Composite oxide catalyst, method for preparing the same, and use thereof

Abstract

The application discloses a composite oxide catalyst, a preparation method and application thereof, and the catalyst is composed of M / Cr x O3-Al y O3, wherein x+y=2, Cr x O3-Al y O3 is a main catalyst, M represents a metal assistant component, the main catalyst is obtained by mixing and calcining Cr2O3 and Al2O3 through ball milling, and a fluorine-chlorine exchange reaction is carried out by using two reactors in series to react trifluoromethane and chloroform under the action of the catalyst to obtain a reaction product containing difluoromonochloromethane and monofluorodichloromethane. The catalyst can exhibit high reaction activity in the fluorine-chlorine exchange reaction of HFC-23 and CHCl3 without fluorination pretreatment, and can still meet the stability requirements of industrial application without adding a gas for eliminating carbon deposition in the fluorine-chlorine exchange reaction of HFC-23 and CHCl3.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, and specifically relates to a composite oxide catalyst, its preparation method, and its application. Background Technology

[0002] Trifluoromethane (HFC-23, R23) is an unavoidable byproduct of the industrial production of difluorochloromethane (HCFC-22, R22). Its greenhouse effect potential is 14,800 times that of CO2, making it a typical strong greenhouse gas. HFC-23 is generally treated by high-temperature incineration at 1200℃. This method involves large investments, significant pollution, high energy consumption, and the decomposition product, hydrogen fluoride, easily corrodes equipment. Although the use of HCFC-22 as a refrigerant is being phased out, its use as a raw material in the production of fluorinated hydrocarbons such as tetrafluoroethylene will persist for a long time, thus its byproduct, trifluoromethane, will continue to be produced. Therefore, resource utilization of HFC-23 is a solution that achieves both economic efficiency and environmental protection.

[0003] Currently, there are many reported methods for the resource utilization of HFC-23. For example, patent US3009966A discloses a method for thermal cracking to prepare tetrafluoroethylene and hexafluoropropylene; patent CN104628514A discloses a method for co-cracking with CH4 to prepare vinylidene fluoride; and WO96 / 29296 discloses a method for co-cracking with fluoroalkanes to form macromolecular fluoroalkanes. However, these methods are difficult to industrialize due to harsh reaction conditions, low product selectivity, and short catalyst lifetime. In contrast, patents CN112979410A and CN112973685A disclose a method for the fluorine-chlorine exchange of HFC-23 and CHCl3 to generate HCFC-22 and HCFC-21 under Lewis acid catalyst catalysis. This method has relatively mild reaction conditions and high product selectivity, making it basically meet the requirements for industrialization. However, its catalyst lifetime is still relatively short. Therefore, to improve catalyst lifetime, gases such as oxygen, chlorine, and hydrogen are usually added during the reaction stage to promote the elimination of carbon deposits and improve the catalyst's catalytic efficiency and stability. However, this also inevitably leads to the generation of some byproducts during the reaction, such as carbon monoxide, carbon dioxide, chloroform (R11), and dichloroform (R12). These byproducts, along with unreacted carbon dioxide, can affect the subsequent product separation and purification, especially oxidizing substances like oxygen. Even HCFC-22 feedstock containing trace amounts of oxygen poses a significant risk during the cracking process to produce TFE (tetrafluoroethylene). Moreover, even if byproducts such as oxygen, carbon monoxide, and carbon dioxide are removed through distillation during HCFC-22 post-treatment, additional separation costs and product losses are incurred. Furthermore, the catalysts currently disclosed in patents require activation with AHF before use, which is time-consuming, costly, energy-intensive, and risky. Additionally, the conversion rate of HFC-23 is relatively low, typically not exceeding 30% in a single pass. Large quantities of HFC-23 and CHCl3 need to be recycled, leading to increased energy consumption, heavier equipment load, and decreased process efficiency. Therefore, it is of great significance to develop a catalyst that can still meet the industrial application requirements for conversion rate and stability without adding a gas to eliminate carbon deposits during the HFC-23 and CHCl3 fluorine-chlorine exchange reaction. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a composite oxide catalyst, its preparation method, and its application. It exhibits high reactivity in the HFC-23 and CHCl3 fluorine-chlorine exchange reaction without requiring fluorination pretreatment, and it still meets the stability requirements for industrial applications without adding a gas to eliminate carbon deposits during the HFC-23 and CHCl3 fluorine-chlorine exchange reaction.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: First, a composite oxide catalyst is provided, the composition of which is M / Cr x O3-Al y O3, where x+y=2. Among them, Cr x O3-Al y O3 is the main catalyst, obtained by ball milling and calcining Cr2O3 and Al2O3. M represents the metal additive component, with an addition amount of 0.1~10wt%.

[0006] Preferably, the metal additive component is selected from any one or two of the metals W, Mo, V, and Nb.

[0007] In addition, a method for preparing the composite oxide catalyst is also provided, comprising the following steps: Step 1: Add Al2O3 nanoparticles and Cr2O3 nanoparticles to deionized water and stir evenly. Then transfer to a ball mill, ball mill for a set time, and dry and calcine the ball-milled slurry to obtain a solid product. Step 2: The metal additive component is incorporated into the solid product obtained in Step 1 by impregnation, and then dried and calcined to obtain the final product, the composite oxide catalyst.

[0008] Preferably, the particle size of the Al2O3 nanoparticles and Cr2O3 nanoparticles in step 1 is 20~200nm.

[0009] Preferably, the mass ratio of Al2O3 nanoparticles to Cr2O3 nanoparticles in step 1 is 1:(0.01~1).

[0010] Preferably, the total mass ratio of Al2O3 nanoparticles and Cr2O3 nanoparticles to deionized water in step 1 is (0.5~1):1.

[0011] Preferably, the ball milling time in step 1 is 2 to 10 hours, and the ball milling speed is 100 to 500 r / min.

[0012] Preferably, the roasting temperature in step 1 is 400~700℃, the roasting time is 5~15h, and the roasting atmosphere is air.

[0013] Preferably, the metal additive in step 2 is selected from any one or two of W, Mo, V, and Nb, and the amount added is 0.1~10 wt.%.

[0014] Furthermore, an application of the aforementioned composite oxide catalyst in a fluoride-chlorine exchange reaction is also provided, the fluoride-chlorine exchange reaction comprising the following steps: Under the action of the catalyst, trifluoromethane and chloroform are reacted in two reactors in series to obtain reaction products containing difluorochloromethane and difluorodichloromethane, at a reaction temperature of 150~350℃. At the outlet of the first reactor, the reaction products containing dichlorofluoromethane and dichlorofluoromethane are separated by distillation, and the raw materials trifluoromethane and chloroform are fed into the second reactor to continue the reaction. The dichlorofluoromethane and dichlorofluoromethane separated at the outlets of the two reactors are recovered and reused after separation.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. The inventors discovered through research that the present invention prepares the composite oxide catalyst by mechanical ball milling. The mechanical force generated during the high-speed operation of the machine causes Cr2O3 and Al2O3 particles to break and refine under high-energy collisions, leading to lattice distortion in alumina. This allows some Cr atoms to enter the Al2O3 lattice and replace Al atoms, ultimately yielding a structurally stable Cr... x O3-Al y O3. Chromium-doped alumina enhances the structural stability of catalysts primarily through four mechanisms: ionic radius compensation, suppression of phase transitions, and modulation of alumina acidity and electronic structure characteristics. Firstly, ionic radius compensation and suppression of phase transitions are crucial. Pure alumina undergoes a phase transition at high temperatures and in special atmospheres such as HF, leading to a sharp decrease in specific surface area. Due to... The ionic radius of the six-coordinate ion is approximately 0.615 Å, which is slightly larger than that of the six-coordinate ion. (The radius of the six-coordinate ion is approximately 0.535 Å), when After incorporating alumina, Alternative Upon entering the crystal lattice, the mismatch in ionic radii causes minute displacements in the positions of surrounding atoms, disrupting the original periodic arrangement of the lattice and resulting in lattice distortion and a stress field. This lattice distortion and stress field generate elastic stress in localized regions, affecting the material's mechanical and thermal properties and hindering… The lattice rearrangement is achieved. Simultaneously, Cr doping can create a "pinning" effect on the surface to suppress grain boundary migration, slow down atomic diffusion rates, and form a stable oxide layer on the surface, enhancing matrix bonding. Furthermore, Cr can increase the coordination unsaturation of oxygen on the surface, delaying the condensation and sintering of surface hydroxyl groups under reaction conditions, thereby maintaining the structural stability of the material. Secondly, it alters the acidity and electronic structure characteristics of alumina. Since ions possess empty orbitals and can accept electron pairs, doping Cr on the surface or in the lattice of a material can form new Lewis acid sites. This process also alters the original electronic structure of Al and modulates the strength of the metal-oxygen bond. In harsh reactions, this modulation can reduce structural collapse caused by carbon deposition or loss of the active phase, allowing the catalyst to maintain crystalline phase stability during the reaction.

[0016] 2. The composite oxide catalyst provided by this invention can exhibit high reactivity in the HFC-23 and CHCl3 fluorine-chlorine exchange reaction without fluorination pretreatment, and can maintain a long service life even without adding a gas to eliminate carbon deposits during the reaction, making it suitable for industrial applications.

[0017] 3. The series reactor provided by the present invention can greatly improve the single-pass conversion rate of reactants, reduce material circulation, improve raw material utilization, and reduce equipment load.

[0018] The specific technical solution of the present invention and its beneficial effects will be described in detail in the following specific embodiments in conjunction with the accompanying drawings. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings and specific embodiments: Figure 1 The X-ray diffraction patterns are of the catalysts prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention. Figure 2 The X-ray diffraction patterns are those of Example 1 after 3870 hours of reaction and Comparative Example 3 after 720 hours of reaction in reactor 1 of the present invention. Detailed Implementation

[0020] This invention provides a composite oxide catalyst for the fluorine-chlorine exchange reaction of HFC-23 (trifluoromethane) and CHCl3 (trichloromethane, i.e., chloroform), wherein the composite oxide catalyst has an M / Cr composition. x O3-Al y O3, where x+y=2, and Cr x O3-Al y O3 is the main catalyst, and M represents the metal auxiliary component, which is selected from any one or two of the metals W, Mo, V and Nb, with an addition amount of 0.1~10wt%.

[0021] Among them, the main catalyst Cr x O3-Al y O3 is obtained by doping Al2O3 with Cr2O3, followed by ball milling and calcination. The metal additive M is preferably at least one or both of W and Mo, which can further significantly enhance the catalyst activity.

[0022] The inventors discovered that in the fluoride-chloride exchange reaction of HFC-23 and CHCl3, the L acidic sites of the catalyst are the active centers of the reaction, and the number of L acidic sites is crucial to the catalyst activity. The inventors also found that the products of the above-mentioned fluoride-chloride exchange readily undergo disproportionation reactions on the catalyst surface, leading to carbon deposition on the catalyst. Therefore, the larger the catalyst surface area, the more active sites there are, the higher the activity, the stronger the ability to accommodate carbon deposits, and the better the stability. Al2O3 catalysts have high reactivity but poor stability, and Al2O3 is difficult to exist stably in the reaction, gradually being fluorinated to AlF3, causing a significant decrease in specific surface area, thus resulting in poor catalyst stability. Cr2O3, on the other hand, has a stable structure in the fluoride-chloride exchange reaction, and even in the presence of pure HF, it is difficult to form CrF3. However, it has fewer surface acidic sites and has almost no reactivity in the HFC-23 and CHCl3 fluoride-chloride exchange reaction. Therefore, this invention utilizes the structural characteristics of Cr2O3 and Al2O3 through ball milling to synthesize Cr-doped Al2O3 materials. The synergistic effect of Cr2O3 and Al2O3 effectively suppresses the structural transformation of Al2O3. Furthermore, this invention further modulates the surface acidity distribution and the number of surface acid sites of the catalyst by impregnating this material with supporting additives, resulting in a catalyst with high catalytic activity and stability.

[0023] The present invention also provides a method for preparing the main catalyst Cr x O3-Al y A method for preparing O3 includes: adding Al2O3 nanoparticles and Cr2O3 nanoparticles to deionized water, stirring slowly until homogeneous, then transferring the mixture to a ball mill and milling for a period of time. The milled slurry is then dried, and the dried solid is calcined in a muffle furnace. After cooling, Cr2O3 is obtained. x O3-Al y O3 solid.

[0024] The mass ratio of Al2O3 nanoparticles to Cr2O3 nanoparticles is 1:(0.01~1), preferably 1:(0.1~0.5), for example 1:0.1, 1:0.5, 1:0.3. Under this mass ratio, the prepared Cr-doped Al2O3 catalyst has a suitable specific surface area and structure, can effectively suppress the structural transformation of Al2O3 in the reaction, and has good stability.

[0025] The mass ratio of the deionized water to the total mass of Al2O3 nanoparticles and Cr2O3 nanoparticles is 1:(0.5~1), preferably 1:(0.5~0.8), for example 1:0.5, 1:0.6, 1:0.7, 1:0.8. Under this mass ratio, the two nanoparticles can be better combined, and the resulting catalyst is more uniform.

[0026] The Cr2O3 and Al2O3 nanoparticles are spherical particles with a particle size of 20~200nm, such as 20nm, 50nm, 100nm, 150nm, and 200nm. The average particle size of the Cr2O3 nanoparticles is preferably 50~100nm, such as 50nm, 60nm, 70nm, 80nm, 90nm, and 100nm. The average particle size of the Al2O3 nanoparticles is preferably 20~50nm, such as 20nm, 30nm, 40nm, and 50nm.

[0027] The ball milling mixture is carried out using a ball mill with a rotation speed of 100-500 r / min and a milling time of 2-10 h. Preferably, the ball mill rotation speed is 300-400 r / min and the milling time is 4-6 h; the ball mill rotation speed is 300 r / min and the milling time is 6 h; the ball mill rotation speed is 400 r / min and the milling time is 4 h; and the ball mill rotation speed is 350 r / min and the milling time is 5 h.

[0028] The drying temperature of the slurry is 100~180℃, preferably 120~140℃, for example 120℃, 130℃, 140℃, and the drying is carried out in an oven.

[0029] The calcination is carried out in an air atmosphere at a temperature of 400-700°C, preferably 500-600°C, for a duration of 5-15 hours. For example, a calcination temperature of 500°C for 15 hours, a calcination temperature of 600°C for 5 hours, or a calcination temperature of 550°C for 10 hours.

[0030] The inventors discovered that the mechanical ball milling method provided by this invention, used to prepare the composite oxide catalyst, utilizes the mechanical force generated during high-speed machine operation to cause Cr2O3 and Al2O3 particles to break and refine under high-energy collisions. This leads to lattice distortion in alumina, allowing some Cr atoms to enter the Al2O3 lattice and replace Al atoms, ultimately resulting in a structurally stable Cr2O3 catalytic oxide. x O3-Al y O3. Research has found that only under specific ratios of Cr and Al, specific water content, and specific energy levels can Al2O3 undergo lattice distortion, allowing Cr atoms to replace Al atoms and thus yield structurally stable Cr. x O3-Al y O 3。

[0031] The method for adding the metal additive in this invention can employ conventional methods for preparing existing catalysts, such as wet mixing or impregnation with a metal salt solution precursor followed by calcination. Preferably, the metal additive is added via precursor impregnation.

[0032] This invention also provides a method for the resource utilization of HFC-23, namely, the application of the above-mentioned composite oxide catalyst in the trifluoromethane fluorine-chlorine exchange reaction. It uses CHCl3 and HFC-23 as raw materials, and the above-mentioned composite oxide catalyst as the reaction catalyst, to convert HFC-22 and HCFC-21 through a fluorine-chlorine exchange reaction.

[0033] (1) Under the action of the catalyst, HFC-23 and CHCl3 were reacted in two reactors in series to obtain reaction products containing HCFC-22 and HCFC-21, and the reaction temperature was 150~330℃. (2) The reaction products containing HCFC-22 and HCFC-21 are separated by distillation at the outlet of the first reactor, and the raw materials HFC-23 and CHCl3 are sent to the second reactor to continue the reaction. The HCFC-22 and HCFC-21 separated at the outlets of the two reactors are recycled after separation.

[0034] The method provided by the present invention uses a molar ratio of 1:1 to 1:3 between the raw materials HFC-23 and CHCl3, for example, 1:1, 1:2, or 1:3.

[0035] The method provided by this invention requires the reaction temperatures of the two reactors to meet different conditions: the reaction temperature of the first reactor is 250~330℃, and the reaction temperature of the second reactor is 150~250℃.

[0036] More preferably, the reaction temperature of the first reactor is 280~330℃, and the reaction temperature of the second reactor is 180~220℃. For example, the reaction temperature of the first reactor is 280℃, and the reaction temperature of the second reactor is 220℃; the reaction temperature of the first reactor is 330℃, and the reaction temperature of the second reactor is 180℃; or the reaction temperature of the first reactor is 300℃, and the reaction temperature of the second reactor is 200℃.

[0037] In the method provided by this invention, the reaction pressure is 0~0.7MPa during the reaction stage.

[0038] More preferably, the reaction pressure is 0.1~0.3MPa, for example 0.1MPa, 0.2MPa, or 0.3MPa.

[0039] The method provided by this invention requires the raw material residence time in the two reactors to meet different conditions: the raw material residence time in the first reactor is 0.1~5s, and the raw material residence time in the second reactor is 5~140s.

[0040] More preferably, the raw material residence time in the first reactor is 1-4 s, and the raw material residence time in the second reactor is 24-100 s. For example, the raw material residence time in the first reactor is 2 s, and the raw material residence time in the second reactor is 40 s; or the raw material residence time in the first reactor is 3 s, and the raw material residence time in the second reactor is 60 s. Furthermore, the composite catalyst can be applied to the resource utilization of HFC-23 without fluorination pretreatment.

[0041] Example 1: 1. Weigh 300g of deionized water, 30g of Cr2O3 nanoparticles (average particle size 50nm), and 180g of Al2O3 nanoparticles (average particle size 50nm). Stir well at room temperature, then place the mixture into a ball mill jar. Control the ball mill speed at 400r / min and ball mill for 3h. After ball milling, separate the grinding balls from the slurry. Dry the slurry at 120℃ for 12h, then calcine it in a muffle furnace at 500℃ for 5h with a heating rate of 2℃ / min to obtain Cr2O3 nanoparticles. x O3-Al y O3 solid was compressed into tablets and sieved to 10-20 mesh for later use, and designated as catalyst 1.

[0042] The catalyst 1 was impregnated: 100g of catalyst 1 was weighed into a beaker, and a certain concentration and amount of ammonium metatungstate solution was weighed according to a loading of 5wt.%. The mixture was stirred and impregnated for 4h, then dried at 110℃ for 12h, and calcined in air at 450℃ for 5h to obtain the catalyst, which was designated as catalyst 2.

[0043] Example 2: The operation in this embodiment is the same as in Example 1, except that: Cr2O3 nanoparticles with an average particle size of 100 nm are used, and the amount remains the same. The catalyst obtained is designated as catalyst 3.

[0044] Example 3: The operation in this embodiment is the same as in Embodiment 1, except that the average particle size of both Cr2O3 nanoparticles and Al2O3 nanoparticles is 100 nm, and the amount used remains the same. The catalyst prepared is designated as catalyst 4.

[0045] Example 4: The operation of this embodiment is the same as that of embodiment 1, except that the amount of Cr2O3 nanoparticles is increased to 50g, and the catalyst obtained is referred to as catalyst 5.

[0046] Example 5: The operation of this embodiment is the same as that of embodiment 1, except that the amount of Cr2O3 nanoparticles is increased to 90g, and the catalyst prepared is referred to as catalyst 6.

[0047] Example 6: The operation of this embodiment is the same as that of embodiment 1, except that the amount of deionized water is reduced to 225g, and the catalyst obtained is referred to as catalyst 7.

[0048] Example 7: The operation of this embodiment is the same as that of embodiment 1, except that the amount of deionized water is increased to 400g, and the catalyst obtained is referred to as catalyst 8.

[0049] Example 8: The operation of this embodiment is the same as that of embodiment 1, except that the ball milling time is controlled to be 10 hours, and the catalyst obtained is denoted as catalyst 9.

[0050] Example 9: The operation of this embodiment is the same as that of embodiment 1, except that the impregnation solution is replaced by ammonium molybdate solution instead of ammonium metatungstate solution, and the catalyst obtained is referred to as catalyst 10.

[0051] Example 10: The operation of this embodiment is the same as that of embodiment 1, except that the impregnation solution is replaced by ammonium metatungstate solution and the catalyst obtained is referred to as catalyst 11.

[0052] Example 11: The operation of this embodiment is the same as that of embodiment 1, except that the concentration and amount of ammonium metatungstate impregnation solution are adjusted according to a loading of 1 wt.%, and the catalyst obtained is referred to as catalyst 12.

[0053] Example 12: The operation of this embodiment is the same as that of Embodiment 1, except that the concentration and amount of ammonium metatungstate impregnation solution are adjusted according to a loading of 10 wt.%, and the catalyst obtained is referred to as catalyst 13.

[0054] Comparative Example 1: The operation of this comparative example is the same as that of Example 1, except that the amount of Cr2O3 nanoparticles is 0, and other conditions remain unchanged. The catalyst obtained is referred to as catalyst B1.

[0055] Comparative Example 2: The operation of this comparative example is the same as that of Example 1, except that the amount of Al2O3 nanoparticles is 0, and other conditions remain unchanged. The catalyst obtained is denoted as catalyst B2.

[0056] Comparative Example 3: Weigh out the Al2O3 nanoparticles from Example 1 and impregnate them directly with an equal amount of ammonium metatungstate without ball milling. Under the same conditions, the resulting catalyst is denoted as catalyst B3.

[0057] Comparative Example 4: The operation of this comparative example is the same as that of Example 1, except that the solid after ball milling and calcination is not impregnated with ammonium metatungstate, and other conditions remain unchanged. The catalyst obtained is referred to as catalyst B4.

[0058] Application Example 1: The catalysts prepared in the above examples and comparative examples were used in the fluoride-chlorine exchange reaction of HFC-23 and CHCl3, and the specific operation is as follows: 20 mL of each of Examples 1 to 12 and Comparative Examples 1 to 4 was packed into the reactor bed. A mixture of trifluoromethane and chloroform in a molar ratio of 1:2 was introduced into the reactor for fluorine-chlorine exchange reaction. The reaction temperature of the first reactor was 300°C and the reaction residence time was 4 s. The reaction temperature of the second reactor was 180°C and the reaction residence time was 80 s.

[0059] Separation and distillation: The reaction products from the first reactor are first condensed and separated by gas-liquid separation to remove unreacted chloroform. The remaining material is then distilled through a multi-stage distillation column. Unreacted HFC-23 is obtained at the top of the distillation column, and a stream containing HCFC-22 and HCFC-21 is obtained at the bottom of the distillation column. The unreacted chloroform, along with the unreacted HFC-23 at the top of the distillation column, is then fed into the next reactor for further reaction.

[0060] The results after 50 hours of reaction are shown in Table 1 below: Table 1 Results of the trifluoromethane fluoride-chloride exchange reaction and catalyst evaluation Catalyst 2 69.2 51.5 48.4 Catalyst 3 68.6 52.2 47.7 Catalyst 4 70.2 52.1 47.8 Catalyst 5 67.4 50.4 49.5 Catalyst 6 68.4 50.2 49.7 Catalyst 7 67.6 52.5 47.4 Catalyst 8 77.7 53.4 46.5 Catalyst 9 67.4 51.4 48.5 Catalyst 10 70.7 51.5 48.4 Catalyst 11 71.2 52.7 47.2 Catalyst 12 69.3 51.7 48.2 Catalyst 13 68.5 50.9 49.0 Catalyst B1 66.2 50.6 49.3 Catalyst B2 3 50.3 49.6 Catalyst B3 69.2 50.9 49.0 Catalyst B4 45.4 50.5 49.4 .

[0061] Examples 1-12 show that, under given catalyst preparation conditions such as different average particle sizes of Cr2O3 and Al2O3 nanoparticles, the ratio of Cr2O3 to Al2O3, and the amount of water, the catalyst provided by this invention exhibits high conversion rates and selectivity for the target product in the fluoride-chlorine exchange reaction of HFC-23 and CHCl3. Examples 1, 2, and 4 show that Cr2O3 alone has very low catalytic activity, and chromium itself is not an active reaction center. A comparison of Examples 1, 3, and 4 shows that the metal promoter component described in this invention can significantly improve the catalyst's reactivity.

[0062] Application Example 2: 20 mL of the catalysts from Example 1 and Comparative Example 3 were respectively packed into the reactor bed. A mixture of trifluoromethane and chloroform in a molar ratio of 1:2 was introduced into the reactor for fluorine-chlorine exchange reaction. The reaction temperature in the first reactor was 300 °C and the reaction residence time was 4 s. The reaction temperature in the second reactor was 180 °C and the reaction residence time was 80 s. Stability evaluations were performed on each reactor.

[0063] Separation and distillation: The reaction products from the first reactor are first condensed and separated by gas-liquid separation to remove unreacted chloroform. The remaining material is then distilled through a multi-stage distillation column. Unreacted HFC-23 is obtained at the top of the distillation column, and a stream containing HCFC-22 and HCFC-21 is obtained at the bottom of the distillation column. The unreacted chloroform, along with the unreacted HFC-23 at the top of the distillation column, is then fed into the next reactor for further reaction.

[0064] The evaluation results are shown in Tables 2 and 3 below: Table 2. Catalyst stability evaluation results in Example 1 10 67.5% 52.5% 47.4% 35 67.9% 52.7% 47.2% 60 69.4% 53.2% 46.7% 100 68.2% 51.6% 48.3% 135 70.5% 51.5% 48.4% 180 69.7% 51.6% 48.3% 260 70.9% 51.5% 48.4% 357 67.7% 52.0% 47.9% 450 71.0% 51.5% 48.4% 590 70.5% 51.1% 48.8% 720 71.9% 54.1% 45.8% 1000 67.2% 52.8% 47.1% 1345 67.1% 52.9% 47.0% 1678 66.6% 51.5% 48.4% 2358 67.1% 50.0% 49.9% 2578 65.2% 52.5% 47.4% 2940 63.2% 52.7% 47.2% 3459 60.3% 51.5% 48.4% 3870 60.4% 51.8% 48.1% Table 3. Results of catalyst stability evaluation in Comparative Example 3 10 69.5% 52.5% 47.4% 35 68.2% 52.7% 47.2% 60 67.1% 53.2% 46.6% 100 68.2% 51.6% 48.3% 135 69.5% 51.5% 48.3% 180 66.7% 51.6% 48.2% 260 63.9% 51.4% 48.4% 357 58.7% 52.0% 47.8% 450 52.0% 53.5% 46.4% 590 45.5% 54.1% 45.7% 720 36.9% 56.1% 43.8% As can be seen from the activity results of the catalysts in the examples and comparative examples shown in Tables 1, 2 and 3 above, the catalyst provided by the present invention exhibits high conversion rate, target product selectivity and catalytic stability when used in the fluoride-chlorine exchange reaction of HFC-23 and CHCl3. After 3870 hours of reaction, the catalyst still has high activity and selectivity (HFC-23 conversion rate 67.5%, HCFC-21+HCFC-22 selectivity 99.9%). Compared with Comparative Example 3, under the same conditions, the catalyst lifetime is significantly improved, achieving the effect of simultaneously achieving good catalyst activity and stability, and is suitable for industrial production scale-up.

[0065] from Figure 1 and Figure 2 It can be seen that the intensity ratio of the characteristic peaks at 2θ=66.5° and 2θ=68.2° in the X-ray diffraction pattern of the composite catalyst of the present invention is different from that of the known Al2O3 standard spectrum, indicating that a new crystal phase or doped structure has been formed. This structure can suppress the Al2O3 structural transformation in the stability experiment.

[0066] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that the present invention includes, but is not limited to, the content described in the above specific embodiments. Any modifications that do not depart from the functional and structural principles of the present invention will be included within the scope of the claims.

Claims

1. A composite oxide catalyst, characterized in that, The composite oxide catalyst has the composition M / Cr x O3-Al y O3, where x+y=2. Among them, Cr x O3-Al y O3 is the main catalyst, obtained by ball milling and calcining Cr2O3 and Al2O3. M represents the metal additive component, with an addition amount of 0.1~10wt%; The metal additive component is selected from any one or two of the metals W, Mo, V, and Nb; The preparation method of the composite oxide catalyst includes the following steps: Step 1: Add Al2O3 nanoparticles and Cr2O3 nanoparticles to deionized water and stir evenly. Then transfer to a ball mill, ball mill for a set time, and dry and calcine the ball-milled slurry to obtain a solid product. Step 2: The metal additive component is incorporated into the solid product obtained in Step 1 by impregnation, and then dried and calcined to obtain the final product, the composite oxide catalyst. The mass ratio of Al2O3 nanoparticles to Cr2O3 nanoparticles in step 1 is 1:(0.01~1). The total mass ratio of Al2O3 nanoparticles and Cr2O3 nanoparticles to deionized water in step 1 is (0.5~1):

1.

2. The composite oxide catalyst according to claim 1, characterized in that, The particle size of the Al2O3 nanoparticles and Cr2O3 nanoparticles mentioned in step 1 is 20~200nm.

3. The composite oxide catalyst according to claim 1, characterized in that, The ball milling time in step 1 is 2~10h, and the ball milling speed is 100~500r / min.

4. The composite oxide catalyst according to claim 1, characterized in that, The roasting temperature in step 1 is 400~700℃, the roasting time is 5~15h, and the roasting atmosphere is air.

5. The application of the composite oxide catalyst according to claim 1 in the fluorine-chlorine exchange reaction, characterized in that, Using CHCl3 and HFC-23 as raw materials and the composite oxide catalyst as the reaction catalyst, HCFC-22 and HCFC-21 were obtained through a fluorine-chlorine exchange reaction.

6. The application of the composite oxide catalyst according to claim 5 in the fluorine-chlorine exchange reaction, characterized in that, The fluoride-chlorine exchange reaction includes the following steps: Under the action of the catalyst, trifluoromethane and chloroform are reacted in two reactors in series to obtain reaction products containing difluorochloromethane and difluorodichloromethane, at a reaction temperature of 150~350℃. At the outlet of the first reactor, the reaction products containing dichlorofluoromethane and dichlorofluoromethane are separated by distillation, and the raw materials trifluoromethane and chloroform are fed into the second reactor to continue the reaction. The dichlorofluoromethane and dichlorofluoromethane separated at the outlets of the two reactors are recovered and reused after separation.

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