Abstract
The phase behavior (PβTβx) of propylene carbonate was studied using a variable volume view cell for the regions applicable to supercritical fluid chromatography (SFC) and extraction (SFE). Type 5 phase behavior was observed. Phase separation was shown to significantly alter retention and selectivity in the analysis of coal extracts by capillary SFC. Propylene carbonate was found to have limited use as a modifier in capillary SFC. With 5.1 mol% propylene carbonate at 60Β°C, a single phase is maintained only at pressures above 250 atm.
Twentyβtwo methods used to estimate critical pressure (P~c~), twentyβseven methods used to estimate critical temperature (T~c~), and thirty methods used to estimate critical volume (V~c~) were evaluated for various modifiers employed in supercritical fluid chromatography (SFC). None of the methods could predict P~c~, T~c~, or V~c~ to within a 5% relative error for all of the modifiers tested. However, several of the methods were successful in predicting P~c~, T~c~, or V~c~ to within 5% for select chemical classes of compounds.
Four methods used to estimate the vaporβliquid critical loci of binary mixtures not only failed to accurately predict vaporβliquid separation, but failed to predict the type of phase separation occurring. None of the above methods could reliably estimate the critrical parameters of propylene carbonate or the critical parameters of the mixture.