Defining effective microporosity in carbon molecular sieves
A pseudo equilibrium method is described for establishing the micropore distribution in carbon molecular sieves (CMS) having micropore sizes below 6 Å. The method uses a series of carefully selected molecular probes varying in their minimum Van der Waals diameter between 3.7 and 6.0 Å. Various small...
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Published in | Microporous materials Vol. 2; no. 4; pp. 229 - 236 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
Elsevier B.V
01.05.1994
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Subjects | |
Online Access | Get full text |
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Summary: | A pseudo equilibrium method is described for establishing the micropore distribution in carbon molecular sieves (CMS) having micropore sizes below 6 Å. The method uses a series of carefully selected molecular probes varying in their minimum Van der Waals diameter between 3.7 and 6.0 Å. Various small-pore zeolites were used to validate the method. Over the critical micropore size range these probes can establish the “effective” microporosity which can be modified by post-treatment to produce an O
2-selective CMS useful for air separation. This method coupled with kinetic measurements of O
2 and N
2 uptake indicates that pores larger than 4 Å are not highly O
2-selective. Results from these molecular probe studies in combination with porosimetry and pycnometry measurements show that the O
2-selective carbons have an unusual bimodal pore distribution with no significant mesoporosity. We found obtaining pore distributions from equilibrium analysis of N
2 or O
2 isotherms at cryogenic conditions was inappropriate on these carbons. The study clearly demonstrates the importance of the method which monitors the size and relative amounts of micropores which are O
2-selective. |
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ISSN: | 0927-6513 1873-3107 |
DOI: | 10.1016/0927-6513(93)E0057-N |