(293b) Measurement of Infinite Dilution Activity Coefficients of Alkanes in Ionic Liquid Using Gas-Liquid Chromatography

The infinite dilution activity coefficients of octane, nonane and decane in 4-methyl-n-butylpyridinium tetrafluoroborate (C₁₀H₁₆BF₄N, MW=237.05) were measured by gas-liquid chromatography (GC) using the ionic liquid as stationary phase. Chromosorb W AW DMCS (mesh 100/120) was used as the support material for the ionic liquid in the GC column. Helium was used as carrier gas. The hydrocarbons were injected into the GC with air. The retention times were measured by a thermal conductivity detector. According to Cruickshank et al., the infinite dilution activity coefficients are derived from the standardized retention volumes obtained by the retention times. The measurements were carried out at several temperatures between 305 and 345 K. The retention times were affected by the volumes of the samples injected into the GC. The sample volumes were adjusted to be less than 0.5x10^-6 L, in which region the retention times were independent of the sample sizes, to keep the condition of infinite dilution. The infinite dilution activity coefficients were also affected by the flow rate of carrier gas. The infinite dilution activity coefficients were determined by extrapolating the flow rate of carrier gas to zero. The infinite dilution activity coefficients determined in this work somewhat are larger than those of the literature values because the effect of flow rate of carrier gas is not considered in the literature. The experimental results were correlated by using the ASOG which is one of the successful group contribution activity coefficient models. The group interaction parameters were determined by using the Complex method to minimize the deviation between the experimental and calculated values. The correlated results are in good agreement with the experimental results.