Process for the destruction of halocarbons

Details Process for the destruction of halocarbons Process for the destruction of halocarbons

1995-03-30

1996-08-13

Lewis, Michael

Chemistry of inorganic compounds

Halogen or compound thereof

Binary compound containing metal

4234994, 423DIG12, 588201, 588206, C01D 316

Patent

active

055453902

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process for the destruction of halocarbons.
World wide concern over the depletion of ozone in the upper atmosphere has led to stringent international measures covering the production and use of halocarbons, particularly chlorofluorocarbons (CFCs) used in refrigeration, foam blowing, aerosols, etc. Intense work in the developed world is being targetted towards the search for some "ozone friendly" alternative compounds for use in these applications. However, considerable quantities of CFCs are presently "locked-up" in existing equipment. As this equipment comes to the end of its useful life there would be great value in being able to extract the CFCs and destroy the material in a process which would remove the halocarbons from the atmosphere.
We have now developed a process in which halocarbons are converted from materials with a high ozone depletion potential into stable solid phase compounds.
Accordingly, the present invention provides a process for the destruction of a halocarbon, which process comprises reacting the halocarbon with molten sodium at an elevated temperature to produce the appropriate sodium halide or halides in the solid phase.
The reaction of the present invention is surprising since it would have been predicted that a very violent, if not explosive reaction, would occur when the halocarbon contacted the molten sodium.
The process of the present invention, although specifically designed to address the chlorofluorocarbon problem, could also be used to treat a wide range of other halocarbons, such as dry cleaning fluids, degreasing fluids, polychlorobiphenyls, etc.
In carrying out the process of the present invention, the molten sodium is maintained at a temperature in the range of from 98.degree. to 500.degree. C., preferably at a temperature in the range of from 200.degree. to 300.degree. C.
The halocarbon which is to be destroyed in the present invention may be bubbled through the molten sodium, or may be admixed with an inert gas, such as, nitrogen, helium or argon.
The halocarbon to be treated according to the process of the present invention is preferably bubbled from a reservoir through the molten sodium, for example by introducing the gas into the bottom of a reaction vessel containing molten sodium.
The halocarbons react with the molten sodium to produce solid products each of which is denser than molten sodium. The products therefore tend to sink to the base of the reactor from which they are preferably removed, unless the reaction mixture is stirred vigorously when the products will tend to stay on top of the molten sodium. The densities and melting points of the various species involved are given below.


______________________________________ Density Melting Point .degree.C. ______________________________________ Sodium 0.97 97.8 Sodium Bromide 3.203 747 Sodium Chloride 2.165 801 Sodium Floride 2.557 993 Carbon 1.8-2.2 3600 ______________________________________
A typical process is, for example, the destruction of dichlorodifluoromethane (R12), a typical domestic refrigerant, which reacts according to the following equation:
The products of the process of the present invention are solid, dry products which are easily separable from the molten sodium. The products are, furthermore, valuable e.g. the carbon produced is in finely divided form with a very high surface area and is useful as a catalyst carrier or absorbent, etc. Should the treated halocarbon contain a bromine atom the resultant bromide products so produced may be readily converted into elemental bromine. Because no aqueous products are formed in the reaction, the process is particularly suitable for use as an environmentally friendly method for the destruction of ozone depleting volatile halocarbons.
The present invention will be described by way of a specific example thereof with reference to the single Figure of the accompanying drawings which illustrates an appartus for carrying out the process.
Referring to the drawing, a reaction vessel 1 is filled with mol

REFERENCES:
patent: 4392888 (1983-07-01), Eckert et al.
patent: 4755628 (1988-07-01), Adams
Pytlewski, L. L. et al., U.S. Environ. Prot. Agency. Off Res. Dev., 1980, 72-6 (abstract only).

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