Interfacial properties of the tetrahydrofuran + carbon dioxide binary mixture, a trilogy: experiments, simulation, and theory

Tetrahydrofuran (THF) is routinely used as thermodynamic hydrate promoter (THP) that produces a pronounced shift on the hydrates coexistence curves. Different authors have used THF for applications as the reduction of the... [ view full abstract ]

Tetrahydrofuran (THF) is routinely used as thermodynamic hydrate promoter (THP) that produces a pronounced shift on the hydrates coexistence curves. Different authors have used THF for applications as the reduction of the equilibrium pressure of hydrates of carbon dioxide (CO₂) for environmental concerns. This work focuses on the description of the interfacial behaviour of this mixture at several temperatures and pressure, and can be considered as a preliminary study to predict the phase equilibrium of hydrates of mixtures of THF with carbon dioxide. We consider three alternative but complementary approaches to characterise the interfacial properties of the system: experiments, molecular dynamics simulations, and theory. From a theoretical modelling point of view, computer simulation and theory offer complementary insight into atomic level phenomena. Additionally, comparison with experimental data allows to check the capability of the theoretical approaches in predicting the interfacial behaviour. We determine interfacial tension, coexisting densities, concentration profiles along the interfacial region, surface activities, and relative Gibbs adsorption isotherms for the mixture at several vapour-liquid equilibrium conditions. Measurements are based on the use of a high-pressure pendant drop tensiometer coupled to a high-pressure densimeter. Theoretical modelling is carried out coupling the  SAFT-γ Mie approach with the Square Gradient Theory. Finally, simulations are performed in the NVT canonical ensemble. We use two different unit-atom models for THF and a coarse-grained model based on the SAFT-γ Mie. Theoretical models and computer simulation results indicate that CO₂ accumulates at the liquid interface. Agreement between theoretical modelling and experiment is analysed in this contribution.