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.
Phys Chem Chem Phys. 2013 Jun 14;15(22):8795-804. doi: 10.1039/c3cp44381g. Epub 2013 May 2.
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.
我们研究了正构烷烃异构体在沸石咪唑酯骨架 ZIF-8 上的吸附平衡等温线和微分吸附热。研究在 373 K 下使用压力计装置与微量量热计相结合进行。我们发现，对于所有四种异构体（正己烷、2-甲基戊烷、2,2-二甲基丁烷和 2,3-二甲基丁烷），朗缪尔模型都很好地描述了等温线。线性和单支链异构体吸附良好，但 2,2-二甲基丁烷完全被排除在外。将微分吸附热与负载作图显示，正己烷和 2-甲基戊烷有初始平台。然后缓慢上升，表明吸附剂-吸附剂相互作用。对于二支链异构体，微分吸附热随负载的增加而降低。为了更深入地了解，我们使用巨正则蒙特卡罗方法进行了分子模拟。将模拟和实验结果进行比较表明，ZIF 骨架模型需要阻止笼的形成，因为 2,2-二甲基丁烷无法通过方钠石型窗口通过。实际上，这意味着 ZIF-8 是一种在 373 K 下提高汽油辛烷值的极有前途的候选物，因为它可以将 2,2-二甲基丁烷和 2,3-二甲基丁烷从 2-甲基戊烷中分离出来。我们的结果证明了 ZIF-8 作为一种新型吸附剂的潜力，它可以通过在汽油中混合二支链烷烃来用于生产高辛烷值汽油的总异构化过程的升级。
