Fouling of composite water vapor transport membranes by aerosol nanoparticles

Abstract

Composite membranes combining a structural microporous substrate with a dense selective layer are used in various water vapor transport applications. The impact of exposure to aerosols on the water vapor permeance is investigated to develop an understanding of the potential for air pollution to degrade the membrane performance. Samples of commercial membranes were loaded with hygroscopic NaCl and non-hygroscopic graphite nanoparticles. Permeance measurements showed that the deposition of both particle types under dry loading conditions (RH<20%) had minimal influence on the membrane. However, when membranes loaded with hygroscopic particles in dry conditions were subsequently exposed to an elevated humidity (RH>75%) and the associated surface condensation, the membrane permeance reduced by up to 16%. This permeance reduction is shown to be caused by pore narrowing, which results in increased resistance of the microporous substrate. SEM analysis of the fouled membrane surfaces confirmed a reduction in the average pore diameter of degraded samples, proportional to the fouling degree. The reversibility of the fouled membrane permeance, achieved through membrane cleaning, implies that re-crystallization of salt ions, entrained onto the edges of the substrate pores in an aqueous form, is a potential explanation for the permeance changes observed.