Characterization and quantification of structure and flow in multichannel polymer membranes by MRI

Abstract

Polymeric multichannel hollow fiber membranes were developed to reduce fiber breakage and to increase the volume-to-membrane-surface ratio and consequently the efficiency of filtration processes. These membranes are commonly used in ultrafiltration and are operated in in-out dead-end mode. However, some of the filtration details are unknown. The filtration efficiency and flow in the multichannel membranes depend on filtration time and are expected to vary along spatial coordinates. In the current work, in-situ magnetic resonance imaging was used to answer these questions. Velocities were quantified in the feed channels to obtain a detailed understanding of the filtration process. Flow and deposits were measured in each of the seven channels during filtration of sodium alginate, which is a model substance for extracellular polymeric substances occurring in water treatment. Volume flow and flow profiles were calculated from phase contrast flow images. The flow in zdirection in the center channel was higher than in the surrounding channels. Flow profiles variate depending on the concentration of Ca 2+ , which changes the filtration mechanism of aqueous solutions of sodium alginate from concentration polarization to gel layer filtration.

Shell and lumen side flow and pressure communication during permeation and filtration in a multibore polymer membrane module

“…The axial velocity magnitude at the shell side is highest at the maximum distance between the membrane and inner tube wall, caused by small local pressure differences on the lumen side [33]. This is in good agreement with the CFD results shown in Figure 3 and Figure 4.…”

“…Recently, Schuhmann et al used MRI to investigate the filtration behavior in multibore membranes [33]. The authors hypothesize that the location of the membrane in the module might influence the velocity field.…”

Structural Characterisation of Deposit Layer during Milk Protein Microfiltration by Means of In-Situ MRI and Compositional Analysis

“…The MIONs with a mean diameter of 100 nm are composed of iron oxide clusters embedded in a matrix of dextran and are coated with casein proteins to be chemically compatible with the feed. In previous studies [21][22][23][24][25]27,28], it was shown that the contrast agent is embedded in the deposit layer and does not diffuse back into the feed solution separately from the deposit nor significantly permeates the membrane. To confirm and investigate the behaviour of these MIONs, the deposit layer was taken out of the hollow fibre membrane after filtration with MIONs and put into a glass tube filled with skim milk, also including the contrast agent.…”

“…Viscosities of water and permeate were measured with an Anton Paar MCR 302 rheometer (Anton Paar, Graz, Austria) using the double-gap geometry. The rehydrated skim milk powder is referred to as skim milk hereafter [23].…”

“…In previous studies [21][22][23][24][25][26], nuclear magnetic resonance imaging (MRI) was used as a non-invasive and non-destructive technique to assess the growth of a deposit layer during filtration of diverse materials as a function of filtration time. These works mostly studied model systems consisting of inorganic particles or defined hydrocolloids such as alginate in aqueous solution.…”