Patent GB-1114430-A (GB)
Title: Manufacture of chlorine
IPC: C01B7/05
Filed: 1965-10-29
Abstract: <PICT:1114430/C1/1> Chlorine and nitrogen dioxide are produced from HCl and/or NOCl or a mixture of Cl2 and NOCl by contacting the chlorine containing compound or compounds with an oxidizing reaction medium circulating countercurrentwise, the oxidizing medium comprising a liquid phase obtained by mixing a nitric acid solution of concentration of at least 60% by weight (preferably 65 to 99%), with a nearly saturated aqueous solution of one or more metal nitrates, the reaction temperature being maintained between 60 DEG and 100 DEG  C. (preferably 75-90 DEG  C.), the reaction medium containing sufficient nitrate to ensure equilibrium under the reaction conditions between the intial reaction medium and the vapour phase over it containing nitric acid, gaseous reactants, their oxidation products and water vapour in which the amount of nitric acid is at least 750 g. HNO3 per kg. of the vapour phase, the quantity of nitrate being also compatible with the solubility of the nitrate or nitrates in the reaction medium, the amount of water in the medium being always less than 500 g/kg. "Nearly saturated" is used to mean at least 90% saturated at at least 60 DEG  C. Examples of suitable nitrates are those of Mg, Zn, Cd, Fe, Cu, Al, Ca, Li, either singly or in mixture.  The minimum concentration of HNO3 in the vapour phase for the reaction to be complete is between 990 g/kg. at 60 DEG  C. and 750 g/kg. at 60 DEG  C.  The nearly saturated aqueous solution of a metal nitrate may be an aqueous solution of Mg(NO3)2 containing 670 to 720 g/kg., the point representing the composition of the initial reaction medium, Mg(NO3)2/HNO3/H2O, on the triangular equilibrium diagram, Fig. 3a (not shown), for the system Mg(NO3)2-HNO3-H2O being situated in the solubility field of Mg(NO3)2 corresponding to the reaction temperature, the concentration of Mg(NO3)2 being preferably greater than 300 g/kg. Diagrams, e.g. Fig. 6, show curves giving minimum compositions of the reaction phase nitrate/HNO3/H2O necessary for the vapour phase to contain the concentration of HNO3 in g/kg. represented on each curve for Mg.Zn. Cd and mixed Zn and Mg nitrates.  When the metal nitrate is Zn(NO3)2 or Cd(NO3)2 the point representing the intial reaction medium, Zn(NO3)2 or Cd(NO3)2/HNO3/H2O on the diagrams or Figs. 6 or 7 (not shown) respectively is situated above the curve corresponding to the reaction temperature.  A solution containing about 79% by weight of mixture of 20-30% by weight Zn(NO3)2 and 80-70% by weight Mg(NO3)2 may be used, the reaction temperature preferably being about 100 DEG C. and the point representing the initial reaction medium Mg(NO3)2/Zn(NO3)2/HNO3/H2O on the diagram of Fig. 8 (not shown) being situated above the curve corresponding to the reaction temperature. If nitric acid of concentration 65% by weight or greater is used the spent solution leaving the base of the oxidation chamber may be distilled, after addition of enough 65% HNO3 to restore the reaction phase to its original acid concentration, to regenerate the initial nitric acid which is returned to the oxidation chamber, and a solution of nitrate which is returned to the oxidation chamber after having been concentrated to its initial strength.  If 60% to 65% nitric acid is used the spent solution from the oxidation is separated into dilute nitric acid and a nitrate solution which after concentration is recycled.  The nitrogen oxide produced may be used, preferably as a liquid mixed with HNO3, to react with HCl and/or chlorides of ammonium, alkali metals or alkaline earth metals to yield nitric acid, the nitrates, and NOCl.