THERMODYNAMIC EQUILIBRIA IN XYLENE ISOMERIZATION .2. THE THERMODYNAMIC PROPERTIES OF M-XYLENE

Measurements leading to the calculation of the ideal-gas thermodynamic properties for m-xylene are reported. Experimental methods included a diabatic heat-capacity calorimetry (5 K to 430 K), vibrating-tube dens itometry (323 K to 523 K), comparative ebulliometry (309 K to 453 K), and differential-scanning calorimetry (DSC). The critical temperature was measured by DSC. Saturation heat capacities for the liquid phase b etween 430 K and 550 K and the critical pressure were derived with the vapor-pressure and DSC results. Results were combined with an enthalp y of combustion reported in the Literature to derive standard molar en tropies, enthalpies, and Gibbs free energies of formation at selected temperatures between 250 K and 550 K. The standard state is defined as the ideal gas at the pressure p=p(o)=101.325 kPa. Standard entropies are compared with those calculated statistically on the basis of assig ned vibrational spectra for the vapor phase. Al results are compared w ith literature values.