Catalyst for heptafluoroisobutyramide dehydration reaction and preparation method thereof

Abstract

The present invention discloses a catalyst for heptafluoroisobutyramide dehydration reaction and a preparation method thereof, and relates to the technical field of catalysis, the catalyst comprises an active component, a carrier, an auxiliary agent and a complexing agent, the active component is a monodispersed high valence metal-oxygen species, the carrier is one or more of porous silicon dioxide or porous gamma-Al2O3, and the auxiliary agent is one or more of sodium hydroxide and sodium hydroxide. The auxiliary agent is one of nitrates containing Na, K or Cs; the complexing agent is one of acetic acid, citric acid, urotropine, hexadecyl trimethyl ammonium bromide or hexadecyl trimethyl ammonium hydroxide; the high-valence metal-oxygen species refer to M-Ox, M is one of W, Mo, V, Cr, Mn or Co, and X is equal to 1.0 to 3.0. The preparation method comprises the steps of dissolving, dipping, drying, roasting and the like. The active components in the catalyst are highly dispersed, the catalyst has excellent catalytic dehydration performance, the atom utilization rate is high, the preparation method is simple, no three wastes are discharged, and the catalyst has good industrial application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysis, in particular to a catalyst for heptafluoroisobutyramide dehydration reaction and a preparation method thereof. Background Art

[0002] Sulfur hexafluoride (SF6) is a colorless, odorless, non-corrosive, non-toxic, and inert gas with a density greater than air. SF6 is primarily used as an insulating medium in various electrical equipment, such as circuit breakers and high-voltage transmission lines. However, as the most potent greenhouse gas, SF6 has a global warming potential (GWP) of 23,600 and an atmospheric lifetime of 3,200 years. It is one of the six greenhouse gases whose emissions are prohibited under international treaties such as the Kyoto Protocol and the Montreal Protocol, and its use and emissions are gradually being restricted in various countries. Heptafluoroisobutyronitrile, an environmentally friendly insulating gas with a low greenhouse effect and high dielectric strength, is the most promising alternative to SF6.

[0003] Currently, the production of heptafluoroisobutyronitrile primarily involves the dehydration of heptafluoroisobutyramide, which can be divided into two methods: the acid anhydride method and the catalytic method. The acid anhydride method involves reacting heptafluoroisobutyramide with a dehydrating agent in an organic solvent to produce heptafluoroisobutyramide; the catalytic method involves catalytic dehydration of heptafluoroisobutyramide with a catalyst in a fixed bed. Common dehydrating agents used in the acid anhydride method include organic acid anhydrides, phosphorus oxychloride, and phosphorus pentoxide (Chinese patents CN108395382A, CN108424375A, CN110642750A, and CN108395382A), and the organic solvents used include one or more of N,N-dimethylformamide, pyridine, 1,4-dioxane, and dimethyl sulfoxide. Although this method is simple in principle and mature in process, it suffers from significant drawbacks: 1. Both the dehydrating agent and the organic solvent are single-use and cannot be recycled, resulting in the generation of large amounts of fluorinated organic acidic waste liquids and solids, causing significant pollution; 2. The dehydrating agent requires high corrosion resistance from the equipment, posing significant operational risks.

[0004] CN114105820A discloses a method for preparing heptafluoroisobutyronitrile via molecular sieve-catalyzed dehydration. This method uses molecular sieve as a catalyst to react with heptafluoroisobutyramide to produce heptafluoroisobutyronitrile. While this method is simple and highly selective, it suffers from the fact that a large amount of water in the reaction product is adsorbed by the molecular sieve, covering the catalytically active sites and causing rapid catalyst deactivation.

[0005] CN109320436A discloses a method for preparing heptafluoroisobutyronitrile using metal oxide vapor-phase catalysis. This method involves an amination reaction between heptafluoroisobutyrate and a primary amine to produce heptafluoroisobutyramide. Using one or more oxides of aluminum, copper, cobalt, or niobium as catalysts, the heptafluoroisobutyramide is vaporized at high temperature and then directly subjected to a catalytic dehydration reaction to produce heptafluoroisobutyronitrile. This method achieves high product purity and yield, but utilizes the precious metals cobalt and niobium, and the catalyst preparation process is complex, prone to deactivation, and difficult to recover.

[0006] CN118056811A discloses a dehydration catalyst for amide compounds, which uses a mixed solution of amide compounds and acetonitrile as a raw material, and molybdenum oxide, tungsten oxide, and palladium oxide solids as catalysts. The method uses acutely toxic acetonitrile as a solvent, and its vapor and air can form an explosive mixture, which is dangerous to cause combustion and explosion when exposed to open flames and high heat. The catalyst preparation process includes liquid phase synthesis, roasting, grinding, molding, crushing, screening and other steps, and finally obtains bulk oxide particles directly as a dehydration catalyst. Not only is the preparation process complicated, the atomic utilization rate is low, and only the active sites on the particle surface play a catalytic role. This oxide catalyst also has the problems of low porosity and low strength compared to the molded catalyst.

[0007] CN111848444A discloses a method for synthesizing heptafluoroisobutyronitrile. The method uses heptafluoroisobutyrate and ammonia as raw materials and oxides or salts of aluminum, manganese, boron, vanadium, barium, zirconium, cerium and thorium as catalysts. However, excessively high reaction temperatures cause decomposition of the raw materials and products, leading to carbon deposition on the catalyst, resulting in poor catalyst selectivity and life.

[0008] The above-mentioned process for preparing heptafluoroisobutyronitrile by dehydrating heptafluoroisobutyramide has problems such as high emission of three wastes, poor catalyst selectivity, and low atom utilization. Summary of the Invention

[0009] The present invention aims to provide a catalyst for the dehydration reaction of heptafluoroisobutyramide and its preparation method. The catalyst is a monodisperse, high-valent metal-oxygen species catalyst. The active components are highly dispersed, resulting in excellent catalytic dehydration performance and high atomic utilization. The preparation method is simple, and no three wastes are emitted, suggesting promising prospects for industrial application.

[0010] To solve the above technical problems, the technical solution of the present invention is: a catalyst for the dehydration reaction of heptafluoroisobutyramide, comprising an active component, a carrier, an auxiliary agent and a complexing agent, wherein the active component is a monodispersed high-valent metal-oxygen species, the carrier is one or more of porous silica or porous γ-Al2O3, the auxiliary agent comprises a nitrate of Na, K or Cs; and the complexing agent is one of acetic acid, citric acid, urotropine, cetyltrimethylammonium bromide or cetyltrimethylammonium hydroxide.

[0011] The high-valent metal-oxygen species refers to MO x , M is one of W, Mo, V, Cr, Mn or Co, and x=1.0-3.0. The high-valent metal refers to W, Mo, V, Cr, Mn or Co.

[0012] The porous silica may be Silicalite-1, SBA-15, commercial porous SiO2, or the like.

[0013] Furthermore, a method for preparing a catalyst for the dehydration reaction of heptafluoroisobutyramide comprises the following steps: (1) Adding a high-valent metal precursor, an additive, and a complexing agent into a solvent and dissolving them to obtain a mixed solution, wherein the mass fraction of the high-valent metal (calculated as the high-valent metal element) is 0.01 wt% to 40 wt%, and the mass fraction of the additive (calculated as Na, K, Cs elements) is 0.01 wt% to 5 wt%; (2) adding the carrier to the mixed solution obtained in step (1) by an equal volume impregnation method, stirring, and drying the obtained mixture in an oven at 60-120°C for 12 hours; (3) The dried solid is calcined at 350-450°C for 1-3 hours to obtain a monodispersed high-valent metal-oxygen species catalyst.

[0014] The precursor of the high-valent metal may be one or more of ammonium metatungstate, tungsten hexachloride, ammonium molybdate, ammonium vanadate, cobalt nitrate, manganese nitrate, cobalt nitrate, and the like.

[0015] The auxiliary agent is one of the nitrates of Na, K and Cs, preferably sodium nitrate, potassium nitrate or cesium nitrate.

[0016] The complexing agent is one of acetic acid, citric acid, hexamethylenetetramine, hexadecyltrimethylammonium bromide or hexadecyltrimethylammonium hydroxide.

[0017] The solvent is one or more of water, methanol, ethanol, etc., preferably water.

[0018] The carrier can be in the form of 10-80 mesh powder, 2-3 mm sphere or column.

[0019] The catalyst provided by the present invention has excellent water vapor resistance and carbon deposition resistance in the catalytic dehydration reaction of heptafluoroisobutyramide, has high selectivity for the reaction product heptafluoroisobutyronitrile, is simple in preparation method, has high atom utilization rate, is easy to scale up industrially, and has good application prospects.

[0020] The prepared monodispersed high-valent metal-oxygen species catalyst was loaded into a fixed bed reactor, and heptafluoroisobutyramide was heated to 140°C and vaporized. The catalyst was then introduced into the catalyst bed along with the carrier gas for reaction at normal pressure. The reaction temperature was 350-450°C, and the mass space velocity of heptafluoroisobutyramide was 0.1-2.0h-1. -1 The carrier gas is a mixture of nitrogen or helium and oxygen, with an oxygen content of 0.1% to 0.5% and a carrier gas flow rate of 0.3 to 2.0 L / min, preferably 1.0 to 1.2 L / min.

[0021] Furthermore, the mass space velocity of heptafluoroisobutyramide is 0.1~2.0h -1 , preferably 0.2~1.0h -1 .

[0022] Furthermore, the reaction temperature is 350°C to 450°C.

[0023] The catalyst prepared by the present invention is used for the dehydration reaction of heptafluoroisobutyramide, the conversion rate of heptafluoroisobutyramide reaches 98%, the selectivity exceeds 99%, and the catalyst life is 500-2000 hours.

[0024] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a monodisperse high-valent metal-oxygen species catalyst for preparing heptafluoroisobutyronitrile by intramolecular catalytic dehydration of heptafluoroisobutyramide. The catalyst comprises a catalyst surface acidity and alkalinity controlled by an auxiliary agent, thereby improving the selectivity of the target product. The catalyst surface acidity and alkalinity controlled by an auxiliary agent are improved by the introduction of a complexing agent, thereby improving the dispersion of the active metal-oxygen species and the activity of the catalyst. The catalyst surface acidity and alkalinity controlled by an auxiliary agent are improved by the introduction of a complexing agent, thereby improving the activity of the catalyst. The catalyst surface acidity and alkalinity controlled by an auxiliary agent are improved by the introduction of a complexing agent ...

[0025] The active component of the catalyst provided by the present invention is a monodispersed high-valent metal-oxygen species (MO x , M is W, Mo, V, Cr, Mn, Co), and is used for the catalytic dehydration of heptafluoroisobutyramide to prepare heptafluoroisobutyronitrile. It has the advantages of high atom utilization and high catalytic activity, and the catalyst preparation process is simple, the reaction conditions are safe and controllable, and the production efficiency is greatly improved, which is convenient for engineering scale-up and industrial production.

[0026] The process used in the present invention is a green production process, which avoids the use of dehydrating agents and toxic solvents and solves the problems of complex anhydride dehydration process route, high equipment requirements and large-scale organic waste liquid discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of a fixed bed reactor apparatus.

[0028] Figure 2 This is the Raman diagram of the monodisperse molybdenum oxide species catalyst in Example 2.

[0029] Figure 3 This is the XRD pattern of the support and monodisperse tungsten oxide species catalyst in Example 5.

[0030] Figure 4 This is the performance evaluation of the monodisperse tungsten oxide species catalyst in Example 5. DETAILED DESCRIPTION

[0031] The present invention will be described in detail below by way of examples, but the present invention is not limited to the examples.

[0032] The catalyst is represented by xMyNzP / support, wherein: x represents the percentage of highly dispersed metal species elements in the total mass of the catalyst × 100; M represents highly dispersed metal species elements; y represents the percentage of promoter elements in the total mass of the catalyst × 100; N represents the additive metal element; z represents the percentage of the mass of the complexing agent to the total mass of the catalyst × 100; P represents a complexing agent, wherein A is acetic acid, C is citric acid, and H is one of hexamethylenetetramine, hexadecyltrimethylammonium bromide, or hexadecyltrimethylammonium hydroxide.

[0033] Examples 1 to 6 describe the preparation processes of different catalysts.

[0034] Example 1

[0035] (1) Take 10-50 mesh SBA-15 molecular sieves and place them in a 150°C oven to dry for 3 hours to remove adsorbed impurities; (2) Adding a high-valent metal precursor, an auxiliary salt, and a complexing agent into a solvent and dissolving them to obtain a mixed solution, wherein the W element content is 5 wt%, the K element content is 2 wt%, and the amount of acetic acid is 0.01 wt%; (3) Add the carrier treated in step (1) to the mixed solution obtained in step (2) by equal volume impregnation and stir for 0.5 h; (4) The mixture obtained in step (3) was dried in an oven at 60°C for 12 h; then, the mixture was pyrolyzed in a muffle furnace at 450°C for 3 h to obtain the catalyst 5W2K0.01A / SBA-15. Detailed parameters are shown in Table 1.

[0036] Example 2

[0037] (1) Take 2mm spherical SiO2 and place it in a 150℃ oven to dry for 3 hours to remove adsorbed impurities; (2) Adding a high-valent metal precursor, an auxiliary salt, and a complexing agent into a solvent and dissolving them to obtain a mixed solution, wherein the content of Mo element is 10 wt%, the content of Na element is 1 wt%, and the amount of acetic acid is 2 wt%; (3) Add the carrier treated in step (1) to the mixed solution obtained in step (2) by equal volume impregnation and stir for 0.5 h; (4) The mixture obtained in step (3) was dried in an oven at 120°C for 12 h, and then pyrolyzed in a muffle furnace at 400°C for 2 h to obtain the catalyst 10Mo1Na2A / SiO2. Detailed parameters are shown in Table 1.

[0038] Example 3

[0039] (1) Take 10-50 mesh SBA-15 and place it in a 150°C oven to dry for 3 hours to remove adsorbed impurities; (2) Adding a high-valent metal precursor, an auxiliary salt, and a complexing agent into a solvent and dissolving them to obtain a mixed solution, wherein the W element content is 30 wt%, the Na element content is 0.1 wt%, and the amount of acetic acid is 0.1 wt%; (3) Add the carrier treated in step (1) to the mixed solution obtained in step (2) by equal volume impregnation and stir for 0.5 h; (4) The mixture obtained in step (3) was dried in an oven at 120°C for 12 h, and then pyrolyzed in a muffle furnace at 425°C for 2 h to obtain the catalyst 30W0.1Na0.1A / SBA-15. Detailed parameters are shown in Table 1.

[0040] Example 4

[0041] (1) Take 10-50 mesh SBA-15 and place it in a 150°C oven to dry for 3 hours to remove adsorbed impurities; (2) Adding a high-valent metal precursor, an auxiliary salt, and a complexing agent into a solvent and dissolving them to obtain a mixed solution, wherein the V element content is 20 wt%, the Cs element content is 1 wt%, and the amount of citric acid is 1 wt%; (3) Add the carrier treated in step (1) to the mixed solution obtained in step (2) by equal volume impregnation and stir for 0.5 h; (4) The mixture obtained in step (3) was dried in an oven at 80°C for 12 h and then pyrolyzed in a muffle furnace at 450°C for 2 h to obtain the catalyst 20V1Cs1C / SBA-15. Detailed parameters are shown in Table 1.

[0042] Example 5

[0043] (1) Take 2mm columnar porous SiO2 and place it in a 150℃ oven to dry for 3h to remove adsorbed impurities; (2) Adding a high-valent metal precursor, an auxiliary salt, and a complexing agent into a solvent and dissolving them to obtain a mixed solution, wherein the W element content is 20 wt%, the K element content is 0.01 wt%, and the amount of hexadecyltrimethylammonium bromide is 0.01 wt%; (3) Add the carrier treated in step (1) to the mixed solution obtained in step (2) by equal volume impregnation and stir for 0.5 h; (4) The mixture obtained in step (3) was dried in an oven at 120°C for 12 h, and then pyrolyzed in a muffle furnace at 425°C for 3 h to obtain the catalyst 20W0.01k0.01H / SiO2. Detailed parameters are shown in Table 1.

[0044] Example 6

[0045] (1) Take 2mm columnar porous SiO2 and place it in a 150℃ oven to dry for 3h to remove adsorbed impurities; (2) adding a high-valent metal precursor to a solvent and dissolving it to obtain a mixed solution, wherein the W element content is 5 wt % and no auxiliary salt or complexing agent is added; (3) Add the carrier treated in step (1) to the mixed solution obtained in step (2) by equal volume impregnation and stir for 0.5 h; (4) The mixture obtained in step (3) was dried in an oven at 120°C for 12 h, and then pyrolyzed in a muffle furnace at 425°C for 3 h to obtain the catalyst 5W / SiO2. Detailed parameters are shown in Table 1.

[0046] The catalyst preparation method of Examples 7 to 11 refers to that of Example 1, and the detailed parameters of the preparation conditions are shown in Table 1.

[0047]

[0048] Different catalysts were used in the experiment of preparing heptafluoroisobutyronitrile by intramolecular dehydration of heptafluoroisobutyramide. The catalysts prepared in Examples 1-6 were evaluated in a fixed bed reactor. Figure 1 Schematic diagram of a fixed-bed catalytic reactor, where the inner diameter of the fixed-bed reactor is 10 mm, the length is 200 mm, the catalyst loading is 10 g, the reaction temperature is 425 ° C, the reaction time is 5 h, and the mass space velocity of heptafluoroisobutyramide is 0.2 h -1 The carrier gas was a mixture of 99.8% nitrogen and 0.2% oxygen at a flow rate of 0.8 L / min. The reaction products were sampled and analyzed by gas chromatography. The catalyst performance evaluation results are shown in Table 2.

[0049]

[0050] Figure 2This is the Raman spectra of the catalyst reaction in Example 2, 976 cm -1 A strong characteristic vibration peak appeared, which was the characteristic stretching vibration of Mo=O in the monodisperse [MoO4] active site, confirming the monodisperse nature of the active species. Figure 3 The XRD patterns of the support and catalyst in Example 5 are shown in FIG. Figure 3 It can be seen that the XRD diffraction peaks of the support and the catalyst are basically consistent, and there are no other obvious characteristic diffraction peaks, indicating that the W element is in the form of WO x It is in a monodisperse state and no metal oxide particles are formed. The introduction of complexing agent improves WO x The dispersion of active centers and the introduction of alkali metals adjust the acidity and alkalinity of the catalyst surface and improve product selectivity.

[0051] The catalyst prepared in Example 5 was subjected to a life evaluation experiment in a fixed bed reactor (see Figure 4 ), the catalyst was continuously fed and regenerated four times. After each regeneration, the catalyst performance was restored to the activity level of the fresh catalyst. It can be seen that this monodispersed high-valent metal-oxygen species catalyst not only has excellent conversion rate and selectivity, but also has excellent cyclic stability.

Claims

1. A catalyst for the dehydration reaction of heptafluoroisobutyramide, comprising an active component, a carrier, an auxiliary agent and a complexing agent, characterized in that: The invention is used for the catalytic dehydration reaction of heptafluoroisobutyramide, wherein the active component is a monodispersed high-valent metal-oxygen species, the carrier is one or more of porous silica or porous γ-Al2O3, the auxiliary agent is a nitrate containing Na, K or Cs; the complexing agent is one of acetic acid, citric acid, hexamethylenetetramine, hexadecyltrimethylammonium bromide or hexadecyltrimethylammonium hydroxide, and the high-valent metal-oxygen species is MO x , M is one of W, Mo, V, Cr, Mn or Co, and X = 1.0~3.

0.

2. The catalyst according to claim 1, characterized in that The porous silica refers to Silicalite-1, SBA-15 or commercial porous SiO2.

3. A method for preparing a catalyst for the dehydration reaction of heptafluoroisobutyramide, characterized in that: The following steps are involved: (1) Adding a high-valent metal precursor, an auxiliary agent, and a complexing agent into a solvent and dissolving them to obtain a mixed solution, wherein the mass fraction of the high-valent metal is 0.01 wt% to 40 wt% and the mass fraction of the auxiliary agent is 0.01 wt% to 5 wt%; (2) adding the carrier to the mixed solution obtained in step (1) by an equal volume impregnation method, stirring, and drying the obtained mixture in an oven at 60-120°C for 12 hours; (3) The dried solid is calcined at 350-450°C for 1-3 hours to obtain a monodispersed high-valent metal-oxygen species catalyst.

4. The preparation method according to claim 3, characterized in that The high-valent metal precursor is one or more of ammonium metatungstate, tungsten hexachloride, ammonium molybdate, ammonium vanadate, cobalt nitrate, manganese nitrate, and cobalt nitrate.

5. The preparation method according to claim 3, characterized in that The auxiliary agent is one of the nitrates of Na, K or Cs.

6. The preparation method according to claim 5, characterized in that The auxiliary agent is sodium nitrate, potassium nitrate or cesium nitrate.

7. The preparation method according to claim 3, characterized in that The complexing agent is one of acetic acid, citric acid, hexamethylenetetramine, hexadecyltrimethylammonium bromide and hexadecyltrimethylammonium hydroxide.

8. The preparation method according to claim 3, characterized in that The solvent is one or more of water, methanol and ethanol.

9. The preparation method according to claim 3, characterized in that The carrier is in the form of 10~80 mesh powder, 2~3mm sphere or column.

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