Diaphragm Electrolyzer Technology

How does the Diaphragm process work?

HCl Absorption and Treatment

When integrated with MDI/TDI plants, the process starts with anhydrous hydrogen chloride gas, which is conditioned in an absorption unit. The absorption of HCl in water or dilute hydrochloric acid is strongly exothermic. Industrial applications typically require hydrochloric acid concentrations between 28 and 37 wt.%.

Electrolyzer with Anolyte and Catholyte Recycles

The concentrated aqueous hydrochloric acid is fed to both the anolyte and catholyte systems. Separate acid recycle loops are used for anolyte and catholyte, each operating at different concentrations: approximately 23 wt.% in the anode compartment and 21 wt.% in the cathode compartment.

Within the electrolyzer cell, chlorine and hydrogen are generated. Depleted hydrochloric acid with a concentration of approximately 17 wt.% exits both compartments. The anolyte flows through the anode chambers connected in parallel, while the catholyte flows through the cathode chambers in a similar configuration. Solid impurities are removed via filtration, and heat exchangers are used to maintain the thermal balance of the process.

A partial stream of the 17 wt.% hydrochloric acid is diverted from the catholyte recycle, reconcentrated with hydrogen chloride to approx. 28-37 wt.% in the absorption unit, and then returned to both electrolyte recycle loops.

Product Treatment

After cooling and filtration, the wet chlorine gas is either fed directly to downstream consumers or dried and compressed. The chlorine can then be routed back to the consumer to close the chlorine recycle loop or liquefied for storage in tanks.

Hydrogen is produced as a valuable by-product. Once cooled and scrubbed with caustic soda, it can be supplied to hydrogen consumers, such as hydrogenation plants.