Liquid-Phase Activity Coefficients for Saturated HF/H₂O Mixtures with Vapor-Phase Nonidealities Described by Molecular Simulation

Abstract

Isothermal-isobaric Monte Carlo molecular simulations are performed to estimate the vaporphase fugacity coefficients of hydrogen fluoride and water in their mixtures, covering the full range of composition at experimentally known saturation temperatures and 1 atm pressure. These results are combined with three sets of established experimental data for vapor-liquid coexistence in this system to compute corresponding liquid-phase activity coefficients for each. Application of an integral thermodynamic consistency test shows that the new values of the activity coefficients are greatly improved over previously reported values, which had been computed using an ideal-gas treatment for the vapor phase. The consistency test also gives reason to prefer the data of Munter et al. [Ind. Eng. Chem. 1947, 39, 427] and Vieweg [Chem. Tech. (Berlin) 1963, 15 (12), 734] in relation to results reported more recently by Miki et al. [J. Electrochem. Soc. 1990, 137 (3), 787], but any such conclusions should be taken only with due consideration to the approximations inherent in the analysis.

Association Patterns in (HF)m(H2O)n (m + n = 2−8) Clusters

“…This is mainly because of the deficiency of the model in incorporating the strong HF−water interactions. Such complex interactions in this system are also reinforced by the evaluation of the thermodynamic consistency of three experimental data sets available for this mixture at 1 atm ,, and also from molecular simulation studies on this mixture. Both approaches indicate that the dilute HF and dilute water regions of this mixture may result in unusual infinite dilution fugacity coefficients and a fluorophobic-like effect, which only goes toward providing more evidence as to the complexity of this mixture and the modeling challenges this system possesses.…”

New Molecular-Mechanics Model for Simulations of Hydrogen Fluoride in Chemistry and Biology

“…9,10 HF is miscible with H 2 O in all proportions; 12 vapor and liquid HF-H 2 O mixtures are also used widely, for example for etching in semiconductor production and for pickling of stainless steel, respectively. 13 Notwithstanding their widespread use in chemical and industrial processes, both pure and aqueous HF (also known as hydrofluoric acid) are highly toxic and corrosive. Handling of these substances thus requires rigorous safety precautions.…”

“…It is used in the preparation of most fluorine-containing compounds, − including the hydrofluorocarbons and hydrochlorofluorocarbons employed as refrigerants. HF is also used in the production of inorganic fluorides, in uranium enrichment and aluminum manufacture, and as a catalyst in the production of high-octane gasoline. , HF is miscible with H 2 O in all proportions; vapor and liquid HF-H 2 O mixtures are also used widely, for example for etching in semiconductor production and for pickling of stainless steel, respectively . Notwithstanding their widespread use in chemical and industrial processes, both pure and aqueous HF (also known as hydrofluoric acid) are highly toxic and corrosive.…”

Evaluating the Thermodynamic Consistency of Experimental Data for HF + H2O at 101.325 kPa

“…While performing this research, an ongoing study evaluating the thermodynamic consistency of the aqueous HF system using molecular simulation came to our attention …”

“…While performing this research, an ongoing study evaluating the thermodynamic consistency of the aqueous HF system using molecular simulation came to our attention. 17 These authors use a biasing technique within the Monte Carlo simulation to determine the vapor-phase fugacity coefficients and, ultimately, perform an integral test on the experimental data. The simulation work paints a different picture of the behavior for the fugacity coefficients, especially in the dilute/concentrated regions.…”