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Adsorption and Separation Properties of Metal-Organic Framework

Author: DongXianYing
Tutor: DuanLinHai
School: Liaoning University of Petroleum \u0026 Chemical Technology
Course: Chemical processes
Keywords: Metal-organic framework Adsorption behaviour Separation Xylene Breathing effect
CLC: O647.31
Type: Master's thesis
Year: 2012
Downloads: 281
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Metal-organic frameworks (MOFs) is a new type of porousmaterial over the past years, and it has many advantage, such as stableporous structure, large surface areas, structure of designing and clippingand well-defined surface properties, which makes researchers interestabout it in adsorption, separation, catalysis and some other fields.In this paper, Metal-organic Frameworks MIL-53(Al), with a largespecific surface area, pore volume and pore size, has beenhydrothermally synthesized and investigated by means of X-raydiffraction (XRD) and N2adsorption-desorption experiment. Adsorptionisotherms of C8aromatic isomers, including para-xylene, ortho-xylene,meta-xylene, and ethylbenzene, in metal-organic framework Mil-53(Al)has been systematically investigated by using intelligent gravimetricanalyzer (IGA) at303K,333K and373K. The results indicate thatadsorption isotherms at303K present type-I isotherms. Adsorptionisotherms can quickly reach equilibrium, and O-xylene has the largestadsorption capacity. With increasing of adsorption temperature,adsorption isotherms appear slight step, indicating that the breathingeffect of the framework begins to occur. When the sorption temperaturerises to373K, it is obviously to two steps of adsorption process forisotherms. The deviation from normal Langmuir model of the isothermsat higher temperature can be, however, found because of the breathingeffect of Mil-53(Al) framework. After the adsorption platform, theadsorption capacities of o-xylene, m-xylene and p-xylene are still ableto reach a high level, while ethylbenzene has been a serious impactresulting in lower adsorption capacity. That provides a theoretical foundation for the separation of the mixed components. From the heatof adsorption data, the framework has the strongest interaction effectwhen it adsorbed a small amount of o-xylene molecules and theadsorption of p-xylene is reverse. With the increase of adsorptioncapacities, molecules in the pores occurred to rearrangements, andappeared interaction effect. The diffusion coefficient from the Fick’smodel calculations shows that o-xylene in the pores has the maximumdiffusion rate, and the ethylbenzene is the lowest in all.TG/DTG curve analysis and molecular simulation results show thatthere are two forms of adsorption behaviour for xylene andethylbenzene isomers on MIL-53(Al). The first is alkyl chains of theadsorbate molecules interacting with the framework, the other is π-πinteractions between adsorbate molecules and between adsorbatemolecules and the framework.Through the fixed bed breakthrough curves and gas chromatographyanalysis, one can obtain separation capabilities for adsorption binaryblending component in the MIL-53(Al) material.O-xylene/ethylbenzene has very good separation ability, which canpreferentially uptake o-xylene and outflow ethylbenzene. Especially inthe373K, the separation factor achieved9.2. P-xylene/ethylbenzenemixed component also has a good separation performance.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > The physical chemistry of surface phenomena > Adsorption > Adsorption theory
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