Gas Permeation Characteristics of Zirconia-Silica Composite Membranes at High Temperature.

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Permeabilities for pure gases of H2, He, CH4, NH3, H2O, N2, N2, O2 and CO2 were measured at trans-membrane pressures up to 0.2 MPa and 303, 423, 523 and 773 K for two types (with small pores and large pores) of composite zirconia-silica membranes coated on the surface of porous ceramic tubes (0.5μm). The composition of the metal-alkoxides solution used successfully in the coating process was Zr (OC3H7) 4 : 3.09, Si (OC2H5) 4 : 7.20, Y (CH3COO) 3.4H2O : 0.21, i-PrOH : 89.50 in molar %. At low temperatures, with large-and small-pore membranes, the permeation mechanism for H2O, NH3 and CO2 is surface diffusion, and for other gases it is Knudsen flow. At higher temperature, with a large-pore membrane, the permeation mechanism for H2O, NH3, CO, and CH4 is Knudsen flow, and for other gases it is a combination of Knudsen flow and activated diffusion. With a small-pore membrane, for H2O it is Knudsen flow, and for all other gases it is activated diffusion.
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