A carbon-coated fluorochlorohydrocarbon hydrogenation dechlorination catalyst, a preparation method and application thereof

Abstract

The application discloses a carbon-coated fluorochlorohydrocarbon hydrogenation dechlorination catalyst and a preparation method and application thereof, the catalyst is formed by taking phenolic resin as a carbon source, platinum as a main catalyst, copper as an additive, and the platinum and copper being coated inside the carbon source and being carbonized by calcination under an inert atmosphere; the platinum element loading of the catalyst is 2-3wt%, and the copper element loading is 8-12%. The preparation of the carbon-coated Pt-Cu alloy catalyst disclosed by the application involves reducing platinum salt and copper salt to obtain Pt-Cu alloy nanoparticles in a phenolic resin reaction system in the presence of hydrazine hydrate, the generated alloy nanoparticles are coated by the resin, and then carbonization is carried out to obtain the carbon-coated Pt-Cu alloy catalyst. The carbon-coated catalyst provided by the application can greatly reduce the loss of the active component in the catalyst during the reaction process since the active component is wrapped inside the carbon material, the stability of the catalyst is improved, and the service life of the catalyst is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of chemical catalysis technology, and particularly relates to a carbon-coated fluorochlorocarbon hydrogenation dechlorination catalyst as well as a preparation method and application thereof. BACKGROUND

[0002] Fluorochlorocarbons are halogenated alkanes composed of chlorine, fluorine and carbon, and are important organic chemicals, which are widely used in industrial production and people's daily life, such as refrigerants, aerosol propellants, cleaning solvents and foam blowing agents. However, the large-scale use of CFCs can cause damage to the ozone layer in the stratosphere, thus leading to global climate change. In addition to causing ozone layer holes, CFCs, like other volatile chemicals, can dissolve from the atmosphere into the environment, causing pollution to soil and groundwater. Therefore, it is necessary to convert excess CFCs into environmentally clean substances.

[0003] Catalytic hydrogenation dechlorination technology (HDC) is a highly potential organic chlorinated waste treatment technology. It can convert harmful chlorinated waste into useful non-toxic products by using a special catalyst to replace chlorine atoms with hydrogen atoms. This method can selectively remove the chlorine atoms in the CFCs molecules that are harmful to the ozone layer, and convert CFCs into clean products without side effects on the environment.

[0004] Current hydrogenation dechlorination catalysts are mainly divided into two categories: non-noble metal catalysts and noble metal catalysts. Hydrogenation dechlorination catalysts are mainly supported catalysts, and the active components mainly include non-noble metals such as Ni, Cr, Cu and Zn, and noble metals such as Ru, Pd and Pt. The supports used mainly include different types of activated carbon, silicon dioxide, aluminum oxide, magnesium oxide and silicon carbide.

[0005] CN 105944734 A discloses a catalyst for the catalytic hydrogenation dechlorination of trifluorotrichloroethane to prepare trifluorochloroethylene and a preparation method thereof. SiO2 particles are used as the carrier. Metal Co, Rh, Cr or Mn, KCl or perrhenic acid and Ni are used as the active components, and the SiO2 particles are impregnated with an equal volume. The catalyst prepared by this method has high catalytic activity, and the conversion rate is above 90%, but the stability is poor.

[0006] CN 112547070 A discloses a catalyst for preparing trifluorochloroethylene and a preparation method thereof. The catalyst carrier is a sintered porous copper-nickel alloy, the active component is Pd, the Pd active component loading amount is 0.15wt%, the average pore size of the sintered porous copper-nickel alloy is 50-300nm, the sintered porous copper-nickel alloy has a hollow structure, and the wall thickness is 0.525mm.

[0007] Supported catalysts have a wide range of applications in catalytic reactions, but their stability problems have been a key factor restricting their development. Because the active components of supported catalysts are prone to agglomeration, loss and other phenomena during the reaction, which leads to the decline of the performance of the catalyst, limiting its application range.

[0008] To solve this problem, carbon-coated metal catalysts have gradually become a research hotspot. Carbon-coated metal catalysts refer to a layer of carbon material coated on the surface of metal particles to form a core-shell structure. Due to the presence of the carbon layer, metal particles are spatially isolated from each other, which can effectively prevent metal particles from agglomeration or loss during the reaction, and improve the stability of the catalyst. Therefore, it is a difficult problem to be solved to invent a carbon-coated fluorochlorohydrocarbon hydrogenation dechlorination catalyst with high activity and high stability. SUMMARY

[0009] In view of the problems existing in the prior art, in order to solve the problems of easy loss of active components and high cost of existing fluorochlorohydrocarbon hydrogenation dechlorination catalysts, a carbon-coated fluorochlorohydrocarbon hydrogenation dechlorination catalyst and its preparation method and application are provided. The catalyst has the advantages of high activity, low cost and long service life, and has great application prospect.

[0010] The technical scheme adopted by the present application is as follows:

[0011] A carbon-coated fluorochlorohydrocarbon hydrogenation dechlorination catalyst, the catalyst is prepared by using phenolic resin as carbon source, platinum as main catalyst and copper as additive, platinum and copper are coated inside the carbon source, and then calcination and carbonization are carried out under inert atmosphere; the platinum element loading in the catalyst is 2-3wt%, and the copper element loading is 8-12%.

[0012] The preparation method of the carbon-coated fluorochlorohydrocarbon hydrogenation dechlorination catalyst comprises the following steps:

[0013] 1) Under intense magnetic stirring, mix hexadecyl trimethyl ammonium bromide (CTAB), soluble platinum salt aqueous solution, soluble copper salt aqueous solution and deionized water uniformly, add excess hydrazine hydrate and carry out reduction reaction under stirring to obtain Pt-Cu alloy nanoparticles by reducing platinum salt and copper salt;

[0014] 2) Add resorcinol and formaldehyde to the reaction solution of step 1), heat the solution to boiling and reflux;

[0015] 3) Add pH adjuster to the reaction solution of step 2) to adjust the pH to alkaline, continue to heat to boiling and reflux to react; after the reaction is completed, centrifuge and wash the solution to obtain a catalyst precursor of resin-coated Pt-Cu alloy nanoparticles;

[0016] 4) The catalyst precursor of step 3) is calcined and carbonized under inert atmosphere to obtain the carbon-coated fluorochlorohydrocarbon hydrogenation dechlorination catalyst.

[0017] Further, in step 1), the molar concentration of CTAB in the solution is 0.001-0.005 mol / L, the molar amount of hydrazine hydrate is 1.5-8.5 times the total molar amount of the platinum salt and the copper salt, the platinum salt is chloroplatinic acid hexahydrate or potassium chloroplatinate, and the copper salt is copper nitrate trihydrate or copper chloride.

[0018] Further, in step 1), the dispersion concentration of the platinum salt and the copper salt in the reaction solution is that the concentration of Pt element is 0.05-0.1 mg / mL, and the concentration of Cu element is 0.05-0.35 mg / mL.

[0019] Further, in step 1), the reduction reaction temperature is 20-50℃, and the reaction time is 5-20 min.

[0020] Further, in step 2), the solid-liquid ratio of the intermediate phenylenediamine and formaldehyde is 1g:1.2-1.5 mL, and the mass ratio of the intermediate phenylenediamine to the Pt element of the platinum salt of step 1) is 50-75:1.

[0021] Further, in step 2), the reflux time under boiling is 10-15 min.

[0022] Further, in step 3), the pH adjuster is ammonia water, the mass fraction of which is 25-30%, and the volume of which is 0.1-1% of the volume of the deionized water of step 1); and the reflux time under boiling in step 3) is 25-40 min.

[0023] Further, in step 3), the inert atmosphere is nitrogen, and the calcination and carbonization are carried out in two steps, the first step being calcination at 250-350℃ for 1-3 h, and the second step being calcination at 650-750℃ for 3-5 h.

[0024] The application further provides application of the carbon-coated fluorochlorohydrocarbon hydrogenation dechlorination catalyst in a reaction of catalytic hydrogenation dechlorination of trifluorotrichloroethane to prepare trifluorochloroethylene, the reaction temperature of the catalytic hydrogenation dechlorination being 280-320℃, the molar ratio of hydrogen to the raw material trifluorotrichloroethane being 1.2-2:1, and the reaction space velocity being 900h -1 .

[0025] The application has the following beneficial effects:

[0026] 1) The catalyst preparation method of this invention is simple, quick, and easy to operate. Its activity, selectivity, and applicability under relatively mild conditions all exhibit significant advantages and good industrial development value. The preparation of the carbon-coated Pt-Cu alloy catalyst of this invention involves reducing platinum and copper salts in the presence of hydrazine hydrate in a phenolic resin reaction system to obtain Pt-Cu alloy nanoparticles. The generated alloy nanoparticles are then coated with resin and carbonized to obtain the carbon-coated Pt-Cu alloy catalyst. The carbon-coated catalyst provided by this invention, because the active components are encapsulated within the carbon material, can greatly reduce the loss of active components during the reaction process, improve catalyst stability, and thus extend the catalyst's lifespan.

[0027] 2) This invention uses a carbon coating method instead of a carbon loading method. The presence of the carbon layer spatially isolates the metal particles, preventing their aggregation and loss during the reaction, thus ensuring the high stability of the catalyst. The catalyst of this invention, applied to the catalytic hydrodechlorination reaction system of trifluorotrichloroethane to produce trifluorochloroethylene, exhibits high reactivity, high selectivity, and long lifetime, showing great application potential. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0029] Example 1

[0030] A method for preparing a carbon-coated hydrodechlorination catalyst for chlorofluorocarbons includes the following steps:

[0031] 1) Under vigorous magnetic stirring, 0.12g CTAB, 0.53g chloroplatinic acid aqueous solution with a platinum mass fraction of 4wt%, 0.42g copper nitrate aqueous solution with a copper mass fraction of 20wt%, and 300ml deionized water were stirred and mixed in a three-necked flask. 0.40g hydrazine hydrate (mass fraction of 85%) was added, and the mixture was heated to 40℃ and reacted for 10min.

[0032] 2) Add 1.25g resorcinol and 1.75ml formaldehyde to the reaction solution in step 1). Heat the solution to boiling (about 120°C) and reflux for 10 minutes. Add 1.25ml ammonia (25% by mass). Continue heating the solution to boiling (about 120°C) and reflux for 40 minutes. Allow it to cool naturally to room temperature.

[0033] 3) The reaction solution from step 2) was centrifuged and washed three times alternately with ethanol and water to obtain the catalyst precursor, which was then dried at 90°C for 8 hours. The dried product was carbonized and heated to 300°C at a rate of 2°C / min under a nitrogen atmosphere, held at 300°C for 2 hours, then heated to 700°C at a rate of 2°C / min, held at 700°C for 4 hours, and naturally cooled to room temperature to obtain a carbon-coated hydrodechlorination catalyst for chlorofluorocarbons, with a mass of approximately 1 g. The gas flow rate throughout the process was 60 ml / min. Calculations showed that the loading of Pt nanoparticles in the catalyst was approximately 2 wt%, and the loading of Cu nanoparticles was 8 wt%.

[0034] Example 2

[0035] The catalyst preparation method is the same as in Example 1, except that in step 1), the amount of copper nitrate aqueous solution with a copper mass fraction of 20 wt% is replaced from 0.42 g to 0.48 g, while the other conditions remain unchanged. The resulting carbon-coated hydrodechlorination catalyst for chlorofluorocarbons is carbon-coated. The catalyst contains 2 wt% Pt nanoparticles and 9 wt% Cu nanoparticles.

[0036] Example 3

[0037] The catalyst preparation method is the same as in Example 1, except that in step 1), the amount of copper nitrate aqueous solution with a copper mass fraction of 20 wt% is replaced from 0.42 g to 0.53 g, while the other conditions remain unchanged. The resulting carbon-coated hydrodechlorination catalyst for chlorofluorocarbons is carbon-coated. The catalyst contains 2 wt% Pt nanoparticles and 10 wt% Cu nanoparticles.

[0038] Example 4

[0039] The catalyst preparation method is the same as in Example 1, except that the amount of copper nitrate aqueous solution with a copper mass fraction of 20 wt% in step 1) is replaced from 0.42 g to 0.58 g, while the other conditions remain unchanged. The resulting carbon-coated hydrodechlorination catalyst for chlorofluorocarbons was obtained. The catalyst contained 2 wt% Pt nanoparticles and 11 wt% Cu nanoparticles.

[0040] Example 5

[0041] The catalyst preparation method is the same as in Example 1, except that in step 1), the amount of copper nitrate aqueous solution with a copper mass fraction of 20 wt% is replaced from 0.42 g to 0.63 g, while the other conditions remain unchanged. The resulting carbon-coated hydrodechlorination catalyst for chlorofluorocarbons is carbon-coated. The catalyst contains 2 wt% Pt nanoparticles and 12 wt% Cu nanoparticles.

[0042] Example 6

[0043] The catalyst preparation method is the same as in Example 1, except that the amount of copper nitrate aqueous solution with a copper mass fraction of 20wt% in step 1) is replaced by 0g instead of 0.42g, that is, no copper nitrate aqueous solution is added. The other conditions remain unchanged, and the carbon-coated chlorofluorocarbon hydrodechlorination catalyst is finally obtained.

[0044] Comparative Example 1

[0045] 1) Sift 30g of 10-18 mesh coconut shell activated carbon into a three-necked flask, add 75ml of nitric acid solution (68% nitric acid concentration) and 30ml of deionized water, and reflux in an 80℃ water bath at 500r / min for 6 hours. After reflux, wash repeatedly with distilled water until neutral, and dry at 110℃ for 6 hours. Store in a desiccator for later use.

[0046] 2) Take 0.53g of chloroplatinic acid solution (4wt% platinum), 0.42g of copper nitrate aqueous solution (20wt% copper), and 1.1g of deionized water, mix them thoroughly, and prepare an impregnation solution. Take 1g of activated carbon treated in step 1) and place it in a beaker. Add the impregnation solution evenly to the activated carbon and impregnate it by equal volume for 15 hours at room temperature. Dry the impregnated activated carbon at 110℃ for 6 hours to obtain the catalyst precursor. Place the catalyst precursor in a nitrogen atmosphere and heat it from room temperature to 600℃ at a rate of 6℃ / min. Calcinate it at 600℃ for 2 hours, and then allow it to cool naturally to room temperature to obtain the desired catalyst. The gas flow rate during the entire process is 60ml / min. The catalyst has a Pt nanoparticle loading of 2wt% and a Cu nanoparticle loading of 8wt%.

[0047] Comparative Example 2

[0048] The catalyst was prepared using the same method as Comparative Example 1, except that in step 1), the amount of 20 wt% copper nitrate aqueous solution was replaced from 0.42 g to 0.48 g, and the amount of deionized water was replaced from 1.1 g to 1.04 g. All other conditions remained unchanged. The catalyst was then obtained. The catalyst contained 2 wt% Pt nanoparticles and 9 wt% Cu nanoparticles.

[0049] Comparative Example 3

[0050] The catalyst was prepared using the same method as Comparative Example 1, except that in step 1), the amount of the 20wt% copper nitrate aqueous solution was replaced from 0.42g to 0.53g, and the amount of deionized water was replaced from 1.1g to 0.99g. All other conditions remained unchanged, and the catalyst was finally obtained. The catalyst contained 2wt% Pt nanoparticles and 10wt% Cu nanoparticles.

[0051] Comparative Example 4

[0052] The catalyst was prepared using the same method as Comparative Example 1, except that in step 1), the amount of 20 wt% copper nitrate aqueous solution was replaced from 0.42 g to 0.58 g, and the amount of deionized water was replaced from 1.1 g to 0.89 g. All other conditions remained unchanged, and the catalyst was finally obtained. The catalyst contained 2 wt% Pt nanoparticles and 11 wt% Cu nanoparticles.

[0053] Comparative Example 5

[0054] The catalyst was prepared using the same method as Comparative Example 1, except that in step 1), the amount of 20 wt% copper nitrate aqueous solution was replaced from 0.42 g to 0.63 g, and the amount of deionized water was replaced from 1.1 g to 1.42 g. All other conditions remained unchanged, and the catalyst was finally obtained. The catalyst contained 2 wt% Pt nanoparticles and 12 wt% Cu nanoparticles.

[0055] Comparative Example 6

[0056] The catalyst preparation method is the same as in Example 1, except that step 2) is replaced by adding 5g of sucrose, heating the solution to boiling, and refluxing for 40min. All other conditions remain unchanged, and the catalyst is finally obtained with a mass of approximately 1g. According to calculations, the Pt nanoparticle loading in the catalyst is 2wt%, and the Cu nanoparticle loading is 8wt%.

[0057] Comparative Example 7

[0058] The catalyst preparation method is the same as in Example 1, except that step 2) is replaced by adding 1.67 g of aniline, heating the solution to boiling, and refluxing for 40 min. All other conditions remain unchanged, and the catalyst is finally obtained with a mass of approximately 1 g. According to calculations, the loading of Pt nanoparticles in the catalyst is 2 wt%, and the loading of Cu nanoparticles is 8 wt%.

[0059] Comparative Example 8

[0060] The catalyst preparation method is the same as in Example 1, except that step 2) is replaced by adding 1.82 g of polyethylene glycol 400, heating the solution to boiling, and refluxing for 40 min. All other conditions remain unchanged, and the catalyst is finally obtained with a mass of approximately 1 g. According to calculations, the loading of Pt nanoparticles in the catalyst is 2 wt%, and the loading of Cu nanoparticles is 8 wt%.

[0061] Application Example 1:

[0062] The catalysts prepared in Examples 1-6 and Comparative Examples 1-8 were subjected to performance tests: 1g of catalyst was loaded into the reaction tube of a fixed-bed catalytic converter, with an inner diameter of 15mm; the temperature was increased from room temperature to 300℃ at a heating rate of 5℃ / min, the molar ratio of hydrogen to the feedstock trifluorotrichloroethane was 1.5:1, and the reaction space velocity was 900h⁻¹. -1 Gas chromatography was used to analyze the reaction products, and the conversion rates of the reactants and the selectivity of the target olefin products were calculated. The results are summarized in Table 1.

[0063] Table 1. Conversion of trifluorochloroethane and selectivity of trifluorochloroethylene with different catalysts

[0064]

[0065]

[0066] A comparison of the data from Examples 6 and 1-5 shows that although the catalyst without additives exhibits excellent activity at the initial stage of the reaction, it rapidly deactivates with increasing reaction time. The main reason for catalyst deactivation is carbon deposition. The addition of copper additives reduces the acidity of the catalyst, inhibits carbon deposition, and thus improves the hydrodechlorination performance of the catalyst.

[0067] A comparison of the data from Examples 1-5 and Comparative Examples 1-5 shows that although the hydrodechlorination catalyst prepared by the traditional equal-volume impregnation method exhibits high catalytic activity at the initial stage of the reaction, its activity significantly decreases and its stability is poor after 100 hours of reaction. In contrast, the carbon-coated hydrodechlorination catalyst for chlorofluorocarbons shows a much lower deactivation rate after 100 hours of reaction compared to the hydrodechlorination catalyst prepared by the impregnation method. The carbon layer effectively reduces the loss of active components and promoters from the catalyst, thus improving its stability.

[0068] A comparison of the data from Example 1 and Comparative Examples 6-8 shows that the carbon-coated chlorofluorocarbon hydrodechlorination catalyst prepared using phenolic resin as a carbon source exhibits superior catalytic activity compared to other carbon sources.

[0069] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. The application of a carbon-coated hydrodechlorination catalyst for chlorofluorocarbons in the catalytic hydrodechlorination of trifluorotrichloroethane to prepare trifluorochloroethylene, characterized in that, The catalyst uses phenolic resin as a carbon source, platinum as the main catalyst, and copper as an auxiliary agent. Platinum and copper are coated inside the carbon source and carbonized by calcination under an inert atmosphere. The catalyst has a platinum loading of 2-3 wt% and a copper loading of 8-12%. The method for preparing the catalyst includes the following steps: 1) Under vigorous magnetic stirring, cetyltrimethylammonium bromide (CTAB), soluble platinum salt aqueous solution, soluble copper salt aqueous solution and deionized water were mixed evenly, and excess hydrazine hydrate was added to carry out a reduction reaction under stirring to reduce platinum salt and copper salt to obtain Pt-Cu alloy nanoparticles. 2) Add resorcinol and formaldehyde to the reaction solution in step 1), heat the solution to boiling and reflux; 3) Add a pH adjuster to the reaction solution in step 2) to adjust the pH to alkaline, continue heating to boiling and reacting under reflux; after the reaction is completed, centrifuge and wash the solution to obtain the catalyst precursor of resin-coated Pt-Cu alloy nanoparticles. 4) The catalyst precursor in step 3) is calcined and carbonized under an inert atmosphere to obtain the carbon-coated chlorofluorocarbon hydrodechlorination catalyst.

2. The application as described in claim 1, characterized in that, In step 1), the molar concentration of CTAB in the solution is 0.001-0.005 mol / L, and the molar amount of hydrazine hydrate is 1.5-8.5 times the total molar amount of platinum salt and copper salt. The platinum salt is chloroplatinic acid hexahydrate or potassium chloroplatinate, and the copper salt is copper nitrate trihydrate or copper chloride. The dispersion concentrations of platinum salt and copper salt in the reaction solution in step 1) are respectively 0.05-0.1 mg / mL for Pt and 0.05-0.35 mg / mL for Cu.

3. The application as described in claim 1, characterized in that, In step 1), the reduction reaction temperature is 20-50℃ and the reaction time is 5-20 min.

4. The application as described in claim 1, characterized in that, Step 2) The solid-liquid ratio of hydroquinone to formaldehyde is 1g:1.2-1.5mL, and the mass ratio of hydroquinone to Pt element in platinum salt in Step 1) is 50-75:

1.

5. The application as described in claim 1, characterized in that, In step 2), the reflux time under boiling is 10-15 minutes.

6. The application as described in claim 1, characterized in that, In step 3), the pH adjuster is ammonia water, with a mass fraction of 25-30% and a volume of 0.1-1% of the volume of deionized water in step 1); in step 3), the reflux time under boiling is 25-40 min.

7. The application as described in claim 2, characterized in that, In step 3), the inert atmosphere is nitrogen. The calcination and carbonization are carried out in two steps: the first step is to calcine at 250-350℃ for 1-3 hours, and the second step is to calcine at 650-750℃ for 3-5 hours.

8. The application as described in claim 1, characterized in that... The reaction temperature for catalytic hydrodechlorination is 280-320℃, the molar ratio of hydrogen to the feedstock trifluorotrichloroethane is 1.2-2:1, and the reaction space velocity is 500-1500 h⁻¹. -1 .

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