Mineral oils: processes and products – Refining – Halogen contaminant removal
Reexamination Certificate
2000-02-01
2003-11-18
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Refining
Halogen contaminant removal
C208S262500, C585S469000, C585S641000, C585S733000, C588S253000, C588S253000
Reexamination Certificate
active
06649044
ABSTRACT:
The present invention relates to a process for the reductive dehalogenation of halogenated hydrocarbons through chemical reaction with reducing metals in the presence of a hydrogen donating compound characterized in that the dehalogenation reaction is carried out in the presence of an amine.
Halogenated hydrocarbons in this context are aliphatic, aromatic and mixed aliphatic-aromatic hydrocarbons, which contain at least one hologen in a molecule, including those hydrocarbons, which, in addition to halogen, contain other functional groups, for instance chlorophenols.
Hydrogen donating compounds in this context are all compounds, which can provide hydrogen formally as protons or atomic hydrogen in order to saturate anions and radicals respectively, for instance alcohols, amines, aliphatic hydrocarbons.
Halogenated hydrocarbons are toxic. This can be attributed to the presence of halogen in the molecule. Accordingly, toxic halogenated hydrocarbons can be detoxified through removal of the halogen. Since one single halogen in a molecule can cause a disproportionate high toxicity, it is essential, therefore, to dehalogenate multiply halogenated hydrocarbons in such a way that all the halogen atoms will be removed. This is chemically possible only in case of a reductive dehalogenation.
Halogenated aromatics like polychlorinated biphenyls (PCB), polychlorinated phenols (PCP) and polychlorinated dibenzodioxins and dibenzofurans (PCDD/PCDF) are extremely toxic. PCDD/PCDF, which generally are subsumed under the term “dioxins” are regarded as ultratoxic. Aliphatic halogenated compounds like hexochloro-cyclohexane (HCH) or mixed aliphatic-aromatic compounds like trichloro-bis(chlorophenyl)ethane (DDT) are also toxic even though they are not classified as ultratoxics in general. All these compounds quoted here are, along with other halogenated hydrocarbons, widely spread in the environment. Due to their bioavailability they own a high hazard potential which to abolish must be regarded as an important demand of environmental relevance.
BACKGROUND OF THE INVENTION
There is a number of processes which deal with the reductive dehalogenation of halogenated hydrocarbons. According to EP 0 099 951 PCB is dehalogenated by means of finely dispersed molten sodium at 100 to 160° C. According to U.S. Pat. No. 4,973,783 halogenated aromatics are reacted with alkali metal in the presence of hydrosiloxane. In U.S. Pat. No. 4,639,309 halogenated hydrocarbons are dehalogenated with sodium or potassium at 100° C. with the aid of mechanical abrasion of the formed halogenides. According to U.S. Pat. No. 4,950,833 halogenated aromatics are reacted with alkali metal in the presence of ammonium salts at 40 to 60° C. and according to the Canadian Application 2026506, in which a whole lot of further processes are quoted referring to the state of the art, halogenated aromatics are treated with finely dispersed sodium or calcium in the presence of methanol, ethanol or isopropanol at temperatures below 100° C. A process of particular effectiveness seems to be described in EP 0 225 849, in which halogenated aliphatic or aromatic compounds are reacted with sodium in an inert solvent in the presence of a C
1
- to C
5
-alkohole at temperatures between 10 and 150° C.
The quoted processes have some significant disadvantages. The most important drawback is that said processes are restricted to the use of alkali and earth alkali metals, further in that, as a rule, the reaction temperature must be above the melting point of sodium and that the reaction must be carried out in a homogenous liquid medium in an atmosphere of protecting gas. Said processes are, on no account, applicable to the solution of environmental problems in practice, for instance, to dehalogenate PCB in sludge, dioxins in wet soil, PCP in sand, HCH in a mix of waste material in landfills etc.
Therefore, it would be highly desirable to provide a process efficient to chemically and technically simply dehalogenate halogenated hydrocarbons of whatsoever origin as such or as contaminants in other materials without the restrictions and drawbacks as quoted above.
SUMMARY OF THE INVENTION
In accordance with the present invention there is now provided a process for the reductive dehalogenation of halogenated hydrocarbons through chemical reaction with reducing metals in the presence of a hydrogen donating compound characterized in that the dehalogenation reaction is carried out in the presence of an amine.
DETAILED DESCRIPTION
Amines applicable within the scope of the present invention are aliphatic primary, secondary and tertiary amines or diamines or amines with additional functional groups, in particular amino alcohols, or mixes of said amines or mixes of said amines with hydrogen donating compounds selected from other chemical families.
It is very much surprising that dehalogenating reactions can be accelerated through the addition even of very low proportions of amines in such a way that, for instance, the dehalogenation of trichlorobenzene with finely dispersed sodium will take place at room temperature in the form of a deflagration within less than one second. Without the addition of amine the same reaction will need a reaction temperature around 120° C. and a reaction time of greater than 30 minutes.
It might be assumed that the acceleration of the dehalogenating reaction through an amine is based on its reaction with sodium yielding an amide, which, as a extremely highly reactive intermediate, may react vigorously with the chloro compound. However, this cannot be true, because tertiary amines have the same accelerating effect.
It is helpful, from a practical point of view, to imagine that the amine covers the metal surface substantively thus protecting the metal from being covered with an inhibiting layer comprising metal halogenide and halogenated hydrocarbons attached via radical anions.
These layers, which will be created without the addition of amines, deactivate the metal surface in such a way that the reaction comes to a standstill even in case highly reactive metals are applied, for instance sodium or potassium. For the same reason less reactive metals like iron, zinc, aluminum, magnesium do react not at all. Only through the addition of amines said metals can be rendered applicable. Within the scope of the present invention lithium, potassium, calcium, sodium, magnesium, aluminum and zinc, including the corresponding alloys, are of particular effectiveness.
The choice of the metal to be applied depends on the target. For the dehalogenation of halogenated hydrocarbons as such, i.e. in its undiluted form, sodium and potassium are too reactive in the presence of amines. In this case it is necessary to dilute the halogenated hydrocarbons with sand or other inert materials, in particular inert liquids. For this reason it is recommended to make use of iron, magnesium or aluminum. The application of zinc is restricted to special cases because of the potential toxicity of this metal.
The reaction with the less reactive metals can be carried out best by vigorous mixing at increased temperatures, for instance at 40 to 160° C. In order to dehalogenate halogenated hydrocarbons in solid materials, for instance dioxins as a contaminant in filter dust, sodium is the preferably used as the reducing metal; the reaction takes place in a vibrating ball mill in the presence of amines at room temperature.
It is obvious that there is a close relationship between the concentration of the halogenated hydrocarbons, the redox potential of the metal, the temperature, the reaction time, the intensity of mixing and the metal particle size respectively. However, the reaction itself is practically independent of the type of the halogenated hydrocarbons and of the amine as well. Therefore, it is easy for a person skilled in the art to determine how a special dehalogenation project has to be carried out. If necessary, a simple laboratory test will provide the optimum reaction parameters.
With a given concentration of halogenated hydrocarbons (which includes the number of halogen at
Bölsing Friedrich
Habekost Achim
DCR International Environmental Services B.V.
Griffin Walter D.
Norris & McLaughlin & Marcus
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