Removal of inorganic compounds via supercritical water : fundamentals and applications

Desalination is seen as one of the key technologies to satisfy the growing global water demand due to urbanization, population growth and depletion of natural water resources. One of the major drawbacks of current desalination technologies is the production of a liquid brine stream as a waste stream. This thesis introduces supercritical fluids - a highly regarded technology in process engineering and chemical industry - in a new field: the treatment and purification of aqueous streams. The resulting technology - a new approach to remove inorganic compounds from these streams and to offer a way for desalination without the production of a liquid waste stream -, its basics, its options and potential are the tenor of this thesis. The separation principle of this approach is based on the changed solvation behavior of supercritical water. While water represents an excellent solvent at ambient conditions, it changes to a poor one at supercritical conditions (T > 647 K; p > 22.1 MPa). The decreased solubility of inorganic compounds leads to precipitation and formation of an additional solid phase. This behavior allows for treatment of saline streams without production of a waste stream; an option that current technologies like Reverse Osmosis and Multi-Stage-Flash do not offer. New and unique experimental data on behavior and solubility of inorganic compounds in supercritical water are presented. Relations between solubility, system parameters and properties of the inorganic compounds are shown. Process options and concepts are discussed regarding their potential, their sustainability and their synergy with other technologies.