Synthesis gas to olefin ferrous-type molten iron catalyst and its preparation and pretreatment method

Abstract

This invention relates to the field of catalytic conversion technology of syngas, specifically disclosing a ferrous fused iron catalyst for syngas-to-olefins and its preparation and pretreatment methods. The catalyst contains 80%–95% FeO by mass and includes transition metal promoters, structural promoters, and auxiliary promoters. The preparation method involves first uniformly mixing the various promoters, then mixing them with iron-containing raw materials and reduced iron powder, followed by melting. After melting, the catalyst is obtained by cooling, crushing, ball milling, and sieving. Pretreatment does not use hydrogen reduction, but only activation in a CO atmosphere. This catalyst and method can be used for direct olefin production from syngas, especially suitable for high-temperature Fischer-Tropsch synthesis, promoting the formation of an active phase favorable for olefin formation and improving total olefin selectivity and C content. 4+ It exhibits α-olefin selectivity and also offers advantages such as simplified process, lower energy consumption, and better catalyst strength and stability.

Description

Technical Field

[0001] This invention relates to the field of catalytic conversion technology of syngas, specifically to an ferrous fused iron catalyst for the direct synthesis of olefins from syngas, its preparation method, and a pretreatment activation method. The catalyst can be applied to fixed-bed or fluidized-bed high-temperature Fischer-Tropsch synthesis reactions, and is particularly suitable for improving the total olefin selectivity and C content of the reaction products. 4+ α-olefin selectivity. Background Technology

[0002] Olefins are important chemical raw materials, widely used in chemical products such as plastics, rubber, and fibers. In particular, long-chain olefins are key raw materials for lubricant production and higher alcohol synthesis. Due to insufficient domestic production, depletion of petroleum resources, and environmental pollution, and considering my country's energy structure of being rich in coal, poor in oil, and lacking in gas, it is crucial to develop a direct conversion technology for olefins from syngas prepared from coal, natural gas, and biomass, especially for long-chain olefins.

[0003] Currently, methods for preparing long-chain olefins include ethylene oligomerization and paraffin cracking. Paraffin cracking yields mixed olefins with many impurities, while ethylene oligomerization produces products containing only even-numbered carbons, resulting in a relatively limited product distribution. Therefore, many researchers are exploring one-step direct synthesis of olefins, especially long-chain olefins, from syngas.

[0004] Currently, the Na-Ru / SiO2 catalyst developed by the Shanghai Advanced Research Institute of the Chinese Academy of Sciences exhibits a CO conversion rate of 45.8% and a total olefin selectivity of about 80% at 260℃ and 1 MPa. Its products are mainly long-chain olefins. However, from the perspective of catalyst economy, Ru is relatively expensive, and the reaction temperature is relatively low, so its advantages in industrial applications are relatively weak, especially in fluidized bed applications.

[0005] In addition, some research institutes have reported on the synthesis of olefins from syngas. Most of the catalysts are prepared by precipitation or hydrothermal methods. The main problems are insufficient catalyst strength and stability. Molten iron catalysts have significant advantages in this regard, but the pretreatment process before application is particularly important. Many studies generally use high-temperature hydrogen reduction followed by carbonization treatment. This process not only consumes a lot of energy, but the complex pretreatment process can also affect the catalyst structure to some extent, thus affecting the catalyst strength and performance. Summary of the Invention

[0006] Given that some precious metal catalysts in the existing syngas direct to olefins catalyst system have high costs and insufficient economic viability for industrial applications, while existing iron-based catalysts prepared by precipitation or hydrothermal methods generally suffer from insufficient strength and stability; at the same time, existing molten iron catalysts usually require a complex pretreatment process of high-temperature hydrogen reduction followed by carbonization before application, which not only consumes a lot of energy but also easily has an adverse effect on the catalyst structure and mechanical strength, thus limiting their application performance under fixed bed and fluidized bed reaction conditions.

[0007] Based on this, the present invention aims to provide a ferrous fused iron catalyst for direct synthesis of olefins from syngas and its preparation and pretreatment method. By constructing a ferrous fused iron catalyst system rich in FeO and employing a process route that does not involve hydrogen reduction but only pretreatment and activation in a CO-containing atmosphere, the catalyst can form an active phase more conducive to olefin formation while maintaining high structural strength. This results in higher CO conversion, higher total olefin selectivity, and higher C content in the direct synthesis of olefins from syngas. 4+ α-olefin selectivity.

[0008] According to a first aspect of the present invention, an ferrous molten iron catalyst for the direct synthesis of olefins from syngas is provided, wherein the FeO content in the catalyst is 80% to 95% by weight of the total catalyst, and the catalyst further comprises a transition metal promoter component, a structural promoter component, and an auxiliary promoter component; The transition metal promoter component includes one or more of Mn, Zn, Co, and Cr, accounting for 0.5% to 8.0% of the total mass of the catalyst; The structural additive component includes one or more of MoO3, SiO2, Al2O3, ZrO2, and CeO2, accounting for 1.0% to 5.0% of the total mass of the catalyst; The auxiliary agent components include one or more of alkali metals, alkaline earth metals, and rare earth metals, accounting for 0.5% to 3.0% of the total mass of the catalyst.

[0009] In some technical solutions, the FeO content is 80% to 90% based on the total mass of the catalyst.

[0010] In some technical solutions, the alkali metal is one or more of Li, Na, K, and Cs, the alkaline earth metal is one or more of Mg and Ca, and the rare earth metal is one or more of La and Ce.

[0011] In some technical solutions, the components of the catalyst, based on the total mass of the catalyst, include: 0.5%–4.0% Mn promoter, 0.5%–2.0% K2O, 0.5%–3.0% CaO, 0.8%–2.0% La2O3, 2.0%–5.0% ZrO2, and one or more of ZnO, Cr2O3, and MgO, mainly one or a combination of ZnO and MgO, with a content of 0.2%–3.0%.

[0012] According to a second aspect of the present invention, a method for preparing the above-mentioned ferrous molten iron catalyst is further provided, comprising the following steps: The additive components are mixed evenly according to the formula. The mixed additives are then mixed with iron-containing raw materials and reduced iron powder and loaded into a melting furnace for melting treatment. After melting, the mixture is cooled and then crushed, ball-milled and sieved to obtain the ferrous molten iron catalyst.

[0013] In some technical solutions, the iron-containing raw material includes one or both of magnetite and hematite; The reduced iron powder is used to promote the formation of a Viussitic ferrous oxide host phase; In some technical solutions, the resulting ferrous molten iron catalyst has a particle size of 10–200 μm and an average particle size of 30–60 μm.

[0014] According to a third aspect of the present invention, a pretreatment method for a ferrous molten iron catalyst is provided, wherein the ferrous molten iron catalyst described above or the ferrous molten iron catalyst prepared by the above preparation method is not subjected to hydrogen reduction treatment, but is pretreated and activated only by a CO atmosphere, so that the catalyst forms an active phase suitable for the direct synthesis of olefins from syngas.

[0015] In some technical solutions, the CO-containing atmosphere is a pure CO atmosphere, or a mixed atmosphere formed by CO, Ar, and / or N2; the volume fraction of CO in the CO-containing atmosphere is 10% to 50%, preferably 20% to 30%; In some technical solutions, the pretreatment temperature is 340–500℃, the pretreatment pressure is 0.1–4.0 MPa, the pretreatment space velocity is 1000–8000 mL / (g·h), and the pretreatment time is 10–40 h. Preferably, the pretreatment temperature is 350–400℃, the pressure is 0.5–2.0 MPa, and the pretreatment time is 10–30 h.

[0016] According to a fourth aspect of the present invention, a method for direct synthesis of olefins from syngas is further provided, comprising the following steps: The ferrous molten iron catalyst was prepared by the above preparation method, and then activated by the above pretreatment method. The activated catalyst was then used for the direct synthesis of olefins from syngas.

[0017] In some technical solutions, the conditions for the direct synthesis of olefins from syngas are: H2 / CO volume ratio of 1 to 4, reaction temperature of 300 to 450°C, reaction pressure of 1.0 to 4.0 MPa, and reaction space velocity of 2000 to 10000 mL / (g·h); the reaction is a high-temperature Fischer-Tropsch synthesis reaction.

[0018] According to a fifth aspect of the invention, the above-described ferrous molten iron catalyst, or a ferrous molten iron catalyst activated by the above-described pretreatment method, is further provided to improve the total olefin selectivity and C content in the direct synthesis of olefins from syngas. 4+ Selective applications of α-olefins.

[0019] The present invention, by employing the above technical solution, has at least the following beneficial effects: 1. The catalyst provided by this invention is a ferrous molten iron catalyst system rich in FeO. By controlling the FeO content in the catalyst and coordinating the design of transition metal promoters, structural promoters and auxiliary promoters, it is beneficial to obtain a catalyst with both high mechanical strength and good reaction performance, thus making it more suitable for application in high-temperature Fischer-Tropsch synthesis reaction systems in fixed beds or fluidized beds.

[0020] 2. This invention employs a melting method in the catalyst preparation process and utilizes reduced iron powder to regulate the formation of the ferrous main phase, which is beneficial for obtaining molten iron catalysts with high ferrous oxide content. Compared to catalysts prepared by precipitation or hydrothermal methods, this type of molten iron catalyst has a better foundation for application in terms of strength and stability.

[0021] 3. The pretreatment activation method of the present invention no longer adopts the traditional complex route of carbonization after high-temperature hydrogen reduction, but only uses a CO-containing atmosphere for pretreatment activation, which significantly simplifies the catalyst activation process, reduces pretreatment energy consumption, and avoids the adverse effects that complex hydrogen reduction processes may have on the catalyst structure. Therefore, it has the advantages of simple processing technology, convenient operation and better meeting the requirements of green production.

[0022] 4. This invention utilizes the synergistic effect of FeO-rich ferrous molten iron catalyst and CO-only pretreatment process to facilitate the formation of a higher content of iron carbide active phase during catalyst pretreatment, thereby improving the catalyst activity and olefin selectivity in the direct synthesis of olefins from syngas.

[0023] 5. The technical solution provided by this invention can achieve superior reaction performance. Under the same catalyst composition and reaction conditions, compared with 10%CO / Ar, 20%CO / Ar, 50%CO / Ar and hydrogen-containing H2 / 30%CO pretreatment schemes, the catalyst using 30%CO / Ar pretreatment exhibits higher CO conversion, higher total olefin selectivity, and higher C content.4+ α-olefin selectivity, with CO conversion reaching 94.5% and total olefin selectivity reaching 69.0%, C 4+ The selectivity for α-olefins reached 47.6%. Attached Figure Description

[0024] Figure 1 This is a comparison of the XRD patterns of a fresh sample and a sample after reduction treatment of the ferrous molten iron catalyst in Example 1 of the present invention. Figure 2 This is a graph showing the results of a long-term stability experiment of the ferrous molten iron catalyst in Example 10 of the present invention; Figure 3 This is a Raman spectroscopy result diagram of the ferri-type molten iron catalyst in Example 10 of the present invention; Figure 4 This is a logic diagram illustrating the effect of the ferrous molten iron catalyst in an embodiment of the present invention. Detailed Implementation

[0025] The technical solution of the present invention will be further described below with reference to specific embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention. Equivalent substitutions, simplified transformations, or conventional adjustments made by those skilled in the art based on the present invention specification without departing from the core concept of the present invention should all fall within the scope of protection of the present invention.

[0026] This invention relates to a ferrous fused iron catalyst for the direct synthesis of olefins from syngas. The core of this invention lies in constructing a FeO-rich ferrous host phase, and synergistically regulating it with transition metal promoters, structural promoters, and auxiliary promoters. Furthermore, it utilizes pretreatment activation in a CO-containing atmosphere without hydrogen reduction to form an active phase more conducive to olefin formation, thereby improving the total olefin selectivity and C2O3 in the direct synthesis of olefins from syngas. 4+ α-Olefin selectivity. Any catalyst system, preparation method, pretreatment method, and application method constructed using the above technical approach can be considered as an implementation of this invention.

[0027] In this invention, the FeO content is the content based on the total mass of the catalyst. Besides FeO, the ferrous molten iron catalyst may also contain small amounts of other iron phases or reaction-formed phases. As long as the catalyst as a whole is still characterized by a FeO-rich ferrous main phase and can achieve the technical effects described in this invention, it falls within the protection scope of this invention.

[0028] In this invention, the transition metal auxiliary component includes one or more of Mn, Zn, Co, and Cr; the structural auxiliary component includes one or more of MoO3, SiO2, Al2O3, ZrO2, and CeO2; and the auxiliary auxiliary component includes one or more of alkali metals, alkaline earth metals, and rare earth metals. In specific implementations, the above-mentioned auxiliary components can be added in the form of corresponding oxides, carbonates, nitrates, acetates, or other precursors that can be converted into the target auxiliary component, as long as they can form the corresponding auxiliary component in the catalyst after melt treatment.

[0029] In this invention, the iron-containing raw material can be one or both of magnetite and hematite, or other iron-containing materials capable of participating in the formation of the ferrous main phase under molten conditions. Reduced iron powder is used to regulate the formation and content of FeO in the catalyst and to promote the formation of the ferrous main phase. In specific implementations, the amount of reduced iron powder added can be adjusted according to the target FeO content, raw material composition, and melting conditions.

[0030] In this invention, the melting process can be a single melting process or multiple melting processes, either two or more. The cooling method after melting can be selected according to actual needs, and the crushing, ball milling, and sieving steps can also be conventionally adjusted according to the target particle size requirements. As long as the obtained catalyst meets the compositional characteristics and performance requirements of this invention, it should be considered an embodiment of this invention.

[0031] In this invention, using only a CO-containing atmosphere for pretreatment activation means that a hydrogen reduction step is not used in the pretreatment stage; instead, a pure CO atmosphere or a mixed atmosphere of CO and an inert gas is used to activate the catalyst. The inert gas can be Ar and / or N2. The volume fraction of CO in the CO-containing atmosphere, the pretreatment temperature, the pretreatment pressure, the pretreatment space velocity, and the pretreatment time can all be adjusted within the scope disclosed in this invention according to the catalyst composition, apparatus conditions, and target reaction performance.

[0032] In this invention, the direct synthesis of olefins from syngas is preferably carried out via a high-temperature Fischer-Tropsch synthesis reaction. The volume ratio of H2 to CO in the syngas, the reaction temperature, the reaction pressure, and the reaction space velocity can be adjusted according to the specific reactor type, catalyst loading method, and target product distribution. For fixed-bed or fluidized-bed reactors, as long as the high-FeO ferrous molten iron catalyst of this invention is used in synergistic system with CO pretreatment only, and the olefin products, especially C2O2, are produced... 4+ The improvement of α-olefin selectivity is within the scope of application of this invention.

[0033] The terms "preferred," "more preferred," and "further preferred" in this specification are used only to describe preferred embodiments and do not imply a limitation on the scope of protection of this invention. The endpoint values ​​of each numerical range described in this specification, and any values ​​between the endpoints, can be combined individually to form feasible technical solutions of this invention. Without departing from the essential content of this invention, these technical solutions derived from the extension or combination of numerical ranges should also be understood as falling within the scope of this invention.

[0034] Example 1 Preparation method: First, 13.5g of manganese carbonate, 16.5g of potassium carbonate, 17.0g of calcium carbonate, 20.5g of zinc carbonate, 8.0g of zirconium oxide, and 7.8g of lanthanum oxide are mixed evenly according to the weight ratio. Then, 450g of magnetite powder and 270g of iron powder are mixed according to the weight ratio. The mixture is melted for 4 hours, rapidly cooled, and crushed to obtain particles with a size of 20-150 micrometers and an average particle size of 60 micrometers.

[0035] The catalyst pretreatment conditions were as follows: 10% CO / Ar carbonization pretreatment, 350℃, 2.0 MPa, and GHSV = 5000 h⁻¹. ~1 Carbonization was performed for 15 hours. After pretreatment, the process was switched to synthesis conditions: reaction temperature 320℃, reaction pressure 2.4 MPa, H2 / CO ratio 3.0, and space velocity GHSV = 6000 h⁻¹. ~1 Under the experimental conditions, the CO conversion rate was 85.0%, the methane selectivity was 11.5 wt%, the C2-C4 alkane selectivity was 10.5 wt%, the C2-C4 olefin selectivity was 25.0 wt%, the total olefin selectivity was 60.5%, and the C4-C4 olefin selectivity was 60.5%. 4+ α-olefin selectivity 38.5%.

[0036] like Figure 1 As shown, XRD tests were performed on fresh ferrous fused iron catalyst samples. Figure 1 It is evident that the diffraction peak positions and intensities differ among different samples, indicating that the phase composition of the catalyst changes before and after treatment. This result demonstrates that the present invention, by controlling the formation of a high-FeO ferrous host phase through reduced iron powder and combining it with CO atmosphere pretreatment, facilitates the formation of catalyst activity-related phases.

[0037] Example 2 Preparation method: First, 13.5g of manganese carbonate, 16.5g of potassium carbonate, 17.0g of calcium carbonate, 20.5g of zinc carbonate, 8.0g of zirconium oxide, and 7.8g of lanthanum oxide are mixed evenly according to the weight ratio. Then, 450g of magnetite powder and 270g of iron powder are mixed according to the weight ratio. The mixture is melted for 4 hours, rapidly cooled, and crushed to obtain particles with a size of 20-150 micrometers and an average particle size of 60 micrometers.

[0038] The catalyst pretreatment conditions were as follows: 20% CO / Ar carbonization pretreatment, 350℃, 2.0 MPa, and GHSV = 5000 h⁻¹. ~1 Carbonization was performed for 15 hours. After pretreatment, the process was switched to synthesis conditions: reaction temperature 320℃, reaction pressure 2.4 MPa, H2 / CO ratio 3.0, and space velocity GHSV = 6000 h⁻¹. ~1 Under the experimental conditions, the CO conversion rate was 88.5%, the methane selectivity was 10.0 wt%, the C2-C4 alkane selectivity was 7.6 wt%, the C2-C4 olefin selectivity was 27.5 wt%, the total olefin selectivity was 62.0%, and the C4-C4 olefin selectivity was 62.0%. 4+ α-olefin selectivity 40.3%.

[0039] Example 3 Preparation method: First, 13.5g of manganese carbonate, 16.5g of potassium carbonate, 17.0g of calcium carbonate, 20.5g of zinc carbonate, 8.0g of zirconium oxide, and 7.8g of lanthanum oxide are mixed evenly according to the weight ratio. Then, 450g of magnetite powder and 270g of iron powder are mixed according to the weight ratio. The mixture is melted for 4 hours, rapidly cooled, and crushed to obtain particles with a size of 20-150 micrometers and an average particle size of 60 micrometers.

[0040] The catalyst pretreatment conditions were as follows: 25% CO / Ar carbonization pretreatment, 350℃, 2.0 MPa, and GHSV = 5000 h⁻¹. ~1 Carbonization was performed for 15 hours. After pretreatment, the process was switched to synthesis conditions: reaction temperature 320℃, reaction pressure 2.4 MPa, H2 / CO ratio 3.0, and space velocity GHSV = 6000 h⁻¹. ~1 Under the experimental conditions, the CO conversion rate was 90.5%, the methane selectivity was 8.4 wt%, the C2-C4 alkane selectivity was 7.0 wt%, the C2-C4 olefin selectivity was 29.0 wt%, the total olefin selectivity was 64.0%, and the C4-C4 olefin selectivity was 64.0%. 4+ α-olefin selectivity 42.5%.

[0041] Example 4 Preparation method: First, 13.5g of manganese carbonate, 16.5g of potassium carbonate, 17.0g of calcium carbonate, 20.5g of zinc carbonate, 8.0g of zirconium oxide, and 7.8g of lanthanum oxide are mixed evenly according to the weight ratio. Then, 450g of magnetite powder and 270g of iron powder are mixed according to the weight ratio. The mixture is melted for 4 hours, rapidly cooled, and crushed to obtain particles with a size of 20-150 micrometers and an average particle size of 60 micrometers.

[0042] The catalyst pretreatment conditions were as follows: 30% CO / Ar carbonization pretreatment, 350℃, 2.0 MPa, and GHSV = 5000 h⁻¹. ~1Carbonization was performed for 15 hours. After pretreatment, the process was switched to synthesis conditions: reaction temperature 320℃, reaction pressure 2.4 MPa, H2 / CO ratio 3.0, and space velocity GHSV = 6000 h⁻¹. ~1 Under the experimental conditions, the CO conversion rate was 94.5%, the methane selectivity was 6.4 wt%, the C2-C4 alkane selectivity was 6.0 wt%, the C2-C4 olefin selectivity was 32.5 wt%, the total olefin selectivity was 69.0%, and the C4-C4 olefin selectivity was 69.0%. 4+ α-olefin selectivity 47.6%.

[0043] Example 5 Preparation method: First, 13.5g of manganese carbonate, 16.5g of potassium carbonate, 17.0g of calcium carbonate, 20.5g of zinc carbonate, 8.0g of zirconium oxide, and 7.8g of lanthanum oxide are mixed evenly according to the weight ratio. Then, 450g of magnetite powder and 270g of iron powder are mixed according to the weight ratio. The mixture is melted for 4 hours, rapidly cooled, and crushed to obtain particles with a size of 20-150 micrometers and an average particle size of 60 micrometers.

[0044] The catalyst pretreatment conditions were as follows: 35% CO / Ar carbonization pretreatment, 350℃, 2.0 MPa, and GHSV = 5000 h⁻¹. ~1 Carbonization was performed for 15 hours. After pretreatment, the process was switched to synthesis conditions: reaction temperature 320℃, reaction pressure 2.4 MPa, H2 / CO ratio 3.0, and space velocity GHSV = 6000 h⁻¹. ~1 Under the experimental conditions, the CO conversion rate was 92.5%, the methane selectivity was 7.3 wt%, the C2-C4 alkane selectivity was 7.5 wt%, the C2-C4 olefin selectivity was 30.5 wt%, the total olefin selectivity was 65.5%, and the C4-C4 olefin selectivity was 65.5%. 4+ α-olefin selectivity 44.0%.

[0045] Example 6 Preparation method: First, 13.5g of manganese carbonate, 16.5g of potassium carbonate, 17.0g of calcium carbonate, 20.5g of zinc carbonate, 8.0g of zirconium oxide, and 7.8g of lanthanum oxide are mixed evenly according to the weight ratio. Then, 450g of magnetite powder and 270g of iron powder are mixed according to the weight ratio. The mixture is melted for 4 hours, rapidly cooled, and crushed to obtain particles with a size of 20-150 micrometers and an average particle size of 60 micrometers.

[0046] The catalyst pretreatment conditions were as follows: 40% CO / Ar carbonization pretreatment, 350℃, 2.0 MPa, and GHSV = 5000 h⁻¹. ~1 Carbonization was performed for 15 hours. After pretreatment, the process was switched to synthesis conditions: reaction temperature 320℃, reaction pressure 2.4 MPa, H2 / CO ratio 3.0, and space velocity GHSV = 6000 h⁻¹. ~1Under the experimental conditions, the CO conversion rate was 87.4%, the methane selectivity was 10.5 wt%, the C2-C4 alkane selectivity was 9.7 wt%, the C2-C4 olefin selectivity was 28.5 wt%, the total olefin selectivity was 62.0%, and the C4-C4 olefin selectivity was 62.0%. 4+ α-olefin selectivity 40.8%.

[0047] Example 7 Preparation method: First, 13.5g of manganese carbonate, 16.5g of potassium carbonate, 17.0g of calcium carbonate, 20.5g of zinc carbonate, 8.0g of zirconium oxide, and 7.8g of lanthanum oxide are mixed evenly according to the weight ratio. Then, 450g of magnetite powder and 270g of iron powder are mixed according to the weight ratio. The mixture is melted for 4 hours, rapidly cooled, and crushed to obtain particles with a size of 20-150 micrometers and an average particle size of 60 micrometers.

[0048] The catalyst pretreatment process conditions were as follows: 50% CO / Ar carbonization pretreatment, 350℃, 2.0 MPa, and GHSV = 5000 h⁻¹. ~1 Carbonization was performed for 15 hours. After pretreatment, the process was switched to synthesis conditions: reaction temperature 320℃, reaction pressure 2.4 MPa, H2 / CO ratio 3.0, and space velocity GHSV = 6000 h⁻¹. ~1 Under the experimental conditions, the CO conversion rate was 82.0%, the methane selectivity was 12.6 wt%, the C2-C4 alkane selectivity was 11.0 wt%, the C2-C4 olefin selectivity was 24.3 wt%, the total olefin selectivity was 58.0%, and the C4-C4 olefin selectivity was 58.0%. 4+ α-olefin selectivity 36.0%.

[0049] Example 8 Preparation method: First, 13.5g of manganese carbonate, 16.5g of potassium carbonate, 17.0g of calcium carbonate, 20.5g of zinc carbonate, 8.0g of zirconium oxide, and 7.8g of lanthanum oxide are mixed evenly according to the weight ratio. Then, 450g of magnetite powder is mixed with it according to the weight ratio. Unlike the above, no iron powder is added in this preparation process. The melting time is 4 hours, followed by rapid cooling and crushing to obtain particles with a size of 20-150 micrometers and an average particle size of 60 micrometers.

[0050] The catalyst pretreatment conditions were as follows: 30% CO / Ar carbonization pretreatment, 350℃, 2.0 MPa, and GHSV = 5000 h⁻¹. ~1 Carbonization was performed for 15 hours. After pretreatment, the process was switched to synthesis conditions: reaction temperature 320℃, reaction pressure 2.4 MPa, H2 / CO ratio 3.0, and space velocity GHSV = 6000 h⁻¹. ~1Under the experimental conditions, the CO conversion rate was 84.8%, the methane selectivity was 13.0 wt%, the C2-C4 alkane selectivity was 12.3 wt%, the C2-C4 olefin selectivity was 23.0 wt%, the total olefin selectivity was 55.5%, and the C4-C4 olefin selectivity was 55.5%. 4+ α-olefin selectivity 34.9%.

[0051] Example 9 Preparation method: First, 13.5g of manganese carbonate, 16.5g of potassium carbonate, 17.0g of calcium carbonate, 20.5g of zinc carbonate, 8.0g of zirconium oxide, and 7.8g of lanthanum oxide are mixed evenly according to the weight ratio. Then, 450g of magnetite powder and 540g of iron powder are mixed according to the weight ratio. The difference from the above is that the amount of iron powder added is doubled in the preparation process, while the other processes remain unchanged. The melting time is 4 hours, followed by rapid cooling and crushing to obtain particles with a size of 20-150 micrometers and an average particle size of 60 micrometers.

[0052] The catalyst pretreatment conditions were as follows: 30% CO / Ar carbonization pretreatment, 350℃, 2.0 MPa, and GHSV = 5000 h⁻¹. ~1 Carbonization was performed for 15 hours. After pretreatment, the process was switched to synthesis conditions: reaction temperature 320℃, reaction pressure 2.4 MPa, H2 / CO ratio 3.0, and space velocity GHSV = 6000 h⁻¹. ~1 Under the experimental conditions, the CO conversion rate was 88.5%, the methane selectivity was 7.8 wt%, the C2-C4 alkane selectivity was 6.5 wt%, the C2-C4 olefin selectivity was 31.3 wt%, the total olefin selectivity was 67.5%, and the C4-C4 olefin selectivity was 67.5%. 4+ α-olefin selectivity: 44.8%.

[0053] Example 10 For performance stability experiments conducted using the catalyst and pretreatment conditions described in Example 4, such as... Figure 2 As shown, during the 100-hour long-term experiment, the CO conversion rate remained stable above 94%, and the selectivity of C2-C4 olefin products remained stable at around 32%. Samples were taken and analyzed at 50 and 100 hours of reaction, and the total olefins and C2-C4 olefins were analyzed twice. 4+ The selectivity for α-olefins remained at around 69% and 47%, respectively. Overall, the catalyst exhibited good stability in terms of both activity and product selectivity.

[0054] Raman spectroscopy results of the ferri-type catalyst after reaction ( Figure 3 It can be seen that the reaction at different times The catalysts after the reaction all exhibited strong D and G peaks. Compared to the reaction time of 50 h, the intensity of the graphitic carbon peak in the catalyst did not significantly increase with the reaction time of 100 h, further explaining why the catalyst performance was superior and its long-term performance was stable when 30% CO / Ar was used for pretreatment.

[0055] Combining the results of Examples 1-10 and Figure 4 It is understood that the technical effect of this invention stems from the synergistic effect between the high-FeO ferrous molten iron catalyst and CO pretreatment activation. The high-FeO ferrous host phase is beneficial for catalyst activation and the formation of the iron carbide active phase, while appropriate CO atmosphere pretreatment, especially 30% CO / Ar pretreatment, can further promote the formation of olefin-related active phases and reduce adverse effects, thereby improving catalyst activity, total olefin selectivity, and C content. 4+ α-olefin selectivity. Conversely, low FeO content or excessively high CO concentration during pretreatment are detrimental to catalyst performance improvement.

[0056] Comparative Example 1 Preparation method: First, 13.5g of manganese carbonate, 16.5g of potassium carbonate, 17.0g of calcium carbonate, 20.5g of zinc carbonate, 8.0g of zirconium oxide, and 7.8g of lanthanum oxide are mixed evenly according to the weight ratio. Then, 450g of magnetite powder and 270g of iron powder are mixed according to the weight ratio. The mixture is melted for 4 hours, rapidly cooled, and crushed to obtain particles with a size of 20-150 micrometers and an average particle size of 60 micrometers.

[0057] The catalyst pretreatment conditions were: H2 / 30%CO carbonization pretreatment, 350℃, 2.0MPa, and GHSV space velocity of 5000h⁻¹. ~1 Carbonization was performed for 15 hours. After pretreatment, the process was switched to synthesis conditions: reaction temperature 320℃, reaction pressure 2.4 MPa, H2 / CO ratio 3.0, and space velocity GHSV = 6000 h⁻¹. ~1 Under the experimental conditions, the CO conversion rate was 91.5%, the methane selectivity was 8.8 wt%, the C2-C4 alkane selectivity was 7.0 wt%, the C2-C4 olefin selectivity was 29.3 wt%, the total olefin selectivity was 63.5%, and the C4-C4 olefin selectivity was 63.5%. 4+ α-olefin selectivity 41.4%.

[0058] As can be seen from the above embodiments and comparative examples: 1. Compared to the H2 / CO mixed gas pretreatment process, the ferrous fused iron catalyst prepared above exhibits superior performance under suitable CO / Ar atmosphere pretreatment, especially 30% CO / Ar. The catalyst demonstrates high catalytic activity, enabling high-value utilization of syngas conversion. It achieves high single-pass CO conversion and a total olefin selectivity of approximately 70%. 4+ The selectivity for α-olefins is as high as 47.6%, which is mainly due to the pure CO treatment. The molten iron catalyst has a higher degree of carbonization, resulting in a high content of iron carbide active phase, which is conducive to the formation of olefins.

[0059] 2. In mixed atmosphere pretreatment processes, using excessively high CO concentrations is detrimental to improving activity and olefin selectivity, such as... Figure 1 As shown, excessively high CO concentrations during pretreatment increase the degree of carbon deposition on the catalyst surface, thereby reducing catalyst activity and olefin selectivity.

[0060] 3. For catalysts with low FeO content, it is not conducive to catalyst activation and the formation of a high-content iron carbide active phase, resulting in reduced catalyst activity and olefin selectivity. Excessive FeO content does not effectively improve catalytic performance.

[0061] The embodiments described above are merely examples illustrating several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A ferrous molten iron catalyst for the direct synthesis of olefins from syngas, characterized in that, The FeO content in the catalyst is 80% to 95% based on the total mass of the catalyst, and the catalyst also includes transition metal auxiliaries, structural auxiliaries, and auxiliary auxiliaries. The transition metal promoter component includes one or more of Mn, Zn, Co, and Cr, accounting for 0.5% to 8.0% of the total mass of the catalyst; The structural additive component includes one or more of MoO3, SiO2, Al2O3, ZrO2, and CeO2, accounting for 1.0% to 5.0% of the total mass of the catalyst; The auxiliary agent components include one or more of alkali metals, alkaline earth metals, and rare earth metals, accounting for 0.5% to 3.0% of the total mass of the catalyst.

2. The ferrous molten iron catalyst according to claim 1, characterized in that, The FeO content is 80%–90% based on the total mass of the catalyst; and / or, The alkali metal is one or more of Li, Na, K, and Cs; the alkaline earth metal is one or more of Mg and Ca; and the rare earth metal is one or more of La and Ce.

3. The ferrous molten iron catalyst according to claim 1 or 2, characterized in that, The catalyst comprises, by total mass, 0.5%–4.0% Mn promoter, 0.5%–2.0% K2O, 0.5%–3.0% CaO, 0.8%–2.0% La2O3, 2.0%–5.0% ZrO2, and one or more of ZnO, Cr2O3, and MgO, with a content of 0.2%–3.0%.

4. A method for preparing a ferrous molten iron catalyst according to any one of claims 1 to 3, characterized in that, Includes the following steps: The additive components are mixed evenly according to the formula. The mixed additives are then mixed with iron-containing raw materials and reduced iron powder and loaded into a melting furnace for melting treatment. After melting, the mixture is cooled and then crushed, ball-milled and sieved to obtain the ferrous molten iron catalyst.

5. The preparation method according to claim 4, characterized in that, The iron-containing raw material includes one or both of magnetite and hematite; The reduced iron powder is used to promote the formation of a Viussitic ferrous oxide host phase; And / or, the resulting ferrous molten iron catalyst has a particle size of 10–200 μm and an average particle size of 30–60 μm.

6. A pretreatment method for a ferrous molten iron catalyst, characterized in that, For the ferrous molten iron catalyst according to any one of claims 1 to 3 or the ferrous molten iron catalyst prepared by the preparation method according to claim 4 or 5, no hydrogen reduction treatment is used, but only CO atmosphere is used for pretreatment activation, so that the catalyst forms an active phase suitable for the direct synthesis of olefins from syngas.

7. The pretreatment method according to claim 6, characterized in that, The CO-containing atmosphere is a pure CO atmosphere, or a mixed atmosphere formed by CO and Ar and / or N2; the volume fraction of CO in the CO-containing atmosphere is 10% to 50%, preferably 20% to 30%; and / or, The pretreatment temperature was 340–500℃, the pretreatment pressure was 0.1–4.0 MPa, the pretreatment space velocity was 1000–8000 mL / (g·h), and the pretreatment time was 10–40 h.

8. A method for the direct production of olefins from syngas, characterized in that, Includes the following steps: The ferrous molten iron catalyst is prepared by the preparation method described in claim 4 or 5, and then activated by the pretreatment method described in claim 6 or 7. The activated catalyst is then used for the direct synthesis of olefins from syngas.

9. The method according to claim 8, characterized in that, The conditions for the direct synthesis of olefins from syngas are: an H2 / CO volume ratio of 1 to 4, a reaction temperature of 300 to 450°C, a reaction pressure of 1.0 to 4.0 MPa, and a reaction space velocity of 2000 to 10000 mL / (g·h); the reaction is a high-temperature Fischer-Tropsch synthesis reaction.

10. The ferrous molten iron catalyst according to any one of claims 1 to 3, or the ferrous molten iron catalyst activated by the pretreatment method according to claim 6 or 7, improves the total olefin selectivity and C content in the direct synthesis of olefins from syngas. 4+ Selective applications of α-olefins.

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