Conversion of Methanol on Other Medium-pore Zeolites

Conversion of Methanol on Other Medium-pore Zeolites. - Much less attention has been paid to the other end-member of the pentasil-series ZSM-11, probably because it was soon recognized that the shape-selective properties of ZSM-5 were superior to those of ZSM-11. 3 

In the conversion of methanol to gasoline on ZSM-11, much less Ci-Cj products are observed than with ZSM5 while the Cg -aliphatics are more abundant. Whereas on ZSM-5 the aromatics fraction is mainly composed of xylenes, on ZSM-11 more aromatics are produced. Harrison et al. defined in this context product selectivity as the ratio of xylenes to trimethylbenzenes. The ratio varied from 2.5 to 0.5 for the conversion of methanol on ZSM-5 and ZSM-11, respectively. The difference in shape selectivity was also illustrated by the (m+p) o-xylene ratio, which was 13 on HZSM-5 but only 3 on HZSM-11. This was attributed to the relative dimensions of the channel intersections, 50% of which are 30% larger in ZSM-11, and to the difference in relative length of the straight (ZSM-5, ZSM-11) and tortuous channels (ZSM-5). Furthermore, since ZSM-11 contains only one type of channel, the molecular traffic control shape selectivity should, in principle, not occur in this catalyst. This provides a possible explanation for the higher yield of polysubstituted aromatics methanol reactant and aromatic products cannot avoid counterdiffusion as in ZSM-5 and this increases the probability of alkylation of the aromatics. 

Chang et al. claimed the use of another high-silica medium- 

It is clear that the 02-04 olefin s selectivity on both catalysts is comparable (38.1 wt% and 40.2 wt% for HZSM-48 and HZSM-5, respectively). The major difference is to be found in the production of higher molecular weight olefins, which is apparently significantly higher on HZSM-48, as already concluded by Ohang et ai.i65 Fewer aromatics are produced on HZSM-48 (5.7 vs. 13.7 wt%). The high yield of paraffins in conjunction with the low yield of aromatics is indicative of severe coke laydown. Indeed, the deactivation of ZSM-48 with its one-dimensional pore-structure was much faster than that of ZSM-5. 

Zeolite EU-2, developed by Casci et al.,is another medium-pore high-silica zeolite. When synthesized with a Si/Al-ratio of at least 120, ZSM-48 is isostructural with Zeolite EU-2 . A high selectivity toward propylene and butene and a low selectivity toward aromatics were reported in the conversion of methanol on Zeolite EU-2.166 

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