Avoiding convergence problems in VLE predictions using an equation of state

Abstract

Owing to certain advantages, the equation-of-state (EOS) approach is preferable to mixed models for VLE predictions in hydrocarbon processing at high pressures. However, the EOS approach leads to convergence problems, typically yielding what are referred to as trivial solutions for single models. Despite the use of this approach for over three decades, not much attention has been given to this aspect until recently. An attempt is made here to analyse the problem systematically and to suggest a solution. A procedure, providing initial estimates of pressure and temperature for VLE predictions, is also a long-felt need. Correlations are suggested for this purpose. Finally, an algorithm is proposed which can resolve trivial solutions and other convergence problems.