Stereoisomeric effects on volumetric properties under pressure for the system cis- + trans-decalin

Abstract

In order to study the influence of stereoisomeric effects on the volumetric properties, an extensive experimental study of the density of the binary system composed of the two stereoisomeric molecular forms of decalin – cis and trans – have been measured (294 points) for 7 different compositions including the pure compounds at 3 temperatures (303.15, 323.15 and 343.15 K) and 14 isobars up to 65 MPa with a vibrating-tube densimeter. The experimental relative uncertainty is estimated to be 0.05%. The isothermal compressibility and the isobaric thermal expansivity have been derived and discussed with respect to their behavior due to stereoisomerism. These results have been interpreted as due to the molecular structure as well as changes in the molecular distance and free volume. Three different types of equations of state (EoS) are studied in order to investigate how they take the stereoisomeric influence and effect into account through their required model parameters, revealing that some model parameters are influenced by stereoisomerism, whereas other parameters are not. In all cases for the density, the models are able to distinguish between the two stereoisomeric decalin compounds. The considered models are the PR EoS, the PC-SAFT approach and a molecular dynamics approach. Further, based on the analysis of the model parameters performed on the pure compounds, it has been found that the use of simple mixing rules without introducing any binary interaction parameters is sufficient in order to predict the density of cis- + trans-decalin mixtures with the same accuracy in comparison with the experimental values as obtained for the pure compounds.