Azo dyes make up the largest group of synthetic dyes by number. They are used as food dyes, artists’ colors, basic colors for four-color printing (yellow and magenta), as well as textile dyes on a large scale. Over 350,000 tons of azo dyes are used worldwide only for the dyeing of natural fibers.
Dye syntheses in modern plants run around the clock in 4 shifts. Virtually all essential reaction steps are pH-dependent so that the optimization of product yield is based on a reliable, low-maintenance pH measurement.
The diazotation reaction requires much hydrochloric acid and is therefore correspondingly corrosive. The reactors are protected by an enamel coating, the coupling reactors also by a rubber coating. The extreme conditions for the measuring point are as follows:
pH = 1
Temperature = 90 °C,
Pressure = 6 bar.
The pH electrodes have a service life of 8 hours up to several weeks. Automation of these measuring points with conventional retractable fittings is only possible when Hastelloy C4 is used. Nevertheless, these expensive fittings require high maintenance effort. The fitting must be removed and serviced several times a year.
The Ceramat WA 150 retractable fitting together with the Unical 9000 automatic cleaning and calibration system allows complete automation of this difficult measuring point with maximum availability. The Ceramat fitting consists of a corrosion-proof, ultrahard, superpolished, rotating ceramic part and a corrosion-resistant, carbon-reinforced, non-moved plastic housing made of PEEK.
After 24 months run time the Ceramat does not show any wear on sealings, probe housing, or other parts.
Download the complete report: “pH Measurement During Dye Synthesis – Azo dyes”