Patent Application
20100247412
This invention relates to a method for removing ClO3F in a gas containing ClO3F as an impurity.
Perchloryl fluoride (ClO3F) is produced in general by a reaction of chlorate of alkali metal or alkaline earth metal with a gas containing fluorine (F2) or a gas containing F2, or by a reaction of a perchlorate of alkali metal or alkaline earth metal with a fluorinating agent [for example, fluorosulfaric acid (HSO3F) or the like].
ClO3F is a thermally very stable compound and therefore cannot thermally decompose if it is not heated to 470° C. Additionally, it has such a characteristic as to be insoluble in water and not to be able to be decomposed with alkali. Further, in case that ClO3F is contained in a gas which is similar in physical property to ClO3F, it is difficult to make a separation and a concentration by a distillation, so that there is a problem that removal of it is difficult.
In general, as a method for removing an impurity contained in a gas, it has been reported to thermally decompose the impurity by using the difference in thermal stability between the gas and the impurity to be removed so as to remove the impurity contained in the gas (see Patent Citation 1).
As other methods for removing an impurity contained in a gas, a method using a purification agent such as zeolite, for example, in a purification of NF3 used as a cleaning gas for a semiconductor (see Non-patent Citation 1).
Additionally, a method using a reducing agent has been reported as a method for removing NOx as a impurity in a gas (see Patent Citation 2); however, a method for removing ClO3F has not been reported.
Non-patent Citation 1: Chem. Eng. 84, 116, (1977)
In case that ClO3F is contained, for example, in a material gas or a cleaning gas used in production of a semiconductor in a field requiring a high purity, it is required to remove ClO3F to a low concentration. Additionally, ClO3F is highly toxic and therefore required to be removed to not higher than 3 ppm as a TLV value.
In a method for thermally decomposing an impurity by using the above-mentioned thermal stability in order to remove ClO3F, ClO3F is thermally very stable, so that ClO3F can be removed in case of being contained as an impurity in a similarly thermally stable gas.
Additionally, also in a method using the above-mentioned purification agent such as zeolite or the like, ClO3F cannot be removed.
Thus, there is no report regarding a method for removing ClO3F.
Accordingly, an object of the present invention is to provide an inexpensive method for removing ClO3F.
The present inventors have found that ClO3F can be removed by reacting a gas containing ClO3F with a reducing agent thereby reducing ClO3F.
That is, a first aspect of the present invention is a method for removing ClO3F by reacting a gas containing ClO3F as an impurity with a reducing agent.
A second aspect of the present invention is to use the reducing agent having a standard electrode potential of not higher than −0.092V in an aqueous solution, in the method as described in the above-mentioned first aspect.
A third aspect of the present invention is to use the reducing agent in form of an aqueous solution, for a reaction, in the method as described in the above-mentioned first or second aspect.
A fourth aspect of the present invention is to allow a base to coexist in the aqueous solution containing the reducing agent, in the method as described in the above-mentioned third aspect.
According to the present invention, it is made possible to remove ClO3F as an impurity contained in a gas.
Hereinafter, the content of the present invention will be discussed.
Here, a reducing agent means a compound lower in standard electrode potential than ClO3F in an aqueous solution, in which the reducing agent is preferably a compound having a standard electrode potential of not higher than −0.092 V in an aqueous solution. As the standard electrode potential in the compound is lower, better effects can be obtained. For example, examples of the compound are described in “Chemical Great Dictionary” (Tokyo Kakagu doujin, the Fourth edition II-465). Of these described compounds, sodium dithionite (Na2S2O4) is particularly preferable, and sodium sulfite (Na2SO3) and sodium bisulfite (Na2S2O3) are also preferable. Additionally, the condition of the reducing agent is not particularly limited.
As a method of using the reducing agent, there are a solid-gas contact method and a gas-liquid contact method. In the solid-gas contact method, it is possible to remove ClO3F by passing a gas containing ClO3F through a packed column which is filled with the reducing agent. Taking account of a contact efficiency, it is preferable to use the gas-liquid contact method in which the reducing agent is used in the form of an aqueous solution. It is more preferable that a base coexists in the aqueous solution containing the reducing agent when the reducing agent is used. The effect of the coexisting base is a role for preventing a deterioration of the reducing agent under the action of an acid produced after a reduction. Kinds of the base are not particularly limited as far as the base does not directly react with the reducing agent.
In case that the reducing agent is used in the form of an aqueous solution, a counter flow contact or a parallel flow contact can be used as a method for contacting the reducing agent with a gas containing ClO3F as a impurity. The counter flow contact is preferable, taking account of the contact efficiency between a gas and a liquid.
A temperature of a contact reaction with the reducing agent is not particularly recommended. It is assumed that a removal effect lowers at a temperature not lower than a temperature at which the reducing agent decomposes, and therefore it is preferable to use the reducing agent at the temperature lower than the temperature at which the reducing agent decomposes. For example, in case of Na2S2O4, it is preferable to be used at not higher than 60° C.
Additionally, in case that the reducing agent is used in the form of an aqueous solution, it is preferable that the concentration of the reducing agent is, for example, not less than 0.29 mol/l when Na2S2O4 is used as the reducing agent. If the concentration is less than 0.29 mol/l, a sufficient removal effect cannot be exhibited. Hereinafter, the present invention will be discussed in detail with reference to Examples.
Hereinafter, the present invention will be discussed in detail with reference to Examples.
A wet harm removing apparatus 3 includes a packed column 5 filled with packing, a reaction liquid 6 to be reacted with the introduced treatment object gas, a liquid tank 8 for storing the reaction liquid 6, and a liquid feed pump 4 for liquid-feeding the reaction liquid 8 within the liquid tank 5 into a position above the packing, in which the ClO3F removal treatment object gas which is introduced from the bottom section of the packed column 5 makes a counter flow contact with the reaction liquid 6 in the packed column 5 and is released from the upper section of the packed column 5.
The gas of the object of the ClO3F removal treatment from a steel bottle 1 filled with the gas of ClO3F removal treatment object is controlled to have a certain flow amount by using a massflow controller 2 and introduced into the wet harm removing apparatus 3 so as to make a counter flow contact with the reaction liquid 6. Thereafter, a gas released from the wet harm removing apparatus 3 is trapped by an empty container 7.
The gas trapped in the empty container 7 is subjected to an analysis using a Fourier transform infrared spectrophotometer (FT-IR (IG-1000 produced by Otsuka Electronics Co., Ltd.)) having a detection lower limit for ClO3F being 0.5 volppm, in which the concentration of ClO3F is measured.
A packed column 5 made of vinyl chloride and having a length of 1700 cm and an inner diameter of 50 mm were filled with Raschig rings having a diameter of 6 mm and made of SUS. N2 containing 1410 volppm of ClO3F as the gas of the ClO3F removal treatment object was introduced at 274 Nml/min by using the massflow controller 2 into the wet harm removing apparatus 3 provided with an aqueous solution whose Na2S2O4 concentration was 1.5 mol/l and KOH concentration was 0.15 mol/l, the aqueous solution being used as the reaction liquid 6. Thereafter, a gas released from the wet harm removing apparatus 3 was trapped by the empty container 7.
The ClO3F concentration in the gas trapped in the empty container 7 was analyzed by the FT-IR (IG-1000 produced by Otsuka Electronics Co., Ltd.). As a result, ClO3F in N2 was less than 0.5 volppm which was the detection lower limit, so that it was confirmed that ClO3F could be removed.
A procedure was conducted in the same condition as that in Example 1 with the exception that CH4 containing 2280 volppm of ClO3F was used as the gas of the ClO3F removal treatment object. Similarly to Example 1, the ClO3F concentration in the gas trapped after passing through the wet harm removing apparatus 3 was analyzed by the FT-IR (IG-1000 produced by Otsuka Electronics Co., Ltd.).
As a result, the ClO3F concentration was less than 0.5 volppm which was the detection lower limit, so that it was confirmed that ClO3F in CH4 could be removed.
A procedure was conducted in the same condition as that in Example 1 with the exception that NF3 containing 2280 volppm of ClO3F was used as the gas of the ClO3F removal treatment object. Similarly to Example 1, the ClO3F concentration in the gas trapped after passing through the wet harm removing apparatus 3 was analyzed by the FT-IR (IG-1000 produced by Otsuka Electronics Co., Ltd.).
As a result, the ClO3F concentration was less than 0.5 volppm which was the detection lower limit, so that it was confirmed that ClO3F in CH4 could be removed.
A procedure was conducted in the same condition as that in Example 1 with the exception that NF3 containing 6680 volppm of ClO3F was used as the gas of the ClO3F removal treatment object. Similarly to Example 1, the ClO3F concentration in the gas trapped after passing through the wet harm removing apparatus 3 was analyzed by the FT-IR (IG-1000 produced by Otsuka Electronics Co., Ltd.).
As a result, the ClO3F concentration was less than 0.5 volppm which was the detection lower limit, so that it was confirmed that ClO3F in NF3 could be removed.
A procedure was conducted in the same condition as that in Example 1 with the exception that N2 containing 2280 volppm of ClO3F was used as the gas of ClO3F removal treatment object and that an aqueous solution whose Na2S2O4 concentration was 1.0 mol/l and NaOH concentration was 1.0 mol/l was used as the reaction liquid 6. Similarly to Example 1, the ClO3F concentration in the gas trapped after passing through the wet harm removing apparatus 3 was analyzed by the FT-IR (IG-1000 produced by Otsuka Electronics Co., Ltd.).
As a result, the ClO3F concentration was less than 0.5 volppm which was the detection lower limit, so that it was confirmed that ClO3F in N2 could be removed.
A procedure was conducted in the same condition as that in Example 1 with the exception that N2 containing 2358 volppm of ClO3F was used as the gas of the ClO3F removal treatment object and that an aqueous solution whose Na2S2O4 concentration was 1.0 mol/l was used as the reaction liquid 6. Similarly to Example 1, the ClO3F concentration in the gas trapped after passing through the wet harm removing apparatus 3 was analyzed by the FT-IR (IG-1000 produced by Otsuka Electronics Co., Ltd.).
As a result, the ClO3F concentration was less than 0.5 volppm which was the detection lower limit, so that it was confirmed that ClO3F in N2 could be removed.
A procedure was conducted in the same condition as that in Example 1 with the exception that N2 containing 2280 volppm of ClO3F was used as the gas of the ClO3F removal treatment object and that an aqueous solution whose Na2S2O4 concentration was 0.2 mol/l and KOH concentration was 1.0 mol/l was used as the reaction liquid 6. Similarly to Example 1, the ClO3F concentration in the gas trapped after passing through the wet harm removing apparatus 3 was analyzed by the FT-IR (IG-1000 produced by Otsuka Electronics Co., Ltd.).
As a result, the ClO3F concentration was 6.7 volppm, so that it was confirmed that ClO3F in N2 could be removed.
A procedure was conducted in the same condition as that in Example 1 with the exception that N2 containing 2280 volppm of ClO3F was used as the gas of the ClO3F removal treatment object and that an aqueous solution whose Na2S2O4 concentration was 0.15 mol/l and KOH concentration was 1.0 mol/l was used as the reaction liquid 6. Similarly to Example 1, the ClO3F concentration in the gas trapped after passing through the wet harm removing apparatus 3 was analyzed by the FT-IR (IG-1000 produced by Otsuka Electronics Co., Ltd.).
As a result, the ClO3F concentration was 17.2 volppm, so that it was confirmed that ClO3F in N2 could be removed.
A procedure was conducted in the same condition as that in Example 1 with the exception that N2 containing 4459 volppm of ClO3F was used as the gas of the ClO3F removal treatment object and that an aqueous solution whose Na2SO3 concentration was 1.0 mol/l and KOH concentration was 1.0 mol/l was used as the reaction liquid 6. Similarly to Example 1, the ClO3F concentration in the gas trapped after passing through the wet harm removing apparatus 3 was analyzed by the FT-IR (IG-1000 produced by Otsuka Electronics Co., Ltd.).
As a result, the ClO3F concentration was 1502 volppm, so that it was confirmed that ClO3F in N2 could be removed.
A procedure was conducted in the same condition as that in Example 1 with the exception that N2 containing 2280 volppm of ClO3F was used as the gas of the ClO3F removal treatment object and that water was used as the reaction liquid 6 in the wet harm removing apparatus 3. Similarly to Example 1, the ClO3F concentration in the gas trapped after passing through the wet harm removing apparatus 3 was analyzed by the FT-IR (IG-1000 produced by Otsuka Electronics Co., Ltd.).
As a result, the ClO3F concentration was 2280 volppm, so that it was confirmed that ClO3F in N2 could not be removed.
A procedure was conducted in the same condition as that in Example 1 with the exception that N2 containing 3580 volppm of ClO3F was used as the gas of the ClO3F removal treatment object and that a HF aqueous solution having a 4% concentration was used as the reaction liquid 6 in the wet harm removing apparatus 3. Similarly to Example 1, the ClO3F concentration in the gas trapped after passing through the wet harm removing apparatus 3 was analyzed by the FT-IR (IG-1000 produced by Otsuka Electronics Co., Ltd.).
As a result, the ClO3F concentration was 3580 volppm, so that it was confirmed that ClO3F in N2 could not be removed.
The above-mentioned measurement results are shown in Table 1.
The present invention can be used as a harm removing means for discharged gas from a semiconductor plant, a chemical plant or the like which uses, for example, chloride gas or fluoride gas, or as a purifying means used during production of chloride gas or fluoride gas.
[
1: gas steel bottle containing ClO3F
2: massflow controller
3: wet harm removing apparatus
5: packed column
6: reaction liquid
7: empty container
8: liquid tank
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-312218 | Dec 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/069352 | 10/24/2008 | WO | 00 | 6/2/2010 |
