An Application of Statistical Chain Theories on Thermodynamic Properties of Binary and Ternary Hydrocarbon Mixtures

Abstract

This paper discusses the mathematical model for computing the thermodynamic properties for binary and ternary mixtures of propane, n-butane and iso-butane in their fluid phase with an aid of statistical chain theory. The constants required to compute like the characteristic temperatures of rotation, electronic state etc., and the moments of inertia are obtained analytically applying the knowledge of the atomic structure of the molecule. In the paper is presented the procedure for calculating essential thermodynamic properties such as pressure, speed of sound, the Joule-Thomson coefficient, compressibility, enthalpy and thermal expansion coefficient. This paper will discuss, for the first time, the application of statistical chain theory and accuracy for binary and ternary mixtures among propane, n-butane and iso-butane, in their entire fluid phases for all the important thermodynamic properties. To calculate the thermodynamic properties of Lennard-Jones chains,we have used the Liu-Li-Lu and Tang-Lu models. The thermodynamic properties of the Lennard-Jones mixtures are obtained using the one-fluid theory. In recent years thermodynamic theories based on statistical thermodynamics have been rapidly developed. Fluids with chain bonding and association have received much attention in recent years. Interests for these fluids are prompted by the fact that they cover much wider range of real fluids than spherical ones. A good theory for these fluids will be very beneficial to chemical engineering applications by reducing the number of parameters and making them more physically meaningful and more predictable. In technical practice energy processes are of vital importance. In order to design devices of this field of activity, it is necessary to be familiar with the equilibrium and nonequilibrium thermodynamic properties of state in a one and two phase environment for pure refrigerants and their mixtures. To calculate the thermodynamic properties of real fluid Liu-Li-Lu (LLL) (revisited Cotterman) equation of state based on simple perturbation theory and SAFT-VR equation of state for LJ chain fluid was applied. We developed the mathematical model for the calculation of all equilibrium thermodynamic functions of state for pure hydrocarbons and their mixtures. To compare the thermodynamic properties of real fluid obtained by SAFT theory we used REFPROP model. The analytical results obtained by classical and statistical thermodynamics are compared with the experimental data and they show relatively good agreement. NOMENCLATURE.