Advanced association theory for monoethylene glycol: thermodynamic perturbation theory, Monte Carlo simulation, and equation of state parametrization

Thermodynamic perturbation theory (TPT) is a breakthrough in developing an equation of state for systems containing hydrogen bonding. In this work, we derive the association contribution to Helmholtz's free energy for spherical particles composed of four patchy sites and verified it by performing Monte Carlo (MC) simulations. The theory suggests that the site placement significantly impacts the system's phase behavior at constant temperature and density. We apply our theory to correlate and predict the experimental phase behavior data of pure monoethylene glycol (MEG) and its binary mixtures with non-associating molecules (including methane, ethane, propane, and hydrogen) and compare the theory's performance with the case where the association contribution to the system's pressure is based on first-order TPT (TPT1). Our theory outperforms TPT1 in terms of error and predictive capabilities for the physical properties of pure MEG. In the binary mixture application, TPT1 presents a better predictive ability for the mole fraction of the non-associating molecule in the glycol-rich liquid than our theory.