Method for producing carbonyl sulfide

Abstract

To provide a method for efficiently producing carbonyl sulfide by a gas-phase flow process without using a catalyst.SOLUTION: The method for producing carbonyl sulfide comprises the steps of: exciting a feed gas containing a starting material that includes carbon, sulfur, and oxygen atoms, by thermal plasma; and cooling the plasma-excited feed gas.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing carbonyl sulfide. [Background technology]

[0002] Carbonyl sulfide (COS) is known as a useful gas for etching carbon hard masks in semiconductor manufacturing processes.

[0003] Known methods for producing carbonyl sulfide in the gas phase include a method in which carbon dioxide gas and carbon disulfide are reacted in the presence of a catalyst (Patent Documents 1 and 2), and a method in which sulfur and carbon monoxide are reacted in the presence of a catalyst (Patent Document 3).

[0004] All of the above production methods use a catalyst. However, a method for producing carbonyl sulfide that does not use a catalyst has also been proposed (Patent Document 4), which involves causing a discharge while continuously flowing a raw material gas containing starting materials consisting of CS2 and at least one selected from the group consisting of CO2, CO, O2, and O3, and then continuously releasing the gas outside the discharge region. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 47-40632 [Patent Document 2] U.S. Patent No. 3,409,399 [Patent Document 3] Japanese Patent Application Publication No. 52-131993 [Patent Document 4] International Publication No. 2020 / 262319 Summary of the Invention [Problem to be solved by the invention]

[0006] The production methods of Patent Documents 1 to 3 all use a catalyst, and continuous production is difficult due to the yield decreasing as the activity of the catalyst decreases. The production method of Patent Document 4 does not use a catalyst, so this problem does not occur, but it is desired to achieve a higher level of yield of carbonyl sulfide.

[0007] Therefore, an object of the present invention is to provide a method for producing carbonyl sulfide in a high yield using a gas-phase flow system without using a catalyst. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to achieve the above object and have found that exciting a predetermined raw material gas with thermal plasma and then cooling it is effective in obtaining carbonyl sulfide in a high yield, thereby completing the present invention. Here, thermal plasma is plasma generated under pressures of 0.03 MPa or higher (e.g., atmospheric pressure), in which electrons, gas molecules, and radicals are all at high temperatures. It is distinct from vacuum plasma, which is generated under pressures of 0.0001 MPa or lower, in which only the electrons are at high temperatures.

[0009] The present invention has an object to advantageously solve the above-mentioned problems, and relates to a method for producing carbonyl sulfide, which includes the steps of exciting, with thermal plasma, a raw material gas containing a starting material that contains carbon atoms, sulfur atoms, and oxygen atoms, and cooling the plasma-excited raw material gas.

[0010] In the method for producing carbonyl sulfide of the present invention, a raw material gas is excited by thermal plasma to convert starting materials containing carbon, sulfur, and oxygen atoms into activated species that can serve as precursors of COS, and the raw material gas is then cooled, causing the activated species to recombine to produce carbonyl sulfide. Thus, according to the present invention, carbonyl sulfide (COS) can be produced in a high yield using a gas-phase flow system without using a catalyst.

[0011] In the present invention, it is advantageous to continuously supply the raw material gas to a thermal plasma generating device at a flow rate of 15 slm or more and excite it within the device, as this improves the raw material conversion rate and allows carbonyl sulfide to be obtained in a high yield. Here, slm (Standard Litter per Minute) is a volumetric flow rate unit, and the measurement conditions are a temperature of 0°C and a pressure of 1 atm (1013 hPa).

[0012] The starting material can be composed of CS2 and at least one selected from the group consisting of CO2, CO, O2, and O3. These combinations are advantageous in that they can suitably generate active species consisting of CS active species, CO active species, and oxygen alone, which can serve as precursors of COS. [Effects of the Invention]

[0013] According to the present invention, carbonyl sulfide can be produced in a high yield by a gas-phase flow method without using a catalyst. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is an example of an apparatus for generating thermal plasma that can be used in the method for producing carbonyl sulfide of the present invention.

[0015] Hereinafter, embodiments of the present invention will be described in detail.

[0016] [Source gas] The starting material contains carbon, sulfur, and oxygen atoms. The starting material can be either an element or a compound, and usually consists of two or more types. The starting material does not contain only carbonyl sulfide.

[0017] The starting material is preferably a combination of CS2 and at least one selected from the group consisting of CO2, CO, O2, and O3. By using these combinations, it is possible to suitably generate CS active species, CO active species, active species consisting of elemental oxygen, active species consisting of elemental sulfur, and the like, which can serve as precursors of COS. The combination of CS2 and CO2 is more preferred because it allows COS to be obtained efficiently.

[0018] From the viewpoint of the selectivity to carbonyl sulfide, the ratio of the volume of CS to the total volume of at least one selected from the group consisting of CO, CO, O, and O is preferably 0.05 or more (volume of CS / (total volume of at least one selected from the group consisting of CO, CO, O, and O)). From the viewpoint of the selectivity to COS, it is more preferably 0.10 or more. Furthermore, the volume ratio can be, for example, 2.00 or less, and from the viewpoint of obtaining good selectivity while maintaining the raw material conversion, it is preferably 0.70 or less.

[0019] The raw material gas may contain an inert gas. Examples of the inert gas include N2, He, Ne, Ar, Xe, and Kr, with N2, Ar, and He being preferred, and N2 and Ar being more preferred. When an inert gas is used, the inert gas may be used alone or in combination of two or more kinds.

[0020] When an inert gas is used, the content of the inert gas in the raw material gas can be 60% by volume or less, preferably 30% by volume or less, or may be 0% by volume.

[0021] In addition to the starting materials and any inert gas, the raw material gas may contain impurities that are inevitably mixed in from the surrounding environment. Examples of impurities include moisture. The raw material gas may consist of the starting materials and the inevitable impurities.

[0022] The volumetric ratio of CS2 in the source gas is preferably 2% by volume or more, and is preferably 70% by volume or less. If the volumetric ratio is within this range, COS can be obtained sufficiently.

[0023] The source gas may contain a starting material and an arbitrary inert gas when energy is applied for plasma excitation. For example, the starting material and the arbitrary inert gas may be supplied separately as gases to a plasma device (hereinafter simply referred to as a "plasma device") that generates thermal plasma, or may be supplied as a premixed gas to form the source gas. Alternatively, a portion of the premixed gas may be supplied separately from the remaining gas to form the source gas.

[0024] The flow rate of the raw material gas when supplied to the device for generating thermal plasma is preferably 15 slm or more, more preferably 20 slm or more, in order to stabilize the plasma. The upper limit of the flow rate is not particularly limited and can be set depending on the device used. For example, the flow rate can be 5000 slm or less, but is not limited thereto. When CS2 is vaporized in a vaporization chamber and supplied, the flow rate of CS2 can be, for example, 0.3 slm to 200 slm, but is not limited thereto. The flow rates of starting materials other than CS2 and optional inert gases can be adjusted according to the flow rate of CS2. The flow rate is the total amount of starting materials and optional inert gases supplied to the plasma device.

[0025] It is preferable to use a starting material that is a gas under standard conditions or a liquid that has a sufficiently high vapor pressure and is easily vaporized by heating, etc. Such starting materials can be supplied to the plasma device as a gas without a separate vaporization chamber, etc., but it is preferable to vaporize a liquid in a separate vaporization chamber before supplying it to the plasma device. Supply can be continuous. The supply flow rate can be controlled using a mass flow controller, etc.

[0026] When the starting material is a liquid or solid with a low vapor pressure under standard conditions, it can be vaporized in a separate vaporization chamber and then supplied to the plasma device. For example, CS2 (boiling point 46°C) is preferably vaporized in a vaporization chamber and then supplied to the plasma device. When the starting material is solid, it can be heated to a liquid state and then introduced into the vaporization chamber, or it can be directly sublimated in the vaporization chamber.

[0027] For example, the starting material can be vaporized by introducing it in a liquid state into a vaporization chamber maintained at a temperature and pressure at which the starting material is sufficiently vaporized. The temperature and pressure of the vaporization chamber are preferably maintained at a temperature and pressure at which the starting material can be instantaneously vaporized. By using such a vaporization chamber, the starting material can be continuously introduced into the vaporization chamber as a liquid, instantaneously vaporized in the vaporization chamber, and continuously supplied to the plasma device as a gas. When the starting material is in a solid state, it can be heated to a liquid state and then introduced into the vaporization chamber, or it can be directly sublimated in the vaporization chamber and continuously supplied to the plasma device as a gas.

[0028] The supply flow rate can be controlled by controlling the gas vaporized in the vaporization chamber with a mass flow controller or the like, or by controlling the starting material when it is continuously introduced into the vaporization chamber in a liquid state with a liquid mass flow controller or the like. When the vaporized starting material is introduced into the plasma device, it may be diluted with an inert gas or the like.

[0029] The vaporization chamber may be filled with a filler to adjust the flow rate. Examples of fillers include Helipak, glass beads, and SUS mesh. In particular, when CS2 is used as the starting material, it is advantageous to heat it in a vaporization chamber filled with the filler to increase the supply rate.

[0030] [Discharge] The production method of the present invention utilizes a reaction field created by thermal plasma. Specifically, a plasma device that generates thermal plasma is used to generate activated species that can serve as COS precursors from a source gas in the thermal plasma region.

[0031] Thermal plasma can be generated by electrical methods, such as arc discharge, high-frequency discharge, pulse discharge, and multi-phase AC discharge. The arc discharge may be a DC arc or an AC arc. A multi-phase AC arc is preferred because it allows for processing at a large flow rate. Regarding high-frequency discharge, inductively coupled high-frequency discharge plasma is advantageous in terms of efficient processing.

[0032] [Plasma equipment] Figure 1 shows an example of an apparatus for generating thermal plasma that can be used in the manufacturing method of the present invention. This plasma apparatus utilizes arc discharge.

[0033] The plasma device 1 includes a combustion tube 10 inside a cooling jacket 30, and cooling water flows through the cooling jacket 30. The combustion tube 10 is preferably made of ceramic from the viewpoint of heat resistance.

[0034] A cathode 11 is installed above the combustion tube 10, and an anode 12 is installed inside the combustion tube 10. An ignition wire 34 is arranged on the cathode side. A voltage is applied between the cathode 11 and the anode 12 to cause discharge. The discharge conditions are not particularly limited, but can be, for example, a voltage of 300 to 600 V and a current of 1 to 20 A. The size of the combustion tube 10 and the distance between the electrodes can be set appropriately. The anode 12 side of the plasma generated by the discharge is downstream of the plasma.

[0035] A gas supply pipe 21 is connected to the plasma device 1 on the cathode 11 side. A source gas is supplied from this gas supply pipe 21, and a plasma state is created within the device, generating activated species that can serve as COS precursors. The installation position of the gas supply pipe 21 is not limited to the position shown in FIG. 1 . For example, a pipe may be inserted from a gas recovery port 22, and the source gas may be supplied from the pipe.

[0036] A gas recovery port 22 is provided at the bottom of the plasma device 1. The source gas excited within the plasma device 1 is recovered from the gas recovery port 22 to the outside of the plasma device 1. Active species generated by cooling during this process combine to produce carbonyl sulfide. Recovery can be performed by connecting a vacuum pump, for example, to the gas recovery port 23.

[0037] [Target substance] By cooling the plasma-excited source gas, the generated active species recombine to produce the target substance, carbonyl sulfide. Cooling can be achieved by continuously releasing the plasma-excited source gas from the plasma device. Continuous release can be achieved at a space velocity corresponding to the continuous flow of the source gas.

[0038] After the plasma-excited raw material gas is released from the plasma device, it may be further introduced into a heat exchanger for cooling. The type of heat exchanger is not particularly limited, and examples thereof include air-cooling and water-cooling. Since the product after cooling may contain substances other than carbonyl sulfide, carbonyl sulfide may be separated and purified by an optional separation and purification step. Examples of separation and purification methods include distillation, absorption into a solution, and membrane separation. [Example]

[0039] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0040] Example 1 A long DC arc plasma device (volume: 6.5 L, distance between electrodes: 300 mm) made of Hastelloy was used as the plasma device 1. A cylindrical mullite ceramic tube (inner diameter 42 mm, length 600 mm) was installed inside the plasma device 1 as the combustion tube 10. CO2, which serves as the plasma parent gas, was introduced at 20 slm through a gas supply pipe 21 attached to the ceramic tube, and plasma ignition was performed at a current value of 10 A.

[0041] After plasma ignition, CO was introduced into the plasma device 1 at 20 slm from the gas supply pipe 21, and CS vaporized through a vaporizer heated to 75°C was introduced into the plasma device 1 at 2 slm from the gas supply pipe 21. The gas in the plasma device was discharged from the system through the gas recovery port 22, and the recovered gas discharged from the system was collected in an aluminum bag and then detoxified with a KOH aqueous solution.

[0042] The collected gas was analyzed by gas chromatography-mass spectrometry (GC-MS) (Agilent 7890A, manufactured by Agilent). The raw material conversion rate and yield of carbonyl sulfide were calculated from the area values ​​of each component obtained by GC-MS analysis. The results are shown in Table 1.

[0043] (Examples 2 and 3) The procedure was the same as in Example 1, except that the flow rate of CS2 was changed to the amount shown in Table 1. The results are shown in Table 1.

[0044] (Examples 4 and 5) The procedure was the same as in Example 2, except that N2, which serves as the base gas for plasma, was further introduced from the gas supply pipe 21 at a flow rate shown in Table 1. The results are shown in Table 1.

[0045] [Table 1]

[0046] Table 1 shows that in the examples, carbonyl sulfide can be produced in good yield without using a catalyst. [Industrial Applicability]

[0047] According to the present invention, carbonyl sulfide can be produced in a high yield by a gas-phase flow method without using a catalyst. [Explanation of symbols]

[0048] 1. Plasma equipment 10 Combustion tube 11 Cathode 12 Anode 21 Gas supply pipe 22 Gas recovery port 30 Cooling jacket 31 Cooling water supply port 32 Cooling water outlet 34 Ignition wire

Claims

1. A method for producing carbonyl sulfide, comprising the steps of: exciting a raw material gas containing a starting material containing carbon atoms, sulfur atoms, and oxygen atoms with thermal plasma; and cooling the plasma-excited raw material gas.

2. 2. The method for producing carbonyl sulfide according to claim 1, wherein the raw material gas is continuously supplied to a device for forming thermal plasma at a flow rate of 15 slm or more and excited in the device.

3. The starting material is CS ２ and CO ２ , CO, O ２ and O ３ The method for producing carbonyl sulfide according to claim 1 or 2, wherein the carbonyl sulfide is a mixture of at least one selected from the group consisting of:

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