Method for regulating and controlling byproducts in fluorine-chlorine exchange reaction process of trifluoromethane

Abstract

The invention discloses a method for regulating and controlling byproducts in a trifluoromethane fluorine-chlorine exchange reaction process, the fluorine-chlorine exchange reaction is to prepare monochlorodifluoromethane and dichloromonofluoromethane by taking trifluoromethane and trichloromethane as raw materials under the action of a catalyst, and the catalyst comprises an aluminum-based catalyst and a metal oxide or fluoride. The aluminum-based catalyst is selected from at least one or a mixture of more than two of Al2O3, AlF3, Al2 (SO4) 3 and AlPO4, and the metal catalyst is selected from at least one of metal oxides or fluorides of Cr, Sc, Ti or V. The adsorption force of the product on the surface of the catalyst is regulated and controlled through metal doping, and the product is quickly desorbed and does not further participate in the reaction, so that the generation of byproducts in the fluorine-chlorine exchange reaction of the HFC-23 can be effectively inhibited.

Description

Technical Field

[0001] The invention relates to the field of technology and catalysts, and in particular to a method for regulating byproducts in a trifluoromethane fluorine-chlorine exchange reaction process. Background Art

[0002] HFC-23 (CHF3, trifluoromethane, R23) is an inevitable byproduct of the industrial production of HCFC-22 (difluorochloromethane, R22 or CHClF2), and its GWP value is as high as 14800. my country's HFC-23 byproduct production accounts for about 70% of the global production, which is equivalent to 220 million tons of CO2 equivalent based on an annual output of 15,000 tons. HFC-23 is generally treated by high-temperature incineration at 1200℃, which is highly polluting and has high operating costs. Therefore, the resource utilization of HFC-23 is an important topic in achieving energy conservation and emission reduction.

[0003] There are many HFC-23 resource conversion methods reported at present, such as: pyrolysis to prepare TFE and hexafluoropropylene (HFP), co-cracking with CH4 to prepare vinylidene fluoride (VDF) and iodination reaction to prepare CF3I, etc., but these methods are generally considered to be difficult to industrialize due to the harsh reaction conditions or short catalyst life. The patent CN104628513A discloses the fluorine-chlorine exchange of CHF3 and CHCl3 under Lewis acid catalysis to generate HCFC-22 and HCFC-21, which has mild reaction conditions and high product selectivity, and has the prospect of industrial application. In order to further realize industrial application, the patents CN109748775A, CN112979410A, CN112979410A and CN112973685A combine the deactivation mechanism of the catalyst, from skillfully using carbon burning gas in situ regeneration to catalyst modification optimization, etc., effectively improving the life of the catalyst, so that the activity and life of the catalyst basically meet industrial application. However, some byproducts are inevitably produced in the fluorine-chlorine exchange reaction of CHF3 and CHCl3, such as trichlorofluoromethane (R11) and dichlorodifluoromethane (R12), which have a great impact on the subsequent products and the purification of recycled raw materials. Therefore, regulating the byproducts during the fluorine-chlorine exchange reaction of CHF3 and CHCl3 is of great significance to the industrial application of this route. Summary of the invention

[0004] The object of the present invention is to provide a method for regulating by-products during the fluorine-chlorine exchange reaction of trifluoromethane, by regulating the adsorption force of the product on the catalyst surface through metal doping and making it desorb quickly and not further participate in the reaction, thereby effectively inhibiting the generation of by-products in the fluorine-chlorine exchange reaction of HFC-23.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] A method for regulating byproducts during a fluorine-chlorine exchange reaction of trifluoromethane, wherein the fluorine-chlorine exchange reaction is to prepare difluoromonochloromethane (HCFC-22) and monofluorodichloromethane (HCFC-21) using trifluoromethane and trichloromethane as raw materials under the action of a catalyst, wherein the catalyst comprises an aluminum-based catalyst and a metal oxide or fluoride, wherein the aluminum-based catalyst is selected from at least one of Al2O3, AlF3, Al2(SO4)3 and AlPO4 or a mixture of two or more thereof, and the metal catalyst is selected from at least one of metal oxides or fluorides of Cr, Sc, Ti or V.

[0007] In the fluorine-chlorine exchange reaction of HFC-23, chloroform is first adsorbed on the active site of the catalyst, dechlorinated to fluorine after activation, and desorbed from the active site to generate R21, and then trifluoromethane is adsorbed on the active site, defluorinated to chlorine after activation, and desorbed from the active site to generate R22; in the whole catalyst cycle, as long as the adsorption forces of the products R22 and R21 on the catalyst surface are not much different, the possibility of further reaction will be relatively small; therefore, the present invention obtains a doped catalyst by doping a metal oxide or a fluoride on the basis of an aluminum-based catalyst, and regulates the adsorption of the catalyst to the products R22 and R21, thereby suppressing the generation of by-products.

[0008] The aluminum-based catalyst is preferably AlF3 or a mixture containing AlF3. The metal oxide or fluoride is preferably at least one of Sc, V or Ti. The metal oxide or fluoride is further preferably Ti.

[0009] The catalyst is obtained by doping metal oxide or fluoride on the basis of aluminum-based catalyst, and performing ball milling, mixing and calcining.

[0010] The mass of the metal oxide or fluoride accounts for 0.1% to 80% of the mass of the aluminum-based catalyst, and the percentage is mass percentage. The mass of the metal oxide or fluoride accounts for 2% to 20% of the mass of the aluminum-based catalyst.

[0011] The raw material stays on the catalyst surface for 4 to 100 seconds.

[0012] When the residence time of reaction materials such as trifluoromethane and trichloromethane on the catalyst surface is controlled within a certain range, the generation of by-products in the reaction can be effectively suppressed. A short residence time is equivalent to external force pushing the desorption of the product, which is beneficial to suppressing the generation of by-products. Conversely, a long residence time of the product on the catalyst surface is more likely to generate by-products.

[0013] Preferably, the raw material resides on the catalyst surface for 10 to 100 seconds.

[0014] More preferably, the raw material stays on the catalyst surface for 10 to 50 seconds. More preferably, the raw material stays on the catalyst surface for 10 to 20 seconds.

[0015] The by-products are added to the raw materials. The by-products can be directly added or controlled to a desired content by methods such as mixed distillation or adsorption of the reacted gas.

[0016] The content of byproducts in the raw materials is 0.05-0.5%. When a certain amount of byproducts is contained in the reaction materials of trifluoromethane and trichloromethane, the concentration of the byproducts on the catalyst surface can be high, thereby inhibiting the generation of byproducts. Too high a content will cause the byproducts to further react with new byproducts, such as R12 with too high a concentration in the material will further react to generate R13. If the content is too low, the chemical reaction on the catalyst surface cannot be pushed to move in the direction of inhibiting byproducts, thereby not affecting the byproduct selectivity.

[0017] The content of by-products in the raw materials is preferably 0.1-0.3%, which can significantly reduce the selectivity of the added by-products and the total by-product selectivity.

[0018] Furthermore, the content of by-products in the raw material is preferably 0.15-0.3%, which can further significantly reduce the selectivity of the added by-products and the total by-product selectivity.

[0019] Preferably, the by-product added to the raw material is R12.

[0020] The catalyst is used for resource utilization of trifluoromethane after pretreatment, and the pretreatment step includes:

[0021] A1. Fluorination treatment at 250℃~450℃ for 1~6h in HF / N2 mixed atmosphere;

[0022] A2. Treat at 300-500℃ for 2-8h in HF atmosphere;

[0023] A3. Cool down by nitrogen purge.

[0024] In step A1, the HF / N2 mixed atmosphere includes 1-20v% hydrogen fluoride and 80-99v% nitrogen.

[0025] The present invention obtains a doped catalyst by doping metal oxides or fluorides on the basis of an aluminum-based catalyst, regulates the adsorption capacity of the catalyst to the products R22 and R21, and simultaneously adds a suitable amount of by-products to the raw materials and controls a suitable reaction space velocity, thereby further suppressing the generation of by-products.

[0026] Preferably, byproducts are added to the raw materials, the content of byproducts in the raw materials is 0.1-0.3%, and the residence time of the raw materials on the catalyst surface is 10-20s. On the basis of metal doping, byproducts can be added and the residence time on the catalyst surface can be controlled to further inhibit the generation of byproducts.

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

[0028] In the above-mentioned HFC-23 fluorine-chlorine exchange reaction process of the present invention, the molar ratio of trifluoromethane to trichloromethane is: 1 to (1:3), the reaction temperature is 250 to 400° C., and the reaction pressure is 0.1 to 3 bar.

[0029] Preferably, the molar ratio of trifluoromethane to trichloromethane is 1 to (1:2), the reaction temperature is 300 to 360° C., and the reaction pressure is 0.1 to 2 bar.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The present invention changes the adsorption force of the catalyst surface to the product by metal doping, so that no further by-products are generated during the reaction, and the product is desorbed as soon as possible after it is generated without further disproportionation reaction to produce by-products, thereby effectively reducing the generation of by-products.

[0032] 2. The present invention further controls the content of by-products in the reaction materials so that there is a certain concentration of by-products in the catalyst surface environment during the reaction, thereby directing the surface reaction in a direction of suppressing the generation of by-products, effectively controlling the generation of by-products, and simultaneously improving the selectivity of the main products R22 and R21.

[0033] 3. The present invention further selects the residence time of the reaction materials on the catalyst to achieve rapid reaction and rapid desorption, thereby avoiding further reaction of species on the catalyst surface and inhibiting the generation of by-products. DETAILED DESCRIPTION

[0034] The present invention is 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 possible alternatives, improvements and equivalents within the scope of the claims.

[0035] Example 1

[0036] The method for regulating byproducts during the trifluoromethane fluorine-chlorine exchange reaction provided in this embodiment is achieved by the following steps:

[0037] S1. Take 100 ml of AlF3-doped catalyst containing 5.0% Sc2O3 and put it into a ball mill at a speed of 400 r / min. After the ball mill is rotated for 4 hours, the ground sample is pressed and sieved to 10 to 20 mesh and then loaded into the reactor to form a catalyst bed;

[0038] S2. Fluorination pretreatment: 1) fluorination treatment at 250 ° C for 2 hours in a mixed atmosphere of 10% hydrogen fluoride and 90% nitrogen; 2) treatment at 300 ° C for 5 hours in a hydrogen fluoride atmosphere; 3) cooling by nitrogen purge;

[0039] S3. Fluorine-chlorine exchange reaction: Chloroform is transported to the vaporizer by a liquid pump for vaporization, and then fully mixed with trifluoromethane in the gas mixer before entering the reactor. Reaction conditions: the molar ratio of HFC-23 to trifluoromethane is 1:1.2, the reaction temperature is 330°C, the reaction pressure is 0.1 bar, and the residence time is 100s.

[0040] During the fluorine-chlorine exchange reaction, the results of the catalytic reaction for 50 hours and the by-product selectivity are shown in Table 1 below.

[0041] Example 2

[0042] The operation of this embodiment is the same as that of embodiment 1, except that the catalyst is an AlF3-doped catalyst containing 5% Ti2O3, and other conditions remain unchanged.

[0043] Example 3

[0044] The operation of this embodiment is the same as that of embodiment 1, except that the catalyst is an AlF3-doped catalyst containing 5% V2O5, and other conditions remain unchanged.

[0045] Example 4

[0046] The operation of this embodiment is the same as that of embodiment 1, except that the catalyst is an AlF3-doped catalyst containing 5% TiF4, and other conditions remain unchanged.

[0047] Comparative Example 1

[0048] The operation of this comparative example is the same as that of Example 1, except that the catalyst is an AlF3-doped catalyst containing 5% Fe2O3, and other conditions remain unchanged.

[0049] Comparative Example 2

[0050] S1. Take 100ml AlF3 and put it into a ball mill at a speed of 400r / min. After 4h of revolution and rotation, the ground sample was pressed and sieved to 10-20 mesh and then loaded into the reactor to form a catalyst bed;

[0051] S2. Fluorination pretreatment: 1) fluorination treatment at 250 ° C for 2 hours in a mixed atmosphere of 10% hydrogen fluoride and 90% nitrogen; 2) treatment at 300 ° C for 5 hours in a hydrogen fluoride atmosphere; 3) cooling by nitrogen purge;

[0052] S3. Fluorine-chlorine exchange reaction: Chloroform is transported to the vaporizer by a liquid pump for vaporization, and then fully mixed with trifluoromethane in the gas mixer before entering the reactor. Reaction conditions: the molar ratio of HFC-23 to trifluoromethane is 1:1.2, the reaction temperature is 330°C, the reaction pressure is 0.1 bar, and the residence time is 100s.

[0053] During the fluorine-chlorine exchange reaction, the catalytic reaction results and by-product selectivity of the catalysts in Examples 1-4 and Comparative Examples 1-2 are shown in Table 1.

[0054] Table 1 Effect of metal-doped catalysts on by-products in the fluorine-chlorine exchange reaction of trifluoromethane

[0055]

[0056] Example 5

[0057] The operation of this example is the same as that of Example 2, except that the residence time in the reaction is 50 seconds, and other conditions remain unchanged. During the fluorine-chlorine exchange reaction, the catalytic reaction results and by-product selectivity are shown in Table 2 below.

[0058] Example 6

[0059] The operation of this example is the same as that of Example 2, except that the residence time in the reaction is 20 seconds, and other conditions remain unchanged. During the fluorine-chlorine exchange reaction, the catalytic reaction results and by-product selectivity are shown in Table 2 below.

[0060] Example 7

[0061] The operation of this example is the same as that of Example 2, except that the residence time in the reaction is 10 s, and other conditions remain unchanged. During the fluorine-chlorine exchange reaction, the catalytic reaction results and by-product selectivity are shown in Table 2.

[0062] Table 2 The effect of residence time on by-products in the fluorine-chlorine exchange reaction of trifluoromethane

[0063]

[0064] Example 8

[0065] The operation of this example is the same as that of Example 6, except that the content of R12 in the reaction material is 0.05%, and other conditions remain unchanged. During the fluorine-chlorine exchange reaction, the catalytic reaction results and by-product selectivity are shown in Table 3.

[0066] Example 9

[0067] The operation of this example is the same as that of Example 6, except that the content of R12 in the reaction material is 0.1%, and other conditions remain unchanged. During the fluorine-chlorine exchange reaction, the catalytic reaction results and by-product selectivity are shown in Table 3.

[0068] Example 10

[0069] The operation of this example is the same as that of Example 6, except that the content of R12 in the reaction material is 0.15%, and other conditions remain unchanged. During the fluorine-chlorine exchange reaction, the catalytic reaction results and by-product selectivity are shown in Table 3.

[0070] Embodiment 11

[0071] The operation of this example is the same as that of Example 6, except that the content of R12 in the reaction material is 0.3%, and other conditions remain unchanged. The catalytic reaction results and by-product selectivity during the fluorine-chlorine exchange reaction are shown in Table 3.

[0072] Example 12

[0073] The operation of this embodiment is the same as that of embodiment 6, except that the content of R12 in the reaction material is 0.5%, and other conditions remain unchanged. In the fluorine-chlorine exchange reaction process, the catalytic reaction results and the selectivity of by-products (wherein, other by-products refer to by-products other than R12) are shown in Table 3.

[0074] Table 3 The effect of the by-product R12 content in the reaction material on the by-product in the fluorine-chlorine exchange reaction of trifluoromethane

[0075]

[0076] Application Example 1

[0077] The catalyst prepared in Example 3 of the present invention is used for resource conversion and utilization of trifluoromethane and trichloromethane, and the specific operation is as follows:

[0078] 500 mL of 5% Ti2O3 / AlF3 was loaded into the reactor bed, and a mixture of trifluoromethane, chloroform and oxygen in a molar ratio of 1:2:0.1 was introduced into the reactor for fluorine-chlorine exchange reaction. The reaction temperature was 380°C, the reaction pressure was normal pressure, and the residence time was 18 seconds. At the same time, the stability of the catalyst was evaluated. The results are shown in Table 4.

[0079] Table 4 Trifluoromethane fluorine-chlorine exchange reaction results and catalyst evaluation

[0080]

Claims

1. A method for regulating byproducts during a fluorine-chlorine exchange reaction of trifluoromethane, wherein the fluorine-chlorine exchange reaction is to prepare difluorochloromethane and monofluorodichloromethane using trifluoromethane and trichloromethane as raw materials under the action of a catalyst, characterized in that: The catalyst includes an aluminum-based catalyst and a metal oxide or fluoride, wherein the aluminum-based catalyst is selected from at least one or a mixture of two or more of Al2O3, AlF3, Al2(SO4)3 and AlPO4, and the metal catalyst is selected from at least one of the metal oxides or fluorides of Cr, Sc, Ti or V.

2. The method for regulating byproducts in the process of trifluoromethane fluorine-chlorine exchange reaction according to claim 1, characterized in that: The catalyst is obtained by doping metal oxide or fluoride on the basis of aluminum-based catalyst, and then mixing and calcining the metal oxide or fluoride. The mass of the metal oxide or fluoride accounts for 0.1% to 80% of the mass of the aluminum-based catalyst, and the percentage is mass percentage.

3. The method for regulating byproducts in the process of trifluoromethane fluorine-chlorine exchange reaction according to claim 1, characterized in that: The mass of the metal oxide or fluoride accounts for 2% to 20% of the mass of the aluminum-based catalyst.

4. The method for regulating byproducts in a trifluoromethane fluorine-chlorine exchange reaction according to claim 1, characterized in that: The raw material stays on the catalyst surface for 4 to 100 seconds.

5. The method for regulating byproducts in the process of trifluoromethane fluorine-chlorine exchange reaction according to claim 1, characterized in that: The raw material stays on the catalyst surface for 10 to 100 seconds.

6. The method for regulating byproducts in a trifluoromethane fluorine-chlorine exchange reaction according to claim 1, characterized in that: By-products are added to the raw materials.

7. The method for regulating byproducts in a trifluoromethane fluorine-chlorine exchange reaction according to claim 6, characterized in that: The content of by-products in the raw materials is 0.05-0.5%, and the percentage is mass percentage.

8. The method for controlling byproducts in the process of trifluoromethane fluorine-chlorine exchange reaction according to any one of claims 1 to 7, characterized in that: The catalyst is used for resource utilization of trifluoromethane after pretreatment, and the pretreatment step includes: A1. Fluorination treatment at 250°C to 450°C for 1 to 6 hours in a HF / N2 mixed atmosphere comprising 1 to 20v% hydrogen fluoride and 80 to 99v% nitrogen; A2. Treat at 300-500℃ for 2-8h in HF atmosphere; A3. Cool down by nitrogen purge.

9. The method for controlling byproducts in the process of trifluoromethane fluorine-chlorine exchange reaction according to any one of claims 1 to 7, characterized in that: By-products are added to the raw materials, the content of the by-products in the raw materials is 0.1-0.3%, and the residence time of the raw materials on the catalyst surface is 10-20s.

10. The method for controlling byproducts in a trifluoromethane fluorine-chlorine exchange reaction according to any one of claims 1 to 7, characterized in that: The molar ratio of trifluoromethane to chloroform is 1:1 to 1:5, the reaction temperature is 300 to 400° C., and the reaction pressure is 0 to 0.50 MPa.

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