Mass transfer coefficient and retention of PEGs in low pressure cross-flow ultrafiltration through asymmetric membranes

Abstract

The flow and retention of 0.1 % w/w aqueous solutions of several polyethylene glycols with molecular weights ranging from 300 to 12000 Daltons are studied when they are tangentially filtered through three commercially available asymmetric membranes, with transmembrane pressure differences up to 650 kPa. The mass transfer coefficients are obtained for low applied pressures below 60 kPa, within the frame of the film layer theory for the concentration polarization phenomena. The resulting variation of K m with the feed recirculation velocity and the molecular weight is analyzed. In the transition between laminar and turbulent regime, the experimental dependencies of K m are compared with those predicted by friction and non-friction models for the Sherwood equations. The mass transfer coefficient is used to compute the true retention standard curves, allowing estimate of the mean pore radii of the membranes.