盐度对正戊烷在水溶液中扩散的影响

Effect of Salinity on Diffusion of n-Pentane in Aqueous Solution

以烷烃为代表的有机质对海洋、湖泊及地层水的污染日趋严重。研究有机质在水溶液中的扩散,对分析其在海水、地层水等多电解质溶液中的扩散现象有指导作用,对于海洋污染的治理、油田采出液的脱水有重要意义。本研究采用动态悬滴体积分析技术,分析了正戊烷在不同盐度水溶液中的扩散强度。首先,实验基于正戊烷液滴面积扩张率的变化,评价盐度对扩散的影响。然后,通过Materials Studio软件进行分子动力学模拟,解释盐度对正戊烷扩散强度的影响。实验结果表明:随着盐度的增加,正戊烷在水溶液中扩散强度先增加后降低;存在转折盐度(0.5‰)使得正戊烷扩散最强。分子动力学模拟发现:低盐度时,离子水化使水分子在离子周围定向排布,使非极性分子——正戊烷分子组成的疏水单元周围出现可扩散的空腔,增加非极性分子的扩散强度。盐度增加导致离子间争夺水分子,打乱水分子的定向排布,减弱非极性分子的扩散强度。

Organic matter,represented by alkanes,is increasingly polluting oceans,lakes,and groundwater.Studying the diffusion of organic matter in aqueous solutions provides guidance for analyzing its diffusion phenomena in multielectrolyte solutions such as seawater and formation water,and it is also of great significance for the control of marine pollution and the dehydration of oilfield produced fluids.The diffusion intensity of n-pentane in aqueous solutions of different salinity was analyzed using dynamic droplet volume analysis technology.Firstly,the effect of salinity on diffusion was evaluated based on the experiment of the change in the expansion rate of n-pentane droplet area.Then,the effect of salinity on the diffusion intensity of n-pentane was explained by molecular dynamics simulation using Materials Studio software.The experimental results indicate that as salinity increases,the diffusion intensity of n-pentane in aqueous solution first increases and then decreases,and there is a salinity of 0.5‰with the strongest diffusion of n-pentane.Molecular dynamics simulations show that at low salinity,ion hydration causes water molecules to orientedly arranged around the ions,creating diffusible cavities around the hydrophobic units composed of non-polar molecules(n-pentane molecules),and increasing the diffusion intensity of non-polar molecules.The increase in salinity leads to competition between ions for water molecules,disrupting the directional arrangement of water molecules,and weakening the diffusion intensity of non-polar molecules.