Method for preparing heptafluoropropane

Abstract

The invention discloses a method for preparing heptafluoropropane, which comprises the following steps: carrying out dehydration reaction on heptafluoroisobutyramide through a reactor filled with a catalyst to obtain heptafluoropropane at the reaction temperature of 150-300 DEG C for 10-60 seconds; the catalyst is a molecular sieve, and the molar ratio of silicon to aluminum of the molecular sieve is 0-300. The catalyst is selected from at least one of an HY molecular sieve, a 5A molecular sieve, a gamma-Al2O3 molecular sieve, a ZSM-5 molecular sieve, an Hbeta molecular sieve and the like. The method is simple and convenient in process operation, high in catalyst selectivity, free of environmental pollution, mild in reaction condition and easy for industrial production.

Description

Technical Field

[0001] The invention relates to a method for preparing heptafluoropropane. Background Art

[0002] Heptafluoropropane is a clean gas chemical fire extinguishing agent that mainly uses chemical fire extinguishing and also has physical fire extinguishing effects. Its molecular formula is CF3CHFCF3. It is colorless, odorless, low-toxic, non-conductive, non-corrosive, easy to store, has no environmental restrictions, has a short atmospheric retention period, has a relatively low fire extinguishing concentration, does not pollute the protected object, and has a high fire extinguishing efficiency. Heptafluoropropane extinguishes fires through both chemical and physical methods, mainly chemical methods. The fire extinguishing mechanism is to inhibit chemical chain reactions. The fire extinguishing concentration is generally 7%~10%. In recent years, heptafluoropropane fire extinguishing agent has been widely used in gas fire extinguishing systems due to its reliable fire extinguishing performance and superior environmental protection characteristics, such as industrial warehouses, generator rooms, databases, equipment rooms, substations, transportation and other important places. With the promotion and application of heptafluoropropane in engineering projects, it is very necessary to actively carry out research on the preparation method of heptafluoropropane.

[0003] At present, the main methods for preparing heptafluoropropane include hexafluoropropylene fluorination method, heptachloropropane catalytic fluorination method, etc.

[0004] Patent document CN1867530A reports a method for preparing heptafluoropropane, in which heptafluoropropane is prepared by addition reaction of hexafluoropropylene and hydrogen fluoride in the presence of a chlorofluorination catalyst. During implementation, the operation is difficult, the side reactions are complex, the catalyst selectivity is low, and the emission of three wastes is large.

[0005] Patent document CN1594250A reports a method for producing 1,1,1,2,3,3,3-heptafluoropropane. This method produces heptafluoropropane by addition reaction of hexafluoropropylene and hydrogen fluoride under the action of a modified activated carbon catalyst. During the implementation process, the reaction temperature is high and the highly toxic substance octafluoroisobutylene may be generated, posing a hidden danger to the environment and production safety.

[0006] Patent document CN101456787A reports a hydrogen fluoride addition reaction catalyst and a method for preparing fluorinated alkanes. In this method, heptafluoropropane is prepared by addition reaction of hexafluoropropylene and hydrogen fluoride under the action of a four-way catalytic system catalyst. During the implementation process, the problem of this process is that the reaction pressure is relatively high, which makes it difficult to be suitable for industrial production.

[0007] Patent document CN102617268A reports a method for preparing heptafluoropropane by gas phase catalytic fluorination. This method uses heptachloropropane and hydrogen fluoride in the presence of a catalyst to prepare heptafluoropropane. During implementation, although this method breaks the limitation of using hexafluoropropylene as a raw material, it has the problem of limited raw material sources, making it difficult to achieve industrial production.

[0008] In summary, the existing preparation methods have the disadvantages of difficult process operation, poor catalyst selectivity, serious pollution, high reaction pressure, and difficulty in industrialization. Therefore, it is urgent to develop a heptafluoropropane synthesis process with simple process operation, good catalyst selectivity, green environmental protection, mild reaction conditions, and easy engineering scale-up. Summary of the invention

[0009] The object of the present invention is to provide a method for preparing heptafluoropropane, which has the advantages of simple process, high catalyst selectivity, green and pollution-free, normal pressure reaction, easy industrialization, etc.

[0010] To achieve the above object, the technical solution of the present invention is: a method for preparing heptafluoropropane, comprising the following steps: dehydrating heptafluoroisobutyramide through a reactor equipped with a catalyst to obtain heptafluoropropane, the reaction temperature is generally 150-300°C, preferably 200-250°C; the residence time is generally 10-60s, preferably 20-50s. The catalyst is a molecular sieve, and the silicon-aluminum molar ratio of the molecular sieve is generally 0-300, preferably 25-150.

[0011] The reaction steps are shown below:

[0012] The catalyst is selected from at least one of HY molecular sieve, 5A molecular sieve, γ-Al2O3 molecular sieve, ZSM-5 molecular sieve, Hbeta molecular sieve, etc., preferably at least one of ZSM-5 molecular sieve and Hbeta molecular sieve.

[0013] Furthermore, a method for preparing heptafluoropropane comprises the following steps: (1) After the catalyst is activated, it is added into the reactor, and then preheated heptafluoroisobutyramide is added to carry out a dehydration reaction. The preheating temperature is generally 100-200°C, preferably 150-200°C; (2) After the reaction, the gas passes through alkali solution, water and desiccant respectively, and then the target product heptafluoropropane is collected by freezing. The boiling point of heptafluoropropane is -16.4°C, and it can be condensed and liquefied at a low temperature of -50~-30°C for easy collection to obtain the heptafluoropropane. The alkali solution may be a saturated aqueous solution of NaOH, and the desiccant may be CaO.

[0014] In the present invention, the catalyst activation refers to heating the catalyst at 100-600° C. in a nitrogen atmosphere for 4-48 h, preferably at 200-500° C. in a nitrogen atmosphere for 8-36 h.

[0015] In the present invention, the liquid collected by freezing is sampled and analyzed by gas chromatography to determine that the product is heptafluoropropane and obtain its purity.

[0016] In the present invention, heptafluoroisobutyramide is dehydrated under the action of a catalyst to obtain heptafluoropropane, which has the following advantages over the traditional method: simple process operation, high catalyst selectivity, no pollution to the environment, mild reaction conditions, and easy industrial production. DETAILED DESCRIPTION

[0017] The implementation process of the present invention is described in detail below in conjunction with specific implementation cases, but the protection scope of the present invention is not limited thereto.

[0018] Embodiments 1 to 9 Take a ZSM-5 molecular sieve with a silicon-aluminum molar ratio of 40 and heat it at 400°C for 12h in a nitrogen atmosphere, take 90g into a reactor, take 200g of heptafluoroisobutyramide and preheat it to 160°C and send it into the reaction container. After the reaction is completed, the reactor vent valve is passed through a saturated NaOH aqueous solution, water and desiccant CaO respectively, and heptafluoropropane is collected in a low-temperature freezing tank (-50~-30°C), and the purity of heptafluoropropane is determined by gas chromatography. The reaction temperature, residence time and purity of heptafluoropropane are shown in Table 1.

[0019] Table 1 Experimental data of Examples 1 to 9

[0020] Embodiments 10 to 18 Take Hbeta molecular sieve with a silicon-aluminum molar ratio of 25 and heat it at 400°C for 12h under nitrogen atmosphere, take 90g in a reactor, take 200g of heptafluoroisobutyramide and preheat it to 160°C and send it into the reaction container. After the reaction is completed, pass the reactor vent valve through a saturated NaOH aqueous solution, water and desiccant CaO respectively, collect heptafluoropropane in a low-temperature freezer (-50~-30°C), and determine the purity of heptafluoropropane by gas chromatography. The reaction temperature, residence time and purity of heptafluoropropane are shown in Table 2.

[0021] Table 2 Experimental data of Examples 10 to 18

[0022] Embodiments 19 to 24 Take HY molecular sieve with a silicon-aluminum molar ratio of 25 and heat it at 400°C for 12h under nitrogen atmosphere, take 90g in a reaction container, take 200g of heptafluoroisobutyramide and preheat it to 160°C and send it into the reaction container. After the reaction is completed, pass the vent valve of the reaction container through a saturated NaOH aqueous solution, water and desiccant CaO respectively, collect heptafluoropropane in a low-temperature freezing tank (-50~-30°C), and determine the purity of heptafluoropropane by gas chromatography. The reaction temperature, residence time and purity of heptafluoropropane are shown in Table 3.

[0023] Table 3 Experimental data of Examples 19 to 24

[0024] Embodiments 25 to 33 Take Hbeta molecular sieve with a silicon-aluminum molar ratio of 60 and heat it at 400°C for 12h under nitrogen atmosphere, take 90g in a reaction container, take 200g of heptafluoroisobutyramide and preheat it to 160°C and send it into the reaction container. After the reaction is completed, pass the saturated NaOH aqueous solution, water and desiccant CaO through the vent valve of the reaction container, collect heptafluoropropane in a low-temperature freezer (-50~-30°C), and determine the purity of heptafluoropropane by gas chromatography. The reaction temperature, residence time and purity of heptafluoropropane are shown in Table 4.

[0025] Table 4 Experimental data of Examples 25 to 33

[0026] Embodiments 34 to 42 Take Hbeta molecular sieve with a silicon-aluminum molar ratio of 150 and heat it at 400°C for 12h under nitrogen atmosphere, take 90g into a reaction container, take 200g of heptafluoroisobutyramide and preheat it to 160°C and then send it into the reaction container. After the reaction is completed, pass the saturated NaOH aqueous solution, water and desiccant CaO through the vent valve of the reaction container, collect heptafluoropropane in a low-temperature freezer (-50~-30°C), and determine the purity of heptafluoropropane by gas chromatography. The reaction temperature, residence time and purity of heptafluoropropane are shown in Table 5.

[0027] Table 5 Experimental data of Examples 34 to 42

Claims

1. A method for preparing heptafluoropropane, comprising the following steps: Heptafluoroisobutyramide is dehydrated in a reactor equipped with a catalyst to obtain heptafluoropropane, the reaction temperature is 150-300°C, and the residence time is 10-60s; the catalyst is a molecular sieve, and the silicon-aluminum molar ratio of the molecular sieve is 0-300.

2. The method according to claim 1, characterized in that: The reaction temperature is 200-250°C; the residence time is 20-50 s; and the silicon-aluminum molar ratio of the molecular sieve is 25-150.

3. The method according to claim 1, characterized in that The catalyst is selected from at least one of HY molecular sieve, 5A molecular sieve, γ-Al2O3 molecular sieve, ZSM-5 molecular sieve and Hbeta molecular sieve.

4. The method according to claim 1, characterized in that: The catalyst is selected from at least one of ZSM-5 molecular sieve and Hbeta molecular sieve.

5. The method according to claim 1, characterized in that The following steps are involved: (1) After the catalyst is activated, it is added into the reactor, and then preheated heptafluoroisobutyramide is added for dehydration reaction, and the preheating temperature is 100-200°C; (2) After the reaction, the gas passes through alkali solution, water and desiccant respectively, and then the target product heptafluoropropane is collected by freezing.

6. The method according to claim 5, characterized in that The preheating temperature is 150~200℃.

7. The method according to claim 5, characterized in that The catalyst activation refers to heating the catalyst at 100-600° C. in a nitrogen atmosphere for 4-48 hours.

8. The method according to claim 5, characterized in that The catalyst activation refers to heating the catalyst at 200-500° C. in a nitrogen atmosphere for 8-36 hours.

9. The method according to claim 5, characterized in that The freezing collection temperature is -50~-30℃.

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