Vítor Magueijo

Numerical and experimental study of mass transfer in lysozyme ultrafiltration

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, 8.8×10-12 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 mm×30 mm×1.2 mm that simulates the two-dimensional hydrodynamic flow conditions in a spiral wound 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/m3) 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, vp, and another to predict the lysozyme concentration polarization.

Effect of Membrane Pore Size and Membrane-Solute Interactions on Lysozyme Ultrafiltration

A model based on steric hindrance mechanisms [1] is used to determine the pore sizes of two ultrafiltration (UF) membranes. The lysozyme rejection coefficients of those membranes are predicted through the same model after modification of the pore size and solute radius by taking into account the development of electric double layers. Two asymmetric cellulose acetate membranes M1 and M2 were prepared and characterized. Membrane M1 has an hydraulic permeability of 2.1x10-6 m/s/bar, a molecular weight cut-off (MWCO) of 30,000 Da and an average pore radius of 2.6 nm. Membrane M2 has an hydraulic permeability of 5.9x10-6 m/s/bar, a molecular weight cut-off (MWCO) of 60,000 Da and an average pore radius of 5.3 nm. Aqueous solutions of lysozyme containing a NaCl concentration of 0.1M were ultrafiltrated through membranes M1 and M2. The predicted lysozyme rejections considering the development of electric double layers on the protein and membrane pore surfaces, are in good agreement with the experimental results.

Electrolytic Reactors for the Recovery of Cadmium from Leaching Solutions

A study has been made of the cathodic deposition of cadmium ions from artificial aqueous and dilute solutions produced by the leaching of spent nickel-cadmium batteries. These solutions contained about 20 g/L Cd, 50 g/L Ni and 1 g/L Co. Two types of electrochemical reactors have been used: a parallel-plate reactor and a packed bed reactor with and without solution recirculation. The deposition processes were carried out galvanostatically and the effect of several electrolysis parameters on the recovery of cadmium was analysed. The concentrations of CdSO4 during and after electrodeposition were determined by atomic absorption spectroscopy. The minimum electrode potentials required for electrodeposition to be achieved were established; in addition the composition of the electrodeposits was also estimated. Extraction efficiencies of 80% Cd were achieved. Electrodeposit compositions were about 70% Cd, 10 % Ni, < 0.5% Co, and ∼20% Na2SO4, Fe, oxides. It has been shown that the parallel-plate reactor is the most suitable for our purpose leading to figures of merit with high efficiency values.