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Sodium hydroxide, or caustic soda, is manufactured as an electrolytic co-product of chlorine. Concentration of aqueous solutions of sodium hydroxide is presented by the 8500 model as %NaOH.
Sodium hydroxide is used in several industries either in concentrated form or in dilutions down to 400 ppm. In practice, the product can be measured with high accuracy in a well-equipped laboratory using off-line density meters. When the product must be measured inline with the same degree of accuracy, other methods are required. Inline sensor systems, like conductivity sensors, refractive index meters or coriolis meters, simply lack sensitivity for specific applications, or do not seem to respond anymore at larger concentrations of NaOH. Chemical methods, like titration analyzers are only needed when the sample exist of different dissolved solids. As the speed of sound is depending on the temperature, the concentration is compensated for temperature changes by means of the integrated thermistor. The TAM (Total Accuracy of the Measurement) is depending on the selected range. | 0-1 w/w% | TAM=0,001% | | 0-15 w/w% | TAM=0,002% | | 15-30 w/w% | TAM=0,005% | | 30-50 w/w% | TAM=0,01% |
For 30-50 w/w% NaOH the TAM is 0.01%, which is much better then any other online analyser. Lower levels have even a higher accuracy, because the speed of sound is lower.
Therefor, the Rhosonics 8500 is the best choice for the online (insitu and extractive) measurement of sodium hydroxide in the full range of dilution.
For this application a choice of different cells can be made.
The MP-130 measuring cell, is the best choice for an inline continuous explosion proof analyser with an extreme high accuracy and repeateability. Alternatively, the MP-54 probe or the recently introduced MP-48 may be chosen, as it is more cost-effective for applications that do not call for explosion-proof equipment. This probe is mounted inside a special pre-fabricated pipe section, ensuring minimal obstruction of the flow of the liquid.
For applications, demanding for the extraction of the sample out of the product line, the MP-42 sensor with cell is the most suitable solution. The cell is equipped with Swagelok connectors for convenient integration is the process line.
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