Mechanical and thermochemical properties of nano-structured membranes for gas separation in fossil-fired power plants

The mechanical and thermochemical properties of nano-structured porous SiO2-membrane layers with porous ceramic and metallic substrates were studied aiming at their applications for the carbon dioxide separation in the pre-combustion systems in fossil-fired power plants. Since the thin membrane layers demand a mechanically robust substrate material, alumina materials as promising substrates with different porosity and pore sizes were characterized with respect to their mechanical properties. In the asymmetric gas separation membrane, the porosity of the substrate should be maximized in order to minimize its resistance against permeate gas. However, an increase in porosity usually reduces Young’s moduli and fracture stress of the substrate material. In this study, two types of alumina substrate materials with similar porosity but micro-porous and nano-porous microstructure, respectively, were investigated in order to assess the influence of the pore size on mechanical properties. As an alternative substrate material, porous metallic Intermediate Temperature Metal (ITM) coated with γ-Al2O3 interlayer and functional SiO2-membrane was also investigated with respect to its mechanical properties. An acoustic emission test was adopted to determine the correlation deformation- failure behaviour of this composite membrane system. Another focus of the work was a determination of the gas permeability of various gases through SiO2 and amino-modified SiO2 membranes, in which the adopted gas systems were single gas, binary gas mixtures and binary gas mixtures plus water vapour. The gas transport mechanism was investigated via the single gas permeation tests. The application of membranes in the flue gas was simulated by permeation tests with binary gas mixture plus water vapour. Meanwhile, the enhanced affinity of CO2 towards amino-modified SiO2- membranes with and without water vapour was also investigated via annealing tests and infrared spectroscopy. Furthermore, the effect of mechanical pre-deformation onto the membrane system was also investigated via the permeation tests. A change of gas transport mechanism through the membranes was analysed by comparing the permeation results of non-deformed and predeformed specimens with metallic substrate.