Improved Estimates of the Critical Point Constants for Large n‑Alkanes Using Gibbs Ensemble Monte Carlo Simulations

• Published in: Journal of chemical and engineering data Vol. 61; no. 10; pp. 3640 - 3649
• Main Authors: Messerly, Richard A, Rowley, Richard L, Wilding, W. Vincent
• Format: Journal Article
• Language: English
• Published: American Chemical Society 13-10-2016
• ISSN: 0021-9568; 1520-5134
• DOI: 10.1021/acs.jced.6b00574

In this work, we present improved estimates of the critical temperature (T c), critical density (ρc), critical pressure (P c), and critical compressibility factor (Z c) for n-alkanes with chain lengths as large as C48. These are obtained for several different force field models with Gibbs ensemble Monte Carlo simulations. We implement a recently proposed data analysis method designed to reduce the uncertainty in T c, ρc, P c, and Z c when predicted with molecular simulation. The results show a large reduction in the uncertainties compared to the simulation literature with the greatest reduction found for ρc, P c, and Z c. Previously, even the most computationally intensive molecular simulation studies have not been able to elucidate the n-alkane P c trend with respect to larger carbon numbers. The results of this study are significant because the uncertainty in P c is small enough to discern between conflicting experimental data sets and prediction models for large n-alkanes. Furthermore, the results for T c resolve a discrepancy in the simulation literature with respect to the correct T c trend for large n-alkanes. In addition, the Z c results are reliable enough to determine the most accurate prediction trend for Z c. Finally, finite-size effects are shown to not be significant even for the relatively small system sizes required for efficient simulation of longer chain lengths.