CHARACTERIZATION OF THE COKE FORMED FROM O-XYLENE OVER MORDENITES AT DIFFERENT PRESSURES UNDER N-2 AND H-2

The influence of the carrier gas (H-2 or N-2), at different pressures, on coking over two mordenite samples during o-xylene transformation w as evaluated at 623 K. The results showed that the carrier gas has a s ignificant effect on the amount and on the composition of the coke for med. For the two samples used, coke formed in the presence of H-2 cons isted mainly of CH2Cl2 soluble molecules, while under N-2 the formatio n of insoluble coke was favoured. Whatever the carrier gas or the tota l pressure, the same families of compounds were identified in the solu ble fraction, the main ones being CnH2n-28, CnH2n-22 and CnH2n-16. For the sample strongly dealuminated, increasing the pressure decreased t he 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 whate ver 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 relativ ely small amount of coke render it inactive indicating that deactivati on is due to pore mouth blockage. (C) 1998 Elsevier Science B.V.