JP2017078069A - Method for producing methyl fluoride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of obtaining mixed gas comprising methyl fluoride and acid fluoride by the pyrolysis of a raw material compound in a gas phase, wherein the methyl fluoride and the acid fluoride included in the mixed gas are separated simply and easily.SOLUTION: A method for producing methyl fluoride has the steps for: (1) obtaining mixed gas comprising methyl fluoride and acid fluoride by the pyrolysis of a raw material compound in a gas phase; and (2) rectifying the mixed gas obtained in the step (1) to obtain methyl fluoride. The raw material gas is fluorine-containing methyl ether represented by formula (1).SELECTED DRAWING: None

Description

  The present invention relates to a method for producing methyl fluoride useful as a dry etching gas.

Hydrofluorocarbon is useful as an etching gas for microfabrication of semiconductors, liquid crystals, and the like, and in particular, methyl fluoride (CH ₃ F) has attracted attention as an etching gas for forming the most advanced microstructure.

  As a method for producing methyl fluoride, for example, a method of obtaining a mixed gas containing methyl fluoride and acid fluoride by thermally decomposing a raw material compound in a gas phase is known (Patent Document 1).

  In the above, as a method for separating methyl fluoride and acid fluoride contained in the obtained mixed gas, by cooling the mixed gas, from a low boiling point component mainly composed of methyl fluoride (boiling point -79 ° C.) And a non-reacted raw material (1,1), mainly composed of a gas component and an acid fluoride (for example, 3,3,3-trifluoro-2- (trifluoromethyl) propanoyl fluoride (boiling point 32 ° C.)). , 3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether (boiling point 68.5 ° C., etc.) has been proposed (patented). Reference 1).

  As another separation method, a method in which the obtained mixed gas is brought into contact with water or an aqueous alkaline solution to dissolve and remove the acid fluoride in the aqueous phase has been proposed (Patent Document 1). In this case, it has also been proposed to use alcohol instead of water and an aqueous alkali solution. Combustion treatment is facilitated by producing an ester by contacting with alcohol. In the conventional method, a gas containing a large amount of methyl fluoride obtained as described above is further subjected to a rectification operation to purify methyl fluoride.

JP 2014-114277 A

  The present invention provides a method for separating methyl fluoride and acid fluoride contained in a mixed gas more easily in a method for obtaining a mixed gas containing methyl fluoride and acid fluoride by thermally decomposing a raw material compound in a gas phase state. It is an issue to provide.

The present inventors have intensively studied to achieve the above-described object. As a result, it has been found that methyl fluoride can be selectively obtained by subjecting the mixed gas to the rectification operation as it is. The present invention has been completed as a result of further research based on these findings.
Item 1. A method for producing methyl fluoride, comprising:
(1) A step of obtaining a mixed gas containing methyl fluoride and acid fluoride by thermally decomposing the raw material compound in a gas phase; and (2) rectifying the mixed gas obtained in the step (1). A process comprising the step of obtaining methyl fluoride by
Item 2. Item 2. The method according to Item 1, wherein in the step (2), the mixed gas obtained in the step (1) is supplied to a rectification column.
Item 3. Item 3. The method according to Item 2, wherein the supplying is performed at a pressure exceeding atmospheric pressure.
Item 4.
Item 4. The method according to any one of Items 1 to 3, wherein the raw material compound is a fluorine-containing methyl ether represented by General Formula (1).

Wherein R ¹ and R ² are the same or different and may be substituted, a linear or branched monovalent aliphatic hydrocarbon group, monovalent aromatic hydrocarbon group or monovalent A cyclic aliphatic hydrocarbon group; a hydrogen atom or a halogen atom).

  According to the present invention, methyl fluoride can be purified from a mixed gas more easily in a method for obtaining a mixed gas containing methyl fluoride and acid fluoride by thermally decomposing the raw material compound in a gas phase state. Specifically, it is as follows. Conventionally, before purification, the mixed gas is cooled to perform fractional distillation, washed with water or an aqueous alkali solution, or contacted with alcohol or the like to dissolve and remove the acid fluoride in the aqueous phase. There was a need. On the other hand, in the present invention, it is not necessary to perform such an operation before purification. For this reason, the present invention is advantageous in that the operation is simpler. Furthermore, when the acid fluoride is removed by contact with alcohol, it is inevitable that a component corresponding to the industrial waste treatment product is generated by esterification. In the present invention, such an industrial waste treatment product may be produced. There is also an advantage that the object to be treated is easy to handle.

The method of the present invention is a method for producing methyl fluoride,
(1) A step of obtaining a mixed gas containing methyl fluoride and acid fluoride by thermally decomposing the raw material compound in a gas phase; and (2) rectifying the mixed gas obtained in the step (1). To obtain methyl fluoride.

1. Raw Material Compound The raw material compound used in the present invention is not particularly limited as long as it is a compound that generates a mixed gas containing methyl fluoride and acid fluoride by thermal decomposition in a gas phase state.

  A reaction that generates a mixed gas containing methyl fluoride and acid fluoride by thermal decomposition in a gas phase is already known, and is disclosed in, for example, Japanese Patent Application Laid-Open No. 2014-114277.

  In the present invention, the fluorine-containing methyl ether represented by the general formula (1) is preferably used as the raw material compound.

Wherein R ¹ and R ² are the same or different and may be substituted, a linear or branched monovalent aliphatic hydrocarbon group, monovalent aromatic hydrocarbon group or monovalent A cyclic aliphatic hydrocarbon group; a hydrogen atom or a halogen atom).

  There is no limitation in particular about the manufacturing method of fluorine-containing methyl ether used as a raw material compound, The compound obtained by arbitrary methods can be used.

In the general formula (1), preferably R ¹ and R ² are the same or different and may be substituted, a linear or branched monovalent aliphatic hydrocarbon group having 1 to 30 carbon atoms. , A monovalent aromatic hydrocarbon group having 6 to 12 carbon atoms or a monovalent cyclic aliphatic hydrocarbon group having 6 to 12 carbon atoms. More preferably, R ¹ and R ² are the same or different and may be substituted, a linear or branched monovalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, or 6 to 10 carbon atoms. A monovalent aromatic hydrocarbon group or a monovalent cycloaliphatic hydrocarbon group having 6 to 10 carbon atoms.

  In the above, the linear or branched monovalent aliphatic hydrocarbon group having 1 to 10 carbon atoms is not particularly limited, and examples thereof include an alkyl group having 1 to 10 carbon atoms.

  Specifically, examples of the alkyl group having 1 to 10 carbon atoms include a methyl group, an ethyl group, a trimethyl group, a propyl group, a 2-methylethyl group, a hexyl group, and an octyl group.

  Among the alkyl groups having 1 to 10 carbon atoms, alkyl groups having 1 to 6 carbon atoms are preferable, alkyl groups having 1 to 4 carbon atoms are more preferable, and alkyl groups having 1 to 3 carbon atoms are more preferable.

  The monovalent aromatic hydrocarbon group having 6 to 10 carbon atoms is not particularly limited, and examples thereof include a phenyl group, a methylphenyl group, and an ethylphenyl group.

  The monovalent cyclic aliphatic hydrocarbon group having 6 to 10 carbon atoms is not particularly limited, and examples thereof include a cyclohexyl group, a methylcyclohexyl group, and an ethylcyclohexyl group.

  In the above, the monovalent aliphatic hydrocarbon group, monovalent aromatic hydrocarbon group or monovalent cyclic aliphatic hydrocarbon group is at least one hetero selected from the group consisting of a fluorine atom, a chlorine atom and a bromine atom. At least one hydrogen atom may be substituted with an atom, or all hydrogen atoms may be substituted.

  In the above, the halogen atom is preferably a fluorine atom, a chlorine atom or a bromine atom, and more preferably a fluorine atom.

Although not particularly limited, examples of specific compounds that can be used as raw materials include 1,
1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether and the like.

In particular, perfluoroisobutylene ((CF ₃ ) ₂ C = CF ₂ )) produced as a by-product when producing hexafluoropropene used as a raw material for fluororesin has been conventionally discarded as an unnecessary substance. By reacting with methanol, 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether can be obtained, and by using this as a raw material of the method of the present invention, the waste can be effectively utilized. Therefore, the target product can be obtained at low cost by using a low-cost raw material. In the present invention, when 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether as a raw material is “obtained by reacting perfluoroisobutylene with methanol” Means that the 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether is limited to those obtained by such a reaction and is not obtained by any other reaction. To do. The method of obtaining 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether by reacting perfluoroisobutylene with methanol is a known method, and may be performed according to known reaction conditions. . For example, the reaction may be performed according to the method described in JP-T-2001-506261.

2. Process (1)
Step (1) of the present invention is a step of obtaining a mixed gas containing methyl fluoride and acid fluoride by thermally decomposing the above-described raw material compound in a gas phase state.

(I) Catalyst As the catalyst, any catalyst can be used without particular limitation as long as it is active for the thermal decomposition reaction in the gas phase. Examples of such a catalyst include metal oxides, fluorinated metal oxides, metal fluorides, and the like, and these can be used alone or in combination of two or more.

Among these, as the metal oxide, alumina, chromium oxide, titanium oxide, zinc oxide, and the like are preferable. Further, a fluorinated metal oxide obtained by fluorinating a part of these metal oxides can also be used. The fluorinated metal oxide catalyst may be a fluorinated metal oxide catalyst previously using hydrogen fluoride or the like, and a part of the fluorinated metal oxide catalyst was fluorinated in the reaction process of the production method of the present invention. Metal oxide catalysts may be used. As the metal fluoride, AlF ₃ , TiF ₄ , CrF _3, ZnF _{2 and the} like are preferable.

Among the metal oxides, alumina is preferable, and α-alumina and activated alumina can be used. As the activated alumina, ρ-alumina, χ-alumina, κ-alumina, η-alumina, pseudo-γ-alumina, γ-alumina, δ-alumina, θ-alumina and the like are used. Among these, γ-alumina and η-alumina are preferable, and γ-alumina is particularly preferable. Also,
Silica alumina (SiO ₂ / Al ₂ O ₃ ) can also be used as a catalyst as a composite oxide. The composition of silica SiO ₂ of silica alumina is preferably 20% by weight to 90% by weight, and more preferably 50% by weight to 80% by weight.

  The larger the pore volume of the catalyst, the higher the activity, and it is preferably 0.4 ml / g or more, particularly preferably 0.5 ml / g or more. The upper limit of the pore volume of the catalyst is not particularly limited, but is usually 5 ml / g or less, and preferably 2 ml / g or less in terms of reaction rate and catalyst strength. The pore volume can be measured by a gas adsorption method, a mercury intrusion method, or the like.

The catalyst may carry fluorides of alkali metals and alkaline earth metals such as KF, NaF and MgF ₂ .

The method for obtaining the fluorinated metal oxide is not particularly limited. For example, the fluorination reaction proceeds by bringing the metal oxide into contact with anhydrous hydrogen fluoride or chlorofluorocarbon under heating. Thus, a fluorinated metal oxide can be obtained. The method of bringing the metal oxide into contact with hydrogen fluoride is not particularly limited, and may be a continuous method in which hydrogen fluoride is circulated in a reaction tube filled with the catalyst, and hydrogen fluoride or fluorocarbon is contained in a container containing the catalyst. May be a batch type. In particular, the distribution method is preferable in that the processing time is short.
A fluorocarbon having a large number of fluorine atoms and a small number of carbon atoms is preferable. Examples thereof include trifluoromethane, difluorochloromethane, octafluoroethane and the like.

  The degree of fluorination of the metal oxide is not particularly limited, but the fluorine content is preferably about 5 to 50% by weight based on the weight of the entire fluorinated metal oxide.

  The temperature of the fluorination treatment of the metal oxide is preferably higher than the thermal decomposition reaction described later, for example, preferably about 150 to 500 ° C, more preferably about 200 ° C to 400 ° C, and about 250 ° C to 350 ° C. Is more preferable. If the temperature of the fluorination treatment is too low, the effect of the catalyst is small because the fluorination is insufficient, and if the treatment temperature is too high, a heat-resistant material is specially required, which is not practical.

(Ii) Thermal decomposition reaction conditions A specific method in which the thermal decomposition reaction of fluorinated methyl ether can proceed by bringing the fluorinated methyl ether into contact with the catalyst in the gas phase in the presence of the above-described catalyst. Is not particularly limited, for example, using a tubular flow reactor, filling the reactor with the catalyst described above, introducing fluorine-containing methyl ether used as a raw material into the reactor, The method of making it contact with a catalyst can be mentioned.

  As for the temperature of the thermal decomposition reaction, if the temperature is too low, the conversion rate of the raw material is lowered, and if it is too high, impurities tend to increase. For this reason, it is preferable to set it as about 100 to 400 degreeC, it is more preferable to set it as about 100 to 300 degreeC, and it is especially preferable to set it as about 100 to 250 degreeC.

  If the pressure in the reaction tube during the pyrolysis reaction is too low, there is a possibility that air may be mixed in. Therefore, if it is too high, it is necessary to consider the pressure resistance of the equipment, and the possibility of leakage increases. . From these points, the pressure is preferably about 0.05 to 1 MPa, more preferably about 0.1 to 0.5 MPa, and in particular, a pressure of about atmospheric pressure (about 0.1 MPa) is preferable for the reaction operation. .

The contact time for the reaction is not particularly limited, but the flow rate F (0 ° C., one atmospheric pressure (about 0.1 MPa)) of fluorinated methyl ether, which is the raw material gas supplied to the reaction tube, is cc / sec. The ratio of the catalyst filling amount W (g) to W) is preferably about 1 to 100 g · sec / cc, and the contact time represented by W / F (g · sec / cc) is preferably 1 to 50 g · sec. / Cc is more preferable, and about 5 to 30 g · sec / cc is still more preferable. If the contact time is too long, it takes a long time to obtain the product. Therefore, it is preferable to shorten the contact time in order to increase the production amount. However, if the contact time is too short, the conversion rate tends to decrease. . For this reason, the contact time with the highest productivity may be selected according to the type of catalyst used, the amount of catalyst, the reaction conditions, and the like, in terms of the conversion rate of raw materials and the selectivity of the target product. Usually, it is desirable to carry out the reaction by selecting a contact time at which the conversion rate is 100% according to the type of catalyst used, the amount of catalyst, reaction conditions, and the like.

(Iii) Mixed gas By the step (1), a mixed gas containing methyl fluoride and acid fluoride is obtained. The mixed gas contains, in addition to the target methyl fluoride (boiling point -79 ° C.), acid fluoride that is simultaneously generated by thermal decomposition, and at least any one of the raw material compounds and by-products, and impurities. One kind may be included. By-products such as propene (boiling point −47.7 ° C.), methyl chloride (boiling point −24 ° C.), propylene pentafluoride (boiling point −21.1 ° C.) and propane (boiling point) vary depending on the raw material compound. -1.4 ° C).

3. Step (2)
Step (2) of the present invention is a step of obtaining methyl fluoride by rectifying the mixed gas obtained in the step (1).

  Thereby, it is not necessary to perform fractional distillation operation, washing with water or removal of acid fluoride by alcohol in advance before purification, and methyl fluoride can be easily separated from acid fluoride.

  The acid fluoride usually has a boiling point of room temperature or higher such that the boiling point of 3,3,3-trifluoro-2- (trifluoromethyl) propanoyl fluoride is 32 ° C., and methyl fluoride (boiling point− 79 ° C.). In the mixed gas, methyl fluoride and acid fluoride are present in a molar ratio of 1: 1. When the mixed gas is left in an environment near room temperature as it is, acid fluoride is expected to condense.Unexpectedly, an interaction occurs between these two components, and the mixed gas becomes a whole as a whole. We found a phenomenon in which it behaves as a gas that does not condense even near room temperature (under a predetermined pressure condition). In the present invention, using this knowledge, the mixed gas can be directly subjected to a rectification operation to efficiently separate methyl fluoride.

  In the step (2), preferably, the mixed gas obtained in the step (1) is supplied to the rectification column. It is preferable to perform this supply at a pressure exceeding atmospheric pressure. This makes it easy to feed the mixed gas into the rectification column. The pressure at this time is more preferably 0.2 MPa to 0.15 MPa. When the pressure is within this range, the mixed gas can be effectively supplied to the rectification column while avoiding condensation of the mixed gas. The higher the temperature of the gas after the reaction, the more the reaction gas can be fed into the rectification column at a higher pressure. Usually, the gas after reaction is often sent to a rectification column by a compressor. In addition, since the pressure of the rectification column is lowered by cooling the temperature of the rectification column, a pressure difference between the suction side and the discharge side of the compressor gas tends to be generated, and the mixed gas is supplied to the rectification column. It becomes easy. In the cooling of the rectifying column, the effect of lowering the pressure of the rectifying column is particularly increased by cooling the kettle of the rectifying column in which the liquid is stored, and the supply of the mixed gas to the rectifying column is facilitated.

  The rectification is not particularly limited, but usually, two rectification columns are provided, a low boiling point component such as methane or ethylene is extracted from the top of the first rectification column, and the remaining components containing methyl fluoride and acid fluoride Is obtained from the bottom of the column, and this is further subjected to a second rectifying column to extract methyl fluoride from the top of the column. At this time, the purity of methyl fluoride finally obtained from the tops of the two rectification columns is 99.999% by weight or more.

  Hereinafter, the present invention will be described in more detail with reference to examples.

1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether was introduced into a reactor filled with a γ-alumina catalyst heated to 150 ° C. in a gas state and thermally decomposed. The gas after the pyrolysis reaction was collected in the cooled first rectification column under a pressure of 0.15 MPa. The composition of the collected reaction gas was as follows.
Methane 0.002mol%
0.0036 mol% ethylene
Methyl fluoride 46.17 mol%
Propylene 0.0092 mol%
1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether 7.58 mol%
Acid fluoride 46.17 mol%
Other components 0.0652 mol%
After removing low-boiling compounds such as methane and ethylene in the first rectification column, the remaining components were transferred to the second rectification column. After purification in the second rectification column, methyl fluoride was extracted from the top of the rectification column and collected. The purity of the obtained methyl fluoride was 99.999 mol%. Since neither acid nor water such as hydrogen fluoride is generated, a washing tower for removing acid, an alkali tower and a drying tower containing molecular sieves for removing water are not required.

  The high-boiling components remaining in the rectification tank of the second rectification column were directly introduced into the incinerator through the stainless steel pipe and decomposed.

<Comparative Example 1>
The reaction gas after the thermal decomposition reaction obtained in the same manner as in the Examples was sequentially passed through a washing tower, an alkali tower containing 5% potassium hydroxide aqueous solution, and a drying tower containing molecular sieves. Then, it transferred to the 1st rectification tower. After removing low-boiling compounds such as methane and ethylene in the first rectification column, the remaining components were transferred to the second rectification column. Purification was carried out while refluxing in the second rectification column, and methyl fluoride was extracted from the top of the rectification column and collected. The purity of the obtained methyl fluoride was 99.999 mol%.

  However, in the method of Comparative Example 1, not only the washing tower and the alkali tower need additional equipment and the equipment cost is high, but also the unwashed 1,1,3,3, A mixed solution containing carboxylic acid and hydrofluoric acid formed by hydrolysis of 3-pentafluoro-2-trifluoromethylpropyl methyl ether and acid fluoride accumulated. Since this waste is a mixed solution of an organic substance and a water-soluble substance, there is a problem that it is difficult to treat as an industrial waste. Moreover, since this waste liquid has high acidity and corrodes the metal, it cannot be directly passed through a metal pipe made of stainless steel or the like, and is difficult to transfer to an incinerator. In order to transfer the waste liquid, a lined pipe or container such as a fluororesin is required. In addition, since this waste liquid contains a large amount of moisture, extra energy was required to burn it.

<Comparative example 2>
The reaction gas after the thermal decomposition reaction obtained in the same manner as in the Examples was sequentially passed through an absorption tower containing an aqueous methanol solution and a drying tower containing molecular sieves, and then transferred to the first rectification tower. In the first rectification column, low-boiling compounds such as methane and ethylene were removed. Thereafter, the remaining components were transferred to the second rectification column. Purification was carried out while refluxing in the second rectification column, and methyl fluoride was extracted from the top of the rectification column and collected. The purity of the obtained methyl fluoride was 99.999 mol%.

  However, a large amount of methanol and additional equipment for the absorption tower are required, which not only increases the chemical cost and the equipment cost, but also includes an unreacted 1,1,3,3,3-pentafluoro- A mixed solution containing ester and hydrogen fluoride formed by reacting 2-trifluoromethylpropyl methyl ether and acid fluoride with methanol accumulated. Although this waste is an organic matter, it contains hydrogen fluoride, which causes a problem that it is difficult to treat as an industrial waste. Although this waste liquid is mainly composed of organic substances, its acidity is not high, but hydrogen fluoride gradually corrodes the metal, so it cannot be flowed into metal pipes such as stainless steel for a long time and should be transferred to an incinerator. It was difficult. In order to transfer the waste liquid, a lined pipe or container such as a fluororesin is required. In addition, since this waste liquid contains a large amount of hydrogen fluoride, extra energy was required to burn it.

Claims (4)

A method for producing methyl fluoride, comprising:
(1) A step of obtaining a mixed gas containing methyl fluoride and acid fluoride by thermally decomposing the raw material compound in a gas phase; and (2) rectifying the mixed gas obtained in the step (1). A process comprising the step of obtaining methyl fluoride by The method according to claim 1, wherein in the step (2), the mixed gas obtained in the step (1) is supplied to a rectification column. The method according to claim 2, wherein the supplying is performed at a pressure exceeding atmospheric pressure. The method as described in any one of Claims 1-3 whose said raw material compound is a fluorine-containing methyl ether represented by General formula (1).

Wherein R ¹ and R ² are the same or different and may be substituted, a linear or branched monovalent aliphatic hydrocarbon group, monovalent aromatic hydrocarbon group or monovalent A cyclic aliphatic hydrocarbon group; a hydrogen atom or a halogen atom).