JP2014181194A - Method for purifying pentafluorobutane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently purifying 1,1,1,3,3-pentafluorobutane useful as a gas for plasma reactions targeting semiconductors.SOLUTION: A crude 1,1,1,3,3-pentafluorobutane including chlorofluorinated hydrocarbons as impurities is mixed with a solvent, and after the 1,1,1,3,3-pentafluorobutane has been deposited at a low temperature, the deposited solid is filtered and separated so as to remove the impurities and to purify the 1,1,1,3,3-pentafluorobutane. The residual solvent can, furthermore, be subsequently removed based on water washing.

Description

  The present invention relates to 1,1,1,3, which is a fluorine-containing alkane useful as a gas for plasma reaction such as etching, CVD, etc., a fluorine-containing pharmaceutical intermediate, or a hydrofluorocarbon solvent useful in the field of manufacturing semiconductor devices. Related to 3-pentafluorobutane. Highly purified 1,1,1,3,3-pentafluorobutane is an etching gas for plasma, a gas for chemical vapor deposition (CVD), etc., particularly in the field of manufacturing semiconductor devices using a plasma reaction. It is suitable for.

  The miniaturization of semiconductor manufacturing technology is progressing, and the line width of 20 nm and further 10 nm generation has been adopted in the most advanced process. The technical difficulty at the time of processing is also improved with miniaturization, and technical development is advanced by approach from various fields, such as a material to be used, an apparatus, and a processing method.

Against this background, we have developed a dry etching gas that can be used in the most advanced dry etching processes, and a moderately fluorinated saturated hydrocarbon containing 1,1,1,3,3-pentafluorobutane. However, it has been found that a multilayer laminated film composed of a silicon nitride film and a silicon oxide film can be etched simultaneously (Patent Document 1).
On the other hand, several methods are known as methods for producing 1,1,1,3,3-pentafluorobutane. In the method described in Patent Document 2, chlorofluorobutane is fluorinated with hydrogen fluoride under an antimony pentachloride catalyst to obtain 1,1,1,3,3-pentafluorobutane. In the method of Patent Document 3, again, antimony pentachloride, group V and group VI chlorides are used as catalysts, 1,1,1,3,3-pentachlorobutane is used as a raw material, and fluorine is used with hydrogen fluoride. Is disclosed, and a method of recirculating a part of unreacted hydrogen fluoride is employed.
Several methods for purifying crude 1,1,1,3,3-pentafluorobutane obtained by the above reaction are also disclosed. In Patent Document 4, in order to remove chlorofluoroalkenes contained as impurities, alkene is halogenated by treatment with a halogen gas such as chlorine gas or fluorine gas, and 1,1,1,3,3 -Conversion to a compound having a higher boiling point than pentafluorobutane, followed by distillation separation. In Patent Document 5, chlorine gas is added to C4 olefin under light irradiation to convert it into a compound having a high boiling point. Furthermore, Patent Document 6 discloses a method for removing chlorofluoroolefins using a method selected from chlorine and hydrogen fluoride treatment (addition reaction), distillation, extractive distillation, adsorbent treatment, oxidation reaction, and the like. Has been.

Japanese Patent Application No. 2012-284353 Japanese Patent Laid-Open No. 8-099918 Special Table 2007-500228 Special Table 2002-524431 Special Table 2004-521120 JP-T-2004-505936

  When crude 1,1,1,3,3-pentafluorobutane is produced by the methods described in Patent Literature 2 and Patent Literature 3, the 1,1,1,3,3-pentachlorobutane used as a raw material is Since the reaction of fluorination with hydrogen fluoride is adopted, the elimination of hydrogen chloride from the raw material 1,1,1,3,3-pentachlorobutane occurs during the reaction, producing C4 alkenes. Is inevitable.

  Therefore, a method of adding a halogen gas such as chlorine or fluorine gas to the olefin is employed in order to facilitate the removal of the C4 alkene as described in Patent Document 4 and Patent Document 5. Such a method has the advantage that the C4 olefin to which halogen is added is converted into a compound having a high boiling point, so that it can be easily separated by distillation. However, a highly corrosive halogen gas must be used. Moreover, due to the high reactivity of the halogen gas, 1,1,1,3,3-pentafluorobutane itself has a drawback that it is partially halogenated, and it is very difficult to control the halogenation reaction.

  Patent Document 6 describes that a chemical removal method by treatment with chlorine, hydrogen fluoride, or an oxidizing agent, and a removal method of chloroolefins selected from physical methods such as distillation and extractive distillation can be applied. However, the chemical removal method such as the former is difficult to proceed with the reaction to chloroolefins contained in trace amounts, and its effect is low. The latter method is very difficult to control the distillation. It is.

  As a result of intensive studies on the above problems, we have found a method for efficiently separating impurities and chlorinated fluorinated hydrocarbons contained in 1,1,1,3,3-pentafluorobutane. In particular, as a material applied to the plasma reaction, a material with reduced impurities is preferable as much as possible, and further reduction is desired from this viewpoint.

Thus, according to the present invention, crude 1,1,1,3,3-pentafluorobutane containing chlorinated fluorinated hydrocarbon as an impurity is mixed with alcohol, and 1,1,1,3,3 at low temperature. There is provided a method for purifying 1,1,1,3,3-pentafluorobutane, wherein 3-pentafluorobutane is precipitated, and the precipitated solid is separated by filtration to remove impurities.
The freezing point of 1,1,1,3,3-pentafluorobutane is described in Journal of American Chemical Society, Vol. 67, 1197 (1945) describes -35.01 ° C. However, even when commercially available 1,1,1,3,3-pentafluorobutane was cooled to −40 ° C. to −50 ° C., no solidification was observed and the liquid state was maintained. Further, it was found that as the temperature was lowered, 1,1,1,3,3-pentafluorobutane solidified between −55 to −60 ° C. and a white solid was precipitated. Based on this knowledge obtained, we have completed the present invention.

  The 1,1,1,3,3-pentafluorobutane used in the present invention can be produced, for example, by the methods described in JP-A-8-99918 and JP-T2007-500228. In either case, chloro (fluoro) butane is used as a starting material, metal chloride of group V or group VI such as antimony pentachloride is used as a catalyst, and chlorine is replaced with fluorine by hydrogen fluoride.

  On the other hand, when impurities in commercially available 1,1,1,3,3-pentafluorobutane were analyzed, (E) -1,1,1-trifluoro-3-chloro-2-butene, (Z)- It was found that it mainly contains impurities having 4 carbon atoms such as 1,1,1-trifluoro-3-chloro-2-butene, 1-chloro-1,1,3,3-tetrafluorobutane. .

  As the alcohol used in the present invention, it is essential to have a freezing point lower than the freezing point of 1,1,1,3,3-pentafluorobutane. Therefore, methanol (freezing point: −98 ° C.), ethanol (freezing point: -114 ° C.), n-propanol (freezing point: −126 ° C.), alcohol having 3 carbon atoms such as isopropanol (freezing point: −89 ° C.), n-butanol (freezing point: −90 ° C.), isobutanol (freezing point: −108). C), 2-butanol (freezing point: −117 ° C.), and the like. Among these, methanol, ethanol, and isopropanol are preferable. In the subsequent step of separating residual alcohol using water, From the viewpoint of ease of separation of 1,1,1,3,3-pentafluorobutane, methanol and ethanol are Ri preferred.

  The addition amount of these alcohols is preferably 20 to 60% by weight, more preferably 30 to 50% by weight, based on 1,1,1,3,3-pentafluorobutane. If the amount of alcohol added is too small, the removal efficiency of the chlorofluorohydrocarbon, which is an impurity, will be reduced. If the amount of alcohol is too large, the amount of 1,1,1,3,3-pentafluorobutane recovered will be low. The yield per treatment is reduced.

  The temperature at which the liquid mixture with the alcohol is cooled to precipitate (crystallize) 1,1,1,3,3-pentafluorobutane is at least the freezing point of 1,1,1,3,3-pentafluorobutane. (The temperature we have confirmed: between -55 and -60 ° C). The temperature is preferably in the range of −60 to −100 ° C., more preferably in the range of −70 to −90, but is set according to the melting point of the alcohol used. If the cooling temperature is too high, the amount of 1,1,1,3,3-pentafluorobutane deposited decreases, and the recovery rate decreases with respect to the amount of 1,1,1,3,3-pentafluorobutane charged. . On the other hand, when the cooling temperature is set low, the cooling device is loaded, which is disadvantageous in terms of energy.

  Filtration is used as a method for separating the precipitated 1,1,1,3,3-pentaflurobutane and the mother liquor mainly composed of alcohol. The filtration device itself is preferably set to a temperature at which 1,1,1,3,3-pentafluorobutane is precipitated (crystallization) or lower. If the cooling temperature is too high, a part of the precipitated 1,1,1,3,3-pentafluorobutane solid melts, and the recovered amount of 1,1,1,3,3-pentafluorobutane increases. Go down. If the cooling temperature is too low, the cooling device is loaded, which is disadvantageous in terms of energy.

  The filtration operation is preferably performed quickly under reduced pressure or under pressure. Since filtration under atmospheric pressure requires time, a part of the 1,1,1,3,3-pentafluorobutane solid melts, resulting in 1,1,1,3,3-pentafluorobutane. There is a possibility that the amount of recovered material will decrease.

  The filtered solid is washed with the alcohol used. The alcohol at this time is also preferably at the same temperature as the temperature at which 1,1,1,3,3-pentafluorobutane is precipitated (crystallized). When the temperature is too high, a part of the precipitated solid is melted, and the recovered amount of 1,1,1,3,3-pentafluorobutane is lowered. If the temperature is too low, the viscosity of the alcohol increases, so that a long time is required for washing.

  The amount of alcohol used for washing is preferably 10 to 60% and more preferably 20 to 50% by weight based on the charged 1,1,1,3,3-pentafluorobutane. If the amount of cleaning alcohol is too small, the effect of removing impurities adhering to the solid surface of the deposited 1,1,1,3,3-pentafluorobutane decreases, and if the amount of alcohol is too large, The part melts and the recovered amount of 1,1,1,3,3-pentafluorobutane decreases.

  Solid 1,1,1,3,3-pentafluorobutane washed with alcohol is melted by gradually raising the temperature and returns to a liquid state. In many cases, 1,1,1,3,3-pentafluorobutane that has returned to the liquid state is in a mixed state with alcohol, and thus the alcohol is removed. Since the alcohol used in the present invention has a higher boiling point than 1,1,1,3,3-pentafluorobutane (boiling point: 40 ° C.), distillation separation can also be applied. It cannot be said that it is advantageous from the viewpoint of energy efficiency, and is not applicable when an azeotrope is formed like ethanol.

  Therefore, in order to efficiently and easily remove alcohol from 1,1,1,3,3-pentafluorobutane, water washing is performed. The amount of water used for washing is 1 to 5 times by weight with respect to a mixture of 1,1,1,3,3-pentafluorobutane and alcohol in which the precipitated solid is dissolved, more preferably 2 ~ 4 times the amount. If the amount of washing water is too small, the effect of removing alcohol decreases, so it is necessary to increase the number of washings. If the amount of washing water is too large, the amount of drainage increases, which is not preferable.

  As a method of washing, put a mixture of 1,1,1,3,3-pentafluorobutane and alcohol and a predetermined amount of water in a container, stir for a while, let stand, separate into two layers, Alternatively, the mixture may be taken out, or a mixture of 1,1,1,3,3-pentafluorobutane and alcohol and a predetermined amount of water may be circulated and allowed to stand or be separated into two layers. The mixture of alcohol and water in the upper layer can be recovered by distillation and reused according to a usual method. On the other hand, 1,1,1,3,3-pentafluorobutane in the lower layer can reduce the incorporated moisture by using a desiccant such as alumina or molecular sieve.

  As described above, crude 1,1,1,3,3-pentafluorobutane containing chlorinated fluorinated hydrocarbon as an impurity is mixed with alcohol, and 1,1,1,3,3-penta is mixed at a low temperature. Fluorobutane is precipitated, and the precipitated solid is separated by filtration and washed with water to reduce the amount of chlorinated fluorinated hydrocarbon impurities and obtain 1,1,1,3,3-pentafluorobutane. can do.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited the range by the following Examples. Note that “%” represents “% by weight” unless otherwise specified.

The analysis conditions adopted below are as follows.
・ Gas chromatography analysis (GC analysis)
Apparatus: Product name “HP-6890” manufactured by Agilent
Column: GL Sciences, product name “Inert Cap-1”, length 60 m, inner diameter 0.25 mm, film thickness 1.5 μm
Column temperature: held at 40 ° C. for 10 minutes, then heated at 20 ° C./minute, and then held at 240 ° C. for 10 minutes Injection temperature: 200 ° C.
Carrier gas: nitrogen split ratio: 100/1
Detector: FID

・ Impurity analysis (gas chromatography mass spectrometry)
GC part: manufactured by Agilent, product name "HP-6890"
Column: GL Sciences, product name “Inert Cap-1”, length 60 m, inner diameter 0.25 mm, film thickness 1.5 μm
Column temperature: held at 40 ° C. for 10 minutes, then heated at 20 ° C./minute, and then held at 240 ° C. for 10 minutes MS part: manufactured by Agilent, product name “5973 NETWORK”
Detector EI type (acceleration voltage: 70eV)

[Analysis Example 1]
As a result of analyzing impurities in 1,1,1,3,3-pentafluorobutane manufactured by Apollo Scientific using a gas chromatography mass spectrometer, (E) -1,1,1 was obtained as chlorine-containing impurities. -Detected trifluoro-3-chloro-2-butene, (Z) -1,1,1-trifluoro-3-chloro-2-butene, 1-chloro-1,1,3,3-tetrafluorobutane It was done.

[Example 1]
26 g of 1,1,1,3,3-pentafluorobutane (manufactured by Apollo Scientific) and 10.9 g of methanol were placed in a 100 mL eggplant flask equipped with a stir bar and stirred and mixed. The eggplant flask was immersed in an ethanol bath, and dry ice was added little by little to gradually lower the temperature. The ethanol bath was lowered to -75 ° C to maintain that temperature. Several minutes later, a white solid began to precipitate in the eggplant flask, and the stirring bar became non-rotatable. The precipitated white solid was hard enough to be loosened by a spoon. Separately, a glass filter whose periphery was cooled with dry ice was prepared, and the solid deposited in the eggplant flask was quickly transferred to the glass filter and filtered under reduced pressure. The solid remaining in the glass filter was washed with 10 ml (7.9 g) of methanol that had been cooled to -70 ° C. The glass filter was gradually returned to room temperature, and 19.35 g of the dissolved liquid was recovered in a 50 mL eggplant flask. When the liquid in the eggplant flask was analyzed by gas chromatography, 59.9% of 1,1,1,3,3-pentafluorobutane was recovered. The change in the amount of impurities is as shown in Table 1.

[Example 2]
In Example 1, the same operation as in Example 1 was performed, except that 10.9 g of methanol was changed to a mixed solvent of 11.3 g of ethanol and 10 ml (7.6 g) of ethanol for washing. In a 50 mL eggplant flask, 18.53 g of liquid was recovered and further analyzed by gas chromatography. As a result, 51.7% of 1,1,1,3,3-pentafluorobutane was recovered. The change in the amount of impurities is as shown in Table 1.

[Example 3]
In Example 1, the same operation as in Example 1 was performed except that 10.9 g of methanol was changed to a mixed solvent of 11.8 g of isopropanol and 10 ml (7.9 g) of isopropanol for washing. When 20.7 g of liquid was recovered in a 50 mL eggplant flask, and further analyzed by gas chromatography, 64.1% of 1,1,1,3,3-pentafluorobutane was recovered. The change in the amount of impurities is as shown in Table 1.

[Example 4]
19.3 g of a mixture of 1,1,1,3,3-pentafluorobutane and methanol obtained in Example 1 and 40 g of water were placed in a 100 ml eggplant flask, and the interface was maintained for 10 minutes with a stir bar. The mixture was vigorously stirred so as not to separate into two layers. The contents were transferred to a separatory funnel and allowed to stand and separated into two layers. When the lower layer was extracted, 14.1 g of 1,1,1,3,3-pentafluorobutane was recovered. As a result of analysis by gas chromatography, it was confirmed that methanol was removed. (Gas chromatography detection limit: 12 ppm)

[Comparative Example 1]
In Example 1, the same operation as in Example 1 was performed except that 10.9 g of methanol was changed to 11.7 g of acetone. After standing for 30 minutes, slight white solid deposition was confirmed, but the stirrer was rotating. 1.17 g of liquid was recovered in a 50 mL eggplant flask and further analyzed by gas chromatography. As a result, 3.0% of 1,1,1,3,3-pentafluorobutane was recovered. It wasn't too much.

[Comparative Example 2]
In Example 1, the same operation as in Example 1 was performed except that 10.9 g of methanol was changed to 13 g of toluene. After standing for 10 minutes, precipitation of a white solid was confirmed, but it was a very hard solid, could not be loosened even with a spoon, and was very difficult to remove from the eggplant flask. When 6.65 g of liquid was recovered in a 50 mL eggplant flask and further analyzed by gas chromatography, 17.7% of 1,1,1,3,3-pentafluorobutane was recovered. It wasn't too much.

From the above results, the content of chlorofluorohydrocarbon can be reduced to 1/3 or less by crystallizing crude 1,1,1,3,3-pentafluorobutane using alcohol. .

Claims (4)

Crude 1,1,1,3,3-pentafluorobutane containing chlorinated fluorinated hydrocarbon as an impurity is mixed with alcohol, and 1,1,1,3,3-pentafluorobutane is precipitated at a low temperature. And purifying the precipitated solid by filtration at a low temperature to remove impurities, and a method for purifying 1,1,1,3,3-pentafluorobutane. The purification method according to claim 1, wherein the alcohol has 4 or less carbon atoms and a melting point of -80 ° C or less. The 1,1,1,3,3-pentafluorobutane obtained by filtration at low temperature is returned to room temperature, and the 1,1,1,3,3-pentafluorobutane that has become liquid is washed with water. The purification method according to claim 1 or 2, further comprising a step of removing residual alcohol in 1,1,1,3,3-heptafluorobutane. 4. The purification method according to claim 1, wherein the alcohol is methanol and / or ethanol.