Highly Selective, High‐Capacity Separation of o‐Xylene from C₈ Aromatics by a Switching Adsorbent Layered Material

Abstract

Purification of the C 8 aromatics (xylenes and ethylbenzene) is particularly challenging because of their similar physical properties.I ti sa lso relevant because of their industrial utility.Physisorptive separation of C 8 aromatics has long been suggested as an energy efficient solution but no physisorbent has yet combined high selectivity (> 5) with high adsorption capacity (> 50 wt %). Now ac ounterintuitive approach to the adsorptive separation of o-xylene from other C 8 aromatics involves the study of aknownnonporous layered material, [Co(bipy) 2 (NCS) 2 ] n (sql-1-Co-NCS), whichc an reversibly switch to C 8 aromatics loaded phases with different switching pressures and kinetics,m anifesting benchmark oxylene selectivity (S OX/EB % 60) and high saturation capacity (> 80 wt %). Structural insight into the observed selectivity and capacity is gained by analysis of the crystal structures of C 8 aromatics loaded phases.The separation and purification of chemical feedstocks currently uses 10-15 %o fw orldwide energy production; traditional separation processes (for example,d istillation, drying, evaporation) account for more than 80 %o ft his energy. [1] Given that there will be ever-increasing demand for commodities in the coming decades,m ore energy-efficient purification technologies are urgently required for large-scale separation processes.O ne of the most challenging and important separations in this context involves xylene isomers and ethylbenzene,t he C 8 aromatics.T hese compounds are used for the industrial production of fibers,plastics,solvents, and fuel additives. [2] However,t heir similar sizes and boiling points make their separation difficult. Presently,h igherboiling ortho-xylene (OX) is the main component isolated by distillation with more than 150 theoretical plates,w hile meta-xylene (MX) and para-xylene (PX) are separated by (complexation-based) fractional crystallization and/or adsorption. Ethylbenzene (EB) is mainly produced by alkylation of benzene with ethylene,b ecause it is extremely energy-intensive to isolate it by superfractionation with more than 300 theoretical plates. [3] Although adsorption-based technology has been well studied for C 8 aromatics separa-tion, [4] widespread implementation is hindered by the capacity and selectivity limitations of the current generation of adsorbents.F or example,z eolites only offer moderate capacity (ca. 10-20 wt %) and selectivity (ca. 5), [5] overshadowing their advantages of low cost and ready availability.

Simultaneous interlayer and intralayer space control in two-dimensional metal−organic frameworks for acetylene/ethylene separation

“…Owing to their inherent diversity, these materials enable precise control of pore shape, pore chemistry and pore size, thereby providing a versatile platform for separation processes [8][9][10][11][12][13][14][15] . In terms of trace gas removal, numerous studies have focused on the rational design of three-dimensional (3D) MOFs with uniform sub-nanometer pores [16][17][18][19][20][21][22][23][24][25] . Despite significant achievements, designing new materials that outperform existing benchmark adsorbents remains a formidable challenge.…”

Efficient separation of xylene isomers by a guest-responsive metal–organic framework with rotational anionic sites

“…Porous materials with designable pore topology and selective binding sites open up unexpected possibilities for recognition of xylene isomers [13][14][15][16][17][18][19][20] . Different kinds of metal-organic frameworks (MOFs) or porous coordination polymers, including MIL (Materials of Institut Lavoisier) series and MOFs with coordinatively unsaturated metal sites (CUSs), have been investigated for the separation of xylene isomers, both in vapor and liquid phases [21][22][23][24][25][26][27][28][29][30][31] . However, MIL-47 and MIL-125-NH 2 can hardly discriminate pX and mX, and the pX/mX selectivity of MIL-47 is 1.1 (calculated from breakthrough data) 23 .…”

High Working Capacity Acetylene Storage at Ambient Temperature Enabled by a Switching Adsorbent Layered Material

“…To better understand stepwise the C 2 H 2 isotherms exhibited by sql-1-Cu-BF 4 , molecular simulations using the density functional theory (DFT) were conducted based on structural analogues. 44 , 47 , 57 As revealed by Figure 5 , C 2 H 2 molecules (violet) occupy the interlayer space in sql-1-Cu-BF 4 ·1C 2 H 2 ( Figure 5 a) and sql-1-Cu-BF 4 ·2C 2 H 2 ( Figure 5 b). Extra C 2 H 2 molecules (red) reside in the square cavity for sql-1-Cu-BF 4 ·6C 2 H 2 ( Figure 5 c) and sql-1-Cu-BF 4 ·8C 2 H 2 ( Figure 5 d).…”

“…We have studied the sorption behavior of the square lattice ( sql ) coordination network [Co(bpy) 2 (NCS) 2 ] n (bpy = 4,4′-bipyridine), sql-1-Co-NCS , and found that it exhibits a reversible switching behavior induced by CO 2 or C 8 aromatic isomers. 46 , 47 Although sql-1-Co-NCS is a type of FMOM, its sudden switching behavior makes it distinctive 48 and more desirable than FMOMs with type F-I or F-II isotherms. 49 , 50 We classified this type of 2D MOM as a switching adsorbent layered material (SALMA).…”

“… 49 , 50 We classified this type of 2D MOM as a switching adsorbent layered material (SALMA). 47 The prototypal SALMA is the related sql coordination network [Cu(bpy) 2 (BF 4 ) 2 ] n , also known as ELM-11 . 51 The switching behavior of ELM-11 has been studied for a range of adsorbates such as CO 2 , N 2 , CH 4 , O 2 , Ar, and n -butane.…”