石油学会誌 Sekiyu Gakkaishi, 35, (2), 185-189 (1992) 185 [Regular Paper] stream of velocities of disproportionation and side reactions are in the following ascending order; disproportionation<isomerization<dealkylation. This relationship brought about the constant yield of p-xylene, which is maintained for more than 160h, as shown above. The sites for these three reactions are likely to be different in nature from one another, since the velocities of these reactions decreased at different rates during a prolonged run.