Inhibition of the thermal decomposition of HCO 3− A novel approach to the problem of alkaline scale formation in seawater desalination plants

Abstract

Alkaline scale formation in seawater desalination plants is triggered by the thermal decomposition of the HCO 3 −ion. The various techniques used for retarding or eliminating scaling in evaporation units are reviewed in brief. The thermal decomposition of HCO 3 − 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 Ca 2+ ions is well documented, inhibition has never been reported before. Three polymaleate compounds, commonly used as anti-scale agents, were discovered to inhibit HCO 3 − 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 HCO 3 − 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.