Interfacial Tensions, Solubilities, and Transport Properties of the H₂/H₂O/NaCl System: A Molecular Simulation Study

Abstract

Data for several key thermodynamic and transport properties needed for technologies using hydrogen (H 2 ), such as underground H 2 storage and H 2 O electrolysis are scarce or completely missing. Force field-based Molecular Dynamics (MD) and Continuous Fractional Component Monte Carlo (CFCMC) simulations are carried out in this work to cover this gap. Extensive new data sets are provided for (a) interfacial tensions of H 2 gas in contact with aqueous NaCl solutions for temperatures of (298 to 523) K, pressures of (1 to 600) bar, and molalities of (0 to 6) mol NaCl/kg H 2 O, (b) self-diffusivities of infinitely diluted H 2 in aqueous NaCl solutions for temperatures of (298 to 723) K, pressures of (1 to 1000) bar, and molalities of (0 to 6) mol NaCl/ kg H 2 O, and (c) solubilities of H 2 in aqueous NaCl solutions for temperatures of (298 to 363) K, pressures of (1 to 1000) bar, and molalities of (0 to 6) mol NaCl/kg H 2 O. The force fields used are the TIP4P/2005 for H 2 O, the Madrid-2019 and the Madrid-Transport for NaCl, and the Vrabec and Marx for H 2 . Excellent agreement between the simulation results and available experimental data is found with average deviations lower than 10%.

Computation of Electrical Conductivities of Aqueous Electrolyte Solutions: Two Surfaces, One Property

“…In our recent work, we proposed the Madrid-Transport force field, , which uses a scaled charge of q = ±0.75 and that is able to reproduce transport properties, such as the viscosities and diffusion coefficients of water and ions in the whole concentration range. This force field has also been able to reproduce transport properties in the presence of hydrogen . It should be mentioned that the introduction of scaled charges improves a number of properties of electrolytes but deteriorates the value of the free energy of solvation (although it can be corrected via theoretical corrections).…”

Hydrogen and air storage in salt caverns: a thermodynamic model for phase equilibrium calculations

“…Concerning phase equilibrium between air and saturated brines, no specific model has been found in the literature probably due to the lack of experimental data, although molecular simulation is more and more used as a complementary tool to experiments in this field [14]. Nevertheless, we can mention the modeling work recently proposed by Chabab et al on N 2 + brine and O 2 + brine systems with the Soreide and Whitson equation of state [15].…”

Thermodynamic and Transport Properties of H2/H2O/NaB(OH)4 Mixtures Using the Delft Force Field (DFF/B(OH)4–)

“…This is consistent with the increase of viscosities as a function of NaB(OH) 4 molalities as the self-diffusivities of gasses and viscosities of the solution are inversely related. 40,41 As shown in Figure 6b, the self-diffusivities of H 2 have an Arrhenius relation with respect to the temperature (D Hd 2 ∝ exp[−A/T]). These findings are consistent with other simulations and experiments for gas diffusion in aqueous solutions.…”

“…The fitting constants of eq 12 for the self-diffusivities of H 2 are listed in Table 4. This empirical correlation has also been used to model the selfdiffusivities of H 2 in aqueous NaCl solutions 40 for a wide range of temperatures (298−523 K) and concentrations (0−6 mol NaCl/kg water).…”

“…These findings are consistent with other simulations and experiments for gas diffusion in aqueous solutions. 40,41 3.5. Solubilities of H 2 and Activities of Water in Aqueous NaB(OH) 4 Solutions.…”