Interfacial and mass transport phenomena in the tri-ethylene glycol-methane system at process conditions of natural gas dehydration

Understanding the phase and interphase behavior at equilibrium and during the mass transfer between two adjacent fluid phases is relevant for optimizing and designing efficient separation processes. This study experimentally investigates the interfacial and transport behavior of systems comprising tri-ethylene glycol (TEG) and methane (CH₄) under conditions relevant to the gas dehydration process. A comprehensive review of the interfacial tension (IFT) and diffusivity of systems involving non-polar and polar compounds at elevated pressures was studied. However, a research gap exists, particularly concerning the interfacial tension of systems involving TEG, TEG + water, and different types of gases as well as the diffusivity of CH₄ in TEG. To address this gap, this study presents new data on mixture densities, interfacial tension, and drop volumes of TEG and TEG + water in CH₄ and CH₄ + CO₂ mixtures at temperatures ranging from 20 to 50 °C and pressures up to 250 bar using the oscillating U-tube and pendant drop methods, respectively. Additionally, time-dependent fluid mixture densities and TEG droplet volumetric expansion, coupled with an analytical approach for the binary diffusion were applied to determine the CH₄ solubility and diffusivity in TEG. The results show that IFT and drop volume of TEG and TEG + water in CH₄ and CH₄ + CO₂ mixtures decrease with increasing pressure. The presence of water increases the IFT of TEG-CH₄ up to \(\sim\) $\sim$ 5mN/m, while CO₂ reduces it by \(\sim\) $\sim$ 2mN/m. Interestingly, the IFT and drop volume of TEG-CH₄ show no significant change at elevated pressures when temperatures rise from 20 to 50 °C. IFT remains relatively constant over time at moderate pressures but decreases by \(\sim\) $\sim$ 3mN/m at an elevated pressure of 150 bar, suggesting methane solubilization into TEG to have a significant influence which is confirmed by TEG drop volume expansion. The diffusivity of CH₄ in TEG at 150 bar and 50 °C is determined to be in the range of 10^–10 m²/s, which is in agreement with the diffusivity of CH₄ in liquids of similar viscosity, i.e. according correlations may be applied as good engineering practice. To the best of our knowledge, there is no such comprehensive work on the properties of fluid mixtures relevant in gas dehydration processes published up to date.