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 Ž . 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 l s1.25 and the dimer of l s1.5. Two constant-pressure slices of the phase 11 22 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 methaneqn-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. q 1999 Elsevier Science B.V. All rights reserved.