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Elevated temperatures, the presence of chlorine and high salt concentration throughout the chlor-alkali process make stable and reliable pH measurement with conventional pH sensors a constant challenge. Further, the conditions mean sensor lifetime is usually short, so sensor maintenance and replacement costs are high.
Evonik Industries Fine Chemicals Co., Ltd. is a Sino-German joint venture that produces cyanuric chloride as well as the main raw materials for its production: sodium cyanide and chlorine.
For chlorine production, Evonik uses the membrane cell chlor-alkali process. Here, aqueous sodium chloride is electrolyzed in large cells to produce chlorine gas.
Accurate pH measurement is vital in many of the production steps, but the diaphragm on the pH sensors that Evonik was using were being clogged by brine crystals, necessitating regular and time-consuming sensor cleaning and calibration. In addition, chlorine was diffusing through the diaphragm, affecting measurement reliability and reducing sensor lifetime.
METTLER TOLEDO introduced Evonik to our InPro 4850i, a pH sensor designed specifically for chlor-alkali processes. The InPro 4850i features two glass membranes: one for measuring pH and one as a reference for the sodium level in the brine. By measuring the difference between the potentials of the two glass membranes, the pH of the solution can be accurately determined. The sodium reference is a completely closed system; it has no diaphragm, so there is no possibility of sensor poisoning or clogging. Therefore, there is no need for frequent sensor cleaning or calibration.
Another significant design feature of the InPro 4850i is that it communicates digitally with its transmitter. Being digital, the output signal from the sensor is always 100% stable and arrives at the transmitter unaffected by the electrical interference that can affect other chlor-alkali pH sensors.
Find out more on how Evonik solved their pH measurement issues in our Success Story.
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