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Chlor-Alkali (pH/ORP)

Chlor Alkali Processing

The chlor-alkali process involves the electrolysis of NaCl brine.

The resulting chlorine gas, hydrogen, and caustic from this process form the building blocks for many well known end products.
  • Plastics (Nylons, PVC, Polycarbonates)
  • Pesticides
  • Paint additives
  • Disinfectants (Sodium Hypochlorite)
  • Surfactants (Soaps and shampoos)
Since the chlor-alkali plant provides feedstock to the finished chemical plant it will often be on-site or close-by. Accurate, reliable pH measurement is critical to ensuring efficient operation of the chlor-alkali facility. This paper will explore this application and make recommendations on proper pH sensor selection.

Measurement Challenges
pH measurement of the brine is difficult for multiple reasons. During the purification phases, impurities can plug the porous reference junction of the pH sensor. Precipitated heavy metals such a barium and strontium attack the Ag/AgCl reference element within the sensor thus causing high offsets in the reading. The presence of chlorine, a strong oxidizing agent can also damage the reference. Throughout the process the elevated temperature and high ionic strength of the brine can etch the glass electrode. All these factors combine to increase calibration intervals and shorten the pH sensor lifespan.

Barben Analytical's Performance Series pH sensors are specifi cally designed to deal with the harsh chlor-alkali process. The patented Axial Ion Path® solid state reference cell acts as a fi lter to prevent precipitated brine impurities from clogging the porous reference. Calibration / cleaning intervals can be extended as fouling of the Barben probe is much more diffi cult than traditional multi-junction pH designs. The same Axial Ion Path® reference design also effectively blocks strong chemicals and heavy metals from penetrating into the sensor. This ensures that the Ag/AgCl reference element is not poisoned and the sensor output remains stable.
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