Chemistry of Organophosphonate Scale Inhibitors, Part 4: Stability of Amino-tris-(Methylene Phosphonate) Towards Degradation by Oxidizing Biocides

Organic additives are broadly used in water-treatment applications such as mineral scale, corrosion inhibitors, and dispersing agents. Phosphonates find extensive use as inhibitors for the formation of sparingly soluble salts such as calcium carbonates, phosphates, calcium sulfates, and others, commonly formed in open recirculating cooling systems. In such systems, biocides also are added to control microbiological growth. Some of these biocides are strong oxidants (e.g., ClO−, BrO−, etc.) and affect other water treatment chemicals that are sensitive to oxidative degradation. This study reports the effect of a hypobromite-based biocide towards the triphosphonate amino-tris-(methylene phosphonate) (AMP). AMP reacts rapidly with the biocide at room temperature. AMP degradation continues, but it slowly reaches a plateau after 1000 min. Even after 50 h of reaction time, only 20% of the AMP has decomposed. AMP reacts with the biocide to give orthophosphate much more rapidly at 43°C than at 25°C due to faster kinetics of decomposition.