Carbon dioxide expanded liquids, which are mixtures of organic liquids and compressed CO2, are novel media used in chemical processing. We 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. We report values of translational diffusion coefficients, rotational correlationtimes and shear viscosities of the liquids as function of CO2 mole fraction. The simulation results are 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 compositionthat 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.

Acetonitrile:CO2 mixture at mole fraction x=0.5	Translational diffusion of CO2 component in acetonitrile:CO2 mixtures

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