Gas separation: processes – Solid sorption – Including reduction of pressure
Reexamination Certificate
2002-06-19
2004-06-22
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Solid sorption
Including reduction of pressure
C095S119000, C095S127000, C095S130000, C095S139000, C096S130000, C096S132000, C096S133000, C096S144000
Reexamination Certificate
active
06752851
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a gas separation and purification process and an apparatus therefor, more specifically to a process and an apparatus for recovering a valuable gas in the form of purified product, and particularly to a gas separation and purification process and an apparatus therefor, which can be most suitably used for recovering and recycling valuable noble gases such as krypton and xenon to be used as atmospheric gases in semiconductor manufacturing equipment and the like.
BACKGROUND ART
In a process for manufacturing semiconductor products such as semiconductor integrated circuits, liquid crystal panels, solar panels and magnetic discs, there are used a wide variety of devices which generate plasma in a noble gas atmosphere to carry out various kinds of treatments for semiconductor products by the plasma thus generated, for example, sputtering machines, plasma CVD reactors, reactive ion etching machines, etc.
Such processing devices are operated as follows: When substrates and the like to be treated are fed into a processing chamber, a nitrogen gas atmosphere is formed in the processing chamber, and when a plasma treatment is carried out, a noble gas is charged singly or optionally together with a gas which promotes the reaction to the chamber to generate plasma by high-frequency discharge and carry out treatment of the substrates therewith. Subsequently, the chamber is purged by charging nitrogen gas thereto, and the substrates are taken out therefrom. As the gas for promoting the reaction in a treatment, for example, in a plasma oxidation treatment, a certain quantity of oxygen is added.
While argon has predominantly been used as the noble gas to be employed in such treatments, krypton and xenon having low ionization potentials are coming to the fore for more sophisticated applications.
Krypton and xenon are extremely expensive, since they are present in air at very low ratios and require intricate separation processes, so that the processes employing such gases are appreciated economically, only on the premise that used gases are recovered, purified and recycled.
A mixed gas containing a noble gas to be separated and purified consists mainly of a noble gas and nitrogen. In a plasma oxidation treatment, such a mixed gas containing additionally a certain quantity of oxygen is used. Meanwhile, in a plasma CVD treatment and a reactive ion etching treatment, a metal hydrogen compound gas and a halogenated carbon gas are additionally used respectively. Further, moisture, carbon monoxide, carbon dioxide, hydrogen, hydrocarbons, etc. are occasionally contained as trace impurities.
Xenon is also drawing attention for its application as an anesthetic gas in the form of mixture with a predetermined amount of oxygen (usually ca. 30%). The mixed gas to be subjected to the separation and purification treatment is a patient's exhalation containing, for example, oxygen, nitrogen, carbon dioxide and moisture in addition to xenon. In this case, it is necessary to remove nitrogen, carbon dioxide, etc. from the mixed gas in order to recycle xenon.
Referring to the prior art to recover a specific component from a mixed gas by the pressure swing adsorption (PSA) process and purifying it, it is described extensively, for example, in a literature “Pressure Swing Adsorption, 1994 VCH Publishers Inc., collaborated by D. M. Ruthven, S. Farooq and K. S. Knaebel”, Chapter 6.
Paragraph 6.5 of the literature explains a four-column PSA process for recovering hydrogen from various kinds of mixed gases and purifying it. This hydrogen PSA process utilizes the nature of hydrogen that it is extremely difficult to adsorb compared with other components of the mixed gas. Table 6.2 in the above literature shows test conditions and performance data of the four-column hydrogen PSA purification system. It is disclosed in Table 6.2 that if a high product (hydrogen) concentration of 99.9% or more is to be obtained in the conventional hydrogen PSA process, the rate of hydrogen recovery reduces to less than 80%.
Paragraph 6.6 of the above literature also explains a four-column PSA process for recovering carbon dioxide gas from a combustion waste gas and purifying it. Table 6.4 in the literature shows performance data of the PSA process for recovering carbon dioxide gas from a combustion waste gas and purifying it. It is disclosed in Table 6.4 that even if the product had a relatively low concentration of about 99%, the recovery rate of carbon dioxide gas was at most about 72%.
Paragraph 6.7 of the above literature also explains a PSA process for recovering methane from a gas occurring in dumpsite. It is disclosed in Paragraph 6.7 that when a recovery rate of 90% or higher is to be obtained by the conventional methane recovering PSA process, the product had a methane concentration of 89%.
Meanwhile, Japanese Unexamined Patent Publication No. H6-182133 (182133/94) discloses a process and an apparatus for recovering and purifying a noble gas in a high yield. This invention relates to recovery and purification of helium, and helium is recovered while an off-gas from the PSA process having been conventionally treated as a waste gas is recycled to be admixed to a raw gas, thus achieving high yield. However, the mixed raw gas is treated batchwise in this invention and cannot be treated continuously.
Japanese Unexamined Patent Publication No. H10-273307 (273307/98) discloses as follows: “The chamber is purged with a purge gas to form a gaseous outflow containing a noble gas and the purge gas, and the outflow is recovered from the chamber for recycling. The purge gas is preferably selected from hydrogen, steam, ammonia, carbon dioxide, carbon monoxide, oxygen and hydrocarbons having 2 to 6 carbon atoms. A noble gas flow is preferably separated from the outflow by means of membrane separation, condensation, adsorption, absorption, crystallization or by a combination thereof.”
Further, Japanese Unexamined Patent Publication No. H11-157814 (157814/99) discloses a process relating to switching between an operation of introducing a noble gas-containing off-gas discharged from a plant where the noble gas is used to a recovery system and an operation of discharging it therefrom. However, this invention merely discloses as follows: “While adsorption, membrane separation and the like can be employed, a getter type purification apparatus employing a metal such as titanium, vanadium, zirconium and nickel or an alloy thereof is suitably used.”
Japanese Unexamined Patent Publication No 2000-171589 discloses a process for recovering krypton/xenon using natural zeolite as a process for recovering a radioactive noble gas. Although this invention discloses adsorption of the noble gas contained in helium gas, there is no disclosure of desorption, recovery nor recycling thereof.
Japanese Unexamined Patent Publication No. 2000-26319 discloses a process for recovering lower hydrocarbons from an off-gas from a polyolefin manufacturing plant by means of PSA process. This invention is directed to carrying out a recycling operation of mixing a purge off-gas to a raw gas so as to obtain a high recovery rate. However, according to embodiments of the invention, the recovery rate was about 90% when the lower hydrocarbon concentration was 99.9%, and 10% of lower hydrocarbons remained unrecovered.
As described heretofore, there has so far been neither process nor apparatus for recovering a specific component in a mixed gas by a PSA process continuously at a high purity and in a high recovery rate of 95 to 99% or more. Further, there are a very few published adsorption data on krypton and xenon. For example, Journal of Colloid and Interface Science, Vol. 29, No. 1, January 1969 describes adsorption data of krypton onto activated carbon and zeolite 5A at 25° C. According to the data, it can be understood that activated carbon adsorbent adsorbs a large amount of krypton over zeolite 5A. A process for recovering an easily adsorbable component in the form of high-purity product is disclosed, for example, in Japanese Unexami
Hayashida Shigeru
Kawai Masato
Nagasaka Tooru
Nakamura Akihiro
Armstrong Kratz Quintos Hanson & Brooks, LLP
Nippon Sanso Corporation
Spitzer Robert H.
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