January 2020

Process Optimization

A new liquid-phase isomerization process for xylene loop debottleneck and energy savings

In a typical xylene loop, C8 aromatics are fractionated out of a heavy reformate C8+ aromatics stream and collected in the xylene column overhead. Then, paraxylene (PX) from the C8 aromatics stream is recovered as product—usually by an adsorption or crystallization process—in the PX recovery section.

Mhatre, S., Warke, V., Reliance Industries Ltd.; Choi, A., Molinier, M., Saple, A., ExxonMobil Chemical Co.

In a typical xylene loop, C8 aromatics are fractionated out of a heavy reformate C8+ aromatics stream and collected in the xylene column overhead. Then, paraxylene (PX) from the C8 aromatics stream is recovered as product—usually by an adsorption or crystallization process—in the PX recovery section. The remaining PX-depleted C8 aromatics stream is processed in a vapor phase isomerization (VPI) unit, where ethylbenzene (EB) is converted to benzene and PX-depleted xylenes are isomerized to equilibrium xylenes. VPI invariably yields traces of C9 and C10 aromatics due to undesirable side reactions—hence, the VPI C8+ aromatics effluent is returned to the xylene column for fractionation. C8 aroma

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