Evaluation of maleic acid based polymers as scale inhibitors and dispersants for industrial water applications

• Prevention of scale formation and particles dispersion important for fouling minimization.
• Polymers and copolymers of maleic acid are excellent compounds for these purposes.
• Polymer molecular weight and functional groups control fouling and dispersion.

The formation of inorganic scale deposits of the alkaline earth metals is a persistent problem. Dispersion of solid particles separating out from the fluids is also very important for fouling due to deposition. Scale formation and stabilization of suspensions are often overcome through the use of water soluble polymers. In the present work, a series of polymeric compounds were tested as inhibitors of calcium carbonate and calcium sulfate dihydrate (gypsum) precipitation and as dispersion agents of hematite (Fe2O3) suspensions in electrolyte solutions. Acrylic acid (AA) and maleic acid (MA) polymers were found to inhibit the precipitation of calcium carbonate and gypsum from supersaturated solutions to extents exceeding 90% at concentrations as low as 2 ppm. The molecular weight (MW) was an important parameter in determining the activity of the tested inhibitors. Lower MW polymers (ca. 2000) proved to be more efficient than higher MW polymers. A similar trend was exhibited for the dispersion ability of the hematite particles. AA and MA copolymers in which functional groups were introduced (pyrrole, sulfono and amide groups) were efficient precipitation inhibitors and dispersion agents, but the efficiency depended strongly on the co-polymer architecture. Copolymers containing sulfono groups improved inhibitory activity and dispersion ability and showed higher calcium ion tolerance.