Mineral oils: processes and products – Refining – Halogen contaminant removal
Reexamination Certificate
1997-01-24
2001-11-06
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Refining
Halogen contaminant removal
C208S262100, C588S253000, C588S253000
Reexamination Certificate
active
06312587
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to dechlorination of polychlorinated aromatic compounds that are environmental pollutants. More particularly, the present invention relates to a method of treating polychlorobiphenyl contained in a hydrocarbon oil, especially in an insulating oil used in a transformer.
The present invention also relates to a method of treating a polychlorinated aromatic compound which is advantageous by antipollution considerations. This method allows the removal of chlorine from polychlorobiphenyl contained in an insulating oil. The resultant reaction product is thus an organic compound with no chlorine content, and may be disposed of as an industrial waste and a municipal waste. In addition, the oil after treatment may be recycled as a harmless hydrocarbon oil.
2. Description of the Prior Art
Polychlorinated aromatic compounds such as polychlorobiphenyl (PCB) are known as environmental pollutants. Such compounds are contained in, for example, insulating (hydrocarbon) oils used in a transformer. The insulating oil polluted with the polychlorinated aromatic compound is recovered and stored under present technical conditions.
Some articles disclose the decomposition of PCB by means of heating the composition (such as oil) containing PCB at a high temperature. This method, however, requires special facilities and some supplementary facilities to generate a high temperature. Such facilities may also be required to purify the exhaust gas because there is a possibility of causing incomplete decomposition of PCB. Alternatively, the polychlorinated aromatic compound, such as PCB-contained in the hydrocarbon oils may be removed therefrom through chemical decomposition. In this method, the hydrocarbon oil is stirred while heating along with polyethylene glycol and an alkali metal hydroxide. This technique is disclosed in, for example, Japanese Patent Laid-Open Nos. 49-126651 and 60-114278.
It is known that the chlorine of PCB in these methods remains in the polyethylene glycol layer as a reaction product which has a bound chlorine (organic chlorine compound) rather than being removed completely.
In other words, it is only possible to remove PCB from the hydrocarbon oil but another problem occurs on disposal of the organic chlorine compound remained in the polyethylene glycol layer. In addition, typical chemical methods of removing PCB require a solvent or solvents added to the composition from which PCB is to be removed for decomposing the latter. This means that the treating process becomes complicated due to the necessary steps of separating and recovering the hydrocarbon oil and the solvent after the reaction, and of treating the used solvent.
As mentioned above, the known methods are insufficient by practical considerations because PCB is not completely dechlorinated, even by using the specific facilities and/or complicated treating process.
Accordingly, an object of the present invention is to provide a safe, effective method of dechlorinating polychlorinated aromatic compounds that are environmental pollutants.
Another object of the present invention is to provide a method of removing polychlorobiphenyl contained in a hydrocarbon oil, especially in an insulating oil used in a transformer.
Yet another object of the present invention is to provide a method of removing chlorine from polychlorobiphenyl to achieve complete removal of an organic chlorine compound from the entire system after reaction.
SUMMARY OF THE INVENTION
The present inventors had made tremendous studies about the above mentioned problems. As a result, it has revealed that the bound chlorine in the polychlorinated aromatic compound can be removed almost completely as an inorganic chlorine by using an alkali metal tert-butoxide as a reactant. The present invention was thus completed.
More specifically, the present invention is a method of treating a polychlorinated aromatic compound or a hydrocarbon oil containing a polychlorinated aromatic compound comprising the step of: heating while stirring the polychlorinated aromatic compound or the hydrocarbon oil containing the polychlorinated aromatic compound with an alkali metal tert-butoxide used as a reactant to remove chlorine from the polychlorinated aromatic compound, the alkali metal tert-butoxide being represented by the general formula:
wherein M is an alkali metal,
to provide a post-reaction system with no chlorine content.
In the method of treating a polychlorinated aromatic compound disclosed above, the alkali metal tert-butoxide may be potassium tert-butoxide.
In the method of treating a polychlorinated aromatic compound disclosed above, the polychlorinated aromatic compound may be polychlorobiphenyl.
In the method of treating a polychlorinated aromatic compound disclosed above, the treatment may be conducted without a solvent.
In the method of treating a polychlorinated aromatic compound disclosed above, the treatment may be conducted in the presence of a single solvent or a mixture of solvents.
The polychlorinated aromatic compounds applicable to the present invention include polychlorobiphenyl (PCB), dioxin, polychlorobenzene, and dichlorodiphenyl trichloroethane (DDT). Of these, polychlorobiphenyl can be treated most advantageously.
The polychlorinated aromatic compound alone may be treated by the present invention. In addition, the method of the present invention can be applied to a mixture containing the compound(s). The method of the present invention is particularly applicable to a hydrocarbon oil, such as an insulating oil, containing the polychlorobiphenyl. There is no limitation on the concentration of the polychlorobiphenyl in the hydrocarbon oil. The present invention can be applied to a hydrocarbon oil containing the polychlorobiphenyl in an extremely small amount, as well as to the polychlorobiphenyl alone.
Examples of the alkali metal tert-butoxide used in the present invention include lithium tert-butoxide, sodium tert-butoxide, and potassium tert-butoxide. Of these, potassium tert-butoxide is preferable. The amount of the alkali metal tert-butoxide used is preferably 10 times or more, by molar amount, relative to the amount of the polychlorinated aromatic compound.
The method of treating the polychlorinated aromatic compound according to the present invention may be conducted without a solvent. With this method, the entire reaction system becomes simple, eliminating the necessity of fully analyzing the chlorinated aromatic compound(s) remaining in the solvent. In addition, this method also eliminates the necessity of providing measures to treat and reuse these solvents. The dechlorination according to the present invention can thus be conducted completely without using any solvent, as will be apparent from the examples described below.
Alternatively, a solvent or solvents may be used in the present invention. The solvent(s) used may be polar and/or non-polar one(s). Examples of such solvents include, but are not limited to, polyalkylene glycol; monoalkyl ether of polyalkylene glycol; dialkyl ether of polyalkylene glycol; aromatic hydrocarbons; non-aromatic hydrocarbons; sulfoxides; amines; alcohols; ketones; ethers; cyclic ethers; amide; nitrogen-containing ring aromatic compounds; nitriles; and phosphoroamides. These solvents may be used as an anhidlide or, as a case may be, a hidlide.
The polyalkylene glycol used is represented by the general formula:
HO—[R—O—]
n
H,
wherein n is from 1 to 30, R is a linear or branched alkylene group having from 2 to 7 carbon atoms. More specifically, the polyalkylene glycol may be, for example, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, or butylene glycol.
The monoalkyl ether of polyalkylene glycol is represented by the general formula:
HO—[R—O—]
n
R
1
,
wherein n is from 1 to 30, R is a linear or branched alkylene group having from 2 to 7 carbon atoms, and R
1
is an alkyl group having from 1 to 5 carbon atoms. More specifically, the monoalkyl e
Kaneda Hisasi
Ohno Masayuki
Flynn ,Thiel, Boutell & Tanis, P.C.
Griffin Walter D.
Kansai Tech Corporation
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