Reliability of the correlation allowing the kij to switch from an alpha function to another one in hydrogen-containing systems

Due to its very low critical temperature, the reduced temperature of hydrogen can easily overcome 10 in chemical processes. As a consequence, the many alpha functions available in the literature - the parameters of which are determined at low temperature - lead to totally different a(H2)(T) values in the temperature range of industrial interest. As a consequence, the k(ij) value used in the classical VdW1f mixing rules to correlate the VLE data of hydrogen-containing systems strongly depends on the selected equation of state (EoS) and/or alpha function. For hydrogen-containing systems, the k(ij) may indeed vary from a large negative value to a large positive value by only changing the alpha function. This is a major concern since commercial process simulators generally provide a unique k(ij) value which is assumed to be appropriate regardless of the equation of state and/or the alpha function. It was thus a challenge to check whether the relationship developed by our research group in 2010 - and aimed at calculating the k(ij) for a desired thermodynamic model knowing the corresponding value for another one - could predict such large changes. This study concluded that such a correlation performed well and could thus be useful to simulate chemical processes in which H-2 is a key component. (c) 2012 Elsevier B.V. All rights reserved.