GB890268A - Improvements relating to the production of cyanogen halides - Google Patents

Abstract

Cyanogen chloride and bromide are prepared by bringing the appropriate halogen and nitrogen into contact with carbon at a temperature of 1800 DEG to 3600 DEG C., quenching the product gases to 500 DEG C. or below and condensing and separating the cyanogen halide formed. A suitable type of reactor consists of a jacketted quartz (or alumina or other refractory material that is inert towards the halogen and its reaction products with carbon and nitrogen at the required reaction temperature) tube enclosing an electrically heated graphite rod. On a large scale, an electric resistance furnace or an electric-arc furnace containing a fluidized or stationary bed of carbon particles may be used. In a fluidized carbon-bed reactor, graphite, other forms of carbon, alumina or other inert refractory material may be used as the materials of construction. Non-electrical heat sources, e.g. construction reactions and focused solar heat rays may also be used. The carbon used may be in the form of bars, filaments, rods or beds of particulate material having any shape. The halogen used in the process must be free from impurities such as H2, O2, H2O and other compounds containing H2 or O2, which would preferentially combine at the reaction temperature with the halogen or carbon. The nitrogen must also be free from reactive impurities. The carbon and halogen may be formed in situ from compounds thereof, e.g. CCl4, tetrachloroethylene, and hexachloroethane, decomposing at the reaction temperature. The reaction temperature is preferably between 2400 DEG and 3000 DEG C., and pressures between 0,1 and 3 atmospheres are preferred. The nitrogen/halogen ratio (by volume) should be between 2:1 and 3:1 when the reaction temperature is between 2400 DEG and 3000 DEG C., and 1:1 when the range is 1800 DEG to 2400 DEG C. The carbon that reacts to form the cyanogen halide is in the gas phase, the amount of carbon present being in considerable excess of the amount needed for the reaction. The time of contact of the reactants must be long enough for equilibrium to be attained at the reaction temperature, and after this the gaseous products are quenched to 500 DEG C. or below in from 1 to 10 milliseconds. The quenched gases are further cooled and the cyanogen halide collected, unreacted nitrogen and halogen being recycled. In Example 1, the graphite heating element is heated to 2700 DEG C. and the molar ratio N2:Cl2 is 2,3:1, the reaction time being 40 to 45 minutes. Example 2 is similar, the reaction time being 145 minutes at a temperature of 2850 DEG C. In Example 3, a bed of graphite heated to 2600 DEG C. is used.