A process for the production of olefins from synthesis gas

Abstract

The application relates to a method for preparing olefins from synthesis gas, belonging to the technical field of carbon monoxide catalysis. In the method, the surface hydroxyl group of non-toxic, edible and easily-degradable guar gum is introduced into an iron-based catalyst, then the modified iron-based catalyst is obtained by further doping alkali metals, and the modified iron-based catalyst is used to catalyze the reaction of preparing olefins from synthesis gas, so that the selectivity of the catalyst to the olefins is successfully improved. The surface hydroxyl group of the modified catalyst significantly enhances the CO adsorption capacity and the oxidation resistance of the iron-based catalyst, meanwhile, the doping of the alkali metals successfully inhibits the excessive hydrogenation reaction of the iron-based catalyst, the manufacturing method is simple, green, and has excellent CO conversion rate and olefin selectivity, meanwhile, the introduction of the hydroxyl group endows the catalyst with excellent stability, so that the catalyst shows extremely high olefin space-time yield.

Description

Technical Field

[0001] This invention belongs to the field of carbon monoxide catalysis technology and relates to a method for preparing olefins from syngas, specifically using a hydroxyl-modified metal catalyst to catalyze the conversion of syngas into olefins. Background Technology

[0002] Olefins are a core raw material for modern chemical industries, widely used in the production of bulk synthetic materials such as polyethylene and polypropylene, as well as high-end functional materials such as lightweight components for new energy vehicles, medical polymer materials, and biodegradable plastics. The scale and technological level of the olefin industry directly affect the development quality of the chemical sector and the core competitiveness of a nation's economy. Currently, the global olefin industry is at a critical stage of resource restructuring and green, low-carbon transformation. The development and promotion of syngas-to-olefins technology is not only an inevitable choice to address changes in the energy and resource landscape, but also an important path to promote the high-quality development of the chemical industry.

[0003] From a global energy resource utilization perspective, traditional olefin production routes are highly dependent on petroleum resources, mainly through processes such as naphtha cracking. However, the uneven distribution of global petroleum resources and the frequent fluctuations in oil prices due to deepening economic globalization, coupled with the resource structure constraints of some countries—rich in coal but lacking in oil and gas—pose serious challenges to the stability and economic viability of traditional petroleum-based olefin production routes. As the world's largest producer and consumer of olefins, my country faces this contradiction particularly acutely—although my country's ethylene self-sufficiency rate will increase to 72% by 2025, a certain supply gap still exists, and its dependence on imported oil remains high, resulting in significant pressure on energy security. Against this backdrop, developing alternative olefin production routes based on non-petroleum resources has become a strategic requirement for ensuring national energy security and the stable development of the chemical industry. To reduce dependence on petroleum and expand raw material sources, the production of olefins from non-petroleum resources (coal, natural gas, biomass) via syngas has become a research hotspot both domestically and internationally.

[0004] Currently, syngas-to-olefins technology is mainly divided into two categories: indirect and direct methods. The indirect method requires the conversion of methanol / dimethyl ether intermediates into olefins. This technology is mature and has been industrialized, but it has inherent drawbacks such as a lengthy process flow, high equipment investment and energy consumption, and the need to improve olefin selectivity.

[0005] The direct process refers to the direct conversion of syngas into olefins under the action of a catalyst, without the need for intermediate product steps. It boasts significant advantages such as a short process flow, low investment costs, and low energy consumption, making it a crucial development direction in this field. However, the industrialization of the direct process is currently severely constrained, with the core bottleneck being that the performance of existing catalysts cannot meet the demands for efficient and stable production.

[0006] To address the technical challenges of low product yield, poor stability, and difficulty in process control in direct olefin production processes, researchers both domestically and internationally have conducted extensive research on catalyst design and modification, reaction process optimization, and reactor structure innovation. For example, efforts have been made to improve olefin selectivity and catalyst stability by controlling the particle size and crystal structure of active catalyst components (such as transition metals like Fe, Co, and Ni), introducing promoters (such as K, Mn, and La) to adjust the electronic properties and surface acidity of the catalyst, and constructing metal-molecular sieve composite catalytic systems to enhance the synergistic effect of CO activation and C / C bond directional growth. However, existing improvement schemes still have many shortcomings. For instance, while some modified catalysts can improve olefin selectivity, their activity decreases significantly; while some catalysts show improved stability, the amount of byproducts generated remains high, making it difficult to achieve synergistic optimization of activity, selectivity, and stability simultaneously through a simple method.

[0007] Therefore, developing a green, convenient, and stable modification method to significantly improve the overall performance of catalysts in existing syngas-to-olefins processes has become an urgent need to promote the industrialization of this technology. Current research on the role of hydroxyl groups in syngas processes mostly focuses on the hydroxyl groups inherent on the surface of supports (such as Al2O3, TiO2, SiC, SiO2, LDH, etc.), with few reports on direct and stable hydroxyl modification methods targeting the active sites of catalysts, especially for iron-based catalysts. Therefore, developing an efficient hydroxyl modification strategy for iron-based catalysts is of great significance for optimizing the syngas-to-olefins process and enhancing its industrial application prospects. Summary of the Invention

[0008] To address the problems of low olefin yield and poor stability caused by insufficient catalyst performance in existing technologies, the present invention aims to provide a highly efficient method for catalytic synthesis of olefins from syngas. This method utilizes a hydroxyl-modified iron-based catalyst to catalyze the syngas-to-olefin reaction. The invention directly introduces non-toxic, edible, and easily degradable hydroxyl groups from the surface of guar gum into the iron-based catalyst for modification. The modified surface hydroxyl groups significantly enhance the CO adsorption capacity and antioxidant capacity of the iron-based catalyst. Simultaneously, the doping of alkali metals successfully inhibits the excessive hydrogenation reaction of the iron-based catalyst, successfully improving its selectivity for olefins. The preparation method is simple, environmentally friendly, and exhibits excellent CO conversion and olefin selectivity. Furthermore, the introduction of hydroxyl groups endows the catalyst with excellent stability, resulting in a very high olefin space-time yield (STY).

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for preparing olefins from syngas includes the following steps:

[0011] S1. Preparation of GK-Fe catalyst: GK-Fe catalyst was prepared by co-precipitation and impregnation methods, using guar gum solution as a dispersant.

[0012] S2. GK-Fe catalyst reduction: GK-Fe catalyst is reduced using high-purity H2 under set temperature, pressure, and mass hourly space velocity conditions;

[0013] S3. Syngas to olefins: The reduced GK-Fe catalyst is packed into the isothermal section of a fixed reaction bed, and a reaction gas is introduced to carry out the reaction to obtain olefins.

[0014] In S1, the GK-Fe catalyst preparation process is as follows: iron source aqueous solution and precipitant aqueous solution are simultaneously added dropwise to guar gum solution and stirred. During the dropwise addition, the pH of the system is maintained at 7~9 and the stirring temperature is maintained at 70℃~90℃. After either the iron source aqueous solution or the precipitant aqueous solution is added, the resulting suspension is freeze-dried and calcined sequentially to obtain the Fe-based catalyst G-Fe catalyst modified by guar gum. Then, using the impregnation method (IWI), guar gum solution is used as a dispersant and impregnated with alkali metal for 10 min~30 min, followed by freeze-drying and calcination again to finally obtain the GK-Fe catalyst.

[0015] In S3, the reactant gas consists of CO and H2, where the molar ratio of H2 to CO is H2:CO = 1~4.

[0016] In S2, the GK-Fe catalyst is compressed, crushed, and passed through a 20-40 mesh sieve before being loaded into the isothermal section of a stationary reactor.

[0017] In S2, the reduction conditions are: temperature 300℃~420℃, time 2h~12h, pressure 0.1MPa~0.6MPa, and H2 mass hourly space velocity 3000mL·h. -1 ·g -1 ~9000 mL·h -1 ·g -1 .

[0018] In S3, the reaction conditions are: temperature 230℃~380℃, pressure 0.2MPa~4.0MPa, H2 / CO molar ratio 1~4, and mass hourly space velocity (MHV) of the reaction gas 3000 mL·h. -1 ·g -1 ~300000 mL·h -1 ·g -1 .

[0019] This invention provides a method for preparing olefins from syngas. By introducing guar gum as a hydroxyl donor during the co-precipitation catalyst preparation process, stable hydroxyl groups are grafted onto the iron-based surface. The hydroxyl groups on the catalyst surface act as proton donors, promoting the activation and dissociation of CO molecules to enhance catalytic activity. Simultaneously, they modulate the electronic properties of the catalyst surface to suppress excessive hydrogenation, making the reaction pathway more inclined towards CC coupling to generate olefins rather than byproducts such as methane. Based on this mechanism, the catalyst of this invention achieves a synergistic improvement in activity, selectivity, and stability—the surface hydroxyl groups effectively inhibit methane formation, significantly improving olefin selectivity while maintaining high CO conversion; simultaneously, the confined microenvironment constructed by the hydroxyl groups delays carbon deposition covering active sites, and the carbon skeleton formed by calcination of guar gum effectively inhibits high-temperature sintering of iron particles, greatly enhancing the catalyst's operational stability and promoting rapid dispersion of reaction heat to avoid local overheating, making the reaction process more mild and controllable.

[0020] In the process of modifying the catalyst, this invention involves doping the iron-based catalyst with alkali metals. The alkali metals inhibit hydrogen adsorption by transferring electrons to the catalyst, while promoting the activation of carbon monoxide. This results in a carbon-rich and hydrogen-poor surface environment on the catalyst surface, which inhibits the reverse water-gas reaction and the hydrogenation reaction. In addition, alkali metals can promote the formation of iron carbide, which is an active site more conducive to olefin formation. Therefore, with the introduction of alkali metals, the selectivity of the byproduct CO2 in the reaction decreases, while the selectivity of total olefins increases.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. This invention optimizes the reaction pathway from the perspective of reaction principle and solves the bottleneck of existing technology from the perspective of process effect through a green and convenient hydroxyl modification strategy, which is of great significance to promoting the industrialization of syngas direct olefin production technology.

[0023] 2. The catalyst prepared in this invention possesses both excellent catalytic activity and ultra-high stability. When using syngas to prepare olefins, this invention achieves stability at 300,000 mL / h. -1 ·g -1 Under reaction conditions with ultra-high gas space velocities, the CO conversion rate reaches a maximum of 86.3%, and the selectivity for low-carbon olefins reaches a maximum of 40.9%. Furthermore, this invention exhibits excellent space yield performance when using syngas to prepare olefins: the space yield for low-carbon olefins reaches a maximum of 11743.6 g·kgcat. -1 ·h -1 The highest space-time yield of total olefins reached 21283.9 g·kgcat. -1 ·h -1Furthermore, the GK-Fe catalyst also exhibited high carbon monoxide conversion, olefin selectivity, and olefin space-time yield at low temperatures (250℃), demonstrating strong potential for industrial applications. Attached Figure Description

[0024] Figure 1 The reaction performance of G-Fe catalysts modified with guar gum at different temperatures was studied.

[0025] Figure 2 The images show the XPS O1s spectra of Fe and G-Fe catalysts; where (a) represents Fe and (b) represents G-Fe.

[0026] Figure 3 SEM images of Fe and G-Fe catalysts are shown; (a) is Fe and (b) is G-Fe.

[0027] Figure 4 The images show TEM images of Fe and G-Fe catalysts; where (a) is Fe and (b) is G-Fe.

[0028] Figure 5 The catalytic performance of GK-Fe catalysts with different K contents is shown.

[0029] Figure 6 The proportions of olefins in hydrocarbons with different carbon numbers in the GK-Fe catalysts of different embodiments are shown; where (a) is Example 1, (b) is Example 2, and (c) is Example 3.

[0030] Figure 7 The X-ray photoelectron spectroscopy (XPS) of the Fe-based catalyst after the reaction is shown in the figure; where (a) represents G-Fe and (b) represents G-0.5%K-Fe.

[0031] Figure 8 For the G-Fe and GK-Fe catalysts after the reaction 57 Fe Mössbauer diagram; where (a) represents G-Fe and (b) represents G-0.5%K-Fe.

[0032] Figure 9 The catalytic performance of GK-Fe catalysts at different temperatures is shown.

[0033] Figure 10 The figures represent the proportions of olefins in hydrocarbons with different carbon numbers in the GK-Fe catalyst in different examples; where (a) is Example 5, (b) is Example 6, (c) is Example 3, and (d) is Example 7. Detailed Implementation

[0034] This invention provides a method for preparing olefins from syngas, comprising the following steps:

[0035] S1. Preparation of GK-Fe catalyst: Under conditions of stable pH of 7-9, temperature of 70℃-90℃, and continuous stirring, aqueous solutions of acidic iron salt (preferably ferric nitrate, Fe(NO3)3·9H2O) and aqueous solutions of soluble alkali salt (preferably ammonium carbonate, (NH3)2CO3) are simultaneously added dropwise at a mass ratio of acidic iron salt to soluble alkali salt of 1:(1.5-2.0) (preferably 1:2.0). The mixture is stirred in a guar gum solution. After any solution is added dropwise, the resulting suspension is freeze-dried and then calcined at 500℃~700℃ for 5h~8h to obtain the G-Fe catalyst. Using a 0~0.01M guar gum solution as a dispersant, an alkali metal is impregnated for 10min~30min, followed by freeze-drying and calcination at 500℃~700℃ for 5h~8h again to finally obtain a GK-Fe catalyst with an alkali metal mass fraction of 0.5wt%~2wt%. The alkali metal is one of K, Na, and Li, preferably K, and more preferably potassium carbonate for impregnation.

[0036] The mass ratio of Fe source to precipitant is 1:(1.5~2.0), more preferably 1:2.0; the Fe source is an acidic iron salt, preferably ferric nitrate (Fe(NO3)3·9H2O); the precipitant is a soluble alkaline salt, preferably ammonium carbonate ((NH3)2CO3).

[0037] In the preparation of G-Fe and GK-Fe catalysts, the concentration of guar gum solution, calcination temperature, and calcination time were all the same; the concentration of guar gum solution was 0 M, 0.001 M, 0.005 M, and 0.01 M, more preferably 0.005 M; the calcination temperature was 500℃~700℃, and the calcination time was 5h~8h.

[0038] The alkali metal is one of K, Na, and Li, preferably K, and more preferably potassium carbonate is used for impregnation;

[0039] In the GK-Fe catalyst, the mass fraction of alkali metal is 0.5~2wt%, preferably 0.5wt%.

[0040] S2. GK-Fe catalyst reduction: The GK-Fe catalyst was tableted, crushed, and passed through a 20-40 mesh sieve, then loaded into the isothermal section of a stationary reactor. The catalyst was then subjected to a reaction at 300℃-420℃ and 0.1MPa-0.6MPa, with a reaction rate of 3000 mL / h. -1 ·g -1 ~9000 mL·h -1 ·g -1The GK-Fe catalyst was reduced by passing high-purity H2 with a purity of 99.999% or higher through the mass hourly space velocity for 2 h to 12 h.

[0041] S3. Syngas to Olefins: The reduced GK-Fe catalyst was packed into the isothermal section of a stationary reaction bed and subjected to a reaction at 230℃~380℃ and 0.2MPa~4.0MPa, with a reaction rate of 3000 mL·h⁻¹. -1 ·g -1 ~300000 mL·h -1 ·g -1 A reaction gas consisting of H2 and CO in a molar ratio of H2 / CO = 1 to 4 is introduced at a mass hourly space velocity to produce an olefin.

[0042] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments to facilitate understanding of the invention by those skilled in the art. It is particularly important to note that the embodiments are merely illustrative of the invention and should not be construed as limiting the scope of protection of the invention. Non-essential improvements and adjustments made to the invention by those skilled in the art based on the above description should still fall within the scope of protection of the invention. Furthermore, all raw materials mentioned below, unless otherwise specified, are commercially available products; all process steps or preparation methods not mentioned in detail are process steps or preparation methods known to those skilled in the art.

[0043] Catalytic performance testing: To evaluate the catalytic performance of the prepared catalyst, a fixed-bed reactor with an inner diameter of 6 mm was used. Before the reaction, the catalyst was subjected to a mass hourly space velocity (WHSV) of 3000 mL·h⁻¹. -1 ·g -1 ~9000 mL·h -1 ·g -1 The reactor was reduced with high-purity H2 at a reduction temperature of 300℃~420℃ and a pressure of 0.1MPa~0.6MPa for 2h~12h. After reduction, the reactor was allowed to cool naturally to room temperature. Then, CO / H2 reaction gas (H2 / CO molar ratio 1~4) was introduced into the reactor, and the system temperature and pressure were gradually increased to 230℃~380℃ and 0.2MPa~4.0MPa, respectively. W / F 3.5g·h·mol -1(Relative to the weight of GK-Fe). To collect heavy hydrocarbons and eliminate the water byproduct produced by the reaction, an ice trap was placed between the reactor and the back pressure valve, and 2 g of octane was added to the ice trap to absorb the heavy hydrocarbons. After the reaction, the product in the ice trap was collected, and 0.2 g of dodecane was added to the oil phase as an internal standard. An offline gas chromatograph (Shimadzu GC-2014) equipped with a flame ionization detector (FID) and a DB-1 capillary column was used to detect the oil and aqueous phase products. Two online gas chromatographs (GLSciences GC320 and Shimadzu GC-2014) were used to identify the gas phase products: one was equipped with a thermal conductivity detector (TCD, GC320) and an activated carbon column for analyzing Ar, CO, CH4, and CO2; the other was equipped with a flame ionization detector (FID, GC-2014) and a GS-ALUMINA capillary column for analyzing light hydrocarbons.

[0044] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0045] Example 1:

[0046] 1. Preparation of G-Fe catalyst:

[0047] 10g of Fe(NO3)3·9H2O was dissolved in 100mL of deionized water, designated as solution A. Simultaneously, 25g of (NH4)2CO3 was dissolved in another 100mL of deionized water in a beaker, designated as solution B. Both solutions were then added dropwise to 100mL of guar gum solution (0.005M), with stirring. During stirring, the pH was maintained at 8 and the temperature at 80℃. The reaction stopped when either solution was exhausted. The resulting suspension was freeze-dried and calcined at 600℃ for 6 hours to obtain the catalyst, denoted as G-Fe.

[0048] 2. Reactions for the preparation of olefins from syngas:

[0049] The G-Fe catalyst was tableted, crushed, and passed through a 20-40 mesh sieve before being packed into the isothermal section of a fixed-bed reactor. Before the reaction, the G-Fe catalyst was reduced with hydrogen under the following conditions: temperature 400℃, time 10 h, pressure 0.1 MPa, and mass hourly space velocity (WHSV) 6000 mL·h. -1 ·g -1 Then CO and H2 are introduced to carry out the reaction under the following conditions: temperature 320℃, pressure 3.0 MPa, H2 / CO molar ratio of 3, and mass hourly space velocity (HHSV) of 300,000 mL·h. -1 ·g -1 The reaction results are shown in Table 1 and Figure 1 .

[0050] Example 2:

[0051] In this embodiment, all catalyst preparation steps are the same as in Example 1, except that the reaction temperature is changed. While keeping other reaction conditions constant, the reaction temperature of the reactant gas is changed to 340℃. The reaction results are shown in Table 1 and... Figure 1 .

[0052] Table 1. Summary of catalytic performance of the reaction processes in Examples 1 and 2;

[0053] ;

[0054] From Table 1 and Figure 1 As shown, Example 1 was performed at 300,000 mL·h -1 ·g -1 Even at extremely high gas flow rates, it still maintains an extremely high CO conversion rate. XPS tests on Fe and G-Fe catalysts before and after guar gum modification revealed that ( Figure 2 The G-Fe catalyst modified with guar gum has a higher hydroxyl content, which provides more stable activity points for CO adsorption and activation. Furthermore, SEM and TEM tests show that… Figure 3 , Figure 4 Due to the high viscosity of the guar gum solution, the iron-based catalyst can be better dispersed during the co-precipitation process, resulting in better dispersibility and smaller particle size for the G-Fe catalyst. The smaller particle size and better dispersibility increase the contact area between the catalyst and the reactant gas, thereby improving the overall reaction efficiency. This also explains why the pure Fe-based catalyst can still maintain a high CO conversion rate at ultra-high gas flow rates. After changing the reaction temperature, the catalytic performance test results showed that as the reaction temperature increased, the olefin selectivity in Example 2 showed a significant upward trend, increasing from 32.0% to 37.2%. Figure 6 Meanwhile, the selectivity of low-carbon olefins, which has a wider range of industrial applications, also improved, increasing from 20.1% to 26.9%. Correspondingly, the space-time yields of both low-carbon olefins and total olefins also significantly improved. The performance changes in Examples 1 and 2 are due to the fact that higher reaction temperatures are more conducive to olefin desorption, thereby suppressing secondary hydrogenation. Higher temperatures are also more conducive to carbon chain termination, which explains why Example 2 exhibits stronger olefin selectivity.

[0055] Example 3:

[0056] 1. Preparation of GK-Fe catalyst:

[0057] The G-Fe catalyst obtained in Example 1 was loaded with alkali metal K using an impregnation method. First, it was impregnated with K₂CO₃ for 10-30 minutes (using a 0.005M guar gum solution as a dispersant during impregnation). Then, 0.5 wt% K was loaded onto the G-Fe catalyst, followed by stirring and ultrasonic treatment. Finally, it was calcined at 600°C for 6 hours in a tube furnace. The resulting metal catalyst is designated G-0.5%K-Fe.

[0058] 2. Reactions for preparing olefins from syngas:

[0059] The G-0.5%K-Fe catalyst was tableted, crushed, and passed through a 20-40 mesh sieve before being packed into the isothermal section of a fixed-bed reactor. Before the reaction, the Fe catalyst was reduced with hydrogen under the following conditions: temperature 400℃, time 10h, pressure 0.1MPa, and mass hourly space velocity (WHSV) 6000mL·h. -1 ·g -1 Then CO and H2 are introduced to carry out the reaction under the following conditions: temperature 320℃, pressure 3.0 MPa, H2 / CO molar ratio of 3, and mass hourly space velocity (HHSV) of 300,000 mL·h. -1 ·g -1 The reaction results are shown in Table 2 and Figure 4 .

[0060] Example 4:

[0061] In this embodiment, the catalyst preparation was identical to Example 1 except that the loading ratio of alkali metal K was changed to 1 wt%. The final catalyst prepared in this embodiment was named G-1%K-Fe. The reaction conditions for the synthesis of olefins from syngas were exactly the same as in Example 3, and the reaction results are shown in Table 2. Figure 4 .

[0062] Table 2. Summary of catalytic performance of the reaction processes in Examples 1, 3, and 4;

[0063] ;

[0064] Table 3. 57 Table of Fe Mössbauer spectrum fitting results;

[0065] ;

[0066] From Table 2, Figure 5 and Figure 6 As shown, compared to Example 1, Example 3 exhibited higher CO conversion and olefin selectivity (90.1% vs. 86.6%, 57.2% vs. 20.1%) with the introduction of alkali metal K. XPS was performed on the catalysts after the reactions of Examples 1 and 3. Figure 7 )and 57 Fe Mössbauer analysis ( Figure 8 As shown in Table 3, the catalyst G-0.5%K-Fe in Example 3 has a higher content of carbon-iron active phase compared to the catalyst G-Fe in Example 1. This is because the addition of alkali metal K promotes the carbonization process of the Fe-based catalyst, thereby generating more iron carbide active phase. Previous studies have shown that for the hydrogenation reaction of CO, the core active phase for olefin formation is iron carbide. Simultaneously, the introduction of K also inhibits the secondary hydrogenation of olefins and promotes the adsorption and dissociation of CO, which explains why G-0.5%K-Fe in Example 3 exhibits stronger CO conversion and low-carbon olefin selectivity. However, with the increase of K loading, the CO conversion and olefin selectivity in Example 4 both decreased compared to Example 3 (90.1% vs. 85.0%, 57.2% vs. 52.5%). This is because the introduction of excess K covers the active sites of the Fe-based catalyst, reducing the specific surface area of ​​the catalyst and thus decreasing its activity.

[0067] When the K loading was 0.5 wt%, the catalyst exhibited the best reaction performance, achieving a CO conversion of 90.1% and an olefin selectivity of 57.2%. It also demonstrated the highest space-time yields of low-carbon olefins and total olefins, at 10167.3 g·kgcat, respectively. -1 ·h -1 and 21471.4 g·kgcat -1 ·h -1 .

[0068] Example 5:

[0069] In this embodiment, all catalyst preparation steps are the same as in Example 3, except that the reaction temperature is changed to 280℃ while keeping other reaction conditions constant. The reaction results are shown in Table 4 and... Figure 9 .

[0070] Example 6:

[0071] In this embodiment, all catalyst preparation steps are the same as in Example 3, except that the reaction temperature is changed to 300℃ while keeping other reaction conditions constant. The reaction results are shown in Table 4 and... Figure 9 .

[0072] Example 7:

[0073] In this embodiment, all catalyst preparation steps are the same as in Example 3, except that the reaction temperature is changed to 340℃ while keeping other reaction conditions constant. The reaction results are shown in Table 4 and... Figure 9 .

[0074] Table 4. Summary of catalytic performance of reaction processes in Examples 3, 5-7;

[0075] ;

[0076] From Table 4 and Figure 9 As shown, with decreasing temperature, the CO conversion rate of the catalyst also decreased from 90.1% to 42.0%. This is because lower temperature limits CO activation, and excessively low temperatures also affect CO diffusion and adsorption, thus reducing the catalyst's CO conversion rate. However, the study found that the introduction of hydroxyl groups significantly enhanced the catalyst's adsorption performance for CO gas. This characteristic allowed it to maintain a relatively high CO conversion rate of 42.0% even when the reaction temperature was lowered to 280℃. Simultaneously, the lower reaction temperature not only inhibited the dissociation and adsorption of H2 but also effectively blocked the secondary hydrogenation side reaction of olefins. Based on this, the olefin selectivity in Example 5 showed a significant improvement compared to Example 3, increasing from 57.2% to 66.4%. Figure 10 It is worth noting that, even at a relatively low reaction temperature of 280°C, the catalyst in Example 5 still exhibited excellent catalytic activity, with a space-time yield of 5935.4 g·kgcat for low-carbon olefins. -1 ·h -1 The space-time yield of total olefins reached 9630.9 g·kgcat. -1 ·h -1 .

[0077] When the reaction temperature was 300°C, Example 6 exhibited the best overall reaction performance, achieving a CO conversion of 90.1% and an olefin selectivity of 61.3%, while also demonstrating the highest space-time yields of low-carbon olefins and total olefins, at 11743.6 g·kgcat. -1 ·h -1 and 21283.9g·kgcat -1 ·h -1 .

[0078] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing olefins from syngas, characterized in that, Includes the following steps: S1. Preparation of GK-Fe catalyst: GK-Fe catalyst was prepared by co-precipitation and impregnation methods, using guar gum solution as a dispersant. S2. GK-Fe catalyst reduction: GK-Fe catalyst is reduced using H2 under set temperature, pressure, and mass hourly space velocity conditions; S3. Syngas to olefins: The reduced GK-Fe catalyst is packed into the isothermal section of a fixed reaction bed, and a reaction gas is introduced to carry out the reaction to obtain olefins; wherein the reaction gas is composed of CO and H2 in a molar ratio of H2:CO = 1~4.

2. The method for preparing olefins from syngas according to claim 1, characterized in that, In S1, the GK-Fe catalyst preparation process is as follows: iron source aqueous solution and precipitant aqueous solution are simultaneously added dropwise to guar gum solution and stirred. During the dropwise addition, the pH of the system is maintained at 7~9 and the stirring temperature is maintained at 70℃~90℃. After either the iron source aqueous solution or the precipitant aqueous solution is added, the resulting suspension is freeze-dried and calcined in sequence to obtain the Fe-based catalyst G-Fe catalyst modified by guar gum. Then, the impregnation method is used, with guar gum solution as dispersant, and alkali metal is impregnated for 10 min~30 min. After that, freeze-drying and calcination are carried out again to finally obtain the GK-Fe catalyst.

3. The method for preparing olefins from syngas according to claim 2, characterized in that, The alkali metal is one of K, Na, or Li; The mass ratio of Fe source to precipitant is 1:(1.5~2.0); wherein the Fe source is an acidic iron salt and the precipitant is a soluble alkaline salt.

4. A method for preparing olefins from syngas according to claim 2 or 3, characterized in that, In the preparation of G-Fe and GK-Fe catalysts, the concentration of guar gum solution, calcination temperature, and calcination time were all the same; the concentrations of guar gum solution were 0M, 0.001M, 0.005M, and 0.01M; the calcination temperature was 500℃~700℃, and the calcination time was 5h~8h.

5. A method for preparing olefins from syngas according to claim 1 or 2, characterized in that, In S2, the GK-Fe catalyst is compressed, crushed, and passed through a 20-40 mesh sieve before being loaded into the isothermal section of a stationary reactor.

6. A method for preparing olefins from syngas according to claim 1 or 2, characterized in that, In S2, the reduction conditions are: temperature 300℃~420℃, time 2h~12h, pressure 0.1MPa~0.6MPa, and H2 mass hourly space velocity 3000mL·h. -1 ·g -1 ~9000 mL·h -1 ·g -1 .

7. A method for preparing olefins from syngas according to claim 1 or 2, characterized in that, In S3, the reaction temperature is 230℃~380℃, the reaction pressure is 0.2MPa~4.0MPa, and the mass hourly space velocity of the reaction gas is 3000mL·h. -1 ·g -1 ~300000 mL·h -1 ·g -1 .

Images