Preparation Method and Application of a Composite Catalyst of Aluminum Fluoride / Wave Absorbing Material

Abstract

The present invention discloses a preparation method of a composite catalyst of aluminum fluoride / wave-absorbing material and its application in the fluorochlorination exchange reaction of chloroform and fluorinated alkanes. The preparation method includes: obtaining the composite catalyst of aluminum fluoride / wave-absorbing material by ball milling and roasting aluminum fluoride and wave-absorbing material. The composite catalyst of aluminum fluoride / wave-absorbing material of the present invention is applied to the fluorochlorination exchange reaction of chloroform and fluorinated alkanes, and the molecular formula of the fluorinated alkane is C x H y F z , where 1≤x≤2, 1≤z≤4, and y + z = 2x + 2. Especially in the fluorochlorination exchange reaction of HFC-23, after microwave heating, the conversion rate of raw materials and the stability of the catalyst can be significantly improved.

Description

Technical Field

[0001] The present invention relates to the field of catalysts, and particularly to a composite catalyst of aluminum fluoride / wave-absorbing material, a preparation method thereof, and an application thereof in the fluorine-chlorine exchange reaction of chloroform and fluorohydrocarbons in a microwave electromagnetic field. Background Art

[0002] Hydrofluorocarbons (HFCs), as substitutes for chlorofluorocarbons (CFCs), have been widely used in the fields of refrigerants, cleaning agents, foaming agents, aerosols, aerosol propellants, etc. However, HFCs are extremely strong greenhouse gases, and their impact on climate warming is far stronger than that of an equal amount of carbon dioxide. Therefore, the conversion of chlorofluorocarbons (CFCs) is also a way.

[0003] At present, the main methods for converting chlorofluorocarbons are hydrodechlorination and fluorine-chlorine exchange. The hydrodechlorination method requires the use of noble metal catalysts, but it faces problems such as high production costs, easy loss of active components, easy sintering, short service life, and difficulties in regeneration and recovery after repeated use. The gas-phase fluorine-chlorine exchange method has the advantages of easy control, high material utilization rate, easy regeneration of the catalyst, and convenient large-scale continuous production, and is currently a commonly used method for converting chlorofluorocarbons.

[0004] Trifluoromethane (CHF3, HFC-23) is an inevitable by-product in the industrial production of dichlorofluoromethane (CHClF2, HFC-22). Currently, the industrial treatment mainly adopts high-temperature incineration (above 1200 °C), but the incineration treatment cost is high and there is a waste of resources. Therefore, the resource-based conversion of trifluoromethane is of great significance. At present, the research on the resource-based utilization of trifluoromethane mainly focuses on the conversion of trifluoromethane through the fluorine-chlorine exchange reaction.

[0005] Patent CN112979410A discloses that the fluorine-chlorine exchange reaction of HFC-23 and halogenated hydrocarbons is realized under the catalytic action of a main catalyst and a metal oxide. The catalyst for the fluorine-chlorine exchange reaction includes a main catalyst and a metal oxide. The main catalyst is a chromium, aluminum, magnesium-based catalyst or a catalyst in which chromium, aluminum, and magnesium are supported on activated carbon / graphite. The metal oxide is selected from at least one metal oxide of K, Na, Fe, Co, Cu, Ni, Zn, or Ti. This catalyst is suitable for general fluorine-chlorine exchange reactions, but it is difficult to activate stable CHF3.

[0006] Patent CN109772377A discloses a catalyst for fluorine-chlorine exchange reaction and a preparation method thereof. By adding a surfactant during the preparation process, the prepared catalyst has a multi-sided prismatic structure. When the catalyst provided by the present invention is used in the fluorine-chlorine exchange reaction of trifluoromethane and trichloromethane, it not only has high selectivity, but also has high conversion rate and very good stability. However, the preparation method of this catalyst is relatively complex and the cost is relatively high, making it difficult to realize industrial application.

[0007] Patent CN104628513A discloses a method for converting trifluoromethane and chloroform into HCFC-22 under the action of a Lewis acid catalyst. However, the Lewis acid catalyst has strong acidity, and there is an obvious phenomenon of catalyst deactivation caused by carbon deposition and sintering.

[0008] The atmospheric lifetime of trifluoromethane is as high as 264 years, its molecular structure is very stable, and the C-F bond energy is as high as 533.9 kJ / mol. When using traditional fluorine-chlorine exchange reaction catalysts, including magnesium fluoride, aluminum fluoride, and chromium oxyfluoride, etc., the conversion rate of trifluoromethane is generally only 20-30%, which is difficult to further improve, and the catalyst is prone to deactivation. Summary of the Invention

[0009] In order to solve the above technical problems, the present invention provides a composite catalyst of aluminum fluoride / absorbing material, a preparation method thereof, and an application thereof in the resource utilization of trifluoromethane.

[0010] The object of the present invention is achieved by the following technical solutions:

[0011] A preparation method of a composite catalyst of aluminum fluoride / absorbing material, the preparation method comprising: the composite catalyst of aluminum fluoride / absorbing material is obtained by ball milling and roasting aluminum fluoride and an absorbing material.

[0012] The ball milling is carried out by a ball mill, the rotation speed of the ball mill is 100-500 r / min, and the ball milling time is 2-10 h. Preferably, the rotation speed of the ball mill is 300-400 r / min, the ball milling time is 4-6 h, and the ball mill grinds in both forward and reverse directions.

[0013] The roasting is carried out in a nitrogen atmosphere, and the roasting temperature is 320-450 °C, preferably the roasting temperature is 360-450 °C.

[0014] Preferably, the roasted sample is pressed into tablets at a pressure of 15-20 MPa and sieved to 10-20 mesh.

[0015] The mass ratio of aluminum fluoride to the absorbing material is 1:0.1-1, preferably 1:0.2-0.8, more preferably 1:0.4-0.6.

[0016] The wave-absorbing material is selected from at least one of silicon carbide, silicon nitride, carbon nanotubes, graphene, ferrites, elemental iron powder, elemental cobalt powder or elemental nickel powder.

[0017] The inventor of the present invention has found through research that the aluminum fluoride / wave-absorbing material composite catalyst prepared by mechanical grinding, while fully and evenly mixing the materials, through the action of mechanical force, the particles break and refine under high-energy collision, the specific surface area of the crystal grains increases, lattice defects are generated in the crystal structure, and unsaturated bonds are generated by the breakage of surface chemical bonds, so that the acidity of the catalyst surface is greatly improved, and the catalyst performance is further improved.

[0018] The aluminum fluoride of the present invention is prepared by a coprecipitation method.

[0019] Specifically, the aluminum fluoride of the present invention is obtained through the following steps:

[0020] Take aluminum nitrate nonahydrate and dissolve it in deionized water. Under the condition of stirring with water bath heating (40-80 °C), slowly add ammonium fluoride solution to obtain a white precipitate; continue to separate the solid and liquid of the white precipitate, and the solid is dried to obtain aluminum fluoride.

[0021] The present invention also provides an aluminum fluoride / wave-absorbing material composite catalyst prepared by the preparation method described in any one of the above.

[0022] The present invention also provides the application of the aluminum fluoride / wave-absorbing material composite catalyst prepared by the preparation method described in any one of the above. Specifically, the aluminum fluoride / wave-absorbing material composite catalyst is used as a catalyst for the fluorochloride exchange reaction of chloroform and fluoroalkanes. The molecular formula of the fluoroalkane is C x H y F z , where 1 ≤ x ≤ 2, 1 ≤ z ≤ 4, and y + z = 2x + 2. Preferably, the fluoroalkane is selected from at least one of CH3CH2F, CH3CF3, CHF3 or CH2FCF3.

[0023] The present invention also provides a method for the resource utilization of trifluoromethane. Using chloroform and trifluoromethane as raw materials, it is converted through a fluorochloride exchange reaction. In particular, the aluminum fluoride / wave-absorbing material composite catalyst prepared by the preparation method described in any one of the above is used as the reaction catalyst, and the reaction formula is as follows:

[0024]

[0025] The fluorochloride exchange reaction can be carried out under conventional heating or microwave heating for conversion.

[0026] Preferably, microwave reaction heating is used. Specifically, the microwave heating conditions are 500-2000 W and 1000-3000 MHz.

[0027] The molar ratio of trifluoromethane to chloroform is 1:1 to 1:5, the reaction temperature is 300 °C to 400 °C, and the reaction pressure is 0 to 0.50 MPa. Preferably, the molar ratio of trifluoromethane to chloroform is 1:2 to 1:3, the reaction temperature is 320 to 380 °C, and the reaction pressure is 0.30 to 0.50 MPa.

[0028] In the present invention, through the preparation of the aluminum fluoride / wave-absorbing material composite catalyst and supplemented by microwave heating, under the action of the aluminum fluoride / wave-absorbing material composite catalyst, it is helpful to absorb the energy of microwaves, activate the C-F bond in the CHF3 molecules on the catalyst surface, and accelerate the activation and reaction of CHF3. This composite catalyst has good activity and stability for the fluorine-chlorine exchange reaction in the microwave field, improving the conversion rate of CHF3 and the service life of the catalyst.

[0029] Compared with the prior art, the beneficial effects of the present invention include:

[0030] 1. The aluminum fluoride / wave-absorbing material composite catalyst prepared by mechanical grinding in the present invention has an increased specific surface area, and a large number of lattice defects are generated during the preparation process, resulting in a significant increase in the surface acidity of the catalyst.

[0031] 2. The present invention uses the aluminum fluoride / wave-absorbing material composite catalyst and combines microwave heating to achieve the activation and reaction of trifluoromethane. It can not only quickly increase the temperature of the overall catalyst bed layer and ensure uniform heating of the catalyst, eliminating the "wall effect", but also significantly improve the stability of the catalyst. At the same time, the dipole polarization of the catalyst in the microwave field is intensified, greatly improving the efficiency of converting electromagnetic energy into molecular internal energy in the reaction, which is beneficial to activating the stable C-F bond and accelerating the fluorine-chlorine exchange reaction of CHF3.

[0032] 3. The microwave field is a high-frequency alternating electromagnetic field. When the reaction materials with uneven charge center distribution enter the electromagnetic field, they will vibrate at a high frequency with the change of the electromagnetic field direction, increasing the internal energy of the reactant molecules, which is beneficial to the breaking of chemical bonds on the catalyst surface, thereby increasing the conversion rate of the reaction. Specific Embodiments

[0033] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternative, improved, and equivalent solutions that may be included within the scope of the claims.

[0034] Example 1

[0035] This example provides a preparation method of an aluminum fluoride / wave-absorbing material composite catalyst, and the specific steps are as follows:

[0036] 0.02 mol of Al(NO3)3·9H2O and 0.06 mol of NH4F were separately dissolved in deionized water. Under the conditions of heating and stirring in a water bath at 60 °C, the NH4F solution was slowly added to the aluminum nitrate solution, and a white precipitate was obtained through a coprecipitation reaction. After solid-liquid separation, drying treatment was carried out to obtain aluminum fluoride.

[0037] 20 g of the prepared AlF3 and 16 g of silicon carbide (SiC) were mixed and put into a ball mill. The rotational speed of the ball mill was 300 r / min. After ball milling in both forward and reverse directions for 4 h, the ground sample was put into a muffle furnace for calcination treatment. The calcination temperature was 380 °C, and a programmed temperature rise was adopted with a heating rate of 2 °C / min. After heating to 390 °C, it was continuously calcined for 4 h. After the calcination ended, it was naturally cooled to room temperature to obtain the AlF3 / SiC catalyst, denoted as Cat1. The silicon carbide-doped aluminum phosphate catalyst was first tableted and then sieved to 10 - 20 mesh for standby.

[0038] Example 2

[0039] The operation of this example was the same as that of Example 1, except that: the wave-absorbing material was silicon nitride, and the amount of silicon nitride used remained unchanged. The obtained AlF3 / Si3N4 catalyst was denoted as Cat2.

[0040] Example 3

[0041] The operation of this example was the same as that of Example 1, except that: the wave-absorbing material was carbon nanotubes, and the amount of carbon nanotubes used remained unchanged. The obtained AlF3 / CNTs catalyst was denoted as Cat3.

[0042] Example 4

[0043] The operation of this example was the same as that of Example 1, except that: the fluorine-containing material was graphene, and the amount of graphene used remained unchanged. The obtained AlF3 / GOs catalyst was denoted as Cat 4.

[0044] Example 5

[0045] The operation of this example was the same as that of Example 1, except that: the amount of silicon carbide was reduced to 12 g. The obtained AlF3 / SiC catalyst was denoted as Cat 5.

[0046] Example 6

[0047] The operation of this example was the same as that of Example 1, except that: the amount of silicon carbide was reduced to 8 g. The obtained AlF3 / SiC catalyst was denoted as Cat 6.

[0048] Comparative Example 1

[0049] The operation of this example is the same as that of Example 1, except that: instead of using microwave absorbing materials, only aluminum fluoride is used as the raw material, and the obtained catalyst is denoted as Cat B1.

[0050] Example 7

[0051] This example provides a method for the resource utilization of trifluoromethane, including:

[0052] Using CHF3 and CHCl3 as raw materials, under the action of Cat1 - Cat6 and CatB1, the fluoro - chloro exchange reaction is carried out under conventional heating and microwave heating conditions respectively. The specific steps are as follows:

[0053] The catalysts are respectively loaded into a fixed - bed reactor and a microwave reactor (the microwave heating conditions are a power of 1000 w and a frequency of 2450 MHz). The catalyst loading is 2.5 mL. CHF3 and CHCl3 are introduced, with a flow rate of CHF3:CHCl3 = 1:2, a residence time of 3 s, and a reaction temperature of 380 °C. The reaction results are shown in Table 1 below:

[0054] Table 1 Results of the fluoro - chloro exchange reaction of CHF3

[0055]

[0056] As can be seen from Table 1 above, compared with the aluminum fluoride catalyst without microwave absorbing materials, the aluminum fluoride / microwave absorbing material composite catalyst of the present invention has a significantly improved stability under conventional heating conditions; under microwave heating conditions, both the activity (raw material conversion rate) and stability of the catalyst have been significantly improved.

[0057] Different microwave absorbing materials also affect the activity and stability of the catalyst. Among them, SiC has the best effect as a microwave absorbing material. At the same time, the increase of SiC helps to improve the catalytic activity and the stability of the catalyst.

[0058] Example 8

[0059] The operation of this example is the same as that of Example 7, except that: taking Cat1 as an example, the catalyst filling amount of the fluoro - chloro exchange reaction is increased to 50 ml, the temperature is reduced to 320 °C, and the residence time is 6 s. The stability of the catalyst is evaluated under mild conditions. The reaction results are shown in Table 2 below:

[0060] Table 2 Evaluation results of the stability of the fluoro - chloro exchange reaction of CHF3 under mild conditions

[0061]

[0062] As can be seen from Table 2 above, the conditions of the fluoro - chloro exchange reaction are relatively mild, and the stability and service life of the catalyst have been significantly improved.

[0063] Example 9

[0064] The operation of this example is the same as that of Example 7, and the difference is only that: taking Cat1 as an example, the temperature of the fluorine-chlorine exchange reaction is changed, and the reaction results are shown in Table 3 below:

[0065] Table 3 Results of the fluorine-chlorine exchange reaction of CHF3 at different temperatures

[0066]

[0067] It can be seen from Table 3 above that the higher the temperature of the fluorine-chlorine exchange reaction, the stronger the catalyst activity. Correspondingly, the service life is reduced. At each temperature, the performance of the catalyst under microwave heating conditions is better than that under conventional heating.

[0068] Example 10

[0069] This example provides the application of the aluminum fluoride / wave-absorbing material composite catalyst in the fluorine-chlorine exchange reaction of CH3CH2F, including:

[0070] Using CH3CH2F and CHCl3 as raw materials, and using Cat1 to Cat4 and Cat B1 as catalysts, the catalysts are filled into a fixed-bed reactor with a catalyst filling amount of 2.5 mL. CH3CH2F and CHCl3 are introduced with a flow rate of CH3CH2F:CHCl3 = 1:2 and a residence time of 6 s. The reaction temperature is 350 °C, and the reaction results are shown in Table 4 below:

[0071] Table 4 Results of the fluorine-chlorine exchange reaction of CH3CF3

[0072]

Claims

1. A preparation method of a composite catalyst of aluminum fluoride / wave-absorbing material, characterized in that: The aluminum fluoride / wave-absorbing material composite catalyst is obtained by ball-milling and mixing aluminum fluoride and a wave-absorbing material and then calcining them; The mass ratio of the aluminum fluoride to the wave-absorbing material is 1:0.1 - 1. Ball-milling and mixing are carried out using a ball mill. The rotation speed of the ball mill is 100 - 500 r / min, and the ball-milling time is 2 - 10 h. Calcination is carried out in a nitrogen atmosphere, and the calcination temperature is 320 - 450 °C; The wave-absorbing material is selected from at least one of silicon carbide, silicon nitride, carbon nanotubes, graphene, ferrite, elemental iron powder, elemental cobalt powder, or elemental nickel powder.

2. The preparation method of the aluminum fluoride / wave-absorbing material composite catalyst according to claim 1, characterized in that: The aluminum fluoride is prepared by a co-precipitation method from aluminum nitrate nonahydrate and ammonium fluoride at 40 - 80 °C.

3. The preparation method of the aluminum fluoride / wave-absorbing material composite catalyst according to claim 1, characterized in that: The sample after calcination is tableted at a pressure of 15 - 20 MPa and sieved to 10 - 20 mesh.

4. An aluminum fluoride / wave-absorbing material composite catalyst prepared by the preparation method according to any one of claims 1 - 3.

5. Use of the aluminum fluoride / wave-absorbing material composite catalyst prepared by the preparation method according to any one of claims 1-3, characterized in that: The aluminum fluoride / wave-absorbing material composite catalyst is used as a catalyst for the fluorochlorination exchange reaction of chloroform and fluorinated alkanes. The molecular formula of the fluorinated alkane is C x H y F z , where 1 ≤ x ≤ 2, 1 ≤ z ≤ 4, and y + z = 2x + 2; the fluorochlorination exchange reaction is converted under microwave heating.

6. Use of the aluminum fluoride / wave-absorbing material composite catalyst according to claim 5, characterized in that: The fluoroalkane is selected from at least one of CH3CH2F, CH3CF3, CHF3, or CH2FCF3.

7. A method for the resource utilization of trifluoromethane, which uses chloroform and trifluoromethane as raw materials and is converted through a fluorine-chlorine exchange reaction, is characterized in that: Using the aluminum fluoride / wave-absorbing material composite catalyst prepared by the preparation method according to any one of claims 1 - 3 as a reaction catalyst, and the fluorochloride exchange reaction is carried out under microwave heating for conversion.

8. The method for resource utilization of trifluoromethane according to claim 7, wherein: The microwave heating conditions are a power of 500 - 2000 W and a frequency of 1000 - 3000 MHz.

9. The method for resource utilization of trifluoromethane according to claim 7 or 8, characterized in that: The molar ratio of trifluoromethane to chloroform is 1:1 - 1:5, the reaction temperature is 300 - 400 °C, and the reaction pressure is 0 - 0.50 MPa.

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