Preparation of a double metal oxide solid acid catalyst for hexafluoropropylene oxide based on metal synergistic effect

Abstract

The present application relates to the preparation of hexafluoropropylene oxide, disclose a kind of based on metal synergistic effect can be used for the continuous preparation of hexafluoropropylene oxide in gas phase bimetallic oxide solid acid catalyst, using hexafluoropropylene and oxygen as raw material, with Cu oxide as the first active center, loading is 0.5-5wt%, Ce, Co, Cr oxide as the second active center, loading is 0.1-5wt% and does not exceed the loading of Cu, solid acid is the carrier of multimetallic oxide system as catalyst, can realize the continuous preparation of hexafluoropropylene oxide.The present application utilizes the bimetallic synergistic effect and the specific acid sites of solid acid, greatly improves the reaction activity of catalyst.The method involved in the present application does not involve the use of solvent reduces the difficulty of post-processing, greatly reduces the temperature and pressure required for reaction.

Description

Technical Field

[0001] This invention belongs to the field of fluorochemicals and includes the synthesis of hexafluoropropylene oxide by a gas-phase method using molecular sieve catalysts and the preparation of the catalyst used. Specifically, it relates to a bimetallic oxide solid acid catalyst for the preparation of hexafluoropropylene oxide based on the metal synergistic effect. Background Technology

[0002] Hexafluoropropylene oxide (HFPO) is an important fluoride intermediate with high added value and is a major raw material for the preparation of hexafluoroisopropanol, perfluoroalkyl vinyl ethers, and perfluoropolyethers. Currently, hexafluoropropylene oxide is mainly prepared by epoxidation of hexafluoropropylene using different processes.

[0003] US3358003 mentions a scheme using an aqueous solution of hydrogen peroxide containing acetonitrile as an oxidant. Although this method yields relatively few byproducts, the low-temperature reaction requires a large amount of energy, which is not conducive to industrialization. US4902810 and EP0473398A1 mention a method for producing hexafluoropropylene oxide using an aqueous solution of sodium hypochlorite as an oxidant. This reaction involves a three-phase reaction of an aqueous solution of sodium hypochlorite, a phase transfer catalyst, and an organic phase of hexafluoropropylene, which can achieve high selectivity. However, the residual liquid produced by the reaction contains unreacted sodium hypochlorite and salts, which are difficult to process and may lead to a series of environmental problems.

[0004] With current technology, using molecular oxygen as the oxygen source is a more feasible operating method, which can effectively prevent the formation of unreacted oxidizing substances in the residual liquid and effectively reduce the pressure of post-processing. CN1955169A mentions a method of using chlorofluorocarbons and ether compounds as solvents to dissolve the reaction of hexafluoropropylene with oxygen in a high-pressure reactor. CN102675255A mentions a method using perfluoropolyether as the reaction solvent. However, perfluoropolyether is expensive, which is not conducive to the industrial application of such methods.

[0005] Because the molecular oxygen phase reaction does not require solvents, it is relatively environmentally friendly and represents a promising method for the synthesis of hexafluoropropylene oxide. US3775438 and US3775439 disclose a method for the direct oxidation of hexafluoropropylene by oxygen in a fixed bed using Davison silica gel as a catalyst, and the catalyst's lifespan can be extended by using hydrochloric acid. US4288376 provides a method using barium compounds as catalysts, specifically barium oxide, barium hydroxide, barium fluoride, barium carbonate, and barium sulfate. CN1954911A formulated an Ag-based catalyst for the gas-phase preparation of hexafluoropropylene oxide, with a composition of 10–50% Ag, 1–20% alkali metal compounds, and 49–89% support, effectively improving the conversion rate and selectivity of the reaction. The gas-phase method does not use solvents and does not generate waste liquid requiring post-treatment, significantly reducing the environmental impact of the production process.

[0006] However, in previous molecular oxygen phase catalytic epoxidation reactions, the catalytic systems used were too simple, with the catalytic activity often being a single active site supported on a carrier. This required high temperatures and pressures. Furthermore, the supported catalysts used in previous reactions were prone to aggregation due to their high loading rates. Summary of the Invention

[0007] To address the problems in the prior art, this invention provides a bimetallic oxide solid acid catalyst for preparing hexafluoropropylene oxide based on metal synergistic effects. The catalyst uses Cu as the first active metal and Ce, Co, or Cr as the second active metal. The loading of Cu is 0.5-5 wt%, and the loading of the second active metal is 0.1-5 wt%, not exceeding the loading of Cu. The first and second active metals are supported on a solid acid, which is an HZSM-5 molecular sieve with a silicon-aluminum molar ratio of 20-50.

[0008] Furthermore, the preferred loading of the second active metal is 0.1-1 wt%.

[0009] Furthermore, the catalyst is prepared by the following steps:

[0010] 1) Calculate the mass of the first active metal precursor, the second active metal precursor, and the solid acid by the required loading amount, dissolve the precursor and the solid acid in an ethanol aqueous solution and stir to obtain a mixture, and heat and dry the mixture until it becomes a solid.

[0011] 2) Grind the solid into powder and dry it, then calcine the dried powder to obtain the catalyst;

[0012] Wherein, the first active metal precursor is copper nitrate, and the second active metal precursor is one of cerium nitrate, cobalt nitrate hexahydrate, or chromium nitrate nonahydrate; the pore size of the solid acid is 0.53-0.58 nm, and the specific surface area of ​​the HZSM-5 molecular sieve used as the catalyst support is 300-500.

[0013] Further, in step 1), the mass ratio of ethanol to water in the ethanol-water solution is 1:1; the heating and drying is carried out by heating to 80-100℃.

[0014] Further, in step 2), the drying temperature is 60-100℃, and the powder is sieved through a mesh size of 40-60; the calcination temperature is 450-700℃, preferably 500℃, the heating rate is 5-20℃ / min, and the calcination time is 3-6h, preferably 5h.

[0015] The present invention also provides a method for the continuous gas-phase preparation of hexafluoropropylene oxide using the catalyst, comprising the following steps:

[0016] a) The catalyst is loaded into a fixed-bed reactor and activated by heating with an activation gas;

[0017] b) A mixture of hexafluoropropylene and oxygen is introduced into a fixed-bed reactor for reaction.

[0018] Further, in step a), the activating gas is a mixture of hexafluoropropylene and oxygen in a volume ratio of 4, the activation temperature is 250-280℃, and the activation time is 3-5h.

[0019] Further, in step b), the reaction temperature is 140-220℃, the reaction pressure is 0.3-0.4 MPa, and the volume hourly space velocity of the hexafluoropropylene is 5-12 h⁻¹. -1 The volume ratio of hexafluoropropylene to oxygen is 2:1 to 5:1.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] The method provided by this invention has the advantages of occurring in a gas-solid reaction, effectively avoiding post-treatment of waste liquid, making it environmentally friendly. Furthermore, the reaction occurs in the gas phase, resulting in low reaction pressure, fast reaction rate, simple and safe operation, and high process safety. This invention employs a one-pot synthesis method for the catalyst, adding Cu and a second active metal to HZSM-5, making the preparation method more suitable for industrial production. This invention utilizes a bimetallic system with synergistic effects, solving the problem of a single active center in existing technologies, further improving the catalytic activity of the catalyst. Moreover, this method can achieve high conversion rates and selectivity at low loading levels, reducing production costs and avoiding metal agglomeration during preparation, minimizing catalyst activity loss. Regarding reaction conditions, due to the increased catalyst activity, the reaction can be carried out at lower temperature and pressure levels, improving production safety and reducing production costs. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a fixed-bed reactor.

[0023] Figure 2 This is a TEM image of HZSM-5 after loading Cu species. Detailed Implementation

[0024] The present invention will be further described and illustrated below with reference to specific embodiments. The embodiments described are merely examples of the content of this disclosure and do not limit the scope of the invention. The technical features of each embodiment in the present invention can be combined accordingly, provided that there is no mutual conflict.

[0025] This invention, based on the gas-phase method, adds a solid acid as a support to disperse the active metal centers, improving the utilization rate of the active metal, reducing the amount of metal material in the catalyst, and lowering industrial production costs. Simultaneously, it employs a second active metal as an aid, utilizing the synergistic effect between supported metal oxides to prepare a bimetallic solid acid catalytic system, significantly enhancing reaction activity. This method allows for continuous reaction in a fixed bed, meeting the needs of industrial production. Compared to liquid-phase methods, it requires lower reaction pressures. Compared to catalytic systems using SiO2, it significantly reduces the required reaction temperature, greatly lowers equipment requirements, and improves production safety.

[0026] This invention first impregnates the catalyst. Based on the loading amount, the corresponding amounts of solid acid support and nitrate are weighed and dissolved in 80 ml of ethanol-water solution. The solution is stirred vigorously for 3 hours. The liquid is then heated at 80°C while stirring to prevent stratification. After the liquid solidifies, it is ground into powder and further dried overnight at 80°C. The fully dried catalyst powder is then calcined in a tube furnace at 500°C for 5 hours. The prepared catalyst is then packed into a fixed bed. Hexafluoropropylene and oxygen are introduced into the reactor at a 4:1 ratio, and the reactor is heated at 260°C for 3-6 hours for activation. The reactor pressure is controlled at 0.3-0.5 MPa. The fixed bed is cooled to the reaction temperature, and a certain proportion of hexafluoropropylene and oxygen are introduced. After the bed stabilizes, the gas exiting the fixed bed is collected and analyzed by gas chromatography to calculate the reaction conversion and selectivity.

[0027] In this invention, the method for calculating the mass of the metal precursor and the mass of the solid acid by means of the required loading is as follows:

[0028]

[0029] Where m is the required mass of the precursor when modifying n gHZSM-5 molecular sieve (solid acid), M is the molecular mass of the corresponding substance, and ω is the mass fraction of the active metal loaded in the catalyst.

[0030] The microstructure of the catalyst surface can be observed using transmission electron microscopy (TEM). TEM observation of the CuO / HZSM-5 catalyst prepared according to this method, such as... Figure 2 As shown in the figure, HZSM-5 has a relatively regular hexagonal plate-like structure. The copper species are uniformly distributed on the prepared catalyst.

[0031] Comparative Example 1:

[0032] 10 g of HZSM-5 and 0.297 g of copper nitrate were weighed and a catalyst was prepared according to the above procedure, wherein the copper loading in the catalyst was 1%. 10 g of the catalyst was packed into a fixed bed and activated under the above conditions. After activation for 3 h, the reaction temperature was controlled at 180 °C, and then a mixture of hexafluoropropylene and oxygen was introduced into the reactor at a volume ratio of 3:1, with a space velocity of 11.25 h⁻¹ for both hexafluoropropylene and the catalyst. -1 The outlet gas was collected, and the conversion rate of the reaction was calculated to be 7.34% and the selectivity to be 42% by gas chromatography.

[0033] Comparative Example 2:

[0034] 10 g of HZSM-5 and 1.187 g of copper nitrate were weighed and a catalyst was prepared according to the above procedure, wherein the copper loading in the catalyst was 4%. 10 g of the catalyst was packed into a fixed bed and activated under the above conditions. After activation for 3 h, the reaction temperature was controlled at 180 °C, and then a mixture of hexafluoropropylene and oxygen was introduced into the reactor at a volume ratio of 3:1, with a space velocity of 11.25 h⁻¹ for both hexafluoropropylene and the catalyst. -1 The outlet gas was collected, and the conversion rate of the reaction was calculated to be 35.7% and the selectivity to be 28.7% by gas chromatography.

[0035] Example 1:

[0036] Weigh 10g of HZSM-5, 0.297g of copper nitrate, and 0.235g of cerium nitrate, and prepare the catalyst according to the above procedure. The catalyst has a copper loading of 1% and a cerium loading of 1%. 10g of the catalyst is packed into a fixed bed and activated under the above conditions. After activation for 3 hours, the reaction temperature is controlled at 180℃, and then a mixture of hexafluoropropylene and oxygen is introduced into the reactor. The volume ratio of hexafluoropropylene to oxygen is 3, and the space velocity of hexafluoropropylene and the catalyst is 11.25 h⁻¹. -1 The outlet gas was collected, and the conversion rate of the reaction was calculated to be 12.9% and the selectivity to be 42.3% by gas chromatography.

[0037] Example 2:

[0038] 10g of HZSM-5, 0.297g of copper nitrate, and 0.498g of cobalt nitrate hexahydrate were weighed and a catalyst was prepared according to the above procedure, wherein the loading of copper in the catalyst was 1% and the loading of cobalt was 1%. 10g of the catalyst was packed into a fixed bed and activated under the above conditions. After activation for 3 hours, the reaction temperature was controlled at 180℃, and then a mixture of hexafluoropropylene and oxygen was introduced into the reactor. The volume ratio of hexafluoropropylene to oxygen was 3, and the space velocity of hexafluoropropylene and the catalyst was 11.25 h⁻¹. -1 The outlet gas was collected, and the conversion rate of the reaction was calculated to be 12.2% and the selectivity to be 49.8% by gas chromatography.

[0039] Comparative Example 3:

[0040] 10 g of HZSM-5, 0.297 g of copper nitrate, and 213 μL of manganese nitrate were weighed and a catalyst was prepared according to the above procedure. The catalyst contained 1% copper and 1% manganese. 10 g of the catalyst was packed into a fixed bed and activated under the above conditions. After activation for 3 h, the reaction temperature was controlled at 180 °C, and then a mixture of hexafluoropropylene and oxygen was introduced into the reactor at a volume ratio of 3:1, with a space velocity of 11.25 h⁻¹ for both hexafluoropropylene and the catalyst. -1The outlet gas was collected, and the conversion rate of the reaction was calculated to be 9.3% and the selectivity to be 6.5% by gas chromatography.

[0041] Example 3:

[0042] 10g of HZSM-5, 0.297g of copper nitrate, and 0.777g of chromium nitrate nonahydrate were weighed and a catalyst was prepared according to the above procedure, wherein the loading of copper in the catalyst was 1% and the loading of chromium was 1%. 10g of the catalyst was packed into a fixed bed and activated under the above conditions. After activation for 3 hours, the reaction temperature was controlled at 180℃, and then a mixture of hexafluoropropylene and oxygen was introduced into the reactor. The volume ratio of hexafluoropropylene to oxygen was 3, and the space velocity of hexafluoropropylene and the catalyst was 11.25 h⁻¹. -1 The outlet gas was collected, and the conversion rate of the reaction was calculated to be 14.6% and the selectivity to be 42.1% by gas chromatography.

[0043] Comparative Example 4:

[0044] 10g of HZSM-5, 0.297g of copper nitrate, and 0.159g of silver nitrate were weighed and a catalyst was prepared according to the above procedure, wherein the loading of copper in the catalyst was 1% and the loading of silver was 1%. 10g of the catalyst was packed into a fixed bed and activated under the above conditions. After activation for 3 hours, the reaction temperature was controlled at 180℃, and then a mixture of hexafluoropropylene and oxygen was introduced into the reactor. The volume ratio of hexafluoropropylene to oxygen was 3, and the space velocity of hexafluoropropylene and the catalyst was 11.25 h⁻¹. -1 The outlet gas was collected, and the conversion rate of the reaction was calculated to be 6.4% and the selectivity to be 0% by gas chromatography.

[0045]

[0046] As can be seen from the above examples and comparative examples, although increasing the Cu loading can promote the reaction conversion, it leads to over-oxidation and a decrease in selectivity. The catalytic system prepared by co-impregnating Cu with Ce, Co, and Cr can further improve the reaction conversion selectivity, while the presence of metals such as Mn and Ag will reduce the catalytic effect. This indicates that Cu can form a metal synergy with Ce, Co, and Cr to promote the further conversion of the epoxidation reaction.

[0047] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. Those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for the continuous gas-phase preparation of hexafluoropropylene oxide using a bimetallic oxide solid acid catalyst based on metal synergistic effects, characterized in that, The catalyst uses Cu as the first active metal and Ce, Co, or Cr as the second active metal. The loading of Cu is 0.5-5 wt%, and the loading of the second active metal is 0.1-5 wt%, not exceeding the loading of Cu. The first and second active metals are supported on a solid acid, which is an HZSM-5 molecular sieve with a silicon-aluminum molar ratio of 20-50. The method includes the following steps: a) The catalyst is loaded into a fixed-bed reactor and activated by heating with an activation gas; b) A mixture of hexafluoropropylene and oxygen is introduced into a fixed-bed reactor for reaction.

2. The method according to claim 1, characterized in that, The catalyst is prepared by the following steps: 1) Calculate the mass of the first active metal precursor, the second active metal precursor, and the solid acid by the required loading amount, dissolve the precursor and the solid acid in an ethanol aqueous solution and stir to obtain a mixture, and heat and dry the mixture until it becomes a solid. 2) Grind the solid into powder and dry it, then calcine the dried powder to obtain the catalyst; The first active metal precursor is copper nitrate, and the second active metal precursor is one of cerium nitrate, cobalt nitrate hexahydrate, or chromium nitrate nonahydrate; the pore size of the solid acid is 0.53-0.58 nm.

3. The method according to claim 2, characterized in that, In step 1), the mass ratio of ethanol to water in the ethanol-water solution is 1:1; the heating and drying is carried out by heating to 80-100℃.

4. The method according to claim 2, characterized in that, In step 2), the drying temperature is 60-100℃; the calcination temperature is 450-700℃, the heating rate is 5-20℃ / min, and the calcination time is 3-6h.

5. The method according to claim 1, characterized in that, In step a), the activating gas is a mixture of hexafluoropropylene and oxygen in a volume ratio of 4, the activation temperature is 250-280℃, and the activation time is 3-5h.

6. The method according to claim 1, characterized in that, In step b), the reaction temperature is 140-220℃, and the reaction pressure is 0.3-0.4 MPa; the volume hourly space velocity (VHSV) of the hexafluoropropylene is 5-12 h⁻¹. -1 The volume ratio of hexafluoropropylene to oxygen is 2:1 to 5:1.

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