TOLUENE DISPROPORTIONATION OVER ZSM-5 ZEOLITE - EFFECTS OF CRYSTAL SIZE, SILICON-TO-ALUMINUM RATIO, ACTIVATION METHOD AND PELLETIZATION

The catalytic activity and selectivity of ZSM-5 zeolite in toluene disproportionation were studied as a function of crystal size, silicon-to-aluminum ratio, acidity, activation method and pelletization of zeolite. Although para-xylene formation was slightly favoured by increasing the crystal size, high para-selectivity was not achieved. At the lowest silicon-to-aluminum ratio, catalytic activity was enhanced with a drop on the selectivity to disproportionation, suggesting the presence of "super acid sites" related with extra lattice aluminum species. From IR spectroscopy measurements with adsorption/desorption of pyridine it was observed that during the activation step, a high H+ concentration in the cation exchange increases the strength of Bronsted sites, increasing the number of acid sites which are active in toluene disproportionation. Subsequent calcination completes zeolite activation, increasing the number of Bronsted acid sites active in that reaction. In the pelletization there is a cation exchange between Na+ from the montmorillonite and H+ from the zeolite when both are mixed and suspended in water. Nevertheless, sodium montmorillonite proved to be a suitable binder of ZSM-5 provided that the catalysts are reactivated after pelletization.