Equations of State with Group Contribution Binary Interaction Parameters for Calculation of Two-Phase Envelopes for Synthetic and Real Natural Gas Mixtures with Heavy Fractions

Three equations of state with a group contribution model for binary interaction parameters were applied to calculate the vapor-liquid equilibria of synthetic and real natural gas mixtures with heavy fractions. Critical temperatures, critical pressures, and acentric factors of binary constituents of the mixture were considered to estimate the binary interaction parameters. To perform phase equilibrium calculations, the heavy fractions were first discretized into 12 Single Carbon Numbers (SCN) using generalized molecular weights. Using the generalized molecular weights and specific gravities, the SCN were then characterized. Phase equilibrium calculations were performed employing a set of (nc + 1) equations (nc = number of known components plus 12 SCN. The equations were solved iteratively using Newton�s method. Predictions indicated that the use of binary interaction parameters for highly sour natural gas mixtures is quite important and must be done. For sweet natural gas mixtures, the use of binary interaction parameters is less remarkable.