Production of chlorine, carbon monoxide and optionally hydrogen

An electrolysis apparatus for electrochemical conversion of carbon dioxide and alkali metal chloride solution by a process wherein the carbon dioxide is electrochemically reduced at a gas diffusion electrode as cathode in an aqueous alkali metal chloride-containing solution as catholyte and, at the same time, chlorine is produced anodically from an aqueous alkali metal chloride-containing solution as anolyte (15a), where the alkali metal salt of carbonic acid formed in the catholyte, selected from alkali metal carbonate, alkali metal hydrogencarbonate or mixtures thereof, is then reacted with hydrogen chloride to give carbon dioxide and alkali metal chloride, and the carbon dioxide (38a) released is returned to the cathode space for the gas diffusion electrode and the alkali metal chloride produced is returned either to the anode space and/or to the cathode space, the electrolysis apparatus at least comprising

• (i) at least one carbon dioxide gas source and
• (ii) at least one electrolysis cell, at least comprising
• a cathode half-shell having a cathode, a catholyte feed, a catholyte drain, and a gas space in fluid connection to the carbon dioxide gas source via a first gas inlet, and connected to a first gas outlet for gaseous reaction product-containing gas, further comprising an anode half-shell, wherein the anode half-shell has been provided at least with a second gas outlet for the anode reaction product, an anolyte feed for the introduction of an aqueous alkali metal chloride-containing solution as anolyte and an anolyte drain, and an anode, and a separator disposed between the anode half-shell and cathode half-shell, for separation of anode space and cathode space,
• further comprising electrical power leads for connection of anode and cathode to a DC voltage source,
• wherein the cathode is designed as a gas diffusion electrode for conversion of carbon dioxide gas, and cathode, anode and the separator are arranged with their main extent vertically, and a gap as electrolyte space for passage of the catholyte by the principle of a falling liquid film is disposed between separator and cathode, and
• wherein the catholyte drain and the anolyte drain are connected directly or indirectly via pipe conduits to an electrolyte collector, the electrolyte collector is provided via pipe conduit with a carbonate breakdown unit, and the carbonate breakdown unit at least with a recycle line for dissociated carbon dioxide, a controllable feed for hydrogen chloride and a recycle conduit for electrolyte, and the recycle conduit is connected both to the catholyte feed and to the anolyte feed.