KR100283711B1 - Method for preparing hexafluoroethane - Google Patents

Abstract

Hexafluoroethane is produced safely and with high efficiency from hydrofluorocarbons and fluorine gas.

Hydrofluorocarbons containing two carbon atoms in the molecule and fluorine gas are subjected to gas phase reaction at 250 to 500 ° C in the presence of diluent gas.

Description

Method for preparing hexafluoroethane

The present invention relates to a method for producing hexafluoroethane by gas phase reaction of hydrofluorocarbons containing two carbon atoms in a molecule with fluorine gas at elevated temperature in the presence of diluent gas.

Hexafluoroethane (hereinafter referred to as "FC-116" or "CF ₃ CF ₃ ") is used, for example, for dry etching of semiconductors.

As for the manufacturing method of FC-116, various methods have been proposed conventionally. For example, (1) electrolytic fluorination using ethane and / or ethylene as a raw material, (2) pyrolysis using pyrolysis of ethylene tetrafluoride, etc., and (3) metal fluoride using acetylene, ethylene and / or ethane. And fluorination with (4) dichlorotetrafluoroethane or chloropentafluoroethane with hydrogen fluoride, and (5) direct fluorination with reacting with ethane using fluorine gas.

The method of (1) has many side reactions, and there is a problem in separation or purification of the product. The method of (2) requires a high reaction temperature and a low yield. The method of (3) improves the control of the heat of reaction, but has problems such as regeneration by fluorine gas of metal fluoride or consumption of fluorine. The method of (4) generates a large amount of hydrochloric acid as a by-product in the reaction using hydrogen fluoride, and requires a high temperature so that the yield is low.

As the reaction of (5), the following examples are known. (a) A method of reacting fluorine gas with ethane (C ₂ H ₆ ) in a jet reactor to obtain tetrafluoromethane or C ₂ F ₆ : using nitrogen in diluent gas [J. Amer. Chem. Soc., 77 3307 (1955), J Amer. Chem. Soc., 82, 5827 (1960)], (b) Fluorination of CH with fluorine gas in a reactor having a porous alumina tube [EP 3131519 (1981)]. (c) Method of fluorinating linear hydrocarbons with fluorine gas in the presence of diluent gas in a reactor having a porous metal tube (double tube structure): SF ₆ , CF ₆ , C ₂ F ₆ , C ₃ as diluent gas F ₈ use (EP 32210 (1981)) and the like are known.

Examples of reactions using other fluorine gases include (e) a method for producing hydrofluorocarbons by reacting fluorine gas with saturated or unsaturated hydrocarbons or partially fluorinated hydrocarbons [US5406008 (1995)] or with alkenes Also known are methods of producing fluorinated alkene from carbon containing adsorption of fluorine gas (Japanese Patent Laid-Open No. 2-207052).

As described above, since the direct fluorination method using fluorine gas uses highly reactive fluorine gas, there is a risk of explosion or corrosion between the organic compound as the substrate and the fluorine gas, and furthermore, the There is a risk of side reactions such as abrupt reaction or explosion due to cleavage or polymerization, and carbon production or deposition. For example, in the case of the perfluoro compound by the direct fluorination method using linear hydrocarbon and fluorine gas, the following enormous heat of reaction is involved.

C ₂ H ₆ + 6F ₂ → C ₂ F ₆ + 6HF

(△ H = -690kcal / mol)

CH ₄ + 4F ₂ → CF ₄ + 4HF

(△ H = -479kcal / mol)

In the case of Scheme 1 using ethane as a raw material, 6 mol of fluorine per mol of ethane is required, and in the case of Scheme 2 using methane as a raw material, 4 mol of fluorine gas is required per mol of methane.

In this way, the heat of reaction is proportional to the number of moles of fluorine, and the larger the amount of fluorine, the greater the heat of reaction. For this reason, breakage or explosion of C-C bonds due to heat generation is likely to occur, and furthermore, yield is lowered, resulting in industrial manufacturing and operation problems. For this reason, as a method of suppressing the rapid generation of heat of reaction in the direct fluorination method, fluorine is diluted with another inert gas (nitrogen or helium), and the organic compound as a substrate is dissolved in a solvent inert to fluorine at low temperature. When the reaction is carried out in a low temperature region and the reaction is carried out in the gas phase, a device such as a jet reactor has been devised so that fluorine is gradually brought into contact with the organic compound as a substrate.

The present invention has been made to solve the above problems or problems, and therefore, the object is to produce FC-116 safely and economically in a direct fluorination method using an organic compound and fluorine gas as a substrate. It is to provide a manufacturing method that can be.

The above problem can be solved by providing a method for producing hexafluoroethane in which gaseous reaction of hydrofluorocarbons (HFC) containing two carbon atoms in a molecule with fluorine gas is carried out at elevated temperature in the presence of a diluent gas.

The diluent gas preferably contains at least one of tetrafluoromethane, hexafluoroethane, octafluoropropane and hydrogen fluoride, more preferably rich in hydrogen fluoride.

The organic compound serving as a substrate is a hydrofluorocarbon (HFC) containing two carbon atoms in a molecule, and a compound containing three or more fluorine atoms in the molecule. Preferably 1,1,1,2-tetrafluoroethane (CF ₃ CH ₂ F), 1,1,2,2-tetrafluoroethane (CF ₂ CHF ₂ ) and / or pentafluoroethane, More preferably 1,1,1,2-tetrafluoroethane is preferable.

When carrying out the present reaction, the reactor inlet concentration of hydrofluorocarbons containing two carbon atoms in the molecule is in the range of 6 mol% or less, preferably in 1,1,1,2-tetrafluoroethane. It is preferable to set the inlet concentration to 4 mol% or less.

Moreover, it is preferable to make reaction temperature into the range of 250-500 degreeC in a temperature rising range. It is preferable to carry out at reaction pressure within the range of 0-3 MPa.

Hereinafter, the manufacturing method of FC-116 of this invention is demonstrated in detail.

The organic compound used as the starting material of the present invention is a hydrofluorocarbon containing two carbon atoms in a molecule, represented by the following formula (1).

C ₂ HxFy

In Chemical Formula 1, x is an integer of 1 ≦ x ≦ 5, y is an integer of 1 ≦ y ≦ 5, and x and y are compounds satisfying the conditions of x + y = 6, specifically, fluoroethane (C ₂ H ₅ F), 1,2-difluoroethane (CH ₂ FCH ₂ F), 1,1-difluoroethane ((CHF ₂ CH ₃ ), 1,1,1-trifluoroethane (CF ₃ CH ₃ ), 1,1,2-trifluoroethane (CHF ₂ CHF ₂ ), 1,1,1,2-tetrafluoroethane (CF ₃ CH ₂ F), 1,1,2, It is a compound of 2-tetrafluoroethane (CHF ₂ CHF ₂ ) and pentafluoroethane (CH ₃ CHF ₂ ), and these raw materials may be used alone or as a mixture of two or more thereof.

As described above, the reaction between the organic compound and the fluorine gas involves a very large heat of reaction, and the heat of reaction is proportional to the number of fluorine water, and considering that the higher the amount of fluorine, the greater the heat of reaction, the smaller the substitution of H and F, the more problematic. It becomes easy to control the reaction heat, and the amount of expensive fluorine can be reduced. For this reason, among the above-mentioned hydrofluorocarbons, preferably, a compound containing three or more fluorine atoms in the molecule is preferable, and more preferably a compound containing four or more fluorine atoms, specifically 1, 1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane and / or pentafluoroethane.

1,1,2,2-tetrafluoroethane or pentafluoroethane is industrially produced as an alternative to chlorofluorocarbons (CFCs) or hydrochlorofluorocarbons (HCFCs), is easy to purchase and has a purity of 99.9 Higher than% In the case of production of FC-116 using these compounds and fluorine gas, the following heat of reaction is generated.

CF ₃ CH ₂ F + 2F ₂ → CF ₃ CF ₃ + 2HF

(△ H = -231kcal / mol)

CF ₃ CHF ₂ + F ₂ → CF ₃ CF ₃ + HF

(△ H = -119kcal / mol)

When 1,1,1,2-tetrafluoroethane or pentafluoroethane is used as a starting material, the heat of reaction is about 1/3 to 1/6 as compared with the production of FC-116 by fluorine gas of hydrocarbon compound. It can be suppressed.

In addition, when 1,1,1,2-tetrafluoroethane and pentafluoroethane are compared, 1,1,1,2-tetrafluoroethane is more preferable. The reason for this is that 1,1,1,2-tetrafluoroethane is used as a raw material for high reaction activity, and another important issue is the purity of these products currently produced industrially. 1,1,1,2-tetrafluoroethane has a purity of 99.9% or more, and most of 1,1,2,2-tetrafluoroethane is an isomer as an impurity, and almost no chlorine-containing compound is included.

In contrast, pentafluoroethane forms an azeotropic composition with chloropentafluoroethane (CF ₃ CClF ₂ ), and the product contains several hundred ppm to several thousand ppm even when distilled or purified. 1,1,1,2-tetrafluoroethane is particularly useful because this chlorine-containing compound is not preferable because it generates chlorine fluoride or chlorine by reaction.

This reaction causes the fluorine gas of the above hydrofluorocarbons to react at an elevated temperature in the presence of a diluent gas.

As the diluent gas, an inert gas such as nitrogen, helium or argon is generally used, but considering the separation and purification of the target substance and these inert gases, the method is not advantageous in terms of cost. The present invention is a diluent gas, tetrafluoromethane (boiling point: -127.9 ℃), hexafluoroethane (boiling point: -78.5 ℃), octafluoropropane (boiling point: -37.7 ℃) and hydrogen fluoride (boiling point: 20 ℃ (A boiling point: -268.9 ° C), etc. are used as a diluent gas, and they have a high boiling point and an effect of suppressing combustion or explosion, and the energy cost of separation and purification becomes advantageous. .

Moreover, More preferably, it is the method of using the hydrogen fluoride rich component as a dilution gas.

For example, as shown in Scheme 3, one mole of FC-116 and two moles of hydrogen fluoride are produced in a reaction of 1 mole of 1,1,1,2-tetrafluoroethane and 2 moles of fluorine. FC-116 as a target product and hydrogen fluoride as a by-product have a difference in boiling point of about 100 ° C., and a component rich in hydrogen fluoride can be obtained by a simple method such as fractionation, which is economical when used as a diluent gas. In addition, hydrogen fluoride may be newly added as a dilution gas. In addition, in the direct fluorination method using fluorine gas, carbon formation, deposition, etc., occur due to the cleavage of C-C bonds or the like as described above in the long-term reaction. Although carbon formation or deposition may cause a sudden reaction or explosion with fluorine gas, hydrogen fluoride can be used as a diluent gas to suppress the formation and deposition of carbon. Abundance of hydrogen fluoride means that hydrogen fluoride is a main component.

The reaction is carried out in the presence of the substrate, fluorine gas and diluent gas of the reaction, but prior to introduction into the reactor, it is common to dilute either or both of the substrate and fluorine gas of the reaction with diluent gas and then introduce it into the reactor. In consideration of safety, it is desirable to make both the substrate and the fluorine gas of the reaction as low as possible with diluent gas.

As a raw material, the above-mentioned hydrofluorocarbons and fluorine gas are reacted in the presence of the diluent gas as described above, but the reaction temperature is also one of the important conditions for the efficient progress of the reaction, and the reaction temperature is the contact time or the starting material. The optimum range changes depending on the type of hydrofluorocarbon. For example, in the case of the reaction of 1,1,1,2-tetrafluoroethane and fluorine, when the contact time is long (contact time 15 seconds), the reaction occurs from the reaction temperature of about 50 ° C and the conversion rate at about 250 ° C. Is about 100%. The reaction temperature is in an elevated temperature range, preferably in the range of 250 to 500 ° C.

If the reaction temperature is less than 250 ° C, the conversion of hydrofluorocarbon is lowered, and if it is over 500 ° C, the cleavage or polymerization of CC bonds occurs, so that the yield is lowered, and problems such as corrosion or high energy cost of the reactor, etc. It is not desirable.

Although the contact time is not particularly limited, for example, in the range of 0.1 to 120 seconds, if the contact time is increased, the reactor becomes large and it is not economical, so it is generally 1 to 30 seconds, more preferably 3 to 30 seconds, It is also important to improve the mixing of the reaction substrate with the fluorine gas.

Since the direct fluorination method using fluorine gas as described above uses fluorine which is highly reactive, the organic compound (particularly, a compound containing hydrogen) that is a substrate has a risk of burning or exploding upon contact with fluorine.

In this reaction, since hydrofluorocarbon containing hydrogen is used as an organic compound as a substrate, explosion prevention of hydrofluorocarbons and fluorine becomes an important point. To prevent explosion it is necessary to ensure that the composition of the mixed gas does not fall within the explosion range. The inventors of the present invention have examined the explosion range between hydrofluorocarbons and fluorine gas, and as a result, the concentration of pentafluoroethane is about 6%, and the concentration of 1,1,1,2-tetrafluoroethane is about 4%. It discovered that it was a lower limit and employ | adopted the safe range of the organic compound inlet concentration of this reaction.

The molar ratio of the hydrofluorocarbons to the reaction system and the fluorine gas is preferably in the range of 0.5 to 5.0, more preferably in the range of 1.0 to 3.0. If the supply molar ratio of the fluorine gas is less than 0.5, the reaction does not proceed and the efficiency is poor. If the supply molar ratio is more than 5.0, the fluorine gas is excessively excessive, and equipment for recovery thereof is not economical.

In this reaction, the reaction pressure is also important for preventing the risk of explosion and the like. Since the range increases generally as the pressure increases, the reaction is preferably performed at a lower pressure, and the reaction pressure is preferably within the range of 0 to 3 MPa.

Moreover, as a material of a reactor, what has resistance to a corrosive gas is preferable, As an example, nickel, inconel, Hastelloy, etc. are mentioned.

EXAMPLE

Examples of the present invention are shown below.

First, the raw material used for this invention is shown below.

[1,1,1,2-tetrafluoroethane]

Currently, the Ecolo Ace 134a (brand name) supplied as a substitute for CFC-12 (CCl ₂ F ₂ ) was used. The purity was 99.99% or more, contained about 20 ppm of isomer 1,1,2,2-tetrafluoroethane, and almost no chlorine-containing compound was detected.

[Pentafluoroethane]

Currently, Echolo Ace 125 (trade name) was used as a substitute for HCFC-22 (CHClF ₂ ). Purity is at least 99.95% and contains 1,1,1,2-tetrafluoroethane and 1,1,1-trifluoroethane as impurities or chloropentafluoroethane, 1-chloro-1 as chlorine-containing compound And 2,2,2-tetrafluoroethane.

Example 1

Nitrogen gas was supplied to a reactor made of Inconel 600 having an internal diameter of 20.6 mm ψ and a length of 500 mm (electric heater heating method: passivation treatment at a temperature of 600 ° C. with fluorine gas) at 30 NL / h, and the temperature was raised to 280 ° C. 1,1,1,2-tetrafluoroethane was supplied at 1.8 NL / h as a hydrofluorocarbon to 50 Nl / h of hydrogen and again to the one of the gas streams whose flow direction was diverted. After that, the fluorine gas is supplied at 3.9 NL / h to the other side of the gas stream whose flow direction is divided in the same manner, and reacted.

The reactor inlet concentration of 1,1,1,2-tetrafluoroethane was 2.1 mol% and the reaction temperature was 280 ° C.

After 3 hours, hydrogen fluoride and unreacted fluorine gas were removed with an aqueous potassium hydroxide solution and potassium iodide solution, and then the composition was analyzed by gas chromatography. The gas composition was as follows.

CF ₄ 0.56%, C ₂ F ₆ 84.59%

CF ₃ CHF ₂ 14.45% CF ₃ CH ₂ F Trace,

Other 0 40% (% by volume)

[Examples 2 to 5]

The reaction is carried out under the same operating conditions as in Example 1 except that the reaction temperature is changed. The reaction temperature and the results obtained are shown in Table 1.

FC-14 in the table is CF ₄ , FC-116 is CF ₃ CF ₃ , HFC-125 is CF ₃ CHF ₂ , and HFC-134a is CF ₃ CH ₂ F.

Others in Table 1 are mostly CO ₂ , but produce C ₃ F ₈ at 550 ° C. As can be seen from the results, the yield of FC-116, which is the target product, is poor at low temperatures, the selectivity is lowered at high temperatures of 550 ° C., and C ₃ perfluoro compounds are produced by promoting the cleavage or polymerization of CC bonds.

[Examples 6 to 8]

In the same reactor as in Example 1, 3.6NL / h of pentafluoroethane as hydrofluorocarbon, 3.9NL / h of fluorine gas, 50NL / h of hydrogen fluoride and 30NL / h of nitrogen gas as diluent gas were prepared in the same manner as in Example 1. It reacts by operation similar to Example 1 except supplying and changing reaction temperature. The reaction temperature and the results obtained are shown in Table 2.

Others in Table 2 are mostly CO ₂ , and Cl compounds are mainly composed of chloropentafluoroethane and 1-chloro-1,2,2,2-tetrafluoroethane.

As can be seen from the results, pentafluoroethane has a lower reactivity with fluorine gas than with 1,1,1,2-tetrafluoroethane (low temperature range), but a high yield of FC-116 can be obtained. However, in Example 8, chlorine and chlorine fluoride are detected.

Example 9

1,1,1,2-tetrafluoroethane 2.2NL / h as hydrofluorocarbon, 4.8NL / h fluorine gas, hydrogen fluoride 60NL / h as diluent gas, 20NL tetrafluoroethane in the same reactor as in Example 1 / h is supplied and reacted by operation similar to Example 1 at reaction temperature of 480 degreeC. The results obtained are shown below.

CF ₄ 1.46%, C ₂ F ₆ 95.98%,

CF ₃ CHF ₂ 1.78%, CF ₃ CH ₂ F-,

0.78% (% by volume).

30 days of continuous reaction was performed under these conditions, and the composition analysis of the reaction outlet gas on the 30th day showed little difference with the above result. Thereafter, the reaction was timed to cool down to room temperature while supplying nitrogen gas, and the inside surface of the reactor was observed with a fiber scope (endoscope), but no deposition or deposition of carbon or the like was found.

In the method for preparing FC-116 of the present invention, it is possible to produce an industrially safe high yield FC-116 by reacting hydrofluorocarbons containing two carbon atoms in a molecule with fluorine gas in the presence of diluent gas in the gas phase. .

Claims (8)

250-500 ° C. in the presence of a difluorocarbon containing two or more carbon atoms in the molecule and one or more of fluorogas containing tetrafluoromethane, hexafluoroethane, octafluoropropane and hydrogen fluoride Method for producing hexafluoroethane, characterized in that the gas phase reaction in. The production method according to claim 1, wherein the dilution gas is a gas rich in hydrogen fluoride. The method according to claim 1, wherein the hydrofluorocarbons containing two carbon atoms in the molecule are hydrofluorocarbons containing three or more fluorine atoms. 4. Hydrofluorocarbons according to claim 3, wherein the hydrofluorocarbons containing two carbon atoms in the molecule are contained in 1,1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane and pentafluoroethane. At least one manufacturing method. The production method according to claim 4, wherein the hydrofluorocarbons containing two carbon atoms in the molecule are 1,1,1,2-tetrafluoroethane. The method according to claim 1, wherein the reaction is performed at a reactor inlet concentration of hydrofluorocarbons containing two carbon atoms in a molecule of 6 mol% or less. The process according to claim 6, wherein the reactor inlet concentration of 1,1,1,2-tetrafluoroethane is 4 mol% or less. The process according to claim 1, wherein the reaction is carried out at a reaction pressure of 0 to 3 Mpa.