Vapour-liquid equilibria of aroma compounds in hydroalcoholic solutions: Measurements with a recirculation method and modelling with the NRTL and COSMO-SAC approaches

Aqueous solutions of aroma compounds are commonly encountered in the food and biofuel industries, and the knowledge of their thermodynamic properties is very important for process design. Here, we report the measurements of the vapour-liquid equilibria of water-ethanol solutions containing 13 aroma compounds (alcohols, aldehydes and esters), for temperatures between 351 and 366 K, and ethanol concentration ranging from 10 to 90% (v/v). The new data were obtained with a recirculation apparatus and are represented with the non-random two liquid (NRTL) activity coefficient model. It is observed that the partition coefficients of the aroma compounds can decrease of several orders of magnitude by increasing the proportion of ethanol. The COSMO-SAC (conductor-like screening model-segment activity coefficient) model provides reasonable predictions of the new data for alcohols and aldehydes, but underestimates the partition coefficients of the long ethyl esters. It is observed that the COSMO-SAC predictions depend a lot on the molecular conformations used to generate the sigma profiles, in agreement with previous studies. The COSMO-SAC predictions can be empirically improved by changing the real space cut-off distance employed in the ab initio calculations. The COSMO-SAC model is then reliable not only at infinite dilution but also over a whole composition range. The model is used to define a limit of validity for the infinite dilution approximation.