Separation of Xylene Isomers in the Anion‐Pillared Square Grid Material SIFSIX‐1‐Cu

Abstract

Xylene isomer separation is considered one of the seven separation challenges that changed the world. In addition, the high‐energy demand of xylene separation highlights the need for efficient novel adsorbents. Herein, the liquid‐phase separation potential of the anion‐pillared hybrid material SIFSIX‐1‐Cu was studied for preferential adsorption of o‐xylene and m‐xylene over p‐xylene, which was inspired by a previous complexation crystallization method for separating m‐xylene. We report detailed experimental liquid‐phase adsorption experiments, yielding selectivities of 3.0 for o‐xylene versus p‐xylene and 2.6 for m‐xylene versus p‐xylene. Our theoretical calculations thus provide a reasonable explanation that the xylene adsorption selectivity is attributed to the C−H⋅⋅⋅F interaction, and the host–guest interaction order agrees with the adsorption priority: o‐xylene > m‐xylene > p‐xylene.

Selective Adsorption and Separation of o-Xylene Using an Aluminum-Based Metal–Organic Framework

“…To determine the adsorption performance, the single-component adsorption isotherms were measured at 298 K. As shown in Figure a, the results indicate that this Al-MOF has the potential to separate C8 aromatics, and the adsorption order for C8 aromatics is o -xylene > p -xylene > m -xylene > ethylbenzene. It is worth mentioning that the adsorption capacity of o -xylene is rapidly increased and the maximum adsorption capacity is 2.14 mmol·g –1 , which is higher than those in various o -xylene-selectivity adsorbents, such as CAU-13, SIFSIX-Cu, and CPO-27-Ni . Although there are many materials with high adsorption capacities, such as Co 2 (dobdc), UiO-66, MFM-300­(In), and so on, they exhibited a poor selectivity toward o -xylene and m -xylene.…”

“…Various porous materials, such as zeolites, , and nonporous crystals have been studied as adsorbents for xylene separation. Generally, many materials adsorbed more amount of p -xylene than other C8 aromatics since the pore size of the adsorbent can be easily controlled so that p -xylene with a small molecular size is preferentially adsorbed . In addition to selective adsorption of p -xylene, o -xylene-selective adsorbents with high selectivities also receive more and more attention.…”

“…Generally, many materials adsorbed more amount of p-xylene than other C8 aromatics since the pore size of the adsorbent can be easily controlled so that p-xylene with a small molecular size is preferentially adsorbed. 16 In addition to selective adsorption of p-xylene, o-xylene-selective adsorbents with high selectivities also receive more and more attention. It is because the adsorption-based process with this material can not only replace the energy-intensive distillation technology but also avoid the separation challenge of o-xylene and m-xylene in the downstream process.…”

Efficient Separation of Xylene Isomers by a Pillar-Layer Metal–Organic Framework

“…This implied that there was an electron transfer interaction between the adsorbent framework and adsorbate molecules. Then, we used the calculated interaction energies (Δ E ) to further illustrate the difference in interactions between these three isomers with the adsorbent framework, as shown in Figure a. , A smaller Δ E value indicated stronger adsorption and a more stable configuration after adsorption. The conformational geometries of all adsorbate molecules and the Co­(aip)­(bpy) 0.5 adsorbent were optimized before calculation.…”

“…The host−guest interaction energies were calculated from the density functional theory (DFT) calculations using the Materials Studio (version 6.0) DMol3 Module. 30 The DFT calculations were performed using the Perdew−Burke−Ernzerhof (PBE) exchange-correlation functional within the generalized gradient approximation (GGA). 31 The set optimization convergence standard SCF tolerance value was 0.001 meV/atom.…”