Characterization of the coke formed from o-xylene over mordenites at different pressures under N 2 and H 2

Abstract

The influence of the carrier gas (H 2 or N 2), at different pressures, on coking over two mordenite samples during o-xylene transformation was evaluated at 623 K. The results showed that the carrier gas has a significant effect on the amount and on the composition of the coke formed. For the two samples used, coke formed in the presence of H 2 consisted mainly of CH 2Cl 2 soluble molecules, while under N 2 the formation of insoluble coke was favoured. Whatever the carrier gas or the total pressure, the same families of compounds were identified in the soluble fraction, the main ones being C n H 2 n−28 , C n H 2 n−22 and C n H 2 n−16 . For the sample strongly dealuminated, increasing the pressure decreased the coke build up under H 2, confirming the inhibition effect of H 2 on coke formation, but an opposite effect was observed under N 2. Due to its mesoporous system, this sample has a rather stable activity whatever the carrier gas. For the sample with a high density of acid sites, the limiting quantity of coke was rapidly attained, deactivation was relatively fast and poisoning by coke was greater under N 2. A relatively small amount of coke render it inactive indicating that deactivation is due to pore mouth blockage.