Thermodynamic Equilibria in Xylene Isomerization. 5. Xylene Isomerization Equilibria from Thermodynamic Studies and Reconciliation of Calculated and Experimental Product Distributions

Thermodynamic equilibria calculations based upon new calorimetric and physical-property measurements published in the first four papers of this series corroborate the assertion by Amelse (1993) that the existing thermodynamic data are in error. The largest errors are associated with the entropy of o -xylene in the liquid and gas states. New equilibria calculations described here are in excellent accord (within 0.7%) with product distributions determined experimentally by Amelse (1993). Deviations derived with previously available thermodynamic property compilations are three to four times larger. Statistical analysis shows that the uncertainties in the product distribution percentages derived from the thermodynamic measurements are approximately 2. 5 % for m -xylene, 2. 0 % for p -xylene, and 1. 5 % for o -xylene under typical processing conditions. Equations are provided for the calculation of equilibrium product distributions for xylene isomerization for all temperatures above T = 250 K. Claims in the scientific and patent literature of isomerizations to p -xylene concentrations in excess of equilibrium are shown to be the result of errors in the thermodynamic literature and overstatement of the precision of the thermodynamic calculations. Literature compilations of thermodynamic functions for the xylenes and ethylbenzene are compared with those of this research. Origins of differences are discussed.