Numerical and experimental study of mass transfer in lysozyme ultrafiltration

摘要

This paper addresses protein ultrafiltration (UF) and its dependence on UF operating conditions. Cellulose acetate (CA) asymmetric membranes are laboratory made by the phase-inversion method and characterized in terms of pure water permeability, 8.8X10~(-12) m/s/Pa, and molecular weight cut-off (10000 Da for 98% of rejection). The important feature of the permeation cell is the slit feed channel of 200 mmX30 mmx1.2 mm that simulates the two-dimensional hydrodynamic flow conditions in a spiral would membrane module. Permeation experiments were carried out for solutions of reference solutes in order to characterize the membranes and for lysozyme solutions under different operating conditions. The influence of the ionic strength in the permeation flux and protein rejection is studied by performing permeation tests with a solution of lysozyme (0.3 kg/m~3) containing different NaCl concentrations. Experimentally was observed a decline in the permeate flux with increasing ionic strength. The membrane is almost completely retentive in relation to lysozyme, since the apparent rejection coefficient,f,for this protein is always higher than 95% (in almost all cases, higher than 98%). Two distinct sets of CFD simulations were performed. One to predict the permeation velocities, v)p, and another to predict the lysozyme concentration polarization.