Composite carbon membranes for the desalination of water
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007.
Electrodialysis is a method of water desalination which involves the separation of TDS through an ion-exchange membrane under a potential gradient. In this study it was attempted to reverse engineer the composite carbon ion-exchange membrane used in a prototype plant and electrochemically evaluate a prototype desalination cell. The influence of applied potential on the capacitance of the various electrode surfaces and possible electrode reactions was investigated. A model was also suggested to describe the conductivity through the membrane. The composition of composite carbon membranes were determined by compositional analysis using various analytical tools. Elemental analysis, done with PIXE and EDS, showed that the membranes contained chloride, fluoride, oxygen, carbon, and possibly hydrogen. With LC-MS and IR it was established that the membranes consisted of two polymers with no carbonyl or aromatic functional groups. After further thermal analysis the following possible compounds remained: hexafluoropropylene tetrafluoroethylene copolymer, polychlorotrifluoroethylene (PCTFE), polyoxyethylene oxide (PEO) and polyethylene glycol (PEG). This assessment is in good agreement with the contents of US patent 4,153, 661, which describes the composite membrane.