Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment
Reexamination Certificate
2001-08-10
2003-07-01
Phasge, Arun S. (Department: 1753)
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
C205S688000, C205S701000, C205S742000, C205S763000, C588S253000, C204S242000, C204S275100, C204S277000, C204S278000
Reexamination Certificate
active
06585882
ABSTRACT:
This application is a 371 application of PCT/J00/000745 filed on Feb. 10, 2000.
FIELD OF THE INVENTION
The present invention relates to processes and apparatus for treating a gas containing reducing substances such as malodorants or pollutants by performing hydrothermal reaction and electrolytic reaction. Combination of hydrothermal reaction and electrolysis is herein referred to as hydrothermal electrolysis. Gases that are treated by processes of the present invention (influent gases) include gaseous materials containing reducing substances such as low-molecular weight organics, volatile organic halogen compounds, ammonia, hydrogen sulfide and cyanide gases with the balance being nitrogen, argon, air and oxygen. The present invention relates to processes and apparatus for converting reducing substances contained in said influent gases into harmless components such as carbon dioxide gas, nitrogen gas, sulfide ion, chloride ion or the like.
PRIOR ART
Gases containing reducing substances have been conventionally treated by gas phase catalytic oxidation, activated carbon adsorption, UV oxidation, etc. Gas phase catalytic oxidation involves mixing a gas containing reducing substances with an oxidizer such as air and bringing said mixture into contact with a catalyst under conditions of almost normal pressure and 160-300° C. to oxidatively degrade malodorous components into carbon dioxide gas, nitrogen and water, whereby various malodorous components such as ammonia, low-molecular weight amines, mercaptans and aldehydes can be treated. However, this gas phase catalytic oxidation often suffers from a local temperature rise in the catalytic layer caused by autogenous combustion when the gas contains a lot of reducing substances. If the untreated gas contains a nitrogen compound (ammonia, amines, etc.), such a local temperature rise produces a high NOx fuel gas. If the gas contains reducing substances containing sulfur in the molecule, SOx may be produced. If the influent gas contains an organic halogen compound, a halic acid is produced in the catalytic layer. Once a halic acid is produced, the catalyst is readily poisoned. The catalyst is also often poisoned when the influent gas contains a dust component such as phosphorous compounds, sulfur compounds, silica. Especially, noble metal catalysts are more liable to be poisoned. Even when reducing substances free from these heteroatoms such as low-molecular weight hydrocarbons are treated by gas phase catalytic oxidation, incomplete combustion products such as CO gas may be produced under some process conditions. In order to advance complete oxidative degradation in catalytic oxidation, the.temperature of the catalytic layer must be strictly controlled. If the temperature is too high, the catalyst may be deteriorated or NOx may be produced. If the temperature is too low, however, reducing substances remain undegraded in the effluent gas. Therefore, it is very difficult to treat some kinds or levels of reducing substances contained in the influent gas by catalytic oxidation.
Activated carbon adsorption involves retaining reducing substances in pores of activated carbon by physical or chemical adsorption. Activated carbon adsorption typically takes place at normal temperature and pressure. Needless to say, reducing substances adsorbed to activated carbon must be further treated by burning or other means. When the molecular size of reducing substances is not suited to the pore diameter of activated carbon or reducing substances have no functional group suitable to be adsorbed, any adsorptive effect may not be produced for smoothly advancing the treatment of the gas. When the gas contains water or dust, adsorptive ability may be greatly lowered. When the influent gas contains reducing substances at high concentrations, a large amount of activated carbon is needed so that the cost for regenerating or treating such a large amount of activated carbon rises.
UV oxidation involves mixing a gas containing reducing substances with air and irradiating said mixture with UV rays to make the mineralization of the reducing substances into carbon dioxide gas or the like by accelerating a radical chain reaction. When a bond that absorbs a specific UV wavelength exists in reducing substance molecules, UV oxidation allows efficient degradation because radical reactions are readily chained. Especially when the gas contains such a component as trichloroethylene, UV oxidation is sometimes effective. However, reducing substances must be contained at relatively high concentrations in the influent gas to improve the chain reaction because the reaction proceeds by a radical chain reaction in this UV oxidation. When organochlorine compounds are to be treated, a special care is required about by-products such as dioxin because main degradative reaction is a radical reaction. Even if target reducing substances are effectively degraded, they are not always degraded into harmless inorganic components such as carbon dioxide gas but high concentrations of carbon monoxide or the like may be produced as a by-product.
In this way, processes of the prior art for treating a gas containing various reducing substances still have problems.
DISCLOSURE OF THE INVENTION
As a result of careful studies to overcome the above problems to find a process capable of efficiently degrading a gas containing various reducing substances, we accomplished the present invention on the basis of the finding that various reducing substances can be efficiently degraded by treating the gas by the hydrothermal electrolytic process.
We previously filed a patent application based on the finding that an aqueous medium containing reducing substances can be treated to efficiently degrade the reducing substances while inhibiting generation of hydrogen gas and oxygen gas by performing hydrothermal reaction and electrolytic reaction at the same time under predetermined conditions (hydrothermal electrolytic reaction) (International Patent Application PCT/JP 98/03544; International Publication WO99/07641). The disclosure of International Application PCT/JP 98/03544 is incorporated herein as a whole as reference. As a result of later studies, we accomplished the present invention on the basis of the finding that this hydrothermal electrolytic reaction process can be applied to the treatment of a gas containing reducing substances to degrade and remove the reducing substances in the gas.
Accordingly, an aspect of the present invention provides a process for treating a gas containing reducing substances by hydrothermal electrolysis, comprising supplying a gas containing reducing substances into a reactor charged with an aqueous medium containing a halide ion under application of a direct current at a temperature of 100° C. or more but not more than the critical temperature of said aqueous medium and at a pressure that allows said aqueous medium to be kept in the liquid phase.
The present invention also provides an apparatus for performing the process described above, ie, an apparatus for treating a gas containing reducing substances by hydrothermal electrolysis, comprising a reactor having an inlet for introducing the gas containing reducing substances and an outlet for discharging the effluent gas and capable of resisting the pressure of hydrothermal reaction, and a pair of electrodes for performing electrolysis in said reactor.
In the present invention, an aqueous medium containing a halide ion such as chloride ion is mixed with a gas containing reducing substances and the mixture is electrolytically reacted at predetermined high temperature and high pressure to oxidatively degrade the reducing substances. In electrolysis, oxidation reaction proceeds at the anode to produce oxygen gas or a halogen-based oxidizer such as a hypohalous acid. Generally, oxidation reaction readily proceeds in the presence of an oxidizer such as oxygen gas at high temperature and high pressure of hydrothermal reaction. In the present invention, reducing substances such as organics and ammonia can be effectively oxidatively degraded
Isaka Masahiro
Kubota Yoko
Nishimura Tatsuya
Serikawa Roberto Masahiro
Su Qingquan
Ebara Corporation
Phasge Arun S,.
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