Chlor-alkali purification

Chlorine gas and Caustic Soda are today produced by electrolysis of brine on membranes. We have described in the previous section the Alkaline earth metals removal which is the main purification application, but in some cases, others impurities have also to be removed such as Aluminium, Mercury, Iode, Iron, Silica, …

Aluminium could be a cation in acidic conditions, non-ionic in neutral pH and anionic in alkaline conditions. Removing Al3+ is possible after acidification of the brine using an iminodiacetic acid resin. Silica will also be removed at the same time.

In cases where chlor-alkali plants combine mercury and membrane technologies, mercury is a potential contaminant which is poisoning the electrodes but also the chelating resin for the alkaline earth metal removal, and has to be removed when present in the brine. We will propose a chelating resin with a thiol functional group able to remove Hg2+ at less than 50 ppb at 50°C. Thiol resins are regenerable, but some plant prefers to replace the exhausted resin and in such case non-regenerable thiourea or thiouronium resins will be proposed.

Iode could affect the membrane in case of precipitation, and has to be limited at less than 0,2 ppm in the feed brine. A strong base anion type 1 will remove iodine I- after a step of oxidation in order to exchange the chloride of the resin with (I₂Cl)^- . Regeneration and condition of process can be describe by contacting Lenntech support team.

Nickel in brine is fouling the membrane, and can be removed at less than 10 ppb using an Iminodiacetic (IDA) or an aminophosphonic (AMP) resin after adjusting the pH in acidic conditions.

Iron will be removed from feed brine on both IDA and AMP resins, but in case of high concentration, IDA shall be preferred for easier regeneration.