Organic compounds -- part of the class 532-570 series – Organic compounds
Patent
1991-08-02
1993-05-04
Evans, Joseph E.
Organic compounds -- part of the class 532-570 series
Organic compounds
570230, 570237, C07C 1904, C07C 1900, C07C 1724, C07C 1726
Patent
active
052083934
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a process for the preparation of chloroform (CHCl.sub.3), starting out from carbon tetrachloride (CCl.sub.4)
There are references in the literature concerning several methods for reducing the halogen content of a range of organohalogenated compounds. Nevertheless, the majority are impractical and of no commercial interest because of their excessive sophistication.
As a result of the declining market for carbon tetrachloride, there is a growing excess of this product. In view of this situation, researchers are trying to revalue this product by searching for methods allowing it to be used as a raw material for the manufacture of chloroform, the market demand for which is, on the contrary, growing.
Thus, the Dow Chemical Co. U.S. Pat. No. 2,886,605 of 1959 teaches a method of hydrodehalogenation of polyhalogenated hydrocarbons, using a cuprous chloride catalyst in a fluidized bed. The greatest drawback of this method for commercial exploitation is that it is run at so high temperatures (350.degree. C. to 550.degree. C.) that such an abundant carbonization occurs that it becomes necessary continuously or very frequently to regenerate the catalyst.
Another Dow Chemical Co. patent (U.S. Pat. No. 3,579,596 of 1971) teaches a process for producing chloroform from gas phase carbon tetrachloride, using a fixed catalyst bed of platinum on a substrate. This method, nevertheless, suffers from serious limitations, for example, that stoichiometric amount encourages the production of methane and, furthermore, extraordinarily hinders the recovery of the reaction products, and for a 100% theoretical selectivity of chloroform production), making it very hard to control the temperature. According to trials carried out by the inventors, hot spots are formed in the catalyst in the gas phase process, encouraging the formation of free radicals which, in turn, give rise to the formation of heavy polychlorinated compounds. When these are deposited on the catalyst surface they almost immediately and irreversibly deactivate it.
SUMMARY OF THE INVENTION
According to the present invention, liquid carbon tetrachloride is reacted with hydrogen gas or with a molecular hydrogen-containing gas, at a pressure below 8,000 kPa and at a temperature below 250.degree. C. in the presence of a catalyst comprising a metal deposited on a powdered substrate. The metal is palladium, rhodium, ruthenium or platinum. The reaction takes place with the catalyst in suspension in the liquid.
According to the invention, the reaction is conducted in liquid phase, with a supported powdered metal catalyst in suspension in contact with the molecular hydrogen. The catalyst active component is a metal selected from the group formed by palladium, rhodium, ruthenium and platinum. Thus, under the conditions to be described hereinafter, the carbon tetrachloride is converted into chloroform, at low temperature, with high conversion and selectivity rates.
The process has proved to be particularly effective when the chosen metal is palladium.
The present inventors have discovered, and this is a very important advantage of this invention, that when the reaction is conducted under the abovementioned conditions, the drawbacks mentioned above are avoided.
A further important advantage of the process of the invention is that it allows the temperature to be easily controlled, thereby avoiding the formation of chlorinated polymers and it also allows the activity of the catalyst to be maintained for sufficient time to make the process commercially profitable.
Yet a further important advantage of the process of the invention over other known processes, is that the liquid phase system allows a low excess of hydrogen to be used, representing an undeniable financial saving. Furthermore, under these conditions, the production of methane and other unprofitable by-products is avoided, this being yet a further advantage of the new process.
The catalyst used in the process of the invention is formed by a metal selected from the grou
REFERENCES:
patent: 5097081 (1992-03-01), Correia et al.
Arcoya Martin Adolfo
Cortes Arroyo Antonio
Seoane Gomez Xose L.
Sule Gimenez Jose M.
Tijer Miquel Emilio
Ercros S.A.
Evans Joseph E.
Striker Michael J.
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