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Issue 22, 2013

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

Supplementary files

Article information


Submitted
05 Dec 2012
Accepted
05 Apr 2013
First published
02 May 2013

This article is Open Access

Phys. Chem. Chem. Phys., 2013,15, 8795-8804
Article type
Paper

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

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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