Ammonia distillation-polymerization carbonization one-step preparation method and application of carbon-modified copper-silicon catalyst

Abstract

The invention relates to an ammonia distillation-polymerization carbonization one-step preparation method and application of a carbon-modified copper-silicon catalyst. According to the method, carbon is introduced through aldol condensation on the basis of an ammonia distillation method Cu / SiO2 catalyst, and a carbon modified Cu / Si C-x catalyst is prepared; the proper carbon content can promote dispersion of copper on the surface, increase the proportion of Cu < + > / (Cu < + > + Cu0) and remarkably increase the number of Cu < + > sites on the surface of the catalyst, so that the catalytic performance of the catalyst is improved. According to the method, the purpose of carbon modification is achieved without any template agent or acid-base etching agent, a good methyl laurate hydrogenation effect is achieved, and meanwhile the catalyst preparation process is environmentally friendly.

Description

Technical field:

[0001] The present invention relates to the field of industrial catalysis, and in particular to a method for preparing a carbon-modified copper silicon catalyst by ammonia vaporization polymerization-carbonization. Background technology:

[0002] The history of human progress and development is also the history of energy development. In today's context of economic globalization and rapid economic growth, energy issues have become a major challenge facing human society. Currently, traditional fossil fuels still dominate. Although their share of consumption continues to decline in 2023, they still account for 81.8% of total energy consumption. High carbon emissions and significant environmental pressures pose urgent challenges that need to be addressed. As a renewable carbon source, biomass energy, with its zero-carbon cycle characteristics and diverse applications, is reshaping the energy landscape.

[0003] Achieving the efficient utilization of biomass energy is a key topic in the field of fatty alcohol synthesis. Fatty alcohols are alcohol compounds composed of a hydroxyl group linked to an aliphatic hydrocarbon group. Their molecular structure, characterized by both hydrophilic hydroxyl groups and hydrophobic hydrocarbon groups, gives them excellent interfacial activity and emulsifying properties, leading to their widespread application in the chemical, pharmaceutical, and food processing industries.

[0004] Due to their unique structure, fatty alcohols have important applications in a wide range of fields, and their consumption is increasing year by year. With the development of human society and the pursuit of green chemistry, traditional synthetic fatty alcohol processes are gradually being replaced by emerging natural fatty alcohol processes. Within natural fatty alcohol processes, fatty acid ester hydrogenation has become a current research focus due to its mild reaction conditions, low cost, and strong environmental performance.

[0005] Due to the difficulty in separating homogeneous catalysts and the high cost of supported precious metal catalysts, current catalyst research in fatty acid ester hydrogenation processes has focused on supported non-precious metal catalysts. Copper-based catalysts have garnered widespread attention due to their excellent hydrogenation performance and high selectivity for alcohols. However, copper-based catalysts suffer from structural instability at high temperatures, significantly impacting their ester hydrogenation activity and stability. Summary of the invention:

[0006] The purpose of this invention is to address the limitations of current technologies and provide a method for preparing a carbon-modified copper-silicon catalyst by ammonia vapor polymerization-carbonization. This method introduces carbon into the Cu / SiO2 catalyst prepared by ammonia vaporization through aldol condensation to prepare a carbon-modified Cu / Si@Cx catalyst. The appropriate carbon content can promote the dispersion of surface copper and improve the Cu + / (Cu + +Cu 0 ) ratio, significantly increasing the Cu +Compared with the existing technology, the present invention does not require any template or acid-base etchant to achieve the purpose of carbon modification. While achieving good methyl laurate hydrogenation effect, the catalyst preparation process is environmentally friendly.

[0007] The technical solution adopted by the present invention to solve its technical problem is:

[0008] A one-step preparation method of a carbon-modified copper-silicon catalyst by ammonia evaporation-polymerization carbonization comprises the following steps:

[0009] (1) Ammonia water is added to a copper nitrate solution to adjust the pH value of the solution to 11, and then the solution is reacted at room temperature in a water bath with stirring for 30 to 60 minutes to obtain a copper ammonia solution; silica sol is then added dropwise thereto, and the stirring is continued for 12 to 20 hours, and then the temperature is raised to 80 to 100° C. to evaporate ammonia until the pH value of the solution is 7, and the upper liquid is removed to obtain a copper silicon catalyst matrix;

[0010] Among them, add 7-25 ml of silica sol to every 100 ml of copper nitrate solution;

[0011] The concentration of copper nitrate solution is 0.2-0.5 mol / L;

[0012] (2) The copper-silicon catalyst precursor obtained in the previous step is mixed with water, and then a phenolic substance, formaldehyde solution, and anhydrous sodium carbonate are added, and polymerization is carried out at 30-50° C. for 4-8 hours. The obtained solid is dried in an oven at 70-100° C. overnight, and then carbonized in a tube furnace under an argon atmosphere at 400-600° C. for 2-6 hours to obtain a carbon-modified copper-silicon catalyst;

[0013] For every 5g of copper-silicon catalyst precursor, 0.015-0.15g of phenolic substance, 0.0211-0.211g of formaldehyde solution, and 0.004-0.04g of anhydrous sodium carbonate are added; for every 5g of copper-silicon catalyst precursor, 3-10ml of water is added;

[0014] The phenolic substance is resorcinol or phenol.

[0015] The carbon-modified copper-silicon catalyst prepared by the method is used as a catalyst in the hydrogenation reaction of methyl laurate.

[0016] The specific steps include: using an intermittent reactor, loading the carbon-modified copper-silicon catalyst, the reaction raw material methyl laurate and the solvent n-hexane; replacing the air in the reactor with nitrogen, then pressurizing it with hydrogen at 4-6 MPa, heating it to 190-220° C., and the reaction space velocity is 0.5-1 h -1 , to obtain lauryl alcohol.

[0017] The stirring speed is 600-800 rpm, and the heating rate is 2-5°C / min;

[0018] The catalyst must be reduced in a tubular furnace at 250-350° C. under a hydrogen atmosphere for 2-6 hours before being loaded into the kettle, and passivated with 1% O 2 -Ar for 30-60 minutes before being taken out.

[0019] The essential features of the present invention are:

[0020] During the preparation of copper-silicon catalysts by the ammonia evaporation method, a carbon component is introduced through the aldol condensation reaction of the hydroxyl group of phenolic substances and the aldehyde group of formaldehyde under alkaline conditions, and further carbonization is performed to prepare a carbon-modified copper-silicon catalyst.

[0021] The beneficial effects of the present invention are:

[0022] The preparation process of the present invention is simple and has low production cost. On the basis of the copper-silicon catalyst prepared by the traditional ammonia distillation method, the modification of an appropriate amount of carbon can promote the dispersion of surface copper and improve the Cu + / (Cu + +Cu 0 ) ratio and Cu on the catalyst surface + The number of sites increases, thereby improving the catalyst's catalytic performance. When applied to the hydrogenation of methyl laurate to lauryl alcohol, the Cu / Si@C-1 catalyst achieved a space-time yield of 0.45 g / (g catalyst h) for lauryl alcohol at a carbon content of 1 wt.%, 1.5 times that of the Cu / SiO2 catalyst. This demonstrates a significant advantage in the hydrogenation of methyl laurate over the Cu / SiO2 catalyst. Description of the drawings:

[0023] Figure 1 is the X-ray diffraction (XRD) pattern of the catalyst after reduction in Examples 1 to 5;

[0024] Figure 2 TEM images and particle size statistics of the catalysts after reduction in Examples 1 to 5;

[0025] Figure 3 These are the evaluation results of the catalysts in Examples 1 to 5. Specific implementation method:

[0026] Example 1

[0027] Preparation of Cu / SiO2 catalyst

[0028] The copper-silicon catalyst was prepared by the ammonia evaporation method.

[0029] 21mmol of copper nitrate trihydrate was placed in a 500ml three-necked round-bottom flask, 100ml of deionized water was added to dissolve it, and then the pH of the solution was adjusted to 11 with ammonia water. The round-bottom flask was placed in a water bath and stirred at room temperature for 30 minutes to fully mix the copper nitrate and ammonia water to form a copper ammonia solution. 15ml of silica sol was slowly added dropwise to the round-bottom flask and continued to age and stir for 12 hours. Ammonia was then evaporated at 80°C, and the pH value of the solution was continuously monitored during the process until the pH reached 7. The obtained solid was dried in an oven at 80°C overnight and then calcined at 500°C for 2 hours in a tube furnace under an argon atmosphere. A Cu / SiO2 catalyst was obtained.

[0030] Example 2

[0031] Preparation of Cu / Si@C-0.5 catalyst

[0032] Carbon-modified copper-silicon catalyst was prepared by ammonia evaporation polymerization followed by carbonization.

[0033] Place 21mmol of copper nitrate trihydrate in a 500ml three-necked round-bottom flask, add 100ml of deionized water to dissolve it, and then use ammonia water (25%) to adjust the pH of the solution to 11. Place the round-bottom flask in a water bath and stir at room temperature for 30 minutes to fully mix the copper nitrate and ammonia water to form a copper ammonia solution. Slowly add 15ml of silica sol (30%) to the round-bottom flask and continue aging and stirring for 12 hours. Then, evaporate ammonia at 80°C, and continuously monitor the pH value of the solution during the process until the pH is 7. Remove the remaining water in the upper layer, and add the 5g solid obtained back to the round-bottom flask, use 5mL of deionized water to mix with the solid, and stir until the filter cake and deionized water are evenly mixed. Add 0.015g of resorcinol, 0.0211g of formaldehyde solution (37%), and 0.004g of anhydrous sodium carbonate, and polymerize at 38°C for 4 hours. The obtained solid was dried in an oven at 80° C. overnight and then carbonized in a tube furnace under an argon atmosphere at 500° C. for 2 hours to obtain a Cu / Si@C-0.5 catalyst.

[0034] Examples 3-5

[0035] The other steps were the same as those in Example 2, except that 0.015 g of resorcinol and 0.0211 g of formaldehyde solution were replaced with 0.03 g of resorcinol and 0.0422 g of formaldehyde solution; 0.075 g of resorcinol and 0.1055 g of formaldehyde solution; and 0.150 g of resorcinol and 0.2110 g of formaldehyde solution, to obtain catalysts with different loadings, which were named Cu / Si@C-1, Cu / Si@C-2.5, and Cu / Si@C-5, respectively.

[0036] It is named Cu / Si@Cx (x is the theoretical loading of carbon, that is, the mass content of carbon in the copper-silicon catalyst in the phenolic resin generated by complete polymerization, that is, x = theoretical mass of carbon / theoretical mass of copper-silicon catalyst × 100%, wt.%).

[0037] Example 6

[0038] The other steps are the same as those in Example 2, except that resorcinol is replaced by phenol.

[0039] The obtained material properties are close;

[0040] Example 7 (Catalyst Application Example)

[0041] A batch reactor was used, and the catalysts obtained in Examples 1-5 were respectively charged (five groups of experiments were conducted), and the reaction raw material methyl laurate and the solvent n-hexane were added; the air in the reactor was replaced with nitrogen, and then the reactor was pressurized with hydrogen to 5 MPa, and the reaction space velocity was 1 h -1 , stirring speed is 800 rpm, reaction temperature is 210°C, and heating rate is 5°C / min to obtain lauryl alcohol.

[0042] The carbon-modified copper-silicon catalyst used was reduced before use: first, the catalyst was reduced in a tubular furnace at 350°C under a hydrogen atmosphere for 2 hours before being loaded into the kettle, and passivated with 1% O2-Ar for 30 minutes before being taken out. The hydrogen pressure should be 5 MPa.

[0043] from Figure 3 It can be seen from the results that the selectivity of all catalysts for lauryl alcohol is higher than 97% and does not change with carbon modification.

[0044] Example 8

[0045] The other steps are the same as those in Example 7, except that the hydrogen pressure is replaced by 6 MPa from 5 MPa; the rotation speed is replaced by 600 rpm from 800 rpm; the reaction temperature is replaced by 190 ° C from 210 ° C; the heating rate is replaced by 2 ° C / min from 5 ° C / min; the reduction at 350 ° C for 2 h is replaced by the reduction at 300 ° C for 4 h; the 1% O2-Ar passivation for 30 min is replaced by 1% O2-Ar passivation for 60 min; the reaction space velocity is replaced by 1 h -1 Replaced with 0.5h -1 .

[0046] Matters not covered by the present invention are known technologies.

Claims

1. A one-step preparation method of a carbon-modified copper-silicon catalyst by ammonia evaporation-polymerization carbonization, characterized by: The method comprises the following steps: (1) adding ammonia water to a copper nitrate solution to adjust the pH value of the solution to 11, and then reacting the solution at room temperature in a water bath with stirring for 30 to 60 minutes to obtain a copper ammonia solution; then adding silica sol dropwise thereto, continuing stirring for 12 to 20 hours, then heating to 80 to 100° C. to evaporate ammonia until the pH value of the solution is 7, and then removing the upper liquid to obtain a copper silicon catalyst matrix; Among them, add 7-25 ml of silica sol to every 100 ml of copper nitrate solution; The concentration of copper nitrate solution is 0.2-0.5 mol / L; (2) The copper-silicon catalyst precursor obtained in the previous step is mixed with water, and then a phenolic substance, formaldehyde solution, and anhydrous sodium carbonate are added, and polymerized at 30-50° C. for 4-8 hours; the obtained solid is dried in an oven at 70-100° C. overnight, and then carbonized in a tube furnace under an argon atmosphere at 400-600° C. for 2-6 hours to obtain a carbon-modified copper-silicon catalyst; Wherein, 0.015-0.15g of phenolic substance, 0.0211-0.211g of formaldehyde solution and 0.004-0.04g of anhydrous sodium carbonate are added to every 5g of copper silicon catalyst matrix; the phenolic substance is resorcinol or phenol.

2. The one-step preparation method of carbon-modified copper-silicon catalyst by ammonia evaporation-polymerization carbonization according to claim 1, characterized in that: The concentration of the formaldehyde solution is 30-55%.

3. A one-step preparation method of carbon-modified copper-silicon catalyst by ammonia evaporation-polymerization carbonization, characterized by: In step (2), 3 to 10 ml of water is added to every 5 g of copper-silicon catalyst precursor.

4. The use of the carbon-modified copper-silicon catalyst prepared by the method according to claim 1, characterized in that: Used as a catalyst in the hydrogenation reaction of methyl laurate.

5. The use according to claim 4, characterized in that The method comprises the following steps: using an intermittent reactor, loading the carbon-modified copper-silicon catalyst, the reaction raw material methyl laurate and the solvent n-hexane; replacing the air in the reactor with nitrogen, then pressurizing it with hydrogen at 4-6 MPa, heating it to 190-220°C, and reacting at a space velocity of 0.5-1h -1 , to obtain lauryl alcohol.

6. The use according to claim 5, characterized in that The catalyst must be reduced in a tubular furnace at 250-350° C. for 2-6 hours under a hydrogen atmosphere before being loaded into the kettle, and passivated with 1% O 2 -Ar for 30-60 minutes before being taken out.

7. The use according to claim 5, characterized in that the stirring speed is 600-800 rpm and the heating rate is 2-5°C / min.

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