(20c) Emerging Technology for p-Xylene Production

p-Xylene is a valuable aromatic compound because of its great demand for its oxidation to terephthalic acid, a major component in forming polyester fibers and resins.  It is usually recovered from mixed–xylene streams of various sources, e.g., naphtha reformate and pyrolysis gasoline.  Toluene is also commercially converted to equimolar amounts of mixed-xylene and benzene by disproportionation reaction. Efforts have been made to develop a new technology to convert toluene by reacting with methanol producing mixed-xylene with p-xylene significantly higher than equilibrium concentration. 

SABIC has developed a phosphorus (P) modified ZSM-5 catalyst for toluene alkylation with methanol for p-xylene production.  The P-modified ZSM-5 zeolite was formed into shaped catalyst by extruding with Al₂O₃.  The formed catalyst has 7.0-9.0 wt. % P, BET SA 220-250 m²/g, and a total pore volume of 0.15-0.19 ml/g.  The catalyst has shown to provide shape selectivity giving ≥85% p-xylene selectivity.  The catalyst was scaled-up to semi-commercial scale.  Using the scaled-up catalyst the toluene methylation technology was demonstrated in a bench unit having multiple reactors in series capable of staging methanol to each of the reactor inlets.  The catalyst has been shown to give stable performance more than 18 months under different reaction conditions with over 20 regenerations.

The present talk will discuss toluene methylation technology, catalyst formation, catalytic performance and regeneration.