Inorganic microporous membranes for gas separation in fossil fuel power plants

CO2 capture and storage might have an important role in stabilising the global concentration of CO2. Power plants are primary candidates for CO2 capture and storage because they have great potential (up to 45% of CO2 emission reduction in the year 2050 compared to 2005). Inorganic membranes (Zeolites or TiO2-ZrO2) are candidates for separating H2 from CO2 (precombustion) or CO2 from the flue gas (mainly N2) at the End-of-Pipe (postcombustion) in fossil fuel power plants. All-silica Dodecasil 1H (DOH) zeolite type was selected for the hydrothermal stability and possible ability to separate H2 from other gasses under precombustion concept conditions. The DOH crystal size can be synthesised to thin hexagonal plates with sizes in the order of 10 μm. This crystal size is too large for membrane formation or to act as seeds for the layer formation, by means of secondary growth of DOH nuclei. The removal of the complete structure directing agent (SDA) content from the pores in the DOH structure could not be obtained through calcination in air for extended periods at elevated temperatures. Quasi SDA-free DOH, with a high crystallinity, was obtained after calcination at 900ºC for 5 hours when the atmospheric pressure was increased twice to 50 MPa for 30 min. The prepared all-silica DOH, that is quasi SDA-free, might present hydrothermal stable microporous material with pores that are inaccessible for CO2 and accessible to H2. Polymeric Y2O3 or TiO2 mixed ZrO2 sols are synthesised for the preparation of ultramicroporous powders and thin films on -Al2O3 intermediate layers supported by - Al2O3 disks as potential gas separation membranes. Two routes have been selected being the Ketone- and the Amine-approach based on the precursor modifiers. 8 mol% yttria stabilised zirconia (8YSZ) calcined at 450ºC is microporous with a BET specific surface area of ~50 m2/g. 8YSZ layers might form microporous layers with low permeability. 30-50 nm thin cubic 8YSZ films, prepared by the Ketone-approach, show He and N2 transport by Knudsen diffusion due to defects or to the too large pores in the final membrane layer. As expected from the linear polymeric Amine-Sols, the amorphous binary TiO2-ZrO2 materials are microporous between 400 and 500ºC. The highest BET specific surface area of ~200 m2/g with an estimated pore size of ~1.0 nm (gas physisorption) is obtained for the Ti0.5Zr0.5O2 calcined at 500ºC using the Amine-approach. The crystallisation temperature of orthorhombic Ti0.5Zr0.5O2 is between 550 and 600ºC which is ~250ºC higher than that of single oxides.