PREDICTION OF VL AND VLL EQUILIBRIA OF MIXTURES CONTAINING PETROLEUM RESERVOIR FLUIDS AND METHANOL WITH A CUBIC EOS

A cubic equation of state, with simple non-density-dependent mixing ru les, is used to represent the phase behaviour of multicomponent mixtur es containing hydrocarbons up to n-octane, nitrogen, carbon dioxide, h ydrogen sulphide, water and methanol. The reliability of the model is tested against diverse experimental VL and VLL equilibrium data of mul ticomponent systems. The proposed correlation can be applied for effic ient design and operation of transfer lines and processing units. The practical value of the theoretically correct concept of density depend ence is tested on a density-dependent version of the above mixing rule s. It is demonstrated that while both mixing rules produce very simila r results when only one polar component is present, the density-depend ent mixing rules may be inferior for mixtures containing both water an d methanol, owing to an inherent deficiency. It is also demonstrated t hat an invariant version of the proposed non-density-dependent mixing rule may not lead to indisputably improved predictions for the studied systems.