“Green” scale inhibitors in water treatment processes: the case of silica scale inhibition

Abstract

This paper focuses on scale control approaches using a number of “green” silica scale inhibitors. These findings may be of interest to chemists and engineers in the fields of cooling and boiler water, pulp and paper, detergents, oil, gas, etc. In light of increasing environmental concerns, this research acquires significant interest. Also, in this paper, the effects of biological and synthetic polymers on the formation of amorphous silica are discussed. The importance of synergies between polyelectrolytes on silica inhibition is also discussed. A specific example of a zwitterionic polymer phosphonomethylated chitosan (PCH) is further analyzed for its inhibitory activity. Specifically, the ability of PCH to retard silicic acid condensation at circumneutral pH in aqueous supersaturated solutions is explored. Furthermore, the effects of either purely cationic (polyethyleneimine, PEI) or purely anionic (carboxymethylinulin) polyelectrolytes on the inhibitory activity of PCH are systematically studied. It was found that the action of inhibitor blends is not cumulative. PCH/PEI blends stabilize the same level of silicic acid as PCH alone in both short-term (8 h) and long-term (72 h) experiments. Lastly, six polyethylene glycol polymers are used as silica scale inhibitors. Their Molecular Weights range from 1,550 to 20,000. There is a profound dependence of inhibitory performance on the additive Molecular Weight. However, this dependence seems to be less significant for Molecular Weights > 10,000. Mechanistic implications will be discussed as well.

Keywords:

• Water treatment
• Green additives
• Silica scale
• Scale inhibitors
• Polyethylene glycol
• Inulin

Acknowledgments

Acknowledgments are due to the European Union for funding the Research Program SILICAMPS-153, under the ERA.NET-RUS Pilot Joint Call for Collaborative S&T projects, the General Secretariat of Science and Technology (Contract # GSRT 170c) and the University of Crete for funding.

Notes

Presented at the 13th International Conference on Environmental Science and Technology (CEST 2013), 5–7 September 2013, Athens, Greece