Chemistry Reference
In-Depth Information
Fig. 12 A typical gas chromatogram of the reactor e
uent from the MTH reaction over
BEA zeolite at 78% conversion.
Fig. 13 Cross section of the largest pore vs. kinetic diameter of largest product. Cross
sections are calculated assuming a perfectly elliptical pore whose axes are the largest and
smallest diameters. This is not entirely correct for all materials. The kinetic diameters were
found in refs. 163-166.
Figure 12 nicely illustrates the complexity of the MTH product mixture
and the need for selectivity-enhancing catalysts. In the following, only
main products and product groups will be considered.
3.4.1 Product shape selectivity. The channel dimensions of a number
of zeolite catalysts were described in Table 3. Figure 13 shows a plot of
the kinetic diameter of the largest product formed in appreciable
amounts (W4% yield, thereby omitting products likely to be formed on
the outer zeolite surface) in the MTH reaction over each of those ma-
terials versus the cross-sectional area of their largest channel. A general,
direct correlation between these two parameters is observed, which
demonstrates that proper selection of channel diameter gives a distinct
cut-off in the euent product distribution. As may be seen, products
diffusing out of 8-ring channels are limited to linear alkenes, while the
