Inhibition of the thermal decomposition of HCO3− A novel approach to the problem of alkaline scale formation in seawater desalination plants Original Research Article

Alkaline scale formation in seawater desalination plants is triggered by the thermal decomposition of the HCO3−ion. The various techniques used for retarding or eliminating scaling in evaporation units are reviewed in brief. The thermal decomposition of HCO3− is a kinetically controlled, first-order reaction. Like all rate reactions, it is prone to be catalyzed or decelerated by specific agents. Whilst catalysis by Ca2+ ions is well documented, inhibition has never been reported before. Three polymaleate compounds, commonly used as anti-scale agents, were discovered to inhibit HCO3− decomposition. The extent of inhibition depended on the nature and concentration of the additive used. The rate constants of the decomposition reaction were computed at 100°C. The tested compounds were, however, relatively weak inhibitors. Inhibition of the thermal decomposition of HCO3− presents a novel approach to combat scale formation, hitherto not applied before. The present paper is a call for a search for better inhibitors, to be combined with polymers with dispersing activity, to obtain new anti-scale agents with powerful properties.