title: Sieving di-branched from mono-branched and linear alkanes using ZIF-8: experimental proof and theoretical explanation.
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.
authors: Laboratory of Separation and Reaction Engineering, Associate Laboratory LSRE/LCM, Department of Chemical Engineering, Faculty of Engineering, University of Porto, Rua Dr Roberto Frias, Porto, Portugal.
authors: Alexandre F P
authors: AF
authors: Ferreira
authors: Marjo C
authors: MC
authors: Mittelmeijer-Hazeleger
authors: Miguel Angelo
authors: MA
authors: Granato
authors: Vanessa F Duarte
authors: VF
authors: Martins
authors: Alírio E
authors: AE
authors: Rodrigues
authors: Gadi
authors: G
authors: Rothenberg
mesh_terms: D000473:Alkanes / Q000737:chemistry*; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D009010:Monte Carlo Method; D017641:Zeolites / Q000737:chemistry*
chemical_list: D000473:Alkanes; D017641:Zeolites