烷烃油滴在超临界二氧化碳中溶解的分子动力学模拟

采用分子动力学模拟方法研究5种正构烷烃油滴在超临界CO2(sc CO2)中的溶解过程及其微观作用机制。结果表明:烷烃在sc CO2中的溶解能力随其链长的增加而逐渐降低。链长小于18时,烷烃易溶于sc CO2;链长大于18时,sc CO2对烷烃的溶解能力较弱。色散作用在sc CO2溶解烷烃的过程中起主要作用。色散作用随烷烃链长的增加而减弱,其强弱导致了不同链长的烷烃在sc CO2中的溶解能力不同。短链烷烃分子与CO2接触的概率较大,同时烷烃分子在sc CO2中的伸展程度随其链长的增加而减弱,导致烷烃与CO2间色散作用强弱不同。

Molecular dynamics simulation of dissolution of n-alkanes droplets in supercritical carbon dioxide

Molecular dynamics simulations were performed to study the dissolution process and the microscopic mechanism of five n-alkanes droplets in supercritical CO₂ (scCO₂). The simulation results show that the dissolution capability of n-alkanes droplets in scCO₂ decreases with the increase of chain length. When the alkane chain length is less than 18, the alkane could dissolved easily in scCO₂. However, when the alkane chain length is longer than 18, the dissolution of alkane in scCO₂ is difficult. The researches indicate that the dispersion interaction plays crucial role during the dissolving of alkanes in scCO₂, and it decreases with the increase of the alkane chain length. The distinction of the dispersion interaction leads to the different dissolution capability of alkanes in scCO₂. Moreover, these alkanes with short chain are found possessing high possibility to contact with CO₂ than those alkane with long chain. And the stretch degree of the alkane molecule declines with the increase of the chain length of alkanes. These two factors are considered as the essence determining the changing of the dispersion interaction with chain length.