Departament d'Enginyeria Química, ETSEQ, Universitat Rovira i Virgili, Avda. dels Països Catalans 26, 43007 Tarragona, Spain.
J Phys Chem B. 2012 Mar 8;116(9):2787-800. doi: 10.1021/jp2081758. Epub 2012 Feb 27.
Mass diffusion coefficients of CO(2)/brine mixtures under thermodynamic conditions of deep saline aquifers have been investigated by molecular simulation. The objective of this work is to provide estimates of the diffusion coefficient of CO(2) in salty water to compensate the lack of experimental data on this property. We analyzed the influence of temperature, CO(2) concentration,and salinity on the diffusion coefficient, the rotational diffusion, as well as the electrical conductivity. We observe an increase of the mass diffusion coefficient with the temperature, but no clear dependence is identified with the salinity or with the CO(2) mole fraction, if the system is overall dilute. In this case, we notice an important dispersion on the values of the diffusion coefficient which impairs any conclusive statement about the effect of the gas concentration on the mobility of CO(2) molecules. Rotational relaxation times for water and CO(2) increase by decreasing temperature or increasing the salt concentration. We propose a correlation for the self-diffusion coefficient of CO(2) in terms of the rotational relaxation time which can ultimately be used to estimate the mutual diffusion coefficient of CO(2) in brine. The electrical conductivity of the CO(2)-brine mixtures was also calculated under different thermodynamic conditions. Electrical conductivity tends to increase with the temperature and salt concentration. However, we do not observe any influence of this property with the CO(2) concentration at the studied regimes. Our results give a first evaluation of the variation of the CO(2)-brine mass diffusion coefficient, rotational relaxation times, and electrical conductivity under the thermodynamic conditions typically encountered in deep saline aquifers.
运用分子模拟研究了深部盐水层系热力学条件下 CO(2)/盐水混合物的质量扩散系数。本工作的目的是提供 CO(2)在咸水中的扩散系数估算值，以弥补该物性缺乏实验数据的不足。我们分析了温度、CO(2)浓度和盐度对扩散系数、旋转扩散以及电导率的影响。我们发现质量扩散系数随温度升高而增加，但如果体系整体为稀溶液，则未发现与盐度或 CO(2)摩尔分数有明显的依赖关系。在这种情况下，我们注意到扩散系数值存在较大的分散性，这使得无法对 CO(2)分子浓度对其迁移率的影响做出明确的结论。水和 CO(2)的旋转弛豫时间随温度降低或盐浓度增加而增加。我们提出了一个关于 CO(2)自扩散系数的关联式，该关联式基于旋转弛豫时间，可以最终用于估算 CO(2)在盐水中的互扩散系数。还在不同热力学条件下计算了 CO(2)-盐水混合物的电导率。电导率随温度和盐浓度的升高而增加。然而，在研究的范围内，我们没有观察到 CO(2)浓度对该性质的任何影响。我们的结果首次评估了深部盐水层系典型热力学条件下 CO(2)-盐水混合物的质量扩散系数、旋转弛豫时间和电导率的变化。
