The influence of sieving & surface charge membrane characteristics on the ultrafiltration of protein solutions

Abstract

Consulta en la Biblioteca ETSI Industriales (Riunet)

[EN] Ultrafiltration of protein solutions is governed both by sieving and electrical charge mechanisms. This thesis addresses membrane characterization through the two key parameters influencing these mechanisms ¿ molecular Weight cut-off (MWCO) and streaming potential. A set of five cellulose acetate laboratory-made membranes are prepared by the phase inversion method to cover a wide range of ultrafiltration permeation properties. They are designated by CA1, CA2, CA3, CA4 and CA5 and the hydraulic permeabilities are 2.1, 27.7, 46.4, 59.8 and 65.4 kg/h/m2/bar, respectively. The MWCOs are 7211, 9733, 12055, 22163 and 31151 Da. The streaming potential of the five membranes is measured with the electrolyte ionic strength ranging from 0.0001M to 0.005M and the pH ranging from 3 to 8.5. For the five membranes, the ultrafiltration (UF) of solutions of bovine serum albumin (BSA) is assessed in terms of permeation fluxes and protein rejection coefficients. The UF operating conditions of transmembrane pressure (TMP) and feed flow-rate were varied over the range of 1, 2, 3 and 4 bars and 100 L/h and 200 L/h, respectively. Three BSA solutions, 600 ppm, with pH of 5.18, 5.62 and 6.69 were investigated. The permeation fluxes exhibited very different patterns. For the highest pH, there is a decrease in the effective permeability and an increase in the protein rejection. For membranes CA2, CA3, CA4 and CA5, the concentration polarization phenomenon takes place, being more severe for the CA5 membrane. The zeta potential of every membrane becomes more negative as the pH increases and the ionic strength of the solution decreases. The results obtained for two the other commercial membranes, made of polyethersulfone, designated by UP005 and UH030, were significantly similar to the previous ones, but the zeta potential values are less negative. Keywords: