Physical and high-temperature permeation features of double-layered cellular filtering membranes prepared via freeze casting of emulsified powder suspensions

Double-layered cellular alumina membranes for use in hot aerosol filtration applications were prepared based on the freeze casting and sintering of high alkane phase emulsified suspensions (HAPES). Membranes were shaped as flat disks with diameter of 3 cm and 8–9 mm of total thickness (about 80% for the support layer and 20% for the filtering layer). Samples displayed open porosity of 77.4 ± 0.1% and bulk density of 891.9 ± 18.9 kg/m3. The mean pore sizes (d50) of the support and filtering layers were respectively 13.0 μm and 5.5 μm. Tortuosity was evaluated by gas diffusion experiments and resulted in an average value of 2.24 ± 0.08. Permeation tests were carried out with airflow in temperatures from 20 to 415 °C and face velocities up to 1.6 m/s. The average room temperature permeability coefficients k1 and k2 based on Forchheimerʹs equation were respectively 2.09 ± 0.47 × 10−12 m2 and 1.80 ± 0.52 × 10−6 m. The increase in airflow temperature resulted in a slight increase of k1 and a decrease of k2. The net effect of airflow temperature was an increase of filter pressure drop, mainly caused by the increase of air viscosity. Up to 415 °C and 3 cm/s, pressure drop through clean membranes remained below 5000 Pa, a value within the range for commercial hot gas filters.