Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Halogenous component
Patent
1997-07-07
2000-04-18
Griffin, Steven P.
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Halogenous component
588213, C01B 700
Patent
active
060511982
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a catalyst for rendering fumigation exhaust gases harmless after their use in the extermination of bacteria and insects from foodstuffs such as fruits and vegetables and cereals, or timber, soil etc., and to a method for effectively purifying fumigation exhaust gases using such a catalyst. In particular, it relates to a catalyst for purifying fumigation exhaust gases by the efficient decomposition of fumigation components such as methyl bromide, chloropicrin, contained in said fumigation exhaust gases.
BACKGROUND OF THE INVENTION
Methods of fumigation involve filling a closed space with gaseous chemicals (fumigants) to eliminate harmful organisms. They are mainly applied to imported foodstuffs such as cereals and fruits and vegetables, and timber as a preventive measure against epidemics, as well as to the extermination of bacteria and insects from green house cultivation soil. From the viewpoint of effectiveness and low cost etc., gases containing organohalogen compounds such as methyl bromide, chloropicrin etc. as fumigation components are used in large amounts as the fumigation gases used in these kinds of fumigation methods.
In actual practice, the above-described kind of fumigation gases containing large amounts of organohalogen compounds are released to the atmosphere after use without being first subjected to any treatment to render them harmless. However, in recent years it has become clear that the ozone layer which plays an important role for the earth's environment is being destroyed by the above-mentioned kind of organohalogen compounds, and restrictions on the use and disposal of organohalogen compounds have become severe worldwide. There is therefore a pressing need for the establishment of a method for purifying fumigation exhaust gases by the effective and low cost decomposition of the organohalogen compounds such as methyl bromide and chloropicrin contained in the fumigation exhaust gases.
Methods of effectively decomposing fumigation components in fumigation exhaust gases have been studied for some time, but due to the above-mentioned situation, are now being increasingly studied from various angles. Even though the concentration of fumigation components contained in the fumigation exhaust gases may be in the order of 1 volume percent at the start of their discharge from the cereal fumigation silo, it drops as the discharge is continued to reach a final value in the order of a number of parts per million. It was found to be extremely difficult to effectively decompose and eliminate the fumigation components discharged over such a wide concentration range.
Direct combustion methods, plasma methods, chemical absorption methods, catalytic oxidation methods, and adsorption methods etc. have so far been proposed, but these methods have the following problems.
Firstly, direct combustion methods usually require high temperatures over 600.degree. C., and have the practical problems that running costs such as fuel costs are extremely high, and that extremely harmful halogen gases, such as Cl.sub.2, BR.sub.2, are generated by the combustion of the organohalogen compounds.
Plasma methods have been actively studied in recent years. However, they consume large amounts of electric power, and require highly expensive noble gases such as helium, argon etc. Accordingly, although they can be said to be suited to the treatment of certain special objects, they are unsuitable as methods for purifying large amounts of fumigation exhaust gases.
Furthermore, with respect to chemical absorption methods, special chemicals are required, and large amounts of waste water are generated which require secondary treatment. Also, the elimination efficiency is low and the method is thus impractical.
The method disclosed in Japanese Patent Application Publication No. Hei 3-289973 is one example of a catalyst oxidation method. With this method, although the organohalogen compounds can be oxidatively decomposed by contact with a composite oxide catalyst, there is the
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Nishikawa Kazuyoshi
Okuhara Kazumi
Sano Kunio
Yoshino Kazunori
Griffin Steven P.
Hendrickson Stuart L.
Nippon Shokubai Co. , Ltd.
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