A catalyst for the dehydration reaction of heptafluoroisobutyramide and a preparation method thereof

Abstract

The application discloses a catalyst for heptafluoroisobutyramide dehydration reaction and a preparation method thereof, relates to the field of catalysis technology, and the catalyst comprises an active component, a carrier, an additive and a complexing agent, wherein the active component is monodispersed high-valence metal-oxygen species, the carrier is one or more of porous silica or porous gamma-Al2O3, the additive refers to one kind of nitrate salt containing Na, K or Cs, and the complexing agent is one of acetic acid, citric acid, urotropine, cetyltrimethylammonium bromide or cetyltrimethylammonium hydroxide; the high-valence metal-oxygen species refers to M-O x , M is one of W, Mo, V, Cr, Mn or Co, and X=1.0-3.0. The preparation method comprises the steps of dissolving, impregnating, drying, calcining and the like. The active component in the catalyst is highly dispersed, has excellent catalytic dehydration performance, has high atomic utilization rate, the preparation method is simple, no three wastes are discharged, and the catalyst has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of catalysis technology, and in particular to a catalyst for the dehydration reaction of heptafluoroisobutyramide and its preparation method. Background Technology

[0002] Sulfur hexafluoride (SF6) is a colorless, odorless, non-corrosive, non-toxic, and denser than air. SF6 is primarily used as an insulating medium in various electrical devices, 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 banned under international treaties such as the Kyoto Resolution and the Montreal Protocol, and its use and emissions are gradually being restricted by various countries. Heptafluoroisobutyronitrile (HEC), as an environmentally friendly insulating gas, possesses advantages such as a weaker greenhouse effect and higher insulation strength, making it the most promising environmentally friendly alternative to SF6.

[0003] Currently, the main process for preparing heptafluoroisobutyronitrile (HBO) involves the dehydration of heptafluoroisobutyramide, and can be divided into the acid anhydride method and the catalytic method. The acid anhydride method involves reacting heptafluoroisobutyramide with a dehydrating agent in an organic solvent to prepare HBO. The catalytic method involves a catalytic dehydration reaction between heptafluoroisobutyramide and a catalyst in a fixed bed. Commonly used dehydrating agents in the acid anhydride method include organic acid anhydrides, phosphorus oxychloride, and phosphorus pentoxide (Chinese patent documents CN108395382A, CN108424375A, CN110642750A, 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 has significant drawbacks: 1. Both the dehydrating agent and the organic solvent are single-use and cannot be recycled, generating large amounts of fluorinated organic acidic waste liquid and solid waste, causing serious pollution; 2. The dehydrating agent requires equipment with high corrosion resistance, posing a significant risk to personnel during operation.

[0004] CN114105820A discloses a method for preparing heptafluoroisobutyronitrile via molecular sieve catalytic dehydration. This method directly uses a molecular sieve as a catalyst to react with heptafluoroisobutyramide in a dehydration reaction, yielding heptafluoroisobutyronitrile. Although this method is simple and highly selective, the rapid deactivation of the catalyst occurs because a large amount of water in the reaction product is adsorbed by the molecular sieve, covering the catalytic active sites.

[0005] CN109320436A discloses a method for preparing heptafluoroisobutyronitrile via gas-phase catalysis using metal oxides. This method first involves an amination reaction of heptafluoroisobutyrate with a primary amine to generate heptafluoroisobutyramide. Using one or more of aluminum, copper, cobalt, and niobium oxides as catalysts, the heptafluoroisobutyramide undergoes direct catalytic dehydration after high-temperature vaporization to obtain heptafluoroisobutyronitrile. This method yields high product purity and yield, but it uses the precious metals cobalt and niobium, and the catalyst preparation process is complex, prone to deactivation, and difficult to recover.

[0006] CN118056811A discloses an amide-based dehydration catalyst, using a mixed solution of amide compounds and acetonitrile as raw materials, and solid molybdenum oxide, tungsten oxide, and palladium oxide directly as catalysts. This method uses acutely toxic acetonitrile as a solvent; its vapor can form an explosive mixture with air, posing a risk of combustion and explosion upon contact with open flames or high heat. The catalyst preparation process includes steps such as liquid-phase synthesis, calcination, grinding, molding, crushing, and sieving, ultimately yielding bulk oxide particles that are directly used as the dehydration catalyst. This process is not only complex and has low atom utilization, but also only the active sites on the particle surface contribute to catalysis. Furthermore, compared to molded catalysts, this oxide catalyst suffers from lower porosity and lower strength.

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

[0008] The above-mentioned process for preparing heptafluoroisobutyramide by dehydration has problems such as high emissions of waste, poor catalyst selectivity, and low atom utilization. Summary of the Invention

[0009] The technical problem to be solved by this invention is to provide a catalyst for the dehydration reaction of heptafluoroisobutyramide and its preparation method, which belongs to the category of monodisperse high-valence metal-oxygen species catalysts. The active components in this catalyst are highly dispersed, exhibiting excellent catalytic dehydration performance, high atom utilization, and a simple preparation method with no waste emissions, thus possessing good prospects for industrial application.

[0010] To solve the above-mentioned technical problems, the technical solution of the present invention is: a catalyst for the dehydration reaction of heptafluoroisobutyramide, comprising an active component, a support, an auxiliary agent, and a complexing agent; the active component is a monodisperse high-valence metal-oxygen species; the support is one or more of porous silica or porous γ-Al2O3; the auxiliary agent contains one of Na, K, or Cs nitrates; and the complexing agent is one of acetic acid, citric acid, hexamethylenetetramine, hexadecyltrimethylammonium bromide, or hexadecyltrimethylammonium hydroxide.

[0011] The high-valence 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-valence metals mentioned refer to W, Mo, V, Cr, Mn, or Co, etc.

[0012] The porous silica can be Silicalite-1, SBA-15, commercial porous SiO2, etc.

[0013] Furthermore, a method for preparing a catalyst for the dehydration reaction of heptafluoroisobutyramide includes the following steps:

[0014] (1) Add the precursor of the high-valence metal, the auxiliary agent, and the complexing agent to the solvent and dissolve to obtain a mixed solution. The mass fraction of the high-valence metal (calculated as high-valence metal element) is 0.01wt%~40wt%, and the mass fraction of the auxiliary agent (calculated as Na, K, Cs element) is 0.01wt%~5wt%.

[0015] (2) The carrier is added to the mixed solution obtained in step (1) by means of equal volume impregnation, stirred, and the resulting mixture is placed in an oven at 60~120℃ and dried for 12h;

[0016] (3) The dried solid is calcined at 350~450℃ for 1~3h to obtain a monodisperse high-valence metal-oxygen species catalyst.

[0017] The precursor of the high-valence metal can be one or more of the following: ammonium metatungstate, tungsten hexachloride, ammonium molybdate, ammonium vanadate, cobalt nitrate, manganese nitrate, cobalt nitrate, etc.

[0018] The auxiliary agent is one of the nitrates of Na, K and Cs, preferably sodium nitrate, potassium nitrate or cesium nitrate.

[0019] The complexing agent is one of acetic acid, citric acid, hexamethylenetetramine, cetyltrimethylammonium bromide, or cetyltrimethylammonium hydroxide.

[0020] The solvent is one or more of water, methanol, ethanol, etc., with water being preferred.

[0021] The carrier can be in the form of 10-80 mesh powder, spherical or columnar shape of 2-3 mm.

[0022] The catalyst provided by this invention exhibits excellent resistance to water vapor and carbon deposition in the catalytic dehydration reaction of heptafluoroisobutyramide, high selectivity for the reaction product heptafluoroisobutyronitrile, simple preparation method, high atom utilization rate, and easy industrial scale-up, showing good application prospects.

[0023] The prepared monodisperse high-valent metal-oxygen species catalyst was packed into a fixed-bed reactor. Heptafluoroisobutyramide was heated to 140°C and vaporized, and then introduced into the catalyst bed along with a carrier gas for reaction at atmospheric pressure. The reaction temperature was 350–450°C, and the heptafluoroisobutyramide mass hourly space velocity was 0.1–2.0 h⁻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.

[0024] Furthermore, the mass hourly space velocity (HHSV) of the heptafluoroisobutyramide is 0.1~2.0 h⁻¹. -1 Preferably, it is 0.2~1.0h. -1 .

[0025] Furthermore, the reaction temperature is 350℃~450℃.

[0026] The catalyst prepared by this invention is used for the dehydration reaction of heptafluoroisobutyramide, achieving a conversion rate of 98%, a selectivity of over 99%, and a catalyst lifetime of 500-2000 hours.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] This invention provides a monodisperse high-valence metal-oxygen species catalyst for the intramolecular catalytic dehydration of heptafluoroisobutyramide to prepare heptafluoroisobutyronitrile. The introduction of an auxiliary agent regulates the acidity and basicity of the catalyst surface and improves the selectivity of the target product; the introduction of a complexing agent improves the dispersion of active metal-oxygen species and enhances the catalyst activity; and trace amounts of oxygen in the carrier gas reduce catalyst carbon deposition and improve catalyst lifetime.

[0029] The catalyst active component provided by this invention is a monodisperse high-valence metal-oxygen species (MO). x (M represents W, Mo, V, Cr, Mn, Co) is used for the catalytic dehydration of heptafluoroisobutyramide to prepare heptafluoroisobutyronitrile. It has the advantages of high atom utilization and high catalytic activity. Moreover, the catalyst preparation process is simple, the reaction conditions are safe and controllable, which greatly improves the production efficiency and facilitates engineering scale-up and industrial production.

[0030] The process used in this invention is a green production process that avoids the use of dehydrating agents and toxic solvents, and solves the problems of complex dehydration process routes, high equipment requirements and large amounts of organic waste liquid discharge in the acid anhydride method. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a fixed-bed reactor device.

[0032] Figure 2 This is the Raman diagram of the monodisperse molybdenum-oxygen species catalyst in Example 2.

[0033] Figure 3 The image shows the XRD patterns of the support and monodisperse tungsten oxide species catalyst in Example 5.

[0034] Figure 4 This is an evaluation of the performance of the monodisperse tungsten-oxygen species catalyst in Example 5. Detailed Implementation

[0035] The present invention will be described in detail below through embodiments, but the present invention is not limited to the embodiments.

[0036] The catalyst is represented as xMyNzP / support, where:

[0037] x represents the percentage of highly dispersed metal species elements in the total mass of the catalyst × 100;

[0038] M represents a highly dispersed metallic species element;

[0039] y represents the percentage of auxiliary elements in the total mass of the catalyst × 100;

[0040] N represents the auxiliary metal element;

[0041] z represents the percentage of the complexing agent's mass to the total catalyst mass × 100;

[0042] P represents a complexing agent, where A is acetic acid, C is citric acid, and H is one of hexamethylenetetramine, cetyltrimethylammonium bromide, or cetyltrimethylammonium hydroxide.

[0043] Examples 1-6 describe the preparation processes of different catalysts.

[0044] Example 1

[0045] (1) Take 10~50 mesh SBA-15 molecular sieve and dry it in an oven at 150℃ for 3h to remove adsorbed impurities;

[0046] (2) The precursor of the high-valence metal, the auxiliary salt, and the complexing agent are added to the solvent and dissolved to obtain a mixed solution, wherein the content of W element is 5wt%, the content of K element is 2wt%, and the amount of acetic acid is 0.01wt%;

[0047] (3) Using an equal-volume impregnation method, the carrier treated in step (1) is added to the mixed solution obtained in step (2) and stirred for 0.5 h;

[0048] (4) The mixture obtained in step (3) was dried in an oven at 60°C for 12 hours; then it was pyrolyzed in a muffle furnace at 450°C for 3 hours to obtain catalyst 5W2K0.01A / SBA-15. Detailed parameters are shown in Table 1.

[0049] Example 2

[0050] (1) Take a 2mm spherical SiO2 and dry it in an oven at 150℃ for 3h to remove the adsorbed impurities;

[0051] (2) Add the precursor of the high-valence metal, the auxiliary salt, and the complexing agent to the solvent and dissolve to obtain a mixed solution, wherein the content of Mo is 10wt%, the content of Na is 1wt%, and the amount of acetic acid is 2wt%;

[0052] (3) Using an equal-volume impregnation method, the carrier treated in step (1) is added to the mixed solution obtained in step (2) and stirred for 0.5 h;

[0053] (4) The mixture obtained in step (3) was dried in an oven at 120°C for 12 hours, and then pyrolyzed in a muffle furnace at 400°C for 2 hours to obtain the catalyst 10Mo1Na2A / SiO2. Detailed parameters are shown in Table 1.

[0054] Example 3

[0055] (1) Take 10~50 mesh SBA-15 and dry it in an oven at 150℃ for 3 hours to remove adsorbed impurities;

[0056] (2) The precursor of the high-valence metal, the auxiliary salt, and the complexing agent are added to the solvent and dissolved to obtain a mixed solution, wherein the content of W element is 30wt%, the content of Na element is 0.1wt%, and the amount of acetic acid is 0.1wt%;

[0057] (3) Using an equal-volume impregnation method, the carrier treated in step (1) is added to the mixed solution obtained in step (2) and stirred for 0.5 h;

[0058] (4) The mixture obtained in step (3) was dried in an oven at 120°C for 12 hours, and then pyrolyzed in a muffle furnace at 425°C for 2 hours to obtain catalyst 30W0.1Na0.1A / SBA-15. Detailed parameters are shown in Table 1.

[0059] Example 4

[0060] (1) Take 10~50 mesh SBA-15 and dry it in an oven at 150℃ for 3 hours to remove adsorbed impurities;

[0061] (2) Add the precursor of the high-valence metal, the auxiliary salt, and the complexing agent to the solvent and dissolve to obtain a mixed solution, wherein the content of V element is 20wt%, the content of Cs element is 1wt%, and the amount of citric acid is 1wt%;

[0062] (3) Using an equal-volume impregnation method, the carrier treated in step (1) is added to the mixed solution obtained in step (2) and stirred for 0.5 h;

[0063] (4) The mixture obtained in step (3) was dried in an oven at 80°C for 12 hours, and then pyrolyzed in a muffle furnace at 450°C for 2 hours to obtain catalyst 20V1Cs1C / SBA-15. Detailed parameters are shown in Table 1.

[0064] Example 5

[0065] (1) Take a 2mm columnar porous SiO2 and dry it in a 150℃ oven for 3h to remove adsorbed impurities;

[0066] (2) The precursor of the high-valence metal, the auxiliary salt, and the complexing agent are added to the solvent and dissolved to obtain a mixed solution, wherein the content of W element is 20wt%, the content of K element is 0.01wt%, and the amount of hexadecyltrimethylammonium bromide is 0.01wt%;

[0067] (3) Using an equal-volume impregnation method, the carrier treated in step (1) is added to the mixed solution obtained in step (2) and stirred for 0.5 h;

[0068] (4) The mixture obtained in step (3) was dried in an oven at 120°C for 12 hours, and then pyrolyzed in a muffle furnace at 425°C for 3 hours to obtain catalyst 20W0.01k0.01H / SiO2. Detailed parameters are shown in Table 1.

[0069] Example 6

[0070] (1) Take a 2mm columnar porous SiO2 and dry it in a 150℃ oven for 3h to remove adsorbed impurities;

[0071] (2) Add the precursor of the high-valence metal to the solvent and dissolve it to obtain a mixed solution, wherein the W element content is 5wt%, and no auxiliary salts or complexing agents are added;

[0072] (3) Using an equal-volume impregnation method, the carrier treated in step (1) is added to the mixed solution obtained in step (2) and stirred for 0.5 h;

[0073] (4) The mixture obtained in step (3) was dried in an oven at 120°C for 12 hours, and then pyrolyzed in a muffle furnace at 425°C for 3 hours to obtain the catalyst 5W / SiO2. Detailed parameters are shown in Table 1.

[0074] Examples 7 to 11 refer to the catalyst preparation method of Example 1, and the detailed parameters of their preparation conditions are shown in Table 1.

[0075]

[0076] Experiments were conducted using different catalysts for the intramolecular dehydration of heptafluoroisobutyramide to prepare heptafluoroisobutyronitrile. The performance of the catalysts prepared in Examples 1-6 was evaluated in a fixed-bed reactor. Figure 1This is a schematic diagram of a fixed-bed catalytic reactor, where the reactor has an inner diameter of 10 mm, a length of 200 mm, a catalyst loading of 10 g, a reaction temperature of 425 °C, a reaction time of 5 h, and a heptafluoroisobutyramide mass hourly space velocity of 0.2 h⁻¹. -1 The carrier gas was a mixture of 99.8% nitrogen and 0.2% oxygen, with a flow rate of 0.8 L / min. The reaction products were sampled and analyzed by gas chromatography, and the catalyst performance evaluation results are shown in Table 2.

[0077]

[0078] Figure 2 For the Raman representation of the catalyst reaction in Example 2, 976 cm -1 A strong characteristic vibrational peak appeared, which is the characteristic stretching vibration of Mo=O in the monodisperse [MoO4] active site, confirming the monodisperse nature of the active species. Figure 3 XRD representation of the support and catalyst in Example 5. (From...) Figure 3 It can be seen that the XRD diffraction peaks of the support and the catalyst are basically consistent, with no other obvious characteristic diffraction peaks, indicating that W element is mainly composed of WO3. x It exists in a monodisperse state and does not form metal oxide particles. The introduction of a complexing agent improves WO3. x The dispersion of active centers and the introduction of alkali metals can adjust the acidity and alkalinity of the catalyst surface and improve product selectivity.

[0079] The catalyst prepared in Example 5 was subjected to a lifetime evaluation experiment in a fixed-bed reactor (see...). Figure 4 The catalyst is continuously fed and regenerated four times. After each regeneration, the catalyst performance can be restored to the activity level of the fresh catalyst. It can be seen that the monodisperse high-valence metal-oxygen species catalyst not only has excellent conversion rate and selectivity, but also excellent cycle stability.

Claims

1. A catalyst for the dehydration reaction of heptafluoroisobutyramide, comprising an active component, a carrier, an auxiliary agent and a complexing agent, the active component is a monodisperse high-valent metal-oxygen species, the carrier is one or more of porous silica or porous γ-Al2O3, the auxiliary agent refers to one containing a nitrate of Na, K or Cs; the complexing agent is one of acetic acid, citric acid, urotropine, cetyltrimethylammonium bromide or cetyltrimethylammonium hydroxide; the high-valent metal-oxygen species refers to M-O X x , M is one of W, Mo, V, X = 1.0-3.

0. The preparation method includes the following steps: (1) Add the precursor of the high-valence metal, the auxiliary agent, and the complexing agent to the solvent and dissolve to obtain a mixed solution. The mass fraction of the high-valence metal is 5wt%~40wt%, and the mass fraction of the auxiliary agent is 0.01wt%~5wt%. (2) The carrier is added to the mixed solution obtained in step (1) by means of equal volume impregnation, stirred, and the resulting mixture is placed in an oven at 60~120℃ and dried for 12h; (3) The dried solid is calcined at 350~450℃ for 1~3h to obtain a monodisperse high-valence metal-oxygen species catalyst; Usage instructions include: The prepared monodisperse high-valent metal-oxygen species catalyst was packed into a fixed-bed reactor. Heptafluoroisobutyramide was heated to 140°C and vaporized, and then introduced into the catalyst bed along with a carrier gas for reaction at atmospheric pressure. The reaction temperature was 350–450°C, and the heptafluoroisobutyramide mass hourly space velocity was 0.1–2.0 h⁻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.

2. The catalyst according to claim 1, wherein 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 as described in claim 1, comprising the following steps: (1) Add the precursor of the high-valence metal, the auxiliary agent, and the complexing agent to the solvent and dissolve to obtain a mixed solution. The mass fraction of the high-valence metal is 5wt%~40wt%, and the mass fraction of the auxiliary agent is 0.01wt%~5wt%. (2) The carrier is added to the mixed solution obtained in step (1) by means of equal volume impregnation, stirred, and the resulting mixture is placed in an oven at 60~120℃ and dried for 12h; (3) The dried solid is calcined at 350~450℃ for 1~3h to obtain a monodisperse high-valence metal-oxygen species catalyst.

4. The preparation method according to claim 3, wherein the precursor of the high-valence metal is one or more of ammonium metatungstate, tungsten hexachloride, ammonium molybdate, and ammonium vanadate.

5. The preparation method according to claim 3, wherein the solvent is one or more of water, methanol, and ethanol.

6. The preparation method according to claim 3, characterized in that, The carrier is in the form of 10-80 mesh powder, or spherical or columnar shapes of 2-3 mm.

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