(604g) Robust Polymer Coatings for Controlling CaCO3 Heterogeneous Nucleation in Thermal Desalination

Authors: 
Zhao, J., Zhejiang University
Wang, M., Massachusetts Institute of Technology
Gleason, K. K., Massachusetts Institute of Technology
Heterogeneous nucleation of CaCO3 widely occurs during inorganic fouling in thermal desalination. The formation of CaCO3 foulants results in increased heat transfer resistance, reduced flow rates, and thus impaired efficiency of desalination processes. Approaches for controlling CaCO3 heterogeneous nucleation are therefore highly desired for energy-efficient and cost-effective solutions for fouling problems in thermal desalination. For industrial applications, any surface treatment must be stable under harsh operational conditions. Additionally, the surface modification layer needs sub-micron thickness to maintain good heat transfer. However, such robust nanoscale thin films for tuning heterogeneous nucleation of CaCO3 have not yet been reported.

In this work, we developed a series of initiated chemical vapor deposited (iCVD) covalently crosslinked organic networks. These ultrathin (≤100 nm) coatings have low surface energy and small work of adhesion with CaCO3. Consequently, the energy barrier for CaCO3 to nucleate on these iCVD polymer surfaces was found over 90% of the Gibbs free energy for CaCO3 homogeneous nucleation. These results lead to slow nucleation kinetics with extended induction periods. We also investigated the nucleation and growth of CaCO3 on untreated and iCVD-coated Cu/Ni foils in hot synthetic sea water similar to the operational conditions in multistage flash (MSF). We found that surface electrochemical oxidation of Cu/Ni during exposure to aqueous electrolyte at elevated temperatures significantly enhances the heterogeneous nucleation of CaCO3. Our iCVD polymer coatings provide excellent passivation for Cu/Ni with corrosion rates as low as 6.8x10-5mm/yr, therefore effectively inhibiting corrosion-induced heterogeneous nucleation of CaCO3. In addition, our iCVD coatings exhibit good stability for long-term exposure to boiling synthetic sea water. The iCVD thin films presented here are promising for inorganic fouling control in thermal desalination processes.