Chromium oxide fluoride catalyst, preparation method thereof and application of chromium oxide fluoride catalyst in fluorine-chlorine exchange reaction

Abstract

The invention discloses a fluorinated chromic oxide catalyst, the composition of the fluorinated chromic oxide catalyst is CrOxFy, and 2x + y = 3, 0lt; xlt; 1.5, 0 lt; yt; Yt; 3. The invention further discloses a preparation method of the chromium fluoride oxide catalyst and application of the chromium fluoride oxide catalyst in fluorine-chlorine exchange reaction, trifluoromethane and chloroform are used as raw materials, and monochlorodifluoromethane and dichloromonofluoromethane are obtained through fluorine-chlorine exchange reaction under the action of the chromium fluoride oxide catalyst. The chromium fluoride oxide catalyst provided by the invention shows good catalytic activity and catalytic stability when applied to fluorine-chlorine exchange reaction.

Description

Technical Field

[0001] The invention relates to the field of catalysts, and in particular to a fluorinated chromium oxide catalyst, a preparation method thereof, and an application thereof in a fluorine-chlorine exchange reaction. Background Art

[0002] Trifluoromethane (CHF3, HFC-23) is the substance with the highest greenhouse effect potential among hydrofluorocarbons, which is 14,800 times that of CO2. It is mainly derived from the by-product of the production process of difluoromonochloromethane (HCFC-22). At present, domestic enterprises mainly adopt high-temperature incineration for disposal, facing high cost pressure and environmental pressure. Therefore, resource conversion of trifluoromethane is a treatment route that takes into account both economic and environmental protection. However, due to the high bond energy of carbon-fluorine bonds and the stable chemical properties of trifluoromethane, how to activate trifluoromethane and convert it into high value-added products is a problem that needs to be solved urgently.

[0003] Patent CN104428273A discloses a method for producing fluoroolefins by reacting a fluorinating agent with a chlorine-containing compound under the action of a catalyst in at least a portion of crystallized chromium oxide or fluorinated fluorinated chromium oxide, which has the advantages of high selectivity and high stability.

[0004] Patent CN109475841A discloses a method for preparing chromium oxide, which can obtain a specified amount of chromium oxide catalyst composition with a molecular weight of about 150-325 m 2 / g of specified surface area and can be used for fluorine-chlorine exchange reactions.

[0005] Patent CN112979410A discloses that trifluoromethane and halogenated hydrocarbons undergo a fluorine-chlorine exchange reaction under the catalytic action of a main catalyst and a metal oxide, wherein the main catalyst is a chromium, aluminum, magnesium-based catalyst or a catalyst supported by chromium, aluminum, and magnesium on activated carbon / graphite, and the metal oxide is selected from at least one metal oxide of K, Na, Fe, Co, Cu, Ni, Zn, or Ti. The catalyst is suitable for general fluorine-chlorine exchange reactions, but has low reaction activity when used for the fluorine-chlorine exchange reaction of trifluoromethane, and is difficult to activate stable CHF3.

[0006] Patent CN104628513A discloses a method for converting trifluoromethane and chloroform into HCFC-22 under the action of a Lewis acid catalyst. Although this method achieves the conversion of trifluoromethane at a relatively low temperature (less than 400°C), due to the use of a strong Lewis acid catalyst, the catalyst has obvious carbon deposition and sintering during the reaction, resulting in deactivation.

[0007] In summary, the Lewis acid of the catalyst is difficult to control, and highly active catalysts are prone to deactivation. In order to stably activate trifluoromethane and maintain good stability, the number of active species of the catalyst can be controlled, thereby regulating the acid properties of the catalyst, studying the structure-activity relationship between it and the reaction, and thus efficiently converting trifluoromethane, it is of great significance to develop a catalyst that can accurately control the fluorine-oxygen ratio. Summary of the invention

[0008] The object of the present invention is to provide a fluorinated chromium oxide catalyst and a preparation method thereof and application thereof in a fluorine-chlorine exchange reaction. The fluorinated chromium oxide catalyst exhibits good catalytic activity and catalytic stability when applied in a fluorine-chlorine exchange reaction.

[0009] The objective of the present invention is achieved through the following technical solutions:

[0010] A fluorinated chromium oxide catalyst, the fluorinated chromium oxide catalyst composition is CrO x F y , where: 2x+y=3,0 <x<1.5,0<y<3。

[0011] Preferably, the fluorinated chromium oxide catalyst is composed of CrO x F y , where: 2x+y=3,1 <x<1.5,0<y<1。

[0012] The present invention also provides a method for preparing the above-mentioned fluorinated chromium oxide catalyst, which comprises: dissolving a chromium source and then dropping an alkaline solution to react and generate Cr(OH)3; then calcining to obtain a Cr2O3 solid; and fluorinating the obtained Cr2O3 solid to obtain a fluorinated chromium oxide catalyst.

[0013] The preparation method specifically comprises: dissolving the chromium source and slowly stirring, adding an alkaline solution dropwise until the pH value is 8.0 to 12.0, allowing the precipitation to stand for 2 to 8 hours, filtering to obtain Cr(OH)3 and drying, calcining the dried solid in a muffle furnace at 200 to 600°C for 2 to 8 hours, and obtaining a Cr2O3 solid after cooling; and fluorinating the obtained Cr2O3 solid to finally obtain a fluorinated chromium oxide catalyst with different fluorine-oxygen ratios.

[0014] The fluorination treatment comprises: calcining Cr2O3 and a fluorine source at 300-700°C in a slow N2 flow or air flow atmosphere for 2-8 hours, wherein Cr2O3 and the fluorine source are uniformly mixed in different FO ratios, transferred to a porcelain boat, and calcined in a horizontal quartz tube.

[0015] The chromium source is selected from one of nitrates or chlorides. The fluorine source is one or a combination of ammonium fluoride and ammonium hexafluorochromate. The alkaline solution is at least one or a combination of ammonia water, potassium hydroxide, sodium hydroxide, ammonium carbonate or ammonium bicarbonate.

[0016] In the preparation method provided by the present invention, during the calcination process, the mixing ratio of Cr2O3 and the fluorine source, the calcination temperature, the calcination time and the atmosphere conditions are changed. HF is in-situ generated by the fluorine source, and at high temperature, fluorine atoms replace oxygen atoms, causing lattice distortion of Cr2O3, and finally obtaining chromium fluoride oxide catalysts with different fluorine-oxygen ratios. It has been found through research that the higher the proportion of the fluorine source, the higher the F / O ratio. Within a specific temperature range, calcination causes fluorine atoms to replace oxygen atoms, and lattice distortion of Cr2O3 occurs, which will lead to a change in the specific surface area of the catalyst and expose more active sites.

[0017] The present invention also provides an application of the above-mentioned chromium fluoride oxide catalyst in the fluorine-chlorine exchange reaction. Using trifluoromethane and chloroform as raw materials, under the action of the chromium fluoride oxide catalyst, difluorochloromethane and chlorodifluoromethane are obtained through the fluorine-chlorine exchange reaction.

[0018] Within the composition range of the chromium fluoride oxide catalyst of the present invention, it can show good catalytic activity and catalytic stability when used in the fluorine-chlorine exchange reaction.

[0019] The molar ratio of the trifluoromethane to the chloroform is 1:1 to 1:5, the reaction temperature is 300 to 400 °C, and the reaction pressure is 0 to 0.5 MPa. Preferably, the molar ratio of the trifluoromethane to the chloroform is 1:2 to 1:3, the reaction temperature is 320 to 380 °C, and the reaction pressure is 0.10 to 0.40 MPa.

[0020] The composition of the chromium fluoride oxide catalyst is CrO x F y , where: 2x + y = 3, 1.2 < x < 1.275, 0.45 < y < 0.6. When applied in the fluorine-chlorine exchange reaction, it shows better catalytic stability and catalytic activity at the same time.

[0021] The excellent effects of the present invention are as follows:

[0022] In the chromium fluoride oxide catalyst provided by the present invention: After Cr2O3 is fluorinated, it forms CrO x F y , CrO x F y species play an important role in the fluorine-chlorine exchange reaction, and it is considered that CrO x F yIt is an active species in the fluorine-chlorine exchange reaction. Fluorine atoms replace oxygen atoms in the crystal lattice, causing lattice distortion, resulting in gaps on the catalyst surface, forming active sites, and exhibiting better catalytic performance.

[0023] The fluorinated chromium oxide catalyst provided by the present invention is applied to the fluorine-chlorine exchange reaction of trifluoromethane and chlorotrifluoromethane to convert low-value-added trifluoromethane into high-value-added monochlorodifluoromethane and monochlorodifluoromethane, has high trifluoromethane conversion activity, and the catalyst has high stability, and is suitable for industrial application. DETAILED DESCRIPTION

[0024] 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.

[0025] Example 1

[0026] Dissolve 20g of chromium nitrate in 100g of water, add ammonia water to pH = 8-9, let stand for 6h after precipitation occurs, and place the filtered solid in an oven at 80℃ for 12h. The dried solid is calcined in a muffle furnace, heated to 300℃ at a heating rate of 5℃ / min, and maintained for 6h. After cooling, Cr2O3 is obtained, which is evenly mixed with 10g of ammonium fluoride, transferred to a porcelain boat, and calcined in a horizontal quartz tube at 500℃ under N2 flow atmosphere. After cooling, the obtained solid is tableted and crushed into 10-20 mesh particles for use, and the composition of the prepared catalyst No. 1 is CrO 1.215 F 0.57 , recorded as catalyst No. 1.

[0027] Example 2

[0028] The operation of this embodiment is the same as that of embodiment 1, except that chromium chloride is used as the chromium source in the same amount. The composition of the prepared fluorinated chromium oxide catalyst is CrO 1.240 F 0.52 , recorded as catalyst No. 2.

[0029] Example 3

[0030] The operation of this embodiment is the same as that of embodiment 1, except that ammonium hexafluorochromate is used as the fluorinating agent in an amount of 50 g. The composition of the prepared fluorinated chromium oxide catalyst is CrO 1.225 F 0.55 , recorded as catalyst No. 3.

[0031] Example 4

[0032] The operation of this embodiment is the same as that of embodiment 1, except that chromium chloride is used as the chromium source in the same amount, and ammonium hexafluorochromate is used as the fluorinating agent in an amount of 50 g. The composition of the prepared fluorinated chromium oxide catalyst is CrO 1.265 F 0.47 , recorded as catalyst No. 4.

[0033] Example 5

[0034] The operation of this embodiment is the same as that of embodiment 1, except that the amount of ammonium fluoride is reduced to 2.5 g. The composition of the prepared fluorinated chromium oxide catalyst is CrO 1.43 F 0.14 , recorded as catalyst No. 5.

[0035] Example 6

[0036] The operation of this embodiment is the same as that of embodiment 1, except that the amount of ammonium fluoride is reduced to 5 g. The composition of the prepared fluorinated chromium oxide catalyst is CrO 1.395 F 0.21 , recorded as catalyst No. 6.

[0037] Example 7

[0038] The operation of this embodiment is the same as that of embodiment 1, except that the amount of ammonium fluoride is increased to 15 g. The composition of the prepared fluorinated chromium oxide catalyst is CrO 1.125 F 0.75 , recorded as catalyst No. 7.

[0039] Example 8

[0040] The operation of this embodiment is the same as that of embodiment 2, except that the amount of ammonium fluoride is reduced to 5 g. The composition of the prepared fluorinated chromium oxide catalyst is CrO 1.380 F 0.24 , recorded as catalyst No. 8.

[0041] Example 9

[0042] The operation of this embodiment is the same as that of embodiment 2, except that the amount of ammonium fluoride is increased to 15 g. The composition of the prepared fluorinated chromium oxide catalyst is CrO 1.115 F 0.77 , recorded as catalyst No. 9.

[0043] Example 10

[0044] The operation of this embodiment is the same as that of embodiment 3, except that the amount of ammonium hexafluorochromate is reduced to 20 g. The composition of the prepared fluorinated chromium oxide catalyst is CrO 1.405 F 0.19 , recorded as catalyst No. 10.

[0045] Embodiment 11

[0046] The operation of this embodiment is the same as that of embodiment 3, except that the amount of ammonium hexafluorochromate is increased to 15 g. The composition of the prepared fluorinated chromium oxide catalyst is CrO 1.205 F 0.59 , recorded as catalyst No. 11.

[0047] Comparative Example 1

[0048] The operation of this embodiment is the same as that of embodiment 1, except that the calcination temperature in the horizontal quartz tube is 200°C. The composition of the prepared fluorinated chromium oxide catalyst is CrO 1.450 F 0.10 , recorded as catalyst No. 12.

[0049] Comparative Example 2

[0050] The operation of this embodiment is the same as that of embodiment 1, except that the calcination temperature in the horizontal quartz tube is 800°C. The prepared fluorinated chromium oxide catalyst has a composition of CrO 1.130 F 0.74 , recorded as catalyst No. 13.

[0051] The catalysts prepared in the examples and comparative examples were characterized by XRF, as shown in Table 1.

[0052] Table 1 Sample characterization data

[0053] Cr / ％ O / ％ F / ％ Example 1 0.36 0.44 0.20 Example 2 0.36 0.45 0.19 Example 3 0.36 0.44 0.20 Example 4 0.37 0.46 0.17 Example 5 0.39 0.56 0.05 Example 6 0.38 0.54 0.08 Example 7 0.35 0.39 0.26 Example 8 0.38 0.53 0.09 Example 9 0.35 0.39 0.27 Example 10 0.39 0.54 0.07 Embodiment 11 0.36 0.43 0.21 Comparative Example 1 0.39 0.57 0.04 Comparative Example 2 0.35 0.39 0.26

[0054] Application Examples

[0055] This application example provides a method for applying the fluorinated chromium oxide catalyst prepared in the above embodiments and comparative examples in a fluorine-chlorine exchange reaction, comprising:

[0056] Using trifluoromethane and chloroform as raw materials, a fluorine-chlorine exchange reaction is carried out under the action of catalysts No. 1 to 13 to generate difluoromonochloromethane and monofluorodichloromethane. The specific steps are as follows:

[0057] 8 mL of catalyst was loaded into a fixed bed reactor, the inner diameter of the tubular reactor was 20 mm, the length of the stainless steel tube was 800 mm, the reaction temperature was 360 ° C, the pressure was 0.1 MPa, the molar ratio of trifluoromethane to trichloromethane was 1:2, and the residence time was 6 s. The reaction products were qualitatively and quantitatively analyzed. The reaction evaluation results of catalysts No. 1 to 13 are shown in Table 2.

[0058] Table 2 Evaluation results of catalyst reaction prepared in Examples and Comparative Examples

[0059]

[0060] As can be seen from Table 1 above, the higher the F content, the higher the conversion rate of CHF3, and the shorter the corresponding catalytic life. The fluorinated chromium oxide catalysts with F composition between 0.45-0.60 (Examples 1-4, Comparative Example 7) show good catalytic stability, while when the F content is low, the catalyst shows low catalytic activity, which is manifested in the low conversion rate of CHF3. In addition, the calcination temperature also has a significant effect on the F / O ratio regulation and catalytic performance of the catalyst. When the calcination temperature is low, fluorination is difficult to carry out, the F ratio is low, the active sites are less, and the conversion rate of CHF3 is low. When the calcination temperature is high, the introduction of F can be effectively improved, but the catalyst structure may be damaged and the stability is poor.

[0061] In summary, the fluorinated chromium oxide catalyst provided by the present invention is used in the fluorine-chlorine exchange reaction of trifluoromethane and trichloromethane. The fluorinated chromium oxide catalyst with a certain F / O ratio can regulate the acidity and specific surface area of ​​the catalyst, so that the active sites are evenly distributed, and the catalyst exhibits good catalytic performance. The moderate acid strength reduces the generation of carbon deposits while ensuring good catalyst activity, and is suitable for industrial applications.

Claims

1. A fluorinated chromium oxide catalyst, characterized in that The fluorinated chromium oxide catalyst is composed of CrO x F y , where: 2x+y=3,0 <x<1.5,0<y<3。 2. The fluorinated chromium oxide catalyst according to claim 1, characterized in that The fluorinated chromium oxide catalyst is composed of CrO x F y , where: 2x+y=3,1 <x<1.5,0<y<1。 3. A method for preparing the fluorinated chromium oxide catalyst according to any one of claims 1 to 2, characterized in that: The preparation method comprises: dissolving a chromium source and then dropping an alkali solution to react and generate Cr(OH)3; then calcining to obtain a Cr2O3 solid; and fluoriding the obtained Cr2O3 solid to obtain a fluorinated chromium oxide catalyst.

4. The method for preparing the fluorinated chromium oxide catalyst according to claim 3, characterized in that: Alkaline solution is added dropwise until the pH value reaches 8.0-12.0, and Cr(OH)3 is calcined at 200-600°C for 2-8h to obtain Cr2O3 solid.

5. The method for preparing the fluorinated chromium oxide catalyst according to claim 3, characterized in that: The fluorination treatment comprises: calcining Cr2O3 and a fluorine source at 300-700°C for 2-8h.

6. The method for preparing the fluorinated chromium oxide catalyst according to claim 3, characterized in that: The chromium source is selected from one of nitrates or chlorides, the fluorine source is one of ammonium fluoride and ammonium hexafluorochromate or a combination thereof, and the alkaline solution is at least one of ammonia water, potassium hydroxide, sodium hydroxide, ammonium carbonate or ammonium bicarbonate or a combination thereof.

7. Use of the fluorinated chromium oxide catalyst according to any one of claims 1 to 2 in a fluorine-chlorine exchange reaction, characterized in that: Using trifluoromethane and chloroform as raw materials, difluorochloromethane and monofluorodichloromethane are obtained through fluorine-chlorine exchange reaction in the presence of chromium oxide fluoride catalyst.

8. Use of the fluorinated chromium oxide catalyst in a fluorine-chlorine exchange reaction according to claim 7, 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 0-0.5MPa.

9. Use of the fluorinated chromium oxide catalyst in a fluorine-chlorine exchange reaction according to claim 7, characterized in that: The molar ratio of trifluoromethane to chloroform is 1:2-1:3, the reaction temperature is 320-380° C., and the reaction pressure is 0.10-0.40 MPa.

10. Use of the fluorinated chromium oxide catalyst in a fluorine-chlorine exchange reaction according to claim 7, characterized in that: The fluorinated chromium oxide catalyst is composed of CrO x F y , where: 2x+y=3,1.2 <x<1.275,0.45<y<0.6。

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