Communication: Fundamental equation of state correlation with hybrid data sets

Abstract

A strategy is proposed for empirical fundamental equation of state correlations for pure fluids on the basis of hybrid data sets, composed of experimental and molecular simulation data. Argon and hydrogen chloride are used as examples.

Uncertainty quantification confirms unreliable extrapolation toward high pressures for united-atom Mie λ-6 force field

“…The main limitation is that the poor extrapolation at high pressures is based solely on the trend of Z with respect to inverse temperature. By contrast, the simulation values that are typically included in hybrid data sets used to generate FEOS are derivatives of the departure (or residual) Helmholtz free energy with respect to inverse temperature and/or density: [7][8][9][10][11] and "long" branched alkanes. However, such a hierarchical approach is unnecessary for our purposes, since the transferable UA Mie λ-6 force field for n-alkanes is capable of reproducing ρ sat l and P sat v , which are the only properties included in D.…”

“…from both experiment and molecular simulation. 7 For example, several recent studies supplement experimental data with molecular simulation results at temperatures and pressures beyond the range of available experimental temperatures and pressures. [8][9][10][11] Specifically, experimental data were available for temperatures and pressures up to 580 K and 130 MPa, 590 K and 180 MPa, 450 K and 2 MPa, and 560 K and 100 MPa for hexamethyldisiloxane, 8 octamethylcyclotetrasiloxane, 9 ethylene Contribution of NIST, an agency of the United States government; not subject to copyright in the United States.…”

“…For example, it was demonstrated that VLE-optimized force fields for small compounds, such as noble gases, hydrogen sulfide, and hydrogen chloride, do adequately represent the homogeneous fluid region. 7 In this study, we investigate how well the traditional force fields for predicting VLE of normal and branched alkanes extrapolate to higher temperatures and pressures, i.e dense supercritical fluids and compressed liquids. This analysis is performed for four normal and four branched alkanes by comparing the simulated compressibility factor (Z) with the REFPROP correlations.…”

“…A dep xy R g T ≡ (1/T ) x ρ y ∂ x+y A dep ∂(1/T ) x ∂ρ y(25)where x and y are integer values and the derivative is of order x+y. There are advantages of using A dep xy for developing FEOS, as this approach eliminates redundant information found in traditional macroscopic properties 2,[4][5][6][7]. For example, the following expressions demonstrate the interdependency of the properties we computed, namely, Z and U dep with their derivatives along isochores and isotherms: 6 However, at least two reasons exist as for why the conclusions of this study are not based on A dep xy .…”

Lennard-Jones force field parameters for cyclic alkanes from cyclopropane to cyclohexane

“…On the basis of accurate force fields, molecular simulation may yield thermophysical data for extending equations of state or proposing new ones from hybrid data [7]. To the best of our knowledge, there are no fundamental equations of state reported in the literature for cyclopropane and cyclobutane, because only few experimental data exist due to the poor chemical stability of these compounds.…”