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High-flux ZSM-5 membranes with an additional non-zeolite pore system by alcohol addition to the synthesis batch and their evaluation in the 1-butene/i-butene separation
Ist Teil von
Separation and purification technology, 2010-05, Vol.72 (3), p.388-394
Ort / Verlag
Kidlington: Elsevier B.V
Erscheinungsjahr
2010
Link zum Volltext
Quelle
Elsevier ScienceDirect Journals Complete
Beschreibungen/Notizen
ZSM-5 membranes were crystallized on tubular TiO
2 supports and evaluated in the permeation of a 50%/50% 1-butene/i-butene mixture. If some of the water in the standard recipe 90 SiO
2:0.225 Al
2O
3:1 Na
2O:3.6 TPAOH:1.8 TPABr:1800 H
2O was substituted by the same molar amount of short-chain length alcohol, the fluxes and permeances increased remarkably but the 1-butene/i-butene shape selectivity decreased only slightly. This experimental finding is attributed to additional non-zeolite micropores which are formed by the presence of alcohols in the synthesis batch. Since the formation of this additional pore system is linked to a decrease of the crystal size in the membrane layer, the increased length of grain boundaries could represent the structural origin of these additional non-zeolite pores. In a membrane preparation if 25% of the molar amount of water was substituted by ethanol, the 1-butene flux increased by the factor of two, but the mixture separation factor decreased by only 30%. Therefore, relatively thick ZSM-5 layers of about 30
μm gave 1-butene permeances of the order of 1
m
3(STP)
m
−2
h
−1
bar
−1 with permselectivities of 20 and mixture separation factor of 6. The testing of the ZSM-5 membranes took place under practice-relevant conditions, i.e. with undiluted feeds and without applying sweep gases or reduced pressure on the permeate side.