Ultrasonic assisted cross-flow ultrafiltration processes

Ultrasonic assisted cross-flow ultrafiltration processes, probed by in-situ SAXS

To improve the performance of the membrane separation process and reduce the limiting phenomenon of fooling, a recent innovation has been the development of ultrafiltration cells (Figs. 1, 2) that allow for the simultaneous application of ultrasonic waves directly to the filtered colloidal suspensions.

Through local observation using SAXS, we have demonstrated that ultrasonic waves prevent particle aggregation in the vicinity of the membrane surface (from 20 μm to 400 μm) and lead to a significant increase in yields, with permeation flux gains ranging from a factor of 2 to 15, depending on the colloids being treated. Two main mechanisms have been highlighted: either an erosion mechanism of concentrated layers for colloids assembled in open structures (Fig. 3,4a), or a mechanism of intensification of the diffusion of water through the porous network thanks to the local agitation induced by ultrasound for denser structuring of the deposits (Fig. 4b).

Références

Hengl N., Jin Y., Pignon F., Baup S., Mollard R., Gondrexon N., Magnin A., Michot L.J., Paineau E. "A new way to apply ultrasound in cross-flow ultrafiltration: application to colloidal suspensions", Ultrasonics Sonochemistry, 21 (3), 1018-1025 (2014). https://doi.org/10.1016/j.ultsonch.2013.11.008
Jin Y., Hengl N., Baup S., Pignon F., Gondrexon N., Magnin A., Sztucki M., Narayanan T., Michot L.J. and Cabane B. " Effects of ultrasound on colloidal organization at nanometer length scale during cross-flow ultrafiltration probed by in- situ SAXS", Journal of Membrane Science, 453, 624-635 (2014). https://doi.org/10.1016/j.memsci.2013.12.001
Jin Y., Hengl N., Baup S., Pignon F., Gondrexon N., Sztucki M., Gésan-Guiziou G., Magnin A., Abyan M., Karrouch M., Blésès D. "Effects of ultrasound on cross-flow ultrafiltration of skim milk: characterization from macro-scale to nano-scale, Journal of Membrane Science, 470, 205-218 (2014). https://doi.org/10.1016/j.memsci.2014.07.043
Jin Y., Hengl N., Baup S., Pignon F., Gondrexon N., Sztucki M., Romdhane A., Guillet A., Aurousseau M., "Ultrasonic assisted cross-flow ultrafiltration of starch and cellulose nanocrystals suspensions: Characterization at multi-scales", Carbohydrate Polymers, 124, 66-76 (2015). https://doi.org/10.1016/j.carbpol.2015.01.073
Gondrexon N., Cheze L., Jin Y., Legay M., Tissot Q., Hengl N., Baup S., Boldo P., PignonF., Talansier E. "Intensification of heat and mass transfer by ultrasound: Application to heat exchangers and membrane separation processes", Ultrasonics Sonochemistry, 25, 40–50 (2015). https://doi.org/10.1016/j.ultsonch.2014.08.010

Fig. 1: scheme of the accumulation of colloidal particles in the vicinity of the membrane surface and the different forces acting, during ultrasonic assisted cross-flow ultrafiltration process.

Fig. 2: Ultrasonic assisted cross-flow ultrafiltration cell enabling characterization by small-angle X-ray scattering (SAXS).

Fig. 3: Temporal and spatial effects of ultrasound on the structure and accumulation of Laponite particles during cross-flow ultrafiltration. Relationships between permeation flux and the concentration profile of particles accumulated near the membrane surface.

Fig. 4: Effect of ultrasound on permeation fluxes over time and volume fraction profiles as a function of distance z to the membrane surface, deduced from SAXS scattering patterns during cross-flow ultrafiltration of dispersions a) of casein micelles and b) of cellulose nanocrystals.

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