Adsorption and Separation of Xylene Isomers and Ethylbenzene on Two Zn-Terephthalate Metal-Organic Frameworks

Metal-organic frameworks (MOFs) with metal-containing secondary building units and organic linkers have great potential for the separation of isomers. In this work, the adsorption and separation of xylene isomers and ethylbenzene (EB) on two Zn-terephthalate MOFs (MOF-5 and MOF-monoclinic) were studied by means of pulse gas chromatography, static vapor-phase adsorption, and breakthrough adsorption. The two studied Zn-terephthalate MOFs showed different selectivity and efficiency for the separation of xylene isomers and EB. On MOF-5, EB eluted first, while other isomers eluted at the same time. MOF-monoclinic showed a preferable adsorption of p-xylene over other isomers. The adsorption and separation of xylene isomers and EB were equilibrium-constant-controlled on MOF-5 and diffusion-dominated on MOF-monoclinic. On the basis of the measured McReynolds constants, MOF-5 was characterized as a stationary phase of nonpolarity, whereas MOF-monoclinic as a stationary phase of intermediate polarity for gas chromatography.