Single-atom catalyst for preparing vinyl chloride from 1,2-dichloroethane, and synthesis and application thereof

Abstract

The present invention provides a single-atom catalyst for the preparation of vinyl chloride from 1,2-dichloroethane, as well as its synthesis and application. In the catalyst, the active centers of magnesium, nickel, cobalt and copper exist entirely in the form of isolated single atoms on the nitrogen-doped carbon material. A nitrogen-containing organic ligand is coordinated with an acetate precursor, and magnesium oxide is used as a hard template. Pyrolysis is carried out in an inert atmosphere for the carbonization-nitridation process. Finally, the magnesium oxide template is removed with acid, and further calcined in an inert atmosphere for the second time to remove volatile components, obtaining the single-atom catalyst. This catalyst can efficiently catalyze the reaction of cracking 1,2-dichloroethane to produce vinyl chloride. Compared with the existing nitrogen-doped carbon materials, it can greatly improve the performance of the catalyst.

Description

Technical Field

[0001] The present invention relates to the reaction of cracking 1,2-dichloroethane to produce vinyl chloride, and specifically relates to a nitrogen-coordinated single-atom catalyst. Background Art

[0002] Vinyl chloride is an important monomer for producing polyvinyl chloride plastics. Currently, there are mainly two industrial methods for producing vinyl chloride: the acetylene method and the ethylene method. The acetylene method refers to the reaction of acetylene with hydrogen chloride to produce vinyl chloride; while the ethylene method is to produce 1,2-dichloroethane through ethylene oxychlorination or direct chlorination, and then dehydrochlorination to obtain vinyl chloride. Among them, the cracking of 1,2-dichloroethane is a key step in the ethylene method. Industrially, vinyl chloride is mainly prepared by high-temperature cracking, directly heating 1,2-dichloroethane to 500 - 550 °C, at which time the conversion rate can reach 50 - 60%, and the selectivity reaches 95 - 99%. This method has a high reaction temperature, high energy consumption, and is prone to coking. Catalytic cracking can significantly reduce the cracking reaction temperature and reduce heat energy loss by selecting a suitable catalyst, and has gradually become a research hotspot. In the past half century, researchers have made important contributions and achieved good research progress in the development of cracking catalysts. The early studied cracking catalysts mainly include metal oxides and metal chlorides, such as BaCl2, Al2O3, etc. Researchers proposed that the metal cation centers (Lewis acid centers) in such catalysts can interact with Cl in 1,2-dichloroethane, while the Cl or O anion centers (Lewis base centers) in the catalyst can interact with H in 1,2-dichloroethane, so that the acid-base centers cooperate to catalyze the removal of HCl in 1,2-dichloroethane at a lower temperature (300 - 400 °C). However, the cracking temperature required for such catalysts is still relatively high, and the catalyst is extremely prone to deactivation. Further, researchers have developed non-metallic basic centers, mainly nitrogen-doped carbon materials for the cracking of 1,2-dichloroethane. The reaction temperature can be reduced to below 300 °C, the conversion rate can reach more than 80%, the selectivity remains above 99%, and it can maintain for dozens of hours without obvious deactivation. In such catalysts, pyridine nitrogen serves as the main dehydrogenation active site, and Cl in 1,2-dichloroethane can fall off at the carbon site next to nitrogen. In the present invention, a single-atom catalyst is used for the cracking of 1,2-dichloroethane to produce vinyl chloride, and the catalyst performance is excellent. Summary of the Invention

[0003] The object of the present invention is to provide a single-atom catalyst for the cracking of 1,2-dichloroethane to produce vinyl chloride.

[0004] The present invention is outlined as follows:

[0005] The present invention discloses a single-atom catalyst for the cracking of 1,2-dichloroethane to produce vinyl chloride, in which the active center metal is one or more of magnesium, nickel, cobalt, and copper, and exists entirely in the form of isolated single atoms on a nitrogen-doped carbon material; the nitrogen element in the nitrogen-containing carbon is doped on the carbon material in the form of a covalent bond; the mass content of nitrogen in the nitrogen-containing carbon is 0.1–20%, preferably 1–12%; the total loading of one or more of magnesium, nickel, cobalt, and copper is 0.01–15%, preferably 0.1–9%. The specific surface area of the single-atom catalyst is 100–800m 2 / g.

[0006] The synthesis method of the single-atom catalyst comprises the following steps:

[0007] Mix a nitrogen-containing organic ligand and a metal salt precursor in a solvent, add magnesium oxide as a hard template, dry, pyrolyze in an inert atmosphere for carbonization, finally remove the magnesium oxide template with an acid, dry, and further calcine in an inert atmosphere for a second time to remove volatile components to obtain the single-atom catalyst.

[0008] The nitrogen-containing organic ligand is phenanthroline; the metal salt precursor is one or more of magnesium acetate, nickel acetate, cobalt acetate, and copper acetate.

[0009] In the synthesis method, the molar ratio of phenanthroline to the metal salt is 0.5–20, preferably 2–7.

[0010] The inert gas is one or more of nitrogen, argon, and helium;

[0011] The temperature of the carbonization process is 400–800 °C, preferably 450–600 °C, and the time is 0.5–12 hours, preferably 1–6 hours.

[0012] The acid for dissolving magnesium oxide is one or more of sulfuric acid, nitric acid, and hydrochloric acid, with a concentration of 0.1–5 mol / L, preferably 0.5–3 mol / L; the time is 0.5–48 hours, preferably 1–24 hours.

[0013] The temperature of the second calcination is 200–500 °C, preferably 250–400 °C, and the time is 0.5–12 hours, preferably 1–6 hours.

[0014] The mass ratio of magnesium oxide to phenanthroline is 20–0.1, preferably 12–0.5;

[0015] The solvent is one or more of ethanol, methanol, and propanol; the concentration of phenanthroline in the solvent is 0.5–200 mg / mL, preferably 5–60 mg / mL.

[0016] The catalyst of the present invention can efficiently catalyze the cracking reaction of 1,2-dichloroethane to produce vinyl chloride. Compared with the existing nitrogen-doped carbon materials, it can greatly improve the catalytic activity of the catalyst. Description of the Drawings

[0017] Figure 1 It is a scanning transmission electron microscope photograph of the magnesium-based single-atom catalyst in Example 1.

[0018] Figure 2 It is a comparison chart of the activities of the magnesium-based single-atom catalysts (Examples 1-5) and the nitrogen-doped carbon catalysts (Comparative Examples 1 and 2).

[0019] Figure 3 It is a scanning transmission electron microscope photograph of the nickel-based single-atom catalyst in Example 7.

[0020] Figure 4 It is a comparison chart of the activities of the transition metal single-atom catalysts (Examples 6-8) and the nitrogen-doped carbon catalyst (Comparative Example 3). Detailed Embodiments

[0021] The technical solution of the present invention will be further elaborated through specific examples below.

[0022] Example 1

[0023] 205.9 mg of Mg(CH3COO)2·4H2O and 960 mg of o-phenanthroline monohydrate solvent were added to 150 mL of absolute ethanol, and 9.6 g of nano-magnesium oxide (50 nm) was added. After stirring in a water bath at 60 °C for 12 hours, it was dried. Further dried in an oven at 60 °C for 12 hours. The dried powder was placed in a quartz boat and heated to 550 °C in nitrogen and maintained for 2 hours to obtain a magnesium-based single-atom catalyst supported on MgO. The MgO in the above material was dissolved with a 2M nitric acid solution, stirred at room temperature for 24 hours, filtered, washed, and dried. Finally, the dried material was heated to 300 °C in N2 and maintained for 2 hours to obtain a magnesium-based single-atom catalyst. The magnesium content measured by an elemental analyzer was 0.52%, and the nitrogen content was 8.6%. The scanning transmission electron microscope photograph of this catalyst can be seen Figure 1 , and it can be seen that magnesium exists in the form of isolated single atoms on the nitrogen-doped carbon material.

[0024] 1,2-Dichloroethane was introduced into the fixed-bed reactor filled with the magnesium-based single-atom catalyst prepared in this example by bubbling through N2. The reaction temperature was 250 °C, the flow rate of N2 was 5 mL / min, the temperature of 1,2-dichloroethane was 5 °C, and the mass of the catalyst was 0.1 g. At this time, the conversion rate of 1,2-dichloroethane was 73%, the selectivity of vinyl chloride was greater than 99%, and the catalyst remained inactive for 40 hours.

[0025] Example 2

[0026] Dissolve 205.9 mg of Mg(CH3COO)2·4H2O and 960 mg of 1,10-phenanthroline monohydrate in 150 mL of absolute ethanol. Add 9.6 g of nano-magnesium oxide (50 nm), stir in a 60 °C water bath for 12 hours, and then dry naturally. Further dry in an oven at 60 °C for 12 hours. Place the dried powder in a quartz boat, heat it to 400 °C in nitrogen and hold for 2 hours to obtain a magnesium-based single-atom catalyst supported on MgO. Dissolve the MgO in the above material with 2M nitric acid solution, stir at room temperature for 24 hours, then filter, wash and dry. Finally, heat the dried material to 300 °C in N2 and hold for 2 hours to obtain a magnesium-based single-atom catalyst. The elemental analyzer measures the magnesium content to be 0.15% and the nitrogen content to be 11.7%.

[0027] Introduce 1,2-dichloroethane into the fixed-bed reactor filled with the magnesium-based single-atom catalyst prepared in this example by bubbling through N2. The reaction temperature is 250 °C, the flow rate of N2 is 5 mL / min, the temperature of 1,2-dichloroethane is 5 °C, and the mass of the catalyst is 0.1 g. At this time, the conversion rate of 1,2-dichloroethane is 42%, the selectivity of vinyl chloride is greater than 99%, and the catalyst remains inactive for 40 hours.

[0028] Example 3

[0029] Dissolve 205.9 mg of Mg(CH3COO)2·4H2O and 960 mg of 1,10-phenanthroline monohydrate in 150 mL of absolute ethanol. Add 9.6 g of nano-magnesium oxide (50 nm), stir and dry after 12 hours in a 60 °C water bath. Further dry in an oven at 60 °C for 12 hours. Place the dried powder in a quartz boat, heat it to 450 °C in nitrogen and hold for 2 hours to obtain a magnesium-based single-atom catalyst supported on MgO. Dissolve the MgO in the above material with 2M nitric acid solution, stir at room temperature for 24 hours, then filter, wash and dry. Finally, heat the dried material to 300 °C in N2 and hold for 2 hours to obtain a magnesium-based single-atom catalyst. The elemental analyzer measures the magnesium content to be 0.17% and the nitrogen content to be 11.7%.

[0030] Introduce 1,2-dichloroethane into the fixed-bed reactor filled with the magnesium-based single-atom catalyst prepared in this example by bubbling through N2. The reaction temperature is 250 °C, the flow rate of N2 is 5 mL / min, the temperature of 1,2-dichloroethane is 5 °C, and the mass of the catalyst is 0.1 g. At this time, the conversion rate of 1,2-dichloroethane is 51%, the selectivity of vinyl chloride is greater than 99%, and the catalyst remains inactive for 40 hours.

[0031] Example 4

[0032] Dissolve 205.9 mg of Mg(CH3COO)2·4H2O and 960 mg of o-phenanthroline monohydrate in 150 mL of absolute ethanol. Add 9.6 g of nano-magnesium oxide (50 nm), stir in a water bath at 60 °C for 12 hours, and then dry. Further dry in an oven at 60 °C for 12 hours. Place the dried powder in a quartz boat, heat it to 500 °C in nitrogen and hold for 2 hours to obtain a magnesium-based single-atom catalyst supported on MgO. Dissolve the MgO in the above material with 2M nitric acid solution, stir at room temperature for 24 hours, then filter, wash and dry. Finally, heat the dried material to 300 °C in N2 and hold for 2 hours to obtain a magnesium-based single-atom catalyst. The elemental analyzer measures the magnesium content to be 0.35% and the nitrogen content to be 10.2%.

[0033] Introduce 1,2-dichloroethane into a fixed-bed reactor filled with the magnesium-based single-atom catalyst prepared in this example by bubbling through N2. The reaction temperature is 250 °C, the flow rate of N2 is 5 mL / min, the temperature of 1,2-dichloroethane is 5 °C, and the mass of the catalyst is 0.1 g. At this time, the conversion rate of 1,2-dichloroethane is 64%, the selectivity of vinyl chloride is greater than 99%, and the catalyst remains inactive for 40 hours.

[0034] Example 5

[0035] Dissolve 205.9 mg of Mg(CH3COO)2·4H2O and 960 mg of o-phenanthroline monohydrate in 150 mL of absolute ethanol. Add 9.6 g of nano-magnesium oxide (50 nm), stir in a water bath at 60 °C for 12 hours, and then dry. Further dry in an oven at 60 °C for 12 hours. Place the dried powder in a quartz boat, heat it to 600 °C in nitrogen and hold for 2 hours to obtain a magnesium-based single-atom catalyst supported on MgO. Dissolve the MgO in the above material with 2M nitric acid solution, stir at room temperature for 24 hours, then filter, wash and dry. Finally, heat the dried material to 300 °C in N2 and hold for 2 hours to obtain a magnesium-based single-atom catalyst. The elemental analyzer measures the magnesium content to be 1.37% and the nitrogen content to be 7.0%.

[0036] Introduce 1,2-dichloroethane into a fixed-bed reactor filled with the magnesium-based single-atom catalyst prepared in this example by bubbling through N2. The reaction temperature is 250 °C, the flow rate of N2 is 5 mL / min, the temperature of 1,2-dichloroethane is 5 °C, and the mass of the catalyst is 0.1 g. At this time, the conversion rate of 1,2-dichloroethane is 41%, the selectivity of vinyl chloride is greater than 99%, and the catalyst remains inactive for 40 hours.

[0037] Example 6

[0038] Dissolve 381.9 mg of Co(CH3COO)2·4H2O and 960 mg of 1,10-phenanthroline monohydrate in 150 mL of absolute ethanol. Add 9.6 g of nano-magnesium oxide (20 nm). Stir in a water bath at 60 °C for 12 hours, then rotary evaporate and dry at 50 °C. Further dry in an oven at 60 °C for 12 hours. Place the dried powder in a quartz boat and heat it to 500 °C in a nitrogen or argon atmosphere and hold for 2 hours with a heating rate of 2 °C / min to obtain the MgO-supported metal-N-C material. Use 2 M nitric acid solution to dissolve MgO in the above material, stir at room temperature for 24 hours, then filter, wash and dry. Finally, heat the dried material to 200 - 300 °C in N2 and hold for 2 hours to obtain a single-atom Co-N-C catalyst. The cobalt content measured by an elemental analyzer is 6.5%, and the nitrogen content is 10.1%.

[0039] Application of the single-atom Co-N-C catalyst: Bubble 1,2-dichloroethane into a fixed-bed reactor filled with the 1,2-dichloroethane cracking catalyst prepared in this example through N2. The reaction temperature is 250 °C, the flow rate of N2 is 5 mL / min, the temperature of 1,2-dichloroethane is 5 °C, and the mass of the catalyst is 0.1 g. At this time, the conversion rate of 1,2-dichloroethane is 14%, the selectivity of vinyl chloride is 87%, and the catalyst remains inactive for 20 hours.

[0040] Example 7

[0041] Dissolve 367.5 mg of Ni(CH3COO)2·4H2O and 960 mg of 1,10-phenanthroline monohydrate in 150 mL of absolute ethanol. Add 9.6 g of nano-magnesium oxide (50 nm). Stir in a water bath at 60 °C for 12 hours, then rotary evaporate and dry at 50 °C. Further dry in an oven at 60 °C for 12 hours. Place the dried powder in a quartz boat and heat it to 500 °C in a nitrogen or argon atmosphere and hold for 2 hours with a heating rate of 2 °C / min to obtain the MgO-supported metal-N-C material. Use 2 M nitric acid solution to dissolve MgO in the above material, stir at room temperature for 24 hours, then filter, wash and dry. Finally, heat the dried material to 300 °C in N2 and hold for 2 hours to obtain a single-atom Ni-N-C catalyst. The nickel content measured by an elemental analyzer is 6.3%, and the nitrogen content is 8.3%. The scanning transmission electron microscope photo of this catalyst is shown in Figure 3 , it can be seen that nickel exists in the form of isolated single atoms on the nitrogen-doped carbon material.

[0042] Application of single-atom Ni-N-C catalyst: 1,2-dichloroethane was introduced into a fixed-bed reactor filled with the 1,2-dichloroethane cracking catalyst prepared in this example by bubbling through N₂. The reaction temperature was 250 °C, the flow rate of N₂ was 5 mL / min, the temperature of 1,2-dichloroethane was 5 °C, and the mass of the catalyst was 0.1 g. At this time, the conversion rate of 1,2-dichloroethane was 36%, the selectivity for vinyl chloride was greater than 99%, and the catalyst remained inactive for 40 hours.

[0043] Example 8

[0044] 299.4 mg of Cu(CH₃COO)₂·H₂O and 960 mg of o-phenanthroline monohydrate were dissolved in 150 mL of absolute ethanol, and 9.6 g of nano-magnesium oxide (100 nm) was added. After stirring in a water bath at 60 °C for 12 hours, it was rotary evaporated and dried at 50 °C. Further dried in an oven at 60 °C for 12 hours. The dried powder was placed in a quartz boat and heated to 500 °C in a nitrogen or argon atmosphere and held for 2 hours with a heating rate of 2 °C / min to obtain a MgO-supported metal-N-C material. 2M nitric acid solution was used to dissolve MgO in the above material, stirred at room temperature for 24 hours, then filtered, washed and dried. Finally, the dried material was heated to 200 - 300 °C in N₂ and held for 2 hours to obtain a single-atom Cu-N-C catalyst. The copper content measured by an elemental analyzer was 5.2%, and the nitrogen content was 8.1%.

[0045] Application of single-atom Cu-N-C catalyst: 1,2-dichloroethane was introduced into a fixed-bed reactor filled with the 1,2-dichloroethane cracking catalyst prepared in this example by bubbling through N₂. The reaction temperature was 250 °C, the flow rate of N₂ was 5 mL / min, the temperature of 1,2-dichloroethane was 5 °C, and the mass of the catalyst was 0.1 g. At this time, the conversion rate of 1,2-dichloroethane was 4%, and the selectivity for vinyl chloride was 74%.

[0046] Comparative Example 1

[0047] 960 mg of o-phenanthroline monohydrate was dissolved in 150 mL of absolute ethanol, and 9.6 g of nano-magnesium oxide (50 nm) was added. After stirring in a water bath at 60 °C for 12 hours, it was rotary evaporated and dried at 50 °C. Further dried in an oven at 60 °C for 12 hours. The dried powder was placed in a quartz boat and heated to 500 °C in a nitrogen or argon atmosphere and held for 2 hours with a heating rate of 2 °C / min to obtain a MgO-supported nitrogen-doped carbon catalyst material. 2M nitric acid solution was used to dissolve MgO in the above material, stirred at room temperature for 24 hours, then filtered, washed and dried. Finally, the dried material was heated to 300 °C in N₂ and held for 2 hours to obtain a nitrogen-doped carbon catalyst.

[0048] 1,2-Dichloroethane was introduced into a fixed-bed reactor filled with the nitrogen-doped carbon catalyst prepared in this example by bubbling through N₂. The reaction temperature was 250 °C, the flow rate of N₂ was 5 mL / min, the temperature of 1,2-dichloroethane was 5 °C, and the mass of the catalyst was 0.1 g. At this time, the conversion rate of 1,2-dichloroethane was 3%, and the selectivity to vinyl chloride was greater than 99%.

[0049] Comparative Example 2

[0050] 960 mg of o-phenanthroline monohydrate was dissolved in 150 mL of absolute ethanol, and 9.6 g of nano-magnesium oxide (50 nm) was added. After stirring in a water bath at 60 °C for 12 hours, it was rotary evaporated and dried at 50 °C. Further dried in an oven at 60 °C for 12 hours. The dried powder was placed in a quartz boat and heated to 550 °C in a nitrogen or argon atmosphere and held for 2 hours with a heating rate of 2 °C / min to obtain a MgO-supported nitrogen-doped carbon catalyst material. 2M nitric acid solution was used to dissolve MgO in the above material, stirred at room temperature for 24 hours, then filtered, washed, and dried. Finally, the dried material was heated to 300 °C in N₂ and held for 2 hours to obtain a nitrogen-doped carbon catalyst with a nitrogen content of 11.5%.

[0051] 1,2-Dichloroethane was introduced into a fixed-bed reactor filled with the nitrogen-doped carbon catalyst prepared in this example by bubbling through N₂. The reaction temperature was 250 °C, the flow rate of N₂ was 5 mL / min, the temperature of 1,2-dichloroethane was 5 °C, and the mass of the catalyst was 0.1 g. At this time, the conversion rate of 1,2-dichloroethane was 2%, and the selectivity to vinyl chloride was greater than 99%.

[0052] Comparative Example 3

[0053] 960 mg of o-phenanthroline monohydrate was dissolved in 150 mL of absolute ethanol, and 9.6 g of nano-magnesium oxide (30 nm) was added. After stirring in a water bath at 60 °C for 12 hours, it was rotary evaporated and dried at 50 °C. Further dried in an oven at 60 °C for 12 hours. The dried powder was placed in a quartz boat and heated to 400 °C in a nitrogen or argon atmosphere and held for 2 hours with a heating rate of 2 °C / min to obtain a MgO-supported nitrogen-doped carbon catalyst material. 2M nitric acid solution was used to dissolve MgO in the above material, stirred at room temperature for 24 hours, then filtered, washed, and dried. Finally, the dried material was heated to 300 °C in N₂ and held for 2 hours to obtain a nitrogen-doped carbon catalyst.

[0054] 1,2-dichloroethane was introduced into a fixed-bed reactor filled with the nitrogen-doped carbon catalyst prepared in this example by bubbling through N2. The reaction temperature was 250 °C, the flow rate of N2 was 5 mL / min, the temperature of 1,2-dichloroethane was 5 °C, and the mass of the catalyst was 0.1 g. At this time, the conversion rate of 1,2-dichloroethane was 0.7%, and the selectivity of vinyl chloride was greater than 99%.

Claims

1. Application of a single-atom catalyst in the cracking of 1,2-dichloroethane to produce vinyl chloride, characterized in that: The synthesis method of the single-atom catalyst is as follows: Dissolve 205.9 mg of Mg(CH3COO)2·4H2O and 960 mg of 1,10-phenanthroline monohydrate in 150 mL of absolute ethanol, add 9.6 g of 50 nm nano-magnesium oxide, stir in a water bath at 60 °C for 12 hours and then dry, further dry in an oven at 60 °C for 12 hours. Place the dried powder in a quartz boat, heat it to 550 °C in nitrogen and hold for 2 hours to obtain a magnesium-based single-atom catalyst supported on MgO. Dissolve the MgO in the above material with 2 M nitric acid solution, stir at room temperature for 24 hours, filter, wash and dry. Finally, heat the dried material to 300 °C in N2 and hold for 2 hours to obtain the magnesium-based single-atom catalyst; Introduce 1,2-dichloroethane into the fixed-bed reactor filled with the above-prepared magnesium-based single-atom catalyst by bubbling through N2. The reaction temperature is 250 °C, the flow rate of N2 is 5 mL / min, the temperature of 1,2-dichloroethane is 5 °C, and the mass of the catalyst is 0.1 g.

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