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Water/hydrogen/hexane multicomponent selectivity of thin MFI membranes with different Si/Al ratios
Catalysis Research Centre, University of Cape Town.
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2008 (English)In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 108, no 1-3, p. 136-142Article in journal (Refereed) Published
Abstract [en]

MFI films with a thickness of about 550 nm were prepared on α-alumina substrates. The surface Si/Al ratios (XPS) were 157 and 62 for silicalite-1 and ZSM-5 films, respectively, and in accordance, XRD data indicated lower ratios for ZSM-5 films. Higher ratios were observed by ICP-AES for crystals grown in the bulk of the synthesis mixtures. Six membranes of each type were prepared. Porosimetry measurements showed that all membranes were of high and similar quality. Single gas permeances for H2, N2, He, CO2 and SF6 at 25 °C were very similar within each type of membranes. However, the average hydrogen permeance was 27% lower and the average H2/SF6 single gas permeance ratio was 67% higher for ZSM-5 membranes. These differences are attributed to a narrower effective pore diameter for the ZSM-5 membranes due to the sodium counter ions. Separation of mixtures of H2O, H2 and n-hexane (helium balance) was investigated in the temperature range 25-350 °C. The highest separation factors α-H2O/H2 were observed at 25 °C and were 14.3 and 19.7 for silicalite-1 and ZSM-5, respectively. The membranes were selective also at 100 °C and the separation factors were about 3.2 and 6 for silicalite-1 and ZSM-5, respectively. However, the selectivity decreased at elevated temperatures and the separation factor approached 1 at temperatures above 180 °C for both membrane types. The observed water selectivity was attributed to weak adsorption of water on polar sites. A low (1.5-3) α-H2O/n-C6 separation factor was observed for both membrane types for the entire investigated temperature range.

Place, publisher, year, edition, pages
2008. Vol. 108, no 1-3, p. 136-142
National Category
Chemical Process Engineering
Research subject
Chemical Technology
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URN: urn:nbn:se:ltu:diva-6240DOI: 10.1016/j.micromeso.2007.04.002ISI: 000252529400016Scopus ID: 2-s2.0-36849074262Local ID: 4707d100-a7eb-11dc-9534-000ea68e967bOAI: oai:DiVA.org:ltu-6240DiVA, id: diva2:979117
Note
Validerad; 2008; 20071211 (linste)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved

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Lindmark, JonasAndersson, CharlotteHedlund, Jonas

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