Preparation and properties of hydrothermally stable gamma-alumina membranes

Supported mesoporous γ-Al2O3 membranes deteriorate and blister in steam-containing environments at high temperatures. This deterioration led us to the development of a new type of supported γ-Al2O3 membrane with significantly improved stability under hostile conditions. Two measures were taken to achieve this result. First, the γ-Al2O3 itself was stabilized by an addition of 6 mol% La2O3 to suppress pore growth of the mesoporous structure. Second, the adherence of the γ-Al2O3 membrane to the α-Al2O3 support was significantly improved by application of phosphate bonding between the membrane layer and the support, using an Al(H2PO4)3 precursor solution. Membranes applied without phosphate bonding were separated from the α-Al2O3 support during high-temperature steam treatment, resulting in complete loss of separative properties. The newly developed membranes could be operated for 100 h at 600°C in H2O/CH4 = 3/1 (by volume) at 2.5 MPa total pressure with no delamination or cracking in the membrane–support interface and with no significant pore growth in the γ-Al2O3 membrane.