CN1561319A

CN1561319A - Method for producing hexafluoroethane and its use

Info

Publication number: CN1561319A
Application number: CNA018017193A
Authority: CN
Inventors: 大野博基; 加贺一有; 大井敏夫
Original assignee: Showa Denko KK
Current assignee: Resonac Holdings Corp
Priority date: 2000-06-21
Filing date: 2001-06-20
Publication date: 2005-01-05
Anticipated expiration: 2021-06-20
Also published as: KR20020019589A; AU7456101A; WO2001098240A3; CN1276903C; WO2001098240A2; KR100516573B1

Abstract

The present invention intends to provide a process for producing CF3CF3 with good profitability using CF3HF2 containing a compound having chlorine atom within the molecule, and use thereof. In the process of the present invention, a gas mixture containing CF3CHF2 and a compound having chlorine atom within the molecule is reacted with hydrogen fluoride in the presence of a fluorination catalyst, thereby converting CC1F2CF3 as a main impurity into CF3CF3, and CF3CHF2 containing CF3CF3 is reacted with fluorine gas in the gaseous phase in the presence of a diluting gas.

Description

Process for producing hexafluoroethane and use thereof

Cross reference to related applications

The present application is filed in accordance with 35u.s.c. § 111(a), and is filed in accordance with 35u.s.c. § 119(e) for the benefit of the application date of provisional application 60/230,806 filed on 9, 7/2000, and is filed in accordance with 35u.s.c. § 111 (b).

Detailed Description

Technical Field

The present invention relates to a process for producing hexafluoroethane, which comprises the steps of: reacting a gas mixture containing pentafluoroethane and a compound having a chlorine atom with hydrogen fluoride in a gas phase in the presence of a fluorination catalyst to fluorinate the compound having a chlorine atom, and reacting the mixture containing pentafluoroethane and the fluorinated compound with a fluorine gas in a gas phase in the presence of a dilution gas. The invention also relates to the use of hexafluoroethane.

Background

Using pentafluoroethane (hereinafter referred to as "CF₃CHF₂") for example as a refrigerant for low temperature applications or as a process for the preparation of hexafluoroethane (hereinafter referred to as" CF₃CF₃") of the starting materials.

For the preparation of CF₃CHF₂For example, the following methods have been proposed:

(1) perchloroethylene (CCl) with hydrogen fluoride₂＝CCl₂) Or ｃA fluoride fluorination method thereof (see JP-A-5-97724 (herein, the term JP-A means "unexamined published Japanese patent application"), JP-A-6-506221, JP-A-7-76534, JP-A-7-118182, JP-A-8-268932 and JP-A-9-511515).

(2) Chloropentafluoroethane (CClF)₂CF₃) A process for carrying out hydrogenolysis.

(3) ｃA method of reacting fluorine gas with halogen-containing ethylene (see JP-A-1-38034).

Preparation of CF Using these₃CHF₂Method of preparation, object CF₃CHF₂Contains a main impurity of a compound having a chlorine atom in its molecule. Having chlorine in the moleculeThe atomic compounds include compounds having one carbon atom in the molecule such as methyl chloride, chlorodifluoromethane and chlorotrifluoromethane, compounds having two carbon atoms in the molecule such as chloropentafluoroethane, dichlorotetrafluoroethane, chlorotetrafluoroethane and chlorotrifluoroethane, and unsaturated compounds such as chlorotrifluoroethylene.

In making CF₃CHF₂With fluorine gas (F)₂) Direct fluorination of the reaction to produce CF₃CF₃If CF₃CHF₂A compound containing chlorine atoms in its molecule, which will generate chlorine, hydrogen chloride and fluorine in reaction with fluorine gasChlorine dioxide or various chlorofluorocarbons. But even in CF₃CHF₂In the case of containing Hydrofluorocarbons (HFC) or perfluorocarbons, no particular problem occurs, for example, methyl Chloride (CH)₃Cl) or chlorodifluoromethane (CHClF)₂) Reacting with fluorine gas to produce chlorotrifluoromethane (CClF)₃). Object CF₃CF₃And chlorotrifluoromethane form azeotropic compositions, therefore, CClF₃Even purification by distillation, adsorption, or the like is difficult to remove. Thus, in CF₃CHF₂Preparation of CF by reaction with fluorine gas₃CF₃In the case of CF₃CHF₂The amount of the compound having chlorine atoms in the molecule contained in (a) should be reduced as much as possible.

Preparation of CF according to the conventional procedure₃CHF₂The total amount of the compound having a chlorine atom in the molecule may be up to 1% by volume. Therefore, the distillation operation is repeated to remove CF₃CHF₂In the presence of these compounds and increase CF₃CHF₂The purity of (2). However, such an operation has problems that the cost of distillation is increased, distillation loss is caused, the yield is lowered, and some compounds having chlorine atoms in the molecule are reacted with CF₃CHF₂An azeotropic mixture or an azeotrope-like mixture is formed, and it is difficult to remove these compounds only by a distillation operation. Especially, CF₃CHF₂Containing chloropentafluoroethane (hereinafter referred to as CClF)₂CF₃) The concentration is generally thousands of ppm or higher, but because of CF₃CHF₂And CClF₂CF₃An azeotropic mixture is formed, and separation can hardly be achieved by distillation, which is a common separation and purification method.

For separating CF₃CHF₂CClF contained therein₂CF₃Various methods have been proposed, for example

(1) At CF₃CHF₂And CClF₂CF₃ｃA method of adding ｃA third component to the mixture of (1) and subjecting the mixture to extractive distillation (see JP-A-6-510980, JP-A-7-258123, JP-A-8-3082, JP-A-8-143486 and JP-A-10-513190),

(2) removal of CF using adsorbent₃CHF₂CClF contained therein₂CF₃(see JP-A-6-92879 and JP-W-8-50847 (herein, the term "JP-W" means an "unexamined published International patent application")),

(3) in the presence of a hydrogenation catalyst, reacting CF with a catalyst₃CHF₂CClF contained therein₂CF₃Conversion to CF₃CHF₂(see JP-A-7-509238, JP-A-8-40949, JP-A-8-301801 and JP-A-10-87525).

However, these methods have problems in that: method (1) requires the removal of the solvent from CClF₂CF₃And a third component, the method (2) requires a step of regenerating the adsorbent, and the method (3) has a shortened catalyst life due to the generation of hydrogen chloride.

Problems to be solved by the invention

The present invention has been made under the above circumstances, and an object of the present invention is to provide a process for producing CF at a high yield₃CF₃In the production of CF₃CF₃In the process of (1), using a catalyst comprising CF₃CHF₂And a compound having a chlorine atom in the molecule, CF₃CF₃Used as an etchant or a cleaner in the process of manufacturing a semiconductor device, and also provides its use.

Means for solving these problems

The inventor has gone throughExtensive and intensive studies have been made to solve the above problems, and it has been found that in the preparation of CF₃CF₃In the process, when containing CF₃CHF₂And a compound having a chlorine atom in the molecule as an impurity, with hydrogen fluoride in the presence of a fluorination catalyst, and CClF contained in the gas mixture₂CF₃Conversion to CF₃CF₃Then in the presence of a dilution gas₃CHF₂And CF₃CF₃The above problems can be solved by directly carrying out the fluorination reaction of the gas mixture of (1) with a fluorine gas in a gas phase. The present invention has been completed based on this finding. The present invention provides for the preparation of CF₃CF₃The method of [1]below and use thereof]-[19]As described in (1).

[1]A process for the preparation of hexafluoroethane comprising the two steps of:

(1) reacting a gas mixture containing pentafluoroethane and a compound having a chlorine atom in the molecule with hydrogen fluoride in a gas phase in the presence of a fluorination catalyst to fluorinate the compound having a chlorine atom;

(2) reacting a fluorinated compound obtained in step (1) and pentafluoroethane-containing gas with a fluorine gas in the presence of a dilution gas.

[2]A process for producing hexafluoroethane as described in [1], wherein the compound having a chlorine atom in the molecule is at least one compound selected from the group consisting of: methyl chloride, chlorotrifluoromethane, chloropentafluoroethane, dichlorotetrafluoroethane, chlorotetrafluoroethane, chlorotrifluoroethane and chlorotrifluoroethylene.

[3]A process for producing hexafluoroethane as described in [1]or [2], wherein the gas mixture of the step (1) contains compounds having chlorine atoms in the molecule in a total amount of 1% by volume or less.

[4]A process for producing hexafluoroethane as described in [1]or [2], wherein the gas mixture of the step (1) contains compounds having chlorine atoms in the molecule in a total amount of 0.5% by volume or less.

[5]A process for producing hexafluoroethane as described in any one of [1]to [4], wherein the fluorination catalyst in the step (1) is a bulk catalyst obtained by adding indium to chromium oxide.

[6]A process for producing hexafluoroethane as described in any one of the processes [1]to [5], wherein, in the step (1), the reaction temperature with hydrogen fluoride in the presence of a fluorination catalyst is in the range of 150 ℃ to 480 ℃.

[7]A process for producing hexafluoroethane as described in any one of [1]to [6], wherein in the step (1), the hydrogen fluoride/gas mixture contains an organic substance in a molar ratio in the range of 0.5 to 5.

[8]A process for producing hexafluoroethane as described in any one of the processes [1]to [7], wherein the step of removing an acid substance containing produced hydrogen chloride is carried out before the step (2).

[9]A process for producing hexafluoroethane as described in any one of [1]to [8], wherein the step of separating chlorotetrafluoroethane and/or chlorotrifluoroethane is carried out before the step (2), and the separated chlorotetrafluoroethane and/or chlorotrifluoroethane is returned to the step (1).

[10]A process for producing hexafluoroethane as described in any one of the processes [1]to [9], wherein, in the step (2), the gas mixture contains a mixture having chlorine atoms in the molecule in a total amount of 0.02% by volume or less.

[11]A process for producing hexafluoroethane as described in any one of the processes [1]to [10], wherein, in the step (2), the gas mixture contains a fluorinated compound mainly comprising hexafluoroethane.

[12]A process for producing hexafluoroethane as described in any one of the processes [1]to [11], wherein, in the step (2), the diluent gas is a gas containing at least one selected from the group consisting of: tetrafluoromethane, hexafluoroethane, octafluoropropane or hydrogen fluoride.

[13]A process for producing hexafluoroethane as described in any one of the processes [1]to [12], wherein, in the step (2), the diluent gas is a hydrogen fluoride-rich gas.

[14]A process for producing hexafluoroethane as described in any one of the processes [1]to [13], wherein, in the step (2), the temperature at which the gas mixture containing the fluorinated compound is reacted with the fluorine gas is in the range of 250 ℃ to 500 ℃.

[15]A process for producing hexafluoroethane as described in any one of the processes [1]to [14], wherein, in the step (2), the temperature at which the gas mixture containing the fluorinated compound is reacted with the fluorine gas is in the range of 350-450 ℃.

[16]A hexafluoroethane product comprising hexafluoroethane having a purity of 99.9997% by volume or more.

[17]A hexafluoroethane product as described in [16], wherein the content of a compound having a chlorine atom is 1volppm or less, and the content of pentafluoroethane is 1volppm or less.

[18]An etching gas comprising the hexafluoroethane product as recited in [16]or [17].

[19]A cleaning gas comprising the hexafluoroethane product as described in [16]or [17].

In summary, the present invention provides "a process for preparing CF₃CF₃The process comprising fluorinating a CF-containing compound in the presence of a catalyst₃CHF₂And a compound having a chlorine atom is reacted with hydrogen fluoride in a gas phase to fluorinate the compound having a chlorine atom, and CF is contained in the gas phase in the presence of a diluent gas₃CHF₂And a step of reacting the gas mixture of the fluorinated compound obtained by the above step with fluorine gas in a gas phase ", the present invention also provides" a gas mixture containing CF having a purity of 99.9997% by volume or more₃CF₃CF of₃CF₃Product "," comprising the above-mentioned CF₃CF₃Etching gas of products "and" containing the above-mentioned CF₃CF₃Cleaning gas of product ".

Modes for carrying out the invention

The preparation of CF according to the present invention is described below₃CF₃And uses thereof.

As described above, the CF used in the present invention₃CHF₂Perchloroethylene (CCl) is generally reacted by means of hydrogen Fluoride (FH)₂＝CCl₂) Or fluorination of fluorides thereof, CF₃CHF₂Containing compounds derived from the starting material and having chlorine atoms, e.g. chloromethane, chlorodifluoromethane, monochloroTrifluoromethane, chloropentafluoroethane, dichlorotetrafluoroethane, chlorotetrafluoroethane and chlorotrifluoroethane. To increase the CF containing these compounds₃CHF₂To a high degree of purity, the existing processes by distillation operations can be employed. However, these methods are due to these compounds and CF₃CHF₂Form an azeotropic mixtureThe compound or the azeotropic mixture has a problem of being uneconomical, the purification by separation is very difficult, the number of plates of the distillation column must be increased or the distillation column must be increased, and the equipment cost or the energy consumption is increased.

In the present invention, CF₃CHF₂The compound containing a chlorine atom as an impurity is fluorinated by hydrogen fluoride at an elevated temperature in the presence of a fluorination catalyst to convert into Hydrofluorocarbons (HFC) or Perfluorocarbons (PFC). For example, CF is reacted with hydrogen fluoride₃CHF₂Containing impurity CClF₂CF₃Or chlorotetrafluoroethane, the following reaction (1) or (2) takes place:

(1)

(2)

the product is an HFC or a PFC without chlorine atoms, producing hydrogen chloride as a by-product.

In this specification, CF is included₃CHF₂And a compound having a chlorine atom are sometimes referred to as "gas mixture raw materials".

In this fluorination reaction, the compounds to be converted into HFC or PFC are methyl chloride, chlorodifluoromethane, chlorotrifluoromethane, chloropentafluoroethane, dichlorotetrafluoroethane, chlorotetrafluoroethane and chlorotrifluoroethane. These compounds are generally contained in CF₃CHF₂In the total amount of (A), the total amount is several ppm on a dry basis or more. When a gas mixture raw material containing these compounds is reacted with a fluorine gas, methane compounds are converted into CClF₃And the ethane compound is converted into CClF₂CF₃Thus, CF obtained after the reaction₃CF₃Containing CClF₃And CClF₂CF₃As the main impurity.

CClF₂CF₃Hardly reacts with fluorine gas at low temperatures. However, according to the studies of the present inventors, for example, at a reaction temperature of 400 ℃ when the gas mixture raw material contains CF₃CClF₂At a concentration of about 800ppm or less, fromCClF₂CF₃CClF produced by decomposition₃In an amount of 1ppm or less when the gas mixture raw material contains CF₃CClF₂In excess of about 2000ppm, about 2ppm CClF is produced₃。CClF₃And CF₃CF₃An azeotropic mixture is formed, and therefore, even if the concentration is low, such a compound is difficult to remove by a purification operation such as distillation, adsorption, or the like. Therefore, it is preferable not only to use CF as a raw material₃CHF₂Wherein CClF is produced in the reaction with fluorine gas₃And CClF should be₂CF₃To as low a concentration as possible.

The total amount of the compounds having chlorine atoms contained in the raw material gas mixture used in the present invention is preferably 1% by volume or less, more preferably 0.5% by volume or less, most preferably 0.3% by volume or less. If the concentration of the compound having a chlorine atom exceeds 1% by volume, the reaction must be carried out at a high temperature, the fluorination catalyst life is disadvantageously shortened, and at the same time, side reactions are carried out, resulting in a decrease in the yield.

The fluorination catalyst comprises at least one element selected from the group consisting of: chromium, nickel, zinc, indium and gallium, may be known catalysts such as supported catalysts or bulk catalysts (bulk catalysts).

In the case of supported catalysts, the support is preferably alumina and/or partially fluorinated alumina, preferably at a loading of 30% by weight or less. In the case of bulk catalysts, preference is given to those having chromium as main component and an atomic ratio of nickel, zinc, indium and/or gallium to chromium of from 0.01 to 0.6. In the present invention, a bulk catalyst obtained by adding indium to chromium oxide is preferable.

In the step of fluorinating the compound having a chlorine atom, the reaction temperature is preferably 150 ℃ to 480 ℃.If the reaction temperature exceeds 480 ℃, the reaction is adversely affected, for example, the catalyst is deteriorated, or side reactions occur, which is undesirable. Although the reaction temperature largely depends on the concentration of such a compound contained in the raw material of the gas mixture, it may be selected according to the kind of the compound. For example, CClF shown in formula (1)₂CF₃In the reaction of (3), the reaction temperature is preferably 400 ℃ or more, and CClFHCF represented by the formula (2)₃In the reaction of (3), the reaction temperature is preferably 300 ℃ or more.

In chlorodifluoromethane (CHClF)₂) In the case of reaction with hydrogen fluoride, a reaction represented by the following formula (3) occurs:

(3)

in this reaction, the reaction temperature is preferably 150 ℃ or more, and if the reaction temperature exceeds 400 ℃ or more, an unfavorable reverse reaction proceeds.

In the step of fluorinating the compound having a chlorine atom, as described above, the reaction temperature may be changed depending on the kind of the compound. Therefore, in the case where a plurality of compounds are contained and the optimum reaction temperature ranges of these compounds are different from each other or the concentration of each compound is high, it is preferable to use two or more reactor units, although usually one reactor unit is sufficient.

HF is used in an amount corresponding to that containing CF₃CHF₂The molar ratio of the organic substance in the raw material gas mixture (HF/organic substance)is preferably from 0.5 to 5, more preferably from 0.5 to 2. If the molar ratio is less than 0.5, the reaction is difficult to proceed, and if it exceeds 5, a large reactor is required, which is disadvantageous.

In the step of fluorinating the compound having a chlorine atom, the reaction pressure is preferably from atmospheric pressure to 1.5 MPa. If the pressure exceeds 1.5MPa, a pressure-resistant apparatus is required, which is also disadvantageous.

In the present invention, the reaction with hydrogen fluoride is carried out in the presence of a fluorination catalyst under the reaction conditions described above, and the reaction product comprises CF₃CHF₂Impurities containing no chlorine atom mainly comprising HF or PFC, and hydrogen chloride as a by-product. At CF₃CHF₂In this case, as the reaction temperature increases, the side reaction with hydrogen chloride as shown in the following formula (4) proceeds more:

(4)

in the case of containing 1, 1, 1, 2-tetrafluoroethane, the side reaction with hydrogen chloride as shown in the following formula (5) proceeds more:

(5)

therefore, it is preferable to remove the acid species containing the generated hydrogen chloride after the fluorination step (1).

The acid species are removed, thereby removing unreacted hydrogen fluoride (excess hydrogen fluoride) and by-product hydrogen chloride. Hydrogen fluoride does not adversely affect the direct fluorination reaction step, and hydrogen chloride is preferably removed because this product sometimes causes generation of a chlorine-containing compound or a chlorofluoride as represented by the formula (4) or (5). The step of removing the acid species is performed prior to the direct fluorination step. Examples of the method for removing acid substances include:

(1) a method for extracting hydrogen chloride from the top of a distillation column by introducing an acid substance-containing effluent into the distillation column under the condition of containing a large amount of unreacted hydrogen fluoride, and extracting an organic substance and hydrogen fluoride from the bottom of the distillation column,

(2) a method of contacting hydrogen chloride and unreacted hydrogen fluoride with a purifying agent,

(3) a method for washing an acid substance with water or alkaline water.

In the present invention, the method for removing the acid substance is not particularly limited, and, for example, the method (3) can be employed. The base used herein may be an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution or the like. The absorbed hydrogen fluoride can be recovered and reused by dehydrating the gas passing through the scrubbing solution using a dehydrating agent such as a zeolite.

By the step of removing acid substances, mainly containing CF₃CHF₂The gas of (A) sometimes also contains the impurity HCFC or CFC, which cannot be fully fluorinated by reaction with hydrogen fluoride, in which case it is preferred that the HCFC or CFC is distilled before the direct fluorination stepAnd (4) removing.

CF₃CHF₂And CF₃CHF₂The main compounds contained and their boiling points are favorable for table 1.

TABLE 1

Name of Compound	Structural formula (I)	Boiling point (. degree.C.)
Name of Compound	Structural formula (I)	Boiling point (. degree.C.)	Tetrafluoromethane	CF₄	-128
Trifluoromethane	CHF₃	-84	Tetrafluoromethane	CF₄	-128
Trifluoromethane	CHF₃	-84	Hexafluoroethane	CF₃CF₃	-78.1
Pentafluoroethane	CF₃CHF₂	-48.5	Hexafluoroethane	CF₃CF₃	-78.1
Pentafluoroethane	CF₃CHF₂	-48.5	Chloropentafluoroethane	CF₃CClF₂	-38.7
2-chloro-1, 1, 1, 2-tetrafluoroethane	CF₃CHClF	-12	Chloropentafluoroethane	CF₃CClF₂	-38.7
2-chloro-1, 1, 1, 2-tetrafluoroethane	CF₃CHClF	-12	2-chloro-1, 1, 1-trifluoroethane	CF₃CH₂Cl	6.1

Will contain mainly CF₃CHF₂Is passed into a distillation column and then CF is extracted from the top of the distillation column₄、CHF₃、CF₃CF₃、CF₃CHF₂And CClF₂CF₃Low boiling fraction, extracting CF from the bottom of the column₃CHClF and CF₃CH₂High boiling point fractions such as Cl. The high boiling fraction extracted from the bottom of the column is recycled to step (1) for reaction with hydrogen fluoride. Here, the compound having a chlorine atom (contained in the extract taken from the top of the column mainly comprising CF)₃CHF₂In the distillate of (a) is preferably 0.02 vol% or less. Mainly comprising CF₃CHF₂The distillate is used as a raw material for direct fluorination reaction with fluorine gasAnd (5) feeding.

The following description mainly includes CF₃CHF₂The step (2) of reacting the gas of (3) with a fluorine gas.

Step (2) is carried out in the presence of a dilution gas which will comprise mainly CF₃CHF₂Is set below the explosive range. Specifically, CF at the inlet of the reactor₃CHF₂The concentration is preferably set to about 6 mol% or less. The diluent gas is a gas comprising at least one gas selected from the group consisting of: tetrafluoromethane, hexafluoroethane, octafluoropropane and hydrogen fluoride, preferably a diluent gas rich in hydrogen fluoride.

According to pair CF₃CHF₂(F₂/CF₃CHF₂) The amount of fluorine gas to be used is preferably in the range of 0.5 to 2, more preferably 0.9 to 1.3 in terms of molar ratio of (A) to (B). The reaction temperature is in the range of 250-500 ℃, preferably in the range of 350-450 ℃. If the reaction temperature exceeds 500 ℃, CF is the object₃CF₃Disadvantageously decompose to produce CF₄And in the presence of CClF₂CF₃In the case of impurities, because of CClF₂CF₃Disadvantageously producing CClF₃. While if the temperature is below 250 c, the reaction proceeds slowly, which is also undesirable.

There is no particular limitation on the method for purifying the gas distilled off from the reaction step (2). The residual unreacted fluorine gas can be removed by adding, for example, trifluoromethane as the HFC, and then distilling the residue to separate, for example, hydrogen fluoride and organic matter. The separated hydrogen fluoride may be reused as a diluent gas in the direct fluorination reaction of step (2), but may also be used as a raw material for the fluorination reaction of step (1). The composition of the organic matter separated varies greatly depending on the diluent gas used for the reaction, and in the case of using a hydrogen fluoride-rich gas or the target is CF₃CF₃In case the obtained organic substance contains CF₃CF₃As the main component. Using tetrafluoromethane or octafluoropropane asIn the case of a diluent gas, the gas is purified by carrying out a redistillation. In either case, by repeating the distillation operation in accordance with the composition ratio of the obtained organic matter, high-purity CF can be obtained₃CF₃。

In the distillation of the purified organic matter, although largely depending on the composition ratio, the inert gas and CF₄Extracted as a low boiling fraction from the top of the first distillation column and mainly comprising CF₃CF₃Is extracted from the bottom and introduced into a second distillation column. Then, the inert gas and trifluoromethane are taken as a low boiling fraction from the top of the second distillation column, mainly comprising CF₃CF₃Is withdrawn from the bottom and sent to a third distillation column to extract high purity CF from the top thereof₃CF₃Thereby completing the purification. CClF-containing liquid collected from the bottom of the third distillation column₂CF₃The gas of (2) may be recycled to the step (1) of reacting with hydrogen fluoride.

CF thus purified₃CF₃Almost free of impurities and capable of obtaining high-purity CF₃CF₃. It has a purity of 99.9997 vol% or more and contains 1volppm or less of a compound having a chlorine atom and 1volppm or less of impurities of pentafluoroethane.

CF having an analytical purity of 99.9997% by volume or higher₃CF₃The method of (4) can use gas chromatography (GP) using TCD method, FID method (each including precut method) or ECD method, or equipment such as gas chromatography mass spectrometry (GC-MS).

The CF obtained by the process of the present invention is described below₃CF₃The use of (1).

High purity CF₃CF₃Can be used as an etchant in an etching step in a process of manufacturing a semiconductor device, and can also be used as a cleaner in a cleaning step in a process of manufacturing a semiconductor device.

In manufacturing semiconductor devices such as LSIs and TFTs, thin or thick films are formed using CVD, sputtering or vapor deposition, and the films are etched to form wiring patterns. In an apparatus for forming a thin or thick film, cleaning is required to remove unwanted deposits accumulated on the inner walls of the apparatus, a jig, etc., since the produced unwanted deposits cause particle generation, and must be removed at any time to obtain a high-quality film.

Using CF₃CF₃The etching method of (2) can be carried out under various dry etching conditions, such as plasma etching and microwave etching, CF₃CF₃Can be mixed with inert gas such as He, N₂And Ar, or with gases such as HCl, O₂And H₂Mixing at proper ratio.

Examples

The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited by these examples.

Raw material example 1

In the presence of a fluorination catalyst, the reaction pressure is 0.4MPa, the reaction temperature is 300 ℃, and tetrachloroethylene (CCl)₂＝CCl₂) Reacting with HF at a HF/tetrachloroethylene molar ratio of 4 (first reaction), and reacting at a reaction pressure of 0.4MPa and a reaction temperature of 330 ℃ to obtain HF/intermediate product (CF)₃CHCl₂+CF₃CHClF) was continued at a molar ratio of 4 (second reaction). After the reaction, removal of acid substances and distillation operation were carried out by a conventional method, and the distillate was analyzed by gas chromatography,as a result, crude CF having the composition as listed in Table 2 was obtained₃CHF₂(CF₃CHF₂Feed 1).

TABLE 2

Compound (I)	Purity (% by volume)
Compound (I)	Purity (% by volume)	CF₃CHF₂	99.4513
CH₃Cl	0.0011	CF₃CHF₂	99.4513
CH₃Cl	0.0011	CHClF₂	0.0008
CHF₃	0.0224	CHClF₂	0.0008
CHF₃	0.0224	CClF₃	0.0005
CF₃CClF₂	0.5216	CClF₃	0.0005
CF₃CClF₂	0.5216	CF₃CHClF	0.0008
CF₃CCl₂F	0.0009	CF₃CHClF	0.0008
CF₃CCl₂F	0.0009	CF₃CH₂Cl	0.0006

Raw material example 2

Repeatedly distilling the CF obtained by the above method by a conventional method₃CHF₂Feed 1, distillate analyzed by gas chromatography, and as a result, crude CF having the composition listed in Table 3 was obtained₃CHF₂(CF₃CHF₂Feed 2).

TABLE 3

Compound (I)	Purity (% by volume)
Compound (I)	Purity (% by volume)	CF₃CHF₂	99.8000
CHClF₂	0.0002	CF₃CHF₂	99.8000
CHClF₂	0.0002	CHF₃	0.0038
CF₃CClF₂	0.1960	CHF₃	0.0038

Catalyst example 1

452 g of Cr (NO) was added dropwise over 1 hour to a 10L vessel containing 0.6L of pure water₃)₃·9H₂O was dissolved in a solution of 1.2 liters of pure water and 0.31 liters of 28% aqueous ammonia while stirring under the condition of controlling the pH of the reaction solution to 7.5 to 8.5. The resulting hydroxide paste was filtered, thoroughly washed with pure water, and then dried at 120 ℃. The solid thus obtained was pulverized and mixed with graphite, and then granulated with a tableting machine. The resulting pellets were calcined at 400 ℃ for 4 hours in a nitrogen stream to obtain a catalyst precursor. This catalyst precursor was filled in a reactor made of Inconel, and then subjected to fluorination treatment (activation of the catalyst) at ambient pressure and 350 ℃ in an HF atmosphere diluted with nitrogen, then in a 100% HF gas flow, and further at 450 ℃ in an HF atmosphere diluted with nitrogen to prepare a catalyst.

Catalyst example 2

452 g of Cr (NO) was added dropwise over 1 hour to a 10-liter vessel containing 0.6 liter of pure water₃)₃·9H₂O and 42 g In (NO)₃)₃·nH₂O (n is about 5) was dissolved in a solution of 1.2 liters of pure water and 0.31 liters of 28% aqueous ammonia while stirring under conditions such that the respective flow rates of the two aqueous solutions were controlled to make the pH of the reaction solution 7.5 to 8.5. The resulting hydroxide paste was filtered, thoroughly washed with pure water, and then dried at 120 ℃ for 12 hours. The solid thus obtained was pulverized and mixed with graphite, and then granulated with a tableting machine. The resulting pellets were calcined at 400 ℃ for 4 hours in a nitrogen stream to obtain a catalyst precursor. This catalyst precursor was filled in a reactor manufactured by Inconel, followed by fluorination treatment (activation of the catalyst) in the same manner as in catalyst example 1 to prepare a catalyst.

Example 1

Step (1)

An Inconel 600 type reactor having an inner diameter of 1 inch and a length of 1 m was filled with 150 ml of the catalyst prepared in catalyst example 1, and the temperature was raised to 440 c while passing nitrogen gas. Thereafter, hydrogen fluoride was fed at a rate of 3.5NL/hr, and then CF obtained in the starting material example 1 was fed at a rate of 3.5NL/hr₃CHF₂Starting material 1. Stop the expertNitrogen was added to initiate the reaction. After 2 hours, the discharged gas was washed with an aqueous potassium hydroxide solution to remove acid substances, and thereafter, the composition of the gas was analyzed by gas chromatography, and as a result, a gas having the composition listed in table 4 was obtained.

TABLE 4

Compound (I)	Purity (% by volume)
Compound (I)	Purity (% by volume)	CF₃CHF₂	99.3273
CF₄	0.0113	CF₃CHF₂	99.3273
CF₄	0.0113	CHF₃	0.0215
CF₃CF₃	0.6120	CHF₃	0.0215
CF₃CF₃	0.6120	CF₃CClF₂	0.0156
CF₃CHClF	0.0112	CF₃CClF₂	0.0156
CF₃CHClF	0.0112	CF₃CH₂Cl	0.0011

Example 2

Step (2)

The reaction and analysis were carried out under the same conditions in the same operation as in example 1, except that 150 ml of the catalyst prepared in example 2 was filled as a catalyst. The analytical results are shown in Table 5.

TABLE 5

Compound (I)	Purity (% by volume)
Compound (I)	Purity (% by volume)	CF₃CHF₂	99.2732
CF₄	0.0170	CF₃CHF₂	99.2732
CF₄	0.0170	CHF₃	0.0212
CF₃CF₃	0.6720	CHF₃	0.0212
CF₃CF₃	0.6720	CF₃CClF₂	0.0068
CF₃CHClF	0.0098	CF₃CClF₂	0.0068
CF₃CHClF	0.0098	CF₃CH₂Cl	0.0015

As can be understood from the analysis results shown in Table 5, when a fluorination catalyst prepared by adding indium to chromium was used, CClF was improved₂CF₃Conversion to CF₃CF₃The conversion of (a).

Example 3

Step (1)

The reaction and analysis were carried out under the same conditions in the same operation as in example 1, except that the reaction temperature was changed to 300 ℃. The analytical results are shown in Table 6.

TABLE 6

Compound (I)	Purity (% by volume)
Compound (I)	Purity (% by volume)	CF₃CHF₂	99.4314
CF₄	0.0023	CF₃CHF₂	99.4314
CF₄	0.0023	CHF₃	0.0221
CF₃CF₃	0.0387	CHF₃	0.0221
CF₃CF₃	0.0387	CF₃CClF₂	0.4829
CF₃CHClF	0.0014	CF₃CClF₂	0.4829
CF₃CHClF	0.0014	CF₃CH₂Cl	0.0005

Example 4

Step (1)

The reaction and analysis were carried out under the same conditions in the same operation as in example 1, except that the reaction temperature was changed to 500 ℃. The analytical results are shown in Table 7.

TABLE 7

Compound (I)	Purity (% by volume)
Compound (I)	Purity (% by volume)	CF₃CHF₂	99.1948
CF₄	0.1488	CF₃CHF₂	99.1948
CF₄	0.1488	CHF₃	0.0168
CF₃CF₃	0.5880	CHF₃	0.0168
CF₃CF₃	0.5880	CHClF₂	0.0069
CF₃CClF₂	0.0148	CHClF₂	0.0069
CF₃CClF₂	0.0148	CF₃CHClF	0.0256
CF₃CCl₂F	0.0021	CF₃CHClF	0.0256
CF₃CCl₂F	0.0021	CF₃CH₂Cl	0.0022

Example 5

Step (1) + step (2)

An Inconel 600 type reactor having an inner diameter of 1 inch and a length of 2 meters was filled with 150 ml of the catalyst prepared in catalyst example 2, and the temperature was raised to 430 c while passing nitrogen gas. Thereafter, hydrogen fluoride was fed at a rate of 5.0NL/hr, and then CF obtained in starting material example 2 was fed at a rate of 8.0NL/hr₃CHF₂Feed 2. Then, the introduction of nitrogen gas was stopped, and after 2 hours of the initiation of the reaction, the discharged gas was washed with an aqueous potassium hydroxide solution to remove acid substances, and thereafter, the composition of the gas was analyzed by gas chromatography, and as a result, a gas having the composition listed in Table 8 was obtained.

TABLE 8

Compound (I)	Purity (% by volume)
Compound (I)	Purity (% by volume)	CF₃CHF₂	99.7922
CF₄	0.0018	CF₃CHF₂	99.7922
CF₄	0.0018	CHF₃	0.0036
CF₃CF₃	0.1980	CHF₃	0.0036
CF₃CF₃	0.1980	CF₃CClF₂	0.0008
CF₃CHClF	0.0036	CF₃CClF₂	0.0008

The gas having the composition listed in table 8 after removing the acid substances was collected under cooling conditions and purified by a conventional distillation method. The gas obtained after purification was analyzed and the results are shown in Table 9.

TABLE 9

Compound (I)	PureDegree (volume%)
Compound (I)	PureDegree (volume%)	CF₃CHF₂	99.7950
CF₄	0.0019	CF₃CHF₂	99.7950
CF₄	0.0019	CHF₃	0.0035
CF₃CF₃	0.1988	CHF₃	0.0035
CF₃CF₃	0.1988	CF₃CClF₂	0.0008

From the analysis results shown in table 9, it was found that most chlorotetrafluoroethane was removed by distillation.

Using a mixture obtained after purification by distillation comprising mainly CF₃CHF₂The gas of (4) is subjected to a direct fluorination reaction with a fluorine gas.

An Inconel 600 type reactor having an inner diameter of 20.6 mm and a length of 500 mm was heated to 420 c (using an electrically heated heating system; the reactor had been passivated with fluorine gas at 500 c) while passing nitrogen at a rate of 30 NL/hr.

Then, hydrogen fluoride was fed at a rate of 50NL/hr, and CF was mainly included at a rate of 3.5NL/hr₃CHF₂Is fed from the dilution gasThe body is divided into one gas flow. Thereafter, fluorine gas was fed into another gas stream branched from the diluent gas at a rate of 3.85NL/hr as well, to effect a reaction. After 3 hours, the gaseous reaction product was washed with an aqueous potassium hydroxide solution and an aqueous potassium iodide solution to remove hydrogen fluoride and unreacted fluorine gas. Subsequently, the composition of the gas was analyzed by gas chromatography, and the analysis results are shown in Table 10.

Watch 10

Compound (I)	Purity (% by volume)
Compound (I)	Purity (% by volume)	CF₃CHF₂	0.0001
CF₄	0.0456	CF₃CHF₂	0.0001
CF₄	0.0456	CF₃CF₃	99.9536
CF₃CClF₂	0.0007	CF₃CF₃	99.9536

The gas after removal of the acid material was collected under cooling conditions and purified by distillation. The purified gas was analyzed by TCD method, FID method, ECD method and GC-MS method, and the analysis results are shown in Table 11.

TABLE 11

Compound (I)	Purity (% by volume)
Compound (I)	Purity (% by volume)	CF₃CHF₂	0.9volppm
CF₄	＜0.4volppm	CF₃CHF₂	0.9volppm
CF₄	＜0.4volppm	SF₆	＜0.4volppm
CF₃CClF₂	＜0.1volppm	SF₆	＜0.4volppm
CF₃CClF₂	＜0.1volppm	CF₃CF₃	99.9998

From the analysis results shown in Table 11, it is understood that CF after purification₃CF₃Hardly containing other impurities. Thus, CF of high purity is obtained₃CF₃The purity thereof is 99.9997% by volume or more.

Comparative example 1

Then, hydrogen fluoride was fed at a rate of 50NL/hr, and CF was mainly included at a rate of 3.5NL/hr₃CHF₂The gas (feed of example 1) was fed into a stream of gas separated from the diluent gas. Thereafter, fluorine gas was fed into another gas stream branched from the diluent gas at a rate of 3.85NL/hr as well for reaction. After 3 hours, the reaction product was washed with an aqueous potassium hydroxide solution and an aqueous potassium iodide solution to remove hydrogen fluoride and unreacted fluorine gas. Subsequently, the composition of the gas was analyzed by gas chromatography, and the analysis results are shown in Table 12.

TABLE 12

Compound (I)	Purity (% by volume)
Compound (I)	Purity (% by volume)	CF₃CHF₂	0.0003
CF₄	0.0568	CF₃CHF₂	0.0003
CF₄	0.0568	CClF₃	0.0036
CF₃CF₃	99.4160	CClF₃	0.0036
CF₃CF₃	99.4160	CF₃CClF₂	0.5233

From the analysis results shown in Table 12, it is understood that CF containing a compound having a chlorine atom in the molecule as an impurity₃CHF₂Upon reaction with fluorine gas, CClF is produced which is difficult to separate₃(chlorotrifluoromethane).

The gas having the composition listed in table 12 after removing the acid substances was collected under cooling conditions and purified by a conventional distillation method. The gas obtained after purification was analyzed, and the results are shown in Table 13.

Watch 13

Compound (I)	Purity (% by volume)
Compound (I)	Purity (% by volume)	CF₃CHF₂	0.0003
CF₄	＜0.0001	CF₃CHF₂	0.0003
CF₄	＜0.0001	CClF₃	0.0036
CF₃CF₃	99.9959	CClF₃	0.0036
CF₃CF₃	99.9959	CF₃CClF₂	＜0.0001

From the analysis results shown in Table 13, CClF₃It is difficult to separate.

Effects of the invention

As described above, by using a gas containing CF₃CHF₂And a compound having a chlorine atom in the molecule, can produce CF of high purity₃CF₃High purity CF prepared according to the invention₃CF₃May be used as an etchant or a cleaner in the manufacture of semiconductor devices.

Claims

1. A process for the preparation of hexafluoroethane comprising the steps of:

(2) reacting a fluorinated compound obtained in step (1) and pentafluoroethane-containing gas with fluorine gas in the presence of a dilution gas.

2. The process for producing hexafluoroethane as claimed in claim 1, wherein said compound having a chlorine atom is at least one compound selected from the group consisting of: methyl chloride, chlorotrifluoromethane, chloropentafluoroethane, dichlorotetrafluoroethane, chlorotetrafluoroethane, chlorotrifluoroethane and chlorotrifluoroethylene.

3. The process for producing hexafluoroethane as claimed in claim 1 or 2, wherein the total amount of the compounds having chlorine atoms in the gas mixture in the step (1) is 1% by volume or less.

4. The process for producing hexafluoroethane as claimed in claim 1 or 2, wherein the total amount of the compounds having chlorine atoms of the gas mixture in the step (1) is 0.5% by volumeor less.

5. The process for producing hexafluoroethane as claimed in any one of claims 1 to 4, wherein in said step (1), the fluorination catalyst is a bulk catalyst obtained by adding indium to chromium oxide.

6. The process for producing hexafluoroethane as claimed in any one of claims 1 to 5, wherein in said step (1), the temperature of the reaction with hydrogen fluoride in the presence of the fluorination catalyst is in the range of 150 ℃ to 480 ℃.

7. The process for producing hexafluoroethane as claimed in any one of claims 1 to 6, wherein in said step (1), the molar ratio of the organic substance contained in the hydrogen fluoride/gas mixture is in the range of 0.5 to 5.

8. The method according to any one of claims 1 to 7, wherein a step of removing produced hydrogen chloride-containing acid species is performed prior to said step (2).

9. The process for producing hexafluoroethane as claimed in any one of claims 1 to 8, wherein the step of separating chlorotetrafluoroethane and/or chlorotrifluoroethane is carried out before the step (2), and the step of returning the separated chlorotetrafluoroethane and/or chlorotrifluoroethane to the step (1).

10. The process for producing hexafluoroethane as claimed in any one of claims 1 to 9, wherein in said step (2), the gas mixture contains the total amount of the compounds having chlorine atoms of 0.02 vol% or less.

11. The process for producing hexafluoroethane as claimed in any one of claims 1 to 10,wherein in said step (2), the gaseous compound contains a fluorinated compound mainly comprising hexafluoroethane.

12. The process for producing hexafluoroethane as claimed in any one of claims 1 to 11, wherein in said step (2), said diluent gas is a gas containing at least one gas selected from the group consisting of: tetrafluoromethane, hexafluoroethane, octafluoropropane, and hydrogen fluoride.

13. The process for producing hexafluoroethane as claimed in any one of claims 1 to 12, wherein in said step (2), said diluent gas is a hydrogen fluoride-rich gas.

14. The process for producing hexafluoroethane as claimed in any one of claims 1 to 13, wherein in the step (2), the temperature at which the gas mixture containing the fluorinated compound is reacted with the fluorine gas is in the range of 250-500 ℃.

15. The process for producing hexafluoroethane as claimed in any one of claims 1 to 14, wherein in said step (2), the temperature at which the gas mixture containing the fluorinated compound is reacted with the fluorine gas is in the range of 350-450 ℃.

16. A hexafluoroethane product comprising hexafluoroethane having a purity of 99.9997 vol% or greater.

17. The hexafluoroethane product as claimed in claim 16, wherein the content of the compound having a chlorine atom is 1volppm or less, and the content of pentafluoroethane is 1volppm or less.

18. An etching gas comprising the hexafluoroethane product as claimed in claim16 or 17.

19. A cleaning gas comprising the hexafluoroethane product of claim 16 or 17.