Method for preserving 3-hydroxy-2-butenoic acid

Abstract

Provided is a method for storing fluoro-2-butene, which is not susceptible to isomerization in storage. Fluoro-2-butene represented by the general formula C4H x F y x is 0 or more and less than 7, y is 1 or more and less than 8, and x+y is 8, with or without hydrogen fluoride as an impurity. When the gas phase portion contains hydrogen fluoride, the hydrogen fluoride concentration is set to 100 ppm by volume or less, and the fluoro-2-butene is stored in a container.

Description

Technical Field

[0001] This invention relates to a method for preserving fluoro-2-butene. Background Technology

[0002] Unsaturated fluorocarbon compounds disclosed in Patent Documents 1 and 2 are used as etching gases in dry etching. Among unsaturated fluorocarbon compounds, fluoro-2-butene has attracted attention as an etching gas that can be used in cutting-edge dry etching processes.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Publication No. 6451810

[0006] Patent Document 2: Japanese Patent Publication No. 034972, 2019 Summary of the Invention

[0007] However, fluoro-2-butene exists as Z-type and E-type geometric isomers, which may undergo isomerization reactions during long-term storage.

[0008] The objective of this invention is to provide a method for preserving fluoro-2-butene that is not prone to isomerization during storage.

[0009] In order to solve the above-mentioned problems, one solution of the present invention is as described in [1] to [3] below.

[0010] [1] A method for preserving fluoro-2-butene, wherein the fluoro-2-butene is produced by the general formula C4H x F y This means that in the general formula, x is greater than or equal to 0 and less than or equal to 7, y is greater than or equal to 1 and less than or equal to 8, and x + y equals 8.

[0011] The fluoro-2-butene is stored in a container to ensure that it is free of hydrogen fluoride as an impurity.

[0012] Alternatively, when the fluoro-2-butene contains the hydrogen fluoride, the concentration of hydrogen fluoride in the gas phase is set to below 100 ppm by volume, and the fluoro-2-butene is stored in a container.

[0013] [2] According to the preservation method of fluoro-2-butene described in [1], the fluoro-2-butene is at least one selected from Z-1,1,1,4,4,4-hexafluoro-2-butene, E-1,1,1,4,4,4-hexafluoro-2-butene, Z-1,1,1,2,4,4,4-heptafluoro-2-butene, E-1,1,1,2,4,4,4-heptafluoro-2-butene, Z-1,1,1,2,3,4,4,4-octafluoro-2-butene and E-1,1,1,2,3,4,4,4-octafluoro-2-butene.

[0014] [3] According to the preservation method of fluoro-2-butene described in [1] or [2], it shall be stored at a temperature above -20°C and below 50°C.

[0015] According to the present invention, the isomerization reaction of fluoro-2-butene is not easily carried out during storage. Detailed Implementation

[0016] Hereinafter, one embodiment of the present invention will be described. Furthermore, this embodiment represents one example of the present invention, and the present invention is not limited to this embodiment. In addition, various modifications or improvements can be made to this embodiment, and such modifications or improvements are also included in the present invention.

[0017] The method for preserving fluoro-2-butene in this embodiment is based on the general formula C4H x F y This refers to a method for storing fluoro-2-butene in which x is 0 or more and 7 or less, y is 1 or more and 8 or less, and x+y is 8. The method involves storing the fluoro-2-butene in a container with or without hydrogen fluoride (HF) as an impurity. When the fluoride is present, the concentration of hydrogen fluoride in the gas phase is set to 100 ppm or less by volume.

[0018] If fluoro-2-butene contains hydrogen fluoride as an impurity, the isomerization reaction of fluoro-2-butene will be promoted due to the catalytic effect of hydrogen fluoride. Therefore, fluoro-2-butene containing hydrogen fluoride may undergo isomerization during storage, resulting in a decrease in purity.

[0019] The fluoro-2-butene preserved by the preservation method of this embodiment does not contain hydrogen fluoride, or if it does, the content is very low. Therefore, even with long-term storage, it is not prone to isomerization reaction and is not likely to cause a decrease in purity. Thus, fluoro-2-butene can be preserved stably for a long time.

[0020] The technologies disclosed in Patent Documents 1 and 2 do not take into account the concentration of hydrogen fluoride in unsaturated fluorocarbon compounds. Therefore, when storing fluoro-2-butene according to the technologies disclosed in Patent Documents 1 and 2, the isomerization reaction of fluoro-2-butene is promoted by hydrogen fluoride. As a result, fluoro-2-butene undergoes an isomerization reaction during storage, leading to a decrease in purity.

[0021] The method for preserving fluoro-2-butene according to this embodiment will be described in more detail below.

[0022] [Fluoro-2-butene]

[0023] The fluoro-2-butene in this embodiment is derived from the general formula C4H x F y This indicates that the fluoro-2-butene must satisfy the following three conditions in the general formula: x is 0 or higher and 7 or lower, y is 1 or higher and 8 or lower, and x+y is 8. There are no particular restrictions on the types of fluoro-2-butene as long as these conditions are met.

[0024] As specific examples of fluoro-2-butene, mention may be made of (Z)-CHF2-CF=CF-CF3, (E)-CHF2-CF=CF-CF3, (Z)-CF3-CH=CF-CF3, (E)-CF3-CH=CF-CF3, (Z)-CH2F-CF=CF-CF3, (E)-CH2F-CF=CF-CF3, (Z)-CHF2-CH=CF-CF3, (E)-CHF2-CH=CF-CF3, (Z)-CHF2-CF=CF-CHF2, (E)-CHF2-CF=CF-CHF2, (Z)-CF3-CH=CH-CF3, (E)-CF3-CH=CH-CF3, (Z)-CH3-CF=CF-CF3, (E)-CH3-CF=CF-CF3, (Z)-CH2F-CH=CF-CF3, (E)-CH2F-CH=CF-CF3, (Z)-CH2F-CF=CH-CF3, (E)-CH2F-CF=CH-CF3, (Z)-CH2F-CF=CF-CHF2, (E)-CH2F-CF=CF-CHF2, (Z)-CHF2-CH=CH-CF3, (E)-CHF2-CH=CH-CF3, (Z)-CHF2-CF=CH-CHF2, (E)-CHF2-CF=CH-CHF2, (Z)-CH3-CH=CF-CF3, (E)-CH3-CH=CF-CF3, (Z)-CH3-CF=CH-CF3, (E)-CH3-CF=CH-CF3, (Z)-CH3-CF=CF-CHF2, (E)-CH3-CF=CF-CHF2, (Z)-CH2F-CH=CH-CF3, (E)-CH2F-CH=CH-CF3, (Z)-CH2F-CH=CF-CHF2, (E)-CH2F-CH=CF-CHF2, (Z)-CH2F-CF=CH-CHF2, (E)-CH2F-CF=CH-CHF2, (Z)-CH2F-CF=CF-CH2F, (E)-CH2F-CF=CF-CH2F, (Z)-CHF2-CH=CH-CHF2, (E)-CHF2-CH=CH-CHF2, (Z)-CH3-CH=CH-CF3, (E)-CH3-CH=CH-CF3, (Z)-CH3-CH=CF-CHF2, (E)-CH3-CH=CF-CHF2, (Z)-CH3-CF=CH-CHF2, (E)-CH3-CF=CH-CHF2, (Z)-CH3-CF=CF-CH2F, (E)-CH3-CF=CF-CH2F, (Z)-CH2F-CF=CH-CH2F, (E)-CH2F-CF=CH-CH2F,(Z)-CH2F-CH=CH-CHF2, (E)-CH2F-CH=CH-CHF2, (Z)-CH3-CH=CH-CHF2 , (E)-CH3-CH=CH-CHF2, (Z)-CH3-CH=CF-CH2F, (E)-CH3-CH=CF-CH2F, (Z)-CH3-CF=CH-CH2F, (E)-CH3-CF=CH-CH2F, (Z)-CH3-CF=CF-CH3, (E)-CH3-CF=CF-CH3 , (Z)-CH2F-CH=CH-CH2F, (E)-CH2F-CH=CH-CH2F, (Z)-CH3-CH=CH-CH2F, (E)-CH3-CH=CH-CH2F, (Z)-CH3-CH=CF-CH3, (E)-CH3-CH=CF-CH3.

[0025] These fluoro-2-butenes can be used alone or in combination of two or more. Furthermore, among the aforementioned fluoro-2-butenes, E / Z geometric isomers exist as described above, but any of the aforementioned geometric isomers of fluoro-2-butene can be used in the fluoro-2-butene preservation method of this embodiment.

[0026] When storing fluoro-2-butene in a container, a gas consisting solely of fluoro-2-butene can be stored in the container, or a mixture of fluoro-2-butene and a diluent gas can be stored in the container. As the diluent gas, at least one selected from nitrogen (N2), helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe) can be used. The content of the diluent gas is preferably 90% by volume or less, more preferably 50% by volume or less, relative to the total amount of gas stored in the container.

[0027] [container]

[0028] Regarding containers for storing fluoro-2-butene, there are no particular restrictions on their shape, size, or material, as long as they can contain and seal the fluoro-2-butene. Containers can be made of metal, ceramic, resin, etc. Examples of metals include manganese steel, chromium-molybdenum steel, stainless steel, HASTELLOY (registered trademark), and INCONEL (registered trademark).

[0029] [Impurities]

[0030] The fluoro-2-butene of this embodiment may or may not contain hydrogen fluoride as an impurity. When the impurity is present, the concentration of hydrogen fluoride in the gas phase is set to 100 ppm or less by volume and stored in a container. Therefore, as described above, the isomerization reaction of fluoro-2-butene is not easily promoted, and as a result, the isomerization reaction of fluoro-2-butene is not easily carried out during storage. Furthermore, if the concentration of hydrogen fluoride in the gas phase is below the aforementioned concentration, the concentration of hydrogen fluoride in the liquid phase is also sufficiently reduced.

[0031] Furthermore, hydrogen fluoride may be generated during the manufacturing process of fluoro-2-butene. Additionally, the concentration of hydrogen fluoride in fluoro-2-butene can be quantified using an infrared spectrophotometer; the absence of the aforementioned impurities refers to situations where quantification using an infrared spectrophotometer is not possible.

[0032] In order to prevent the isomerization reaction of fluoro-2-butene from occurring during storage, the concentration of hydrogen fluoride in the gas phase needs to be less than 100 ppm by volume, preferably less than 50 ppm by volume, and more preferably less than 10 ppm by volume.

[0033] Furthermore, the concentration of hydrogen fluoride in the gas phase can also be above 1 ppm by volume.

[0034] [Method for manufacturing fluorinated 2-butene with low hydrogen fluoride concentration]

[0035] There are no particular limitations on the method for producing fluoro-2-butene with a low concentration of hydrogen fluoride. For example, methods for removing hydrogen fluoride from fluoro-2-butene with a high concentration of hydrogen fluoride can be cited. There are also no particular limitations on the method for removing hydrogen fluoride from fluoro-2-butene; known methods can be used. For example, methods can be used to adsorb hydrogen fluoride onto an adsorbent by contacting it with an adsorbent, methods can be used to react hydrogen fluoride with a reactant by contacting it with a reactant, and methods can be used for separation by distillation. Specific examples of adsorbents include molecular sieves, sodium fluoride, and other metal fluorides.

[0036] [Pressure conditions during storage]

[0037] In the storage method of fluoro-2-butene in this embodiment, the pressure conditions during storage are not particularly limited as long as they can seal the fluoro-2-butene in the container. Preferably, the pressure is 0.05 MPa or more and 5 MPa or less, more preferably 0.1 MPa or more and 3 MPa or less. If the pressure conditions are within the above range, the fluoro-2-butene can be circulated without heating when the container is connected to the dry etching apparatus.

[0038] [Storage temperature conditions]

[0039] The storage temperature in the method for storing fluoro-2-butene in this embodiment is not particularly limited, but is preferably -20°C or higher and 50°C or lower, more preferably 0°C or higher and 40°C or lower. If the storage temperature is -20°C or higher, the container is less likely to deform, thus reducing the possibility of oxygen or water entering the container due to loss of airtightness. If oxygen or water does enter, it may promote the polymerization and decomposition reactions of fluoro-2-butene. On the other hand, if the storage temperature is 50°C or lower, the polymerization and decomposition reactions of fluoro-2-butene can be suppressed.

[0040] [Etching]

[0041] The fluorine-2-butene of this embodiment can be used as an etching gas. In the etching process for manufacturing semiconductors having a silicon (Si) film, when using an etching gas containing the fluorine-2-butene of this embodiment, the selectivity of etching is improved because a protective film is formed on the mask and sidewalls.

[0042] Furthermore, the etching gas containing fluorine-2-butene of this embodiment can be used for either plasma etching using plasma or plasma-free etching without plasma.

[0043] Examples of plasma etching include reactive ion etching (RIE), inductively coupled plasma (ICP), capacitively coupled plasma (CCP), electron cyclotron resonance (ECR) plasma etching, and microwave plasma etching.

[0044] In addition, in plasma etching, plasma can be generated in a chamber where the etched component is located, or the plasma generation chamber and the chamber where the etched component is located can be separated (i.e., remote plasma can also be used).

[0045] Example

[0046] Examples and comparative examples are shown below to illustrate the present invention in more detail. Fluoro-2-butene containing hydrogen fluoride at various concentrations was prepared. Examples of the preparation of fluoro-2-butene are described below.

[0047] (Preparation Example 1)

[0048] Prepare one 10L manganese steel gas cylinder and four 1L manganese steel cylinders. Name these cylinders C, D, and A, B, C, and D respectively. Fill the gas cylinder with 5000g of Z-1,1,1,4,4,4-hexafluoro-2-butene (boiling point: 33℃), and liquefy it by cooling it to 0℃, forming a liquid phase and a gas phase at approximately 100kPa. After depressurizing the internal pressure of cylinders A, B, C, and D to below 1kPa using a vacuum pump, cool them to -78℃.

[0049] 100 mL of 5A molecular sieve manufactured by Union Showa Co., Ltd. was filled into an SUS tube with a diameter of 1 inch and a length of 30 cm. The SUS tube was then connected to a gas cylinder.

[0050] 500g of Z-1,1,1,4,4,4-hexafluoro-2-butene gas is extracted from the upper outlet of the gas phase section of the gas cylinder and supplied to the SUS tube. Then, the Z-1,1,1,4,4,4-hexafluoro-2-butene gas that has passed through the SUS tube is collected into cylinder A under reduced pressure.

[0051] The gas flow rate through the SUS tube was controlled at 500 mL / min using a mass flow controller. The amount of Z-1,1,1,4,4,4-hexafluoro-2-butene gas collected in cylinder A was 491 g.

[0052] Z-1,1,1,4,4,4-hexafluoro-2-butene collected in cylinder A was used as sample 1-1. The gas containing Z-1,1,1,4,4,4-hexafluoro-2-butene collected in cylinder A was extracted from the upper outlet, and the concentration of hydrogen fluoride was determined using an infrared spectrophotometer. The results are shown in Table 1. Furthermore, the measurement conditions for the infrared spectrophotometer are as follows.

[0053] Infrared spectrophotometer: Nicolet iS10FT-IR spectrophotometer manufactured by Thermo Fisher Scientific Corporation

[0054] Total number of times: 128

[0055] Camera movement speed: 0.6329

[0056] Optical path length: 3m

[0057] Air chamber material: SUS316

[0058] Air chamber temperature: 100℃

[0059] Measurement wavelength range: 800~5000cm -1

[0060] Wavelength for hydrogen fluoride measurement: 4038 cm⁻¹ -1

[0061] Table 1

[0062] Sample 1-1 Below 10 Sample 1-2 34 Samples 1-3 89 Samples 1-4 155

[0063] Next, cylinder A was heated to approximately 0°C, forming a liquid phase and a gas phase. 100g of Z-1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the upper outlet of the gas phase in cylinder A and transferred to cylinder B under reduced pressure. Then, 10g of Z-1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the gas cylinder and transferred to cylinder B under reduced pressure. Cylinder B was then heated to room temperature and allowed to stand for 24 hours. The Z-1,1,1,4,4,4-hexafluoro-2-butene after standing was used as samples 1-2. The concentration of hydrogen fluoride was measured using an infrared spectrophotometer by extracting Z-1,1,1,4,4,4-hexafluoro-2-butene gas from the upper outlet of the gas phase in cylinder B after standing. The results are shown in Table 1.

[0064] Similarly, 100g of Z-1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the upper outlet of the gas phase section of cylinder A and transferred to cylinder C under reduced pressure. Then, 100g of Z-1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the gas cylinder and transferred to cylinder C under reduced pressure. Cylinder C was then heated to room temperature and allowed to stand for 24 hours. The Z-1,1,1,4,4,4-hexafluoro-2-butene after standing was used as samples 1-3. The concentration of hydrogen fluoride was measured using an infrared spectrophotometer by extracting Z-1,1,1,4,4,4-hexafluoro-2-butene gas from the upper outlet of the gas phase section of cylinder C after standing. The results are shown in Table 1.

[0065] Similarly, 100g of Z-1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the upper outlet of the gas phase section of cylinder A and transferred to cylinder D under reduced pressure. Then, 200g of Z-1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the gas cylinder and transferred to cylinder D under reduced pressure. Cylinder D was then heated to room temperature and allowed to stand for 24 hours. The Z-1,1,1,4,4,4-hexafluoro-2-butene after standing was used as samples 1-4. The concentration of hydrogen fluoride was measured using an infrared spectrophotometer by extracting Z-1,1,1,4,4,4-hexafluoro-2-butene gas from the upper outlet of the gas phase section of cylinder D after standing. The results are shown in Table 1.

[0066] (Preparation Example 2)

[0067] Using E-1,1,1,4,4,4-hexafluoro-2-butene (boiling point 9°C) as fluoro-2-butene, samples 2-1 to 2-4 were prepared in the same manner as in Preparation Example 1. The hydrogen fluoride concentration of each sample was then determined using an infrared spectrophotometer. The results are shown in Table 2.

[0068] Table 2

[0069] Sample 2-1 Below 10 Sample 2-2 21 Sample 2-3 76 Samples 2-4 123

[0070] (Preparation Example 3)

[0071] Z-1,1,1,2,4,4,4-heptafluoro-2-butene (boiling point 10 °C) was used as fluoro-2-butene, and samples 3-1 to 3-4 were prepared using the same procedure as in Preparation Example 1. The hydrogen fluoride concentration of each sample was then determined using an infrared spectrophotometer. The results are shown in Table 3.

[0072] Table 3

[0073] Sample 3-1 Below 10 Sample 3-2 33 Sample 3-3 86 Sample 3-4 141

[0074] (Preparation Example 4)

[0075] Using E-1,1,1,2,4,4,4-heptafluoro-2-butene (boiling point 10 °C) as fluoro-2-butene, samples 4-1 to 4-4 were prepared in the same manner as in Preparation Example 1. The hydrogen fluoride concentration of each sample was then determined using an infrared spectrophotometer. The results are shown in Table 4.

[0076] Table 4

[0077] Sample 4-1 Below 10 Sample 4-2 38 Sample 4-3 95 Sample 4-4 173

[0078] (Preparation Example 5)

[0079] Using Z-1,1,1,2,3,4,4,4-octafluoro-2-butene (boiling point 1°C) as fluoro-2-butene, samples 5-1 to 5-4 were prepared in the same manner as in Preparation Example 1. The hydrogen fluoride concentration of each sample was then determined using an infrared spectrophotometer. The results are shown in Table 5.

[0080] Table 5

[0081] Sample 5-1 Below 10 Sample 5-2 28 Sample 5-3 71 Sample 5-4 116

[0082] (Preparation Example 6)

[0083] Using E-1,1,1,2,3,4,4,4-octafluoro-2-butene (boiling point 8°C) as fluoro-2-butene, samples 6-1 to 6-4 were prepared in the same manner as in Preparation Example 1. The hydrogen fluoride concentration of each sample was then determined using an infrared spectrophotometer. The results are shown in Table 6.

[0084] Table 6

[0085] Sample 6-1 Below 10 Sample 6-2 31 Sample 6-3 82 Sample 6-4 151

[0086] (Example 1)

[0087] After cylinder A was allowed to stand at 20°C for 30 days, Z-1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the gas phase section of cylinder A. Gas chromatography was used to quantify the concentration of E-1,1,1,4,4,4-hexafluoro-2-butene in sample 1-1. The results showed that E-1,1,1,4,4,4-hexafluoro-2-butene was not detected, meaning no products of the isomerization reaction of Z-1,1,1,4,4,4-hexafluoro-2-butene were detected.

[0088] Furthermore, the determination conditions for gas chromatography are as follows.

[0089] Gas chromatograph: GC-2014 manufactured by Shimadzu Corporation

[0090] Column: Carbopack B phase 1% sp-1000

[0091] Injection temperature: 200℃

[0092] Column temperature: 150℃

[0093] Detector: FID

[0094] Detector temperature: 200℃

[0095] Carrier gas: Helium

[0096] Detection limit: 1 ppm by mass

[0097] (Examples 2-18 and Comparative Examples 1-6)

[0098] The analytical objects and results of Examples 2-18 and Comparative Examples 1-6 are shown in Table 7 in comparison with Example 1. That is, except for the items shown in Table 7, the analysis was performed using the same procedures as in Example 1.

[0099] Table 7

[0100]

Claims

1. A method for preserving fluoro-2-butene, wherein the fluoro-2-butene is produced by the general formula C4H x F y This means that in the general formula, x is greater than or equal to 0 and less than or equal to 7, y is greater than or equal to 1 and less than or equal to 8, and x + y equals 8. When the fluoro-2-butene contains hydrogen fluoride as an impurity, the concentration of hydrogen fluoride in the gas phase is set to below 100 ppm by volume, and the fluoro-2-butene is stored in a container. The fluoro-2-butene is selected from at least one of Z-1,1,1,4,4,4-hexafluoro-2-butene, E-1,1,1,4,4,4-hexafluoro-2-butene, Z-1,1,1,2,4,4,4-heptafluoro-2-butene, E-1,1,1,2,4,4,4-heptafluoro-2-butene, Z-1,1,1,2,3,4,4,4-octafluoro-2-butene, and E-1,1,1,2,3,4,4,4-octafluoro-2-butene.

2. The method for preserving fluoro-2-butene according to claim 1, wherein the fluoro-2-butene is stored at a temperature above -20°C and below 50°C.

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