Selective Toluene Disproportionation to produce para-Xylene over Modified ZSM-5

Industrial demand for p-xylene has been increasing in recent years and the major production is by toluene disproportionation. This research studied the effect of crystal size and the modification by silica deposition on the surface of the zeolite. Shape selective catalysts have been prepared by modifying two different ZSM-5 zeolites with different crystal sizes (0.5 µm, 5 µm) by chemical liquid deposition (CLD) using TEOS (tetraethyl orthosilicate) to deposit inert silica layers. The large ZSM-5 crystals modified with two cycles of silica showed high p-xylene selectivity at typically 84 % with very low conversion. Pressure effect on the reaction was investigated. Selectivity achieved was 40 – 66 % at conversions typically 4-20 % at 10 bar.