In using the Peng-Robinson equation of state (PREOS) described by Sahimi etal., we found discrepancies with their results. By using two separate methodsof computation, we deduced that their method is correct, but that some code orimplementation errors must have caused the observed discrepancies.
The patterns of the phase behavior of CO2/hydrocarbon mixtures have beenstudied previously with the aid of the PREOS. In developing a free-energyminimization (FEM) technique for calculating phase diagrams, we found phasediagrams in serious disagreement with several of those published in Refs. 1 and2. We were unable to trace the errors in the algorithm used by Sahimi et al.for the calculations reported in Refs. 1 and 2. Consequently, we wrote a newcomputer code based on Sahimi et at's method and recomputed the questionablephase diagrams. The results were phase diagrams in full agreement with thoseobtained by FEM phase diagrams in full agreement with those obtained by FEM andin disagreement with those published in Refs. 1 and 2. This means that thecomputational method of Sahimi et al. is correct but that some error or errorsin the original code or in its implementation led to incorrect phasediagrams.
The purpose of this paper is to present corrections to the phase diagrams inRefs. 1 and 2. A brief description of the methods is also given. A moreextensive discussion of the FEM technique and its application is given in Ref.4.