A method for preparing fluorine-containing olefins by removing HF from fluorine-containing alkanes

Abstract

The application belongs to the technical field of organic chemistry, and particularly relates to a method for preparing fluorine-containing olefins by removing HF from fluorine-containing alkanes, wherein the fluorine-containing alkanes are used as raw materials, a catalyst for removing HF is added in a fixed bed reactor, and a reaction of removing HF is performed to obtain corresponding fluorine-containing olefins. The method for preparing fluorine-containing olefins by removing HF from fluorine-containing alkanes is simple in operation, the prepared catalyst for removing HF can realize efficient exposure and structural regulation of active sites, greatly improve the utilization efficiency of aluminum elements and the activity of the catalyst, and enhance the sintering resistance of the catalyst, thereby significantly improving the thermal stability and service life of the catalyst. Meanwhile, the method can obviously improve the selectivity of the prepared fluorine-containing olefins.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of organic chemistry, and particularly relates to a method for preparing fluorine-containing olefin by removing HF from fluorine-containing alkane. BACKGROUND

[0002] The fourth generation refrigerant 2,3,3,3-tetrafluoropropene (HFO-1234yf) is highly concerned, which has the characteristics of zero ozone depletion potential (0DP), micro-flammability and low global warming potential (GWP), and is a new generation of ODS substitute-hydrofluoroolefin (HFO) after hydrochlorofluorocarbon (HCFC) and hydrofluorocarbon (HFC). In recent years, with the recognition of HFO-1234yf by the European Union, HFO-1234yf is most likely to replace HFC-134a (1,1,1,2-tetrafluoroethane) to become a new generation of automobile refrigerant. At present, the main route that has been industrialized is a two-step hydrogenation and two-step dehydrofluorination route using hexafluoropropene as raw material. In the process route of hexafluoropropene, hydrogen gas and hexafluoropropene (HFP) are subjected to catalytic hydrogenation reaction to generate hexafluoropropane, and then dehydrofluorination reaction is performed to generate pentafluoropropene (HFO-1225ye); the generated pentafluoropropene (HFO-1225ye) is also subjected to catalytic addition reaction with hydrogen gas to generate pentafluoropropane, and then dehydrofluorination reaction is performed to finally generate the product 2,3,3,3-tetrafluoropropene (HFO-1234yf).

[0003] In this route, two-step dehydrofluorination reactions are used, and the traditional dehydrofluorination catalyst is generally AlF3 and CrF3. At high temperature, the catalyst is prone to sintering, which causes the activity of the catalyst to decrease and the service life to be shortened. In order to improve the aluminum-based catalyst, various schemes are proposed in the prior art. For example, Chinese patent CN110586142B discloses a preparation method of a κ-AlF3 catalyst, which uses ammonium salt as a fluorine source by a hydrothermal method, avoids the use of HF, and has regular catalyst morphology and high activity, but the Lewis acidity is too strong, which easily causes carbon deposition and deactivation, and the hydrothermal reaction time is relatively long, and the preparation efficiency is low. Chinese patent CN113385201B discloses a fluorine aluminum sulfate catalyst prepared by hydrothermal method, ball milling and other methods, which has suitable acidity and good stability, but the conversion rate is limited in the HFC-134a dehydrofluorination reaction, and some methods still involve HF, which has safety risks.

[0004] Therefore, it has become an important research direction in the field to develop a dehydrofluorination catalyst which has high catalytic activity and selectivity, and excellent thermal stability and safety. SUMMARY

[0005] In order to solve the problems in the prior art, the purpose of the present application is to provide a method for preparing fluorine-containing olefin by removing HF from fluorine-containing alkane.

[0006] The technical scheme of the present application is:

[0007] A method for preparing fluorine-containing olefin by removing HF from fluorine-containing alkane, using fluorine-containing alkane as raw material, adding a HF removal catalyst in a fixed bed reactor to carry out HF removal reaction, and obtaining the corresponding fluorine-containing olefin.

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

[0009] Preferably, the fluorine-containing olefin is one of 1,2,3,3,3-pentafluoropropene (R1225ye) and 2,3,3,3-tetrafluoropropene (R1234yf).

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

[0011] S1, adding a low-silicon-aluminum ratio molecular sieve to an alkali solution, stirring under heating conditions, washing and filtering the molecular sieve after the alkali treatment is completed, and drying the filter cake in an oven to obtain an alkali-treated molecular sieve;

[0012] S2, placing the alkali-treated molecular sieve obtained in step S1 in a cerium nitrate solution with a concentration of 2-3%, using an equal volume impregnation method to impregnate for a period of time, then drying and calcining to obtain a calcined molecular sieve;

[0013] S3, placing the calcined molecular sieve obtained in step S2 in a fixed bed reactor, and passing a mixed gas of nitrogen and trifluoromethane to carry out fluorination reaction, to obtain a HF removal catalyst.

[0014] Preferably, the low-silicon-aluminum ratio molecular sieve in step S1 is one of ZSM-5, ZSM-35, and Y molecular sieve;

[0015] Further preferably, the low-silicon-aluminum ratio molecular sieve is one of ZSM-5 and Y molecular sieve;

[0016] Particularly preferably, the low-silicon-aluminum ratio molecular sieve is ZSM-5.

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

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

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

[0020] Further preferably, the heating temperature of the alkali treatment is 50-80℃, and the alkali treatment time is 4h-10h.

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

[0022] Preferably, the filter cake in step S1 is dried in an oven at 50-60℃ for 20-24h 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 10h-12h, and the drying temperature is 50-60℃.

[0025] Preferably, the calcination temperature in step S2 is 500℃, and the calcination time is 3h.

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

[0027] Further preferably, the fluorination temperature of the alkali-treated catalyst is 300-380℃, and the fluorination time is 8h-10h.

[0028] Particularly preferably, the fluorination temperature of the alkali-treated catalyst is 320-350℃, and the fluorination time is 6h-8h.

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

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

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

[0032] Preferably, in the process of obtaining the corresponding fluorine-containing olefin by using fluorine-containing alkane as raw material, adding a HF removal catalyst in a fixed bed reactor, and carrying out a HF removal reaction:

[0033] The reaction temperature for carrying out the HF removal reaction is 180-320℃, the reaction pressure is 0.01-0.3MPa, and the reaction space velocity is 50-120h -1 ;

[0034] Further preferably, the reaction temperature for carrying out 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 preferably, the reaction temperature is 210-300℃, the reaction pressure is 0.01-0.2MPa, and the reaction space velocity is 60-80h -1 .

[0036] The method for preparing fluorine-containing olefins by removing HF from fluorine-containing alkanes provided by the present application uses a low-silicon aluminum ratio molecular sieve as a catalyst base material, and significantly improves the catalytic performance and stability of the molecular sieve by performing multiple physical and chemical modifications on the molecular sieve. First, the molecular sieve is treated with an appropriate concentration of lye, which selectively removes silicon materials from the surface of the molecular sieve, exposing more aluminum active sites, and thereby improving the utilization efficiency of aluminum elements 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 surface of the molecular sieve into AlF3. These AlF3 crystals have small sizes and uniform distribution, and the surface is rich in strong Lewis acid sites, which endow the catalyst with excellent HF removal capability.

[0038] In addition, during the fluorination process, the AlF3 interacts with the carbon components that may exist in the carrier to form a stable F–Al–O–C interface structure. This structure not only enhances the bonding force between the AlF3 clusters and the carrier, but also effectively inhibits the migration and sintering of the 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 fluorine-containing olefins by removing HF from fluorine-containing alkanes provided by the present application has the following advantages:

[0040] The method for preparing fluorine-containing olefins by removing HF from fluorine-containing alkanes provided by the present application is simple to operate. Through the three-step treatment of desiliconization, loading, and fluorination of the molecular sieve catalyst, the active sites are efficiently exposed and the structure is regulated, the utilization efficiency of aluminum elements and the activity of the catalyst are greatly improved, the sintering resistance of the catalyst is enhanced, and the thermal stability and service life of the catalyst are significantly improved. The method of the present application can significantly improve the selectivity of the prepared fluorine-containing olefins. DETAILED DESCRIPTION

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

[0042] In the following examples and comparative examples, the reagents not specifically mentioned are conventional reagents, which can be purchased from conventional reagent production and sales companies.

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

[0044] The HF removal catalyst was loaded into a reactor, and the reaction temperature was set to 180°C, the reaction pressure was 0.01 MPa, and the reaction space velocity was 50 h -1 The catalytic HF removal reaction was carried out, and the corresponding fluorine-containing olefin 1,2,3,3,3-pentafluoropropene was obtained. The product was detected by gas chromatography.

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

[0046] S1, the ZSM-5 molecular sieve was added to a 10% NaOH alkaline solution, stirred at 40°C for 2h, and after the alkaline treatment was completed, the molecular sieve was washed and suction filtered, and the filter cake was dried in a 60°C oven for 24h to obtain the alkali-treated molecular sieve;

[0047] S2, the alkali-treated molecular sieve obtained in step S1 was placed in a 2% cerium nitrate solution, and an equal volume of impregnation method was used for impregnation for 3h, followed by drying at a temperature of 60°C for 10h, and then calcining at 500°C for 3h to obtain the calcined molecular sieve;

[0048] S3, the calcined molecular sieve obtained in step S2 was placed in a fixed bed reactor, and a mixture of nitrogen and trifluoromethane was introduced for fluorination reaction at 280°C, the molar ratio of the nitrogen and trifluoromethane was 10:1, and the fluorination was carried out for 12h to obtain the required HF removal catalyst.

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

[0050] The HF removal catalyst was loaded into a reactor, and the reaction temperature was set to 320°C, the reaction pressure was 0.3 MPa, and the reaction space velocity was 120 h -1 The catalytic HF removal reaction was carried out, and the corresponding fluorine-containing olefin 2,3,3,3-tetrafluoropropene was obtained. The product was detected by gas chromatography.

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

[0052] S1, the ZSM-35 molecular sieve was added to a 10% NaHCO3 solution, stirred at 80°C for 10h, and after the alkaline treatment was completed, the molecular sieve was washed and suction filtered, and the filter cake was dried in a 60°C oven for 24h to obtain the alkali-treated molecular sieve;

[0053] S2, the ZSM-5 molecular sieve obtained in step S1 is placed in a 3% cerium nitrate solution, impregnated by the equal volume impregnation method for 2h, then dried at a temperature of 50℃ for 12h, and then calcined at 500℃ for 3h 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 mixed gas of nitrogen and trifluoromethane is introduced at 400℃ for fluorination, the molar ratio of the nitrogen and trifluoromethane being 60:1, and after fluorination for 4h, 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] 1,1,1,2,3,3-hexafluoropropane as raw material, the HF removal catalyst is loaded into the reactor, the reaction temperature is set to 210℃, the reaction pressure is 0.05MPa, and the reaction space velocity is 60h -1 , a catalytic HF removal reaction is carried out, and the corresponding fluorine-containing olefin 1,2,3,3,3-pentafluoropropene is obtained, and the product is detected by gas chromatography.

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

[0058] S1, the ZSM-5 molecular sieve is added to a 10% NaOH alkaline solution, stirred at 60℃ for 6h, after the alkaline treatment is completed, the molecular sieve is washed and suction filtered, and the filter cake is dried in a 60℃ oven for 24h to obtain the alkaline treated molecular sieve;

[0059] S2, the alkaline treated molecular sieve obtained in step S1 is placed in a 2% cerium nitrate solution, impregnated by the equal volume impregnation method for 2h, then dried at a temperature of 55℃ for 10h, and then calcined at 500℃ for 3h 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 mixed gas of nitrogen and trifluoromethane is introduced at 350℃, the molar ratio of the nitrogen and trifluoromethane being 20:1, and after fluorination for 5h, 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] 1,1,1,2,3,3-hexafluoropropane as raw material, the HF removal catalyst is loaded into the reactor, the reaction temperature is set to 250℃, the reaction pressure is 0.2MPa, and the reaction space velocity is 80h -1Catalytic dehydrofluorination reaction was carried out to obtain the corresponding fluorine-containing olefin 1,2,3,3,3-pentafluoropropene, and the product was detected by gas chromatography.

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

[0064] S1, the Y molecular sieve was added to a 10% Na2CO3 solution, stirred at 50°C for 4h, and after the alkali treatment was completed, the molecular sieve was washed and suction filtered, and the filter cake was dried in a 60°C oven for 24h to obtain the alkali-treated molecular sieve;

[0065] S2, the alkali-treated molecular sieve obtained in step S1 was placed in a cerium nitrate solution with a concentration of 2.5%, and an equal volume of impregnation method was used for impregnation for 2.5h, then dried at a temperature of 58°C for 12h, and then calcined at 500°C for 3h to obtain the calcined molecular sieve;

[0066] S3, the calcined molecular sieve obtained in step S2 was placed in a fixed bed reactor, and a mixture of nitrogen and trifluoromethane was introduced for fluorination reaction at 320°C, the molar ratio of nitrogen and trifluoromethane was 15:1, and after fluorination for 8h, the desired dehydrofluorination catalyst was obtained.

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

[0068] 1,1,1,2,3-pentafluoropropane was used as raw material, the dehydrofluorination catalyst was loaded into the reactor, the reaction temperature was set to 300°C, the reaction pressure was 0.25MPa, and the reaction space velocity was 100 h -1 Catalytic dehydrofluorination reaction was carried out to obtain the corresponding fluorine-containing olefin 1,2,3,3,3-pentafluoropropene, and the product was detected by gas chromatography.

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

[0070] S1, the ZSM-5 molecular sieve was added to a 10% NaOH solution, stirred at 70°C for 8h, and after the alkali treatment was completed, the molecular sieve was washed and suction filtered, and the filter cake was dried in a 60°C oven for 24h to obtain the alkali-treated molecular sieve;

[0071] S2, the alkali-treated molecular sieve obtained in step S1 was placed in a cerium nitrate solution with a concentration of 2.8%, and an equal volume of impregnation method was used for impregnation for 3h, then dried at a temperature of 60°C for 11h, and then calcined at 500°C for 3h 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 mixed gas of nitrogen and trifluoromethane is introduced at 300℃ to carry out fluorination reaction, the molar ratio of the nitrogen and trifluoromethane is 40:1, after fluorination for 6h, the desired HF removal catalyst is obtained.

[0073] Comparative Example 1, a method for preparing 1,2,3,3,3-pentafluoropropene by using 1,1,1,2,3,3-hexafluoropropane as raw material

[0074] Comparative Example 1 is different from Example 3 in that the ZSM-5 molecular sieve in the preparation step S1 of the HF removal catalyst is replaced by SAPO-34 molecular sieve, and other parameters and operations are the same as those in Example 3.

[0075] Comparative Example 2, a method for preparing 1,2,3,3,3-pentafluoropropene by using 1,1,1,2,3,3-hexafluoropropane as raw material

[0076] Comparative Example 1 is different from Example 3 in that the cerium nitrate solution in the preparation step S2 of the HF removal catalyst is replaced by magnesium nitrate solution, and other parameters and operations are the same as those in Example 3.

[0077] Comparative Example 3, a method for preparing 1,2,3,3,3-pentafluoropropene by using 1,1,1,2,3,3-hexafluoropropane as raw material

[0078] Comparative Example 1 is different from Example 3 in that the trifluoromethane in the preparation step S2 of the HF removal catalyst is replaced by hydrogen fluoride, and other parameters and operations are the same as those in Example 3.

[0079] Comparative Example 4, a method for preparing 1,2,3,3,3-pentafluoropropene by using 1,1,1,2,3,3-hexafluoropropane as raw material

[0080] Comparative Example 1 is different from Example 3 in that in the method for preparing 1,2,3,3,3-pentafluoropropene by using 1,1,1,2,3,3-hexafluoropropane as raw material, the HF removal catalyst used in the catalytic process is replaced by chromium oxide catalyst, and other parameters and operations are the same as those in Example 3.

[0081] Test Example 1, detection of product selectivity and service life of catalyst obtained by using the method of the present application

[0082] The products obtained by the preparation methods of Examples 1-5 and Comparative Examples 1-4 of the present application are detected and analyzed by gas chromatography, and the conversion rate (%) of fluorine-containing alkanes and the selectivity (%) of fluorine-containing alkenes are shown in Table 1.

[0083] The conversion rate (%) of the fluorine-containing alkane and the selectivity (%) of the fluorine-containing olefin of the product after the reaction were detected and analyzed by gas chromatography when the catalyst prepared in Examples 1-5 and Comparative Examples 1-4 was continuously used for 100 h, as shown in Table 2.

[0084] Table 1

[0085]

[0086] Table 2

[0087]

[0088] As shown in Table 1, the selectivity of the fluorine-containing olefin obtained by the catalyst was all above 98% when the product obtained by the method of Examples 1-5 was detected and analyzed by gas chromatography. It can be seen that the catalyst prepared by Examples 1-5 can effectively improve the selectivity of the fluorine-containing olefin.

[0089] As shown in Table 2, the selectivity of the fluorine-containing olefin obtained by the catalyst prepared by Examples 1-5 was still above 96% after 100 h of continuous catalysis. However, the selectivity of the fluorine-containing olefin obtained by the catalyst prepared by Comparative Examples 1-3 or the conventional chromium oxide catalyst prepared by Comparative Example 4 decreased to different degrees after 100 h of continuous catalysis.

[0090] The above examples are only illustrative of the principles and effects of the present application, and are not intended to limit the present application. Any person skilled in the art can modify or change the above examples without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes completed by those skilled in the art without departing from the spirit and technical thought disclosed by the present application should be covered by the claims of the present application.

Claims

1. A process for the production of a fluorine-containing olefin by removing HF from a fluorine-containing alkane, characterized by, The method is: taking fluorine-containing alkane as raw material, adding a de-HF catalyst in a fixed bed reactor to carry out a de-HF reaction, and obtaining a corresponding fluorine-containing olefin; The fluorine-containing alkane is one of 1,1,1,2,3,3-hexafluoropropane and 1,1,1,2,3-pentafluoropropane; The fluorine-containing olefin is one of 1,2,3,3,3-pentafluoropropene and 2,3,3,3-tetrafluoropropene; The preparation method of the de-HF catalyst is as follows: S1, the low-silicon-aluminum ratio molecular sieve is added to an alkali solution, and stirring is carried out under heating conditions, after the alkali treatment is completed, the molecular sieve is washed and suction filtered, the filter cake is dried in an oven, and the alkali-treated molecular sieve is obtained; S2, the alkali-treated molecular sieve obtained in step S1 is placed in a cerium nitrate solution with a concentration of 2-3%, an equal volume impregnation method is used for impregnation for a period of time, and then drying and calcination are carried out, to obtain the calcined molecular sieve; S3, the calcined molecular sieve obtained in step S2 is placed in a fixed bed reactor, a mixed gas of nitrogen and trifluoromethane is introduced, a fluorination reaction is carried out, and the de-HF catalyst is obtained; The low-silicon-aluminum ratio molecular sieve in step S1 is one of ZSM-5, ZSM-35 and Y molecular sieve; The alkali solution in step S1 is one of 10% NaOH solution, 10% NaHCO3 solution and 10% Na2CO3 solution; The heating temperature of the alkali treatment in step S1 is 40-80℃, and the alkali treatment time is 2h-10h; The impregnation 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; The fluorination temperature in step S3 is 280-400℃, and the fluorination time is 4h-12h; The molar ratio of nitrogen to trifluoromethane in step S3 is 10-60:

1.

2. The process for the production of fluorine-containing olefins by the removal of HF from fluorine-containing alkanes according to claim 1, characterized in that, The molar ratio of nitrogen to trifluoromethane in step S3 is 20-40:

1.

3. The process for the production of fluorine-containing olefins by the removal of HF from fluorine-containing alkanes according to claim 1, characterized in that, The reaction temperature in the method for preparing fluorine-containing olefins by removing HF from fluorine-containing alkanes is 180-320℃, the reaction pressure is 0.01-0.3 MPa, and the reaction space velocity is 50-120 h -1 .

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