Methanol Usage in Toluene Methylation with Medium and Large Pore Zeolites

The reaction of toluene methylation was investigated with four acidic zeolites of different pore geometries: the medium poke zeolites H-ZSM5 and H-ZSM11 as well as the large pore zeolites H-MOR, and H-BEA. The methylation, Methanol comsumption, light hydrocarbon formation and disproportionation rates for the,reaction of toluene, p-xylene, and 1,2,4-trimethylbenezene with methanol determined: The products of toluene methylation;(e.g. xylenes, and trimethlbenzenes) were readily Methylated further in both, medium and large pore zeolites. A considerably higher fraction of methanol was used to form light hydrocarbons with the medium pore zeolites than with large pore zeolites. This was related to the fact that the dealkylation of light hydrocarbons from highly methylated aromatics became more favorable relative to methylation at an earlier stage, that is, after fewer methyl groups were added to the aromatic ring. Increasing the effective residence time of bulky aromatic molecules with medium pore zeolites, modified either by coating the surface with tetraethyl orthosilicate or by increasing the intracrystal pore length, converted a larger fraction of methanol to light hydrocarbons via methylation and subsequent dealkylation of light hydrocarbons.