Houndonougbo Yao, Laird Brian B, Kuczera Krzysztof
Center for Environmentally Beneficial Catalysis, Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, USA.
J Chem Phys. 2007 Feb 21;126(7):074507. doi: 10.1063/1.2434968.
Carbon-dioxide-expanded liquids, which are mixtures of organic liquids and compressed CO2, are novel media used in chemical processing. The authors present a molecular simulation study of the transport properties of liquid mixtures formed by acetonitrile and carbon dioxide, in which the CO2 mole fraction is adjusted by changing the pressure, at a constant temperature of 298 K. They report values of translational diffusion coefficients, rotational correlation times, and shear viscosities of the liquids as function of CO2 mole fraction. The simulation results are in good agreement with the available experimental data for the pure components and provide interesting insights into the largely unknown properties of the mixtures, which are being recognized as important novel materials in chemical operations. We find that the calculated quantities exhibit smooth variation with composition that may be represented by simple model equations. The translational and rotational diffusion rates increase with CO2 mole fraction for both the acetonitrile and carbon dioxide components. The shear viscosity decreases with increasing amount of CO2, varying smoothly between the values of pure acetonitrile and pure carbon dioxide. Our results show that adjusting the amount of CO2 in the mixture allows the variation of transport rates by a factor of 3-4 and liquid viscosity by a factor of 8. Thus, the physical properties of the mixture may be tailored to the desired range by changes in the operating conditions of temperature and pressure.
二氧化碳膨胀液体是有机液体和压缩二氧化碳的混合物，是化学加工中使用的新型介质。作者对乙腈和二氧化碳形成的液体混合物的传输性质进行了分子模拟研究，其中在298K的恒定温度下，通过改变压力来调节二氧化碳的摩尔分数。他们报告了液体的平动扩散系数、旋转相关时间和剪切粘度随二氧化碳摩尔分数的变化值。模拟结果与纯组分的现有实验数据吻合良好，并为混合物中很大程度上未知的性质提供了有趣的见解，这些混合物正被视为化学操作中的重要新型材料。我们发现，计算出的量随组成呈平滑变化，可用简单的模型方程表示。乙腈和二氧化碳组分的平动和旋转扩散速率均随二氧化碳摩尔分数的增加而增加。剪切粘度随二氧化碳含量的增加而降低，在纯乙腈和纯二氧化碳的值之间平滑变化。我们的结果表明，调节混合物中二氧化碳的量可使传输速率变化3至4倍，液体粘度变化8倍。因此，通过改变温度和压力的操作条件，可以将混合物的物理性质调整到所需范围。
