Production and use of octafluoropropane

Manufacturing method and use of octafluorinated propane

The present invention relates to the manufacturing method of octafluorinated propane, octafluorinated propane products and their uses.

Propane octafluoride is used, for example, as a dry etching gas and cleaning gas in the manufacturing process of semiconductor devices. The manufacturing method is known,

(1) A method of directly fluorinating hexafluoropropylene with fluorine gas (Japanese Patent Publication No. 62-61572)

(2) Electrolytic fluorination of hexafluoropropylene in hydrogen fluoride (Japanese Patent Publication No. 62-61115)

(3) The method of reacting hexafluoropropylene and fluorine in the presence of a catalyst (Special Gazette No. 1-45455)

(4) A method of reacting hexafluoropropylene with higher metal fluorides (Japanese Patent Publication No. 62-54777), etc.

However, in these methods, tetrafluoromethane (CF₄), hexafluoroethane (C₂F₆) And other by-products are produced by cracking, and C is produced by free radical addition₆F₁₂, C6F₁₄Etc., or cyclization addition to produce a four-membered ring, etc., all reduce the yield and selectivity of the target octafluoropropane. Moreover, among these impurities, there are compounds that are difficult to separate by distillation, and consequently there is a problem that it is difficult to obtain high-purity octafluoropropane. Especially when hexafluoropropylene is used as the starting material, the impurity contained in chloropentafluoroethane (CFC-115) hardly reacts with fluorine gas, and is mixed in the target octafluoropropane. It is difficult to separate by distillation due to the close boiling point. Prepare high-purity octafluorinated propane.

The problem to be solved by the invention

The present invention is completed under this background, and is to provide a method for manufacturing octafluorinated propane used in the manufacturing process of semiconductor devices. High-purity octafluorinated propane and its use are the subject of the present invention.

Means to solve the problem

The inventors of the present invention carefully studied the solution of the above-mentioned problems, and found that if the use includes (1) in the presence of a fluorinated catalyst, the process of obtaining 2H-heptafluoropropane by reacting hexafluoropropene and hydrogen fluoride in the gas phase at 150 to 450°C , And (2) the step of reacting the 2H-heptafluoropropane obtained in step (1) in the gas phase at 250 to 500°C to obtain octafluoropropane without a catalyst, to obtain high-purity octafluoropropane, and Complete the present invention.

That is, the present invention (I) is characterized in that it includes (1) the step of reacting hexafluoropropylene with hydrogen fluoride in the gas phase at 150 to 450°C in the presence of a fluorinated catalyst to obtain 2H-heptafluoropropane, and (2) ) A method for producing octafluoropropane by reacting the 2H-heptafluoropropane obtained in step (1) in a gas phase at 250 to 500°C without a catalyst. In the present invention (I), hexafluoropropene contains at least one Compounds selected from the group consisting of dichlorodifluoromethane, chlorodifluoromethane, chloropentafluoroethane, chlorotetrafluoroethane and chlorotrifluoroethylene. In step (1), the fluorination catalyst is chromium oxide As the main component, adding at least one bulk catalyst selected from the group consisting of indium, zinc and nickel, and a molar ratio of hydrogen fluoride/hexafluoropropylene in the range of 0.8 to 3 is a preferred embodiment.

In addition, the present invention (I) is based on the step (2) before the step of removing impurities contained in 2H-heptafluoropropane. The impurities are at least one selected from the group consisting of tetrafluoromethane, trifluoromethane, chlorotrifluoromethane, and hexafluoroethane. For compounds composed of alkane and pentafluoroethane, the impurity removal step is a distillation step, and the chlorine compound contained in 2H-heptafluoropropane below 0.01% by volume is a preferred embodiment.

Furthermore, in the present invention (I), step (2) is carried out in the presence of a diluent gas, and the diluent gas system is selected from at least one of the group consisting of hydrogen fluoride, tetrafluoromethane, hexafluoroethane and octafluoropropane, In step (2), the molar ratio of fluorine gas/2H-heptafluoropropane is in the range of 0.9 to 1.5, and the concentration of 2H-heptafluoropropane at the reactor inlet is below 8 mol% is a preferred embodiment.

Moreover, the present invention (I) includes recycling at least part of the outlet gas of step (2) as the dilution gas of step (2), and making at least part of the outlet gas of step (2) and The step of reacting hydrofluorocarbons to remove unreacted fluorine contained in the outlet gas. The hydrofluorocarbons are composed of at least one selected from trifluoromethane, tetrafluoroethane, pentafluoroethane, and 2H-heptafluoropropane Group of compounds, separate the hydrogen fluoride contained in the outlet gas of step (2), return the separated hydrogen fluoride to step (1) and/or step (2), and separate at least a part of the gas from which hydrogen fluoride has been separated The octafluorinated propane, the rest of the gas is returned to step (1) and/or step (2) as a preferred embodiment.

The system of the present invention (II) is characterized in that: an octafluorinated propane product with a purity of more than 99.995% by volume is a preferred embodiment with the total amount of compounds containing chlorine atoms and cyclic compounds in the molecule being below 50 volume ppm.

In addition, the present invention (III) is characterized by the etching gas containing the above-mentioned octafluorinated propane product, and the present invention (IV) is characterized by the cleaning gas containing the above-mentioned fluorinated propane product.

The present invention will be described in detail below.

The hexafluoropropylene (CF) used in the present invention (I)₃CF=CF₂), for example, chlorodifluoromethane (CHClF₂) Thermal cracking to produce tetrafluoroethylene (CF₂=CF₂The by-product in the process of ), or as described in JP 4-145033, is prepared by chlorofluorination dehalogenation of propane, propylene or partially halogenated C3 acyclic hydrocarbons. However, the hexafluoropropylene obtained by these methods is mostly mixed with impurities of compounds containing chlorine atoms such as dichlorodifluoromethane, chlorodifluoromethane, chloropentafluoroethane, chlorotetrafluoroethane, chlorotrifluoroethylene, etc. . The present invention provides a method for producing octafluoropropane that can be used as a starting material even with hexafluoropropene containing these impurities. Here, the intermediate 2H-heptafluoropropane, the target product octafluoropropane and the impurities The boiling point is shown in Table 1.

<tables><img file="TWI242545B_D0001.tif" /></tables>

As can be seen from the boiling points shown in Table 1, the compounds with chlorine atoms in the molecule contained in the starting material hexafluoropropene have a boiling point close to that of octafluoropropane, and it is difficult to separate by distillation alone.

For this reason, the manufacturing method of (I) octafluoropropane of the present invention is a step of preparing 2H-heptafluoropropane by reacting hexafluoropropylene and hydrogen fluoride in the gas phase at 150 to 450°C in the presence of a fluorinated catalyst ( 1). Step (1) has the following two main points. which is,

[1] When the hexafluoropropylene is directly fluorinated with fluorine gas, or in the presence of catalysts, advanced metal fluorides, etc., when it is directly fluorinated with fluorine gas, it undergoes a carbon-carbon bond cleavage reaction, resulting in free radicals. Addition reactions, cyclization addition reactions, etc. produce various by-products. Therefore, not only the yield but also the selectivity is low, and it is also difficult to obtain high-purity octafluoropropane. In the present invention, hexafluoropropylene is added with hydrogen fluoride in the presence of a catalyst to obtain an intermediate 2H-heptafluoropropane with good yield and selectivity, and its reaction can inhibit the generation of by-products.

[2] As mentioned above, most hexafluoropropylene contains impurities of compounds with chlorine atoms in the molecule, and these compounds are difficult to separate by distillation. In the present invention, hydrogen fluoride is added to hexafluoropropene to obtain the intermediate 2H-heptafluoropropane. At the same time, the compound containing chlorine atom in the molecule is fluorinated with hydrogen fluoride, which can be converted into a compound that is easy to be separated by distillation.

The addition reaction of hexafluoropropylene with hydrogen fluoride is carried out according to the following formula (1) in the presence of a fluorinated catalyst.

CF₃CF=CF₂+HFCF₃CHFCF₃(1) The fluorinated catalyst can be the commonly used chromium-based catalyst. Hexafluoropropylene contains chlorine-based impurities. When the chlorine-based impurities are fluorinated into other compounds, due to the high reaction temperature, the catalyst has excellent activity (performance) and stability (lifetime). The main component is chromium oxide. It is better to add a bulk catalyst of at least one of indium, zinc and nickel. Supported catalysts (such as alumina carriers) are also possible, but based on activity, the stability is still better with bulk catalysts. Before these catalysts are used in the reaction, they can be activated by fluorination treatment with hydrogen fluoride and then used in the reaction.

In step (1), although the content of impurities in the hexafluoropropylene varies according to the type and content of impurities, the reaction temperature is in the range of 150 to 450°C, preferably 200 to 350°C. When CFC-115 is an impurity in hexafluoropropylene, the reaction temperature is preferably in the range of 350 to 450°C, preferably 350 to 400°C. When the reaction temperature is above 450°C, the stability of the catalyst tends to decrease. If the temperature is below 150°C, the conversion rate of the target reaction will be low, and the fluorination reaction of impurity compounds will be slow and poor.

In addition, the molar ratio (HF/FC-1216) of hydrogen fluoride to hexafluoropropylene (FC-1216) is preferably 0.8 to 3.0, and more preferably 1.0 to 2.0. When the molar ratio of hydrogen fluoride to hexafluoropropene is below 0.8, the conversion rate of hexafluoropropene is low, and when it is above 3.0, there are poor cost requirements such as unreacted HF recovery equipment.

As mentioned above, the raw material hexafluoropropylene may contain impurities, compounds with chlorine atoms in the molecule, these impurities are usually difficult to separate by distillation. Compounds containing chlorine atoms in the molecule include chlorodifluoromethane, chloropentafluoroethane, dichlorodifluoromethane, chlorotrifluoroethylene, and chlorotetrafluoroethane. The present invention (I) is a step of mainly reacting hexafluoropropylene and hydrogen fluoride to obtain 2H-heptafluoropropane in the presence of a fluorinated catalyst, and converting these chlorine-containing compounds into other fluorine-containing compounds that are easy to distill and separate.

For example, the chlorine compound can be converted into another fluorine-containing compound by the reaction of the following formulas (2) to (5).

CHClF₂+HFCHF₃+HCl (2) CF₂=CClF+HFCF₃CHClF (3) CF₃CHClF+HFCF₃CHF₂+HCl (4) CF₃CClF₂+HFCF₃CF₃+HCl (5) The boiling points of these fluorinated compounds and intermediate 2H-heptafluoropropane are shown in Table 2.

<tables><img file="TWI242545B_D0002.tif" /></tables>

As can be seen from Table 2, the boiling point difference between the intermediate 2H-heptafluoropropane and the compound fluorinated by the above reaction is greatly increased, and can be easily separated by distillation.

Secondly, from step (1), the gas whose main component is 2H-heptafluoropropane is introduced into a deacidification step for separating hydrogen fluoride and unreacted hydrogen fluoride. Hydrogen fluoride and hydrogen fluoride are separated by distillation, and the alkaline aqueous solution is used for hydrogen chloride neutralization treatment. In addition, hydrogen fluoride can be returned to the fluorination step of hexafluoropropylene, or it can be neutralized with an aqueous alkali solution. After the hydrogen chloride and hydrogen fluoride are separated in the deacidification step, the gas with 2H-heptafluoropropane as the main component is then carried out to step (2), but it is better to introduce the distillation tower beforehand to remove the impurities contained in the 2H-heptafluoropropane.

The impurities combined with 2H-heptafluoropropane include tetrafluoromethane, trifluoromethane, chlorotrifluoromethane, hexafluoropropylene, pentafluoroethane, etc. These impurities are preferably removed by distillation. In the distillation tower, there are low-boiling components such as tetrafluoromethane, trifluoromethane, chlorotrifluoromethane, hexafluoroethane, and pentafluoroethane from the top of the tower, and 2H-heptafluoropropane from the bottom of the tower. The gas with 2H-heptafluoropropane as the main component can be used as the raw material for the direct fluorination reaction with fluorine gas, but regardless of whether the deacidification step is distilled, the chlorine compound impurities contained in 2H-heptafluoropropane are preferably less than 0.01% by volume, 0.005 The volume% or less is more preferable.

Next, step (2) will be explained.

Step (2) is to react the 2H-heptafluoropropane obtained from the fluorination step of the above step (1) with fluorine gas at a gas phase reaction temperature of 250 to 500°C without a catalyst to obtain the direct fluorination of octafluoropropane The reaction steps have the following three main points. That is, [1] When producing perfluorocarbons by reacting hydrofluorocarbons with fluorine gas, very large heat of reaction is accompanied. The heat of reaction is proportional to the number of moles of fluorine reacted per molecule. The more fluorine, the greater the heat of reaction. It is easy to break the carbon-carbon bond, polymerize, add cyclization, and sometimes explode, reducing the yield. It becomes a problem in industrial manufacturing and operation. Therefore, methods to suppress the intense heat of reaction in the direct fluorination method include a method of diluting fluorine with other inert gases (such as nitrogen, helium, etc.), and a method of diluting the matrix organic matter. Inert gases such as nitrogen, helium, etc., are not an advantageous method for separation and purification from the target perfluorocarbon by distillation and cost considerations. The present invention (I) is selected from hydrogen fluoride, tetrafluoromethane, hexafluoroethane, and At least one type of fluorinated propane is used as a diluent gas to solve the above problems.

[2] In the present invention (I), the reactor inlet concentration of the reaction substrate 2H-heptafluoropropane is adjusted with the dilution gas below the explosive range for the reaction, specifically, the reaction is performed at 8 mol% or less. For the direct fluorination reaction using fluorine gas as described above, because the highly reactive fluorine gas is used, matrix organic compounds (especially hydrogen-containing compounds) are more likely to burn or explode due to fluorine gas. In step (2), because 2H-heptafluoropropane containing hydrogen atoms is used as the substrate, it is important to prevent the explosion of 2H-heptafluoropropane and fluorine gas. In order to prevent explosion, the composition of the mixed gas must be outside the explosion range. The inventors discussed the explosion range of 2H-heptafluoropropane and fluorine gas and found that the lower limit of the explosion range of 2H-heptafluoropropane is below 8 mol%. Set the reactor inlet concentration of 2H-heptafluoropropane within a safe range.

[3] The direct fluorination reaction by reacting 2H-heptafluoropropane with fluorine gas, although using excess 2H-heptafluoropropane compared with fluorine gas, does not require the step of removing fluorine gas, but it brings great difficulties to its subsequent separation and purification. . In step (2) of (I) of the present invention, in order to improve the reaction efficiency, an excess of moles of fluorine gas can be used relative to 2H-heptafluoropropane. When an excess of moles of fluorine gas is used, the reaction product gas flowing out of the reaction step mainly contains perfluorinated gas. Carbides, and excess fluorine gas other than hydrogen fluoride. The method for treating the remaining fluorine gas is known to be a method of reacting inorganic oxides such as alumina and soda lime. This method is not good because water is generated during the reaction, which causes corrosion of equipment materials. In the present invention (I), the excess fluorine gas can be removed by contacting the hydrofluorocarbon with a stoichiometric ratio of 1.1 times the mole.

The direct fluorination reaction of 2H-heptafluoropropane and fluorine gas is carried out according to the following formula (6).

CF₃CHFCF₃+F₂CF₃CF₂CF₃+HF (6) Catalyst can be used for this reaction, but it can also be carried out without catalyst. In addition, as mentioned above, the direct fluorination reaction of the reaction between HFCs and fluorine gas has a large reaction heat, and the reaction is preferably carried out in the presence of a diluent gas. The diluent gas can be at least one selected from hydrogen fluoride, tetrafluoromethane, hexafluoroethane, and octafluoropropane, preferably hydrogen fluoride and/or octafluoride propane, and more preferably a gas rich in hydrogen fluoride.

The method of introducing the dilution gas is to introduce either or both of the 2H-heptafluoropropane and fluorine gas into the reactor before being diluted with the dilution gas. The reactor inlet concentration of the substrate 2H-heptafluoropropane is preferably below 8 mol% below the explosion range, more preferably below 6%. The concentration of the fluorine gas at the reactor inlet is preferably a concentration of fluorine gas/2H-heptafluoropropane molar ratio in the range of 0.9 to 1.5, more preferably in the range of 0.9 to 1.2. The fluorine gas concentration when the molar ratio of fluorine gas/2H-heptafluoropropane is below 0.9 is not good because the conversion rate of 2H-heptafluoropropane is low, and the cost of removing unreacted fluorine gas must be borne when the molar ratio of 2H-heptafluoropropane is above 1.5. In addition, when the molar ratio of fluorine gas/2H-heptafluoropropane is above 1.5, when the outlet gas of step (2) is recycled and reused as the dilution gas of step (2), the fluorine concentration in the circulating gas (dilution gas) becomes higher. There will be problems such as explosions and so on.

The 2H-heptafluoropropane and fluorine gas diluted with diluent gas to a concentration below the explosive range can react in the gas phase. The reaction temperature can be 250 to 500°C, preferably 350 to 450°C. When the reaction temperature is below 250°C, the reaction is slow. When the temperature is above 500°C, the carbon-carbon bond of the target octafluoropropane tends to break.

The outlet gas of this step (2) is mainly hydrogen fluoride and octafluoropropane. In the present invention (I), at least a part of the outlet gas can be recycled, and then used as the dilution gas of step (2). The outlet gas sometimes contains unreacted fluorine gas. The method of detecting the concentration of unreacted fluorine gas can be to continuously introduce a part of the outlet gas into a continuous flowing solution of metal iodide to generate iodine, and then determine the concentration of the solution. A method to calculate the concentration of unreacted fluorine gas by continuously quantifying the visible light transmittance in a specific wavelength range by using the iodine generated continuously. In addition, the method of detecting fluorine compounds to determine the reaction rate can be used to determine the concentration of perfluorocarbon, hydroxide, and hydrogen fluoride contained in the mixed gas by infrared spectroscopy, which can be used for continuous industrial safety conditions. operate.

In addition, when the outlet gas of step (2) contains unreacted fluorine gas in addition to being recycled and reused as a dilution gas, for example, approximately the same amount of reaction outlet gas as the supplied 2H-heptafluoropropane is taken out and introduced to remove unreacted fluorine. The step of removing fluorine gas is better to be contacted with hydrofluorocarbon having a stoichiometric ratio of 1.1 times moles of excess fluorine gas to remove fluorine gas. The contact temperature of the fluorine gas removal step varies with the type of hydrofluorocarbon, but it is preferably 250 to 500°C, more preferably 350 to 450°C. The concentration of fluorine in the outlet gas after the fluorine gas removal step is usually below 50 ppm, and can be below 10 ppm depending on the conditions. The hydrofluorocarbon that reacts with excess fluorine gas can be trifluoromethane, tetrafluoroethane, pentafluoroethane, 2H-heptafluoropropane.

In addition to a part of the outlet gas of step (2) that is recycled and reused as the dilution gas of step (2), when there is fluorine gas remaining, the fluorine removal step is followed by a fractionation step. The main components of the gas are hydrogen fluoride and octafluoride propane. In the fractionation step, the hydrogen fluoride liquid is separated by cooling, and the gas is mainly octafluoride propane. The separated hydrogen fluoride is returned to the fluorination step (1) and/or the direct fluorination step (2) for reuse. The separated gas, which mainly contains octafluorinated propane, undergoes a dehydration step and is boosted into the distillation tower by a compressor.

Introduced into the distillation tower, the gas mainly containing octafluorinated propane, for example, is taken out from the top of the tower with a low boiling point in the first distillation tower. The low boiling point is an inert gas, such as tetrafluoromethane, hexafluoroethane, etc., which can be used as a diluent gas in the direct fluorination step (2). On the other hand, the gas with propane octafluoride as the main component taken out from the bottom is introduced into the second distillation tower, and propane octafluoride is taken out from the top of the second distillation tower with a low boiling point and introduced into the product step. The high-boiling components taken out from the bottom of the second distillation tower can be returned to step (2) to be used as a dilution gas, or it can be decomposed with pesticides or the like depending on the situation.

The target octafluoride propane introduced into the product step shall be purified if necessary, and be introduced into the product tank according to the situation or through the dehydration step. The octafluoropropane introduced into the product barrel can be determined by (1) gas chromatography (GC) TCD method, FID method and ECD method, (2) gas chromatography-mass spectrometer (GC-MS) and other analytical methods purity. The present invention (II) is obtained by the manufacturing method of the present invention (I). The high-purity octafluoride propane with a purity of more than 99.995% by volume contains impurity molecules consisting of compounds containing chlorine atoms and cyclic compounds, and the total amount is 50%. If the volume is less than ppm, the total amount of impurities can also be reduced to less than 10 volume ppm.

Next, the use of the high-purity octafluoropropane obtained by the manufacturing method of the present invention (I) in the present invention (III) and (IV) will be explained.

The high-purity octafluoride propane of the present invention (II) can be used as an etching gas in an etching step in a semiconductor device manufacturing process. In addition, it is also used as a cleaning gas in the cleaning step of the semiconductor device manufacturing process. In the manufacturing process of semiconductor devices such as LIS and TFT, thin films and thick films are formed by CVD, sputtering or vapor deposition, and etching is performed to form circuit patterns. In addition, useless deposits deposited on the inner walls, fixtures, piping, etc. of thin-film and thick-film forming equipment are cleaned for removal. This is because useless deposits become the cause of particles if they are generated, and must be removed at any time in order to produce a good quality film. When used as etching or cleaning gas, the octafluoride propane of the present invention can be used with He, Ar, N₂Wait for the inert gas to dilute, you can also add F₂, NF₃, C₂F₄, HCl, O₂, H₂Other gases are mixed and used in an appropriate ratio.

Example

The following examples and comparative examples illustrate the present invention in more detail, but the present invention is not limited to these examples.

[Raw material example 1]

HCFC-22(CHClF₂) Together with water vapor on alumina to produce TFE (tetrafluoroethylene), the by-product HFP (hexafluoropropylene) is separated, and after distillation, the raw material hexafluoropropylene with the composition in Table 3 is obtained.

<tables><img file="TWI242545B_D0003.tif" /></tables>

[Raw material example 2]

Commercially available hexafluoropropylene was analyzed, and the composition was shown in Table 4.

<tables><img file="TWI242545B_D0004.tif" /></tables>

[Manufacture of fluorinated catalyst]

There is a 10 liter container of 0.6 liter of pure water, with 452 grams of Cr(NO₃)₃9H₂O and 42 grams of In(NO₃)₃NH₂O (n is about 5) dissolved in 1.2 liters of pure water, and 0.31 liters of 28% ammonia water, while stirring *Keep the pH of the reaction solution within the range of 7.5 to 8.5, drip in about 1 hour. The obtained hydroxide slurry was filtered, washed with pure water, and dried at 120°C for 12 hours. The obtained solid is pulverized and mixed with graphite, and then pelletized by an ingot former. Under nitrogen flow, the pellets were calcined at 400° C. for 4 hours to obtain a catalyst precursor. The catalyst precursor is filled in a reactor made by Inconel, and the catalyst is prepared by fluorination treatment (activation treatment of the catalyst) under a nitrogen-diluted HF gas flow at a normal pressure of 350°C.

(Example 1)

100ml of the catalyst prepared by the above method of [Manufacture of Fluorinated Catalyst] was filled in an Inconel 600 reactor with an inner diameter of 1 inch and a length of 1 meter, and the temperature was adjusted to 400°C while venting chlorine gas. Hydrogen fluoride is supplied at 6.32 standard liters/hour, followed by a gas with hexafluoropropylene as the main component in [Raw Material Example 1] at 3.24 standard liters/hour. Stop the supply of nitrogen and start the reaction. After 2 hours, the exhaust gas was washed with sodium hydroxide aqueous solution to remove the acid, and the gas composition was analyzed by gas chromatography, and the composition in Table 5 was obtained.

<tables><img file="TWI242545B_D0005.tif" /></tables>

The gas after the acid content is removed is cooled and trapped in a cylindrical container, and purified by distillation and purification by the conventional method to be divided into low boiling components and high boiling components. The composition after distillation and purification was analyzed by gas chromatography, and the composition in Table 6 was obtained.

<tables><img file="TWI242545B_D0006.tif" /></tables>

From the results in Table 6, it can be seen that the impurity chlorine compounds contained in 2H-heptafluoropropane can be reduced to less than 0.01% by volume by distillation.

(Example 2)

Using the gas containing 2H-heptafluoropropane as the main component after distillation obtained in Example 1, the direct fluorination reaction was carried out with fluorine gas.

A nickel reactor with an inner diameter of 20.6 mm Φ and a length of 500 mm (heated by electric heater: the reactor is passivated with fluorine gas at a temperature of 500°C). Nitrogen is supplied at 20 standard liters/hour, and the temperature is raised to 400°C.

Secondly, the hydrogen fluoride (diluent gas) is supplied in two branches at 60 standard liters/hour, and in the first, the gas with the above 2H-heptafluoropropane as the main component is supplied at 3.24 standard liters/hour. After that, fluorine gas was supplied to another hydrogen fluoride gas stream at 3.55 standard liters/hour, and the supply of nitrogen gas was stopped for direct fluorination reaction. After 3 hours, the reaction gas was washed with sodium hydroxide aqueous solution and potassium iodide aqueous solution, hydrogen fluoride and unreacted fluorine gas were analyzed, and then these acids were removed and analyzed by gas chromatography. The organic gas composition is shown in Table 7.

<tables><img file="TWI242545B_D0007.tif" /></tables>

On the other hand, the amount of unreacted fluorine gas in the reaction outlet gas was 0.26 standard liters/hour.

The gas after the acid content is removed is cooled and trapped in a cylindrical container, and purified by distillation to separate low-boiling components and high-boiling components using known methods. The composition obtained after distillation and purification was analyzed by gas chromatography to obtain the composition in Table 8.

<tables><img file="TWI242545B_D0008.tif" /></tables>

It can be seen from the results in Table 8 that the purity of the obtained octafluoropropane is over 99.999% by volume.

(Example 3)

The outlet gas of the direct fluorination reaction containing unreacted fluorine gas obtained in Example 2 was introduced into a nickel reactor with an inner diameter of 20.6 mm Φ and a length of 500 mm. The gas composition is 62.82 standard liters/hour of hydrogen fluoride, 3.16 standard liters/hour of organic matter, and about 0.26 standard liters/hour of unreacted fluorine gas. The reactor is heated to 390°C and supplied from the inlet of the reactor at about 0.286 standard liters/hour Hydrofluorocarbon trifluoromethane, unreacted fluorine and organic compounds were analyzed by titration and gas chromatography. The amount of unreacted fluorine gas in the outlet gas after reacting with trifluoromethane is below 50 ppm, and the gas composition is shown in Table 9.

<tables><img file="TWI242545B_D0009.tif" /></tables>

Secondly, the outlet gas from which the residual fluorine gas has been removed is washed with potassium hydroxide aqueous solution to remove hydrogen fluoride. The gas after the acid content is removed is cooled and trapped in a cylindrical container, and purified by distillation to separate low-boiling components and high-boiling components using known methods. The gas after distillation and purification was analyzed by gas chromatography, and the composition in Table 10 was obtained.

<tables><img file="TWI242545B_D0010.tif" /></tables>

(Comparative example 1)

Direct fluorination reaction is carried out by reacting hexafluoropropylene with fluorine gas. A nickel reactor with an inner diameter of 20.6 mm Φ and a length of 500 mm (electric heater heating: the reactor is passivated with fluorine gas at 500°C) is supplied with nitrogen 60 standard liters/hour in two, and the temperature is adjusted to 500 on one side °C. A nitrogen gas stream is supplied at 3.24 standard liters/hour with a gas containing hexafluoropropylene as the main component of [Raw Material Example 1], followed by another nitrogen stream with fluorine gas supplied at 3.55 standard liters/hour to perform a direct fluorination reaction. After 2 hours, the gas generated by the reaction was washed with potassium hydroxide aqueous solution and potassium iodide aqueous solution to remove unreacted fluorine gas, and analyzed by gas chromatography. The gas composition is shown in Table 11.

<tables><img file="TWI242545B_D0011.tif" /></tables>

As can be seen from the results in Table 11, the method of producing octafluorinated propane by the direct fluorination reaction of hexafluoropropylene and fluorine gas will have polymerization, cyclization addition, etc., and the yield will be low.

Secondly, the gas after the acid content is removed is cooled and trapped in a cylindrical container, and purified by distillation and purification by a known method, and is divided into low-boiling and high-boiling components. The composition after distillation and purification was analyzed by gas chromatography to obtain the composition in Table 12.

<tables><img file="TWI242545B_D0012.tif" /></tables>

As can be seen from the results in Table 12, octafluoropropane and the chlorine compound chloropentafluoroethane and the cyclic compound octafluorocyclobutane are difficult to separate and highly purified.

(Example 4)

Except that the hexafluoropropylene raw material was changed to [Raw Material Example 2], the reaction was the same as in (Example 1), and the gas analysis after the acid content was removed, and the composition in Table 13 was obtained.

<tables><img file="TWI242545B_D0013.tif" /></tables>

The gas after the acid content is removed is cooled and trapped in a cylindrical vessel, and purified by distillation using a known method. It is divided into low-boiling and high-boiling components. The composition of the purified product is analyzed by gas chromatography to obtain the composition in Table 14. .

<tables><img file="TWI242545B_D0014.tif" /></tables>

It can be seen from the results in Table 14 that the impurity chlorine compounds contained in 2H-heptafluoropropane can be reduced to less than 0.01% by volume by distillation.

(Example 5)

Except that 2H-heptafluoropropane is replaced with the purified product of (Example 4), the reaction is the same as (Example 2). The gas after the acid content is removed is cooled and trapped in a steel cylinder. It is purified by distillation and purified by a known method. The boiling point, the obtained composition is analyzed by gas chromatography, and the composition is shown in Table 15.

<tables><img file="TWI242545B_D0015.tif" /></tables>

As can be seen from the results in Table 15, octafluorinated propane with a purity of more than 99.995% by volume can be obtained.

Effect of invention

As explained above, when the method of the present invention is used, hexafluoropropene containing chlorine-based impurities can be used to produce high-purity octafluoropropane; the high-purity octafluoropropane produced by the present invention can be used as a semiconductor device Etching gas or cleaning gas in the process.