Material development and characterization for high salinity water for desalination by membrane distillation at high temperature and pressure

Ever increasing demand of water for different applications is creating more pressure on limited freshwater resources. In addition to domestic, public, and agricultural usage, industrial use of water is contributing to the water shortage. The use of non-traditional water resources for the energy sector may help meet the expected increase in water demand. Many produced water sources in the US have total dissolved solids (TDS) values more than 50,000 ppm, much higher that the TDS value of the seawater (~35,000 ppm). Desalination of high salinity water, which is currently being disposed by underground injection, can provide an alternative water source for industrial applications. As Reverse osmosis and thermal-based techniques cannot be applied either technically or in a cost-effective manner for treating high TDS water, membrane distillation (MD) might be a potential economically viable option for this purpose. But, current membrane distillation technology that is operated at low temperatures (e.g. ~50???C) produces low water flux. By increasing the driving potential by means of increasing the feed water temperature, flux can be increased. The work lost due to vapor flow through the membrane at low temperature and pressure can be minimized by running the process at the critical condition of water, where the compressibility is almost infinite, and thus eliminating the need for a large pressure differential across the membrane. The focus of this MS research, presented in this thesis, is on the development and characterization of suitable materials for high temperature and pressure MD applications. My future work will aim at developing more advanced materials and systems for MD desalination. Several commercially-available or laboratory-fabricated carbon materials including graphite, porous graphite, diamond-coated stainless steel, and carbon-coated ceramics; and various other ceramics (e.g. TTZ, ZTA etc.) are tested at supercritical conditions of water under oxic and anoxic conditions. Experiments are conducted to establish carbon-based materials as suitable membrane materials for use at supercritical temperature and pressure of water under anoxic conditions. Contact angle measurements of samples before and after exposure to supercritical water are used to show that hydrophobicity of carbon materials does not change due to hydrolysis at supercritical condition of water under anoxic conditions. Samples are extensively characterized using XPS (X-ray Photoelectron Spectroscopy), FTIR (Fourier Transform Infrared spectroscopy), XRD (X-ray Diffraction), AES (Auger Electron Spectroscopy), SEM (Scanning Electron Microscopy), and surface profilometry. Results indicate that the majority of carbon materials tested maintain their original physical and chemical properties after exposure to supercritical water in the absence of dissolved oxygen. However, under oxic conditions, a significant change in the surface chemistry of materials is observed due to oxidation and hydrolysis reactions in supercritical water