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Issue 22, 2013
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Sieving di-branched from mono-branched and linear alkanes using ZIF-8: experimental proof and theoretical explanation

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Abstract

We study the adsorption equilibrium isotherms and differential heats of adsorption of hexane isomers on the zeolitic imidazolate framework ZIF-8. The studies are carried out at 373 K using a manometric set-up combined with a micro-calorimeter. We see that the Langmuir model describes well the isotherms for all four isomers (n-hexane, 2-methylpentane, 2,2-dimethylbutane and 2,3-dimethylbutane). The linear and mono-branched isomers adsorb well, but 2,2-dimethylbutane is totally excluded. Plotting the differential heat of adsorption against the loading shows an initial plateau for n-hexane and 2-methylpentane. This is followed by a slow rise, indicating adsorbate–adsorbate interactions. For the di-branched isomers the differential heat of adsorption decreases with loading. To gain further insight, we ran molecular simulations using the grand-canonical Monte Carlo approach. Comparing the simulation and the experimental results shows that the ZIF framework model requires blocking of the cages, since 2,2-dimethylbutane cannot fit through the sodalite-type windows. Practically speaking, this means that ZIF-8 is a highly promising candidate for enhancing gasoline octane numbers at 373 K, as it can separate 2,2-dimethylbutane and 2,3-dimethylbutane from 2-methylpentane. Our results prove the potential of ZIF-8 as a new adsorbent that can be employed in the upgrade of the Total Isomerization Process for the production of high octane number gasoline, by blending di-branched alkanes in the gasoline.

Graphical abstract: Sieving di-branched from mono-branched and linear alkanes using ZIF-8: experimental proof and theoretical explanation

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Publication details

The article was received on 05 Dec 2012, accepted on 05 Apr 2013 and first published on 02 May 2013


Article type: Paper
DOI: 10.1039/C3CP44381G
Phys. Chem. Chem. Phys., 2013,15, 8795-8804
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    Sieving di-branched from mono-branched and linear alkanes using ZIF-8: experimental proof and theoretical explanation

    A. F. P. Ferreira, M. C. Mittelmeijer-Hazeleger, M. A. Granato, V. F. D. Martins, A. E. Rodrigues and G. Rothenberg, Phys. Chem. Chem. Phys., 2013, 15, 8795
    DOI: 10.1039/C3CP44381G

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