The effects of cross diffusion on the mass transport in the ultrafiltration of water /lysozyme /NaCl solutions
Advancing the chemical engineering fundamentals
Filtration - II (T2-11b)
Keywords: protein ultrafiltration; modelling; CFD, multicomponent diffusion
This work addresses the ultrafiltration of water /lysozyme /NaCl solutions. In particular, it addresses the effects of cross diffusion on the concentration polarization of the solutes and on the membrane permeation rates. Aqueous solutions containing a protein and a salt are ternary systems, and to model effectively the UF of such systems, an accurate description of the multicomponent nature of the mass transport is required. In UF, due to the concentration polarization phenomenon, the species being separated do not have uniform concentrations at the membrane vicinity, and therefore, the cross diffusion of the solutes may play an important role in the overall mass transport.
Ultrafiltration experiments with ternary aqueous solutions of lysozyme (0.3 kg m-3) and NaCl (ranging from 0 to 0.5 M) were carried out in a cell of rectangular cross-section with dimensions of 200mm x 30mm x 1.2mm. The cell top wall is impermeable while the bottom wall supports a semi-permeable membrane. The three cellulose acetate membranes – M1, M2 and M3 – used in this work, were prepared in the laboratory using the phase inversion method and were characterized through the permeation of pure water and reference solutes.
Ultrafiltration (UF) performance depends both on the membrane properties and on the momentum and mass transport phenomena occurring in the feed fluid phase. Using Computer Fluid Dynamics (CFD), the fluid flow and mass transport modelling allows the prediction of the concentration polarization and permeation fluxes. Two different types of CFD simulations were executed: one not taking into account the existence of cross diffusion and another considering the existence of this phenomenon.
The predicted fluxes obtained from the simulations were compared with experimental ones and the results show that cross diffusion plays an important role in the overall mass transport. This importance, however, depends on the permeation and selectivity characteristics of the membrane.
Presented Tuesday 18, 09:05 to 09:25, in session Filtration - II (T2-11b).
