Catalyst – solid sorbent – or support therefor: product or process – Solid sorbent – Free carbon containing
Reexamination Certificate
1998-07-24
2003-02-04
Hendrickson, Stuart L. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Solid sorbent
Free carbon containing
C502S416000
Reexamination Certificate
active
06514907
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is related to Japanese applications Nos. Hei 9(1997)-200371 and Hei 9(1997)-297440 filed on Jul. 25, 1997 and Oct. 29, 1997 respectively, whose priorities are claimed under 35 USC § 119, the disclosures of which are incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bromine-impregnated activated carbon and a process for preparing the same. More particularly, the bromine-impregnated activated carbon is used for removing alkyl sulfides from gas containing the alkyl sulfides in small concentrations.
2. Description of Related Art
Sulfur compounds such as hydrogen sulfide, mercaptans and alkyl sulfides are contained in exhaust gas from sewage treatment plants, raw sewage treatment plants, waste disposal plants, and process gas and exhaust gas from chemical plants for petroleum refining, petroleum chemistry, paper pulp production and the like and from food processing plants.
Various methods for removing sulfur compounds contained in such gases are conventionally known, including an alkali absorbing method, a wet oxidation method, an ozone oxidation method, an activated carbon adsorption method and a combustion method, for example.
These conventional methods are useful for removing many kinds of sulfur compounds. However, alkyl sulfides such as dimethyl sulfide and dimethyl disulfide, which are specific smelly substances, cannot be removed to a satisfactory extent by the conventional methods.
Under these circumstances, Japanese Unexamined Patent Publications Nos. Sho 54(1979)-132470, Sho 50(1975)-130679 and Sho 55(1980)-51422, for example, propose that dimethyl sulfide and dimethyl disulfide can be removed by chemical adsorption by using a bromine-impregnated activated carbon instead of an usual activated carbon in the adsorption method. The chemical adsorption is a mechanism different from physical adsorption by the usual activated carbon.
Surely, in the case where the bromine-impregnated activated carbon is used, specific smelly substances such as dimethyl sulfide and dimethyl disulfide can be more effectively removed than the conventional activated carbon. However, the bromine-impregnated activated carbon differ in quality depending upon various parameters such as the amount of bromine carried by the activated carbon. Accordingly, in the present situation, dimethyl sulfide and dimethyl disulfide cannot always be removed to a satisfactory degree.
SUMMARY OF THE INVENTION
The present invention provides a bromine-impregnated activated carbon wherein the contents of any alkali metal, any alkali earth metal and iron are not higher than 0.3 wt % and the content of bromine is not lower than 3 wt %.
Further, the present invention provides a process for preparing the bromine-impregnated activated carbon comprising the steps of: reducing the contents of any alkali metal, any alkali earth metal and iron in a material activated carbon to 0.3 wt % or lower; and impregnating the activated carbon with bromine such that the content of bromine is not lower than 3 wt %.
In another aspect, the present invention provides a bromine-impregnated activated carbon, wherein the content of a surface oxide is not higher than 2.5 wt % in terms of oxygen and the activated carbon is impregnated with bromine such that the content of bromine is not lower than 3 wt %.
Further, the present invention provides a process for preparing the bromine-impregnated activated carbon of the above comprising the steps of: thermally treating a raw material activated carbon at 500° C. to 1,100° C. in the absence of oxygen to produce a carrier activated carbon; and impregnating the carrier activated carbon with bromine.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As a material activated carbon for producing the bromine-impregnated activated carbon of the present invention, usable is any activated carbon prepared from a raw material such as coal, coke, charcoal, coconut shell, resin, petroleum residuum or the like by a known process that has a specific surface area of about 100 m
2
/g to 2,000 m
2
/g. The material activated carbon may be in any form such as spherical, cylindrical, crushed, powdery, granular, fibriform or honeycombed form.
The alkali metals and alkali earth metals whose contents in the bromine-impregnated activated carbon of the present invention are controlled include Na, K, Mg, Ca, Zn and the like, for example. In whatever form these metals may be present, e.g., in a free form or in the form of a compound such as an oxide, a carbonate or a chloride, the contents thereof in terms of metals is preferably about 0.3 wt % or lower, more preferably about 0.1 wt % or lower, still more preferably about 0.05 wt % or lower, with respect to the weight of a material activated carbon. Especially, in the cases where the alkali metals and alkali earth metals are in a form which enables them to react with bromine, for example, in a free form, or in the cases where the alkali metals and alkali earth metals are ready to react with bromine, for example, in the form of an oxide (hydroxide) or in the form of an iodide, the contents of such metals are preferably about 0.2 wt % or lower in terms of the metals with respect to the weight of the material activated carbon.
The contents of the alkali metals and alkali earth metals are discussed here in wt % with respect to the material activated carbon. However, as described later, since the impregnation amount of bromine is usually within the range from about 3 wt % to about 50 wt % with respect to the material activated carbon, the contents of the alkali metals and alkali earth metals can be calculated, if necessary, in wt % to the bromine-impregnated activated carbon from the amount of bromine with which the bromine-impregnated activated carbon is impregnated. In this case, the contents of the alkali metals and the alkali earth metals are preferably about 0.3 wt % or lower, more preferably about 0.1 wt % or lower, still more preferably about 0.05 wt % or lower, for example, with respect to the weight of the bromine-impregnated activated carbon.
The content of iron in the material activated carbon is preferably about 0.3 wt % or lower, more preferably about 0.1 wt % or lower, still more preferably about 0.05 wt % or lower, and the content of iron in the bromine-impregnated activated carbon is preferably about 0.3 wt % or lower, more preferably about 0.1 wt % or lower, still more preferably about 0.05 wt % or lower. In the cases where the iron is in a form which enables them to react with bromine or in the cases where the iron is ready to react with bromine, the contents of iron is preferably about 0.2 wt % or lower in terms of the metals with respect to the weight of the material activated carbon.
Further, in the present invention, the bromine-impregnated activated carbon having the controlled contents of the alkali metals, alkali earth metals and iron as described above can exhibit more improved adsorption characteristics if the content of surface oxides is controlled as described below.
In the bromine-impregnated activated carbon of the present invention, the surface oxides whose content is controlled include various kinds of oxides such as carbon-oxygen complex (i.e., carbon monooxide, carbon dioxide), oxides of alkali metals and alkali earth metals. The content of such oxides is preferably about 2.5 wt % or lower, more preferably about 2 wt % or lower, still more preferably about 1.5 wt % or lower, in terms of oxygen with respect to the material activated carbon before the impregnation with bromine. In the bromine-impregnated activated carbon of the present invention, oxidative effect of bromine leads to oxidation of the activated carbon with time. As a result, the surface oxides tend to increase to some extent. Therefore, the content of the surface oxides in the bromine-impregnated activated carbon as finally obtained is controlled as discussed above in terms of weight with respect to the material activated carbon before the impregnation with bromi
Fukui Teruo
Kobayashi Ayako
Kobayashi Takashi
Noguchi Katsuya
Tsutsumi Yoshio
Foley & Lardner
Hendrickson Stuart L.
Takeda Chemical Industries Ltd.
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