COMPUTER-SIMULATION OF VAPOR-LIQUID-EQUILIBRIA OF LINEAR QUADRUPOLAR FLUIDS - DEPARTURES FROM THE PRINCIPLE OF CORRESPONDING STATES

Vapor-liquid equilibria of different quadrupolar linear Kihara fluids have been studied, by using the Gibbs ensemble Monte Carlo technique. Coexistence curves for fluids with elongations L*=L/sigma=0.3, 0.6, and 0.8 and different quadrupoles are given. We analyze the effect of quadrupole moment on critical properties. Quadrupole moment increases the critical temperature, pressure, and density. The magnitude of the increase depends on both anisotropy and quadrupole moment. A new way of reducing the quadrupole is proposed, so that the variation of critical properties due to the quadrupole follows a universal behavior. Quadrupole provokes deviations from the principle of corresponding states. A broadening of the coexistence curve is observed due to the quadrupole. The quadrupole moment increases the slope of the vapor pressure curve vs temperature inverse. Simulation data are used to describe vapor-liquid equilibria of carbon dioxide. Good agreement between simulation and experiment is achieved.