Paper #2
Thermodynamic Equilibrium of Xylene Isomerization
in the Liquid Phase
. Rodrigues
LSRE-Laboratory of Separation and Reaction Engineering, Departamento de Engenharia
Química, Faculdade de Engenharia, Universidade do Porto
Description of the problem
Xylenes are aromatic hydrocarbons used as raw material for avariety of
every day products. The most important isp-xylene (PX), which is produced based on two main operations, isomerization and separation. The isomerization reaction is limited by the thermodynamic equilibrium which results in a large recycle loop to achieve the desired amount of p-xylene. Because of the direct influence of the thermodynamic equilibrium in the process, accurate equilibrium values are of the most importance.
Unfortunately, the aforementioned studies presented expressions for the
equilibrium constants as a function of temperature only for the gas phase; this was probably due to the fact that xylene isomerization occurs industrially under gas phase conditions. However, in the past few years new trends in xylene production have focused on the use of xylene isomerization in the liquid phase driven by the environmental benefits of reduction of energy and pollution. Namely, the isomerization is separated in two stages: one in the liquid phase for xylenes and one in the gas phase for ethylbenzene. Moreover, research efforts are being made on process intensification by coupling xylenes isomerization and xylenes separation (both in the liquid phase) in a single unit using the simulated moving bed reactor (SMBR) technology. Following these new approaches, this work is intended to develop similar expressions of the equilibrium for xylene isomerization in the liquid phase based on the thermodynamic functions at saturated conditions presented by Chirico and coworkers.