A shell-core structure bifunctional catalyst, a preparation method and application thereof

Abstract

This invention discloses a core-shell bifunctional catalyst, its preparation method, and its applications. The catalyst's deoxygenation core is an oxide containing one or more of the following non-precious metals: Mn, Cu, Ni, Ce, or precious metals: Pt, Pd, Rh, Ru, Au, Ag. The desulfurization shell is an oxide containing one or more of the following: Al, Mg, Zr, Zn, Fe, Ni, Mo, W, Co. This invention addresses the industry pain points of existing low-temperature methanol washing processes in coal chemical industries, such as lengthy syngas sulfur and oxygen purification processes, easy sulfur poisoning and deactivation of deoxygenation catalysts, and direct CO2 emissions from tail gas causing carbon emissions and resource waste. Through a self-developed core-shell bifunctional catalyst, it simultaneously achieves ultra-deep removal of all forms of sulfides and oxygen from syngas within a single reactor, while simultaneously realizing the high-value reuse of CO2 from tail gas.

Description

Technical Field

[0001] This invention relates to the field of catalysts and gas purification technology, and more specifically to a core-shell bifunctional catalyst, its preparation method, and its application. Background Technology

[0002] my country's energy structure, characterized by abundant coal, scarce oil, and limited natural gas, dictates that coal chemical industry, as a core industry ensuring national energy security and producing basic chemicals such as methanol, occupies a crucial position in the national economy. Low-temperature methanol washing is a core process for gas purification in the coal chemical industry, but it has long suffered from two major industry pain points, severely hindering the industry's low-carbon, efficient, and sustainable development:

[0003] First, carbon emissions and resource waste are prominent issues. The tail gas produced as a byproduct of the low-temperature methanol washing process contains 20%-40% CO2, along with trace amounts of sulfur-containing gases such as H2S and COS. In traditional processes, this tail gas is often directly emitted or burned, causing not only severe air pollution but also massive carbon emissions.

[0004] Secondly, the syngas purification process has inherent shortcomings. Syngas treated with low-temperature methanol washing still retains 50-500 ppm of sulfur and 0.1%-1% of oxygen. These trace impurities severely poison downstream methanol synthesis catalysts, leading to decreased activity and significantly shortened lifespan, necessitating deep pre-treatment. Current technologies typically add separate desulfurization and deoxygenation towers after low-temperature methanol washing to treat sulfur and oxygen impurities in stages. The desulfurization process uses methods such as hydroconversion combined with amine washing and zinc oxide adsorption, achieving high desulfurization efficiency but with a lengthy process and high infrastructure investment, unable to simultaneously address deoxygenation. The deoxygenation process often uses palladium-based catalysts, converting oxygen to water through hydrogenation for removal; however, palladium-based catalysts are easily poisoned and deactivated by sulfides, resulting in poor operational stability, similarly unable to simultaneously address desulfurization. These two independent units not only significantly increase equipment investment, operating energy consumption, and maintenance difficulty but also present problems of complex multi-system coordinated control and large footprint, failing to achieve coordinated sulfur and oxygen purification.

[0005] Therefore, how to provide a catalyst that can simultaneously and deeply remove multiple forms of sulfur and oxygen from industrial waste gas is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of the core deficiencies of existing technologies, this invention aims to solve three major technical problems and achieve its core inventive objective: 1. Develop a simultaneous sulfur and oxygen synergistic purification catalyst to simultaneously and deeply remove all forms of sulfides and oxygen from syngas in a single reactor, fundamentally solving the industry problem of traditional deoxygenation catalysts being easily poisoned and deactivated by sulfur, and protecting downstream methanol synthesis catalysts. 2. Achieve full and zero-emission resource utilization of low-temperature methanol washing tail gas, converting CO2 in the tail gas into methanol synthesis feedstock, significantly reducing carbon emissions, and realizing efficient carbon resource recycling; 3. Significantly simplify the process flow, reduce process units, lower equipment investment, operating energy consumption and overall operation and maintenance costs, avoid the generation of secondary hazardous waste such as sulfur-containing waste liquid and waste residue, and comprehensively improve the environmental protection and economic efficiency of coal-to-methanol process.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A core-shell bifunctional catalyst, wherein the deoxygenation core is an oxide containing one or more of the following non-precious metals: Mn, Cu, Ni, Ce, or precious metals: Pt, Pd, Rh, Ru, Au, Ag; and the desulfurization shell is an oxide containing one or more of the following: Al, Mg, Zr, Zn, Fe, Ni, Mo, W, Co.

[0008] This catalyst is the core component for achieving simultaneous sulfur and oxygen removal. It employs a precise three-layer shell-core structure design that integrates external desulfurization, internal deoxygenation, and interfacial poisoning prevention, simultaneously realizing both desulfurization and deoxygenation functions. This addresses the industry pain point of traditional deoxidizers being prone to sulfur poisoning at its root. The specific structural and functional design is as follows: 1) Overall structure and synergistic mechanism: The catalyst has a complete shell-core composite structure consisting of an outer shell desulfurization active layer, a core-shell interface, and a core deoxygenation active layer, achieving functional zoning and efficient synergy: the outer shell preferentially intercepts and removes all forms of sulfides in the syngas, forming the first sulfur protection barrier for the core; the core is responsible for the efficient catalytic removal of oxygen; the core-shell interface forms an electron-rich protective layer on the surface of the core through directional electron transfer, completely blocking the poisoning of the core deoxygenation active sites by sulfides, and finally achieving simultaneous deep removal of sulfur and oxygen in a single reactor.

[0009] 2) Detailed design and function of each structural layer: a. Shell (Desulfurization Active Layer): The main material is a shell of metal oxides such as Al, Mg, Zr, Zn, Fe, Ni, Mo, W, and Co uniformly coated on the surface of the core. It can be modified by doping with alkali metals, transition metals, and rare earth metals. The shell has multi-level through-pores, high specific surface area, and abundant surface alkaline sites, which can precisely adjust the hydrolysis or hydrogenation activity, preferentially expose highly active sulfur adsorption crystal faces, and adapt to different organic sulfur systems.

[0010] Core functions: selectively adsorbs and converts all forms of sulfides such as H2S, COS, CS2, methanethiol, and thiophene in syngas, converting them into stable sulfide phases for fixation, thus achieving ultra-deep desulfurization; at the same time, it forms the first sulfur protection barrier for the core, preventing sulfides from entering the core.

[0011] b. Core-shell interface: This is the interface between the core and the shell with a high degree of lattice matching, which enables the directional transfer of shell electrons to the core.

[0012] Core function: Forming an electron-rich protective layer on the core surface to inhibit the adsorption and poisoning of sulfides on the core deoxygenation active sites, fundamentally solving the industry problem of sulfur poisoning and deactivation of traditional deoxidizers, and ensuring the long-term stable operation of the catalyst.

[0013] c. Core (Deoxidation Active Layer): The main material is an oxide containing one or more of the following: non-precious metals such as Mn, Cu, Ni, Ce, or precious metals such as Pt, Pd, Rh, Ru, Au, Ag. The morphology is one or more of nanorods, nanosheets, or nanoflowers, which can fully expose highly active deoxidation crystal faces.

[0014] Core function: It efficiently catalyzes the reduction reaction between O2 in the synthesis gas and CO and H2 in the system, completely removing oxygen from the gas phase. It is suitable for a wide range of oxygen concentrations and does not require additional hydrogen for deoxygenation, simplifying the process and reducing energy consumption.

[0015] 3) Core performance indicators of catalyst The saturated sulfur capacity is ≥30%, which is more than 3 times that of traditional desulfurizers; After purification, the total sulfur content of the synthesis gas can be reduced to ≤0.01ppm, the oxygen removal efficiency is ≥99%, the oxygen content can be reduced to below 200ppm, and the optimal reduction is to 1ppm or below; It can be regenerated by roasting in a high-temperature oxidizing atmosphere. After multiple cycles of regeneration, its cumulative service life is ≥100 hours. No secondary hazardous waste is generated during operation. After being scrapped, it can be sent to a gas boiler as sulfur-containing fuel for combustion and energy recovery.

[0016] Preferably, the catalyst is a Mg-Al@Cu-Ce or Ni-Mo@Cu-Ce core-shell composite catalyst, wherein the core is a Cu-Ce composite oxide and the shell is a Mg-Al hydrotalcite composite oxide or a Ni-Mo composite oxide; the mass ratio of the shell to the core is (1.5~2.5):1, preferably 2:1.

[0017] This invention also discloses a method for preparing the above-mentioned core-shell bifunctional catalyst, comprising the following steps: (1) Kernel preparation Using cerium nitrate and copper nitrate as precursors, and with a Ce to Cu molar ratio of (3~5):1, preferably 4:1, Cu-modified CeO2 solid solution nanoflower cores were prepared by hydrothermal method.

[0018] (2) Shell load and crystal formation Magnesium nitrate and aluminum nitrate were used as precursors. The molar ratio of Mg to Al was (2.5~3.5):1, preferably 3:1. The Mg-Al hydrotalcite precursor precipitate was grown in situ on the core surface by in-situ homogeneous precipitation method. After aging, washing, drying and calcining, the Mg-Al@Cu-Ce core-shell composite catalyst was finally obtained. Alternatively, using ammonium heptamolybdate and nickel nitrate as precursors, with a Mo to Ni molar ratio of (2.5~3.5):1, preferably 3:1, Ni-Mo precursor gel is in situ coated on the core surface using a sol-gel deposition coating method; after aging, washing, drying and calcining, the Ni-Mo@Cu-Ce core-shell composite catalyst is finally obtained.

[0019] The core prepared by the above method does not exist as a simple copper oxide phase. Instead, it exists as a Cu-modified CeO2 solid solution composite oxide, with Cu mainly entering the CeO2 lattice in a doped state, replacing part of the Ce. 4+ A cerium-copper solid solution is formed, with only a small amount existing on the CeO2 surface in the form of highly dispersed CuO nanoclusters, and no independent, large-particle CuO crystal phase.

[0020] Preferably, in step (1), urea is used as a precipitant and PVP is used as a surface dispersant in the hydrothermal method. After cerium nitrate and copper nitrate are dissolved and prepared into a homogeneous solution, the product is hydrothermally reacted at 130~150℃ for 5~7h. The product is washed, vacuum dried at 70~90℃, and calcined in air at 330~370℃ for 1.5~3h. Preferably, the product is hydrothermally reacted in a sealed environment at 140℃ for 6h. After washing and vacuum drying at 80℃, the product is calcined in air at 350℃ for 2h.

[0021] Preferably, in step (2), the in-situ uniform precipitation method uses urea as a precipitant and PVP as a surface regulator; the core is dispersed in water, magnesium nitrate and aluminum nitrate are added to form a uniform dispersion, and the mixture is stirred at 80~95℃ for 5~7h, calcined in air at 380~420℃ for 2.5~3.5h, preferably stirred at 90℃ for 6h, and calcined in air at 400℃ for 3h to obtain Mg-Al hydrotalcite composite oxide; In step (2), citric acid is used as a complexing agent in the sol-gel deposition coating method. The core is dispersed in anhydrous ethanol, and ammonium heptamolybdate and nickel nitrate are added to form a homogeneous system. The pH is adjusted to 3.5-4.0, and the reaction is carried out at a constant temperature of 55-65℃ to form a sol. The sol is then calcined at 430-470℃ in air for 2.5-3.5 hours, preferably at a constant temperature of 60℃. The sol is then calcined at 450℃ in air for 3 hours to obtain Ni-Mo composite oxide.

[0022] This invention provides the application of the above-mentioned core-shell bifunctional catalyst in the removal of various forms of sulfur and / or oxygen from gases.

[0023] Another object of the present invention is to provide a method for processing low-temperature methanol washing synthesis gas, comprising the following steps: The purified syngas produced from the low-temperature methanol washing process of the coal-to-methanol process is passed into a sulfur-oxygen co-purification device filled with the catalyst described above, so that sulfur-containing components and oxygen are removed from the syngas simultaneously to obtain purified syngas. The operating temperature is 180~400℃ and the operating pressure is 3.0~6.0MPa.

[0024] Preferably, the operating temperature is 200~300℃ and the operating pressure is 3.5~4.5MPa.

[0025] Preferably, a portion of the tail gas containing carbon dioxide and sulfur components generated in the low-temperature methanol washing process is mixed with the purified syngas and then fed into the methanol synthesis tower; the volume ratio of tail gas to purified syngas is 5% to 15%, preferably 3% to 10%, as excessive CO2 will inhibit the reaction equilibrium and reduce the single-pass conversion rate. Another portion of the exhaust gas is returned to the gasifier in the coal-to-methanol process as pulverized coal gas, or reused in the coal gasification unit during equipment maintenance.

[0026] Preferably, the sulfur-containing components include one or more of hydrogen sulfide, carbonyl sulfide, carbon disulfide, methanethiol, and thiophene; the synthesis gas produced by the low-temperature methanol washing process also contains CO and H2.

[0027] Beneficial effects of this invention: 1) Industry-leading catalyst performance: The independently developed shell-core composite structure catalyst can simultaneously achieve desulfurization and deoxygenation functions. Its saturated sulfur capacity is more than 3 times that of traditional desulfurizers, which fundamentally solves the industry problem of sulfur poisoning of deoxidizers. Moreover, the preparation process is simple, the cost is controllable, and it is easy to achieve industrial scale-up, with extremely strong market application prospects.

[0028] 2) Significantly optimized processes and costs: The traditional two separate processes of desulfurization and deoxygenation are integrated into one step, reducing the number of process steps by about 40%, related equipment investment by about 30%, and the plant floor space by about 25%; no additional hydrogen is needed for deoxygenation, the overall energy consumption of the plant is reduced by about 25%, saving about 12,000 tons of standard coal per year, while significantly reducing the difficulty of multi-system coordinated operation and maintenance.

[0029] 3) Significantly improved production efficiency: The purification precision of syngas has been greatly improved, the single-pass conversion rate of methanol synthesis has increased by more than 4%, the annual methanol production has increased by about 20,000 tons, and the annual economic benefits have increased by more than 20 million yuan; the poisoning and carbonization effects of sulfur and oxygen impurities on methanol synthesis catalysts have been effectively avoided, the catalyst service life has been extended by about 30%, and production and maintenance costs have been further reduced.

[0030] 4) Outstanding achievements in pollution and carbon reduction: Zero emissions and full utilization of low-temperature methanol washing tail gas are achieved, with an annual CO2 recovery and utilization of approximately 700,000 tons, which is equivalent to an annual CO2 reduction of approximately 700,000 tons; no secondary hazardous waste such as sulfur-containing waste liquid or waste residue is generated during operation, achieving multiple goals of pollution and carbon reduction and efficient resource recycling, which is in line with the requirements of the national dual-carbon strategy. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0032] Figure 1 TEM image of the Ni-Mo@Cu-Ce core-shell composite catalyst prepared in Example 1; Figure 2 TEM image of the Mg-Al@Cu-Ce core-shell composite catalyst prepared in Example 2; Figure 3 This is a flowchart of the integrated process for sulfur and oxygen synergistic purification and CO2 resource utilization in Example 3. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1 Preparation method of bifunctional Ni-Mo@Cu-Ce core-shell composite catalyst for hydrodesulfurization and deoxygenation: The core was prepared using a two-step method: hydrothermal synthesis of the core followed by sol-gel deposition of the coating layer. The core steps and key parameters are as follows: 1. Preparation of Cu-Ce deoxygenated core precursor (hydrothermal synthesis method) Cerium nitrate and copper nitrate were used as precursors, with a Ce to Cu molar ratio of 4:1. Urea was used as a precipitant (added at 4 times the total number of moles of metal ions), and polyvinylpyrrolidone (PVP) was used as a surface dispersant (added at 2% of the total mass of the reaction system). After the raw materials were dissolved and prepared into a homogeneous solution, the mixture was subjected to a sealed hydrothermal reaction at 140℃ for 6 hours. The product was washed, vacuum dried at 80℃, and then calcined in air at 350℃ for 2 hours to obtain the Cu-modified CeO2 solid solution nanoflower core precursor.

[0035] 2. Ni-Mo hydrodesulfurization shell loading and crystallization (sol-gel deposition coating method) Ammonium heptamolybdate and nickel nitrate were used as precursors, with a Mo to Ni molar ratio of 3:1 and a shell to core mass ratio of 2:1. Citric acid was used as a complexing agent (added at 1.2 times the total molar amount of Ni and Mo metal ions). The core was dispersed in anhydrous ethanol at a concentration of 10 g / L and ultrasonically dispersed for 30 min to form a homogeneous system. Metal salt raw materials were added to form a homogeneous system, and the pH was adjusted to 3.5. The reaction was carried out at 60℃ to form a sol, which in situ coated the Ni-Mo precursor gel on the surface of the core. The product was aged (aged at room temperature in a sealed environment for 18 h), washed (washed four times by centrifugation with anhydrous ethanol at 10,000 rpm for 8 min each time, until the pH of the supernatant was neutral), dried (vacuum dried at 80℃ for 8 h), and calcined at 450℃ in air for 3 h to finally obtain the Ni-Mo@Cu-Ce core-shell composite catalyst.

[0036] Catalyst core performance evaluation: The outer shell, a Ni-Mo hydrogenated active phase, hydrogenates and breaks bonds of recalcitrant organic sulfur compounds such as H2S, COS, CS2, methanethiol, and especially thiophene, converting them into H2S, which is then adsorbed and fixed in situ, achieving one-step removal of sulfur in all its forms. The core, a Cu-Ce composite oxide, catalyzes the reduction reaction of O2 in the synthesis gas with its own CO and H2, removing sulfur without the need for additional hydrogen. The outer shell first completes the sulfide conversion and fixation, blocking sulfur diffusion to the core, while simultaneously forming an electron-rich protective layer in the core to prevent sulfur poisoning at deoxygenation sites. Specific morphology is as follows: Figure 1 As shown.

[0037] At a reaction pressure of 4.0 MPa and a volume hourly space velocity of 20,000 h⁻¹ -1Raw material gas (syngas after low-temperature methanol washing in coal-to-methanol process (H2 70%, CO)) The desulfurization process involves a catalyst composition of 20% CO2, 5% CO2, 0.5% O2, and 0.1% water vapor, with the balance being N2. It contains 100 ppm total sulfur (H2S, COS, CS2, methanethiol, and thiophene). Under optimal operating conditions at 280℃, it operates continuously for 150 hours. The catalyst loading is 0.5 g, with a particle size of 40-60 mesh. Thiophene conversion rate is ≥99.6%, and H2S, COS, CS2, and methanethiol conversion rates are 100%. Outlet total sulfur is ≤0.01 ppm, and the overall desulfurization efficiency is ≥99.99%. Oxygen removal efficiency is ≥99.95%, outlet O2 concentration is ≤5 ppm, and the total sulfur removal activity retention rate is ≥99.3%, while the deoxygenation activity retention rate is ≥98.8%. It exhibits no sulfur poisoning or carbon buildup deactivation issues. Its saturated sulfur capacity is ≥36.5%, 3.7 times that of traditional zinc oxide desulfurizers, significantly extending the single-cycle operating time. After sulfur capacity saturation, a 5% O2 + 95%... Regeneration is achieved by calcination at 480℃ for 3 hours in an N2 oxidizing atmosphere, with an activity recovery rate ≥96%. After 5 cycles of regeneration, the activity retention rate is still ≥90%. Therefore, the bifunctional Ni-Mo@Cu-Ce core-shell composite catalyst for hydrodesulfurization and deoxygenation provided in this embodiment exhibits excellent bifunctional purification performance under simulated operating conditions, providing a reliable basis for industrial applications.

[0038] Example 2 Preparation method of hydrolytic desulfurization and deoxidation bifunctional Mg-Al@Cu-Ce core-shell composite catalyst The core was prepared using a two-step method: hydrothermal synthesis of the core followed by in-situ homogeneous precipitation coating of the shell. The core steps and key parameters are as follows: 1. Preparation of Cu-Ce deoxygenated core precursor (hydrothermal synthesis method) Cerium nitrate and copper nitrate were used as precursors with a Ce to Cu molar ratio of 4:1. Urea was used as a precipitant (added at 4 times the total number of moles of metal ions), and PVP was used as a surface dispersant (added at 2% of the total mass of the reaction system). After the raw materials were dissolved and prepared into a homogeneous solution, the mixture was subjected to a sealed hydrothermal reaction at 140℃ for 6 hours. The product was washed, vacuum dried at 80℃, and then calcined in air at 350℃ for 2 hours to obtain a Cu-modified CeO2 solid solution nanoparticle core precursor.

[0039] 2. Mg-Al hydrolysis desulfurization shell loading and crystallization (in-situ homogeneous precipitation method) Magnesium nitrate and aluminum nitrate were used as precursors, with a Mg to Al molar ratio of 3:1 and a shell to core mass ratio of 2:1. Urea was used as a precipitant (added at 5 times the total number of moles of metal ions), and PVP was used as a surface modifier (added at 1% of the total mass of the reaction system). The core was dispersed in water at a concentration of 10 g / L and ultrasonically dispersed for 30 min to form a homogeneous system. Metal salt raw materials were added to form a homogeneous dispersion, and the mixture was stirred at 90℃ for 6 h to grow Mg-Al hydrotalcite precursor precipitate in situ on the core surface. The product was aged (aged at room temperature in a sealed environment for 8 h), washed (washed four times by centrifugation with deionized water, each time at 10000 rpm for 8 min), dried (dried in a forced-air environment at 80℃ for 12 h), and then calcined at 400℃ in an air atmosphere for 3 h to form a hydrotalcite-derived Mg-Al composite oxide shell, thus obtaining the Mg-Al@Cu-Ce core-shell composite catalyst.

[0040] Catalyst core performance evaluation: The outer shell is a Mg-Al composite oxide derived from hydrotalcite. With abundant strongly basic sites and surface hydroxyl groups, it catalyzes the hydrolysis of organic sulfur compounds such as COS and CS2 with trace amounts of water vapor in syngas, converting them into H2S. This H2S is then irreversibly adsorbed and fixed in situ at the strongly basic sites, achieving a one-step "hydrolysis-conversion-adsorption-fixation" process with zero hydrogen consumption and no need for hydrogen addition. The core is a Cu-Ce composite oxide, which efficiently catalyzes the reduction reaction of O2 with CO and H2 present in the syngas at low temperatures, highly matching the temperature requirements of hydrolysis desulfurization. The core-shell spatial confinement effect preferentially intercepts and fixes sulfides, and combined with the electron-rich protective layer formed by directional electron transfer at the core-shell interface, it fundamentally inhibits the poisoning of the core deoxygenation sites by sulfides. Specific morphology is as follows: Figure 3 As shown.

[0041] At a reaction pressure of 4.0 MPa and a volume hourly space velocity of 20,000 h⁻¹ -1Raw material gas (syngas after low-temperature methanol washing in coal-to-methanol process, H2 70%, CO) The catalyst composition is 20%, CO2 5%, O2 0.5%, water vapor 0.1%, with the balance being N2. It contains 100ppm total sulfur (H2S, COS, CS2), and operates continuously for 200 hours at optimal temperature (200℃). The catalyst loading is 0.5g, and the catalyst particle size is between 40 and 60 mesh. The COS hydrolysis conversion rate is 100%, and the CS2 hydrolysis conversion rate is ≥99.5%. The outlet total sulfur is ≤0.01ppm, and the total desulfurization efficiency is ≥99.99%. The oxygen removal efficiency is ≥99.92%, the outlet O2 concentration is ≤8ppm, the total sulfur removal activity retention rate is ≥99.1%, and the deoxygenation activity retention rate is ≥98.6%. It avoids sulfation deactivation and hydrothermal aging deactivation problems, solving the problem of easy deactivation during long-term operation of traditional ZnO-based hydrolysis catalysts. The saturated sulfur capacity is ≥34.2%, which is 3.5 times that of traditional zinc oxide desulfurizers. After sulfur capacity saturation, 5% O2 + 95%... The catalyst can be regenerated by calcination at 420℃ for 3 hours under an N2 oxidizing atmosphere, with an activity recovery rate of ≥95%. After 5 cycles of regeneration, the activity retention rate is still ≥88%, demonstrating excellent recyclability. Therefore, the hydrolytic desulfurization and deoxidation bifunctional Mg-Al@Cu-Ce core-shell composite catalyst provided in this embodiment exhibits excellent bifunctional purification performance under simulated operating conditions, providing a reliable basis for industrial applications.

[0042] Example 3 See Figure 1 As shown, this embodiment takes a coal gasification methanol production plant as an example to illustrate the application of catalysts in the process of sulfur-oxygen synergistic purification and CO2 resource utilization.

[0043] The complete set of equipment for this process includes a gasifier 1, a conversion unit 2, a cooling and dust removal unit 3, a low-temperature methanol washing unit 4, a sulfur-oxygen synergistic purification unit 5, a methanol synthesis tower 6, a tail gas compression and buffer unit 7, a pulverized coal conveying pipeline 8, a heat exchanger 9, a gas distribution system one 10, and a gas distribution system two 11.

[0044] The outlet of gasifier 1 is connected to the inlet of converter 2, the outlet of converter 2 is connected to the inlet of cooling and dust removal device 3, and the outlet of cooling and dust removal device 3 is connected to the inlet of low-temperature methanol washing device 4. The tail gas and synthesis gas outlets of low-temperature methanol washing device 4 are connected to the inlet of gas distribution system 10. The outlet of gas distribution system 10 is connected to the inlet of tail gas compression and buffer device 7 and the inlet of sulfur-oxygen co-purification device 5, respectively. The outlet of tail gas compression and buffer device 7 is connected to the pulverized coal conveying pipeline 8 of gasifier 1 or the purging port of gasifier 1. The outlet of sulfur-oxygen co-purification device 5 is connected to the inlet of gas distribution system 21. The outlet of gas distribution system 211 is connected to the circulating gas pipeline of methanol synthesis tower 6.

[0045] Pulverized coal is gasified at high temperature in gasifier 1 to produce crude syngas containing CO, H2, CO2, H2S, etc. The crude syngas then passes through a shift converter 2 (carbon monoxide shift reaction to adjust the H2 / CO ratio), a cooling and dust removal device 3 to recover waste heat, and further cooling and dust removal steps before entering a low-temperature methanol washing device 4 to deeply remove acidic gas components. The low-temperature methanol washing device uses methanol as an absorbent under low temperature and high pressure to wash away most of the H2S, CO2, and other impurities in the syngas, resulting in syngas mainly composed of H2 and CO. However, this purified syngas may still contain small amounts of sulfur-containing impurities such as H2S and trace amounts of oxygen, requiring further purification.

[0046] The low-temperature methanol washing unit 4 releases tail gas byproducts while removing acidic gases. This tail gas mainly consists of high-concentration CO2 obtained from the desorption of the methanol absorbent, and also contains small amounts of unabsorbed H2, CO, and trace amounts of sulfur-containing gases (such as H2S) and O2. In conventional processes, this tail gas is usually directly discharged or burned as waste gas; however, in this invention, it will be utilized as a resource. Specifically, such as... Figure 1 As shown, the tail gas from the low-temperature methanol wash is divided into two streams: the first stream of tail gas is pressurized and stabilized by the tail gas compression and buffer device 7, and then sent to the pulverized coal conveying pipeline 8 of the gasification unit, serving as the carrier gas for pulverized coal pneumatic conveying and the purging gas for the gasifier. The CO2 contained in this tail gas participates in the reaction in the gasifier, converting it into part of the syngas, thus realizing its waste-to-resource conversion; the second stream of tail gas is introduced into the subsequent methanol synthesis process as a resource-based circulating gas through the gas distribution system 10. Since directly introducing a large amount of CO2 into methanol synthesis may affect the reaction balance, in this embodiment, the amount of the second stream of tail gas added is controlled to be about 5% to 15% of the total syngas. This tail gas is mixed with the syngas treated by the sulfur-oxygen co-purification device 5 and used as the feed gas for the methanol synthesis tower 6. By sending the CO2 in the tail gas into the synthesis system through the gas distribution system 1, the carbon utilization rate in the syngas and the methanol yield are improved on the one hand, and the environmental impact caused by direct exhaust of tail gas is avoided on the other hand.

[0047] It should be noted that before the exhaust gas is mixed with the syngas, the syngas has already undergone deep purification treatment by the sulfur-oxygen co-purification device 5, reducing its sulfur and oxygen impurity content to trace levels. Therefore, the introduction of a small amount of exhaust gas will not cause the impurity concentration in the feed gas to exceed the tolerance range of the methanol synthesis catalyst. Furthermore, if the exhaust gas still contains extremely low concentrations of sulfides, these can be further removed by adding a small desulfurization purification unit (such as a zinc-based desulfurizing agent bed) to the exhaust gas branch, ensuring that the total feed gas entering the synthesis system meets the cleanliness requirements. This invention's process, through the optimized combination of exhaust gas diversion and syngas purification, achieves efficient process integration and cascaded energy utilization.

[0048] Sulfur-oxygen synergistic purification device and operation method (taking Mg-Al@Cu-Ce shell-core composite catalyst with simultaneous hydrolysis desulfurization and deoxygenation as an example) This embodiment describes in detail the structure and operation of the sulfur-oxygen synergistic purification device 5 for deep purification of syngas. This purification device is a vertical fixed-bed reactor, internally filled with a Mg-Al@Cu-Ce shell-core composite catalyst of this invention. The syngas inlet is located at the bottom of the reactor, and the purified gas outlet is located at the top. During operation, purified syngas (still containing trace amounts of sulfides such as H2S and COS, and O2) from the low-temperature methanol washing unit 4 passes through the catalyst bed from bottom to top under certain temperature and pressure. In the catalyst bed, sulfides in the syngas undergo hydrolysis with trace amounts of water vapor in the syngas under the catalytic action of the Mg-Al composite oxide component, generating H2S. The generated H2S is then irreversibly adsorbed and fixed in situ through strongly alkaline sites. Simultaneously, O2 in the gas stream reacts with CO in the syngas under the action of the Cu-modified CeO2 catalytic active component, being converted into CO2. Through the above mechanism, the simultaneous removal of sulfur and oxygen impurities is achieved within the same device. The small amount of heat released by the reaction can be absorbed by the heat capacity of the syngas or carried away by the external cooling jacket to maintain a suitable reaction temperature.

[0049] This unit is preferably operated under conditions similar to the methanol synthesis reaction temperature, so that the purified syngas can enter the methanol synthesis tower 6 without significant temperature changes. For example, the sulfur-oxygen synergistic purification reaction can be carried out at 200~300℃ and 3.0~6.0MPa (the specific operating conditions can be optimized according to the syngas composition and catalyst performance). Under the above conditions and with the action of the Mg-Al@Cu-Ce shell-core composite catalyst for simultaneous hydrolysis desulfurization and deoxygenation, the total sulfur content, including H2S, in the outlet syngas can be stably controlled below 0.1ppm, and the O2 concentration can be reduced to below 200ppm (or even undetectable), basically eliminating the toxic effects on the methanol synthesis catalyst. Compared with the traditional deoxygenation process that requires the addition of H2 to remove oxygen, this unit uses the CO naturally present in the syngas as a reducing agent, avoiding the need for external hydrogen, thereby simplifying the process and reducing costs. The purification unit 5 can be regenerated periodically by switching the gas path. When the catalyst's sulfur adsorption capacity is close to saturation or the reaction activity decreases, the syngas is cut off and regeneration gas (such as heated inert gas or oxygen-containing gas) is introduced to restore the catalyst activity. The regenerated catalyst can be reused. If the activity decreases significantly after multiple cycles, a new catalyst should be replaced. As can be seen from Examples 1 and 2, this invention achieves one-step simultaneous desulfurization and deoxygenation of syngas by arranging a dual-functional core-shell structure catalyst for simultaneous desulfurization and deoxygenation on the feed gas line of the methanol synthesis system, and effectively converts and utilizes the tail gas CO2. It eliminates the need for traditional independent desulfurization towers, deoxygenation towers, and auxiliary utilities, greatly simplifying the process.

[0050] Example 4 Pilot-scale factory performance (taking the bifunctional Ni-Mo@Cu-Ce core-shell composite catalyst of Example 1 as an example) This embodiment uses a coal-to-methanol industrial plant with an annual production capacity of 600,000 tons of methanol as an example to illustrate the operational effects of applying the process of this invention. The original process of this plant used conventional low-temperature methanol washing to purify the syngas, and included a subsequent ZnO desulfurization tower and a Pd catalytic deoxygenation tower. After modification, adopting the one-step sulfur-oxygen synergistic purification + tail gas resource utilization scheme of Example 3, significant results were achieved in actual operation: In terms of carbon emission reduction: approximately 700,000 tons / year of CO2 from the low-temperature methanol wash tail gas is recovered and reused, and is no longer directly emitted, which significantly reduces greenhouse gas emissions. Compared with before the renovation, CO2 emissions are reduced by approximately 700,000 tons per year, achieving low-carbon operation of the plant.

[0051] Regarding increased methanol production: Due to the optimized composition of syngas and the increased utilization of CO2 resources, the single-pass conversion rate of methanol synthesis has increased by more than 4% compared to before the upgrade, resulting in an annual increase of approximately 20,000 tons of methanol production, which has significantly improved the production efficiency of the plant.

[0052] In terms of energy consumption reduction: multiple auxiliary units such as desulfurization and deoxygenation have been eliminated, the process flow has been shortened, and deoxygenation does not require the addition of hydrogen. The overall energy consumption of the unit has been reduced by about 25%, saving about 12,000 tons of standard coal per year.

[0053] Catalyst lifespan: Due to the cleaner feed gas, the methanol synthesis catalyst did not exhibit sulfur poisoning or carbonization deactivation. The operating cycle was extended from approximately 2 years before the modification to over 2.6 years, representing a lifespan extension of about 30%. Simultaneously, the core-shell composite catalyst used in the sulfur-oxygen co-purification unit operated stably. After more than 100 hours of continuous operation, the catalyst maintained high desulfurization and deoxygenation efficiency, without exhibiting catalyst poisoning, carbon buildup, or abnormal reactor pressure drops. The overall operation of the unit was smooth and stable, fully verifying the industrial applicability and reliability of the process described in this invention.

[0054] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0055] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A core-shell bifunctional catalyst, characterized in that, Its deoxidation core is an oxide containing one or more of the following non-precious metals: Mn, Cu, Ni, Ce, or precious metals: Pt, Pd, Rh, Ru, Au, Ag; and its desulfurization shell is an oxide containing one or more of the following: Al, Mg, Zr, Zn, Fe, Ni, Mo, W, Co.

2. The core-shell bifunctional catalyst according to claim 1, characterized in that, The catalyst is a Mg-Al@Cu-Ce or Ni-Mo@Cu-Ce core-shell composite catalyst, with the core being a Cu-Ce composite oxide and the shell being a Mg-Al hydrotalcite composite oxide or a Ni-Mo composite oxide; the mass ratio of the shell to the core is (1.5~2.5):

1.

3. The method for preparing a core-shell bifunctional catalyst according to claim 2, characterized in that, Includes the following steps: (1) Kernel preparation Using cerium nitrate and copper nitrate as precursors, and with a Ce to Cu molar ratio of (3~5):1, Cu-modified CeO2 solid solution nanoflower cores were prepared by hydrothermal method. (2) Shell load and crystal formation Magnesium nitrate and aluminum nitrate were used as precursors, and the molar ratio of Mg to Al was (2.5~3.5):

1. The Mg-Al hydrotalcite precursor precipitate was grown in situ on the core surface by in-situ homogeneous precipitation method. After aging, washing, drying and calcination, the Mg-Al@Cu-Ce core-shell composite catalyst was finally obtained. Alternatively, using ammonium heptamolybdate and nickel nitrate as precursors, with a Mo to Ni molar ratio of (2.5~3.5):1, Ni-Mo precursor gel is in situ coated on the core surface using a sol-gel deposition coating method; after aging, washing, drying and calcining, the Ni-Mo@Cu-Ce core-shell composite catalyst is finally obtained.

4. The method for preparing a core-shell bifunctional catalyst according to claim 3, characterized in that, In step (1), urea is used as a precipitant and PVP is used as a surface dispersant in the hydrothermal method. After cerium nitrate and copper nitrate are dissolved and prepared into a homogeneous solution, the mixture is hydrothermally reacted at 130~150℃ for 5~7h. The product is washed, vacuum dried at 70~90℃, and calcined in air at 330~370℃ for 1.5~3h.

5. The method for preparing a core-shell bifunctional catalyst according to claim 3, characterized in that, In step (2), the in-situ uniform precipitation method uses urea as a precipitant and PVP as a surface regulator. The core is dispersed in water, and magnesium nitrate and aluminum nitrate are added to form a uniform dispersion. The mixture is stirred at a constant temperature of 80~95℃ for 5~7h and calcined in air atmosphere at 380~420℃ for 2.5~3.5h to obtain Mg-Al hydrotalcite composite oxide. In step (2), citric acid is used as a complexing agent in the sol-gel deposition coating method. The core is dispersed in anhydrous ethanol, and ammonium heptamolybdate and nickel nitrate are added to form a homogeneous system. The pH is adjusted to 3.5-4.0, and the reaction is carried out at a constant temperature of 55-65℃ to form a sol. The sol is then calcined in an air atmosphere at 430-470℃ for 2.5-3.5 hours to obtain Ni-Mo composite oxide.

6. The application of a core-shell bifunctional catalyst according to claim 1 or 2 in the removal of polymorphic sulfur and / or oxygen from gases.

7. A method for processing low-temperature methanol washing synthesis gas, characterized in that, Includes the following steps: Syngas produced from the low-temperature methanol washing process of the coal-to-methanol process is passed into a sulfur-oxygen co-purification device filled with the catalyst described in claim 1 or 2, so that sulfur-containing components and oxygen are removed from the syngas simultaneously to obtain purified syngas. The operating temperature is 180~400℃ and the operating pressure is 3.0~6.0MPa.

8. The method for processing low-temperature methanol washing synthesis gas according to claim 7, characterized in that, The operating temperature is 200~300℃ and the operating pressure is 3.5~4.5MPa.

9. A method for processing low-temperature methanol washing synthesis gas according to claim 7, characterized in that, The tail gas containing carbon dioxide and sulfur components generated in the low-temperature methanol washing process is mixed with the purified synthesis gas and then sent to the methanol synthesis tower; the volume ratio of tail gas to purified synthesis gas is 5% to 15%. Another portion of the exhaust gas is returned to the gasifier in the coal-to-methanol process as pulverized coal gas, or reused in the coal gasification unit during equipment maintenance.

10. A method for processing low-temperature methanol washing synthesis gas according to claim 7, characterized in that, The sulfur-containing components include one or more of hydrogen sulfide, carbonyl sulfide, carbon disulfide, methanethiol, and thiophene; the synthesis gas produced by the low-temperature methanol washing process also contains CO and H2.

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