Method for preparing green catalyst for methanol synthesis by flame spray pyrolysis

Abstract

The invention provides a method for preparing a green methanol synthesis catalyst through flame spray pyrolysis, which comprises the following steps: (1) uniformly mixing an organic acid solvent and an alcohol solvent according to a volume ratio of 1: 1 at room temperature to obtain a mixed solvent; then, precursor salt containing copper, zinc and zirconium elements is added into the mixed solvent, heating and stirring are conducted in an oil bath, the precursor salt is fully dissolved, and a mixed precursor salt solution is obtained; (2) transferring the mixed precursor salt solution into a flame spray pyrolysis reactor, injecting the mixed precursor salt solution into high-temperature flame through a flame nozzle, and atomizing the mixed precursor salt solution by using surrounding oxygen dispersion gas so as to pyrolyze the mixed precursor salt solution in the high-temperature flame to form nano oxide particles; the high-temperature flame is generated by combustion of premixed gas composed of CH4 / O2, and compressed air around the flame serves as sheath gas to be used for stabilizing reaction airflow; the pyrolytic reaction is carried out under the pressure of 850 to 950 mbar; and (3) collecting to obtain the green catalyst for methanol synthesis.

Description

Technical Field

[0001] The invention relates to the field of methanol synthesis, and in particular to a method for preparing a catalyst for green methanol synthesis by flame spray pyrolysis. Background Art Methanol is a liquid at room temperature and pressure. It can be used to produce olefins, formaldehyde, acetic acid, etc. It can also be directly mixed with gasoline to produce methyl tert-butyl ether (MTBE), biodiesel, dimethyl ether, etc. It is an important chemical raw material and fuel. In 2023, the domestic methanol production capacity has exceeded 100 million tons. The traditional method of synthesizing methanol is mainly to use synthesis gas (CO / H2) to produce methanol, of which coal-to-methanol accounts for about 80%, natural gas-to-methanol accounts for about 10%, and coke oven gas-to-methanol accounts for about 10%. The reaction of synthesizing methanol from synthesis gas is a highly exothermic reaction (90.8kJ / mol), which has high requirements on the heat transfer performance of the reactor and the heat resistance of the catalyst.

[0003] In recent years, the technology of CO2 catalytic synthesis of methanol has attracted widespread attention, especially the technology of preparing green methanol from renewable CO2 and green hydrogen. Green methanol has attracted much attention as a liquid fuel for ships and has developed rapidly. The reaction of CO2 hydrogenation to prepare methanol has a low heat release, but it will produce a large amount of water as a by-product, resulting in rapid catalyst deactivation and high requirements for the hydrothermal resistance of the catalyst. In addition, due to the side reaction of the reverse water gas shift, the selectivity of methanol is low.

[0004] Therefore, the performance of the catalyst used for methanol synthesis plays a key role in methanol production. The existing technology often uses Cu / ZnO / Al2O3 ternary methanol synthesis catalyst, in which Cu is the active component, the Cu / ZnO interface is the real active site, and Al2O3 is used as a carrier to improve the dispersion and stability of Cu, but the hydrothermal resistance needs to be further improved.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a method for preparing a catalyst for green methanol synthesis by flame spray pyrolysis.

[0007] The basic concept of the technical solution of the present invention is as follows: A method for preparing a catalyst for green methanol synthesis by flame spray pyrolysis comprises the following steps: (1) mixing an organic acid solvent and an alcohol solvent at a volume ratio of 1:1 at room temperature to obtain a mixed solvent; then adding a precursor salt containing copper, zinc and zirconium elements to the mixed solvent, heating and stirring in an oil bath to fully dissolve the precursor salt to obtain a mixed precursor salt solution; (2) The mixed precursor salt solution is transferred to a flame spray pyrolysis reactor and injected into a high-temperature flame through a flame nozzle, and the mixed precursor salt solution is atomized by the surrounding oxygen dispersion gas, so as to be pyrolyzed in the high-temperature flame to form nano-oxides; the high-temperature pilot flame is generated by the combustion of a premixed gas composed of CH4 / O2, and the compressed air around the flame is used as a sheath gas to stabilize the reaction gas flow; the pyrolysis reaction is carried out at a pressure of 850 to 950 mbar; (3) Collecting and obtaining the green methanol synthesis catalyst.

[0008] As an implementation mode, the total concentration of the mixed precursor salt solution is 0.1-0.5 mol / L; the molar ratio of copper: zinc: zirconium elements is 6: (2-4): (1-2).

[0009] As an embodiment, the precursor salt of copper is selected from copper nitrate trihydrate, copper acetate monohydrate or copper 2-ethylhexanoate; the precursor salt of zinc is selected from zinc nitrate hexahydrate, zinc acetate dehydrate or zinc 2-ethylhexanoate; the precursor salt of zirconium is selected from a solvent oil solution of zirconium oxynitrate hydrate or 2-ethylhexanoic acid zirconium oxysalt.

[0010] As an embodiment, in step (2), the atomization method is: the flow rate of the mixed precursor salt solution is 2 to 4 mL / min, and the flow rate of the oxygen dispersion gas is 4 to 8 slm.

[0011] As an implementation manner, the flow rate of methane in the high-temperature pilot flame is 2-4 slm, the flow rate of oxygen is twice the flow rate of methane; and the flow rate of sheath gas is 100-200 slm.

[0012] As an embodiment, in step (1), the organic acid solvent is propionic acid, and the alcohol solvent is n-propanol.

[0013] The present invention provides a green methanol synthesis catalyst, which is prepared by any one of the methods described above.

[0014] Compared with the prior art, the present invention has the following advantages: 1. The Cu / ZnO / ZrO2 ternary green methanol catalyst prepared by the method of the present invention retains the advantages of high activity and high selectivity of Cu / ZnO-based catalysts; at the same time, ZrO2 as a carrier has stronger hydrophobicity than Al2O3, thereby improving the hydrothermal resistance of the catalyst.

[0015] 2. The flame spray pyrolysis (FSP) method has the advantages of flexibility, rapidity and scalability. This method can achieve uniform mixing of different components of Cu, Zn and Zr at the nanoscale.

[0016] 3. The nanoparticles of the Cu / ZnO / ZrO2 ternary catalyst prepared by flame spray pyrolysis are small and evenly distributed, showing excellent catalytic performance in the green methanol synthesis process. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings are used to provide a further understanding of the technical solution of the present invention and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of the present invention and do not constitute a limitation on the technical solution of the present invention.

[0018] Figure 1 Schematic diagram of the structure of the flame spray pyrolysis reactor used in the method of the present invention.

[0019] Figure 2 is a TEM image of the catalyst prepared in Example 1.

[0020] Figure 3 This is the EDX elemental analysis diagram of the catalyst prepared in Example 1.

[0021] Labels in the figure: 1-rotary vane pump; 2-filter; 3-particle collection device; 4-nano oxide particles; 5-jet flame; 6-ignition flame; 7-flame nozzle; 8-sintered bronze; 9-mass flow meter. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Figure 1 It is a simplified structural diagram of a flame spray pyrolysis reactor specifically used in the present invention. It is a conventional instrument sold on the market and is only used to assist understanding. Other similar types of flame spray pyrolysis reactors can also be used instead without affecting the realization of the basic effects of the present invention.

[0024] Example 1 A method for preparing a catalyst for green methanol synthesis by flame spray pyrolysis comprises the following steps: (1) At room temperature, propionic acid and n-propanol were added to a glass flask in a volume ratio of 1:1 and mixed evenly to obtain a mixed solvent. Then, appropriate amounts of copper nitrate trihydrate, zinc nitrate hexahydrate and zirconium oxynitrate hydrate were added to the mixed solvent, heated in an oil bath at 60°C and stirred for 1 hour to fully dissolve the precursor salts, and a mixed precursor salt solution with a total metal concentration of 0.2 mol / L was obtained, wherein the molar ratio of Cu:Zn:Zr was 6:3:1; (2) Then, the mixed precursor salt solution is transferred to a flame spray pyrolysis reactor (the schematic diagram of the device is shown in FIG. Figure 1 As shown), the mixed solution is injected into the high-temperature flame through the flame nozzle 7 at a flow rate of 3 mL / min by a pump, and the mixed precursor solution is atomized at a flow rate of 6 slm using oxygen as a dispersion gas, so that the nano oxide particles 4 are pyrolyzed at the injection flame 5 in the high-temperature flame. The high-temperature flame is generated by the combustion of a premixed gas composed of CH4 / O2 (flow rates of 2 slm and 4 slm, respectively), and the compressed air around the flame (flow rate of 1 70 slm) is used as a sheath gas to stabilize the reaction gas flow. The pyrolysis reaction is carried out at a pressure of 900 mbar; (3) The particle collection device 3 located below the filter 2 collects the particles to obtain the green methanol synthesis catalyst.

[0025] The obtained green methanol synthesis catalyst was characterized. Figure 2 and Figure 3 They are respectively a transmission electron microscope image and an EDX elemental analysis image of the catalyst of Example 1 of the present invention.

[0026] From the electron microscope image, it can be seen that the nano-crystals of the Cu / ZnO / ZrO2 ternary catalyst prepared by flame spray pyrolysis are small, generally distributed around 5nm. From the EDX elemental analysis image, it can be found that the elements Cu, Zn, Zr, and O are evenly distributed on the catalyst, indicating that the dispersion of each component is good.

[0027] Example 2 Compared with Example 1, the molar ratio of Cu:Zn:Zr in the mixed precursor salt solution is 6:2:1, and other conditions are the same as those in Example 1.

[0028] Example 3 Compared with Example 1, the molar ratio of Cu:Zn:Zr in the mixed precursor salt solution is 6:4:2, and other conditions are the same as those in Example 1.

[0029] Example 4 Compared with Example 1, the precursor salts of Cu, Zn and Zr are 2-ethylhexanoate copper, 2-ethylhexanoate zinc and 2-ethylhexanoate zirconium oxide, respectively, and other conditions are the same as those in Example 1.

[0030] Comparative Example 1 The difference from Example 1 is that no precursor salt of zirconium element is added to the mixed precursor solution in step (1).

[0031] Comparative Example 2 The difference from Example 1 is that no precursor salt of zinc element is added to the mixed precursor solution in step (1).

[0032] Effect Example 1 In a self-built evaluation device, the performance of the methanol catalysts of Examples 1-4 and Comparative Examples 1-2 when used for producing green methanol by hydrogenation of carbon dioxide was systematically evaluated.

[0033] 1. Catalyst reduction conditions: The catalyst was reduced in a H2 atmosphere (volume ratio: 5% H2 + 95% N2) at a reduction space velocity of 5000 h -1 , pressure 10 bar, temperature 300°C, 1 hour, heating rate 5°C / min.

[0034] 2. Catalytic evaluation reaction conditions: The volume ratio of H2:CO2:N2 in the reaction mixture is 72:24:4, the catalyst particle size is 20-40 mesh, the volume is 1 mL, the pressure is 30 bar, the temperature is 250 ° C, and the space velocity is 5000 h -1 .

[0035] The liquid product was sampled once every 3 hours, weighed and the yield was calculated. After three samplings, the heat resistance procedure was started, the temperature was raised to 380°C and maintained for 5 hours. After the heat resistance was completed, the temperature was lowered to 250°C and the evaluation was continued for 6 hours. The heat resistance retention rate was the ratio of the liquid phase yield of the catalyst before and after heat resistance.

[0036] 3. Analysis method: Quantitative detection by gas chromatography, automatic injection, H2 as carrier gas, N2 as pneumatic valve driving gas, TDX-01 as chromatographic column, Porapak Q as chromatographic column for liquid product analysis, TCD detector, injection port temperature of 120°C, column temperature of 90°C, and detector temperature of 150°C.

[0037] The main products of the reaction are green methanol and carbon monoxide. The catalytic performance of the catalyst in the production of green methanol by hydrogenation of carbon dioxide is shown in Table 1. CO2 It represents the conversion rate of CO2, S CH3OH and S CO are the selectivities for green methanol and carbon monoxide, respectively.

[0038] The results in Table 1 show that: The catalyst prepared by flame pyrolysis has excellent catalytic performance in the process of producing green methanol by hydrogenation of carbon dioxide, such as high CO2 conversion rate and heat retention rate. This is mainly due to the fact that the catalyst prepared by flame pyrolysis has a smaller particle size and better dispersion of active components.

[0039] Comparison of Example 4 with Example 1 shows that, compared with the organic salt precursor, the catalyst prepared using nitrate as a precursor has better catalytic performance, such as higher carbon dioxide conversion rate and heat resistance retention rate.

[0040] Comparison between Comparative Example 1 and Example 1 shows that the introduction of zirconium element improves the catalytic performance, especially the heat resistance retention rate of the catalyst is significantly improved, which is mainly due to the fact that zirconium dioxide improves the hydrothermal resistance of the catalyst.

[0041] Comparison of Comparative Example 2 with Example 1 shows that the introduction of zinc element has a significant improvement effect on the catalytic performance, especially the conversion rate of carbon dioxide, which indirectly verifies that the Cu / ZnO interface in the Cu / ZnO / ZrO2 ternary green methanol synthesis catalyst is the real active site.

[0042] Table 1

[0043] Although the embodiments disclosed in the present invention are as above, the contents described are only embodiments adopted to facilitate understanding of the present invention and are not intended to limit the present invention. Any technician in the field to which the present invention belongs can make any modifications and changes in the form and details of implementation without departing from the spirit and scope disclosed in the present invention, but the patent protection scope of the present invention shall still be subject to the scope defined in the attached claims.

Claims

1. A method for preparing a catalyst for green methanol synthesis by flame spray pyrolysis, comprising the following steps: (1) uniformly mixing an organic acid solvent and an alcohol solvent at a volume ratio of 1:1 at room temperature to obtain a mixed solvent; subsequently, adding a precursor salt containing copper, zinc and zirconium elements to the mixed solvent, heating and stirring in an oil bath to fully dissolve the precursor salt, and obtaining a mixed precursor salt solution; (2) The mixed precursor salt solution is transferred to a flame spray pyrolysis reactor and injected into a high-temperature flame through a flame nozzle, and the mixed precursor salt solution is atomized by the surrounding oxygen dispersion gas, so as to be pyrolyzed in the high-temperature flame to form nano-oxides; the high-temperature flame is generated by the combustion of a premixed gas composed of CH4 / O2, and the compressed air around the flame is used as a sheath gas to stabilize the reaction gas flow; the pyrolysis reaction is carried out at a pressure of 850~950mbar; (3) Collecting and obtaining the green methanol synthesis catalyst.

2. The method for preparing a catalyst for green methanol synthesis by flame spray pyrolysis according to claim 1, characterized in that: The total concentration of the mixed precursor salt solution is 0.1~0.5 mol / L; the molar ratio of copper: zinc: zirconium elements is 6: (2~4): (1~2).

3. The method for preparing a catalyst for green methanol synthesis by flame spray pyrolysis according to claim 1, characterized in that: The precursor salt of copper is selected from copper nitrate trihydrate, copper acetate monohydrate or copper 2-ethylhexanoate; the precursor salt of zinc is selected from zinc nitrate hexahydrate, zinc acetate dehydrate or zinc 2-ethylhexanoate; the precursor salt of zirconium is selected from solvent oil solution of zirconyl nitrate hydrate or 2-ethylhexanoic acid zirconyl salt.

4. The method for preparing a catalyst for green methanol synthesis by flame spray pyrolysis according to claim 1, characterized in that: In step (2), the atomization method is: the flow rate of the mixed precursor salt solution is 2-4 mL / min, and the flow rate of the oxygen dispersion gas is 4-8 slm.

5. The method for preparing a catalyst for green methanol synthesis by flame spray pyrolysis according to claim 1, characterized in that: The flow rate of methane in the high-temperature pilot flame is 2-4 slm, the flow rate of oxygen is twice that of methane; the flow rate of sheath gas is 100-200 slm.

6. The method for preparing a catalyst for green methanol synthesis by flame spray pyrolysis according to claim 1, characterized in that: In the step (1), the organic acid solvent is propionic acid, and the alcohol solvent is n-propanol.

7. A catalyst for green methanol synthesis, characterized in that: Prepared by the method according to any one of claims 1 to 6.

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