P, o-Xylene

The zeolites and catalysts used in this study were prepared as described previously (1,16,18,20). The ortho-xylene sorption rate data, obtained on a computer-controlled Du Pont 951 TGA, were measured at 120°C and P(o-xylene) 3.8 torr. The isomerization and disproportionation data were obtained using a... 

In another study (Pandit, Srivastava and Rao, 2001), the use of kerosene stoves has increased the concentrations of n-hexane, benzene, heptane, toluene, p-/o-xylene and n-decane in indoors significantly above those in the outdoors. For example, the ratios of indoor/outdoor benzene, heptane and decane ranged from 3.3 to 11.6. 

Among the alkylbenzenes, the stereospecific effect of liquid crystals is most marked in the separation of m- and p-xylene. The more linear p-xylene exhibiting a greater retention than the m-isomer (similar retention observed on a- and (3-CD). The retention order on the liquid crystals, m-< p-different from that on common polar and nonpolar stationary phases (p-< m-< o-isomer). In contrast to liquid crystals, o-xy-lene exhibited the lowest retention on a-CD. 

Schleiffelder M and Claudia SB. Crosslinkable copolyimides for the memhrane-based separation of p-/o-xylene mixtures. React Funct Polym 2001 49 205-213. 

The separation behaviour of a p/o xylene mixture is given in Fig. 9.30. The permeation of the paraxylene is much larger than that of the o-xylene at higher temperature, the last one has a permeation which is at the detection limit of the equipment used. The molecule has a diameter which is larger than that of the pore diameter of the MFI and so we have here an example of separation by size exclusion. The flux of p-xylene shows a weak maximum as a /(T) and consequently the separation factor does the same with a peak value of a = 100 at =400 K under the given conditions. The separation factors and the permselec-tivities are equal as expected for the size exclusion mechanism. 

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. 

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