Chromium fluoride catalyst for HF removal reaction of hydrofluorocarbon as well as preparation method and application of chromium fluoride catalyst

Abstract

The invention relates to the technical field of catalysts, in particular to a chromium fluoride catalyst for a hydrofluorocarbon HF removal reaction and a preparation method and application of the chromium fluoride catalyst. Comprising the following steps: (1) precipitating and aging a chromium salt to obtain a trivalent chromium precipitate, mixing the trivalent chromium precipitate with ammonium fluoride, carrying out ball milling, and drying to obtain a chromium fluoride precursor, the mass ratio of the trivalent chromium precipitate to the ammonium fluoride being 1: (0.7-1.4); and (2) carrying out roasting fluorination treatment on the chromium fluoride precursor, and carrying out hydrogen fluoride fluorination treatment to obtain the chromium fluoride catalyst. The trivalent chromium precipitate and ammonium fluoride are subjected to ball-milling mixing, so that ammonium fluoride and chromium hydroxide are subjected to a pre-fluorination reaction, heat release in subsequent roasting fluorination treatment is reduced, the roasting fluorination treatment process is milder, ammonia gas generated during roasting is used as a pore-forming agent, the specific surface area and pore volume of the catalyst are increased, and the specific surface area and pore volume of the catalyst are increased. The sintering of chromium fluoride in the high-temperature roasting process is inhibited, and meanwhile, the generation of high-valence chromium is prevented.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to a chromium fluoride catalyst for HF removal reaction of hydrofluorocarbons, a preparation method and application thereof. Background Art

[0002] Hydrofluoroolefins (HFOs) are a class of compounds that contain carbon, hydrogen and fluorine atoms and at least one carbon-carbon double bond. These compounds are often used as refrigerants, blowing agents and aerosol propellants because they have lower global warming potential (GWP) and ozone depletion potential (ODP). Compared with traditional hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), they have less impact on the environment and show significant advantages in environmental protection and energy conservation. They can be used in the fields of new generation environmentally friendly refrigerants, blowing agents and polymer monomers. In the process of preparing hydrofluoroolefins by dehydrofluorination of hydrofluoroalkanes, the selection and development of catalysts are important factors in improving process efficiency and product selectivity.

[0003] The current mainstream HF removal catalysts include aluminum-based, chromium-based and magnesium-based. The structure of traditional alumina catalysts collapses severely during the fluorination process. Traditional aluminum fluoride catalysts have disadvantages such as insufficient number of active sites, low specific surface area and difficulty in modification by additives. The catalyst surface acidity is too strong, which can easily cause side reactions and cause carbon deposition and deactivation. Although the magnesium-based catalyst has moderate acid strength, it will gradually sinter and deactivate during the reaction, and this process is irreversible. The chromium-based catalyst exhibits good performance in both activity and stability. Among them, fluorochromium oxide is currently considered to be the main active site, but it is made by partial fluorination of chromium oxide, and it is difficult to maintain structural stability. The chromium fluoride catalyst can effectively catalyze the breaking of CF bonds due to its strong Lewis acidity and high affinity for fluorides. It also has the advantages of thermal stability and resistance to carbon deposition.

[0004] Patent CN104907063A provides a chromium-based catalyst, which is a mixture of a trivalent chromium compound and a silicon-containing compound as a catalyst precursor, and is obtained by calcination and hydrogen fluoride activation. However, the hydrogen fluoride activation reaction is a highly exothermic reaction, and directly reacting the catalyst precursor with hydrogen fluoride may cause catalyst sintering due to the strong heat release of fluorination, and the fluorination time is long. Summary of the invention

[0005] The present invention is made to solve the above problems, and aims to provide a chromium fluoride catalyst for HF removal reaction of hydrofluorocarbons, a preparation method and application thereof.

[0006] The first aspect of the present invention provides a method for preparing a chromium fluoride catalyst for the HF removal reaction of hydrofluorocarbons, characterized in that it comprises the following steps: (1) mixing a trivalent chromium precipitate obtained by precipitation and aging of a chromium salt with ammonium fluoride, ball milling the mixture, and drying the mixture to obtain a chromium fluoride precursor, wherein the mass ratio of the trivalent chromium precipitate to the ammonium fluoride is 1:(0.7-1.4); (2) The chromium fluoride precursor is subjected to a calcination and fluorination treatment, and then subjected to a hydrogen fluoride fluorination treatment to obtain the chromium fluoride catalyst.

[0007] In the technical solution of the present invention, a trivalent chromium precipitate is prepared by precipitating and aging a chromium salt, and the main compound of the obtained trivalent chromium precipitate is chromium hydroxide. Since the fluorination reaction of converting chromium hydroxide into chromium fluoride is a highly exothermic reaction, if the chromium hydroxide is directly subjected to fluorination treatment, the particles of the generated chromium fluoride may agglomerate and fuse to form larger particles or block structures, resulting in a reduction in the active surface area of ​​the catalyst and destruction of the pore structure, thereby affecting the activity and stability of the catalyst.

[0008] Therefore, in the technical solution of the present invention, the trivalent chromium precipitate and ammonium fluoride are mixed and then ball-milled, and chromium fluoride is prepared by a roasting method. The particle sizes of the trivalent chromium precipitate and ammonium fluoride are reduced by ball milling, thereby increasing the specific surface area of ​​the prepared catalyst, and at the same time, it can ensure that the chromium hydroxide and ammonium fluoride are evenly mixed, further improving the utilization rate of the raw materials and the efficiency of the fluorination reaction in the roasting and fluorination treatment, thereby shortening the time required for the fluorination reaction and reducing the possibility of catalyst sintering.

[0009] During the ball milling process, chromium hydroxide and ammonium fluoride will react. Calcination of the ball milled product as a chromium fluoride precursor is an important step in the synthesis of chromium fluoride. The ammonia and other volatile substances produced by the chromium fluoride precursor under high-temperature calcination help to form pores and increase the specific surface area and pore volume of the catalyst. This decomposition not only provides pores, but also helps to inhibit the sintering of the chromium fluoride catalyst during high-temperature calcination, while preventing the formation of high-valent chromium.

[0010] Furthermore, since ball milling increases the utilization rate of chromium hydroxide in the trivalent chromium precipitate, the mass ratio of the trivalent chromium precipitate to the ammonium fluoride needs to be set to 1: (0.7-1.4) to ensure that the ammonium fluoride can help the catalyst surface form sufficient active sites and avoid excessive ammonium fluoride blocking the pores on the catalyst surface and reducing the activity of the catalyst. After ball milling and calcination fluorination treatment, most of the trivalent chromium precipitate has formed a pure phase chromium fluoride catalyst with a high specific surface area and a large number of active sites (Lewis acid sites).

[0011] Furthermore, in order to ensure that the trivalent chromium precipitate in the chromium fluoride precursor is completely converted into chromium fluoride, after the roasting fluorination treatment, the hydrogen fluoride fluorination treatment is carried out to convert the residual trivalent chromium precipitate into chromium fluoride. At this time, the hydrogen fluoride fluorination process is relatively mild and is not easy to cause catalyst sintering.

[0012] In summary, through the above steps, a chromium fluoride catalyst with high specific surface area, suitable pore structure and good activity can be prepared, and at the same time has good reproducibility and stability.

[0013] In some embodiments, in step (1), the mass ratio of the trivalent chromium precipitate to the ammonium fluoride is 1:(1-1.1).

[0014] In some embodiments, in step (1), the step of preparing the trivalent chromium precipitate specifically includes: mixing the chromium salt with an auxiliary agent for precipitation, wherein the auxiliary agent includes one or more compounds of iron, magnesium, aluminum, zinc, nickel, lanthanum, cerium, and cobalt.

[0015] In the embodiment, when preparing the trivalent chromium precipitate, an additive is added to help optimize the pore structure of the prepared chromium fluoride catalyst, increase the proportion of micropores or mesopores, thereby increasing the surface area and catalytic efficiency of the catalyst. At the same time, adding certain additives (such as aluminum and magnesium) can improve the thermal stability and chemical stability of the catalyst, making it more durable in high temperature or corrosive environments. Additives such as rare earth elements such as lanthanum and cerium can promote the dispersion of chromium hydroxide on the carrier, thereby increasing the activity of the catalyst. Adding additives such as iron, cobalt, and nickel can increase the number of active sites of the catalyst.

[0016] In some embodiments, in step (1), the precipitation pH is 8-11, and the aging time is 8-48 hours.

[0017] In some embodiments, in step (1), the mass ratio of the mixture of trivalent chromium precipitate and ammonium fluoride to the grinding balls is 1:(5-20).

[0018] In some embodiments, in step (1), the cerium salt is one of cerium nitrate, ammonium cerium nitrate, cerium chloride or cerium sulfate.

[0019] In some embodiments, in step (1), a mechanical ball mill is used for ball milling, the speed power of the mechanical ball mill is set to 20-40 Hz, and the ball milling time is 4-24 hours.

[0020] In some embodiments, in step (2), the calcination atmosphere is nitrogen, argon, air or oxygen, the calcination temperature is 400-800° C., and the calcination time is 2-12 hours.

[0021] In some embodiments, in step (2), the hydrogen fluoride fluorination treatment specifically includes fluorinating the chromium fluoride precursor after the calcination and fluorination treatment using hydrogen fluoride gas, the fluorination temperature is 200-400° C., and the fluorination time is 2-12 hours.

[0022] The second aspect of the present invention provides a chromium fluoride catalyst for the HF removal reaction of hydrofluorocarbons, characterized in that the chromium fluoride catalyst is prepared by any preparation method described in the first aspect.

[0023] The third aspect of the present invention provides an application of a chromium fluoride catalyst for the HF removal reaction of hydrofluorocarbons, characterized in that the chromium fluoride catalyst prepared by the preparation method described in any one of the first aspect or the chromium fluoride catalyst described in any one of the second aspect is used to catalyze the HF removal of hydrofluorocarbons to prepare hydrofluoroolefins, wherein the hydrofluorocarbons include 1,1-difluoroethane (R152a) and 1,1,1,3,3-pentafluoropropane (R245fa).

[0024] By implementing the above technical solution, the present invention has the following beneficial effects: The present invention ball-mills and mixes the trivalent chromium precipitate with ammonium fluoride to allow the ammonium fluoride and chromium hydroxide to undergo a pre-fluorination reaction, thereby reducing the heat release in the subsequent roasting and fluoriding treatment, and making the subsequent roasting and fluoriding treatment process more gentle.

[0025] Furthermore, the present invention utilizes ammonia generated during calcination as a pore-forming agent to increase the specific surface area and pore volume of the catalyst, inhibit the sintering of the chromium fluoride catalyst during high-temperature calcination, and prevent the generation of high-valent chromium.

[0026] Furthermore, the present invention reduces the particle size of trivalent chromium precipitate and ammonium fluoride by ball milling, thereby increasing the specific surface area of ​​the prepared catalyst, and at the same time ensuring uniform mixing of chromium hydroxide and ammonium fluoride, improving the utilization rate of raw materials and the efficiency of fluorination reaction in roasting and fluorination treatment, thereby shortening the fluorination reaction time and reducing the possibility of catalyst sintering.

[0027] Furthermore, since ball milling improves the utilization rate of chromium hydroxide in the trivalent chromium precipitate, the mass ratio of the trivalent chromium precipitate to the ammonium fluoride needs to be set to 1: (0.7-1.4) to ensure that the ammonium fluoride can help form sufficient active sites on the catalyst surface and avoid excessive ammonium fluoride clogging the pores on the catalyst surface and reducing the activity of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the XRD characterization diagram of the catalyst in the embodiment of the present invention; Figure 2 NH3-TPD characterization diagram of the catalyst in the examples and comparative examples of the present invention; Figure 3 This is the life activity diagram of Example 1 of the present invention in the HF removal reaction of R152a. DETAILED DESCRIPTION

[0029] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is described in detail below in conjunction with embodiments and drawings.

[0030] Example 1 Catalyst preparation: Dissolve 50.00g CrCl3·6H2O in a beaker containing 800mL water and stir with a stirring paddle at a rate of 300rpm. Then, slowly drip 6mol / L ammonia solution at a rate of 5rpm with a peristaltic pump to slowly form a precipitate. The titration end point is pH=8.5. After the titration, age for 12h. The precipitate obtained by filtering and washing is dried in an oven at 110℃ for 12h to obtain Cr(OH)3. 5.00g Cr(OH)3 and 5.39g NH4F are placed in a ball mill with a ratio of grinding balls to materials of 10:1. The ball mill is milled for 6h at a frequency of 30Hz. The obtained product is calcined at 500℃ in N2 atmosphere for 4h, and then calcined at 400℃ in HF atmosphere for 4h to finally obtain anhydrous CrF3 catalyst.

[0031] Catalyst HF removal reaction: 2 mL of catalyst was filled into a fixed bed reaction tube with an inner diameter of 8 mm, R152a or R245fa was introduced and diluted with nitrogen in equal proportions, the reaction temperature was 350 ° C, the reaction space velocity was 300 h -1 The catalytic reaction was carried out under the condition of alkali solution, and the reaction product was analyzed by gas chromatography after absorbing hydrogen fluoride. The conversion rate of R152a was 88.2%; the conversion rate of R245fa was 91.5%.

[0032] Example 2 Dissolve 50.00g CrCl3·6H2O in a beaker containing 800mL water and stir with a stirring paddle at a rate of 300rpm. Then, slowly drip 6mol / L ammonia solution at a rate of 5rpm with a peristaltic pump to slowly form a precipitate. The titration end point is pH=10. After the titration, age for 12h. The precipitate obtained by filtering and washing is dried in an oven at 110℃ for 12h to obtain Cr(OH)3. 5.00gCr(OH)3 and 5.39g NH4F are placed in a ball mill with a ratio of grinding balls to materials of 10:1. The ball mill is milled at a frequency of 30Hz for 6h. The obtained product is calcined at 500℃ in N2 atmosphere for 6h, and then calcined at 400℃ in HF atmosphere for 4h to finally obtain anhydrous CrF3 catalyst.

[0033] Catalyst HF removal reaction: 2 mL of catalyst was filled into a fixed bed reaction tube with an inner diameter of 8 mm, R152a or R245fa was introduced and diluted with nitrogen in equal proportions, the reaction temperature was 350 ° C, the reaction space velocity was 300 h -1The catalytic reaction was carried out under the condition of alkali solution, and the reaction product was analyzed by gas chromatography after absorbing hydrogen fluoride. The conversion rate of R152a was 89.0%; the conversion rate of R245fa was 91.8%.

[0034] Example 3 Dissolve 50.00g CrCl3·6H2O in a beaker containing 800mL water and stir with a stirring paddle at a rate of 300rpm. Then, slowly drip 6mol / L ammonia solution at a rate of 5rpm with a peristaltic pump to slowly form a precipitate. The titration end point is pH=8.5. After the titration, age for 24h. The precipitate obtained by filtering and washing is dried in an oven at 110℃ for 12h to obtain Cr(OH)3. 5.00g Cr(OH)3 and 5.39g NH4F are placed in a ball mill with a ratio of grinding balls to materials of 5:1. The ball mill is milled for 6h at a frequency of 30Hz. The obtained product is calcined at 600℃ in N2 atmosphere for 4h, and then calcined at 400℃ in HF atmosphere for 4h to finally obtain anhydrous CrF3 catalyst.

[0035] Catalyst HF removal reaction: 2 mL of catalyst was filled into a fixed bed reaction tube with an inner diameter of 8 mm, R152a or R245fa was introduced and diluted with nitrogen in equal proportions, the reaction temperature was 350 ° C, the reaction space velocity was 300 h -1 The catalytic reaction was carried out under the condition of alkali solution, and the reaction product was analyzed by gas chromatography after absorbing hydrogen fluoride. The conversion rate of R152a was 87.2%; the conversion rate of R245fa was 85%.

[0036] Example 4 Dissolve 50.00g CrCl3·6H2O in a beaker containing 800mL water and stir with a stirring paddle at a rate of 300rpm. Then, slowly drip 6mol / L ammonia solution at a rate of 5rpm with a peristaltic pump to slowly form a precipitate. The titration end point is pH=9. After the titration, age for 12h. The precipitate obtained by filtering and washing is dried in an oven at 110℃ for 12h to obtain Cr(OH)3. 5.00gCr(OH)3 and 3.59g NH4F are placed in a ball mill with a ratio of grinding balls to materials of 20:1. The ball mill is milled at a frequency of 40Hz for 6h. The obtained product is calcined at 500℃ in N2 atmosphere for 6h, and then calcined at 400℃ in HF atmosphere for 12h to finally obtain anhydrous CrF3 catalyst.

[0037] Catalyst HF removal reaction: 2 mL of catalyst was filled into a fixed bed reaction tube with an inner diameter of 8 mm, R152a or R245fa was introduced and diluted with nitrogen in equal proportions, the reaction temperature was 350 ° C, the reaction space velocity was 300 h -1The catalytic reaction was carried out under the condition of alkali solution, and the reaction product was analyzed by gas chromatography after absorbing hydrogen fluoride. The conversion rate of R152a was 84.9%; the conversion rate of R245fa was 86.2%.

[0038] Example 5 Dissolve 50.00g CrCl3·6H2O in a beaker containing 800mL water and stir with a stirring paddle at a rate of 300rpm. Then, slowly drip 6mol / L ammonia solution at a rate of 5rpm with a peristaltic pump to slowly form a precipitate. The titration end point is pH=8.5. After the titration, age for 12h. The precipitate obtained by filtering and washing is dried in an oven at 110℃ for 12h to obtain Cr(OH)3. 5.00g Cr(OH)3 and 7.19g NH4F are placed in a ball mill with a ratio of grinding balls to materials of 10:1. The ball mill is milled for 12h at a frequency of 30Hz. The obtained product is calcined at 600℃ in N2 atmosphere for 8h, and then calcined at 350℃ in HF atmosphere for 8h to finally obtain anhydrous CrF3 catalyst.

[0039] Catalyst HF removal reaction: 2 mL of catalyst was filled into a fixed bed reaction tube with an inner diameter of 8 mm, R152a or R245fa was introduced and diluted with nitrogen in equal proportions, the reaction temperature was 350 ° C, the reaction space velocity was 300 h -1 The catalytic reaction was carried out under the condition of alkali solution, and the reaction product was analyzed by gas chromatography after absorbing hydrogen fluoride. The conversion rate of R152a was 80.8%; the conversion rate of R245fa was 85.3%.

[0040] Example 6 Dissolve 50.00g CrCl3·6H2O and 2.56g ZnCl2 in a beaker containing 800mL water and stir with a stirring paddle at a rate of 300rpm. Then, slowly drip 6mol / L ammonia solution at a rate of 5rpm with a peristaltic pump to slowly form a precipitate. The titration end point is pH=8.5. After the titration is completed, age for 12h. The precipitate obtained by filtering and washing is dried in an oven at 110℃ for 12h to obtain Zn / Cr(OH)3. 5.00g Cr(OH)3 and 5.39g NH4F are placed in a ball mill with a ratio of grinding balls to materials of 10:1. The ball mill is milled for 6h at a frequency of 30Hz. The obtained product is calcined at 500℃ in N2 atmosphere for 4h, and then calcined at 400℃ in HF atmosphere for 4h to finally obtain anhydrous Al / CrF3 catalyst.

[0041] 2 mL of catalyst was filled into a fixed bed reaction tube with an inner diameter of 8 mm, R152a or R245fa was introduced and diluted with nitrogen in equal proportions, the reaction temperature was 350 ° C, the reaction space velocity was 300 h -1The catalytic reaction was carried out under the condition of alkali solution, and the reaction product was analyzed by gas chromatography after absorbing hydrogen fluoride. The conversion rate of R152a was 90.2%; the conversion rate of R245fa was 92.4%.

[0042] Example 7 Dissolve 50.00g CrCl3·6H2O and 4.52g AlCl3·6H2O in a beaker containing 800mL water and stir with a stirring paddle at a rate of 300rpm. Then, slowly drip 6mol / L ammonia solution at a rate of 5rpm with a peristaltic pump to slowly form a precipitate. The titration end point is pH=8.5. After the titration is completed, age for 12h. The precipitate obtained by filtering and washing is dried in an oven at 110℃ for 12h to obtain Al / Cr(OH)3. 5.00g Cr(OH)3 and 5.39g NH4F are placed in a ball mill with a ratio of grinding balls to materials of 10:1. The ball mill is milled for 6h at a frequency of 30Hz. The obtained product is calcined at 500℃ in N2 atmosphere for 4h, and then calcined at 400℃ in HF atmosphere for 4h to finally obtain anhydrous Al / CrF3 catalyst.

[0043] 2 mL of catalyst was filled into a fixed bed reaction tube with an inner diameter of 8 mm, R152a or R245fa was introduced and diluted with nitrogen in equal proportions, the reaction temperature was 350 ° C, the reaction space velocity was 300 h -1 The catalytic reaction was carried out under the condition of alkali solution, and the reaction product was analyzed by gas chromatography after absorbing hydrogen fluoride. The conversion rate of R152a was 91.5%; the conversion rate of R245fa was 92.8%.

[0044] Example 8 Dissolve 50.00g CrCl3·6H2O and 4.80g Mg(NO3)2·6H2O in a beaker containing 800mL water and stir with a stirring paddle at a rate of 300rpm. Then, slowly drip 6mol / L ammonia solution at a rate of 5rpm with a peristaltic pump to slowly form a precipitate. The titration end point is pH=8.5. After the titration is completed, age for 12h. The precipitate obtained by filtering and washing is dried in an oven at 110℃ for 12h to obtain Mg / Cr(OH)3. 5.00g Cr(OH)3 and 5.39g NH4F are placed in a ball mill with a ratio of grinding balls to materials of 10:1. The ball mill is milled for 6h at a frequency of 30Hz. The obtained product is calcined at 500℃ in N2 atmosphere for 4h, and then calcined at 400℃ in HF atmosphere for 4h to finally obtain anhydrous Al / CrF3 catalyst.

[0045] 2 mL of catalyst was filled into a fixed bed reaction tube with an inner diameter of 8 mm, R152a or R245fa was introduced and diluted with nitrogen in equal proportions, the reaction temperature was 350 ° C, the reaction space velocity was 300 h -1The catalytic reaction was carried out under the condition of alkali solution, and the reaction product was analyzed by gas chromatography after absorbing hydrogen fluoride. The conversion rate of R152a was 90.5%; the conversion rate of R245fa was 91.4%.

[0046] Example 9 Dissolve 50.00g CrCl3·6H2O and 8.13g La(NO3)3·6H2O in a beaker containing 800mL water and stir with a stirring paddle at a rate of 300rpm. Then, slowly drip 6mol / L ammonia solution at a rate of 5rpm with a peristaltic pump to slowly form a precipitate. The titration end point is pH=8.5. After the titration is completed, age for 12h. The precipitate obtained by filtering and washing is dried in an oven at 110℃ for 12h to obtain La / Cr(OH)3. 5.00g Cr(OH)3 and 5.39g NH4F are placed in a ball mill with a ratio of grinding balls to materials of 10:1. The ball mill is milled for 6h at a frequency of 30Hz. The obtained product is calcined at 500℃ in N2 atmosphere for 4h, and then calcined at 400℃ in HF atmosphere for 4h to finally obtain anhydrous La / CrF3 catalyst.

[0047] 2 mL of catalyst was filled into a fixed bed reaction tube with an inner diameter of 8 mm, R152a or R245fa was introduced and diluted with nitrogen in equal proportions, the reaction temperature was 350 ° C, the reaction space velocity was 300 h -1 The catalytic reaction was carried out under the condition of alkali solution, and the reaction product was analyzed by gas chromatography after absorbing hydrogen fluoride. The conversion rate of R152a was 91.4%; the conversion rate of R245fa was 89.9%.

[0048] Example 10 Catalyst preparation: Dissolve 50.00g CrCl3·6H2O in a beaker containing 800mL water and stir with a stirring paddle at 300rpm. Then, slowly drip 6mol / L ammonia solution at 5rpm with a peristaltic pump to slowly form a precipitate. The titration endpoint is pH=8.5. After the titration, age for 12h. The precipitate obtained by filtering and washing is dried in an oven at 110℃ for 12h to obtain Cr(OH)3. 5.00g Cr(OH)3 and 1.80g NH4F are placed in a ball mill with a ratio of grinding balls to materials of 10:1. The ball mill is milled for 6h at a frequency of 30Hz. The obtained product is calcined at 500℃ in N2 atmosphere for 4h, and then calcined at 400℃ in HF atmosphere for 4h to finally obtain anhydrous CrF3 catalyst.

[0049] Catalyst HF removal reaction: 2 mL of catalyst was filled into a fixed bed reaction tube with an inner diameter of 8 mm, R152a or R245fa was introduced and diluted with nitrogen in equal proportions, the reaction temperature was 350 ° C, the reaction space velocity was 300 h-1 The catalytic reaction was carried out under the condition of alkali solution, and the reaction product was analyzed by gas chromatography after absorbing hydrogen fluoride. The conversion rate of R152a was 76.7%; the conversion rate of R245fa was 79.1%.

[0050] Embodiment 11 Catalyst preparation: Dissolve 50.00g CrCl3·6H2O in a beaker containing 800mL water and stir with a stirring paddle at a rate of 300rpm. Then, slowly drip 6mol / L ammonia solution at a rate of 5rpm with a peristaltic pump to slowly form a precipitate. The titration end point is pH=8.5. After the titration, age for 12h. The precipitate obtained by filtering and washing is dried in an oven at 110℃ for 12h to obtain Cr(OH)3. 5.00g Cr(OH)3 and 2.69g NH4F are placed in a ball mill with a ratio of grinding balls to materials of 10:1. The ball mill is milled for 6h at a frequency of 30Hz. The obtained product is calcined at 500℃ in N2 atmosphere for 4h, and then calcined at 400℃ in HF atmosphere for 4h to finally obtain anhydrous CrF3 catalyst.

[0051] Catalyst HF removal reaction: 2 mL of catalyst was filled into a fixed bed reaction tube with an inner diameter of 8 mm, R152a or R245fa was introduced and diluted with nitrogen in equal proportions, the reaction temperature was 350 ° C, the reaction space velocity was 300 h -1 The catalytic reaction was carried out under the condition of alkali solution, and the reaction product was analyzed by gas chromatography after absorbing hydrogen fluoride. The conversion rate of R152a was 82.3%; the conversion rate of R245fa was 84.7%.

[0052] Comparative Example 1 Commercially purchased chromium fluoride was calcined at 400°C in HF atmosphere for 4 h to obtain anhydrous chromium fluoride catalyst; 2 mL of catalyst was filled into a fixed bed reaction tube with an inner diameter of 8 mm, R152a or R245fa was introduced and diluted with nitrogen in equal proportions, the reaction temperature was 350 ° C, the reaction space velocity was 300 h -1 The catalytic reaction was carried out under the condition of alkali solution, and the reaction product was analyzed by gas chromatography after absorbing hydrogen fluoride. The conversion rate of R152a was 69.6%; the conversion rate of R245fa was 72.6%.

[0053] Comparative Example 2 Dissolve 50.00g CrCl3·6H2O in a beaker containing 800mL water and stir with a stirring paddle at 300rpm. Then, slowly drip 6mol / L ammonia solution at 5rpm with a peristaltic pump to slowly form a precipitate. The titration endpoint is pH=8.5. After the titration, age for 12h. Filter and wash the precipitate and dry it in an oven at 110℃ for 12h to obtain Cr(OH)3. 5.00g Cr(OH)3 was placed in a 40wt% HF solution for fluorination. The obtained product was filtered and dried and then calcined at 400℃ in a N2 atmosphere for 4h to finally obtain a CrF3 catalyst.

[0054] Catalyst HF removal reaction: 2 mL of catalyst was filled into a fixed bed reaction tube with an inner diameter of 8 mm, R152a or R245fa was introduced and diluted with nitrogen in equal proportions, the reaction temperature was 350 ° C, the reaction space velocity was 300 h -1 The catalytic reaction was carried out under the condition of alkali solution, and the reaction product was analyzed by gas chromatography after absorbing hydrogen fluoride. The conversion rate of R152a was 85.4%; the conversion rate of R245fa was 87.4%.

[0055] Performance Testing The catalyst activity test was carried out on the catalysts prepared in Examples 1 to 11 and Comparative Examples 1 to 2. The test data are as follows: Table 1 Activity data of catalyst in R152a HF removal reaction catalyst Initial activity Activity after 100h Example 1 88.2% 86.5% Example 2 89.0% 87.2% Example 3 87.2% 84.1% Example 4 84.9% 82.3% Example 5 80.8% 76.1% Example 6 90.2% 89.8% Example 7 91.5% 90.5% Example 8 90.5% 89.8% Example 9 91.4% 90.8% Example 10 76.7% 59.9% Embodiment 11 82.3% 84.7% Comparative Example 1 69.6% 43.6% Comparative Example 2 85.4% 69.5% Table 2 Activity data of catalyst in R245fa deHF reaction catalyst Initial activity Activity after 100h Example 1 91.5% 88.5% Example 2 91.8% 89.9% Example 3 85.0% 80.2% Example 4 86.2% 81.6% Example 5 85.3% 80.9% Example 6 92.4% 90.1% Example 7 92.8% 91.7% Example 8 91.4% 88.6% Example 9 89.9% 88.1% Example 10 79.1% 71.6% Embodiment 11 84.7% 79.2% Comparative Example 1 72.6% 53.6% Comparative Example 2 87.4% 63.6% It can be seen from the examples that the content of ammonium fluoride during ball milling has a significant effect on the catalytic performance. If there is too little ammonium fluoride, the degree of fluorination during ball milling and roasting is too low, which reduces the specific surface area of ​​the catalyst; if there is too much ammonium fluoride, excessive HF is released during ball milling and roasting, the degree of fluorination is serious, and the catalyst is sintered; the ratio of grinding balls to raw materials during ball milling affects the particle size and uniformity of the ball milled product.

[0056] The above-mentioned embodiments are preferred examples of the present invention and are not intended to limit the protection scope of the present invention.

Claims

1. A method for preparing a chromium fluoride catalyst for de-HF reaction of hydrofluorocarbons, characterized in that: The following steps are involved: (1) mixing a trivalent chromium precipitate obtained by precipitation and aging of a chromium salt with ammonium fluoride, ball milling the mixture, and drying the mixture to obtain a chromium fluoride precursor, wherein the mass ratio of the trivalent chromium precipitate to the ammonium fluoride is 1:(0.7-1.4); (2) The chromium fluoride precursor is subjected to a calcination fluorination treatment, and then subjected to a hydrogen fluoride fluorination treatment to obtain the chromium fluoride catalyst.

2. The preparation method according to claim 1, characterized in that: In the step (1), the preparation step of the trivalent chromium precipitate specifically includes: mixing the chromium salt with an auxiliary agent for precipitation, wherein the auxiliary agent includes one or more compounds of iron, magnesium, aluminum, zinc, nickel, lanthanum, cerium, and cobalt.

3. The preparation method according to claim 2, characterized in that: In the step (1), the precipitation pH is 8-11, and the aging time is 8-48 hours.

4. The preparation method according to claim 3, characterized in that: In the step (1), the mass ratio of the mixture of trivalent chromium precipitate and ammonium fluoride to the grinding ball is 1:(5-20).

5. The preparation method according to claim 4, characterized in that: In the step (1), the chromium salt is one of chromium chloride, chromium nitrate and chromium sulfate, and the precipitant is sodium hydroxide, potassium oxide or ammonia water.

6. The preparation method according to claim 5, characterized in that: In the step (1), a mechanical ball mill is used for ball milling, the speed power of the mechanical ball mill is set to 20-40 Hz, and the ball milling time is 4-24 hours.

7. The preparation method according to claim 6, characterized in that: In the step (2), the calcination atmosphere is nitrogen, argon, air or oxygen, the calcination temperature is 400-800° C., and the calcination time is 2-12 hours.

8. The preparation method according to claim 7, characterized in that: In the step (2), the hydrogen fluoride fluorination treatment specifically includes fluorinating the chromium fluoride precursor after the calcination and fluorination treatment using hydrogen fluoride gas, the fluorination temperature is 200-400° C., and the fluorination time is 2-12 hours.

9. A chromium fluoride catalyst for the HF removal reaction of hydrofluorocarbons, characterized in that: The chromium fluoride catalyst is prepared by the preparation method according to any one of claims 1 to 8.

10. An application of a chromium fluoride catalyst for the HF removal reaction of hydrofluorocarbons, characterized in that: The chromium fluoride catalyst prepared by the preparation method according to any one of claims 1 to 8 or the chromium fluoride catalyst according to any one of claim 9 is used to catalyze the removal of HF from hydrofluorocarbons to prepare hydrofluoroolefins, wherein the hydrofluorocarbons include 1,1-difluoroethane and 1,1,1,3,3-pentafluoropropane.

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