Gibbs ensemble computer simulation and SAFT-VR theory of non-conformal square-well monomer-dimer mixtures

The phase equilibria of non-conformal square-well monomer-dimer systems are examined using Gibbs ensemble Monte Carlo simulation and compared with results from the statistical associating fluid theory for potentials of variable attractive range (SAFT-VR). For the first system of interest the square-well segments are of equal diameter and well-depth, the monomer has an attractive range of λ₁₁=1.25 and the dimer of λ₂₂=1.5. Two constant-pressure slices of the phase diagram are determined from Gibbs ensemble simulation of the mixture for a range of temperatures. The second system is a united-atom model of the real system methane+n-butane which has been extensively studied with SAFT-VR theory; parameters from the theoretical work are used in the simulation. Constant-pressure and -temperature slices are studied and comparisons made between theoretical predictions and simulation data. We extrapolate the mixture simulation data to estimate the pure component phase equilibria.