Journal of Chemical and Engineering Data, Vol.52, No.1, 168-179, 2007
Comparison of headspace and gas-stripping techniques for measuring the air-water partititioning of normal alkanols (C4 to C10): Effect of temperature, chain length, and adsorption to the water surface
The air-water partition coefficients K-AW(C) of normal alkanols (C4 to C10) were determined as a function of temperature using both the phase ratio variation headspace (PRV-HS) method and the inert gas-stripping (IGS) method. Whereas the results of the PRV-HS experiments conducted at (50 to 90) degrees C were in good agreement with previous measurements for butan-1-ol, penta-1-ol, and heptan-1-ol, the values obtained from the IGS experiments performed at (25, 31, 51, and 69) degrees C were too high when compared to the PRV-HS results, literature values, and predictions based on vapor pressure and water solubility. For the short-chain alkanols and for the at higher temperatures, this discrepancy is likely due to evaporation from the stripping vessel. For the longer chain alkanols at lower temperatures, it is additionally due to adsorption to the air-water interface of the gas bubbles. The magnitude and dependence of the latter artifact on chain length and temperature is consistent with predictions based on interfacial adsorption coefficients (K-IA) and bubble radius. The evaporation effect leads to an overestimation of the temperature dependence of air-water partitioning, whereas the surface adsorption effect can cause the opposite for substances with strong adsorption to the water surface. The validity of previously published air-water partitioning data that have been generated for substances with relatively high K-IA (> 10 mm) using the IGS method should be re-evaluated.