Durable pH Measurement in Chlorine Production

Dec. 3, 2012 - PRLog -- Chlorine is a hugely important chemical with a wide number of uses. Accurate pH measurement is central to maximizing chlorine production, but is very difficult to achieve dependably. Using advanced glass technology and a digital signal, a new sensor solves all measurement issues.

Chlorine is one of the most widely used constituents in the production of industrial and consumer products. It is also the most important chemical used in the treatment of water. Today, total global chlorine production is in excess of 55 million tons.

Membrane cell chlorine production is environmentally friendly
There are three basic processes for the manufacture of chlorine: the mercury cell, the diaphragm cell, and the membrane cell. The first two generate hazardous waste and globally are declining in favor of the environmentally friendly membrane cell process. Here, brine is electrolyzed in large cells that are divided into two chambers. Chlorine is produced in one chamber, and as by-products, caustic soda and hydrogen are generated in the other.

Sensor resists tough conditions
pH value is extremely important in a number of steps throughout the process. Without careful pH control, yield reduces and the expensive membrane that separates the two cell chambers can become damaged. However, reliably measuring pH is not easy as conditions in the chlor-alkali process are very tough on pH electrodes: chlorine seeps into the sensors and affects their ability to operate, and crystalized brine and precipitated impurities also cause problems. The result is poor measurement accuracy resulting in reduced process yield, and membrane damage.  In addition, short sensor lifetime necessitates regular, costly sensor exchange. Frequent cleaning and calibration of pH electrodes can maintain their accuracy and extract the maximum lifetime, but is labor intensive for technicians.

The new InPro 4850i dual-membrane pH electrode from METTLER TOLEDO has been designed specifically for the needs of the chlor-alkali industry. Two features of the sensor make it the ideal choice.

1: Sodium reference system
The InPro 4850i sensor incorporates a glass membrane that is sensitive to sodium ions in the brine used for chlorine production, and actually uses the brine as a reference. The sensor also has a glass membrane that is sensitive to pH. By measuring the difference between the potentials of the pH glass and the sodium reference glass, the pH of the solution can be accurately determined. The reference system is completely sealed; therefore there is no possibility of chlorine, brine crystals or impurities affecting the sensor's ability to measure. Consequently, regular sensor cleaning is not required.

2: Digital signal for stable measurement
Other "dual-membrane" sensors are available, but they suffer greatly from electrical interference. The sodium and pH measurement systems combined have a very high impedance, as does the cable between the sensor and transmitter. This means that the signal that arrives at the transmitter can easily be altered by the presence of surrounding equipment. Touching or even simply approaching the system can also create a change in the measurement shown on the transmitter. And the longer the cable, the worse the affect.

The second significant design feature of the InPro 4850i is that it communicates digitally with its transmitter. Digital signals are very low impedance, and the output signal from the InPro 4850i is always 100% stable and arrives at the transmitter unaffected by electrical interference, cable length or moisture in the environment.

The combination of dual-membranes and digital signal means that the InPro 4850i provides highly dependable, low maintenance performance in chlor-alkali applications.

Find out more about the InPro 4850i, at:
www.mt.com/InPro4850i?crel=ePR_PP_EN
www.mt.com/pro-chlor-alkali?crel=ePR_PP_EN

Contact information:
Mettler-Toledo International Inc.
Im Langacher,  Zip Code 8606
Greifensee, Switzerland
E-Mail    : ePublicRelations@mt.com
Phone     : +41-44-944 33 85
Website  : www.mt.com

About Author:
METTLER TOLEDO specializes in the area of precision instruments for professional use. METTLER TOLEDO laboratory instruments are used in research, scientific, drug discovery, and quality control labs, amongst many others in the pharmaceutical, chemical, food and cosmetics industries. METTLER TOLEDO comprehensive industrial solutions cover the various steps in a host of manufacturing processes at many of the same customers that laboratory serves. Solutions range from receiving raw materials through various manufacturing processes, in-line process control and end-of-line packaging control, to logistics and shipping. Increasingly, these solutions are fully integrated into the customer's IT environment, helping automate their workflows. In food retail, our offering for fresh food management ranges from receiving and pre-packaging, to in-store solutions for self-service departments, deli counters, and checkout terminals.