Carboxymethyl inulin: A new inhibitor for calcium carbonate precipitation

A new polysaccharide-based polycarboxylate, carboxymethyl inulin (CMI), was synthesized recently. The influence of small amounts (0.1-200 ppm) of this material on the crystallization of calcium carbonate, an important scale-forming salt, is studied. The effects of CMI are compared to those of a commercial inhibitor (a copolymer of acrylate and maleate) and of other carboxymethylated saccharides. It is shown that CMI is a good calcium carbonate precipitation inhibitor. CMI influences the spontaneous precipitation of calcium carbonate, the morphology of the formed crystals (vaterite and calcite), and the growth rate of calcium carbonate seed crystals. The effect is related to the carboxylate content, the chainlength, and the concentration of the additive. For the application of CMI as crystallization inhibitor, products with a high degree of substitution (degree of substitution > 1) and a high degree of polymerization (average degree of polymerization = 30) are the most effective. Also, other carboxymethylated polysaccharides (dextrins, cellulose) show good crystallization-inhibition properties, although the performance of the copolymer of acrylate and maleate is not met. A great advantage of CMI, as compared to carboxymethyl cellulose (CMC), is that aqueous solutions of CMI display, contrary to those of CMC, a very low viscosity. A carboxymethylated disaccharide (carboxymethyl sucrose) has no influence on the calcium carbonate crystallization, which shows that the long-chain character is essential for a polycarboxylate inhibitor.