Influence of the Eluent in the MIL-53(Al) Selectivity for Xylene Isomers Separation

Abstract

MetalÀorganic framework MIL-53(Al) pellets were tested for selective adsorption and separation of xylene isomers with the aim of studying the influence of the solvent used at bulk concentrations. In this way, a set of single and multicomponent pulse experiments to measure selectivities was conducted, with iso-octane, n-hexane, and n-heptane as eluents, at 313 K. In order to complete this study, multicomponent breakthrough experiments were also performed, under the same conditions, in the presence of these three eluents, and the obtained selectivities were compared. MIL-53(Al) presented a preference for o-xylene over m-xylene and p-xylene in all experiments. The selectivity was higher when n-heptane was the eluent. For the breakthrough experiments that used nheptane as the eluent, selectivities of 2.1 were obtained for o-xylene over m-xylene and over p-xylene. It was possible to conclude that the choice of eluent influences the adsorption selectivity and capacity of the adsorbent. This could result, among other factors, from the adsorbentÀadsorbate interactions. These interactions may also occur with the eluent molecules (as an adsorbate), which influences the adsorption capacity.

Adsorptive separation on metal–organic frameworks in the liquid phase

“…Inspired by the strong ortho-selectivity of the MIL-53(Al) structure, a study was conducted for finding the appropriate eluent for using this material in industrial process conditions. 61 The group of Rodrigues used single and multicomponent pulse liquid chromatographic experiments to measure selectivities for xylene mixtures with isooctane, n-hexane and n-heptane as eluents. Very low selectivities are obtained with isooctane as solvent, while the ortho-preference is clearly observed for n-hexane and n-heptane.…”

The Parex Process for the Separation of p-Xylene

“…The separation of p-xylene from m-xylene, o-xylene, and ethylbenzene through the SMB principle has been implemented using, in general, faujasitic zeolites X and Y (Broughton, 1982;Neuzil, 1971;Anderson, 1992;Oroskar et al, 1993;Kulprathipanja, 1996;Hotier et al, 1999;Priegnitz et al, 2012;Cheng and Hurst, 2012;Silva et al, 2012a,b). However, this separation has also been studied on other types of zeolites, such as MFI (Guo et al, 2000), ZSM-5 (Yan, 1989) or mordenite (Luna et al, 2010), and other types of materials such as AIPO 4 -n (Chiang et al, 1991;Cavalcante et al, 2000) or MOFs (Gu et al, 2009;B arcia et al, 2011;Moreira et al, 2011).…”

Liquid-Phase Multicomponent Adsorption and Separation of Xylene Mixtures by Flexible MIL-53 Adsorbents

“…EB is dehydrogenated to styrene for polystyrene production, and oX is utilized in the synthesis of phthalic anhydride, a plasticizer. The similarity in molecular structures, close kinetic diameters (5.8–6.8 Å), and similar boiling points (138–144 °C) make cost-effective separation of these four isomers challenging, with the cost of production largely dependent on the cost of separation. ,, While crystallization and azeotropic distillation can be used to separate C 8 mixtures, the currently preferred separation technology is the PAREX process, which is based on simulated moving-bed adsorption. , The adsorbent used is a faujasite (FAU)-type zeolite exchanged with cations like K + or Ba 2+ , and it shows moderate pX selectivity attributed to xylene–cation interactions and favorable packing under high xylene loadings within the zeolite pores . Other zeolites such as MFI and ZSM-5 have also been evaluated for xylene separations. − Recently, metal–organic frameworks have created interest for C 8 isomer separation .…”

“…Other zeolites such as MFI and ZSM-5 have also been evaluated for xylene separations. − Recently, metal–organic frameworks have created interest for C 8 isomer separation . Metal–organic frameworks (MOFs) are a class of crystalline nanoporous materials which have been widely studied for adsorptive separations due to their high surface area, high porosity, and structural tunability by utilizing various combinations of metal centers and organic linkers. − Among the MOFs investigated for xylene mixture separations, the MIL-47 and the MIL-53 series have shown promise for separating xylene mixtures. ,− Both of these MOF types consist of one-dimensional (1D) pores lined with terephthalate ligands. These materials have hydroxy (MIL-53) or oxo (MIL-47) groups connected through coordination bonds to saturated trivalent (MIL-53) or tetravalent (MIL-47) metal centers. , One of the most intriguing features of these MOFs is their framework flexibility, which leads to changes in crystal structure and lattice parameters as a function of temperature, humidity, and adsorption of molecules. − …”