Part 8: Bio- (green) and Synthetic Polymers as Antiscalants and Dispersants
By Zahid Amjad, Ph.D.
The formation of scale-forming salts or mineral scales in boiler, cooling towers, reverse osmosis (RO) membranes, and other equipment surfaces in industrial water systems is a serious problem, often resulting in increased system operational costs (1). Carbonate and sulfate scales of alkaline earth metal ions is of particular concern because of the fact that these salts show inverse solubility with increasing temperature. Additionally, in the case of calcium carbonate (CaCO3) polymorphism is a complicating factor (2). Among the various strategies adopted to retard or prevent scale formation is the use of chemical additives to the feedwater, which, depending on their architecture and the type of scale, inhibit nucleation (threshold inhibitor), crystal growth or both. Additives that have gained acceptance in industrial water systems generally fall in two categories: 1. non-polymeric such as condensed phosphate, organophosphonates, phosphonocitrate; and 2. polymeric such as poly(acrylic acid), PAA; poly(methacrylic acid), PMAA; poly(maleic acid), PMA; poly(aspartic acid), PAS; poly(itaconic acid), PIA; and acrylic acid-/maleic acid-based copolymers.
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