Modelling of phase equilibrium of natural gas mixtures containing associating compounds

The effect of mixing rules and the incorporation of an association term in a cubic equation of state (EoS), on the modelling of phase equilibria of natural gas mixtures in the presence of hydrogen bonding compounds, is investigated. To this purpose, the Peng-Robinson equation of state coupled with the van der Waals one-fluid mixing rules, the UMR-PRU group contribution EoS and the CPA-PR EoS, are evaluated in the prediction of phase equilibrium in ternary and multicomponent mixtures containing natural gas components, water and methanol or monoethylene glycol. It is concluded that UMR-PRU and CPA-PR give significantly improved results over the classical Peng-Robinson EoS, indicating that the use of advanced mixing rules and the explicit implementation of an association term in a cubic EoS is important for modelling the phase equilibrium of natural gas mixtures containing associating compounds.