Experimental Data Assessment Test for Composition of Vapor Phase in Equilibrium with Gas Hydrate and Liquid Water for Carbon Dioxide + Methane or Nitrogen + Water System

Accurate knowledge of the compositions of the equilibrium
phases
in the systems containing gas hydrates is essential for many hydrate-based
separation processes. Unfortunately, there are limited sets of such
experimental data available in the literature partly due to the difficulties
in measurements of the compositions of the phases in equilibrium with
gas hydrate. Consequently, satisfactory accuracy of the measurements
may not be obvious. Therefore, reliability of the corresponding data
should be checked prior to their further applications. In this article,
we present a thermodynamic assessment test (consistency test) based
on the area test approach for the experimental compositional data
of vapor phase in equilibrium with gas hydrate + liquid water for
the carbon dioxide + methane or nitrogen + water system. The van der
Waals and Platteeuw (vdW-P) solid solution theory is used to model
the hydrate phase, and the Valderrama–Patel–Teja equation
of state (VPT-EoS) along with the nondensity dependent (NDD) mixing
rule is applied to deal with the fluid phases. The results show that
only one of the studied experimental data sets seems to be thermodynamically
consistent, and the rest of the data seem to be either not fully consistent
or inconsistent.

对于诸多基于气体水合物（gas hydrates）的分离工艺而言，精准掌握含气体水合物体系中平衡相的组成至关重要。然而，由于直接测定与气体水合物共存的平衡相组成存在诸多技术难题，公开文献中可获取的此类实验数据集极为有限，且部分数据的测量精度亦难以保障。因此，在进一步应用相关实验数据前，需先对其可靠性进行校验。
本文基于面积检验法，针对二氧化碳+甲烷或氮气+水体系中与气体水合物+液态水共存的气相组成实验数据，开展了热力学一致性检验（consistency test）。研究中采用范德华-普拉特尤固溶理论（van der Waals and Platteeuw，vdW-P）对水合物相进行建模，并结合巴尔德拉马-帕特尔-特亚状态方程（Valderrama–Patel–Teja equation of state，VPT-EoS）与非密度依赖（NDD）混合规则，对流体相的热力学行为进行描述。结果表明，在所调研的全部实验数据集中，仅一组数据符合热力学一致性要求，其余数据集要么未完全满足一致性条件，要么完全不符合。