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

Abstract

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.

Hierarchical Nanomanufacturing: From Shaped Zeolite Nanoparticles to High‐Performance Separation Membranes

“…Furthermore, an industrial standard for producing highpurity p-xylene involves catalytic isomerization with product recycle because of thermodynamic equilibrium (24.8 % p-, 53.4 % m-, and 21.8 % o-xylene at 377 8C) [129] limitations. As such, an unprecedented opportunity exists for an MFI membrane reactor capable of selective removal of p-xylene during the reaction to shift the equilibrium and overcome thermodynamic limitations of the isomerization to attain higher yields of p-xylene, all within a compact unit design.…”

Intensification of Paraxylene Production using a Simulated Moving Bed Reactor

“…The chosen equilibrium thermodynamic data found in the literature (Chirico and Steele, 1997) are presented in Table 1 at 250°C and 300°C.…”

“…This analytical model gives PX, OX and MX concentrations knowing the whsv, the temperature and the inlet concentrations. This model uses equilibrium parameters given by Chirico and Steele (1997).…”

Hierarchische Nanofertigung: von geformten Zeolithnanopartikeln zu hochleistungsfähigen Trennmembranen

“…Aufgrund des thermodynamischen Gleichgewichts (24.8 % p-, 53.4 % m-und 21.8 % o-Xylol bei 377 8C) [129] umfasst das industrielle Standardverfahren zur Herstellung von hochreinem p-Xylol außerdem die katalytische Isomerisierung mit Produktrezyklierung. Hier bietet sich die besondere Möglichkeit, durch Verwendung eines MFI-Membranreaktors das p-Xylol während der Reaktion selektiv zu entfernen, sodass das Gleichgewicht verschoben wird und die thermodynamischen Randbedingungen der Isomerisierung aufgehoben werden.…”