Molecular simulation of the vapour-liquid equilibria of pure fluids and binary mixtures containing dipolar components: the effect of Keesom interactions

Gibbs ensemble Monte Carlo simulations are reported using a Keesom-like potential for the vapour-liquid phase coexistence of both pure fluids and binary mixtures containing a dipolar component. The coexistence properties and critical points were determined for dipolar strengths of μ*2 = 0, 1, √2 and 2. Comparison with simulations from the Stockmayer potential indicate that the Keesom potential is a reasonably accurate alternative when μ*2 ⩽ 1>. The effect of long-range dipole interactions is to restrict the extent of two-phase equilibria that would be otherwise induced by the dipole. The vapour-liquid equilibria of binary mixtures containing non-polar, two dipolar (μ1*2 = 1; μ2*2 = 1) and non-polar plus dipolar (μ1*2 = 0; μ2*2 = 1) components are investigated. The extent of vapour-liquid equilibria can be enhanced substantially by dipolar interactions.