Asymmetric mullite membranes manufactured by phase-inversion tape casting from polymethylsiloxane and aluminum diacetate

Abstract

Polymethylsiloxane (MK) and aluminum diacetate have been stoichiometrically combined to synthesize a mullite-based powder (3Al2O3·2SiO2) at 850 °C (5 h) or 1200 °C (3 h). High-purity crystalline mullite (>99%) was obtained by heating the mixture in the air (thermal oxidation) at 1200 °C for 3 h, mainly due to the formation of highly reactive silica and alumina precursors. Afterward, the mullite-based powders were used to prepare planar asymmetric microfiltration membranes by phase-inversion tape casting. The green membranes were sintered at 1600, 1650 or 1700 °C during 2 h. The asymmetric morphology identified in the membranes by scanning electron microscopy analysis reveals a thin skin-layer (microfiltration layer, <10 μm) followed by a porous support, in which two different structures were observed: finger- and/or sponge-like layer. Water permeation performance in a dead-end configuration was investigated at different pressures (3, 4, and 5 bar). The obtained results clearly indicated an improved water permeation flux compared to a symmetric commercial membrane (133.6 m³/m2·h compared to 14.7 m³/m2·h, respectively, at 5 bar). This observation could be ascribed to the asymmetric morphology resultant from the phase-inversion process.