Patent ID: 7341654

Claim:
A process for the production of a halogen gas by the electrolysis of an aqueous hydrohalic acid solution in an electrolytic cell, said cell comprising an electrocatalyst-containing anode; a cathode; an anolyte chamber; a catholyte chamber; an ion-exchange membrane separating said anolyte chamber from said catholyte chamber and not bonded to one or both of said anode and said cathode; said process comprising (a) feeding an aqueous hydrohalic acid feedstock to said anolyte chamber; (b) feeding an aqueous catholyte feedstock to said catholyte chamber, said catholyte feedstock comprising a metal ion species in a first oxidation state operably reducible to a lower and second oxidation state at said cathode to produce a catholyte effluent containing said reduced metal ion species; (c) operably producing said halogen gas at said anode within said anolyte chamber and a depleted hydrohalic acid effluent; (d) collecting said halogen gas and said depleted hydrohalic acid effluent; the improvement wherein said cathode comprises a non-catalyzed 3-dimensional electroconductive comprising one or more layers of porous structure made of electroconductive material resistant to acidic metal ion solution, said porous cathode having a thickness in the range of 0.5 to 10 millimeters providing a cathodically effective surface area of at least ten times its projected area, and said catholyte feedstock is passed through said porous cathode.