Direct calculation of bubble points for alkane mixtures by molecular simulation

This paper extends to flexible molecules an algorithm proposed earlier for the calculation of bubble points of simple fluids by Monte Carlo simulation (Ungerer, P., Boutin, A., and Fuchs, A. H., 1999, Molec. Phys., 97, 523). This algorithm is based on a pseudo-ensemble in which global volume, temper ature and liquid phase mole numbers are fixed. A configurational bias metho d is used to treat flexible molecules, and the underlying assumptions regar ding the molecular partition function for flexible chains are discussed. Mo lecular interactions are determined with an anisotropic united atoms interm olecular potential, recently optimized to represent vapour-liquid phase equ ilibria of n-alkanes. Two applications examples are given, concerning a bin ary mixture (methane + n-pentane) and a ternary system (methane + propanen-decane) for which experimental data are available. Satisfactory convergen ce is obtained, except in the vicinity of critical conditions. Densities an d vapour phase compositions are well represented. Bubble pressures appear s ignificantly underestimated, however. The origin of this discrepancy and re medial methods are discussed.