Abstract
Effect of ultrasonic irradiation on solute permeation across a cellulose membrane was studied under various operating conditions. Sodium salts of carboxylic acids having different alkyl chain length were dissolved in deionized water and the solution used as feed. The membrane was set to face its dense layer to feed side and the supporting layer to receiving side. Ultrasound irradiation of from receiving side enhanced the solute permeation rate rather than that from the feed side. The degree of enhancement was around a few tens percent increase and an extraordinary effect cannot be expected. Interestingly, a "jump" of concentration in receiving side was observed when ultrasound is on. When the ultrasound was off, the concentration went back to the original curve which was extended from the time before ultrasound irradiation. Such a stepwise increase and a regression of the concentration can be interpreted as desorption from the membrane by ultrasonic irradiation. Since the membrane has a porous structure, the membrane retains the solute on its surface. Propagation of ultrasound can help to release adsorbed solute. Flow visualization showed that the existence of standing wave for slower flow when the permeation was enhanced ultrasonically. While for faster flow, the flow disturbed the standing wave and no enhancement was observed. This implies the standing wave adjacent to membrane surface contributes to the enhancement of solute permeation.
