TY - JOUR

T1 - Effect of crystal intergrowth supporting substances (ISS) on the permeation properties of MFI membranes with enhanced Al-content

AU - Noack, M.

AU - Kölsch, P.

AU - Dittmar, A.

AU - Stöhr, M.

AU - Georgi, G.

AU - Eckelt, R.

AU - Caro, J.

PY - 2006/12/29

Y1 - 2006/12/29

N2 - The most frequently prepared molecular sieve membrane is the Al-free MFI type (silicalite 1) which shows high separation factors and a negligible intercrystalline defect permeance. By introduction of Al into the MFI lattice (ZSM-5) the hydrophilicity and the acid sites concentration increase and the adsorption properties are changed. However, for ZSM-5 membranes with increasing Al-content the intercrystalline defect transport is enhanced and, therefore, the selectivity decreases. Searching for the reasons for this behaviour, an increase of the negative surface charge (zeta-potential) of ZSM-5 crystals with enhanced Al-content is found. Since the MFI precursors in the synthesis solution are negatively charged like the growing ZSM-5 layer, it is assumed that a hindered transport and attachment of the precursors to the equally charged crystal surfaces could cause the poor intergrowth of the ZSM-5 crystals to a continuous tight membrane layer. By use of Intergrowth Supporting Substances (ISS) the crystal surface is re-charged and the crystal intergrowth is improved. Suitable ISS are small positively charged molecules, stable in the alkaline region during the synthesis at 180 °C and which can be decomposed by calcination. In this work the effect of different ISS on the permeation properties of ZSM-5 membranes with various Al-content is shown. The membranes are characterized by XRD, SEM, permporosimetry and single gas permeation.

AB - The most frequently prepared molecular sieve membrane is the Al-free MFI type (silicalite 1) which shows high separation factors and a negligible intercrystalline defect permeance. By introduction of Al into the MFI lattice (ZSM-5) the hydrophilicity and the acid sites concentration increase and the adsorption properties are changed. However, for ZSM-5 membranes with increasing Al-content the intercrystalline defect transport is enhanced and, therefore, the selectivity decreases. Searching for the reasons for this behaviour, an increase of the negative surface charge (zeta-potential) of ZSM-5 crystals with enhanced Al-content is found. Since the MFI precursors in the synthesis solution are negatively charged like the growing ZSM-5 layer, it is assumed that a hindered transport and attachment of the precursors to the equally charged crystal surfaces could cause the poor intergrowth of the ZSM-5 crystals to a continuous tight membrane layer. By use of Intergrowth Supporting Substances (ISS) the crystal surface is re-charged and the crystal intergrowth is improved. Suitable ISS are small positively charged molecules, stable in the alkaline region during the synthesis at 180 °C and which can be decomposed by calcination. In this work the effect of different ISS on the permeation properties of ZSM-5 membranes with various Al-content is shown. The membranes are characterized by XRD, SEM, permporosimetry and single gas permeation.

KW - Influence of ISS

KW - Permeation properties

KW - Si/Al-variation

KW - Zeta-potential

KW - ZSM-5 membranes

UR - http://www.scopus.com/inward/record.url?scp=33751343443&partnerID=8YFLogxK

U2 - 10.1016/j.micromeso.2006.07.031

DO - 10.1016/j.micromeso.2006.07.031

M3 - Article

AN - SCOPUS:33751343443

VL - 97

SP - 88

EP - 96

JO - Microporous and Mesoporous Materials

JF - Microporous and Mesoporous Materials

SN - 1387-1811

IS - 1-3

ER -