Chlorine from Aqueous Hydrochloric Acid (Electrolysis)

The process under analysis comprises four major sections: (1) Medium Preparation; (2) Electrolysis; and (3) Hydrogen Recovery; and (4) Chlorine Recovery.

Medium Preparation. Initially, the waste HCl is purified from impurities that could harm electrolysis reaction. The HCl gas is absorbed as it flows counter-currently a circulating solution in a falling-film column, yielding a 28 wt.% HCl solution. This solution is filtered and split to be fed to the anolyte system and to the catholyte system, both with hydrochloric acid recycles. Depleted hydrochloric acid streams are also fed to two compartments, resulting in a hydrochloric acid at 23 wt.% in the anode compartment and at 21 wt.% in the cathode compartment.

Electrolysis. As the electrolysis proceeds in the cells, the anolyte acid and the catholyte acid flow through the respective chambers, yielding chlorine and hydrogen which are directed to purification steps downstream. Hydrochloric acid streams at 17 wt.%, from both cell compartments, are recycled to the respective system.

Hydrogen Recovery. The hydrogen from the cells a column in which most impurities are removed by hydrogen cooling, carried out by direct contact with a circulating dilute acid solution. Residual impurities in the hydrogen gas – namely residual HCl and chlorine – are removed in a tower, where the gas is scrubbed with a caustic solution. The purified hydrogen is compressed and then directed via pipeline to consumers.

Chlorine Recovery. The hot, saturated chlorine gas produced in the electrolyzers is cooled indirectly in titanium heat exchangers. he remaining water is removed by three drying towers where concentrated sulfuric acid circulates as dehydrating agent. The dry chlorine gas is compressed, liquefied.