Prediction of activity coefficients in low-molecular-weight paraffins fromgas chromatographic data

It is shown that gas-liquid partition coefficients measured by gas chromato graphy on nonvolatile paraffin stationary. phases at high temperatures allo w estimation of gas-liquid partition coefficients of solutes at ambient tem peratures in volatile alkanes as solvents. Extrapolation to low temperature s was successful by use of the Kirchhoff equation for the description of th e temperature dependence of the standard chemical potential of the solute r elated to its molal Henry coefficient. A new equation is proposed for the p rediction. of partition data in low-molecular-weight paraffins. It was deri ved by using the Flory-Huggins model as a guide, and it combines theory wit h experiment. It is proposed to accept a combinatorial entropy term determi ned by experiment as a solute property. The necessary experimental informat ion consists of a set of gas chromatographic data measured at at least four temperatures on two pure, high-molecular-weight, paraffins. Molal Henry co efficients extrapolated to low-molecular-weight solvents allowed calculatio n of activity coefficients. Predicted and measured data agreed within +/- 2 0%. The reproducibility of activity coefficients by classical experimental methods is of the same order of magnitude.