In-situ investigation of wetting patterns in polymeric multibore membranes via magnetic resonance imaging

Abstract

Wetting of the membrane to displace air or conditioning liquids is important to exploit the complex porosity of a filtration membrane. This study reveals the details of wetting in multibore membrane-based filtration modules. Using magnetic resonance imaging (MRI), we quantify the fluid distribution patterns during initial membrane wetting in dead-end permeation mode. The spatio-temporal evolution of aqueous copper sulfate solution wetting the membrane fibers was investigated as a function of the applied flux, packing density, and position along the membrane module length. Three initial wetting conditions were examined: delivery-state membranes, ethanol-washed and dried (air-filled) membranes, and ethanol-filled membranes. Significant changes in wetting patterns were observed due to interfacial and polymer swelling effects. This in-situ investigation reveals a slow wetting progression over six hours and more to obtain complete wetting, even at high fluxes of 200 LMH. However, an increased flux leads to faster wetting kinetics as the evolving wetting patterns are flux dependent. The packing density of the multibore fibers additionally impacts the wetting kinetics by shifting the prevalent pressure conditions. Although in dead-end mode, the wetting progression is non-uniform along the membrane module length. In addition to this parameter study, different pre-wetting agents' effect on the displacement behavior was investigated in depth. This study helps to understand (a) complex wetting phenomena inside multibore membranes in dead-end filtration, (b) the membranes' interaction with their surroundings due to neighboring membranes, and (c) the effect of the used fluid system for displacement on the resulting wetting patterns.