The Importance pH & ORP Monitoring in Chlor-alkali Electrolysis
Chlor-alkali electrolysis is an important industrial process that produces chlorine, sodium hydroxide, and hydrogen. The process involves the preparation of a brine, which is then sent through a series of chemical reactions and filtration steps within a membrane cell. pH and ORP measurements are required throughout the process to maintain equipment functionality and to ensure that contaminants are removed properly.
Brine Purification
Dissolving sodium chloride in water creates a saturated brine. When the brine then enters the cell, Na+ and H2O pass through the membrane. Cl- ions oxidize at an anode to produce chlorine gas, and the anolyte produced must then be dechlorinated before it can be recycled.
Meanwhile on the other side of the membrane, at the cathode, water molecules produce hydrogen gas and hydroxide ions. While releasing hydrogen gas, sodium ions react with hydroxide to produce sodium hydroxide, the final byproduct of the process. The sodium hydroxide solution must maintain a precise concentration in order to keep the process running smoothly.
Brine Recycling
When the used brine leaves the electrolytic cells for the recycling phase, it may contain chlorine/chlorate that must be removed before the brine can be re-saturated and returned to the process. ORP monitoring is necessary to detect the chlorine levels in the solution before and after the dechlorination process to ensure the concentrations are correct and to prevent equipment damage. pH measurements determine proper chemical addition for further chlorine extraction.
The Challenge
Harsh conditions in the chlor-alkali electrolysis process can cause corrosion, equipment damage, and measurement interferences. Precipitated heavy metals and dissolved chlorine gas, in addition to the presence of EMI, can offset pH readings and cause the need for frequent calibrations. High temperatures and ionic strengths can also damage sensors and decrease their lifespans.
The Complete Solution
The SE 555 pH/ORP sensor is ideal for use in liquids containing suspended solids. It utilizes modern potentiometric technology with its Omega-glass design and a pressurized gel reference, thus minimizing the potential for sodium error. Memosens technology integrates the benefit of inductive connectivity to eliminate the effects of solution-currents and corrosive environments while minimizing the effects of EMI.
The microprocessor within the head of the Memosens SE 555 facilitates offline calibration and diagnostics when used with a Portavo portable meter or MemoSuite software. Technicians can perform calibrations and troubleshooting remotely in the lab or shop with the Portavo or MemoSuite, therefore preventing exposure to high temperatures and other harsh conditions of the plant.
Stratos series transmitters provide digital process and diagnostic information that operators can view through the DCS. This valuable predictive maintenance data reduces the potential for unscheduled process interruptions and ensures disruption-free measurements.
What was this Customer’s Return on Investment?
- Reduced Operational Costs – Diagnostic data provides valuable insights for predictive maintenance and efficient use of available labor. Precise measurements impede excessive chemical usage, omitting waste and controlling product quality as a result.
- Accurate and Reliable Measurement – Innovative sensor design subverts buildup and sensor drift, which reduces the need for frequent calibrations. Memosens technology ensures long sensor life and stable measurements in the process, minimizing sensor replacements for measurement reliability.
- Higher Process Efficiency – Consistent, accurate measurements and equipment built to withstand harsh conditions make it easier for operators to monitor their process and ensure that parameters are optimal. Diagnostic data gives technicians better control over their PM schedule, which increases operational efficiency.
