Solubility of nitrogen in methane, ethane, and mixtures of methane and ethane at Titan-like conditions: A molecular dynamics study

TL;DR

This study uses molecular dynamics simulations to analyze how nitrogen dissolves in methane, ethane, and their mixtures under Titan-like conditions, revealing temperature effects, surface adsorption phenomena, and interfacial behaviors.

Contribution

It provides the first detailed molecular-level insights into nitrogen solubility and interfacial properties in Titan-relevant hydrocarbon mixtures, aligning with experimental data.

Findings

Nitrogen solubility decreases with increasing temperature.

Higher nitrogen solubility in methane than ethane at low temperatures.

Surface adsorption of nitrogen is strongly temperature-dependent.

Abstract

We have studied the temperature dependence of the solubility of nitrogen in methane, ethane, and mixtures of methane and ethane using vapor-liquid equilibrium simulations of binary and ternary mixtures of nitrogen, methane and ethane for a range of temperatures between 90K and 110K at a pressure of 1.5 atm, thermodynamic conditions that may exist on the Saturn's giant moon, Titan. We find that --(i) the solubility of nitrogen in both methane and ethane decreases with increasing temperature; (ii) the solubility of nitrogen in methane is much larger compared to that in ethane at low temperatures, (iii) solubility of nitrogen in a ternary mixture of methane, ethane, and nitrogen increases upon increasing mole-fraction of methane. Our results are in quantitative agreement with the recent experimental measurement of the solubility of nitrogen in methane, ethane, and a mixture of methane and ethane. Furthermore, we find a strong temperature-dependent surface adsorption of nitrogen at the nitrogen-hydrocarbon interface, previously unknown. We have also investigated surface tension of the gas-liquid interface and find that it decreases upon decreasing temperature. Moreover, we find that the interfacial layer of adsorbed nitrogen and ethane show a preferential orientational ordering at the interface.