Removal of sulfate from chlor alkali brine by nano filtration

In the chlor alkali industry sodium hydroxide (NaOH) and chlorine gas (Cl₂) are produced as a result from electrolysis of NaCl.

Industrial salt (NaCl) is consumed during the chlor-alkali process contains many impurities, including a big amount of sodium sulphate (Na₂SO₄), which can be up to 20 g/L. If the latter is not removed then it will accumulate and cause operational problems due to the fact that the sulphate ions (SO₄^2-) have a negative effect on the plant's Electrolyser.

The sulphate ions in the brine needs to be kept at low levels. During operation, the brine is continuously recycled from the membrane cells and salt recovery systems back to the saturation area, which progressively leads to more sulphate ions being dissolved and reaching concentrations that exceed the process limits.

Figure 1 - diagram of high temperature nanofiltration process for chloralkali brine treatment

The most technical and economical solution to remove sulphates from chlor alkali brine is through nanofiltration membrane technology. Nano filtration membranes can be chosen with high affinity to Na₂SO₄ rejection, allowing to recirculate the NaCl brine more effectively.

A common characteristic of the Chlor-alkali brine is the high temperature (as high as 70^oC) which is characteristic to this process, as a result of the NaCl electrolysis.

Most of the nanofiltration membranes available in the market have a temperature limitation – typically 40-45oC). When these are used in Chlor alkali brine treatment, the brine shall be cooled down and heated up again after treatment, when recirculated back to the system.

Lenntech solution

Lenntech applies high temperature resistant nanofiltration membranes which remove sulfate from the NaCl brine at 70^oC which allows:

• Gain in energy consumption (no losses of heat)
• The Sulphate free brine can be directly treated and used back in the process, without the need to heat exchangers to decrease and increase the temperature of the brine.

Lenntech solution advantages:

Lenntech solution can offer you the following advantages:

• Lower cost of the system
• High energy saving
• High treated brine quality
• Less chemical use for sulfate precipitation

Lenntech can design, engineer and build a nanofiltration system to treat your Chlor alkali brine,  providing you the most technical-economical solution.

Chlorine production in chlor alkali industry

Membrane cell process for chlor alkali production

Removal of Sulphates from Chlor Alkali Brine