A method for gas-phase catalytic preparation of heptafluoroisobutyronitrile

Abstract

This invention discloses a gas-phase catalytic method for preparing heptafluoroisobutyronitrile. The method includes: removing one molecule of water from heptafluoroisobutyramide gas to obtain heptafluoroisobutyronitrile under the action of a catalyst; the catalyst is an oxide of a siderophile element, wherein the siderophile element includes at least one moderate siderophile element selected from tungsten, molybdenum, tin, or gallium, or at least one strong siderophile element selected from osmium, iridium, ruthenium, rhenium, or titanium. This invention uses catalytic dehydration, which is low-cost, produces less waste, and enables continuous gas-phase reaction, making it suitable for industrial production. Furthermore, the catalyst exhibits high catalytic activity and a long catalytic lifetime.

Description

Technical Field

[0001] This invention relates to the preparation of heptafluoroisobutyronitrile, and particularly to a method for preparing heptafluoroisobutyronitrile by gas-phase catalytic dehydration. Background Technology

[0002] Perfluoroisobutyronitrile (C4F7N) exhibits low toxicity and excellent chemical stability. Its global warming potential (GWP) is 2400, only about one-tenth that of sulfur hexafluoride (SF6), and its ozone depletion potential (ODP) is 0. Compared to SF6, its atmospheric lifetime is significantly shorter, demonstrating potential as a substitute for SF6. Currently, the synthesis of heptafluoroisobutyronitrile mainly involves the dehydration of heptafluoroisobutyramide, primarily using dehydrating agents.

[0003] Patent US15997808A discloses a method for producing heptafluoroisobutylamide from methyl heptafluoroisobutyrate and ammonia, followed by a dehydration reaction using pyridine and trifluoroacetic anhydride as dehydrating agents to obtain heptafluoroisobutyronitrile, with a yield of 74.9% in the dehydration step. Patent CN108395382A discloses a method for obtaining heptafluoroisobutyronitrile by dehydration using trifluoroacetic anhydride as a dehydrating agent, with a yield of 76%. Patent CN110642750A discloses a method for obtaining perfluoroalkylnitrile by dehydration of perfluoroalkylamide using fluorinated carboxylic anhydrides (such as trifluoroacetic anhydride, pentafluoropropionic anhydride, heptafluorobutyric anhydride, and heptafluoroisobutyric anhydride) and N,N-dimethylformamide as a combined dehydrating agent. Patent CN107935884A discloses that the main dehydrating agent used in the dehydration process of heptafluoroisobutyramide is one or more of trifluoroacetic anhydride, acetic anhydride, thionyl chloride, phosphorus pentoxide or phosphorus oxychloride, and the organic solvent used is one or more of pyridine, polyphosphoric acid, carbon tetrachloride, N,N-dimethylformamide, N,N-diethylformamide, 1,4-dioxane or dimethyl sulfoxide.

[0004] Although the dehydration process of heptafluoroisobutyramide under the action of dehydrating agent is mature, it has the following defects: (1) It is an intermittent process, which makes it difficult to achieve large-scale continuous production; (2) It uses a large amount of dehydrating agent, which easily generates a large amount of liquid waste or solid waste, and the consumed dehydrating agent is difficult to recycle and reuse; (3) It uses a large amount of solvent, and due to the introduction of dehydrating agent and its by-products, the solvent is difficult to recycle and reuse, generating a large amount of waste liquid and seriously polluting the environment.

[0005] Therefore, research on heptafluoroisobutyramide-catalyzed dehydration gradually emerged.

[0006] Patent CN114105820A discloses a method for obtaining heptafluoroisobutyramide by dehydration reaction under the action of molecular sieve catalyst. The molecular sieve catalyst used is selected from at least one of HY molecular sieve, NaY molecular sieve, β molecular sieve, ZSM-5 molecular sieve, 3A molecular sieve, 4A molecular sieve or 5A molecular sieve.

[0007] Patent CN114057605A discloses a method for preparing nitriles by gas-phase catalytic dehydration, wherein the dehydration catalyst used is a supported catalyst, and the support is any one or more of silica, molecular sieve, activated carbon, diatomaceous earth, montmorillonite, magnesium oxide, chromium oxide, iron oxide, nickel oxide, and zinc oxide, and the active component is any one or more of cobalt chloride, chromium chloride, zinc chloride, nickel chloride, iron chloride, and copper chloride.

[0008] Patent CN109320436A discloses a method for preparing perfluoronitriles by gas-phase catalysis, wherein the catalyst in the dehydration reaction is one or more of alumina, copper oxide, cobalt oxide or niobium oxide.

[0009] Although the above catalytic dehydration methods can reduce the amount of waste by more than 90% and reduce costs by 30-40%, they have drawbacks such as poor catalyst selectivity, short lifespan, difficulty in regeneration and activation, and poor reproducibility of reaction results. Summary of the Invention

[0010] To address the aforementioned technical problems, this invention proposes a gas-phase catalytic method for the preparation of heptafluoroisobutyronitrile, which features low waste, low cost, high catalytic activity, good product selectivity, good reaction reproducibility, and long catalyst life, making it suitable for industrial-scale continuous production.

[0011] The objective of this invention is achieved through the following technical solution:

[0012] A method for preparing heptafluoroisobutyronitrile by gas-phase catalysis, the method comprising:

[0013] Under the action of a catalyst, heptafluoroisobutyramide gas loses one molecule of water to obtain heptafluoroisobutyronitrile; the catalyst is an oxide of a siderophile element, the siderophile element including a moderate siderophile element selected from at least one of tungsten, molybdenum, tin or gallium, or a strong siderophile element selected from at least one of osmium, iridium, ruthenium, rhenium or titanium.

[0014] This invention has discovered that moderately siderophile elements, due to their small ionic radius, high valence, and strong polarization ability, readily form complex anions in the reactions of this invention, enabling them to form relatively stable intermediate states with the enol form of amides. Therefore, the catalyst of this invention is preferably an oxide of at least one moderately siderophile element selected from tungsten, molybdenum, tin, or gallium. More preferably, the catalyst of this invention is molybdenum oxide and / or tungsten oxide.

[0015] The catalytic dehydration reaction temperature of this invention is 150–600℃, the reaction pressure is 1–3 bar, and the residence time is (τ-1)s ≤ (τ+1)s, where τ is calculated as follows:

[0016]

[0017] In the formula, r is the radius of the reaction tube, h is the effective height of the reaction tube (i.e., the catalyst loading height), k is the catalyst packing coefficient, M = 213.05 g / mol, P is the reaction pressure, v is the feed rate, ρ = 1.517 g / mL, R = 8.314 J / (mol·K), and T is the reaction temperature.

[0018] Generally, the feed rate suitable for this invention is 0.1 to 100 mL / min, the radius of the reaction tube is 10 to 300 mm, and the effective height of the reaction tube is 500 to 1000 mm. Therefore, the residence time is basically 0.1 to 50 s.

[0019] Preferably, the reaction temperature is 300–500℃, the reaction pressure is 1–2 bar, and (τ-0.1)s ≤ residence time ≤ (τ+0.1)s.

[0020] The catalyst of the present invention is prepared by the following steps:

[0021] Precipitation was carried out by adding concentrated ammonia dropwise to a metal salt solution, with the temperature controlled at ≤80℃, and the solution was allowed to stand for 12-24 hours. The precursor was then obtained by evaporation crystallization, centrifugation, and drying. Finally, the catalyst was obtained by calcination.

[0022] The metal salt solution is obtained by dissolving or dispersing a raw material containing a siderophile element in water (such as deionized water).

[0023] The siderophile-containing raw material is selected from at least one of metal acids, metal salts, metal alkoxides, chlorides, or ammonium salts. Specifically, the metal acid can be tungstic acid, molybdic acid, or rhenium acid; the metal salt can be sodium tungstate, sodium molybdate, sodium perrhenate, or ruthenium acetate; the metal alkoxide can be tetrabutyl titanate or tetraethyl titanate; the chloride can be tungsten chloride, molybdenum chloride, tin chloride, titanium tetrachloride, osmium chloride, iridium chloride, or ruthenium chloride; and the ammonium salt can be ammonium tungstate, ammonium paratungstate, ammonium molybdate, ammonium osmium chloride, or ammonium iridium chloride, etc.

[0024] At least one of the precursors being a hydroxide or ammonium salt of a siderophile element can be prepared by the above method.

[0025] In one specific embodiment, the catalyst of the present invention is prepared by the following steps:

[0026] The siderophile raw material is dissolved or dispersed in water, and concentrated ammonia (25-28% by mass) is added dropwise to precipitate it. The exothermic temperature is controlled to be <80℃, and the mixture is allowed to stand for aging for 12-24 hours. The precursor is then evaporated and crystallized at a lower temperature (<80℃) for 6-12 hours, separated by centrifugation, and dried in an oven at 60-80℃ for 12-24 hours to obtain the precursor. Then, under nitrogen protection, the precursor is calcined at 300-500℃ for 5-24 hours, and then ground, shaped, crushed, and sieved to obtain the catalyst.

[0027] In a preferred embodiment, the present invention prepares a precursor comprising at least one of a siderophile hydroxide and a siderophile ammonium salt, and the specific preparation steps are as follows:

[0028] A mixture of concentrated ammonia and a second type of salt solution was added dropwise to a first type of metal salt solution to induce precipitation. The temperature was controlled at ≤80℃, and the solution was allowed to stand for 12-24 hours. The precursor was then obtained by evaporation crystallization, centrifugation, and drying. Finally, the catalyst was obtained by calcination.

[0029] The first type of metal salt solution is obtained by dissolving or dispersing at least one of the metal acids, metal salts, metal alkoxides or chlorides of siderophiles in water; the second type of salt solution is obtained by dissolving or dispersing ammonium salts of siderophiles in water.

[0030] Furthermore, the first type of metal salt solution is obtained by dissolving or dispersing at least one of tungstic acid, sodium tungstate, tungsten chloride, molybdic acid, sodium molybdate, or molybdenum chloride in water; the second type of salt solution is obtained by dissolving or dispersing at least one of ammonium tungstate, ammonium paratungstate, or ammonium molybdate in water.

[0031] In the prepared precursor, the molar ratio of the siderophile hydroxide to the siderophile ammonium salt is 1:(0.5-1). Preferably, the molar ratio of the siderophile hydroxide to the siderophile ammonium salt is 1:(0.7-1).

[0032] The prepared catalyst precursor contains not only siderophile hydroxides but also siderophile ammonium salts, resulting in a catalyst with higher activity and longer lifespan.

[0033] When the catalyst prepared above is used in the dehydration of heptafluoroisobutyramide to prepare heptafluoroisobutyronitrile, the catalyst lifetime is 500–2000 h and the space-time yield is 0.5–1.5 t / (m 3 Generally, when the reaction temperature is about 150–350°C, the catalyst lifetime is about 1000–2000 h; when the reaction temperature is about 350–600°C, the catalyst lifetime is about 500–1500 h. Preferably, the catalyst lifetime is 1000–2000 h, and the space-time yield is 1.0–1.5 t / (m³).3 cat·h).

[0034] Furthermore, the catalyst of this invention can be easily regenerated once it becomes deactivated. Specifically, the catalyst is regenerated by purging with air and / or oxygen at 500–800°C.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] The catalyst prepared by this invention for the catalytic dehydration of heptafluoroisobutyramide is not only low in cost, low in waste, and environmentally friendly, but also has good catalytic activity, good product selectivity, good reaction reproducibility, long catalyst life and easy activation and regeneration. Attached Figure Description

[0037] Appendix Figure 1 This is a catalyst lifetime evaluation diagram for tungsten oxide (Cat2) in Example 2 of the present invention. Detailed Implementation

[0038] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternatives, improvements, and equivalents that may be included within the scope of the claims.

[0039] In this embodiment of the invention, gas chromatography was used for analysis. The analytical instrument was a Shimadzu GC-2014; the chromatographic column was a GAS-Pro (60m x 0.32mm x 1.0um). GC analysis method: detector temperature 250℃, vaporization chamber temperature 250℃, column temperature: 60℃ (5min) 10℃ / min, 85℃ (3min) 10℃ / min, 250℃ (4min); carrier gas (N2) flow rate 1.05mL / min, air flow rate 300mL / min, hydrogen flow rate 30mL / min, split ratio 50:1, injection volume 0.2mL.

[0040] Preparation Example 1

[0041] Molybdenum chloride (1.0 eq) was slowly added to 500 mL of deionized water, and some precipitate gradually formed. The exothermic temperature was controlled to be <80℃ (referred to as solution A). Concentrated ammonia (9.0 eq, 28%) and ammonium molybdate (1.0 eq) were mixed (referred to as solution B). Solution B was slowly added to solution A with strong stirring, and the exothermic temperature was controlled to be <80℃. The mixture was allowed to stand for 24 h, centrifuged, and dried in an oven at 80℃ for 12 h to obtain the precursor, which was a mixture of molybdenum hydroxide and ammonium molybdate. Then, under nitrogen protection, the precursor was calcined at 400℃ for 6 h, ground, shaped, crushed, and sieved to obtain molybdenum oxide, referred to as Cat1.

[0042] Preparation Example 2

[0043] Tungsten chloride (1.0 eq) was slowly added to 500 mL of deionized water in batches, and some precipitate gradually formed. The exothermic temperature was controlled to be <80℃ (referred to as solution A). Concentrated ammonia (10.0 eq, 28%) and ammonium paratungstate were mixed (referred to as solution B). Solution B was slowly added to solution A with strong stirring, and the exothermic temperature was controlled to be <80℃. The mixture was allowed to stand for 24 h and crystallized at a lower temperature (<50℃) for 12 h. After centrifugation, the mixture was dried in an oven at 80℃ for 12 h to obtain the precursor, which was a mixture of tungsten hydroxide and ammonium tungstate. Then, under nitrogen protection, the precursor was calcined at 400℃ for 8 h, and tungsten oxide was obtained by grinding, shaping, crushing, and sieving, denoted as Cat2.

[0044] Preparation Example 3

[0045] Tin chloride hydrate (1.0 eq) was slowly added to 500 mL of deionized water in batches, and some precipitate gradually formed. The exothermic temperature was controlled to be <80℃. Concentrated ammonia (2.5 eq, 28%) was slowly added to the reaction solution, and the exothermic temperature was controlled to be <80℃. The mixture was allowed to stand for 24 h, centrifuged, and dried in an oven at 80℃ for 12 h to obtain the precursor, which was tin hydroxide. Then, under nitrogen protection, the precursor was calcined at 400℃ for 8 h, ground, shaped, crushed, and sieved to obtain tin oxide, denoted as Cat3.

[0046] Preparation Example 4

[0047] Gallium chloride (1.0 eq) was slowly added to 500 mL of deionized water, and some precipitate gradually formed. The exothermic temperature was controlled to be <80℃. Concentrated ammonia (3.5 eq, 28%) was slowly added to the reaction solution, and the exothermic temperature was controlled to be <80℃. The mixture was allowed to stand for 24 h, centrifuged, and dried in an oven at 80℃ for 12 h to obtain the precursor, which was gallium hydroxide. Then, under nitrogen protection, the precursor was calcined at 400℃ for 8 h, ground, shaped, crushed, and sieved to obtain gallium oxide, denoted as Cat4.

[0048] Preparation Example 5

[0049] Osmium chloride (1.0 eq) was slowly added to 500 mL of deionized water in batches, and some precipitate gradually formed. The exothermic temperature was controlled to be <80℃. Concentrated ammonia (3.5 eq, 28%) was slowly added to the reaction solution, and the exothermic temperature was controlled to be <80℃. The mixture was allowed to stand for 24 h, centrifuged, and dried in an oven at 80℃ for 12 h to obtain the precursor, which was osmium hydroxide. Then, under nitrogen protection, the precursor was calcined at 400℃ for 8 h, ground, shaped, crushed, and sieved to obtain osmium oxide, denoted as Cat5.

[0050] Preparation Example 6

[0051] Iridium chloride (1.0 eq) was slowly added to 500 mL of deionized water in batches, and some precipitate gradually formed. The exothermic temperature was controlled to be <80℃. Concentrated ammonia (4.5 eq, 28%) was slowly added to the reaction solution, and the exothermic temperature was controlled to be <80℃. The mixture was allowed to stand for 24 h, centrifuged, and dried in an oven at 80℃ for 12 h to obtain the precursor, which was iridium hydroxide. Then, under nitrogen protection, the precursor was calcined at 400℃ for 8 h, ground, shaped, crushed, and sieved to obtain iridium oxide, denoted as Cat6.

[0052] Preparation Example 7

[0053] Ruthenium chloride (1.0 eq) was slowly added to 500 mL of deionized water in batches, and some precipitate gradually formed. The exothermic temperature was controlled to be <80℃. Concentrated ammonia (3.5 eq, 28%) was slowly added to the reaction solution, and the exothermic temperature was controlled to be <80℃. The mixture was allowed to stand for 24 h, centrifuged, and dried in an oven at 80℃ for 12 h to obtain the precursor, which was ruthenium hydroxide. Then, under nitrogen protection, the precursor was calcined at 400℃ for 8 h, ground, shaped, crushed, and sieved to obtain ruthenium oxide, denoted as Cat7.

[0054] Preparation Example 8

[0055] Rhenium chloride (1.0 eq) was slowly added to 500 mL of deionized water in batches, and some precipitate gradually formed. The exothermic temperature was controlled to be <80℃. Concentrated ammonia (5.5 eq, 28%) was slowly added to the reaction solution, and the exothermic temperature was controlled to be <80℃. The mixture was allowed to stand for 24 h, centrifuged, and dried in an oven at 80℃ for 12 h to obtain the precursor, which was rhenium hydroxide. Then, under nitrogen protection, the precursor was calcined at 400℃ for 8 h, ground, shaped, crushed, and sieved to obtain rhenium oxide, denoted as Cat8.

[0056] Preparation Example 9

[0057] Titanium tetrachloride (1.0 eq) was slowly added to 500 mL of deionized water, and some precipitate gradually formed. The exothermic temperature was controlled to be <80℃. Concentrated ammonia (5.0 eq, 28%) was slowly added to the reaction solution, and the exothermic temperature was controlled to be <80℃. The mixture was allowed to stand for 24 h, centrifuged, and dried in an oven at 80℃ for 12 h to obtain the precursor, which was titanium hydroxide. Then, under nitrogen protection, the precursor was calcined at 400℃ for 8 h, ground, shaped, crushed, and sieved to obtain titanium oxide, denoted as Cat9.

[0058] Preparation Example 10

[0059] The operation of this preparation example is the same as that of Preparation Example 1, except that: only concentrated ammonia is used for precipitation, and it is not mixed with ammonium molybdate. The precursor obtained is molybdenum hydroxide. The molybdenum oxide obtained after calcination, grinding, molding, crushing and sieving is denoted as Cat10.

[0060] Comparative Preparation Example 1

[0061] The preparation method of the catalyst in the repeated patent CN109320436A, taking cobalt oxide as an example, is as follows: cobalt nitrate hydrate is dissolved in water, concentrated ammonia is added dropwise for precipitation, the pH value is adjusted to 7.5, then aged for 12 hours, washed with water and filtered, dried in an oven at 80℃ for 36 hours, and then calcined at 450℃ for 8 hours under nitrogen protection to obtain cobalt oxide, denoted as CatD1.

[0062] Comparative Preparation Example 2

[0063] Aluminum trichloride (1.0 eq) was slowly added to 500 mL of deionized water and stirred to dissolve. Concentrated ammonia (3.2 eq, 28%) was slowly added to the reaction solution, and the exothermic temperature was controlled to be <80℃. The mixture was allowed to stand for 24 h, centrifuged, and dried in an oven at 80℃ for 12 h to obtain the precursor, which was aluminum hydroxide. Then, under nitrogen protection, the precursor was calcined at 400℃ for 8 h, ground, shaped, crushed, and sieved to obtain alumina, denoted as CatD2.

[0064] Example 1

[0065] 20 ml of molybdenum oxide (Cat1) prepared in Preparation Example 1 was loaded into a tubular reactor made of Incon alloy with an inner diameter of 10 cm and an internal volume of 50 ml. The preheating furnace temperature was 150 °C, and 60 °C circulating water was introduced into the jacket of the gas-liquid separator.

[0066] Reaction conditions: The reaction temperature was set at 350℃, the reaction pressure at 1 bar, the heptafluoroisobutyramide feed rate at 0.5 mL / min, and the calculated residence time was 6.5 s.

[0067] Reaction process: First, heptafluoroisobutyramide is melted and then fed into a preheating furnace through a high-temperature feed pump for gasification. The gasified heptafluoroisobutyramide undergoes a catalytic dehydration reaction in a tubular reactor. The reactants coming out of the reaction tube are first separated in a gas-liquid separator. The liquid material in the separator is discharged and then circulated back to the preheating furnace through a bypass. The gas undergoes two stages of deep cooling. The first stage separates water at 0°C, and the second stage separates heptafluoroisobutyrone product at -10°C and fills it into a steel cylinder. The non-condensable gas is purged after being washed with alkali.

[0068] GC analysis of the heptafluoroisobutyronitrile product showed a purity of 99.2% and a yield of 98.0%.

[0069] Example 2

[0070] The operation in this embodiment is the same as in Example 1, except that: the tungsten oxide (Cat2) prepared in Example 2 is loaded, and other conditions remain unchanged, and the calculated residence time is 6.5s.

[0071] GC analysis of the heptafluoroisobutyronitrile product showed a purity of 99.5% and a yield of 99.1%.

[0072] Under the reaction conditions of this embodiment, the catalyst lifetime of tungsten oxide (Cat2) was evaluated. Figure 1 The reaction results of a 1000-hour continuous reaction of tungsten oxide (Cat2) are shown in the figure. The method was a continuous reaction, with samples taken for analysis and product weighing every 24 hours. Figure 1 As shown, after 1000 hours of continuous reaction, GC analysis showed that the purity of the heptafluoroisobutyronitrile product decreased from 99.5% to 89.5%, and the yield decreased from 99.1% to 85.0%.

[0073] Examples 3-10

[0074] The procedures for Examples 3-10 were the same as those for Example 1, except that Cat3-Cat10 prepared in Examples 3-10 were loaded separately; all other procedures remained unchanged. The heptafluoroisobutyronitrile products of each example were analyzed by GC, and the product purity and yield are shown in Table 1 below.

[0075] Comparative Examples 1-2

[0076] The procedures for Comparative Examples 1-2 were the same as in Example 1, except that CatD1-CatD2 prepared in Comparative Examples 1-2 were loaded separately; all other procedures remained unchanged. The heptafluoroisobutyronitrile products of each comparative example were analyzed by GC, and the product purity and yield are shown in Table 1 below.

[0077] Table 1 Catalytic reaction results for each catalyst

[0078]

[0079] Example 11

[0080] The operation in this embodiment is the same as in embodiment 1, except that the reaction temperature is set to 450°C and other conditions remain unchanged, and the calculated residence time is 5.6s.

[0081] GC analysis of the heptafluoroisobutyronitrile product showed a purity of 96.1% and a yield of 93.4%.

[0082] Example 12

[0083] The operation in this embodiment is the same as in Example 1, except that the feed rate of heptafluoroisobutyramide is 1.0 mL / min, and other conditions remain unchanged. The calculated residence time is 3.3 s.

[0084] GC analysis of the heptafluoroisobutyronitrile product showed a purity of 90.7% and a yield of 88.5%.

[0085] Example 13

[0086] The operation in this embodiment is the same as in embodiment 1, except that the reaction pressure is 2 bar and other conditions remain unchanged, and the calculated residence time is 13.0 s.

[0087] GC analysis of the heptafluoroisobutyronitrile product showed a purity of 97.9% and a yield of 95.1%.

[0088] Example 14

[0089] The reaction conditions in this embodiment are the same as those in Example 16 of patent CN109320436A, namely: 20 ml of tungsten oxide (Cat2) prepared in Preparation Example 2 is loaded into a tubular reactor made of Incon alloy with an inner diameter of 10 cm and an internal volume of 50 ml.

[0090] Reaction conditions: reaction temperature 400℃, reaction pressure 0.1MPa, contact time of heptafluoroisobutyramide 10s.

[0091] Reaction process: The reaction stream from the reaction tube first flows through a polytetrafluoroethylene bottle for condensation, with the solid remaining at the bottom of the bottle. Then, it passes through a drying tube to remove moisture. Finally, the reaction stream enters a 200mL steel bottle made of 316 stainless steel to collect the gaseous product heptafluoroisobutyronitrile in the reaction system.

[0092] After a 24-hour continuous reaction, samples were taken every 2 hours, and heptafluoroisobutyronitrile was analyzed by GC. The reaction results are shown in Table 2 below:

[0093] Table 2 Selectivity of 24h catalytic reaction of tungsten oxide in Cat2

[0094]

[0095] Comparative Example 3

[0096] The operation of this comparative example is the same as in Example 14, except that CatD1 is used instead of Cat2; all other operations remain unchanged. After a continuous reaction for 24 hours, samples were taken every 2 hours, and the products were analyzed by GC. The reaction results are shown in Table 3 below:

[0097] Table 3 Selectivity results of cobalt oxide catalytic reaction after 24 h

[0098]

[0099] As shown in Table 3, the reaction selectivity continued to decrease after 24 hours of continuous reaction. After 24 hours of reaction, the catalyst was severely coked, and high-temperature (400℃) decomposition products hexafluoropropylene and heptafluoropropane were also present.

[0100] Example 15

[0101] The catalyst from Example 2, after 1000 hours of reaction, was regenerated by purging the reactor with air and heating it to 500°C to burn off the carbon deposits and maintain the hexagonal crystal morphology. The regenerated catalyst was evaluated under the reaction conditions of Example 2, yielding heptafluoroisobutyronitrile with a purity of 98.1% and a yield of 92.7%.

Claims

1. A method for gas-phase catalytic preparation of heptafluoroisobutyronitrile, characterized in that: The method includes: Under the action of a catalyst, heptafluoroisobutyramide gas loses one molecule of water to obtain heptafluoroisobutyronitrile; the catalyst is an oxide of a siderophile element, the siderophile element including a moderate siderophile element selected from at least one of tungsten, molybdenum, tin or gallium, or a strong siderophile element selected from at least one of osmium, iridium, ruthenium, rhenium or titanium.

2. The method for preparing heptafluoroisobutyronitrile by gas-phase catalysis according to claim 1, characterized in that: The catalyst is an oxide of at least one moderately siderophile element selected from tungsten, molybdenum, tin, or gallium.

3. The method for preparing heptafluoroisobutyronitrile by gas-phase catalysis according to claim 2, characterized in that: The catalyst is molybdenum oxide and / or tungsten oxide.

4. The method for preparing heptafluoroisobutyronitrile by gas-phase catalysis according to any one of claims 1-3, characterized in that: The reaction temperature is 150–600℃, and the reaction pressure is 1–3 bar. -1)s≤stay time≤( +1)s, where it is obtained by calculation in the following way: In the formula, r is the radius of the reaction tube, h is the effective height of the reaction tube (i.e., the catalyst loading height), k is the catalyst packing coefficient, M=213.05g / mol, P is the reaction pressure, v is the feed rate, ρ=1.517g / mL, R=8.314J / (mol·K), and T is the reaction temperature.

5. The method for preparing heptafluoroisobutyronitrile by gas-phase catalysis according to claim 4, characterized in that: The reaction temperature is 300℃~500℃, and the reaction pressure is 1~2 bar. -0.1)s≤stay time≤( +0.1)s.

6. The method for preparing heptafluoroisobutyronitrile by gas-phase catalysis according to any one of claims 1-3, characterized in that: The catalyst is prepared by the following steps: Precipitation was carried out by adding concentrated ammonia dropwise to a metal salt solution, with the temperature controlled at ≤80℃, and the solution was allowed to stand for 12-24 hours. The precursor was then obtained by evaporation crystallization, centrifugation, and drying, and finally calcined to obtain the catalyst. The metal salt solution is obtained by dissolving or dispersing a raw material containing a siderophile element in water.

7. The method for preparing heptafluoroisobutyronitrile by gas-phase catalysis according to claim 6, characterized in that: The siderophile-containing raw material is selected from at least one of metal acids, metal salts, metal alkoxides, chlorides, or ammonium salts.

8. The method for preparing heptafluoroisobutyronitrile by gas-phase catalysis according to claim 7, characterized in that: The precursor is at least one of a siderophile hydroxide or an ammonium salt.

9. The method for preparing heptafluoroisobutyronitrile by gas-phase catalysis according to claim 6, characterized in that: The catalyst is prepared by the following steps: A mixture of concentrated ammonia and a second type of salt solution was added dropwise to a first type of metal salt solution to induce precipitation. The temperature was controlled at ≤80℃, and the solution was allowed to stand for 12-24 hours. The precursor was then obtained by evaporation crystallization, centrifugation, and drying. Finally, the catalyst was obtained by calcination. The first type of metal salt solution is obtained by dissolving or dispersing at least one of the metal acids, metal salts, metal alkoxides or chlorides of siderophiles in water; the second type of salt solution is obtained by dissolving or dispersing ammonium salts of siderophiles in water.

10. The method for preparing heptafluoroisobutyronitrile by gas-phase catalysis according to claim 9, characterized in that: The first type of metal salt solution is obtained by dissolving or dispersing at least one of tungstic acid, sodium tungstate, tungsten chloride, molybdic acid, sodium molybdate, or molybdenum chloride in water; the second type of salt solution is obtained by dissolving or dispersing at least one of ammonium tungstate, ammonium paratungstate, or ammonium molybdate in water.

11. The method for preparing heptafluoroisobutyronitrile by gas-phase catalysis according to claim 10, characterized in that: The precursor is a mixture of at least one of a siderophile hydroxide and a siderophile ammonium salt.

12. The method for preparing heptafluoroisobutyronitrile by gas-phase catalysis according to claim 11, characterized in that: The precursor is a siderophile hydroxide: the molar ratio of the siderophile ammonium salt is 1:(0.5~1).

13. The method for preparing heptafluoroisobutyronitrile by gas-phase catalysis according to claim 11, characterized in that: The catalyst has a lifetime of 500–2000 h and a space-time yield of 0.5–1.5 t / (m²). 3 cat·h).

14. The method for preparing heptafluoroisobutyronitrile by gas-phase catalysis according to claim 13, characterized in that: The catalyst is regenerated by purging with air and / or oxygen at 500–800°C.

Images