TY - JOUR
T1 - On defects in highly a-oriented MFI membranes
AU - Kim, Eunjoo
AU - Choi, Jungkyu
AU - Tsapatsis, Michael
N1 - Funding Information:
This work was supported by NSF ( CBET-0855863 ) and also by the Human Resources Development Program of KETEP Grant (No. 20114010203050 ) funded by the Korea Government Ministry of Knowledge Economy . Portions of this work were conducted at the University of Minnesota Characterization Facility, which receives partial support from the National Science Foundation through the NNIN program.
Copyright:
Copyright 2013 Elsevier B.V., All rights reserved.
PY - 2013
Y1 - 2013
N2 - Previously, uniformly a-oriented MFI films were synthesized via the secondary growth of an a-oriented seed layer, which was obtained by chemically depositing ∼2 μm thin-along-the-a-axis particles on a silica-coated α-Al2O3 porous disc (Choi et al., Angew. Chem. Int. Ed. 45 (2006) 1154-1158). Despite the uniformity of the a-orientation throughout the film, we found that the MFI membranes are not applicable for p-/o-xylene separation since they have significant crack and grain boundary defects. Accordingly, a-oriented MFI films were fabricated via alternative methods, motivated by the expected high separation performance that could be comparable to p-/o-xylene separations (100-400 separation factor) of a b-oriented MFI membrane. First, smaller 500 nm thin-along-the-a-axis MFI particles (small seeds) were used instead of 2 μm thin-along-the-a-axis particles (large seeds) for seed deposition. Second, a seed layer was formed by a sonication-assisted physical deposition of the large seeds. Finally, an a-oriented seed layer comprising of the large seeds was epitaxially-grown to be the a-oriented MFI film by conducting two consecutive hydrothermal growth processes. The separation performance of the resultant MFI membranes was investigated via n-/i-butane and p-/o-xylene permeation tests. Maximum separation factors (SF) of ∼4 and ∼17 were achieved for p-/o-xylene and n-/i-butane isomers, respectively. These values are below the expected performance, indicating the presence of non-zeolitic pathways in a-oriented films.
AB - Previously, uniformly a-oriented MFI films were synthesized via the secondary growth of an a-oriented seed layer, which was obtained by chemically depositing ∼2 μm thin-along-the-a-axis particles on a silica-coated α-Al2O3 porous disc (Choi et al., Angew. Chem. Int. Ed. 45 (2006) 1154-1158). Despite the uniformity of the a-orientation throughout the film, we found that the MFI membranes are not applicable for p-/o-xylene separation since they have significant crack and grain boundary defects. Accordingly, a-oriented MFI films were fabricated via alternative methods, motivated by the expected high separation performance that could be comparable to p-/o-xylene separations (100-400 separation factor) of a b-oriented MFI membrane. First, smaller 500 nm thin-along-the-a-axis MFI particles (small seeds) were used instead of 2 μm thin-along-the-a-axis particles (large seeds) for seed deposition. Second, a seed layer was formed by a sonication-assisted physical deposition of the large seeds. Finally, an a-oriented seed layer comprising of the large seeds was epitaxially-grown to be the a-oriented MFI film by conducting two consecutive hydrothermal growth processes. The separation performance of the resultant MFI membranes was investigated via n-/i-butane and p-/o-xylene permeation tests. Maximum separation factors (SF) of ∼4 and ∼17 were achieved for p-/o-xylene and n-/i-butane isomers, respectively. These values are below the expected performance, indicating the presence of non-zeolitic pathways in a-oriented films.
KW - Butane isomers
KW - Film orientation
KW - MFI (silicalite-1) membranes
KW - Secondary (seeded) growth
KW - Xylene isomers
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U2 - 10.1016/j.micromeso.2012.11.023
DO - 10.1016/j.micromeso.2012.11.023
M3 - Article
AN - SCOPUS:84871777573
VL - 170
SP - 1
EP - 8
JO - Microporous and Mesoporous Materials
JF - Microporous and Mesoporous Materials
SN - 1387-1811
ER -