2 MFI Zeolites: ZSM-5 and Silicalite-1
2.1 Structure and Selectivity
Silicalite-1 was one of the first all-silica zeolites to have been synthesized [137] and
almost immediately identified as a promising material for bioethanol and biobutanol
recovery via adsorption [103, 138]. Silicalite-1 is a member of the MFI framework
family and a structural analogue of ZSM-5. MFI zeolites have a channel-type pore
structure, with ten-membered ring pore openings [135, 139]. Two different channels
exist in the structure, which are perpendicular to each other (Fig. 3a). The straight
channels have the biggest size (5.6 Å Â 5.4 Å) and run in the [010] crystallographic
direction. The other channels present in the structure are sinusoidal and run along the
Fig. 2 Vapor adsorption isotherms of ethanol, n-butanol, and water on all-silica LTA (ITQ-29 –
(a), all-silica chabazite (b) and silicalite-1 (c). ITQ-29 and CHA isotherms are at 40
C [59], while
the vapor isotherms on silicalite-1 are at 27
C (ethanol/water) [117] and 35
C (n-butanol)
[136]. Due to diffusional limitations, the n-butanol isotherm on the CHA zeolite is not in complete
equilibrium
Fig. 3 (a) View along the straight channels of MFI zeolites. (b) View along the sinusoidal channels
of MFI zeolites. Structure images were obtained using the drawing tool available on the website of
the International Zeolite Structure Database [140]
90
B. Claessens et al.
2.1 Structure and Selectivity
Silicalite-1 was one of the first all-silica zeolites to have been synthesized [137] and
almost immediately identified as a promising material for bioethanol and biobutanol
recovery via adsorption [103, 138]. Silicalite-1 is a member of the MFI framework
family and a structural analogue of ZSM-5. MFI zeolites have a channel-type pore
structure, with ten-membered ring pore openings [135, 139]. Two different channels
exist in the structure, which are perpendicular to each other (Fig. 3a). The straight
channels have the biggest size (5.6 Å Â 5.4 Å) and run in the [010] crystallographic
direction. The other channels present in the structure are sinusoidal and run along the
Fig. 2 Vapor adsorption isotherms of ethanol, n-butanol, and water on all-silica LTA (ITQ-29 –
(a), all-silica chabazite (b) and silicalite-1 (c). ITQ-29 and CHA isotherms are at 40
C [59], while
the vapor isotherms on silicalite-1 are at 27
C (ethanol/water) [117] and 35
C (n-butanol)
[136]. Due to diffusional limitations, the n-butanol isotherm on the CHA zeolite is not in complete
equilibrium
Fig. 3 (a) View along the straight channels of MFI zeolites. (b) View along the sinusoidal channels
of MFI zeolites. Structure images were obtained using the drawing tool available on the website of
the International Zeolite Structure Database [140]
90
B. Claessens et al.