Influence of Si/Al ratio on hexane isomers adsorption equilibria

In this work we aim to have a better knowledge of the influence of silica/alumina ratio (SAR) on the adsorption equilibrium of hexane isomers on MFI zeolites. With a manometric set-up coupled with a micro-calorimeter we did address adsorption properties and heats of adsorption of n-hexane, 2-methylpentane, 2,2-dimethylbutane and 2,3-dimethylbutane on three samples with different Si/Al ratio. The branched isomers all show a type I isotherm on the three samples, while n-hexane presents a dual site for SAR 1600 and 100, and type I for SAR 50. The Si/Al ratio has a large influence on the adsorption equilibrium properties, in addition the Henry’s constant and initial heats of adsorption increase with aluminium content. The saturation loading decreases with the increasing aluminium content. The differential heat of adsorption of n-hexane increases slightly with loading, whereas the heat of adsorption of branched hexanes presents a decrease with loading. The three MFI zeolite samples present equilibrium selectivity towards n-hexane

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

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

Erratum: Pathogenic Characteristics Of Escherichia Coli Strain Isolated From Newborn Piglets With Diarrhoea In Brazil (veterinary Microbiology (2000) 76 (51-59) Pii: S0378113500002236)

[No abstract available]7819

Adsorption of hexane isomers on MFI type zeolites at ambient temperature: Understanding the aluminium content effect

We investigate the influence of the aluminium content on the adsorption of hexane isomers at 293 K on MFI type zeolites (Si/Al ratios - SAR of 25, 100 and infinity). Adsorption isotherms were assessed with a home-made volumetric system. Temporal up-take curves were recorded using a manometric set-up combined with a Rubotherm suspension balance. All three isomers show dual site adsorption behaviour that is well described with a Dual Site Sips (DSS) model. The Si/Al ratio influences strongly the adsorption equilibrium properties. Regardless of the isomer type, the sample with SAR = 100 shows the highest saturation loadings. At the studied pressures the sorption order in the three samples is: n-hexane > 2-methylpentane > 2,3-dimethylbutane > 2,2-dimethylbutane. Generally, we found that the Henry constant increases with aluminium content Clear diffusional limitations are observed for the di-branched hexane isomers on all three zeolite samples. The sample with SAR = 100 gives the highest diffusion rates for the hexane isomers. Silicalite-1 is the most promising for enhancing gasoline octane numbers at 293 K, as it gives the highest equilibrium 2,3-dimethylbutane/2-methylpentane ratios. (C) 2012 Elsevier Inc. All rights reserved