Ultrafiltration of charge-stabilized dispersions at low salinity.
We present a comprehensive study of cross-flow ultrafiltration (UF) of charge-stabilized suspensions, under low-salinity conditions of electrostatically strongly repelling colloidal particles. The axially varying permeate flux, near-membrane concentration-polarization (CP) layer and osmotic pressure profiles are calculated using a macroscopic diffusion-advection boundary layer method, and are compared with filtration experiments on aqueous suspensions of charge-stabilized silica particles. The theoretical description based on the one-component macroion fluid model (OCM) accounts for the strong influence of surface-released counterions on the renormalized colloid charge and suspension osmotic compressibility, and for the influence of the colloidal hydrodynamic interactions and electric double layer repulsion on the concentration-dependent suspension viscosity η, and collective diffusion coefficient Dc. A strong electro-hydrodynamic enhancement of Dc and η, and likewise of the osmotic pressure, is predicted theoretically, as compared with their values for a hard-sphere suspension. We also point to the failure of generalized Stokes-Einstein relations describing reciprocal relations between Dc and η. According to our filtration model, Dc is of dominant influence, giving rise to an only weakly developed CP layer having practically no effect on the permeate flux. This prediction is quantitatively confirmed by our UF measurements of the permeate flux using an aqueous suspension of charged silica spheres as the feed system. The experimentally detected fouling for the largest considered transmembrane pressure values is shown not to be due to filter cake formation by crystallization or vitrification.
Forschungszentrum Jülich, Institute of Complex Systems (ICS-3), 52425 Jülich, Germany. rafael.roa@helmholtz-berlin.de g.naegele@fz-juelich.de and Helmholtz-Zentrum Berlin, Soft Matter and Functional Materials, 14109 Berlin, Germany.
Rafael
R
Roa
RWTH Aachen University, Chemical Process Engineering, 52064 Aachen, Germany.
Daniel
D
Menne
Forschungszentrum Jülich, Institute of Complex Systems (ICS-3), 52425 Jülich, Germany. rafael.roa@helmholtz-berlin.de g.naegele@fz-juelich.de and Jülich-Aachen Research Alliance, JARA-Soft Matter.
Jonas
J
Riest
RWTH Aachen University, Chemical Process Engineering, 52064 Aachen, Germany and DWI Leibniz Institute for Interactive Materials, 52074 Aachen, Germany.
Pompilia
P
Buzatu
Ukrainian Academy of Sciences, Institute of Bio-Colloid Chemistry, 03142 Kiev, Ukraine.
Emiliy K
EK
Zholkovskiy
Forschungszentrum Jülich, Institute of Complex Systems (ICS-3), 52425 Jülich, Germany. rafael.roa@helmholtz-berlin.de g.naegele@fz-juelich.de and Jülich-Aachen Research Alliance, JARA-Soft Matter, and Physics Department, Heinrich-Heine Universität Düsseldorf, 40225 Düsseldorf, Germany.
Jan K G
JK
Dhont
RWTH Aachen University, Chemical Process Engineering, 52064 Aachen, Germany and Jülich-Aachen Research Alliance, JARA-Soft Matter, and DWI Leibniz Institute for Interactive Materials, 52074 Aachen, Germany.
Matthias
M
Wessling
Forschungszentrum Jülich, Institute of Complex Systems (ICS-3), 52425 Jülich, Germany. rafael.roa@helmholtz-berlin.de g.naegele@fz-juelich.de and Jülich-Aachen Research Alliance, JARA-Soft Matter, and Physics Department, Heinrich-Heine Universität Düsseldorf, 40225 Düsseldorf, Germany.
Gerhard
G
Nägele