UNIQUAC interaction parameters for molecules with -OH groups on adjacent carbon atoms in aqueous solution determined by molecular mechanics - Glycols, glycerol and glucose

UNIQUAC interaction parameters have been determined, using molecular mechanics calculations, for 1,2-ethanediol, 1,2-propanediol, glycerol and glucose with water in aqueous solution. Conformational space for individual pairs of molecules was explored using a stochastic method, the Boltzmann Jump Procedure (BJP). The predicted vapor-liquid equilibrium (VLE) data for the water/1,2-ethanediol system are in excellent agreement with the experimental values and good results were obtained for the water/glycerol system by taking larger samples. This was not true for the other two systems for which there were difficulties in sampling conformational space in a statistically acceptable manner. As the parameters represent interactions per unit molecular surface area and all of the molecules consist of -CH2OH or -CH2-O- units, the values obtained for the water/1,2-ethanediol system were used to predict VLE data for the other systems. This gave results in good agreement with the experimental data. The possibility of transferring interaction parameters is very interesting, especially as it can be applied to systems for which the additivity principle of the UNIFAC method fails. Simulations were carried out for 1,2-ethanediol, 1,2-propanediol and glycerol, surrounded by different numbers of water molecules. The interaction energy was observed to be linearly dependent on the number of water molecules present. This constant increment means that the additional interaction energy for each water molecule added is the same. This might be another aspect of transferability of interaction parameters. (C) 1997 Elsevier Science B.V.