Measurement of sorption in hydrophilic pervaporation: sorption modes and consistency of the data

The problems of consistency of sorption, diffusion and pervaporation data h ave been analyzed from the viewpoint of the method of sorption measurements . Sorption of the water/ethanol mixture by sulphonated polyethylene of diff erent capacities was studied isopiestically and by direct immersion in the solution. For a given method the sorption isotherms per sulphonic group wer e similar for all samples but, in contrast to what had been assumed before, both methods gave completely different results. It was found that direct s orption results were more consistent with pervaporation and diffusion data. It suggests that in pervaporation studies it is preferable to use this kin d of data; use of isopiestic data may lead to serious errors. The practical consequences of this conclusion, such as the possible difference between p ervaporation and vapor permeation, have been also discussed. (C) 2000 Elsev ier Science B.V. All rights reserved.