A methanol catalyst with improved sulfur tolerance and a method for preparing the same

Abstract

This invention provides a catalyst for improving sulfur resistance and its preparation method. The catalyst is a synthetic carbon-shell encapsulated copper-zinc nanoparticle catalyst, where the synthetic carbon shell is a carrier encapsulated on the surface of a binary copper-zinc core, and the copper-zinc nanoparticles are the active centers. The catalyst composition, by mass, includes 30.0%–60.0% copper, 5.0%–25.0% zinc, and 10.0%–27.0% synthetic carbon shell. The preparation method involves first constructing a binary copper-zinc precursor using a co-precipitation method, and then depositing a carbon layer onto the surface of the copper-zinc catalyst. This invention modulates the electronic structure of the carbon layer material, constructing a carbon-encapsulated copper-zinc nanoparticle catalyst with a dual-channel structure, enhancing the interfacial interaction between the carbon layer and the core active components, and improving its sulfur resistance.

Description

Technical Field

[0001] This invention relates to a catalyst for improving sulfur resistance and its preparation method, belonging to the field of catalyst preparation technology. Background Technology

[0002] Methanol is an important chemical raw material and clean fuel with broad application prospects. Currently, Cu / ZnO or Cu / ZnO / Al2O3 methanol synthesis catalysts are mainly used in industrial production. The biggest problem with copper-based catalysts is their poor stability and short service life. One of the main reasons for poor stability and short service life is the catalyst's sensitivity to sulfur and its susceptibility to sulfur poisoning. The feed gas usually contains a small amount of sulfur, which reacts with the active metal components to form sulfides, leading to poisoning and deactivation of the active sites in methanol synthesis. As a preferred co-product chemical, methanol synthesis requires a feed gas sulfur content of <0.1 ppm, while power generation requires a sulfur content of ~50 ppm in coal-based syngas. Reducing the sulfur content of a large amount of coal-based syngas to 0.1 ppm would significantly reduce the overall energy efficiency and economics of the process. Therefore, research on sulfur-resistant methanol synthesis catalysts is of great significance.

[0003] Chinese patent CN108899507B discloses a core-shell structured bilayer carbon-coated metal sulfide composite electrode material. Small-sized metal sulfide nanoparticles are uniformly dispersed within a nitrogen-doped three-dimensional porous carbon support material, which helps prevent particle aggregation. At the same time, the uniformly deposited amorphous carbon layer on the surface further inhibits direct contact between the active material and the electrolyte, improving the cycling stability and high-rate performance of the composite material.

[0004] Chinese patent CN117753454B discloses a core-shell structure of pyrrole nitrogen-doped carbon shell-coated Fe3C core nanospheres prepared by microfluidic coprecipitation. By controlling the microfluidic reaction conditions, calcination yields stable iron carbide particles with a single phase, which are used in Fischer-Tropsch synthesis to produce high-efficiency liquid fuels and fine chemicals, exhibiting excellent performance.

[0005] However, most of the carbon-shell-encapsulated nanocatalysts prepared by the above-mentioned existing technologies have an eggshell structure, with uniformly dispersed carbon shells and concentrated pore size on the surface. They prevent particle aggregation through their stable core-shell structure, resulting in a single function. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a carbon-shell-encapsulated copper-zinc nanoparticle catalyst to improve the sulfur resistance of the methanol synthesis catalyst.

[0007] The methanol catalyst for improving sulfur resistance described in this invention is a synthetic carbon-shell encapsulated copper-zinc nanoparticle catalyst. The synthetic carbon shell is a carrier encapsulated on the surface of a binary copper-zinc core, and the copper-zinc nanoparticles are the active centers. The catalyst components, by mass, contain 30.0%–60.0% copper, 5.0%–25.0% zinc, and 10.0%–27.0% synthetic carbon shell.

[0008] The synthesized carbon shell is one of polypyrrole, melamine, citric acid, polysaccharide, and ethylenediaminetetraacetic acid.

[0009] The technical concept of the preparation method of the methanol catalyst with improved sulfur resistance described in this invention is to first construct a binary copper-zinc precursor using a co-precipitation method, and then deposit a carbon layer onto the surface of the copper-zinc catalyst. Specifically, it includes the following steps: 1) Dissolve one or two of sodium hydroxide, sodium bicarbonate or potassium hydroxide in deionized water, mix well, and prepare solution A with a total molar concentration of 0.1~1.5 mol / L; 2) Dissolve copper nitrate and zinc nitrate in deionized water in a certain proportion, mix well, and prepare solution B with a total molar concentration of 0.1~1.5 mol / L and a copper-zinc atomic molar ratio of 0.5~2.0; 3) In a stirred tank at 60~70℃, add the above solutions A and B dropwise simultaneously and continuously stir the reaction. The pH is maintained at around 9~10 throughout the process. Solution B is completely consumed. The amount of solution A is adjusted by pH control until the final pH is 9.5. 4) After aging and centrifuging the slurry obtained in step (3), wash the lower precipitate with deionized water until the pH of the supernatant is 7-8. 5) Dry the precipitate obtained in step (4) overnight to obtain the binary copper-zinc precursor; 6) Immerse the binary copper-zinc precursor in one of the following solutions: polypyrrole, melamine, citric acid aqueous solution, polysaccharide, or disodium EDTA. Then add an ethanol solution and ultrasonically stir until the ethanol evaporates to a paste. 7) The paste obtained in step (6) is dried, calcined, and then ground and granulated to obtain a methanol catalyst with improved sulfur resistance.

[0010] Further, step 4) involves aging at 60-70°C for 6-10 hours.

[0011] Further, step 5) involves drying at 120°C overnight.

[0012] Further, in step 6), ultrasonically stir at 60~80℃ for 12~24 hours.

[0013] Further, in step 7), the product is dried at 80°C and calcined at 500~800°C for 4 hours.

[0014] Furthermore, in step 7), the particle size of the granulation is 20-40 mesh.

[0015] This invention uses a binary copper-zinc core as a precursor and employs a deposition method to coat the surface of the synthesized nano-(pre)catalyst with a carbon layer, forming a dual-channel structure. This constructs a carbon-encapsulated copper-zinc nanoparticle catalyst with a dual-channel structure, allowing large-molecule H2S gas and small-molecule feed gas molecules to pass through different channels. The large molecules are adsorbed by the carbon shell, preventing them from entering the copper-zinc particles for reaction, effectively improving sulfur resistance. Compared with copper-zinc-aluminum catalysts prepared by traditional co-precipitation methods, the preparation method of this invention is simple and easy to implement, facilitating industrial scale-up. Under a sulfur-containing feed gas atmosphere, the methanol yield does not decrease significantly.

[0016] When applied to catalytic reaction processes, the encapsulation of active metal nanoparticle catalysts in a carbon support blocks their direct contact with sulfur-containing gases, effectively delaying and preventing catalyst deactivation. At the same time, the active valence electrons of the encapsulated nano-metal particles penetrate to the outer surface of the support through interaction with the carbon support, achieving highly efficient catalytic reactions. Attached Figure Description

[0017] Figure 1 This is a pore size distribution diagram of the methanol catalyst with improved sulfur resistance prepared in Example 1.

[0018] By preparing a catalyst with a dual-pore structure, different pore sizes can selectively allow the permeation of feed gas and H2S. Small pores less than 5 nm can allow the permeation of feed gas containing H2, CO, CO2, and N2, while blocking the kinetic macromolecule H2S. Large pores greater than 5 nm can adsorb H2S molecules to prevent them from entering the carbon shell and reducing the activity of copper-zinc nanoparticles. Detailed Implementation

[0019] The following specific examples are only used to further illustrate the technical solution of the present invention, and the effects of the method of the present invention are not limited thereto. Example 1

[0020] Preparation of Cu3Zn4 binary hydrotalcite precursor: Prepare a 0.5 mol / L aqueous solution of NaOH and NaHCO3 (molar ratio 1:1), denoted as A; weigh 7.26 g of copper nitrate trihydrate and 11.90 g of zinc nitrate hexahydrate and dissolve them in 100 mL of aqueous solution, denoted as B; in a stirred tank at 60-70℃, simultaneously add the above solutions A and B dropwise, continuously stirring the reaction and controlling the pH to be maintained at around 9-10; age the resulting slurry at 60-70℃ for 6-10 hours, centrifuge, and wash the lower precipitate with deionized water until the pH of the supernatant is 7-8; dry the precipitate at 120℃ overnight to obtain the binary copper-zinc precursor.

[0021] Preparation of methanol catalysts to improve sulfur resistance: The binary copper-zinc precursor was immersed in 50 mL of polypyrrole and 100 mL of ethanol solution, ultrasonically stirred at 60–80 °C for 12–24 hours, evaporated to a paste, dried at 80 °C overnight, and calcined at 500 °C for 4 hours. After grinding and granulation (20–40 mesh), carbon-coated nano-copper-zinc catalyst 1 was obtained. Example 2

[0022] Preparation of Cu3Zn4 binary hydrotalcite precursor by coprecipitation method Prepare a 0.5 mol / L aqueous solution of NaOH and NaHCO3 (molar ratio 1:1), denoted as A; weigh 7.26 g of copper nitrate trihydrate and 11.90 g of zinc nitrate hexahydrate and dissolve them in 100 mL of aqueous solution, denoted as B; in a stirred tank at 60-70℃, simultaneously add the above solutions A and B dropwise, continuously stirring the reaction and controlling the pH to be maintained at around 9-10; age the resulting slurry at 60-70℃ for 6-10 hours, centrifuge, and wash the lower precipitate with deionized water until the pH of the supernatant is 7-8; dry the precipitate at 120℃ overnight to obtain the binary copper-zinc precursor.

[0023] Preparation of methanol catalysts to improve sulfur resistance: Weigh 20 g of melamine, immerse the binary copper-zinc precursor in melamine and 100 mL of ethanol solution, and ultrasonically stir at 60-80 °C for 12-24 hours. Evaporate the ethanol to a paste, dry at 80 °C overnight, and calcine at 500 °C for 4 hours. After grinding and granulation (20-40 mesh), carbon-coated nano-copper-zinc catalyst 2 is obtained. Example 3

[0024] Preparation of Cu3Zn4 binary hydrotalcite precursor Prepare a 0.5 mol / L aqueous solution of NaOH and NaHCO3 (molar ratio 1:1), denoted as A; weigh 7.26 g of copper nitrate trihydrate and 11.90 g of zinc nitrate hexahydrate and dissolve them in 100 mL of aqueous solution, denoted as B; in a stirred tank at 60-70℃, simultaneously add the above solutions A and B dropwise, continuously stirring the reaction and controlling the pH to be maintained at around 9-10; age the resulting slurry at 60-70℃ for 6-10 hours, centrifuge, and wash the lower precipitate with deionized water until the pH of the supernatant is 7-8; dry the precipitate at 120℃ overnight to obtain the binary copper-zinc precursor.

[0025] Preparation of methanol catalysts to improve sulfur resistance: Prepare a 0.5 mol / L citric acid aqueous solution. Immerse the binary copper-zinc precursor in 50 mL of citric acid aqueous solution and 100 mL of ethanol solution. Sonicate the mixture at 60–80 °C for 12–24 hours. Evaporate the ethanol to a paste state, dry at 80 °C overnight, and calcine at 500 °C for 4 hours. Then grind and granulate (20–40 mesh) to obtain carbon-coated nano-copper-zinc catalyst 3. Example 4

[0026] Preparation of Cu3Zn4 binary hydrotalcite precursor Prepare a 0.5 mol / L aqueous solution of NaOH and NaHCO3 (molar ratio 1:1), denoted as A; weigh 7.26 g of copper nitrate trihydrate and 11.90 g of zinc nitrate hexahydrate and dissolve them in 100 mL of aqueous solution, denoted as B; in a stirred tank at 60-70℃, simultaneously add the above solutions A and B dropwise, continuously stirring the reaction and controlling the pH to be maintained at around 9-10; age the resulting slurry at 60-70℃ for 6-10 hours, centrifuge, and wash the lower precipitate with deionized water until the pH of the supernatant is 7-8; dry the precipitate at 120℃ overnight to obtain the binary copper-zinc precursor.

[0027] Preparation of methanol catalysts to improve sulfur resistance: Weigh 20g of polysaccharide, immerse the binary copper-zinc precursor in a polysaccharide and 100mL ethanol solution, and ultrasonically stir at 60-80℃ for 12-24 hours. Evaporate the ethanol to a paste, dry at 80℃ overnight, and calcine at 500℃ for 4 hours. Then grind and granulate (20-40 mesh) to obtain carbon-coated nano-copper-zinc catalyst 4. Example 5

[0028] Preparation of Cu3Zn4 binary hydrotalcite precursor Prepare a 0.5 mol / L aqueous solution of NaOH and NaHCO3 (molar ratio 1:1), denoted as A; weigh 7.26 g of copper nitrate trihydrate and 11.90 g of zinc nitrate hexahydrate and dissolve them in 100 mL of aqueous solution, denoted as B; in a stirred tank at 60-70℃, simultaneously add the above solutions A and B dropwise, continuously stirring the reaction and controlling the pH to be maintained at around 9-10; age the resulting slurry at 60-70℃ for 6-10 hours, centrifuge, and wash the lower precipitate with deionized water until the pH of the supernatant is 7-8; dry the precipitate at 120℃ overnight to obtain the binary copper-zinc precursor.

[0029] Preparation of methanol catalysts to improve sulfur resistance: Prepare a 0.5 mol / L solution of disodium ethylenediaminetetraacetate (EDTA). Immerse the binary copper-zinc precursor in 50 mL of the disodium EDTA and 100 mL of ethanol solution. Sonicate the mixture at 60–80 °C for 12–24 hours. Evaporate the ethanol to a paste consistency, dry at 80 °C overnight, and calcine at 500 °C for 4 hours. Then grind and granulate (20–40 mesh) to obtain the carbon-coated nano-copper-zinc catalyst 5.

[0030] Comparative Example: Prepared Copper-Zinc-Aluminum Catalyst Prepare a 0.5 mol / L aqueous solution of NaOH and NaHCO3 (molar ratio 1:1), denoted as A. Weigh 7.26 g of copper nitrate trihydrate, 11.90 g of zinc nitrate hexahydrate, and 3.75 g of aluminum nitrate nonahydrate and dissolve them in 100 mL of aqueous solution, denoted as B. In a stirred tank at 60-70℃, simultaneously add solutions A and B dropwise, continuously stirring and maintaining the pH at approximately 9-10. Age the resulting slurry at 60-70℃ for 6-10 hours, centrifuge, and wash the lower precipitate with deionized water until the pH of the supernatant is 7-8. Dry the precipitate at 120℃ overnight and calcine at 500℃ for 4 hours. After grinding and granulation (20-40 mesh), the comparative catalyst is obtained.

[0031] Activity testing conditions: The catalyst loading was 4 mL. Pre-reduction of the catalyst was performed in a fixed-bed reactor at 250℃ and atmospheric pressure with 5 vol% H₂-N₂ overnight. The gas was converted to N₂, purged, and the reaction pressure was increased to 3–5 MPa. The temperature was maintained at 250℃, and after purging for 1 hour, it was converted to syngas. The syngas composition was 15% CO₂, 5% CO, 10% N₂, and 69% H₂. The activity of the CO₂-rich catalytic conversion to methanol was evaluated under the conditions of 250℃, 3–5 MPa, and a space velocity of 10000 h⁻¹, and the initial space-time yield was measured. After treatment in 0.05% H₂S / N₂ for 2 hours, the initial test conditions were returned, and the space-time yield after sulfur tolerance was measured.

[0032] The activity evaluation results are shown in Table 1: Table 1 Activity evaluation results catalyst <![CDATA[Initial activity space-time yield [g / (mL cat ·h)]]]> <![CDATA[Sulfur tolerance, space-time yield [g / (mL cat ·h)]]]> Activity decay rate [%] Example 1 0.86 0.65 24.42 Example 2 0.35 0.19 45.71 Example 3 0.67 0.45 32.84 Example 4 0.23 0.13 43.48 Example 5 0.57 0.35 38.60 Comparative Example 0.95 0.24 74.74 As shown in Table 1 above, the catalyst with polypyrrole as the carbon shell has the lowest activity decay rate after sulfur resistance and the best sulfur resistance performance. The comparative example is the copper-zinc-aluminum coprecipitation catalyst, which has high initial activity but poor activity after sulfur resistance.

[0033] As is known from common technical knowledge, this invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative in all respects and are not the only ones. All modifications within the scope of this invention or its equivalents are included in this invention.

Claims

1. A methanol catalyst for improving sulfur resistance, characterized in that... The catalyst is a synthetic carbon-shell encapsulated copper-zinc nanoparticle catalyst, wherein the synthetic carbon shell is a carrier encapsulated on the surface of a binary copper-zinc core, and the copper-zinc nanoparticles are the active centers. The catalyst components, by mass, contain 30.0% to 60.0% copper, 5.0% to 25.0% zinc, and 10.0% to 27.0% synthetic carbon shell.

2. The methanol catalyst for improving sulfur resistance as described in claim 1, characterized in that: The synthesized carbon shell is one of polypyrrole, melamine, citric acid, polysaccharide, and ethylenediaminetetraacetic acid.

3. The method for preparing the methanol catalyst with improved sulfur resistance according to any one of claims 1 to 2, characterized in that... Includes the following steps: 1) Dissolve one or two of sodium hydroxide, sodium bicarbonate or potassium hydroxide in deionized water, mix well, and prepare solution A with a total molar concentration of 0.1~1.5 mol / L; 2) Dissolve copper nitrate and zinc nitrate in deionized water in a certain proportion, mix well, and prepare solution B with a total molar concentration of 0.1~1.5 mol / L and a copper-zinc atomic molar ratio of 0.5~2.0; 3) In a stirred tank at 60~70℃, add the above solutions A and B dropwise simultaneously and continuously stir the reaction. The pH is maintained at around 9~10 throughout the process. Solution B is completely consumed. The amount of solution A is adjusted by pH control until the final pH is 9.

5. 4) After aging and centrifuging the slurry obtained in step (3), wash the lower precipitate with deionized water until the pH of the supernatant is 7-8. 5) Dry the precipitate obtained in step (4) overnight to obtain the binary copper-zinc precursor; 6) Immerse the binary copper-zinc precursor in one of the following solutions: polypyrrole, melamine, citric acid aqueous solution, polysaccharide, or disodium EDTA. Then add an ethanol solution and ultrasonically stir until the ethanol evaporates to a paste. 7) The paste obtained in step (6) is dried, calcined, and then ground and granulated to obtain a methanol catalyst with improved sulfur resistance.

4. The preparation method according to claim 3, characterized in that... Step 4) Aging at 60~70℃ for 6~10 hours.

5. The preparation method according to claim 3, characterized in that... Step 5) Dry overnight at 120°C.

6. The preparation method according to claim 3, characterized in that... Step 6) Stir ultrasonically at 60~80℃ for 12~24 hours.

7. The preparation method according to claim 3, characterized in that... Step 7) Dry at 80℃ and calcine at 500~800℃ for 4 hours.

8. The preparation method according to claim 3, characterized in that... Step 7) The particle size of the granulation is 20-40 mesh.

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