Mean-Field Lattice-Gas Description of the System CO₂/H₂O

Abstract

The mean-field lattice-gas model in the present form has proven to be well able to describe nearly quantitatively fluid phase behaviour of non-polar and polar pure components and mixtures over a large temperature and pressure range. In our version of the model it is assumed that: all lattice sites have the same volume, independent of temperature and pressure, and that every kind of lattice site has a characteristic interacting surface area. The combinatory entropy of the system is corrected with an empirical parameter. For mixtures the same procedure cart be followed and a description of fluid phase behaviour, based upon the parameters of the pure components and two binary interaction parameters, appear to come out quite reasonably.

The systems CO₂ H₂O and mixtures thereof are most commonly used in supercritical extraction. It is shown here that the lattice-gas model can quite well deal with these systems. Values of the lattice-gas parameters have been derived in the outlined manner and predict the second-type gas-gas demixing, known to occur in this system, in an essentially correct way.