Abstract The solubility of methane in water decreases when a small amount of salt is present. This is usually denoted as the salting out effect (i.e., the methane is expelled from the solution when it contains small amounts of salt). The effect is important, for instance the solubility is reduced by a factor of three in a 4 m (mol/kg) NaCl solution. Some years ago we showed that the salting out effect of methane in water can be described qualitatively by molecular models using computer simulations. However the salting out effect was overestimated. In fact, it was found that the solubility of methane was reduced by a factor of eight. This points to limitations in the force field used. In this work we have carried out direct coexistence simulations to describe the salting out effect of methane in water using a recently proposed force field (denoted as Madrid-2019) based on the use of scaled charges for the ions and the TIP4P/2005 force field for water. For NaCl the results of the Madrid-2019 force field significantly improve the description of salting out of methane. For other salts the results are quite reasonable. Thus the reduction of the charge of the ions also seems to be able to improve the description of salting out effect of methane in water. Besides this we shall show that the brine-methane interface exhibits an increased interfacial tension as compared to that of the water-methane system. It is well known that electrolytes tend to increase the surface tension of liquid water, and this seems also to be the case for the interface between water and methane.

中文翻译：

---

工作中的比例电荷：来自计算机模拟的电解质溶液中甲烷的盐析和界面张力

摘要 当少量盐存在时，甲烷在水中的溶解度会降低。这通常表示为盐析效应（即，当溶液中含有少量盐时，甲烷会从溶液中排出）。效果很重要，例如溶解度在 4 m (mol/kg) NaCl 溶液中降低了三倍。几年前，我们表明可以使用计算机模拟通过分子模型定性描述甲烷在水中的盐析效应。然而，盐析效应被高估了。事实上，发现甲烷的溶解度降低了八倍。这表明所使用的力场存在局限性。在这项工作中，我们基于离子的比例电荷和 TIP4P/2005 力场，使用最近提出的力场（表示为 Madrid-2019）进行了直接共存模拟，以描述水中甲烷的盐析效应为水。对于 NaCl，Madrid-2019 力场的结果显着改善了对甲烷盐析的描述。对于其他盐，结果相当合理。因此，离子电荷的减少似乎也能够改进对甲烷在水中盐析作用的描述。除此之外，我们将表明，与水-甲烷系统相比，盐水-甲烷界面表现出增加的界面张力。众所周知，电解质往往会增加液态水的表​​面张力，