Method for preparing hexafluoroethane at low temperature

Abstract

The invention belongs to the technical field of fluoride preparation, and particularly relates to a method for preparing hexafluoroethane at low temperature. The method comprises the following steps: S1, liquefying tetrafluoroethylene: vacuumizing a reaction kettle, introducing tetrafluoroethylene, and cooling the reaction kettle with liquid nitrogen until tetrafluoroethylene is completely liquefied; s2, preparing hexafluoroethane through reaction of fluorine-nitrogen mixed gas and tetrafluoroethylene: introducing the fluorine-nitrogen mixed gas into the tetrafluoroethylene liquefied in the step S1 in a bubbling manner, stirring and reacting, and continuously stirring and reacting after the introduction of the fluorine-nitrogen mixed gas is finished, so as to obtain the hexafluoroethane; and S3, gas purification: after the reaction is finished, purging the gas phase space of the reaction kettle with nitrogen to remove residual gas in the reaction kettle, then heating the reaction kettle until the hexafluoroethane is gasified, and carrying out alkali washing, drying and rectification to obtain the high-purity hexafluoroethane. In the preparation method disclosed by the invention, the reaction is safer and easier to control under a low-temperature condition, and the preparation method disclosed by the invention is simple in process, high in reaction speed, high in yield, few in product impurity, easy to purify and suitable for industrial production.

Description

Technical Field

[0001] This application belongs to the technical field of fluoride preparation, and specifically relates to a method for preparing hexafluoroethane at low temperature. Background Art

[0002] Hexafluoroethane is a gas with properties such as non-flammability, colorlessness, odorlessness, easy liquefaction, high stability, non-toxicity, and non-corrosiveness. It has the functions of plasma etching and surface cleaning, and is widely used in the manufacturing process of semiconductors. It is also used as a coolant for supercomputers. As an ultra-fine cleaning gas for semiconductor oxide films, hexafluoroethane is mainly used in the production of highly integrated semiconductors. As a new substance with a relatively small output, hexafluoroethane currently has a large market prospect. Therefore, it is necessary to improve the synthesis ability of high-purity hexafluoroethane and explore new synthesis methods.

[0003] Currently, there are several methods for preparing hexafluoroethane as follows:

[0004] The technical document with the application number CN201610476508.8 discloses a method for preparing hexafluoroethane. First, cobalt trifluoride is prepared by using fluorine gas and cobalt difluoride, and then tetrafluoroethylene and cobalt trifluoride are reacted at 200°C to 300°C to obtain hexafluoroethane. The product needs to be subjected to alkali washing, water washing, adsorption, and rectification to obtain high-purity hexafluoroethane. The preparation steps are not only complex, but also the reaction needs to be carried out at high temperature; the Chinese patent with the publication number CN105461507B discloses a method for preparing hexafluoroethane at high temperature. A mixed gas of nitrogen trifluoride and nitrogen, and pentafluoroethane, under the conditions of a temperature of 350 - 450°C and a pressure of 0.1 - 0.15 MPa, is catalyzed by cobalt fluoride to obtain hexafluoroethane. The reaction temperature and pressure are relatively high, and there is a high possibility of by-products being generated due to the high reaction temperature; the Chinese patent with the publication number CN106242944B discloses a method for preparing electronic-grade hexafluoroethane. Hydrogen fluoride and pentafluoroethyl chloride are catalyzed by a novel catalyst in proportion to obtain crude hexafluoroethane at a temperature of 300 - 500°C, and then high-purity hexafluoroethane is obtained through rectification and adsorption treatment; the Chinese patent with the publication number CN12899707B discloses a method for preparing hexafluoroethane. Using alkali metal propionate as the raw material, hydrogen fluoride as the fluorination reagent, and alkali metal fluoride as the conductive medium, electrolytic fluorination is used to prepare hexafluoroethane.

[0005] In summary, the existing technologies for preparing hexafluoroethane have problems such as many product impurities, low yield, incomplete catalysis, difficult control of gas mixing ratio, high reaction temperature, slow reaction speed, and difficult purification. Therefore, there is an urgent need to propose a method for preparing hexafluoroethane with simple process, fast reaction speed, high yield, few product impurities, easy purification, and suitable for industrial production to solve the problems existing in the prior art. Summary of the Invention

[0006] In view of the problems existing in the existing technology for preparing hexafluoroethane, such as many impurities in the product, low yield, incomplete catalysis, difficult control of gas mixing ratio, high reaction temperature, slow reaction rate, and difficult purification, this application proposes a method for preparing hexafluoroethane with simple process, fast reaction rate, high yield, few impurities in the product, easy purification, and suitable for industrial production to solve the problems existing in the prior art.

[0007] The specific solution of this application is as follows:

[0008] A method for preparing hexafluoroethane at low temperature, comprising the following steps:

[0009] Step S1. Liquefaction of tetrafluoroethylene:

[0010] The reaction kettle is evacuated, and then tetrafluoroethylene is introduced. At the same time, the reaction kettle is cooled with liquid nitrogen until all tetrafluoroethylene is liquefied.

[0011] Step S2. Reaction of fluorine-nitrogen mixed gas with tetrafluoroethylene to prepare hexafluoroethane:

[0012] The chemical reaction formula is: F2 + C2F4 → C2F6

[0013] The fluorine-nitrogen mixed gas is introduced into the liquefied tetrafluoroethylene in step S1 in a bubbling manner and stirred for reaction. After the introduction of the fluorine-nitrogen mixed gas is completed, the stirring reaction continues to obtain hexafluoroethane.

[0014] Preferably, the pressure of the evacuation is -0.1 MPa.

[0015] Preferably, the reaction kettle is cooled with liquid nitrogen to -95 to -80 °C.

[0016] Preferably, the purity of the tetrafluoroethylene is ≥99.99%.

[0017] Preferably, in the fluorine-nitrogen mixed gas, the volume fraction of fluorine gas is 10 to 50%, and the rest is nitrogen.

[0018] Preferably, the molar ratio of fluorine gas to tetrafluoroethylene in the fluorine-nitrogen mixed gas is m, and 1 < m ≤ 1.1.

[0019] Preferably, for the reaction conditions, the reaction temperature is -95 to -80 °C, the reaction pressure is 0 to 0.1 MPa, and the time for continuing the stirring reaction after the introduction of the fluorine-nitrogen mixed gas is completed is 1 h.

[0020] Preferably, for the reaction conditions, the pressure is 0 to 0.05 MPa.

[0021] Preferably, the flow rate of the introduced fluorine-nitrogen mixed gas is 300 to 500 mL / min.

[0022] Preferably, the step further includes

[0023] Step S3. Gas purification:

[0024] After the reaction is completed, the gas phase space of the reaction kettle is purged with nitrogen to remove the residual gas in the reaction kettle, and then the temperature in the reaction kettle is raised to vaporize hexafluoroethane, which is then obtained as high-purity hexafluoroethane after alkali washing, drying, and rectification.

[0025] Preferably, the material of the reaction kettle is Inconel alloy or acid-resistant nickel alloy.

[0026] The beneficial effects of this application are as follows:

[0027] (1) In the preparation method of this application, a fluorine-nitrogen mixed gas is used as the fluorine gas source, which is safer than directly using pure fluorine gas. The presence of nitrogen can dilute the concentration of fluorine gas and has a certain protective effect on the reaction system.

[0028] (2) In the preparation method of this application, the reaction is carried out at a low temperature (-95 to -80 °C), which is safer and easier to control. Compared with other current methods for preparing hexafluoroethane by high-temperature reactions, the possibility of combustion, explosion, and fire during the experiment is reduced.

[0029] (3) In the preparation method of this application, the reaction is carried out by reacting a fluorine-nitrogen mixed gas with tetrafluoroethylene. There are few types of materials, the reaction process is simple, and no catalyst or other materials are involved, reducing the occurrence of possible impurities.

[0030] (4) In the preparation method of this invention, the fluorine-nitrogen mixed gas is introduced into liquid tetrafluoroethylene at a certain rate and the reaction is carried out in a bubbling manner, accompanied by continuous stirring of the reaction kettle, and the molar amount of fluorine gas is in excess, which can make the raw material tetrafluoroethylene react fully and thoroughly, with very few amounts and types of impurities generated, and high yield and purity.

[0031] (5) The preparation method of this application is simple, greatly reducing the production cost. Specific embodiments

[0032] To further illustrate the technical means and effects adopted by this application to achieve the intended invention purpose, the following describes in detail the specific embodiments, structures, features, and their effects according to this application in combination with preferred embodiments.

[0033] Example 1

[0034] This example provides a method for preparing hexafluoroethane at low temperature, including the following steps:

[0035] Step S1. Liquefaction of tetrafluoroethylene:

[0036] To avoid the reaction of the reactor with fluorine gas in the fluorine-nitrogen mixed gas, the material of the reactor should be a material that can resist gas corrosion. Since the lowest temperature resistance of carbon steel is -30°C, and liquid nitrogen is used as the refrigerant in the jacket of the reactor, which exceeds the temperature resistance range of carbon steel material, the material of the reactor cannot be carbon steel. A material with both low-temperature resistance and corrosion resistance should be selected. Therefore, the material of the reactor in this embodiment is selected as Inconel alloy.

[0037] Tetrafluoroethylene with a purity of 99.99% (a large part of the impurities in the tetrafluoroethylene raw material are chlorine-containing compounds, and chlorine-containing compounds are likely to form an azeotrope with the product hexafluoroethane. If the hexafluoroethane is rectified and purified later, it is difficult to separate. Therefore, the higher the purity of tetrafluoroethylene, the more beneficial it is for the preparation of high-purity hexafluoroethane) is dried to remove moisture before being introduced into the reactor to avoid moisture affecting subsequent reactions. The reactor with a volume of 2L is evacuated to a pressure of -0.1MPa, and then tetrafluoroethylene is introduced. At the same time, the reactor is cooled to -95°C with liquid nitrogen. Since the introduction of tetrafluoroethylene causes the pressure in the reactor to gradually decrease, when the pressure in the reactor no longer decreases, the temperature of the reactor is maintained at -95°C for 0.5 hours to ensure that all tetrafluoroethylene is liquefied;

[0038] Step S2. Preparation of hexafluoroethane by reacting fluorine-nitrogen mixed gas with tetrafluoroethylene:

[0039] Then, a fluorine-nitrogen mixed gas (the volume fraction of fluorine gas in the fluorine-nitrogen mixed gas is 50%, and the volume fraction of nitrogen gas is 50%) is introduced into the reactor at a ventilation rate of 400 mL / min. The fluorine-nitrogen mixed gas contacts and reacts with the liquid tetrafluoroethylene in the reactor in a bubbling manner. The reactor is continuously stirred during the ventilation reaction to ensure that the reactants are fully in contact and react, preventing local reactions. The pressure during the whole reaction process is 0 - 0.05MPa, and the temperature during the whole reaction process is stably controlled at about -95°C. When the molar ratio of fluorine gas to tetrafluoroethylene in the introduced fluorine-nitrogen mixed gas is 1.1, the introduction of the fluorine-nitrogen mixed gas is stopped, and the reaction conditions are maintained for 1h.

[0040] Step S3. Gas purification:

[0041] After the reaction is completed, the gas phase space of the reactor is purged with nitrogen to remove the residual gas in the reactor. Then, the temperature in the reactor is raised to vaporize hexafluoroethane. Since the vast majority of the product hexafluoroethane is hexafluoroethane, as well as a small amount of fluorine gas, nitrogen gas, etc., in order to obtain higher-purity hexafluoroethane, hexafluoroethane is subjected to alkali washing to remove fluorine gas, drying to remove moisture, and rectification and purification to remove the remaining small amounts of impurities such as oxygen and nitrogen, and then high-purity hexafluoroethane is obtained. The high-purity hexafluoroethane is detected with a GC6600 type gas chromatograph, and the results are shown in Table 1.

[0042] Example 2

[0043] The material of the reactor in this embodiment is selected as nickel-chromium-iron alloy. Tetrafluoroethylene with a purity of 99.999% is dried to remove moisture before being introduced into the reactor to avoid the influence of moisture on subsequent reactions. The reactor with a volume of 2L is evacuated to a pressure of -0.1MPa, and then tetrafluoroethylene is introduced. At the same time, the reactor is cooled to -85°C with liquid nitrogen. Due to the introduction of tetrafluoroethylene, the pressure in the reactor gradually decreases. When the pressure in the reactor no longer decreases, the temperature of the reactor is maintained at -85°C for 0.5 hours to ensure that all tetrafluoroethylene is liquefied;

[0044] Step S2. React fluorine-nitrogen mixed gas with tetrafluoroethylene to prepare hexafluoroethane:

[0045] Then, a fluorine-nitrogen mixed gas (the volume fraction of fluorine in the fluorine-nitrogen mixed gas is 10%, and the volume fraction of nitrogen is 90%) is introduced into the reactor at a ventilation rate of 300 mL / min. The fluorine-nitrogen mixed gas contacts and reacts with the liquid tetrafluoroethylene in the reactor in a bubbling manner, and the reactor is continuously stirred during the ventilation reaction process. The pressure during the whole reaction process is 0 - 0.05MPa, and the temperature during the whole reaction process is stably controlled at about -85°C. When the molar ratio of fluorine to tetrafluoroethylene in the introduced fluorine-nitrogen mixed gas is 1.1, the introduction of the fluorine-nitrogen mixed gas is stopped, and the reaction conditions are maintained for 1h.

[0046] Step S3. Gas purification:

[0047] After the reaction is completed, the gas phase space of the reactor is purged with nitrogen to remove the residual gas in the reactor, and then the temperature in the reactor is raised to vaporize hexafluoroethane. In order to obtain hexafluoroethane with higher purity, hexafluoroethane is subjected to alkali washing to remove fluorine gas, drying to remove moisture, and rectification purification to remove other minor impurities such as oxygen and nitrogen, and then high-purity hexafluoroethane is obtained. The high-purity hexafluoroethane is detected with a GC6600 type gas chromatograph, and the results are shown in Table 1.

[0048] Example 3

[0049] The material of the reactor in this embodiment is selected as nickel-chromium-iron alloy. Tetrafluoroethylene with a purity of 99.999% is dried to remove moisture before being introduced into the reactor to avoid the influence of moisture on subsequent reactions. The reactor with a volume of 2L is evacuated to a pressure of -0.1MPa, and then tetrafluoroethylene is introduced. At the same time, the reactor is cooled to -80°C with liquid nitrogen. Due to the introduction of tetrafluoroethylene, the pressure in the reactor gradually decreases. When the pressure in the reactor no longer decreases, the temperature of the reactor is maintained at -80°C for 0.5 hours to ensure that all tetrafluoroethylene is liquefied;

[0050] Step S2. React fluorine-nitrogen mixed gas with tetrafluoroethylene to prepare hexafluoroethane:

[0051] Then, a fluorine-nitrogen mixed gas (the volume fraction of fluorine gas in the fluorine-nitrogen mixed gas is 40%, and the volume fraction of nitrogen gas is 60%) is introduced into the reaction kettle at a ventilation rate of 500 mL / min. The fluorine-nitrogen mixed gas reacts with the liquid tetrafluoroethylene in the reaction kettle in a bubbling manner, and the reaction kettle is continuously stirred during the ventilation reaction process. The pressure of the entire reaction process is 0 - 0.05 MPa, and the temperature of the entire reaction process is stably controlled at about -80°C. When the molar ratio of fluorine gas to tetrafluoroethylene in the introduced fluorine-nitrogen mixed gas is 1.05, the introduction of the fluorine-nitrogen mixed gas is stopped, and the reaction conditions are maintained for 1 h.

[0052] Step S3. Gas purification:

[0053] After the reaction is completed, the gas phase space of the reaction kettle is purged with nitrogen to remove the residual gas in the reaction kettle, and then the temperature in the reaction kettle is raised to vaporize hexafluoroethane. In order to obtain hexafluoroethane with higher purity, hexafluoroethane is subjected to alkali washing to remove fluorine gas, drying to remove moisture, and rectification purification to remove other minor impurities such as oxygen and nitrogen, and then high-purity hexafluoroethane is obtained. The high-purity hexafluoroethane is detected with a GC6600 type gas chromatograph, and the results are shown in Table 1.

[0054] Example 4

[0055] In this example, the material of the reaction kettle is made of acid-resistant nickel alloy. Tetrafluoroethylene with a purity of 99.99% is dried to remove moisture before being introduced into the reaction kettle to avoid the influence of moisture on subsequent reactions. The reaction kettle with a volume of 2 L is evacuated to a pressure of -0.1 MPa, and then tetrafluoroethylene is introduced. At the same time, the reaction kettle is cooled to -85°C with liquid nitrogen. Due to the introduction of tetrafluoroethylene, the pressure of the reaction kettle gradually decreases. When the pressure of the reaction kettle no longer decreases, the temperature of the reaction kettle is maintained at -85°C for 0.5 h to ensure that all tetrafluoroethylene is liquefied;

[0056] Step S2. Preparation of hexafluoroethane by the reaction of fluorine-nitrogen mixed gas with tetrafluoroethylene:

[0057] Then, a fluorine-nitrogen mixed gas (the volume fraction of fluorine gas in the fluorine-nitrogen mixed gas is 10%, and the volume fraction of nitrogen gas is 90%) is introduced into the reaction kettle at a ventilation rate of 300 mL / min. The fluorine-nitrogen mixed gas reacts with the liquid tetrafluoroethylene in the reaction kettle in a bubbling manner, and the reaction kettle is continuously stirred during the ventilation reaction process. The pressure of the entire reaction process is 0.05 - 1 MPa, and the temperature of the entire reaction process is stably controlled at about -85°C. When the molar ratio of fluorine gas to tetrafluoroethylene in the introduced fluorine-nitrogen mixed gas is 1.05, the introduction of the fluorine-nitrogen mixed gas is stopped, and the reaction conditions are maintained for 1 h.

[0058] Step S3. Gas purification:

[0059] After the reaction is completed, the gas phase space of the reaction kettle is purged with nitrogen to remove the residual gas in the reaction kettle, and then the temperature in the reaction kettle is raised to vaporize hexafluoroethane. In order to obtain higher purity hexafluoroethane, hexafluoroethane is subjected to alkali washing to remove fluorine gas, drying to remove moisture, and rectification purification to remove other minor impurities such as oxygen and nitrogen, and then high-purity hexafluoroethane is obtained. The high-purity hexafluoroethane is detected with a GC6600 gas chromatograph, and the results are shown in Table 1.

[0060] Comparative Example 1

[0061] Compared with Example 1, the product in this comparative example was not subjected to alkali washing, drying, and rectification.

[0062] Comparative Example 2

[0063] The distinguishing feature of this comparative example from Example 1 is that the molar ratio of fluorine gas to tetrafluoroethylene in the fluorine-nitrogen mixed gas is 1.

[0064] Comparative Example 3

[0065] The distinguishing feature of this comparative example from Example 1 is that the reaction temperature is -40°C.

[0066] Comparative Example 4

[0067] The distinguishing feature of this comparative example from Example 1 is that the purity of tetrafluoroethylene is 96%.

[0068] The mixed gas obtained from the reaction in each of the above examples was subjected to gas chromatographic analysis, and the composition results are shown in Table 1 below.

[0069] Table 1

[0070]

[0071] Remarks: 1. The data is from a GC6600 gas chromatograph; 2. Nitrogen in the mixed gas is not included in the above table.

[0072] It can be seen from Examples 1 to 4 that for the preparation method of the present application, the conversion rate of tetrafluoroethylene and the yield of hexafluoroethane are both very high. For the reaction products of all the above examples, the content of hexafluoroethane is greater than 90%, and at the same time, it has a very high selectivity and a small amount of by-products. It can be seen from Examples 1 to 4 and in combination with Comparative Example 3 that when the reaction temperature is relatively low, side reactions such as over-fluorination, cracking, and polymerization are reduced, and the heat release during the reaction is more obvious at low temperatures, promoting the reaction to proceed in the direction of generating hexafluoroethane, with a higher yield of hexafluoroethane and fewer impurities. It can be seen from Examples 1 to 4 and in combination with Comparative Example 2 that an excess of fluorine gas is helpful for the progress of the reaction and the conversion of tetrafluoroethylene. It can be seen from Examples 1 to 4 and in combination with Comparative Example 1 that after the reaction products are subjected to subsequent purification treatments such as alkali washing, drying, and rectification, and it can be seen from Examples 1 to 4 and in combination with Comparative Example 4 that the higher the purity of tetrafluoroethylene, the higher the purity of the product hexafluoroethane.

[0073] As described above, it is only the preferred embodiment of the present application, and there is no restriction on the present application in any form. Although the present application has been disclosed as above with the preferred embodiment, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to equivalent embodiments with equivalent changes within the scope of the technical solution of the present application. However, as long as it does not depart from the content of the technical solution of the present application, any modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application still fall within the scope of the technical solution of the present application.

Claims

1. A method for preparing hexafluoroethane at low temperature, characterized in that, It includes the following steps: Step S1. Liquefaction of tetrafluoroethylene: The reaction kettle is evacuated, and then tetrafluoroethylene is introduced. At the same time, the reaction kettle is cooled with liquid nitrogen until all tetrafluoroethylene is liquefied. Step S2. Preparation of hexafluoroethane by reaction of fluorine-nitrogen mixed gas with tetrafluoroethylene: The fluorine-nitrogen mixed gas is introduced into the liquefied tetrafluoroethylene in Step S1 in a bubbling manner and stirred for reaction. After the introduction of the fluorine-nitrogen mixed gas ends, stirring reaction continues to obtain hexafluoroethane.

2. The method for preparing hexafluoroethane at low temperature according to claim 1, wherein The pressure of the evacuation is -0.1 MPa.

3. A method for preparing hexafluoroethane at low temperature according to claim 1, characterized in that, The reaction kettle is cooled to -95 to -80 °C with liquid nitrogen.

4. A method for preparing hexafluoroethane at low temperature according to claim 1, characterized in that, The purity of the tetrafluoroethylene is ≥99.99%.

5. A method for preparing hexafluoroethane at low temperature according to claim 1, characterized in that, In the fluorine-nitrogen mixed gas, the volume fraction of fluorine gas is 10 - 50%, and the rest is nitrogen.

6. A method for preparing hexafluoroethane at low temperature according to claim 1, characterized in that, The molar ratio of fluorine gas to tetrafluoroethylene in the fluorine-nitrogen mixed gas is m, where 1 < m ≤ 1.

1.

7. A method for preparing hexafluoroethane at low temperature according to claim 1, characterized in that, For the reaction conditions, the reaction temperature is -95 to -80 °C, the reaction pressure is 0 to 0.1 MPa, and the time for continuous stirring reaction after the introduction of the fluorine-nitrogen mixed gas ends is 1 h.

8. A method for preparing hexafluoroethane at low temperature according to claim 1, characterized in that, The flow rate of the introduced fluorine-nitrogen mixed gas is 300 - 500 mL / min.

9. A method for preparing hexafluoroethane at low temperature according to claim 1, characterized in that, The said steps further include Step S3. Gas purification: After the reaction ends, the gas phase space of the reaction kettle is purged with nitrogen to remove the residual gas in the reaction kettle. Then, the temperature in the reaction kettle is raised to vaporize hexafluoroethane, and high-purity hexafluoroethane is obtained after alkali washing, drying, and rectification.

10. A method for preparing hexafluoroethane at low temperature according to claim 1, characterized in that, The material of the reaction kettle is chromium-nickel-iron alloy or acid-resistant nickel alloy.

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