Application of a New Statistical Mechanical Model for Calculating Kirkwood Factors in Alkanol−Heptane Mixtures

Abstract

A recently developed statistical mechanical model for predicting Kirkwood factors in self-associating molecular liquids and their mixtures with nonassociating components has been applied for the simultaneous description of the Kirkwood correlation factor, gK, and the molar enthalpy of mixing, Hm(E), as a function of the composition in alkanol-heptane mixtures. Most of the molecular parameters involved in the theory have been fixed by independent quantum mechanical ab initio calculations of associated molecular clusters. The model is also able to predict other thermodynamic mixture properties such as the enthalpy of mixing. Experimental results of nine alcohol-heptane mixtures taken from the literature have been used to test the new model. The Kirkwood correlation factor gK and the molar enthalpy of mixing Hm(E) can be described simultaneously with an excellent agreement with experimental data covering the whole range of mole fraction, including temperature dependence. Two parameters have been adjusted freely for each system. A third parameter for the nonspecific intermolecular dispersion interactions has been adjusted within a limited range of possible values given by physical arguments. The successful application of the model opens a new way to a more reliable understanding of structures and equilibrium properties of such liquid systems.

Speed of sound, density, and heat capacity for (2-methyl-2-butanol+heptane) at pressures up to 100MPa and temperatures from (293 to 318)K. Experimental results and theoretical investigations

“…The results of ab initio calculations point to energetically favourable hydrogen bonding formation for 2-methyl-2-propanol than for ethanol i.e. the Hbonding enthalpies are shifted to more negative values [10,11,31]. This probably explains the differences noted above between (2-methyl-2-butanol + heptane) and (ethanol + heptane) at higher temperatures.…”

“…This probably explains the differences noted above between (2-methyl-2-butanol + heptane) and (ethanol + heptane) at higher temperatures. Moreover, K c4 , estimated by ab initio studies, is higher for 2-methyl-2-propanol than for ethanol [10,11]. In the ERAS model, applied in this work, the existence of only linear association is assumed.…”

“…The minimum with g k < 1 can be interpreted as a result of the existence of cyclic associates which are assumed to have no dipole moment. Recently, the ERAS model was modified taking into account the cooperative effect of the linear association of alcohol molecules and existence of cyclic tetramers, and applied for the simultaneous description of Kirkwood correlation factor, the excess molar enthalpy and the infrared absorption of monomer alcoholic species as function of the composition in (alkanol + alkane) under atmospheric pressure [10,11]. The ERAS model was also modified, taking into consideration the existence of linear and cyclic structures, in order to describe particularly temperature dependence of excess molar heat capacity under atmospheric pressure [35].…”

“…However, it should be pointed out that the hydroxyl group of the 2-methyl-2-butanol becomes increasingly hindered which effectively reduces the alcohol self-association capability. Moreover, for (alcohol + alkane) systems, including also tertiary alcohols, the results of ab initio calculations show that cyclic trimers are not particularly stable due to the unfavourable steric situation [10,11]. Moreover cyclic associates with more than six molecules are unlikely exist for entropic reasons.…”

Estudio experimental y teórico de mezclas líquidas binarias formadas por 1-alcoholes y ciclohexilamina

“…La misma conclusión se puede extraer de la correspondiente comparación con mezclas de N,Ndimetilformamida y N,N-dimetilacetamida, indican que las disoluciones con aminas están más estructuradas (figura 4.26). La comparación de las curvas de los sistemas 1-heptanol + ciclohexilamina, o + ciclohexano (figura 4.27) revela que la amina rompe mejor la autoasociación del alcohol ya que, en el sistema con el alcano aparece un mínimo en la zona de baja concentración del alcohol [96,122,123,124,125], síntoma inequívoco de la existencia de especies cíclicas, principalmente tetrámeros de momento dipolar nulo [124], que el alcano es incapaz de romper.…”