| Research Abstract |
Measurement apparatus of infinite dilution activity coefficients based on a gas stripping chromatography method have developed. The measurement system consists of a Helium gas cylinder for stripping gas, an equilibrium cell made by Pyrex grass in a temperature controlled water bath, and gas chromatograph for determination of composition. The stripping gas flows through the flow controller into the solvent saturation cell. The cell was filled with solvent. The fritted glass tip in the cell has a pore diameter in the range of 4-8 μm, e.g. the G2 glass filter. The solution is stirred with a magnetic stirrer to help mixing and mass transfer.
An effective test of equilibrium assumption is to change the flow rate of stripping gas and see whether we get a constant value of infinite dilution activity coefficient for a given system using the developed apparatus based on a gas stripping method. The infinite dilution activity coefficient of Hexane in Hexadecane of solvent was measured at 303.15 K. The literature value of this system is very accurately known. The experimental value of infinite dilution activity coefficient is 0.831 in this work. The data is good agreement with the literature value and well reproducibility.
The prediction methods of infinite dilution activity coefficient base on the group contribution method, e.g. original UNIFAC, several kind of modified UNIFAC, and ASOG have proposed. A new approach is proposed by introducing mixture type groups to the modified universal functional activity coefficient model for prediction of infinite dilution activity coefficients in highly nonideal aqueous solution.
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