Improvements in or relating to the recovery of chlorine values from by-product hydrogen chloride

摘要

611,908. Electrolytic recovery of chlorine. WESTVACO CHLORINE PRODUCTS CORPORATION. April 9, 1945, No. 8738. Convention date, April 7, 1944. [Class 41] A continuous process for the recovery of chlorine from hydrogen chloride consists in electrolysing a solution of a reducible polyvalent, metal chloride, such as cupric, ferric or chromic chloride, containing hydrochloric acid, in a cell having a porous cathode, whereby the metal chloride is partially reduced from a higher to a lower valency state, withdrawing chlorine from the cell and the resulting solution through the porous cathode, oxidizing the reduced metal chloride to a higher valency state by contact with hydrogen chloride and oxygen, and returning the solution to the cell. The aqueous electrolyte containing 5 to 17 per cent (preferably 15 per cent) by weight of cupric chloride, or alternatively a molecular equivalent concentration (preferably 18 per cent) of ferric chloride, and 5 to 25 per cent (preferably 18 per cent) by weight of hydrochloric acid enters the annular chamber 13, Fig. 2, at a predetermined rate through the inlet 12 and is partially reduced at the porous graphite cathode 11. The chlorine formed at the graphite anode 10 leaves through the outlet 9. The partially-reduced electrolyte, now containing approximately 10 per cent cupric chloride and 7 per cent cuprous chloride (depending on the initial concentration), or molecular equivalents of ferric and ferrous chloride, passes through the cathode and is drawn off through the pipe 15 to the pipe-line 2 to which other cells may be connected, through the pump 20 to the single oxidizing unit 3, Fig. 1, into which hydrogen chloride and oxygen or air are introduced through the pipeline 4. The hydrogen chloride concentration is restored and the lower chloride re-oxidized, and the solution is pumped to a storage unit 7 from which it flows through the heater 8 back to the cell 1. In the oxidizing tower the oxygen or air and the hydrochloric acid or anhydrous hydrogen chloride may be introduced simultaneously, or additional hydrochloric acid may be introduced into the electrolyte before it enters or after it leaves the tower, and only oxygen or air blown into the tower. The inter-electrode spacing in the cell may be from ¢ to 1 inch and the cathode thickness from “ to 1¢ inches. The electrodes are impregnated against chlorine seepage at the top. The cathode has a permeability between 0.3 and 175 (preferably 30) gals./ft.2/min. for a pressure difference of 5 Ibs./sq. in. through 1 inch of graphite at 70‹ F. The current density is from 42 to 500 (preferably 168) amps./ft.2 for a voltage between 0.72 and 2.69 (preferably 1.24). The optimum flow rate of the electrolyte is 2.7 gal./hr./sq. ft. of cathode area. Instead of cylindrical electrodes, rectangular or polygonal electrodes may be used; the positions of anode and cathode may be reversed. Flat electrodes placed horizontally or vertically may be used, using a diaphragm such as sand or other inert material laid directly on the cathode.