Preparation method of carbon-doped boron nitride catalyst and application of carbon-doped boron nitride catalyst in synthesis of chloroethylene through ethyne hydrochlorination

Abstract

The application discloses a preparation method of a carbon-doped boron nitride catalyst and application of the carbon-doped boron nitride catalyst in synthesis of chloroethylene through ethyne hydrochlorination. The method comprises the following steps: 1) dissolving a boron source and a nitrogen source in a solvent to configure a mixed solution; 2) heating and drying the solution obtained in the step 1) and then calcining to obtain a porous boron nitride precursor; and 3) introducing a carbon source to perform CVD treatment on the precursor obtained in the step 2), so that the carbon-doped boron nitride catalyst is obtained. The carbon-doped boron nitride catalyst can be applied to synthesis of chloroethylene through ethyne hydrochlorination, the single-pass conversion rate of ethyne is above 88.4%, the selectivity of chloroethylene is above 99.2%, and the service life can reach above 400 hours. The application has the characteristics of simple and environment-friendly catalyst preparation process, low cost, superior performance, small industrialization difficulty, good process repeatability and the like, and can replace a mercury catalytic catalyst in an existing calcium carbide method process and solve a mercury emission pollution problem.

Description

Technical Field

[0001] The present invention belongs to the preparation of vinyl chloride by acetylene hydrochlorination, and particularly relates to a preparation method of a carbon-doped boron nitride catalyst and application of the catalyst in the synthesis of vinyl chloride by acetylene hydrochlorination. Background Art

[0002] The production process of polyvinyl chloride (PVC) involves the polymerization of vinyl chloride monomer (VCM), which can be obtained through the ethylene, acetylene, and ethane processes. Due to China's abundant coal resources, low oil production, and limited natural gas resources, the coal-based acetylene process is the primary industrial process in China. This involves the electrophilic addition of coal-based acetylene to hydrogen chloride in the presence of a catalyst. Industrially, the acetylene process for vinyl chloride production uses a 10 wt.% mercuric chloride / activated carbon catalyst (HgCl2 / AC), which exhibits high reactivity, selectivity, and good reaction stability. However, the loss of Hg in the catalyst leads to significant catalyst deactivation and significant environmental pollution.

[0003] One of the main challenges with gold-based catalysts is the easy reduction of gold ions to inactive gold nanoparticles during the reaction, often accompanied by sintering of the nanoparticles. A second issue is the high price of gold, which has led to high costs and limited the industrialization of gold catalysts. While many researchers are currently working to improve efficiency and reduce costs through surface modification of activated carbon supports, such as introducing surface functional groups and heteroatom doping, creating surface defects, adding ionic liquids or additives, ligand modification, and single-atom dispersion, these efforts remain some distance from industrial application.

[0004] Non-precious metal catalysts, such as tin, bismuth, copper, and cobalt, have relatively low metal prices, but their catalytic activity is significantly lower than that of precious metal catalysts. Currently, researchers are improving the reaction performance of catalysts through strategies such as increasing the metal loading, modifying the carrier to load metal catalysts, and modifying metal catalysts with ligands. However, the catalytic performance of non-precious metal catalysts still lags far behind that of precious metal catalysts.

[0005] Non-metallic catalysts, with their excellent performance and low cost, offer a new path for mercury-free production of acetylene hydrochlorination. With increasing research, the reactivity and stability of non-metallic catalysts have steadily improved, with some results now comparable to those of precious metal catalysts. However, the stability of most non-metallic catalysts still needs to be improved. Among the reported non-metallic catalysts, porous boron nitride has achieved excellent performance, but the required temperature is too high and its intrinsic activity is relatively poor. Therefore, the introduction of carbon through doping is expected to further optimize the catalytic ability of boron nitride catalysts in acetylene hydrochlorination.

[0006] The current technology for preparing carbon-doped boron nitride mainly includes precursor pyrolysis, template method, chemical vapor deposition method, molten salt method, etc. For the precursor pyrolysis method, that is, by preparing a boron source, a carbon source, and a nitrogen source into a precursor, carbon-doped boron nitride can be directly prepared in one step by high-temperature calcination. However, since the carbon source and the nitrogen source decompose together during the calcination process to release highly toxic and harmful gases such as (CN)2, HCN and NH3, the large-scale application of this synthesis method is seriously limited. For the template method, the template method for preparing BCN nanomaterials is to use carbon-containing materials such as nanotubes, nanowires and nanosheets as templates, and B and N atoms replace some of the C atoms in the template through reaction to obtain BCN nanomaterials. However, when synthesizing BCN nanomaterials using the template method, a small amount of carbon often remains between the lattice layers, resulting in low purity, and the subsequent process of removing the template agent is complicated. Chemical vapor deposition (CVD) is one of the primary methods for preparing BCN thin films. This method involves introducing gaseous reactants into a reactor, where a chemical reaction produces a solid phase that is deposited onto a substrate. This method can produce high-purity BCN coatings or thin films, but it is incapable of producing porous structures and is difficult to mass-produce. The molten salt method for preparing BCN nanomaterials involves dispersing raw materials such as boric acid, glucose, and urea into a low-melting-point salt system. The low-melting-point salt acts as a reaction medium, providing a liquid environment for the raw materials at a specific temperature, achieving uniform mixing at the molecular or atomic level. However, this method requires subsequent washing with large amounts of solvents, is complex, and, like the precursor pyrolysis method, releases toxic gases. Summary of the Invention

[0007] In response to the above problems, the present invention provides a method for preparing a carbon-doped boron nitride catalyst and its application in the synthesis of vinyl chloride by acetylene hydrochlorination. The catalyst has the characteristics of simple and environmentally friendly preparation process, low cost, superior performance, low industrialization difficulty, and good process repeatability. It is very promising to replace the current mercury-based catalyst in the calcium carbide method.

[0008] In order to achieve the above object, the technical solution of the present invention is as follows:

[0009] In one aspect, the present invention provides a method for preparing a carbon-doped boron nitride catalyst, the method comprising the following steps:

[0010] 1) Mixing: heating in an oil bath, dissolving the boron source and the nitrogen source in a mixed solvent of ethanol and water to obtain a mixed solution;

[0011] 2) Drying: Drying the mixed solution obtained in step 1) to obtain a precursor;

[0012] 3) Calcination: calcining the precursor obtained in step 2) under an inert atmosphere to obtain a boron nitride precursor;

[0013] 4) CVD treatment: The boron nitride precursor obtained in step 3) is introduced into a carbon source for CVD treatment to obtain the carbon-doped boron nitride catalyst.

[0014] In the above technical solution, further, in step 1), the oil bath temperature is 60-90°C; the boron source includes one or both of boric acid and boron oxide; the nitrogen source includes one or more of urea, dicyandiamide, melamine, biuret, dimethylguanidine and various amino acids; the boron content in the mixed solution is 30-45wt%, and the nitrogen content is 30-45wt%; and the volume ratio of ethanol to water in the mixed solvent of ethanol and water is 1:1-4:1.

[0015] In the above technical solution, further, in the step 2), the drying temperature is 120-150°C.

[0016] In the above technical solution, further, in step 3), the inert atmosphere is at least one of nitrogen, helium, argon, krypton, and xenon; the calcination temperature is 1000° C., and the calcination time is 10 hours.

[0017] In the above technical solution, further, in the step 4), the temperature of the CVD treatment is 800°C and the time is 3 to 6 hours; the carbon source is methanol, ethanol, propanol, butanol, isopropanol, isobutanol, acetonitrile, and a molecular formula of C n H 2n+2 (1≤n≤5), C n H 2n-2 (2≤n≤5) and C n H 2n One or more of the low-carbon hydrocarbons (2≤n≤5).

[0018] Another aspect of the present invention provides a carbon-doped boron nitride catalyst prepared by the above preparation method.

[0019] In another aspect, the present invention provides a use of the carbon-doped boron nitride catalyst in the preparation of vinyl chloride by acetylene hydrochlorination.

[0020] In the above technical solution, further, the hydrogen chloride and acetylene raw gas after drying and dehydration are introduced into a gas-solid phase catalytic reactor carrying a carbon-doped boron nitride catalyst for reaction.

[0021] In the above technical solution, further, the volume ratio of hydrogen chloride to acetylene is 1.4:1.0 to 0.6:1.0; the reaction temperature is 140 to 240°C; the reaction space velocity is 30 to 60h -1 ; The reaction pressure is normal pressure.

[0022] The beneficial effects of the present invention are:

[0023] (1) The catalyst prepared by the method provided by the present invention has a low preparation cost compared to expensive gold-based catalysts and is more suitable for current market demand; the prepared carbon-doped boron nitride catalyst has a high specific surface area and a controllable carbon content.

[0024] (2) The catalyst prepared by the method provided by the present invention is completely mercury-free, thereby solving the defects of existing industrial low-mercury activated carbon catalysts such as mercury emission pollution and catalyst deactivation caused by accidental cessation of hydrogen chloride gas, showing good application prospects.

[0025] (3) The preparation method provided by the present invention is to incorporate carbon through a gaseous carbon source after high-temperature calcination, which can avoid the release of highly toxic or harmful gases such as (CN)2, HCN and NH3 in the one-step calcination method, and is safer and more environmentally friendly. Compared with the methods of the prior art, the method of the present invention is easy to prepare in large quantities and easy to achieve large-scale production.

[0026] (4) The carbon sources used in the preparation method provided by the present invention, such as methane, methanol and other gaseous carbon sources, are abundant in reserves and low in cost.

[0027] (5) The catalyst prepared by the method provided by the present invention has a wide temperature application range in the acetylene hydrochlorination process, and has excellent catalytic performance at 140-240°C, a high conversion rate (>88.4%) and selectivity for vinyl chloride (>99.2%), high stability (>400h), and a lower reaction temperature required, which can save a lot of energy, making it have broad prospects for industrial application.

[0028] (6) The catalyst prepared by the method provided by the present invention has a higher intrinsic activity when used in the acetylene hydrochlorination process. If the intrinsic activity is too poor, the addition reaction between acetylene and hydrogen chloride cannot be carried out in a timely manner, and the adsorbed acetylene will polymerize, resulting in carbon deposition and deactivation. However, when the intrinsic activity is improved, the adsorbed acetylene can react with hydrogen chloride in a timely manner and will not polymerize itself, resulting in carbon deposition and deactivation, thereby improving the stability of the catalyst (>400h). BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the XPS spectrum of BCN-AN-1 in Example 2;

[0030] Figure 2 The nitrogen physical adsorption results of BCN-AN-1 in Example 6;

[0031] Figure 3 This is the stability test result of BCN-AN-1 in Example 2. DETAILED DESCRIPTION

[0032] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of the claims of the present invention is not limited by these embodiments. At the same time, the embodiments only provide some conditions for achieving this purpose, but do not mean that these conditions must be met to achieve this purpose.

[0033] The carbon content of the samples can be measured by X-ray photoelectron spectroscopy.

[0034] The specific surface area of ​​the sample can be tested by nitrogen physical adsorption method.

[0035] All raw materials used in the following examples are commercially available. The catalysts were evaluated in a continuous online gas-solid phase reactor. A typical evaluation process involves weighing 1.00 g of catalyst, drying it under argon purge at 120°C for 0.5 h, introducing the reaction gas at 140-240°C to initiate the reaction. The product was detected using an Agilent 7890B gas chromatograph equipped with an FID detector and a PLOT Q column, which has excellent separation and detection performance for the gas components involved.

[0036] Example 1

[0037] (1) Liquid-phase synthesis precursor: Weigh 65.96 g of boric acid and dissolve it in a mixture of 200 ml of water and 400 ml of ethanol at 90°C with stirring until the boric acid dissolves. Then weigh 33.63 g of finely ground melamine powder and gradually add it to the solution with vigorous stirring.

[0038] Stir vigorously for 12 h under sealed conditions, then evaporate the solvent at 120 °C to obtain a white powder, completing the liquid phase synthesis step.

[0039] (2) Calcination: The product obtained above was dried in air at 120°C and then calcined in an inert atmosphere to obtain a porous boron nitride material. The inert gas was helium, the calcination temperature was 1000°C, and the calcination time was 10 hours.

[0040] (3) CVD treatment: Use inert gas to bubble liquid methanol, control the flow rate to 30 ml / min, and perform CVD treatment on the solid obtained in (2) at a treatment temperature of 800° C. for 3 to 6 hours.

[0041] The specific samples, their preparation conditions and carbon contents are shown in Table 1. In the table, BN-1 is a porous boron nitride with low carbon content obtained by the above method but without CVD treatment.

[0042] Table 1 Preparation and parameter properties of carbon-doped boron nitride materials

[0043]

[0044]

[0045] Example 2

[0046] (1) Liquid-phase synthesis of precursors: Weigh 65.96 g of boric acid into a mixture of 400 ml of water and 400 ml of ethanol, heat and stir at 90°C until the boric acid dissolves. Then weigh 33.63 g of finely ground melamine powder and gradually add it to the above solution with vigorous stirring.

[0047] Stir vigorously for 12 h under sealed conditions, then evaporate the solvent at 120 °C to obtain a white powder, completing the liquid phase synthesis step.

[0048] (2) Calcination: The product obtained above was dried in air at 120°C and then calcined in an inert atmosphere to obtain a porous boron nitride material. The inert gas was argon, the calcination temperature was 1000°C, and the calcination time was 10 h.

[0049] (3) CVD treatment: Use inert gas to bubble liquid acetonitrile, control the flow rate to 30 ml / min, and perform CVD treatment on the solid obtained in (2) at a treatment temperature of 800° C. for 3 to 6 h.

[0050] The specific samples, their preparation conditions and carbon contents are shown in Table 2.

[0051] Table 2 Preparation and parameter properties of carbon-doped boron nitride materials

[0052] Sample number CVD processing time / h Carbon content / mass fraction% BCN-AN-1 3 13.25 BCN-AN-2 6 16.77

[0053] Example 3

[0054] (1) Liquid-phase synthesis precursor: Weigh 65.96 g of boric acid into a mixture of 200 ml of water and 400 ml of ethanol, heat and stir at 90°C until the boric acid dissolves. Then weigh 33.63 g of finely ground dicyandiamide powder and gradually add it to the solution with vigorous stirring.

[0055] Stir vigorously for 12 h under sealed conditions, then evaporate the solvent at 120 °C to obtain a white powder, completing the liquid phase synthesis step.

[0056] (2) Calcination: The product obtained above was dried in air at 120°C and then calcined in an inert atmosphere to obtain a porous boron nitride material. The inert gas was helium, the calcination temperature was 1000°C, and the calcination time was 10 hours.

[0057] (3) CVD treatment: Using methane with a flow rate of 30 ml / min, the solid obtained in (2) was subjected to CVD treatment at a temperature of 800° C. for 3 to 6 h.

[0058] The specific samples, their preparation conditions and carbon contents are shown in Table 3.

[0059] Table 3 Preparation and parameter properties of carbon-doped boron nitride materials

[0060] Sample number CVD processing time / h Carbon content / mass fraction% <![CDATA[BCN-CH4-1]]> 3 14.53 <![CDATA[BCN-CH4-2]]> 6 21.68

[0061] Example 4

[0062] (1) Liquid-phase synthesis precursor: Weigh 65.96 g of boric acid and boron oxide into a mixed solution of 400 ml of water and 400 ml of ethanol, heat and stir at 90°C until the boric acid dissolves. Then weigh 33.63 g of finely ground urea powder and gradually add it to the above solution with vigorous stirring.

[0063] Stir vigorously for 12 h under sealed conditions, then evaporate the solvent at 120 °C to obtain a white powder, completing the liquid phase synthesis step.

[0064] (2) Calcination: The product obtained above was dried in air at 120°C and then calcined in an inert atmosphere to obtain a porous boron nitride material. The inert gas was helium, the calcination temperature was 1000°C, and the calcination time was 10 hours.

[0065] (3) CVD treatment: Using ethylene, the flow rate was controlled at 30 ml / min, and the solid obtained in (2) was subjected to CVD treatment at a temperature of 800° C. for 3 to 6 h.

[0066] The specific samples, their preparation conditions and carbon contents are shown in Table 4.

[0067] Table 4 Preparation and parameter properties of carbon-doped boron nitride materials

[0068] Sample number CVD processing time / h Carbon content / mass fraction% <![CDATA[BCN-C2H4-1]]> 3 16.43 <![CDATA[BCN-C2H4-2]]> 6 24.62

[0069] Example 5

[0070] (1) Liquid-phase synthesis precursor: Weigh 65.96 g of boric acid into a mixture of 400 ml of water and 400 ml of ethanol, heat and stir at 90°C until the boric acid dissolves. Then weigh 33.63 g of finely ground melamine powder and gradually add it to the solution with vigorous stirring.

[0071] Stir vigorously for 12 h under sealed conditions, then evaporate the solvent at 120 °C to obtain a white powder, completing the liquid phase synthesis step.

[0072] (2) Calcination: The product obtained above was dried in air at 120°C and then calcined in an inert atmosphere to obtain a porous boron nitride material. The inert gas was argon, the calcination temperature was 1000°C, and the calcination time was 10 h.

[0073] (3) CVD treatment: Use inert gas to bubble liquid ethanol at a flow rate of 30 ml / min, and perform CVD treatment on the solid obtained in (2) at a treatment temperature of 800° C. for 3 to 6 h.

[0074] The specific samples, their preparation conditions and carbon contents are shown in Table 5.

[0075] Table 5 Preparation and parameter properties of carbon-doped boron nitride materials

[0076] Sample number CVD processing time / h Carbon content / mass fraction% BCN-EtOH-1 3 15.16 BCN-EtOH-2 6 20.38

[0077] Example 6

[0078] (1) Liquid-phase synthesis precursor: Weigh 65.96 g of boric acid into a mixture of 400 ml of water and 400 ml of ethanol, heat and stir at 90°C until the boric acid dissolves. Then weigh 33.63 g of finely ground melamine powder and gradually add it to the solution with vigorous stirring.

[0079] Stir vigorously for 12 h under sealed conditions, then evaporate the solvent at 120 °C to obtain a white powder, completing the liquid phase synthesis step.

[0080] (2) Calcination: The product obtained above is dried in air at 120°C and then calcined in an inert atmosphere to obtain a porous boron nitride material. The inert gas is helium, the calcination temperature is 1000°C, and the calcination time is 10 hours.

[0081] (3) CVD treatment: using acetylene with a flow rate of 30 ml / min, the solid obtained in (2) was subjected to CVD treatment at a temperature of 800° C. for 3 to 6 h.

[0082] The specific samples, their preparation conditions and carbon contents are shown in Table 6.

[0083] Table 6 Preparation and parameter properties of carbon-doped boron nitride materials

[0084] Sample number CVD processing time / h Carbon content / mass fraction% <![CDATA[BCN-C2H4-1]]> 3 18.97 <![CDATA[BCN-C2H4-2]]> 6 25.38

[0085] Application Example 1

[0086] While fixed-bed reactions are used as an example, the catalyst is also suitable for use in moving-bed reactors. The apparatus is equipped with a gas mass flow meter and an online product analysis chromatograph (the reactor's exhaust gas is directly connected to the chromatograph's quantitative valve for periodic, real-time sampling and analysis).

[0087] A typical evaluation process is to weigh 1.00g of catalyst, dry it with argon purge at 120℃ for 0.5h, introduce the reaction gas at 180-240℃ to start the reaction, and detect the product by Agilent gas chromatograph 7890B equipped with FID detector and PLOT Q column, which has good separation and detection performance for the gas components involved.

[0088] Changing the temperature, space velocity, and the C₂H₂ / HCl molar ratio in the reaction gas can alter the reaction performance. Acetylene conversion can reach 88.4-99.7%, with selectivity reaching 99.2-99.9%. Table 7 lists specific catalyst applications and performance data.

[0089] Table 7 Specific application of catalyst and its effect data

[0090]

[0091]

[0092] The table above shows that different raw materials and CVD processing conditions directly affect the carbon content of carbon-doped boron nitride, which in turn affects the acetylene conversion rate and vinyl chloride selectivity. In comparison, the conversion rate of BN without CVD carbon doping is only 38.2%.

[0093] Result analysis:

[0094] Figure 1 This is the XPS spectrum of BCN-AN-1 in Example 2, and the results show that the carbon-doped boron nitride catalyst was successfully obtained through the current synthesis method.

[0095] Figure 2 The nitrogen physical adsorption results of BCN-C2H4-1 in Example 6 show that the catalyst has 1274m 2 / g of ultra-high specific surface area.

[0096] Figure 3 The stability test results of BCN-AN-1 in Example 2 are as follows: C2H2 =30h -1 , 180 ° C, C2H2 / HCl molar ratio = 1.2, the stability of Example 2 catalyst BCN-AN-1 was tested. Figure 3 It can be seen that the catalyst maintains good stability within 400 h, and both the conversion rate and conversion efficiency remain above 99%.

[0097] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. The scope of protection of the present invention shall be determined by the scope defined in the claims. Other variations or modifications may be made based on the above description. Obvious variations or modifications derived therefrom shall remain within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon-doped boron nitride catalyst, characterized in that: The method comprises the following steps: 1) Mixing: Dissolve the boron source and nitrogen source in a mixed solvent of ethanol and water under oil bath heating to obtain a mixed solution; 2) Drying: Drying the mixed solution obtained in step 1) to obtain a precursor; 3) Calcination: Calcining the precursor obtained in step 2) under an inert atmosphere to obtain a boron nitride precursor; 4) CVD treatment: The boron nitride precursor obtained in step 3) is introduced into a carbon source for CVD treatment to obtain the carbon-doped boron nitride catalyst.

2. The preparation method according to claim 1, wherein In the step 1), the oil bath temperature is between 60°C and 90°C; The boron source includes one or both of boric acid and boron oxide; The nitrogen source includes one or more of urea, dicyandiamide, melamine, biuret, dimethylguanidine and amino acids; The boron content in the mixed solution is 30-45 wt%, and the nitrogen content is 30-45 wt%. The volume ratio of ethanol to water in the mixed solvent of ethanol and water is 1:1~4:

1.

3. The preparation method according to claim 1, wherein In the step 2), the drying temperature is between 120°C and 150°C.

4. The preparation method according to claim 1, wherein In step 3), the inert atmosphere is at least one of nitrogen, helium, argon, krypton, and xenon; the calcination temperature is 1000° C., and the calcination time is 10 h.

5. The preparation method according to claim 1, wherein In step 4), the CVD treatment temperature is 800° C. and the time is 3 to 6 hours; The carbon sources are methanol, ethanol, propanol, butanol, isopropanol, isobutanol, acetonitrile, and the molecular formula is C n H 2n+2 And 1≤n≤5, C n H 2n-2 And 2≤n≤5 and C n H 2n One or more low-carbon hydrocarbons with 2≤n≤5.

6. A carbon-doped boron nitride catalyst prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the carbon-doped boron nitride catalyst according to claim 6 in the preparation of vinyl chloride by acetylene hydrochlorination.

8. The use according to claim 7, characterized in that The hydrogen chloride and acetylene raw materials after drying and dehydration are introduced into a gas-solid phase catalytic reactor carrying a carbon-doped boron nitride catalyst for reaction.

9. The use according to claim 8, characterized in that The volume ratio of hydrogen chloride to acetylene is 1.4:1.0~0.6:1.0; the reaction temperature is 140~240℃; the reaction space velocity is 30~60h -1 ; The reaction pressure is normal pressure.

Images