Apparatus and process for electrochemically decomposing salt solutions to form the relevant base and acid

A method of electrolysis of a solution of a salt for the production of a solution containing an acid and a solution containing a base, carried out in an electrolyzer which comprises at least one elementary cell divided into a first, a central and a third compartment by means of a first and a second cation-exchange membrane, the first of said compartments contains the first of said membranes and a cathode for the hydrogen evolution and the production of the base, the central compartment defined by said cation-exchange membranes is further divided into two parts by an anion-exchange membrane, the third compartment contains the second of said cation-exchange membranes and an anode, said anode comprises a porous electrocatalytic sheet for hydrogen ionization and a porous rigid current collector, said method comprises:

• feeding the solution of the base to an inlet of the first compartment
• withdrawing a more concentrated solution of the base and hydrogen from an outlet of said first compartment
• feeding the solution of the salt to an inlet of the part of the central compartment defined by said first cation-exchange membrane and the anion-exchange membrane,
• withdrawing an exhausted solution of the salt from an outlet of said part of the central compartment,
• withdrawing a solution of the acid from an outlet of the part of the central compartment defined by the anion-exchange membrane and said second cation-exchange membrane
• feeding a hydrogen-containing gaseous stream to an inlet of said third compartment
• venting rest gas from an outlet of said compartment characterized in that the hydrogen gas diffuses throughout the porous current collector and the porous electrocatalytic sheet and it is ionized at the interface between said electrocatalytic sheet and the membrane to form H.sup.+ ions and said H.sup.+ ions migrate through the membrane into said solution of the acid, said electrocatalytic sheet, said membrane and said current collector are held in contact by means of pressure without bonding.