Method for preparing fluorine-containing olefin by removing HF from fluorine-containing alkane

Abstract

The invention belongs to the technical field of organic chemistry, and particularly relates to a method for preparing fluorine-containing olefin by removing HF (hydrogen fluoride) from fluorine-containing alkane, which comprises the following steps: by taking fluorine-containing alkane as a raw material, adding an HF removal catalyst into a fixed bed reactor, and carrying out HF removal reaction to obtain the corresponding fluorine-containing olefin. The method for preparing fluorine-containing olefin by removing HF from fluorine-containing alkane provided by the invention is simple to operate, the prepared HF-removing catalyst greatly improves the utilization efficiency of an aluminum element and the activity of the catalyst while realizing efficient exposure and structural regulation of active sites, and enhances the anti-sintering performance of the catalyst at the same time; the heat stability and the service life of the catalyst are obviously improved. Meanwhile, by adopting the method disclosed by the invention, the selectivity of the prepared fluorine-containing olefin can be obviously improved.

Description

Technical Field

[0001] This invention belongs to the field of organic chemistry technology, specifically relating to a method for preparing fluorinated olefins by removing HF from fluorinated alkanes. Background Technology

[0002] The fourth-generation refrigerant 2,3,3,3-tetrafluoropropylene (HFO-1234yf) has attracted much attention. This product features zero ozone potential (ODP), slight flammability, and a low global warming potential (GWP), making it a next-generation ODS replacement—hydrofluoroolefins (HFOs)—following HCFCs and HFCs. In recent years, with the EU's approval of HFO-1234yf, it is most likely to replace HFC-134a (1,1,1,2-tetrafluoroethane) as the next-generation automotive refrigerant. Currently, the main industrialized route is a two-step hydrogenation and two-step defluorination route using hexafluoropropylene as a raw material. In the hexafluoropropylene process, hydrogen is first reacted with hexafluoropropylene (HFP) via catalytic hydrogenation to produce hexafluoropropane, followed by HF removal to produce pentafluoropropylene (HFO-1225ye). The produced pentafluoropropylene (HFO-1225ye) is then reacted with hydrogen via catalytic addition to produce pentafluoropropane, followed by HF removal to finally produce the product 2,3,3,3-tetrafluoropropylene (HFO-1234yf).

[0003] This route involves a two-step HF removal reaction. Traditional HF removal catalysts are generally AlF3 and CrF3. At high temperatures, these catalysts are prone to sintering, leading to reduced activity and shortened lifespan. To improve aluminum-based catalysts, various solutions have been proposed in the prior art. For example, Chinese patent CN110586142B discloses a method for preparing a κ-AlF3 catalyst using a hydrothermal method with ammonium salt as the fluorine source, avoiding the use of HF. The catalyst has a regular morphology and high activity, but its Lewis acidity is too strong, easily leading to carbon deposition and deactivation. Furthermore, the hydrothermal reaction time is long, resulting in low preparation efficiency. Chinese patent CN113385201B discloses a fluoroaluminate sulfate catalyst prepared by hydrothermal and ball milling methods. It possesses suitable acidity and good stability, but its conversion rate in the HFC-134a HF removal reaction is limited, and some methods still involve HF, posing safety risks.

[0004] Therefore, developing a deHF catalyst that possesses both high catalytic activity and selectivity, as well as excellent thermal stability and safety, has become an important research direction in this field. Summary of the Invention

[0005] In order to solve the problems existing in the prior art, the purpose of this invention is to provide a method for preparing fluorinated olefins by deHF removal from fluorinated alkanes.

[0006] The technical solution of this invention is:

[0007] A method for preparing fluorinated olefins by removing HF from fluorinated alkanes involves using fluorinated alkanes as raw materials, adding a HF removal catalyst in a fixed-bed reactor, and carrying out the HF removal reaction to obtain the corresponding fluorinated olefins.

[0008] Preferably, the fluorinated alkane is one of 1,1,1,2,3,3-hexafluoropropane (R236ea) and 1,1,1,2,3-pentafluoropropane (R245eb).

[0009] Preferably, the fluorinated olefin is one of 1,2,3,3,3-pentafluoropropylene (R1225ye) and 2,3,3,3-tetrafluoropropylene (R1234yf).

[0010] Preferably, the preparation method of the HF removal catalyst is as follows:

[0011] S1. Add the low silica-alumina ratio molecular sieve to the alkaline solution and stir under heating conditions. After the alkaline treatment is completed, wash and filter the molecular sieve, and dry the filter cake in an oven to obtain the alkaline-treated molecular sieve.

[0012] S2. The alkali-treated molecular sieve obtained in step S1 is placed in a 2-3% cerium nitrate solution and impregnated for a period of time using an equal-volume impregnation method. Then it is dried and calcined to obtain the calcined molecular sieve.

[0013] S3. The calcined molecular sieve obtained in step S2 is placed in a fixed-bed reactor, and a mixture of nitrogen and trifluoromethane is introduced to carry out a fluorination reaction to obtain a de-HF catalyst.

[0014] Preferably, the low silica-to-alumina ratio molecular sieve in step S1 is one of ZSM-5, ZSM-35, or Y molecular sieve;

[0015] More preferably, the low silica-to-alumina ratio molecular sieve is one of ZSM-5 and Y molecular sieve;

[0016] Preferably, the low silica-alumina ratio molecular sieve is ZSM-5.

[0017] Preferably, the alkaline solution in step S1 is one of 10% NaOH solution, 10% NaHCO3 solution, and 10% Na2CO3 solution;

[0018] More preferably, the alkaline solution is one of 10% NaOH solution and 10% NaHCO3 solution; particularly preferably, the alkaline solution is 10% NaOH solution.

[0019] Preferably, the heating temperature for alkali treatment in step S1 is 40-80℃, and the alkali treatment time is 2h-10h;

[0020] More preferably, the heating temperature for the alkali treatment is 50-80℃, and the alkali treatment time is 4h-10h;

[0021] Preferably, the heating temperature for the alkali treatment is 60-80℃, and the alkali treatment time is 6h-8h.

[0022] Preferably, in step S1, the filter cake is dried in an oven at 50-60°C for 20-24 hours to obtain the alkali-treated molecular sieve.

[0023] Preferably, the soaking time in step S2 is 2h-3h.

[0024] Preferably, the drying time in step S2 is 10-12 hours and the drying temperature is 50-60°C.

[0025] Preferably, the roasting temperature in step S2 is 500°C and the roasting time is 3 hours.

[0026] Preferably, the fluorination temperature in step S3 is 280-400℃, and the fluorination time is 4h-12h;

[0027] More preferably, the fluorination temperature of the catalyst after alkali treatment is 300-380℃, and the fluorination time is 8h-10h;

[0028] Preferably, the catalyst after alkali treatment has a fluorination temperature of 320-350℃ and a fluorination time of 6-8h.

[0029] Preferably, the molar ratio of nitrogen to trifluoromethane in step S3 is 10-60:1;

[0030] More preferably, the molar ratio of nitrogen to trifluoromethane is 15-50:1;

[0031] Particularly preferred is that the molar ratio of nitrogen to trifluoromethane is 20-40:1.

[0032] Preferably, in the process of using fluorinated alkanes as raw materials, adding a deHF removal catalyst in a fixed-bed reactor to carry out a deHF removal reaction to obtain the corresponding fluorinated olefins:

[0033] The HF removal reaction is carried out at a temperature of 180-320℃, a pressure of 0.01-0.3 MPa, and a space velocity of 50-120 h⁻¹. -1 ;

[0034] More preferably, the reaction temperature for the HF removal reaction is 200-310℃, the reaction pressure is 0.01-0.25MPa, and the reaction space velocity is 50-100h. -1 ;

[0035] Particularly preferred are the reaction temperature of 210-300℃, the reaction pressure of 0.01-0.2MPa, and the reaction space velocity of 60-80h. -1 .

[0036] In the method for preparing fluorinated olefins from fluoroalkanes using HF removal provided by this invention, a low silica-to-alumina ratio molecular sieve is used as the catalyst base material. Through multi-step physicochemical modification, its catalytic performance and stability are significantly improved. Firstly, treating the molecular sieve with an appropriate concentration of alkaline solution can selectively remove silicon from the surface of the molecular sieve, exposing more aluminum active sites and thus improving the utilization efficiency of aluminum in the catalyst.

[0037] Then, the calcined molecular sieve is subjected to nitrogen and trifluoromethane heat treatment, which fluorinates the aluminum active sites on the outer surface of the molecular sieve into AlF3. These AlF3 crystals are small in size, uniformly distributed, and rich in strong Lewis acid sites on the surface, giving the catalyst excellent HF removal ability.

[0038] Furthermore, during the fluorination process, AlF3 interacts with the carbon components that may be present in the support to form a stable F–Al–O–C interface structure. This structure not only enhances the binding force between the AlF3 cluster and the support, but also effectively inhibits the migration and sintering of active components under high-temperature reaction conditions, thereby significantly improving the thermal stability and service life of the catalyst.

[0039] Compared with the prior art, the method for preparing fluorinated olefins by deHF removal from fluorinated alkanes provided by the present invention has the following advantages:

[0040] This invention provides a simple method for preparing fluorinated olefins from fluorinated alkanes by removing HF. Through a three-stage treatment of the molecular sieve catalyst—desilication, support, and fluorination—the method achieves efficient exposure of active sites and structural regulation, while significantly improving aluminum utilization efficiency and catalyst activity. It also enhances the catalyst's anti-sintering properties, thereby significantly improving its thermal stability and lifespan. The method of this invention can significantly improve the selectivity of the obtained fluorinated olefins. Detailed Implementation

[0041] The present invention will be further described below through specific embodiments, but this is not a limitation of the present invention. Those skilled in the art can make various modifications or improvements based on the basic idea of ​​the present invention, but as long as they do not depart from the basic idea of ​​the present invention, they are all within the protection scope of the present invention.

[0042] Unless otherwise specified, the reagents used in the following examples and comparative examples are conventional reagents and can be purchased from conventional reagent manufacturers and distributors.

[0043] Example 1: A method for preparing 1,2,3,3,3-pentafluoropropene from 1,1,1,2,3,3-hexafluoropropane.

[0044] Using 1,1,1,2,3,3-hexafluoropropane as a raw material, an HF removal catalyst was loaded into a reactor. The reaction temperature was set at 180℃, the reaction pressure at 0.01 MPa, and the reaction space velocity at 50 h⁻¹. -1 A catalytic deHF reaction was carried out to obtain the corresponding fluorinated olefin 1,2,3,3,3-pentafluoropropylene, and the product was detected by gas chromatography.

[0045] The preparation method of the HF removal catalyst is as follows:

[0046] S1. Add ZSM-5 molecular sieve to 10% NaOH alkaline solution and stir at 40℃ for 2h. After alkaline treatment, wash and filter the molecular sieve, and dry the filter cake in a 60℃ oven for 24h to obtain the alkaline-treated molecular sieve.

[0047] S2. The alkali-treated molecular sieve obtained in step S1 is placed in a 2% cerium nitrate solution and impregnated for 3 hours using the equal volume impregnation method. Then it is dried at 60°C for 10 hours and calcined at 500°C for 3 hours to obtain the calcined molecular sieve.

[0048] S3. The calcined molecular sieve obtained in step S2 is placed in a fixed-bed reactor, and a mixture of nitrogen and trifluoromethane is introduced at 280°C to carry out a fluorination reaction. The molar ratio of nitrogen to trifluoromethane is 10:1. After fluorination for 12 hours, the desired HF removal catalyst is obtained.

[0049] Example 2: A method for preparing 2,3,3,3-tetrafluoropropene from 1,1,1,2,3-pentafluoropropane.

[0050] Using 1,1,1,2,3-pentafluoropropane as a raw material, an HF removal catalyst was loaded into a reactor. The reaction temperature was set at 320℃, the reaction pressure at 0.3 MPa, and the reaction space velocity at 120 h⁻¹. -1 A catalytic deHF reaction was carried out to obtain the corresponding fluorinated olefin 2,3,3,3-tetrafluoropropylene, and the product was detected by gas chromatography.

[0051] The preparation method of the HF removal catalyst is as follows:

[0052] S1. Add ZSM-35 molecular sieve to 10% NaHCO3 solution and stir at 80℃ for 10h. After alkali treatment, wash and filter the molecular sieve. Place the filter cake in a 60℃ oven and dry for 24h to obtain the alkali-treated molecular sieve.

[0053] S2. The alkali-treated molecular sieve obtained in step S1 is placed in a 3% cerium nitrate solution and impregnated for 2 hours using the equal volume impregnation method. Then it is dried at 50°C for 12 hours and calcined at 500°C for 3 hours to obtain the calcined molecular sieve.

[0054] S3. The calcined molecular sieve obtained in step S2 is placed in a fixed-bed reactor, and a mixture of nitrogen and trifluoromethane is introduced at 400°C to carry out a fluorination reaction. The molar ratio of nitrogen to trifluoromethane is 60:1. After fluorination for 4 hours, the desired HF removal catalyst is obtained.

[0055] Example 3: A method for preparing 1,2,3,3,3-pentafluoropropene from 1,1,1,2,3,3-hexafluoropropane.

[0056] Using 1,1,1,2,3,3-hexafluoropropane as a raw material, an HF removal catalyst was loaded into a reactor. The reaction temperature was set at 210℃, the reaction pressure at 0.05 MPa, and the reaction space velocity at 60 h⁻¹. -1 The product was subjected to a catalytic deHF reaction to obtain the corresponding fluorinated olefin 1,2,3,3,3-pentafluoropropylene, and the product was detected by gas chromatography.

[0057] The preparation method of the HF removal catalyst is as follows:

[0058] S1. Add ZSM-5 molecular sieve to 10% NaOH alkaline solution and stir at 60℃ for 6h. After alkaline treatment, wash and filter the molecular sieve, and dry the filter cake in a 60℃ oven for 24h to obtain the alkaline-treated molecular sieve.

[0059] S2. The alkali-treated molecular sieve obtained in step S1 is placed in a 2% cerium nitrate solution and impregnated for 2 hours using the equal volume impregnation method. Then it is dried at 55°C for 10 hours and calcined at 500°C for 3 hours to obtain the calcined molecular sieve.

[0060] S3. The calcined molecular sieve obtained in step S2 is placed in a fixed-bed reactor, and a mixture of nitrogen and trifluoromethane is introduced at 350°C. The molar ratio of nitrogen to trifluoromethane is 20:1. After fluorination for 5 hours, the desired HF removal catalyst is obtained.

[0061] Example 4: A method for preparing 1,2,3,3,3-pentafluoropropene from 1,1,1,2,3,3-hexafluoropropane.

[0062] Using 1,1,1,2,3,3-hexafluoropropane as a raw material, an HF removal catalyst was loaded into a reactor. The reaction temperature was set at 250°C, the reaction pressure at 0.2 MPa, and the reaction space velocity at 80 h⁻¹. -1A catalytic deHF reaction was carried out to obtain the corresponding fluorinated olefin 1,2,3,3,3-pentafluoropropylene, and the product was detected by gas chromatography.

[0063] The preparation method of the HF removal catalyst is as follows:

[0064] S1. Add Y molecular sieve to 10% Na2CO3 solution and stir at 50℃ for 4h. After alkali treatment, wash and filter the molecular sieve. Place the filter cake in a 60℃ oven and dry for 24h to obtain the alkali-treated molecular sieve.

[0065] S2. The alkali-treated molecular sieve obtained in step S1 is placed in a 2.5% cerium nitrate solution and impregnated for 2.5 hours using an equal-volume impregnation method. Then it is dried at 58°C for 12 hours and calcined at 500°C for 3 hours to obtain the calcined molecular sieve.

[0066] S3. The calcined molecular sieve obtained in step S2 is placed in a fixed-bed reactor, and a mixture of nitrogen and trifluoromethane is introduced at 320°C to carry out a fluorination reaction. The molar ratio of nitrogen to trifluoromethane is 15:1. After fluorination for 8 hours, the desired HF removal catalyst is obtained.

[0067] Example 5: A method for preparing 2,3,3,3-tetrafluoropropylene from 1,1,1,2,3-pentafluoropropane.

[0068] Using 1,1,1,2,3-pentafluoropropane as a raw material, an HF removal catalyst was loaded into a reactor. The reaction temperature was set at 300℃, the reaction pressure at 0.25 MPa, and the reaction space velocity at 100 h⁻¹. -1 A catalytic deHF reaction was carried out to obtain the corresponding fluorinated olefin 2,3,3,3-tetrafluoropropylene, and the product was detected by gas chromatography.

[0069] The preparation method of the HF removal catalyst is as follows:

[0070] S1. Add ZSM-5 molecular sieve to 10% NaOH alkaline solution and stir at 70℃ for 8 hours. After alkaline treatment, wash and filter the molecular sieve, and dry the filter cake in a 60℃ oven for 24 hours to obtain the alkaline-treated molecular sieve.

[0071] S2. The alkali-treated molecular sieve obtained in step S1 is placed in a 2.8% cerium nitrate solution and impregnated for 3 hours using the equal volume impregnation method. Then it is dried at 60°C for 11 hours and calcined at 500°C for 3 hours to obtain the calcined molecular sieve.

[0072] S3. The calcined molecular sieve obtained in step S2 is placed in a fixed-bed reactor, and a mixture of nitrogen and trifluoromethane is introduced at 300°C to carry out a fluorination reaction. The molar ratio of nitrogen to trifluoromethane is 40:1. After fluorination for 6 hours, the desired HF removal catalyst is obtained.

[0073] Comparative Example 1: A method for preparing 1,2,3,3,3-pentafluoropropene from 1,1,1,2,3,3-hexafluoropropane.

[0074] Compared with Example 3, the difference in Comparative Example 1 is that the ZSM-5 molecular sieve in step S1 of the preparation of the deHF catalyst is replaced with SAPO-34 molecular sieve, while other parameters and operations are the same as in Example 3.

[0075] Comparative Example 2: A method for preparing 1,2,3,3,3-pentafluoropropene from 1,1,1,2,3,3-hexafluoropropane.

[0076] Compared with Example 3, the difference in Comparative Example 1 is that the cerium nitrate solution in step S2 of the preparation of the deHF catalyst is replaced with a magnesium nitrate solution, while other parameters and operations are the same as in Example 3.

[0077] Comparative Example 3: A method for preparing 1,2,3,3,3-pentafluoropropene from 1,1,1,2,3,3-hexafluoropropane.

[0078] Compared with Example 3, the difference in Comparative Example 1 is that the trifluoromethane in step S2 of the preparation of the deHF catalyst is replaced with hydrogen fluoride, while other parameters and operations are the same as in Example 3.

[0079] Comparative Example 4: A method for preparing 1,2,3,3,3-pentafluoropropene from 1,1,1,2,3,3-hexafluoropropane.

[0080] Compared with Example 3, the difference in Comparative Example 1 is that in the method for preparing 1,2,3,3,3-pentafluoropropylene from 1,1,1,2,3,3-hexafluoropropane, the HF removal catalyst used in the catalytic process was replaced with a chromium oxide catalyst, while other parameters and operations were the same as in Example 3.

[0081] Example 1: Detection of product selectivity and catalyst lifetime using the method of this invention.

[0082] The products obtained by the preparation methods of Examples 1-5 and Comparative Examples 1-4 of this invention were analyzed by gas chromatography, and the conversion rate (%) of fluorinated alkanes and the selectivity (%) of fluorinated olefins were obtained as shown in Table 1.

[0083] When the catalysts prepared in Examples 1-5 and Comparative Examples 1-4 of this invention were used continuously for 100 h, the products after the reaction were analyzed by gas chromatography to obtain the conversion rate (%) of fluorinated alkanes and the selectivity (%) of fluorinated olefins, as shown in Table 2.

[0084] Table 1

[0085] Table 2

[0086] As shown in Table 1, the gas chromatography analysis of the products obtained by the methods of Examples 1-5 of the present invention showed that the selectivity of the fluorinated olefins obtained by the catalyst was all above 98%. It can be seen that the catalysts obtained by Examples 1-5 of the present invention can effectively improve the selectivity of the obtained fluorinated olefins.

[0087] As shown in Table 2, after continuous catalysis for 100 h using the HF removal catalysts prepared in Examples 1-5 of this invention, the selectivity of the obtained fluorinated olefins remained above 96%. However, after catalysis for 100 h using the HF removal catalysts prepared in Comparative Examples 1-3 or the conventional chromium oxide catalyst in Comparative Example 4, the selectivity of the obtained fluorinated olefins decreased to varying degrees.

[0088] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing fluorinated olefins by deHF removal from fluorinated alkanes, characterized in that, The method is as follows: using fluorinated alkanes as raw materials, adding a deHF catalyst in a fixed-bed reactor to carry out a deHF reaction, and obtaining the corresponding fluorinated olefins; The fluorinated alkane is one of 1,1,1,2,3,3-hexafluoropropane and 1,1,1,2,3-pentafluoropropane; The fluorinated olefin is one of 1,2,3,3,3-pentafluoropropylene and 2,3,3,3-tetrafluoropropylene.

2. The method for preparing fluorinated olefins by deHF removal from fluorinated alkanes according to claim 1, characterized in that, The preparation method of the HF removal catalyst is as follows: S1. Add the low silica-alumina ratio molecular sieve to the alkaline solution and stir under heating conditions. After the alkaline treatment is completed, wash and filter the molecular sieve, and dry the filter cake in an oven to obtain the alkaline-treated molecular sieve. S2. The alkali-treated molecular sieve obtained in step S1 is placed in a 2-3% cerium nitrate solution and impregnated for a period of time using an equal-volume impregnation method. Then it is dried and calcined to obtain the calcined molecular sieve. S3. The calcined molecular sieve obtained in step S2 is placed in a fixed-bed reactor, and a mixture of nitrogen and trifluoromethane is introduced to carry out a fluorination reaction to obtain a de-HF catalyst.

3. The method for preparing fluorinated olefins by deHF removal from fluorinated alkanes according to claim 2, characterized in that, In step S1, the low silica-to-alumina ratio molecular sieve is one of ZSM-5, ZSM-35, or Y molecular sieve.

4. The method for preparing fluorinated olefins by deHF removal from fluorinated alkanes according to claim 2, characterized in that, The alkaline solution in step S1 is one of 10% NaOH solution, 10% NaHCO3 solution, and 10% Na2CO3 solution.

5. The method for preparing fluorinated olefins by deHF removal from fluorinated alkanes according to claim 2, characterized in that, In step S1, the heating temperature for alkali treatment is 40-80℃, and the treatment time is 2-10 hours.

6. The method for preparing fluorinated olefins by deHF removal from fluorinated alkanes according to claim 2, characterized in that, The soaking time in step S2 is 2h-3h; the drying time is 10h-12h, and the drying temperature is 50-60℃; the calcination temperature is 500℃, and the calcination time is 3h.

7. The method for preparing fluorinated olefins by deHF removal from fluorinated alkanes according to claim 2, characterized in that, The fluorination temperature in step S3 is 280-400℃, and the fluorination time is 4h-12h.

8. The method for preparing fluorinated olefins by deHF removal from fluorinated alkanes according to claim 2, characterized in that, In step S3, the molar ratio of nitrogen to trifluoromethane is 10-60:

1.

9. The method for preparing fluorinated olefins by deHF removal from fluorinated alkanes according to claim 8, characterized in that, In step S3, the molar ratio of nitrogen to trifluoromethane is 20-40:

1.

10. The method for preparing fluorinated olefins by deHF removal from fluorinated alkanes according to claim 1, characterized in that, The method for preparing fluorinated olefins by deHF removal from fluorinated alkanes uses a reaction temperature of 180-320℃, a reaction pressure of 0.01-0.3MPa, and a reaction space velocity of 50-120h⁻¹. -1 .

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