Estimation of DISQUAC interchange energy parameters for linear secondary alcohols + n-alkanes or + cyclohexane mixtures

Abstract

The data available in the literature on vapor-liquid equilibria (VLE), molar excess Gibbs energies ( G E), molar enthalpies ( H E), molar excess heat capacities ( C p E), activity coefficients ( γ i ∞) and partial molar excess enthalpies ( H i E,∞) at infinite dilution of linear secondary alkohols (1) + n-alkanes (2) or + cyclohexane (2) systems are examined on the basis of the DISQUAC group contribution model. The components in the mixtures are characterized by three types of groups of surfaces: hydroxyl (OH group); aliphatic (CH 3, CH 2 and CH groups); and cyclohexane (c-CH 2 group). The purely dispersive parameters of the aliphatic/cyclohexane contacts are available in the literature. The parameters for the secondary OH/aliphatic and secondary OH/cyclohexane interactions are reported in this work. The quasi-chemical parameters are independent of the alkane. The first and third parameters are common for the alkanols investigated. The second quasi-chemical parameter depends on the position of the OH group. So, on the basis of available data, two groups of alcohols are distinguished: 2-alkanols and 3-alkanols. The dispersive parameters change with the alcohol. The model describes consistently the phase equilibria and molar excess functions. Dependence on temperature of C p E is well represented, except at very low temperatures. The absolute mean deviation for 1n γ i ∞ is about 6.6%. For i = 1, the deviation is 9.2%; for i = 2, it is 3.9%. DISQUAC cannot represent H i E,∞, i.e. the calculated H E curves vs. x 1, the mole fraction, are not as steep as the experimental ones at very high dilution of the alcohol. This may be considered the major limitation of the model. So, in terms of DISQUAC, the investigated mixtures behave similarly to 1-alkanol (1) + alkane (2) systems.