Dew-point densities of fluid mixtures – Linkage of experiment and molecular simulation

拟议研究项目的目标是精确测定流体混合物的露点密度。由于露线附近的精确密度测量受到吸附效应和毛细冷凝的影响，本文将开发一种将高精度重力密度测量与分子动力学模拟（MDS）相结合的方法。这种方法将有助于以前所未有的精度全面描述混合物的露线（包括压力、温度、成分和密度）。在此基础上，现有的描述混合物相平衡的状态方程的最新进展可以得到改进。准确地了解混合物的相行为是必不可少的，例如，在天然气运输和碳捕获和利用领域。这需要状态方程，而状态方程又需要精确的实验汽液平衡（VLE）数据作为最重要的输入。这样的数据很少包含气泡点和露点密度，然而，完全需要这些密度来描述相平衡。虽然气泡点密度的精确测量是可能的，但露点密度的精确测量受到干扰表面现象（即吸附和毛细冷凝）的影响，需要了解和考虑。因此，在申请人的Emmy Noether小组内开发并建立了重力精密密度测定法。尽管有这种测量技术，露点密度的直接测量是不可能的，即使是目前最精确的测量也不能准确地揭示“真正的”露点的位置。在这里，分子动力学模拟可以在原子水平上提供更好的理解，从而对实验数据的解释有重要贡献。此外，MDS有望支持在露线附近密度测量的校正模型的发展。

The goal of the proposed research project is the accurate determination of dew-point densities of fluid mixtures. Since precision density measurements near the dew line are affected by sorption effects and capillary condensation, a methodology will be developed, which links highly accurate gravimetric densimetry with molecular dynamics simulation (MDS). This methodology will contribute to a full description of a mixture’s dew line (including pressure, temperature, composition and density) with unprecedented accuracy. Based on this, the current state-of-the-art of existing equations of state describing the phase equilibrium of mixtures can be advanced. Accurately knowing the phase behavior of mixtures is essential, e.g., in the areas of natural gas transport and in carbon capture and utilization. This requires equations of state, which in turn involves accurate experimental vapor-liquid equilibrium (VLE) data as the most important input. Such data rarely comprise bubble-point and dew-point densities, however, exactly these densities are needed to fully describe the phase equilibrium. While, accurate measurements of bubble-point densities are possible, the accurate measurement of dew-point densities is affected by disturbing surface phenomena (i.e., adsorption and capillary condensation), which need to be understood and taken into account. Therefore, gravimetric precision densimetry was developed and set up within the Emmy Noether group of the applicant. Despite this measurement technology, no direct measurement of dew-point densities is possible, and even the presently most accurate measurements do not exactly reveal the location of the „true“ dew point. Here, molecular dynamics simulation can provide a better understanding on an atomistic level and, therewith, significantly contribute to the interpretation of the experimental data. Moreover, MDS is expected to support the development of correction models for density measurements in the vicinity of the dew line.