Mineral oils: processes and products – Refining – Halogen contaminant removal
Reexamination Certificate
2000-02-01
2003-06-10
Dang, Thuan D. (Department: 1764)
Mineral oils: processes and products
Refining
Halogen contaminant removal
C208S262500
Reexamination Certificate
active
06576122
ABSTRACT:
The present invention relates to a process for the reductive dehalogenation of liquid and solid halogenated hydrocarbons as such or as contaminants in liquids and solids through chemical reaction with reducing metals in the presence of a hydrogen donating compound characterized in that the halogenated hydrocarbons or the liquids and solids, which contain the halogenated hydrocarbons, are transformed into a finely dispersed pulverulent solid formulation and said finely dispersed pulverulent solid formulation, which contains the halogenated hydrocarbons, is heated up in the presence of a finely dispersed reducing metal and a hydrogen donating compound to a temperature ranging from 80 to 400° C.
Halogenated hydrocarbons in this context are aliphatic, aromatic and mixed aliphatic-aromatic hydrocarbons, which contain at least one halogen 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 to saturate anions and radicals respectively, for instance alcohols, amines, aliphatic hydrocarbons.
BACKGROUND OF THE INVENTION
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 hexochlorocyclohexane (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.
There are 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
-alcohol at temperatures between 100 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 alkali earth 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 liquid and solid halogenated hydrocarbons as such or as contaminants in liquids and solids through chemical reaction with reducing metals in the presence of a hydrogen donating compound characterized in that the halogenated hydrocarbons or the liquids and solids, which contain the halogenated hydrocarbons are transformed into a finely dispersed pulverulent solid formulation and said finely dispersed pulverulent solid formulation, which contains the halogenated hydrocarbons, is heated up in the presence of a finely dispersed reducing metal and a hydrogen donating compound to a temperature ranging from 80 to 400° C.
DETAILED DESCRIPTION
As reducing metals can be used preferably sodium, magnesium, aluminum and iron but also lithium, potassium, calcium and zinc and the alloys thereof in a finely dispersed form. This finely dispersed form of the metal can be added during the preparation of the finely dispersed, pulverulent solid formulation or during the heating of said solid formulation.
The invention is based on ideas which can be explained most simply by way of an example from practice. For instance, toxic materials such as dioxins, PCB and PCP may be present as contaminants in high concentration in wet soil, which, in addition, is interspersed with oily phases, which also contain toxic halogenated hydrocarbons. In such a case all processes known as chemically applicable to the dehalogenation of halogenated hydrocarbons will fail, because it is not possible to carry out reactions with sodium or potassium in wet soil and because dehalogenating reactions with less reactive metals, like magnesium, aluminum or iron, cannot be used under these conditions. Furthermore, it is impossible to reach the halogenated hydrocarbons in the described heterogeneous mix in order to manage any detoxifying, i.e. dehalogenating chemical reaction. All methods which have been tried so far in order to solve this sort of problem result in an exceptionally costly isolation of the halogenated hydrocarbons, either through extraction with solvents or through thermal stripping processes, for instance in a rotary kiln, and a subsequent high temperature incineration.
However, if the contaminated soil is largely dried thermally or chemically and subsequently disintegrated mechanically to form a pulverulent material, to which a reducing finely dispersed metal along with a hydrogen donating compound and, if necessary, an amine as a reaction accelerator is added and this homogeneous pulverulent mix, which can easily be handled, is heated up for a short time to an appropriate temperature it is possible to dehalogenate the halogenated hydrocarbons because all reaction partners necessary in a dehalogenating reaction are close together in a finely dispersed, i.e. in a highly reactive form. As a matter of fact, the dehalogenation reaction takes place though the reaction is, on closer examination, still a heterogeneous one and it is not easily to recognize, how the halogenated hydrocarbons, adsorptively bonded to the solid particles, can migrate onto the surface of the neighboring metal particles.
However, said course of reaction can be understood if one presumes that the adsorptively bonded halogenated hydrocarbons have access to the metal surface via the gas phase according to their vapor pressure under said reaction conditions. This agrees with the fact that the reaction time can significantly be decreased through the add
Dang Thuan D.
DCR International Environmental Services B.V.
Norris & McLaughlin & Marcus
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