EFFECT OF TRANSMEMBRANE PRESSURE PULSING ON CONCENTRATION POLARIZATION

Previous research [Rodgers and Sparks, AIChE J., 37 (1991) 1517] on transmembrane pressure pulsing indicated that pulsing increased solute flux by as much as two orders of magnitude in crossflow ultrafiltration. While it was clear that pulsing reduced membrane fouling resistance, it was not certain how pulsing effected concentration polarization resistance. The objective of this study was to determine how pulsing affected concentration polarization resistance. This was done by examining the effects of oscillating transmembrane pressure in the ultrafiltration of a totally retained solute. Transmembrane pressure was oscillated by applying pulsatile positive pressure on the filtrate side of the ultrafiltration cell. Solutions of 1% BSA at 7.4 pH in 0.15 M NaCl buffered solution were ultrafiltered in a crossflow module using Amicon YM-30 cellulosic membranes. The studies were carried out at crossflow shear rates between 160 sec-1 and turbulent conditions. The operating pressures were 75 and 140 kPa. Transmembrane pressure pulsing was generated by increasing the filtrate pressure from 5 to 30 kPa above the respective operating pressure at frequencies ranging from 0 to 5 Hz. The results indicated that pulsing increased solvent flux in the ultrafiltration process with laminar crossflow. It was determined that transmembrane pressure pulsing altered the concentration polarization boundary layer by translation of body forces through the membrane and minute but significant membrane motion. This was not the mechanism observed for reduction of membrane fouling in the previous study.