the same method as in Example 1, with only some parameters adjusted as follows:

[0045] In step (2), the carrier is 30g, the volume of the mixed solution is 150mL, the mass concentration of ferric nitrate is 10%, the mass concentration of manganese nitrate is 3%, and the mass concentration of lanthanum nitrate is 1% (equivalent to the absence of potassium nitrate compared to Example 1).

[0046] The catalyst prepared in this example was used in the synthesis of low-carbon olefins from syngas. The reaction process, material types, material ratios, and reaction parameters were the same as in Example 1. The experimental results of the obtained catalyst after 24 hours of synthesis reaction are listed in Table 1.

[0047] Example 4

[0048] The mesoporous catalyst for syngas-to-low-carbon olefins provided in this embodiment is prepared using the same method as in Example 1, with only some parameters adjusted as follows:

[0049] In step (2), the carrier is 30g, the volume of the mixed solution is 150mL, the mass concentration of ferric nitrate is 10%, the mass concentration of lanthanum nitrate is 1%, and the mass concentration of potassium nitrate is 0.5% (equivalent to lacking manganese nitrate compared to Example 1).

[0050] The catalyst prepared in this example was used in the synthesis of low-carbon olefins from syngas. The reaction process, material types, material ratios, and reaction parameters were the same as in Example 1. The experimental results of the obtained catalyst after 24 hours of synthesis reaction are listed in Table 1.

[0051] Comparative Example 1

[0052] The mesoporous catalyst for syngas-to-low-carbon olefins provided in this comparative example is prepared using the same method as in Example 1, with only some parameters adjusted as follows:

[0053] In step (2), a mixed solution of nitrate containing active components and additives is mixed with the mesoporous molecular sieve support prepared in step (1). Specifically, the support is 30g, the volume of the mixed solution is 150mL, the mass concentration of ferric nitrate is 10%, the mass concentration of manganese nitrate is 3%, the mass concentration of lanthanum nitrate is 1%, and the mass concentration of potassium nitrate is 0.5%. After stirring for 8 hours, it is placed in an oven at 110℃ and dried for 24 hours. Then, it is calcined in an air atmosphere in a muffle furnace at 550℃ for 4 hours to obtain the catalyst.

[0054] The catalyst prepared in this comparative example was used in the synthesis of low-carbon olefins from syngas. The reaction process, material types, material ratios, and reaction parameters were the same as in Example 1. The experimental results of the obtained catalyst after 24 hours of synthesis reaction are listed in Table 1.

[0055] Table 1 Catalytic performance of catalysts from different embodiments

[0056]

[0057] As can be seen from Table 1 above, the catalyst of this invention has good catalytic activity, with a CO conversion rate of over 85% and a C conversion rate of over 100%. 2-4 The olefin selectivity is above 42%. Furthermore, with the same active components and support, the catalyst prepared by vacuum freeze-drying in Example 1 exhibits higher CO conversion (91.4%) and olefin selectivity (49.0%) than the catalyst prepared by conventional drying in Comparative Example 1 (87.3% and 40.3%, respectively). This demonstrates that the catalyst prepared by vacuum freeze-drying impregnation in this invention reduces the agglomeration of active components on the catalyst surface during conventional impregnation drying, better maintains the pore structure of the support, and improves the dispersion of active components, thus enhancing its activity and stability.

Claims

1. The application of a mesoporous catalyst in the catalytic synthesis of low-carbon olefins from syngas, characterized in that, The mesoporous catalyst is composed of an active component, an auxiliary agent, and a support. The active component is Fe, the auxiliary agent is Mn, La, and K, and the support is a mesoporous molecular sieve. The catalyst, by weight percentage, consists of 5-30% Fe, 5-20% additives, and the remainder being a support. The mesoporous catalyst was prepared via the following steps: 1) Preparation of mesoporous worm-like molecular sieve carriers After dissolving water, aluminum sulfate, hexadecyltrimethylammonium bromide and tetraethylammonium hydroxide, silica sol was added, and then the mixture was transferred to a reaction vessel and placed in an oven for a period of time. After filtering and drying, the solution was calcined to obtain a mesoporous molecular sieve support. 2) Vacuum freeze-drying method for impregnating active components The mixed solution of nitrate containing active components and additives is mixed with the mesoporous molecular sieve support prepared in step 1), stirred, placed in a petri dish and frozen in a refrigerator, then freeze-dried in a vacuum freeze dryer and calcined to obtain the catalyst. In step 1), aluminum sulfate is calculated as Al, silica sol is calculated as Si, and the molar ratio of Al, Si, hexadecyltrimethylammonium bromide, tetraethylammonium hydroxide, and water is 1:20-30:2-7:10-20:1000-1500. In step 2), after stirring for 6 to 15 hours, the mixture is placed in a petri dish and frozen in a refrigerator for 12 to 48 hours. After being freeze-dried in a vacuum freeze dryer for 24 to 72 hours, it is calcined at 400 to 600°C for 4 to 6 hours to obtain the catalyst.

2. The application of the mesoporous catalyst as described in claim 1 in the catalytic synthesis of low-carbon olefins from syngas, characterized in that, In step 1), place the solution in an oven at 100~140℃ for 24~72 hours; after the oven is set, filter and dry the solution, and then calcine it at 400~600℃ for 4~6 hours.

3. The application of the mesoporous catalyst as described in claim 1 in the catalytic synthesis of low-carbon olefins from syngas, characterized in that, The catalyst is reduced in hydrogen gas before use: reduction pressure is atmospheric pressure, reduction temperature is 350~450℃, reduction time is 4~24h, and space velocity is 500~3000 h⁻¹. -1 ; When synthesizing low-carbon olefins from syngas, the reaction pressure is 1-3 MPa, the reaction temperature is 200-500℃, and the gas hourly space velocity is 500-3000 h⁻¹. -1 The molar ratio of H2 to CO in the feed gas is 1~3:1.

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