Potentiometric titration study of CaCO3 scaling control with non-water soluble polyetherimide and sulfonated polyetherimide films

Abstract

Automatic potentiometric titration (APT) is a chemical analysis method to study the crystallization of CaCO 3 in solution. We demonstrate how APT is also valuable for studying CaCO 3 crystallization using water-insoluble polymer films, ideal for studying surfaces exposed to Ca 2+ and CO 3 2− ions with the capacity to remove Ca 2+ and/or susceptible to scale formation, equipment surfaces, ion exchange surfaces or desalination membranes, etc. Polyetherimide (PEI) and sulfonated polyetherimide (SPEI) films were prepared by solvent casting technique, and their surface studied using FESEM, XPS, Z potential, and contact angle. APT assays were performed with polymer films, using a carbonate buffer (pH 9), dosed with CaCl 2, and monitoring free Ca 2+. The APT curves with PEI showed no significant difference compared to the control, while the presence of SPEI film affected the kinetics of CaCO 3 formation. This was evidenced by changes in the slope and peak maximum of the APT curves. FTIR, XRD, and FESEM of the polymeric films and the CaCO 3 after the APT assays showed control over the types of CaCO 3 polymorphs. We show that the SPEI film is a good candidate to delay the formation of CaCO 3 in water, through the adsorption of Ca 2+ ions and the adsorption of pre-nucleation clusters of CaCO 3.