(83b) Perils of Careless Handling of Phase Equilibria in Chemical Systems

This paper discusses the all-too-common pitfalls, in process simulation work for complex chemical mixtures, when using “built-in” binary interaction parameters for activity coefficient models in commercial process simulators. Part of the problem arises from the fact that the data sources used by the vendors are either undocumented or extremely out of date and do not include the latest information. In some cases, these built-in activity coefficient interaction parameters are based on group contribution methods that could easily be 30-100% in error. Such situations can lead to disastrously wrong results for VLE, LLE, or VLLE systems, especially when the phase equilibria for the most important binaries in the mixture have been characterized improperly.

In this paper, we will discuss the proper methods and procedures to ensure reliable results. We will also discuss guidelines for requesting fresh phase equilibria measurements in the laboratory when available data are insufficient or inaccurate. A few industrial examples will be presented to illustrate these ideas and procedures.