PREDICTING VLE FROM LIQUID DENSITIES
Advancing the chemical engineering fundamentals
Thermodynamics: Hydrocarbons & Petrochemicals (T2-1a)
Keywords: vle, eos, liquid, density, predict
PREDICTING VLE FROM LIQUID DENSITIES
The advent of high precision densitometers, especially since the mid 1980’s, has resulted in an abundance of high quality liquid density measurements. The description of vapor-liquid equilibria (VLE) also recognizes that, in a significant number of systems, non-ideality is concentrated in the liquid phase. Most commonly used P-V-T equations of state (EOS) are continuous functions, purporting to describe some (or most) thermodynamic properties of the vapor and liquid phases, simultaneously.
This study combines the accuracy of modern density measurements, the notion of liquid phase non-ideality, and the dual phase design of P-V-T EOS’s, to investigate the feasibility of predicting VLE from mixture liquid density data. This objective necessitates the EOS’s employed in this investigation to predict pure and mixture liquid densities correctly, without sacrificing the accuracy of other properties (e.g., vapor pressures). This requirement precludes the use of most two-parameter cubic EOS’s. An essential element of this investigation, therefore, is the introduction of a multi-parameter EOS amenable to simultaneously reproducing near-saturation compressed liquid densities, saturation vapor pressures and vapor densities, along with appropriate mixing rules. This is a proof-of-concept study which does not focus on developing this EOS or mixing rules, but simply employs these as vehicles to predict VLE from mixture liquid density data alone.
Several binary and ternary systems are investigated, and their predictions (based on liquid densities only) are compared with VLE measurements. The results are quite encouraging, and, in some cases, very good. With some fine-tuning, this should be considered a viable approach to exploiting the large body of liquid density data available in the literature, as an alternate means to predicting VLE, especially in those instances where equilibrium vapor pressures and compositions are scarce and difficult, unsafe or expensive to measure.
An extension of the above idea is the simultaneous application of VLE and liquid densities. Several systems with only a few VLE data points are simultaneously correlated with mixture liquid densities to reliably extend VLE predictions over a wider concentration range.
Presented Monday 17, 12:11 to 12:30, in session Thermodynamics: Hydrocarbons & Petrochemicals (T2-1a).
