Removal of sulphate in Chloralkali process

For the production of chlorine the industrial sector applies the chlor-alkali process. During this process the sodium chloride salt (NaCl) is dissolved and electrolyzed to produce chlorine gas, hydrogen gas and sodium hydroxide (NaOH).

Figure 1 - Chloralkali process

Product brine impurities

Industrial salt (NaCl) contains impurities which can affect the membrane cell process, like sulfate which can accumulate in the membrane cell when it is not removed from the recycled brine. The accumulation of sulphate in brine will cause precipitation on the electrode surface in the electrolysis cell, which will increase the energy consumption (higher voltage) and reduce the lifetime of the very expensive electrode and the ion exchange membranes of the membrane cell process for the chlor alkali production.

There are different solutions for the removal of the sulphate in brine,

1) Addition of barium salts to the raw brine to precipitate the sulphate as barium sulphate.

2) Addition of calcium salts to the raw brine to precipitate out as calcium sulphate.

3) Purging of the depleted brine or brine with high concentration of sulphate. Local legislation nowadays are usually not allowing this option.

4) Removal of sulphate from brine by nanofiltration (removal of sulfate from chlor alkali process by nanofiltration) and purging out the reject brine with sodium sulphate

The first two processes require addition of barium chloride, barium carbonate or calcium salts to the raw brine for the precipitation of the sulphates in it. However, these processes present many disadvantages which turn these options not appealing (toxicity, performance of the membrane cells, increase of calcium and barium salt contaminants and consequently reduce the performance of the membrane cells.

The removal of sulphate from brine by nanofiltration option presents the best solution due to the technical and economical feasibility.

Lenntech can access and provide you the best solution for chlor alkali brine treatment.

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