Adsorption and diffusion properties of xylene isomers and ethylbenzene in metal-organic framework MIL-53(Al)

Adsorption and diffusion behaviour of C8 aromatic isomers, including para-xylene (PX), ortho-xylene (OX), meta-xylene (MX), and ethylbenzene (EB), in metal-organic framework Mil-53(Al) has been systematically investigated by using intelligent gravimetric analyzer, thermogravimetric analysis and molecular simulation respectively. The results indicate that adsorptions of xylene isomers and ethylbenzene molecules in Mil-53(Al) at 303 K present type-I isotherms. The deviation from normal Langmuir model of the isotherms at higher temperature can be, however, found because of the breathing effect of Mil-53(Al) framework. In order to well understand the selective adsorption process of above adsorbates, the diffusion behaviour has been determined and the diffusion coefficient is in the order: OX > PX > MX > EB. The adsorption thermodynamics have been determined by the isotherms at different temperature. A sharp increase of the heat of sorption Q (st) suggests that a strong interaction between sorbates molecules and between sorbates and the framework appears as the increase of the loading. Two desorption peaks in DTG curves suggests that two sorption locations exist in Mil-53(Al) to C8 alkylaromatics. The molecular simulation results have been used to successfully explain the experimental phenomena and to well understand the underlying adsorption and diffusion features of the systems.