Separation Of Xylene Isomers Research Articles

Solid–Liquid Separation of Xylene Isomers Using a Cu-Based Metallocycle

Solid–Liquid Separation of Xylene Isomers Using a Cu-Based Metallocycle

High-field asymmetric waveform ion mobility spectrometry for xylene isomer separation assisted by helium-chemical modifiers.

We propose a combined helium-chemical modifier method for a faster and more convenient separation and detection of xylene isomers. The method employs high-field asymmetric waveform ion mobility spectrometry (FAIMS) to investigate the separation and identification of three xylene isomers. A homemade hollow needle-ring ion source was used, and five chemical modifiers, represented by methanol, ethanol, acetone, ethyl acetate, and acetic acid, were doped into the xylene target analytes to observe the separation and identification of the three isomers. This was based on the fact that the addition of helium and the increase of the RF voltage could no longer improve the resolution of the field asymmetric waveform ion mobility spectrometry system. The experimental results at an RF field voltage of 15 kV cm-1 showed that the spectral peak shifts of o-, m-, and p-xylene in a normal nitrogen environment were -0.21, -0.21, and -0.24 V, respectively. o-Xylene showed a spectral peak of -1.33 V after the addition of helium; however, the separation was not evident. The FAIMS spectrum of xylene showed multiple cluster ion peaks upon addition of the chemical modifiers on top of helium. The alcohol chemical modifiers caused three spectral peaks, with the best effect for methanol, and the characteristic ion peak positions of -7.16, -6.90, and -6.01 V for o-, m-, and p-xylene, respectively. The separation using proton-based chemical modifiers was confirmed to be stronger than that using non-proton-based chemical modifiers, and appropriate volume fractions of chemical modifiers provided a better separation of the target analytes. This study introduces a novel concept and method for the separation and identification of xylene isomers.

Unblocking a rigid purine MOF for kinetic separation of xylenes.

The separation of xylene isomers still remains an industrially challenging task. Here, porous purine-based metal-organic frameworks (MOFs) have been synthesized and studied for their potential in xylene separations. In particular, Zn(purine)I showed excellent para-xylene/ortho-xylene separation capability with a diffusion selectivity of 6 and high equilibrium adsorption selectivity as indicated by coadsorption experiments. This high selectivity is attributed to the shape and size of the channel aperture within the rigid framework of Zn(purine)I.

Molecular dynamics simulation of adsorption and separation of xylene isomers by Cu-HKUST-1.

Metal-organic frameworks (MOFs) are widely used in the adsorption separation of various gases. A fundamental understanding of the effective separation of xylene isomers helps improve aromatic products' separation efficiency and reduce industrial separation costs. Grand Canonical Monte Carlo (GCMC) simulations combined with Molecular Science is widely used to predict gas adsorption and diffusion in single crystals with metal-organic frameworks. We performed a GCMC + MD combined approach to study xylene isomers' adsorption and separation in Cu-HKUST-1 to predict the permeability and selectivity of the ternary gas mixture in the MOF with the adsorption and diffusion usage data. Most current studies take into account the computational cost and difficulty. Most recent research models are limited to the adsorption of a single or specific molecule, such as hydrogen, methane, carbon dioxide, etc. For this reason, we report an attempt to study the adsorption separation of aromatic gases (p-xylene/o-xylene/m-xylene) based on Cu-HKUST-1 single-crystal materials based on some previous research methods with an appropriate increase in computational cost. To predict the adsorption selectivity and permeability of the ternary mixture of xylene isomers on the MOF surface, the model simulation calculates key parameters of gas adsorption, including gas adsorption volume (N), the heat of adsorption (Q st), Henry coefficient (K), and diffusion coefficient (D).

B-Oriented Mfi Zeolite Membranes for Xylene Isomer Separation - Effect of Xylene Activity on Separation Performance

B-Oriented Mfi Zeolite Membranes for Xylene Isomer Separation - Effect of Xylene Activity on Separation Performance

Novel Short Process for p-Xylene Production Based on the Selectivity Intensification of Toluene Methylation with Methanol.

Toluene methylation using methanol offers a high potential molecular engineering process to produce p-xylene (PX) based on shape-selective catalysts. To further improve the process economics, a novel short process was proposed by reducing the high-energy consumption separation of xylene isomers in existing processes since the PX selectivity of the xylene isomers can be enhanced more than the industrial product quality of 99.7%. The PX selectivity intensification was achieved as a result of decreased contact time by considering factors such as the feed ratio, diluents, temperature, and pressure in a toluene methylation reactor. This proposed short process indicated that the reactor effluent could be purified only through the two conventional distillation towers by removing the methanol recovery and separation of xylene isomers. The raw material utilization, energy consumption, and economic data were also analyzed for the six contrastive cases. The short process using catalyst Si–Mg–P–La/ZSM-5 exhibited the highest effective utilization rates of 96.27 and 95.50% for toluene and methanol, respectively. The short process also showed a good economic value in terms of capital investment and operating costs due to the multistage reactor without benzene byproducts. Thus, the obtained total annual cost (TAC) value of 13 848.1 k$·year–1 was 68.9 and 87.9% of the two existing processes.

Efficient adsorption separation of xylene isomers in zeolitic imidazolate framework-67@MCF hybrid materials

Metal-organic frameworks (MOFs) with metal-containing secondary building units and organic linkers have great potential for the separation of isomers. A type of hybridized materials synthesized by in-situ growth of microporous zeolite imidazolate framework (ZIF-67) on siliceous mesoporous foam (MCF), ZIF-67@MCF, was synthesized and employed in the adsorption separation processes of the petrochemical industry. This study aims to present the adsorption behavior of ZIF-67@MCF for separating xylene isomers. The adsorption separation of xylene isomers on ZIF-67@MCF hybrid materials was studied using the batch vapor-phase adsorption, and liquid-phase breakthrough adsorption. ZIF-67@MCF showed a preferable adsorption of p-xylene over the other two isomers, with the adsorption strength order of p-xylene (pX) ​> ​m-xylene (mX) ​> ​o-xylene (oX). In addition, the adsorption capacity of ZIF-67@MCF materials were studied with the different mole ratio of fluorine to silicon (F/Si ​= ​0, 0.03, 0.06). The higher resolution and larger separation factors for pX/oX and mX/oX, and higher adsorption capacity make ZIF-67@MCF an efficient and reliable alternative adsorbent to the isolation protocols for xylene isomers in the petrochemical industry.

Effect of laminar pulsatile fluid flow on separation of volatile organic compounds from aqueous solution by a hollow fiber membrane-based process

In this study, a laminar pulsatile fluid flow was used for the separation of benzene, toluene, ethylbenzene and xylene isomers (BTEX) from aqueous solutions. The polyethersulfone hollow fiber membrane has been applied to this process. The effects of BTEX concentration, feed, and extraction flow rates were examined. It was found that the application of the pulsatile fluid flow with the frequency of 0.5 Hz significantly enhanced the separation process, and the removal efficiency has increased nearly twice. Moreover, the results showed that BTEX separation under pulsatile fluid flow was affected by the feed flow rate, extraction flow rate and the BTEX concentration as well.

Synthesis of Graphene Oxide Membrane for Separation of p‐Xylene and o‐Xylene by Pervaporation

AbstractIn this study, a graphene oxide (GO) membrane is developed for the separation of p‐xylene (PX, 0.58 nm) from o‐xylene (OX, 0.68 nm). Attributing to the suitable d‐spacing size (0.58 nm), the GO membrane allows more PX to pass through than OX, leading to a high PX/OX selectivity. At 110 °C for the separation of equimolar PX/OX mixture, the PX/OX separation factor is 9.4 and PX flux is 145.3 g m−2h−1, respectively, which is promising for the separation of xylene isomers by pervaporation. The separation performance of the GO membrane is further confirmed by simulation studies.

Synthesis of high-crystallinity MIL-125 with outstanding xylene isomer separation performance

MIL-125 is a metal-organic framework with great potential for the adsorption and separation of xylene isomers. However, MIL-125 is usually synthesized under anhydrous and anaerobic conditions. In this study, homogeneously shaped and highly crystalline MIL-125 was synthesized by introducing water-resistant titanium-containing oligomers into the synthesis process. With the assistance of the novel oligomers, MIL-125 can be synthesized in the presence of water, which meets batch-production requirements. The adsorption separation performance of the obtained highly crystalline MIL-125 was also significantly enhanced. The para-xylene/meta-xylene selectivity can reach 13.5 in mesitylene, which is higher than the selectivity values of most previously reported para-selective adsorbents. The MIL-125 xylene separation performance was verified using both batch adsorption and breakthrough experiments in the liquid phase. In addition, the influence of the solvent effect was evaluated through microcalorimetric experiments, liquid-phase adsorption experiments, and theoretical calculations.

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

The separation of xylene isomers is one of the most challenging issues in the chemical industry because of the similarity of their boiling points and kinetic diameters. This study focuses on the use of pillar-layer MOF-Co(aip)(bpy)0.5 for adsorption and separation of xylene isomers. It was found that Co(aip)(bpy)0.5 exhibited a significant para-selectivity in liquid-phase competitive adsorption of xylene isomers, and the competitive separation factors reached as high as 30 for p-xylene versus m-xylene and 16 for p-xylene versus o-xylene. Desorption experiments further confirmed the preferential adsorption of p-xylene on the adsorbent. Molecular simulations and calculations revealed that the order of interaction strengths for xylene molecules and the adsorbent framework was p-xylene ≫ o-xylene ≈ m-xylene, which illustrated the selective adsorption phenomena arising from the mechanism for microscopic interactions. This work broadens the application of pillar-layer MOF materials in the field of xylene isomer adsorption and separation.

Fine-Tuning Window Apertures in ZIF-8/67 Frameworks by Metal Ions and Temperature for High-Efficiency Molecular Sieving of Xylenes.

Separation of structurally similar components from their mixtures is one of the most promising applications of metal-organic frameworks (MOFs). A high efficiency of such molecular sieving requires fine tuning of the MOF structure. In this work, we investigate subtle metal- and temperature-induced changes in window dimensions of zeolitic imidazolate frameworks (ZIF-8(Zn) and ZIF-67(Co)) and apply such structural tuning for efficient separation of xylene isomers (p-, m-, and o-xylenes). The use of Co instead of Zn favorably modifies window geometry: it accelerates the diffusion of all components by a factor of 2-3 while maintaining closely the same separation efficiency as that of ZIF-8(Zn). Outstanding selectivity above 18:1 and faster isolation of demanded p-xylene from the ternary mixture using ZIF-67(Co) have been demonstrated at room temperature, opening new horizons for its energy-efficient xylene separation. More generally, our findings suggest the prospective ways to tune various MOFs for target liquid-state separations.

Xylene Recognition in Flexible Porous Coordination Polymer by Guest-Dependent Structural Transition.

Xylene isomers are crucial chemical intermediates in great demand worldwide; the almost identical physicochemical properties render their current separation approach energy consuming. In this study, we utilized the soft porous coordination polymer (PCP)'s isomer-specific structural transformation, realizing o-xylene (oX) recognition/separation from the binary and ternary isomer mixtures. This PCP has a flexible structure that contains flexible aromatic pendant groups, which both work as recognition sites and induce structural flexibility of the global framework. The PCP exhibits guest-triggered "breathing"-type structural changes, which are accompanied by the rearrangement of the intraframework π-π interaction. By rebuilding π-π stacking with isomer species, the PCP discriminated oX from the other isomers by its specific guest-loading configuration and separated oX from the isomer mixture via selective adsorption. The xylene-selective property of the PCP is dependent on the solvent; in diluted hexane solution, the PCP favors p-xylene (pX) uptake. The separation results combined with crystallographic analyses revealed the effect of the isomer selectivity of the PCP on xylene isomer separation via structural transition and demonstrated its potential as a versatile selective adsorptive medium for challenging separations.

Comparison of pervaporation and perstraction for the separation of p‑xylene/m‑xylene mixtures using PDMS and CTA membranes

• Separation of xylene isomers using pervaporation and perstraction. • Membranes from industrially relevant materials: PDMS and CTA. • Methanol as membrane entrainer and receiving phase. • Plasticization by methanol assessed using dynamic mechanical analysis. • Higher p -xylene/ m -xylene selectivity for perstraction than for pervaporation. The separation of the individual xylene isomers remains challenging and energy intensive. Since the utilization of membrane separations could bring an improvement, we compare the efficacy of two related membrane methods, pervaporation and perstraction, for the separation of p ‑xylene/ m ‑xylene mixtures using membranes from polydimethylsiloxane (PDMS) and cellulose triacetate (CTA) at 40 °C. Methanol was used as the receiving liquid in perstraction and as a membrane entrainer; feeds containing 0–80 mol.% of methanol were studied. While PDMS showed almost no selectivity to p ‑xylene over m ‑xylene during pervaporation, the selectivity reached up to 1.40 when operated in the perstraction mode with the feed enriched with methanol. CTA performed better than PDMS for all studied mixtures, the highest selectivity of 1.93 was observed for the perstraction of the molten eutectic mixture with no methanol in the feed. The likely reason for the enhancement of the selectivity are the isomer-specific interactions with the polar moieties in the polymer plasticized by methanol. Overall, it was demonstrated that a simple change in the mode of operation from pervaporation to perstraction and the use of a membrane entrainer can appreciably enhance the p ‑xylene to m ‑xylene selectivity of the common and reliable membrane materials.

Metal–Organic Frameworks for Xylene Separation: From Computational Screening to Machine Learning

Separation of xylene isomers is an important process in the chemical industry and there has been considerable interest in developing advanced materials for xylene separation. In this study, we synergize computational screening and machine learning to explore the selective adsorption of p-xylene over o- and m-xylene in metal–organic frameworks (MOFs). First, a large set (4764) of computation-ready experimental MOFs is screened by geometric analysis and molecular simulation. The relationships between MOF structural descriptors (void fraction, volumetric surface area, and largest cavity diameter) and separation performance metrics (adsorption capacity of p-xylene Np-xylene and selectivity of p-xylene over o- and m-xylene Sp/(m+o)) are established. Then two machine-learning methods (back-propagation neural network and decision tree), as well as particle swarm optimization, are utilized to analyze and optimize Np-xylene and Sp/(m+o). The importance of each descriptor for separation is evaluated in six different MOF data sets. In the 100 top-performing MOFs, the pore limiting diameter (PLD) and largest cavity diameter (LCD) are revealed to be key factors governing separation performance. On the basis of the threshold values of Np-xylene > 0.5 mol/kg and Sp/(m+o) > 5, seven top-performing MOFs are identified. By further incorporating framework flexibility, JIVFUQ is predicted to be the best and superior to many reported MOFs in the literature.

Metal-Organic Frameworks for Highly Selective Separation of Xylene Isomers and Single-Crystal X-ray Study of Aromatic Guest-Host Inclusion Compounds.

Separation of hydrocarbon molecules, such as benzene/cyclohexane and o-xylene/m-xylene/p-xylene, is relevant due to their widespread application as chemical feedstock but challenging because of their similar boiling points and close molecular sizes. Physisorption separation could offer an energy-efficient solution to this problem, but the design and synthesis of sorbents that exhibit high selectivity for one of the hydrocarbons remain a largely unmet challenge. Herein, we report a new heterometallic MOF with a unique tortuous shape of channels decorated with aromatic sorption sites [Li2Zn2(bpy)(ndc)3] (NIIC-30(Ph), bpy = 4,4'-bipyridine, ndc2- = naphthalene-1,4-dicarboxylate) and study of its benzene/cyclohexane and xylene vapor and liquid separation. For an equimolar benzene/cyclohexane mixture, it is possible to achieve a 10-fold excess of benzene in the adsorbed phase. In the case of xylenes, microporous framework NIIC-30(Ph) demonstrates outstanding selective sorption properties and becomes a new benchmark for m-/o-xylene separation. In addition, NIIC-30(Ph) is stable enough to carry out at least three separation cycles of benzene/cyclohexane mixtures or ternary o-xylene/m-xylene/p-xylene mixtures both in the liquid and in the vapor phase. Insights into the performance of NIIC-30(Ph) are gained from X-ray structural studies of each aromatic guest inclusion compound.

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

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.

First-principles investigation of dimethyl-functionalized MIL-53(Al) metal–organic framework for adsorption and separation of xylene isomers

Functionalization of organic linker in metal–organic frameworks (MOFs) has been a popular method to utilize the porous material for a wide range of applications. In xylene separation, dimethyl functionalization of MOFs had demonstrated improved adsorptions properties. However, the effect of different xylene isomers on the organic linker is still not fully understood. In this work, the MIL-53(Al) MOF was functionalized with two methyl groups in ortho-, meta- and para-positions. The energy and thermochemical properties of xylene isomers when complexed dimethyl functionalized MIL-53(Al) MOFs were investigated using semiempirical quantum chemical PM6 method. The adsorption model of xylene isomers over meta-dimethyl-MIL-53(Al) (MDM) produced the lowest energy and the most thermochemically stable complex. The electronic properties, natural charge, nuclear magnetic resonance, aromaticity and molecular electrostatic potential of MDM complexes were further characterized using density functional theory (DFT) calculations at B3LYP/6-31G(d) level. DFT calculations revealed that the complex of MDM with m-xylene had the lowest adsorption energy and the highest reactivity, caused by the oxygen atoms surrounding the Al metal ion. In contrast, the complex of MDM with o-xylene had the highest energy of adsorption and the lowest reactivity, mostly governed by weak π interactions. Based on the results, we propose the use of MDM MOF for adsorption and separation of xylene isomers.

Application of gas chromatography separation based on metal-organic framework material as stationary phase

金属有机骨架材料(MOFs)是一类由有机配体和金属离子(或金属簇)自组装形成的新型多功能材料。MOFs具有孔隙度高、比表面积大、孔径可调、化学和热稳定性高等特点,被广泛应用于吸附、分离、催化等多个领域。近年来,MOFs作为新型气相色谱固定相用于分离异构体受到了广泛关注。与传统无机多孔材料相比,MOFs在结构和功能上展现出高度的可调性,通过合理地选择配体和金属中心,可以设计合成具有不同孔道大小和孔道环境的MOFs,从而分别从热力学和动力学角度优化色谱分离效果,有效提高分离选择性。该文结合MOFs的结构,讨论了MOFs气相色谱固定相分离不同类型分析物的分离机理。分离机理主要包括MOFs孔道的分子筛效应或形状选择性,MOFs不饱和的金属位点与分析物中不同的官能团之间产生的相互作用,分析物与MOFs孔道之间产生的不同范德华力、π-π相互作用和氢键相互作用。此外,MOFs的手性分离可能主要依赖于外消旋体与手性MOFs中手性活性位点之间的相互作用。该文也对不同分析目标物进行了归类,综述了多种MOFs气相色谱固定相对烷烃、二甲苯异构体和乙基甲苯、外消旋体、含氧有机物、环境有机污染物的气相色谱分离效果。最后,该文还对MOFs在该领域的应用进行了总结与展望,旨在为MOFs气相色谱高效分离的研究提供参考。

Efficient separation of xylene isomers by using a robust calcium-based metal–organic framework through a synergetic thermodynamically and kinetically controlled mechanism

A microporous metal–organic framework with a robust structure has been developed. The compound exhibited highly efficient separation of xylene isomers which is a result of a synergetic thermodynamic and kinetic mechanism.