Prediction of VLE Values for Systems Containing Hydrogen Using the Van Der Waals Equation

Abstract

The temperature dependence of the cohesion parameter “a” (=Ω_aRT_C ² /P_c) of the van der Waals equation of state has been established for predicting vapor-liquid equilibrium (VLE) values for hydrogen-containing systems at cryogenic conditions. Instead of using one temperature function for Ω_a of hydrogen and another for other components as suggested by Graboski and Daubert, a single temperature function for Ω_a was developed for components of cryogenic interests including hydrogen. The optimal Ω_a values of hydrogen above its critical temperature were determined from VLE values of binary hydrogen - n-alkane systems without using the conventional binary adjustable parameter k_ij, and correlated. The success of the proposed correlation was demonstrated by predicting the VLE values for hydrogen-containing systems, including four binaries with the second component other than a n-alkane, and two ternaries. The van der Waals equation used in the calculation is the simplest cubic equation of state. For the systems considered, the agreement obtained between the calculated and the experimental K values from the proposed correlation is about the same or even better than those obtained from the method of Graboski and Daubert.