Method for removing impurities in hexafluoropropylene oxide

Abstract

The invention relates to the technical field of hexafluoropropylene oxide, and particularly discloses a method for removing impurities in hexafluoropropylene oxide. The method for removing impurities in hexafluoropropylene oxide comprises the following steps that hexafluoropropylene oxide gas containing acyl fluoride substances is conveyed into an alkaline washing tower to be subjected to alkaline washing and impurity removal, and an alkaline buffer system is applied to the interior of the alkaline washing tower for alkaline washing. The method has the advantages that the loss amount of hexafluoropropylene oxide in alkali washing is remarkably reduced, and the process control difficulty is low.

Description

Technical Field

[0001] The present application relates to the technical field of hexafluoropropylene oxide purification, and more specifically, to a method for removing impurities in hexafluoropropylene oxide. Background Art

[0002] Hexafluoropropylene oxide (HFPO) is an intermediate widely used in fluorine chemical industry. The downstream products of hexafluoropropylene oxide are used in chemical industry, aerospace, electronics, medicine, environmental protection, construction, fire protection and other fields.

[0003] At present, the main products that can be synthesized through hexafluoropropylene oxide are: 1. Perfluoropolyether substances; 2. Perfluoroalkyl vinyl ether substances; 3. Hexafluoroacetone and its downstream substances; 4. Perfluorohexanone and its downstream substances.

[0004] Since the industrial synthesis of hexafluoropropylene oxide began in the last century, its synthesis process has undergone many changes and improvements. At present, oxygen liquid phase oxidation is the mainstream method for synthesizing HFPO. In the process of preparing hexafluoropropylene oxide by oxygen liquid phase oxidation, acyl fluoride substances are always produced. Although the production ratio of acyl fluoride substances can be significantly reduced and the selectivity of hexafluoropropylene oxide can be improved by controlling the process conditions, the acyl fluoride by-products cannot be completely eliminated. However, acyl fluoride by-products will affect the separation of products in the subsequent separation process of hexafluoropropylene oxide. Therefore, it is essential to separate acyl fluoride by-products from hexafluoropropylene oxide, and alkaline washing is the most effective way to remove acyl fluoride substances.

[0005] At present, the alkali washing tower using elution method is the most common equipment. Hexafluoropropylene oxide containing acyl fluoride substances enters the tower through the lower part of the alkali washing tower. The hexafluoropropylene oxide containing acyl fluoride substances is fully contacted with the alkali solution from bottom to top to achieve the absorption of the acyl fluoride substances by the alkali solution.

[0006] In the process of post-reaction treatment of hexafluoropropylene oxide, strong alkali formed by alkali metals is generally used to prepare corresponding solutions, such as potassium hydroxide and sodium hydroxide, to remove acyl fluoride substances. Among them, the use of potassium hydroxide alkaline solution for alkali washing has the following advantages: the fluoride salt formed after alkali washing has a high solubility, the salt is not easy to precipitate, and the alkali washing tower is not easy to clog. The advantage of using a strong alkaline substance as the alkali solution solute is obvious, that is, the absorption capacity is strong, and the acyl fluoride substances can be completely absorbed. However, due to the strong alkalinity of alkali metals, the following two problems will occur during their use: first, while the alkali solution absorbs acyl fluoride substances, it will also react with a portion of hexafluoropropylene oxide, causing partial loss of the product, increasing costs, and increasing the consumption of alkali solution; second, as the alkali solution absorbs acyl fluoride substances, the concentration of the alkali solution gradually decreases. When the concentration of the alkali solution drops to a certain level, the pH value will suddenly drop, and it is easy for the alkali solution to be unreplenished in time, which in turn affects the absorption of acyl fluoride substances. Therefore, when using alkali metal solutions for alkali washing, there is a defect that the pH value is not easy to control, and the alkali washing process is difficult to control.

[0007] Therefore, there is an urgent need to develop a new method for removing acyl fluoride substances in hexafluoropropylene oxide. Summary of the invention

[0008] In order to improve the defect of the current alkaline washing process that is difficult to control, the present application provides a method for removing impurities in hexafluoropropylene oxide, using the following technical solution: The present application provides a method for removing impurities in hexafluoropropylene oxide, comprising the following steps: transporting hexafluoropropylene oxide gas containing acyl fluoride substances to an alkali washing tower for alkali washing and impurity removal, wherein an alkaline buffer system is used in the alkali washing tower for alkali washing.

[0009] By adopting the above technical solution, the pH value of the alkaline buffer system is moderate and can react with acyl fluoride substances. However, compared with the strong alkaline solution, the alkaline buffer system does not react with hexafluoropropylene oxide or reacts at a very small ratio, which can significantly reduce the loss rate of hexafluoropropylene oxide. At the same time, the buffer solution has the characteristic of relatively stable pH value, and it is not easy to have a significant sudden drop in pH value during the absorption of acyl fluoride substances, so the pH value of the entire reaction system is easier to control.

[0010] Optionally, the pH of the alkaline buffer system is 8-12.

[0011] By adopting the above technical solution, the pH value of the alkaline buffer system is stabilized in the range of 8-12, and the pH value is not prone to a significant sudden drop, making the alkaline washing process easier to control.

[0012] Optionally, the alkaline buffer system includes any one of a glycine-sodium hydroxide buffer system, a glycine-potassium hydroxide buffer system, a borax-sodium hydroxide buffer system, a borax-potassium hydroxide buffer system, a sodium carbonate-sodium bicarbonate buffer system, a potassium carbonate-potassium bicarbonate buffer system, a sodium carbonate-sodium hydroxide buffer system, a potassium carbonate-potassium hydroxide buffer system, a disodium hydrogen phosphate-sodium hydroxide buffer system, and a dipotassium hydrogen phosphate-potassium hydroxide buffer system.

[0013] Optionally, the alkaline buffer system is selected from any one of a potassium carbonate-potassium bicarbonate buffer system and a potassium carbonate-potassium hydroxide buffer system.

[0014] By adopting the above technical scheme, the buffer system is further optimized. After the buffer system absorbs acyl fluoride, the solubility of potassium fluoride formed is greater than that of sodium fluoride, and it is not easy to form precipitation, thereby not easy to clog related equipment, which is conducive to the alkaline washing reaction.

[0015] Optionally, the pressure in the alkali washing tower is maintained at 0-0.3 MPa.

[0016] Optionally, the pressure in the alkali washing tower is maintained at 0-0.1 MPa.

[0017] Optionally, the temperature in the alkali washing tower is maintained at 10-40°C.

[0018] Optionally, the temperature in the alkali washing tower is maintained at 10-30°C.

[0019] Optionally, the packing in the alkali washing tower includes any one or more of ball rings, Raschig rings and Dixon θ rings.

[0020] Optionally, the packing in the alkali washing tower includes Dixon theta rings.

[0021] In summary, this application has the following beneficial effects: 1. Since the present application adopts an alkaline buffer system to wash hexafluoropropylene oxide containing acyl fluoride substances, the pH value of the alkaline buffer system is moderate and can react with acyl fluoride substances. However, compared with a strong alkaline solution, the alkaline buffer system does not react with hexafluoropropylene oxide or reacts at a very small rate, which can significantly reduce the loss rate of hexafluoropropylene oxide. At the same time, the buffer solution has a relatively stable pH value, and it is not easy to have a significant sudden drop in pH value during the absorption of acyl fluoride substances, so the pH value of the entire reaction system is easier to control; 2. The specific composition of the buffer system is optimized in the present application, and a potassium-based alkali metal buffer system is preferably used. After the buffer system absorbs acyl fluoride, the solubility of the formed potassium fluoride is greater than that of sodium fluoride, and it is not easy to form precipitation, thereby not easily clogging related equipment, which is conducive to the alkaline washing reaction. DETAILED DESCRIPTION

[0022] The present application is further described in detail below with reference to the embodiments.

[0023] Example Example 1

[0024] The present application provides a method for removing impurities in hexafluoropropylene oxide, which is as follows: hexafluoropropylene oxide gas containing acyl fluoride substances is transported to an alkali washing tower for alkali washing and impurity removal, and an alkaline buffer system is used in the alkali washing tower for alkali washing.

[0025] Specifically, the alkaline buffer system used in the present application is a glycine-potassium hydroxide system (wherein the concentration of glycine is 0.5 mol / L and the concentration of potassium hydroxide is 0.5 mol / L); the pressure in this embodiment is controlled at 0-0.1 MPa; the temperature in this embodiment is controlled at 20-30°C, the gas feed rate in this embodiment is 500 g / h, the alkali solution circulation volume is 100 L / h, and the filler used in the alkali washing tower in this embodiment is Dixon θ ring.

[0026] The composition of the hexafluoropropylene oxide gas containing acyl fluoride substances is as follows (molar concentration): hexafluoropropylene oxide 60%, hexafluoropropylene 35%, perfluoroacetyl fluoride 4%, and perfluoromethoxyacetyl fluoride 1%.

[0027] Example 2 The present application provides a method for removing impurities in hexafluoropropylene oxide, which is as follows: hexafluoropropylene oxide gas containing acyl fluoride substances is transported to an alkali washing tower for alkali washing and impurity removal, and an alkaline buffer system is used in the alkali washing tower for alkali washing.

[0028] Specifically, the alkaline buffer system used in the present application is a borax-potassium hydroxide system (wherein the concentration of borax is 0.5 mol / L and the concentration of potassium hydroxide is 0.5 mol / L); the pressure in this embodiment is controlled at 0-0.1 MPa; the temperature in this embodiment is controlled at 20-30°C, the gas feed rate in this embodiment is 500 g / h, the alkali solution circulation volume is 100 L / h, and the filler used in the alkali washing tower in this embodiment is Dixon θ ring.

[0029] The composition of the hexafluoropropylene oxide gas containing acyl fluoride substances is as follows (molar concentration): hexafluoropropylene oxide 60%, hexafluoropropylene 35%, perfluoroacetyl fluoride 4%, and perfluoromethoxyacetyl fluoride 1%.

[0030] Example 3 The present application provides a method for removing impurities in hexafluoropropylene oxide, which is as follows: hexafluoropropylene oxide gas containing acyl fluoride substances is transported to an alkali washing tower for alkali washing and impurity removal, and an alkaline buffer system is used in the alkali washing tower for alkali washing.

[0031] Specifically, the alkaline buffer system used in the present application is a potassium carbonate-potassium bicarbonate system (wherein the concentration of potassium carbonate is 0.5 mol / L and the concentration of potassium bicarbonate is 0.5 mol / L); the pressure in this embodiment is controlled at 0-0.1 MPa; the temperature in this embodiment is controlled at 20-30°C, the gas feed rate in this embodiment is 500 g / h, the alkali liquid circulation volume is 100 L / h, and the filler used in the alkali washing tower in this embodiment is Dixon θ ring.

[0032] The composition of the hexafluoropropylene oxide gas containing acyl fluoride substances is as follows (molar concentration): hexafluoropropylene oxide 60%, hexafluoropropylene 35%, perfluoroacetyl fluoride 4%, and perfluoromethoxyacetyl fluoride 1%.

[0033] Example 4 The present application provides a method for removing impurities in hexafluoropropylene oxide, which is as follows: hexafluoropropylene oxide gas containing acyl fluoride substances is transported to an alkali washing tower for alkali washing and impurity removal, and an alkaline buffer system is used in the alkali washing tower for alkali washing.

[0034] Specifically, the alkaline buffer system used in the present application is a potassium carbonate-potassium hydroxide system (wherein the concentration of potassium carbonate is 0.5 mol / L and the concentration of potassium hydroxide is 0.5 mol / L); the pressure in this embodiment is controlled at 0-0.1 MPa; the temperature in this embodiment is controlled at 20-30°C, the gas feed rate in this embodiment is 500 g / h, the alkali solution circulation volume is 100 L / h, and the filler used in the alkali washing tower in this embodiment is Dixon θ ring.

[0035] The composition of the hexafluoropropylene oxide gas containing acyl fluoride substances is as follows (molar concentration): hexafluoropropylene oxide 60%, hexafluoropropylene 35%, perfluoroacetyl fluoride 4%, and perfluoromethoxyacetyl fluoride 1%.

[0036] Example 5 The present application provides a method for removing impurities in hexafluoropropylene oxide, which is as follows: hexafluoropropylene oxide gas containing acyl fluoride substances is transported to an alkali washing tower for alkali washing and impurity removal, and an alkaline buffer system is used in the alkali washing tower for alkali washing.

[0037] Specifically, the alkaline buffer system used in the present application is a dipotassium hydrogen phosphate-potassium hydroxide system (wherein the concentration of dipotassium hydrogen phosphate is 0.5 mol / L and the concentration of potassium hydroxide is 0.5 mol / L); the pressure in this embodiment is controlled at 0-0.1 MPa; the temperature in this embodiment is controlled at 20-30°C, the gas feed rate in this embodiment is 500 g / h, the alkali solution circulation volume is 100 L / h, and the filler used in the alkali washing tower in this embodiment is Dixon θ ring.

[0038] The composition of the hexafluoropropylene oxide gas containing acyl fluoride substances is as follows (molar concentration): hexafluoropropylene oxide 60%, hexafluoropropylene 35%, perfluoroacetyl fluoride 4%, and perfluoromethoxyacetyl fluoride 1%.

[0039] Example 6 The difference between this embodiment and embodiment 4 is that the pressure in this embodiment is controlled at 0.1-0.2 MPa; the remaining process steps, parameters and gas composition are the same as those in embodiment 4.

[0040] Example 7 The difference between this embodiment and embodiment 4 is that the pressure in this embodiment is controlled at 0.2-0.3 MPa; the remaining process steps, parameters and gas composition are the same as those in embodiment 4.

[0041] Example 8 The difference between this embodiment and embodiment 4 is that the pressure in this embodiment is controlled at 0.3-0.4 MPa; the remaining process steps, parameters and gas composition are the same as those in embodiment 4.

[0042] Example 9 The difference between this embodiment and embodiment 4 is that: in this embodiment, the temperature is controlled at 0-10°C; the remaining process steps, parameters and gas composition are the same as those in embodiment 4.

[0043] Example 10 The difference between this embodiment and embodiment 4 is that the temperature in this embodiment is controlled at 10-20° C.; the remaining process steps, parameters and gas composition are the same as those in embodiment 4.

[0044] Embodiment 11 The difference between this embodiment and embodiment 4 is that the temperature in this embodiment is controlled at 30-40° C.; the remaining process steps, parameters and gas composition are the same as those in embodiment 4.

[0045] Example 12 The difference between this embodiment and embodiment 4 is that the filler used in the alkali washing tower in this embodiment is ball ring; the remaining process steps, parameters and gas composition are the same as those in embodiment 4.

[0046] Embodiment 13 The difference between this embodiment and embodiment 4 is that the filler used in the alkali washing tower in this embodiment is Raschig ring; the remaining process steps, parameters and gas composition are the same as those in embodiment 4.

[0047] Comparative Example Comparative Example 1 The difference between this comparative example and Examples 1-5 is that in this comparative example, the hexafluoropropylene oxide gas containing acyl fluoride substances is transported to an alkali washing tower for alkali washing and impurity removal, and a 1 mol / L potassium hydroxide solution is used for alkali washing in the alkali washing tower.

[0048] Specifically, the pressure in this comparative example is controlled at 0-0.1 MPa; the temperature in this comparative example is controlled at 20-30° C., the gas feed rate in this comparative example is 500 g / h, the alkali solution circulation volume is 100 L / h, and the filler used in the alkali washing tower in this embodiment is Dixon θ ring.

[0049] The composition of the hexafluoropropylene oxide gas containing acyl fluoride substances is as follows (molar concentration): hexafluoropropylene oxide 60%, hexafluoropropylene 35%, perfluoroacetyl fluoride 4%, and perfluoromethoxyacetyl fluoride 1%.

[0050] Performance testing Test method: The gas passing through the alkali washing tower is subjected to infrared testing through the sampling port (each substance is quantitatively calibrated through the characteristic peak), the proportion of each component is calculated, and the remaining gas is introduced into a low-temperature storage tank at -80°C to obtain the total mass of the gas collected after alkali washing.

[0051] Residual amount of acyl fluoride = (mol amount of acyl fluoride after alkali washing / mol amount of acyl fluoride added) * 100% HFPO loss rate = 100% - (mol amount of HFPO after alkali washing / mol amount of HFPO added) * 100% Table 1 Performance test

[0052] Combining the performance test comparison in Table 1, we can find that: 1. By comparing Examples 1-5 with Comparative Example 1, it can be found that in Examples 3 and 4, the residual amount of acyl fluoride is low and the loss rate of HFPO is also low, which is suitable for alkali washing in this patent. In Examples 1 and 2, there is obvious residual acyl fluoride, and the buffer system is not suitable. In Example 5 and Comparative Example 1, although the acyl fluoride substances are absorbed very thoroughly, due to the strong alkalinity, there is obvious loss of HFPO, so it is not suitable for use in this patent; 2. By comparing Examples 6-13 with Example 4, it can be found that in Examples 6-8, the operating pressure of the alkali washing tower is increased, and the loss of hexafluoropropylene oxide after alkali washing is increased, which shows that when the pressure is controlled at 0-0.1MPa, the alkaline buffer solution can effectively remove the acyl fluoride impurities in the hexafluoropropylene oxide gas and greatly reduce the loss of hexafluoropropylene oxide; by comparing Examples 9-11 with Example 4, in Examples 4 and 10, the loss of hexafluoropropylene oxide after alkali washing is low and the acyl fluoride impurities in the hexafluoropropylene oxide gas can be effectively removed, so the temperature is 10-30°C, it is most appropriate to conduct the experiment; in Examples 12 and 13, there are obvious residues of acyl fluoride substances, combined with Example 4, it is shown that Dixon θ ring is most suitable as a filler for the alkali washing experiment of this patent.

[0053] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A method for removing impurities from hexafluoropropylene oxide, characterized in that: The following steps are involved: The hexafluoropropylene oxide gas containing acyl fluoride substances is transported to an alkali washing tower for alkali washing and impurity removal, and an alkaline buffer system is used in the alkali washing tower for alkali washing.

2. A method for removing impurities from hexafluoropropylene oxide according to claim 1, characterized in that: The pH of the alkaline buffer system is 8-12.

3. A method for removing impurities from hexafluoropropylene oxide according to claim 1, characterized in that: The alkaline buffer system includes any one of a glycine-sodium hydroxide buffer system, a glycine-potassium hydroxide buffer system, a borax-sodium hydroxide buffer system, a borax-potassium hydroxide buffer system, a sodium carbonate-sodium bicarbonate buffer system, a potassium carbonate-potassium bicarbonate buffer system, a sodium carbonate-sodium hydroxide buffer system, a potassium carbonate-potassium hydroxide buffer system, a disodium hydrogen phosphate-sodium hydroxide buffer system, and a dipotassium hydrogen phosphate-potassium hydroxide buffer system.

4. A method for removing impurities from hexafluoropropylene oxide according to claim 3, characterized in that: The alkaline buffer system is selected from any one of a sodium carbonate-sodium bicarbonate buffer system, a potassium carbonate-potassium bicarbonate buffer system, a sodium carbonate-sodium hydroxide buffer system, and a potassium carbonate-potassium hydroxide buffer system.

5. A method for removing impurities in hexafluoropropylene oxide according to claim 1, characterized in that: The pressure in the alkali washing tower is maintained at 0-0.3 MPa.

6. A method for removing impurities from hexafluoropropylene oxide according to claim 5, characterized in that: The pressure in the alkali washing tower is maintained at 0-0.1 MPa.

7. A method for removing impurities from hexafluoropropylene oxide according to claim 1, characterized in that: The temperature in the alkali washing tower is maintained at 10-40°C.

8. A method for removing impurities from hexafluoropropylene oxide according to claim 7, characterized in that: The temperature in the alkali washing tower is maintained at 10-30°C.

9. A method for removing impurities from hexafluoropropylene oxide according to claim 1, characterized in that: The packing in the alkali washing tower includes any one or more of Pall rings, Raschig rings and Dixon theta rings.

10. A method for removing impurities from hexafluoropropylene oxide according to claim 9, characterized in that: The packing in the caustic wash tower includes Dixon theta rings.

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