Comprehensive study of the vapour-liquid equilibria of the pure two-centre Lennard-Jones plus pointquadrupole fluid

TL;DR

This study systematically investigates the vapour-liquid equilibria of 30 two-centre Lennard-Jones plus pointquadrupole model fluids using molecular dynamics, providing correlations for critical and saturated properties to aid modeling real fluids.

Contribution

It offers comprehensive simulation data and empirical correlations for the VLE of 2CLJQ fluids, enhancing the understanding and parameterization of these models for real fluid applications.

Findings

Critical temperatures and densities are accurately predicted from correlations.

Vapour pressures and saturated densities are well described within statistical uncertainties.

Simulation data serve as a basis for adjusting model parameters to experimental data.

Abstract

Results of a systematic investigation of the vapour-liquid equilibria (VLE) of 30 individual two-centre Lennard-Jones plus pointquadrupole model fluids (2CLJQ) are reported over a range of reduced quadrupolar momentum $0 \le Q^{*2} \le 4$ and of reduced elongation $0 \le L^* \le 0.8$. Temperatures investigated are from about 55 % to about 95 % of the critical temperature of each fluid. Uniformly the $NpT$+Test Particle Method based on molecular dynamics simulations is used for the generation of vapour pressures, saturated densities, and saturated enthalpies. Critical temperatures $T^*_{\rm c}$ and densities $\rho^*_{\rm c}$ are obtained from Guggenheim's equations. Empirical correlations for critical data $T^*_{\rm c}$ and $\rho^*_{\rm c}$ as well as for saturated densities $\rho'^*$, $\rho''^*$, and vapour pressures $p^*_{\sigma}$ are developed as global functions of the model parameters. In most cases they describe the simulation data within their statistical uncertainties. Critical pressures and acentric factors of the 2CLJQ fluid can be calculated from present correlations. The present simulations are a sound basis for adjustments of the model parameters $Q^{*2}$, $L^*$, $\sigma$, and $\epsilon$ to experimental VLE data of real fluids.