Chemistry of alkaline scale inhibition in seawater desalination by flocon antiscalant 247

Abstract

Alkaline scaling in seawater distillation plants occurs by a series of physicochemical changes which are initiated by the thermal decomposition of bicarbonate ions. FLOCON Antiscalant 247, a new threshold scale inhibitor, suppresses calcium carbonate and magnesium hydroxide foulings by intervention at both the bicarbonate decomposition and mineral deposition stages of the scaling sequence. Kinetic studies in refluxing synthetic seawater which contained 14C-sodium bicarbonate show that FLOCON 247 retards bicarbonate/carbonate decomposition rates, thereby effectively reducing seawater's alkaline scale potential. The formation of Ca +2/Mg +2-antiscalant complexes disrupts calcium and magnesium catalyzed mechanisms for accelerated bicarbonate decomposition. FLOCON Antiscalant 247 was synthesized with 14C-radiolabelled maleic anhydride to determine its threshold interactions with calcium carbonate and magnesium hydroxide scales. High temperature scale control experiments using Atlantic Ocean seawater clearly demonstrate that FLOCON 247 significantly reduced alkaline fouling by incorporation of the antiscalant into the incipient scales. Codeposition of antiscalant with scale impedes further precipitation and disperses the precipitated scales in the blowdown. Formation of sparingly soluble, alkaline earth-antiscalant complexes provides the chemical driving force for the incorporation of antiscalants into alkaline scales under high temperature desalination conditions.