Separation Of P-xylene Research Articles

Highly Selective p-Xylene Separation from Mixtures of C8 Aromatics by a Nonporous Molecular Apohost.

High and increasing production of separation of C8 aromatic isomers demands the development of purification methods that are efficient, scalable, and inexpensive, especially for p-xylene, PX, the largest volume C8 commodity. Herein, we report that 4-(1H-1,2,4-triazol-1-yl)-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (TPBD), a molecular compound that can be prepared and scaled up via solid-state synthesis, exhibits exceptional PX selectivity over each of the other C8 isomers, o-xylene (OX), m-xylene (MX), and ethylbenzene (EB). The apohost or α form of TPBD was found to exhibit conformational polymorphism in the solid state enabled by rotation of its triazole and benzene rings. TPBD-αI and TPBD-αII are nonporous polymorphs that transformed to the same PX inclusion compound, TPBD-PX, upon contact with liquid PX. TPBD enabled highly selective capture of PX, as established by competitive slurry experiments involving various molar ratios in binary, ternary, and quaternary mixtures of C8 aromatics. Binary selectivity values for PX as determined by 1H NMR spectroscopy and gas chromatography ranged from 22.4 to 108.4, setting new benchmarks for both PX/MX (70.3) and PX/EB (59.9) selectivity as well as close to benchmark selectivity for PX/OX (108.4). To our knowledge, TPBD is the first material of any class to exhibit such high across-the-board PX selectivity from quaternary mixtures of C8 aromatics under ambient conditions. Crystallographic and computational studies provide structural insight into the PX binding site in TPBD-PX, whereas thermal stability and capture kinetics were determined by variable-temperature powder X-ray diffraction and slurry tests, respectively. That TPBD offers benchmark PX selectivity and facile recyclability makes it a prototypal molecular compound for PX purification or capture under ambient conditions.

Structural functionalization in robust metal–organic frameworks for p-xylene separation with superior adsorption capacity

The subtle differences between the xylene isomers make the separation of p-xylene/m-xylene/o-xylene mixtures one of the most challenging tasks in the petrochemical industry. In this study, CAU-1 was used as a platform compound to construct functionalized pore environment with high stability for selective PX adsorption and separation. Single-component adsorption tests and liquid-phase multicomponent adsorption experiments showed that a series of functionalized scaffolds exhibited PX selective adsorption compared to the other two isomers, among them functional groups optimized CAU-1-OH ([Al8(OH)4(OCH3)8(BDC-OH)6])(BDC = 1,4-benzenedicarboxylate) showed ultra-high PX adsorption capacity (460 mg/g), superior to most reported MOFs. And the PX/MX selectivity of functionalized CAU-1-OH was improved by 18% compared to the original CAU-1. Furthermore, vapor breakthrough experiments on CAU-1-OH showed that it can effectively extract PX from ternary PX/MX/OX mixtures. The fundamental PX selective adsorption mechanism was also visually illustrated using grand canonical Monte Carlo simulation. In addition, the stability of the adsorbent was investigated under different conditions (RH = 40% and 80%, pH = 1–11, different solvents, and high temperatures), and the unchanged PXRD and BET curves indicate that the adsorbent has excellent structural stability. As thus, the large PX adsorption capacity, ultra-high structural stability, and excellent isomer separation performance make these materials good candidates for industrial PX purification from xylene isomers mixture.

Entrainers Selection and Vapor–Liquid Equilibrium Measurements for Separation of p-Xylene from Ethylbenzene at 101.3 kPa

Entrainers Selection and Vapor–Liquid Equilibrium Measurements for Separation of p-Xylene from Ethylbenzene at 101.3 kPa

A gating ultramicroporous metal-organic framework showing high adsorption selectivity, capacity and rate for xylene separation

Adsorptive separation of p-xylene (pX) from xylene isomers is a key process in chemical industry, but known adsorbents cannot simultaneously achieve high adsorption selectivity, capacity, and rate. Here, we demonstrate gating ultramicropore as a solution for this challenge. Slight modification of the synthetic condition gives rise to isomeric metal-organic frameworks α-[Zn(pba)] (MAF-88, H2pba = 4-(1H-pyrazol-4-yl)benzoic acid) and β-[Zn(pba)] (MAF-89) possessing similar pillared-column structures, porosities, and high pX capacities of 2.0 mmol g−1, but very different framework/pore topologies, pore sizes, and pX selectivities. For binary and ternary mixtures of liquid xylene isomers, MAF-88 with narrow one-dimensional (1D) channels shows pX selectivity of 11 and 1.6, while MAF-89 with 3D-connected quasi-discrete pores shows pX selectivity up to 221 and 46, respectively. Thermogravimetry, differential scanning calorimetry, and time-dependent separation experiments reveal that the kinetic effects of the gating pores play more important roles than the thermodynamic effects, which is further confirmed by single-crystal X-ray diffraction and computational simulations.

Separation of p-xylene and m-xylene by simulated moving bed chromatography with MIL-53(Fe) as stationary phase

The separation of p-xylene (PX) and m-xylene (MX) isomers with near boiling points is a worldwide problem. The metal-organic framework material is an ideal stationary phase for chromatographic separation because of its high porosity, homogeneous pore diameter and good chemical stability. In this paper, a simulated moving bed (SMB) chromatography system with MIL-53(Fe) as the stationary phase and petroleum ether-dichloromethane as the mobile phase was designed to separate PX and MX at ambient temperature. Firstly, according to the elution curves of a single column, nonlinear competitive Langmuir adsorption isotherm equation was confirmed by equilibrium dispersive chromatography model. Then, the SMB separation zone was determined based on triangle theory, and the SMB operating conditions were optimized. Finally, the purity, recovery and productivity of PX reached 100.0%, 99.1% and 93.1 g/L/h, respectively; the purity, recovery and productivity of MX reached 96.4%, 100.0% and 23.5 g/L/h, respectively; the solvent consumption was 0.42 L/g.

金属有機構造体を用いた分子ふるい作用によるパラキシレン分離

Metal-organic frameworks (MOFs) consisting of organic linker such as terephthalic acid or fumaric acid and cation such as Al3+ or Zr4+ were prepared by the hydro- and solvo-thermal methods. MOFs were characterized by XRD, N2 adsorption-desorption isotherm and FE-SEM. The prepared MOFs were mostly crystalline and phase-pure. MOFs were used as the column packing for chromatographic separation of p-xylene from a xylene mixture. With MOFs prepared with large linker molecules, xylenes diffused into the micropores and eluted fundamentally according to kinetic molecular size. With MOFs of low crystallinity or very small micropores, xylenes passed through spaces between MOF particles and separation of p-xylene was not possible. With MOFs consisting of fumaric acid and Zr4+ (MOF-801), o- and m-xylenes eluted quickly and p-xylene eluted later, because o- and m-xylenes passed through spaces between MOF particles, whereas p-xylene diffused into the micropores of MOF-801. Temperature dependence of separation with MOF-801 revealed that at temperatures lower than 140 °C, xylenes could not diffuse into the micropores. At 170 °C, the smallest p-xylene diffused into the micropores and thus p-xylene could be separated from o- and m-xylenes by the molecular-sieving mechanism. MOF-801 was robust against repeated exposure to xylenes and heat treatment at high temperature for elution of adsorbed xylene.

Systematic Analysis Reveals Thermal Separations Are Not Necessarily Most Energy Intensive

Summary At the industrial level, separation of a variety of mixtures is predominantly carried out by thermally driven processes such as distillation. Nevertheless, the current literature seems to suggest that much is to be gained by replacing these processes with alternative non-thermal methods, which will potentially require a fraction of the energy used by distillation. This is primarily due to the widespread perception that thermal separation processes, particularly those that involve vaporization, are highly energy intensive. However, this belief is not well founded, because it is based on extrapolation from comparisons in the literature, many of which make ad-hoc assumptions and result in incorrect conclusions. Our analysis shows that this confusion arises because the processes utilize different types of energy: heat and electricity. Here, we present a consistent framework that enables a fair comparison between different processes that consume different forms of energies. Using this framework, we refute the general perception that thermal separation processes are inherently the most energy intensive and conclusively show through the examples of two challenging mixtures constituting components with low relative volatilities, that distillation processes, when run properly, can consume remarkably lower fuel than non-thermal membrane alternatives, which have often been touted as more energy efficient.

Formation Process of Columnar Grown (101)-Oriented Silicalite-1 Membrane and Its Separation Property for Xylene Isomer

Silicalite-1 membrane was prepared on an outer surface of a tubular α-alumina support by a secondary growth method. Changes of defect amount and crystallinity during secondary growth were carefully observed. The defect-less well-crystallized silicalite-1 membrane was obtained after 7-days crystallization at 373 K. The silicalite-1 membrane became (h0l)-orientation with increasing membrane thickness, possibly because the orientation was attributable to “evolutionally selection”. The (h0l)-oriented silicalite-1 membrane showed high p-xylene separation performance for a xylene isomer mixture (o-/m-/p-xylene = 0.4/0.4/0.4 kPa). The p-xylene permeance through the membrane was 6.52 × 10−8 mol m−2 s−1 Pa−1 with separation factors αp/o, αp/m of more than 100 at 373 K. As a result of microscopic analysis, it was suggested that a very thin part in the vicinity of surface played as effective separation layer and could contribute to high permeation performance.

The Implementation of a Carbon Precursor to Produce ZSM-5 Membranes for the Separation of Isomers in the Pervaporation System.

The separation of p-xylene from its bulkier m-xylene and o-xylene is of great importance in the petrochemical industry. This paper presents the experimental results of the separation of xylene isomers using a zeolite carbon composite membrane in a pervaporation system. The preparation method involves the use of an inexpensive carbon precursor, sucrose, to avoid the lengthy conventional preparation methods used in the literature (e.g., hydrothermal synthesis). The composite membranes that were prepared exhibited a separation performance with a p-xylene/o-xylene separation factor of 5.35 and permeability of 76 g/m2 h for 95% o-xylene at 25 °C. The preparation procedure was designed from an economical perspective to facilitate any possible future commercialization.

A needle-to-post air discharge ion source in tandem with FAIMS system.

A needle-to-post ionization source was designed for high-field asymmetric waveform ion mobility spectrometry (FAIMS). The needle-to-post ion source includes asymmetric electrode comprised of a copper post with a diameter of 2 mm and a stainless-steel needle with 200-μm tip radius and length of 28 mm. With the discharge voltage of -5.6 kV and N2 gas flow, glow discharge was realized at atmospheric pressure. The mass spectra of ionized ions about acetone, ethanol and ethyl acetate were gotten by Thermo Scientific LTQ XL ion trap mass spectrometer (MS). The MS experimental results show that the main ions are protonated and dimer ions. The needle-to-post ion source was mounted on the FAIMS system and FAIMS spectra are gotten successfully. Separation of p-xylene, o-xylene and m-xylene was realized. It shows that the needle-to-post electrode could be used as the ion source in a FAIMS system.

High-Flux High-Selectivity Metal-Organic Framework MIL-160 Membrane for Xylene Isomer Separation by Pervaporation.

Separation of p-xylene (kinetic diameter ca. 0.58 nm) from its bulkier isomers (o-xylene and m-xylene, ca. 0.68 nm) is challenging, but important in the petrochemical industry. Herein, we developed a highly selective and stable metal-organic framework (MOF) MIL-160 membrane for selective separation of p-xylene from its isomers by pervaporation. The suitable pore size (0.5∼0.6 nm) of the MIL-160 membrane selectively allows p-xylene to pass through, while excluding the bulkier o-xylene and m-xylene. For the separation of equimolar binary p-/o-xylene mixtures at 75 °C, high p-xylene flux of 467 g m-2 h-1 and p-/o-xylene selectivity of 38.5 could be achieved. The stability of MIL-160, ensured the separation performance of the MIL-160 membrane was unchanged over a 24 h measurement. The high separation performance combined with its high thermal and chemical stability makes the MIL-160 membrane a promising candidate for the separation of xylene isomers.

Separation of ethylbenzene and p-xylene using extractive distillation with p-dinitrobenzene

Though p-xylene derived from naphtha reformate is in high demand as a raw material in the production of polyesters and polyethylene terephthalates, its separation from the FCC reformate is not easy due to close boiling points among the components in the reformate. When a proper solvent for the p-xylene separation is available, an extractive distillation can be applied in the separation. Currently the separation utilizes an adsorption process requiring a large amount of costly adsorbent and a desorption process followed by distillation. In the proposed extractive distillation here, p-dinitrobenzene has been utilized to improve the separation of p-xylene from its ethylbenzene mixture. The VLE data of the ternary mixture estimated with the UNIFAC were compared to those computed from molecular simulation to show their reliability. An extractive distillation and solvent recovery were applied to obtain 99.6% purity p-xylene with 99.1% recovery. The economics of the proposed process demonstrates its comparability to the existing Parex process.

Separation of p-xylene from aromatic compounds through specific inclusion by acyclic host molecule

The separation of p-xylene from a mixture of four C8 alkylaromatics has been realized through highly selective inclusion by an adamantane-based molecule via crystallization. Further, the host molecule specifically discriminated p-xylene from eight C8 and C9 aromatic compounds.

金属有機構造体(MOF)を用いたキシレン類の分離

金属有機構造体(MOF)を用いたキシレン類の分離

Discovery of novel zeolites and multi-zeolite processes for p-xylene separation using simulated moving bed (SMB) chromatography

We present a multiscale approach for the identification of novel zeolites as well as for the optimization of simulated moving bed (SMB) chromatographic processes for p-xylene separation. Our hierarchical in silico approach pertains to detailed modeling, simulation, and optimization at molecular and process scales. At the molecular scale, it includes geometric-level pore topology characterization, minimum-energy pathway based selectivity prediction, and shape-selectivity based zeolite ranking for separation of xylenes. At the process scale, first principles model-based optimization of industrial-scale SMB process with 24 columns is performed for the selection of top zeolites and optimal process conditions. We develop a generalized mixed-integer nonlinear optimization (MINLP) model which considers both process design and material selection. We also allow for different zeolites to be selected in different columns. The application of the overall framework results in the discovery of several novel zeolites for the most profitable p-xylene separation using SMB chromatography. The top-ranked shape-selective zeolites are OBW, MEL, MWW, MTT, OWE, FER, SZR, IMF, TON and LAU, which have not been considered in the previous literature for p-xylene separation. To that end, we suggest new applications for these zeolites. Our results indicate that significant increase in profit can be achieved by replacing the current adsorbents by MWW and MEL zeolites. Remarkably, a new SMB process with multiple zeolites introduced in different columns provides the maximum profit. Such a materials-based hybrid configuration is found to significantly increase the overall p-xylene separation and profit compared to the cases when a single zeolite is used for the entire process. While the discovery of both new zeolites and process configurations is enabled through the proposed multi-scale systems approach, the findings depend on sound molecular models and call for experimental validation.

Computational Identification and Experimental Evaluation of Metal–Organic Frameworks for Xylene Enrichment

We report the computational discovery and experimental evaluation of nanoporous materials targeted at the adsorptive separation of p-xylene from a C8 aromatics mixture. We first introduce a computational method that is capable of efficiently predicting the p-xylene selectivities and capacities for a large database of porous materials. We then demonstrate the application of this method to screen a database of several thousand metal–organic framework (MOF) structures. Our computational screening methodology predicted that two MOFs with good solvothermal stability and commercially available linkers give comparable performance to the state-of-the-art zeolite BaX currently used in industrial p-xylene separations. The best-performing MOFs are then synthesized, and their xylene separation characteristics are evaluated in detail through breakthrough adsorption experiments and modeling. We find that the selectivities obtained in these materials are higher than that of any MOF previously reported in the literature ...

Quantitative Structure–Relative Volatility Relationship Model for Extractive Distillation of Ethylbenzene/p‐Xylene Mixtures: Application to Binary and Ternary Mixtures as Extractive Agents

Ethylbenzene (EB) and p‐xylene (PX) are important chemicals for the production of industrial materials; accordingly, their efficient separation is desired, even though the difference in their boiling points is very small. This paper describes the efforts toward the identification of high‐performance extractive agents for EB and PX separation by distillation. Most high‐performance extractive agents contain halogen atoms, which present health hazards and are corrosive to distillation plates. To avoid this disadvantage of extractive agents, we developed a quantitative structure–relative volatility relationship (QSRVR) model for designing safe extractive agents. We have previously developed and reported QSRVR models for single extractive agents. In this study, we introduce extended QSRVR models for binary and ternary extractive agents. The QSRVR models accurately predict the relative volatilities of binary and ternary extractive agents. The service to predict the relative volatility for binary and ternary extractive agents is freely available from the Internet at http://qsrvr.opengsi.org/.

Liquid–liquid extraction of p-xylene from their mixtures with alkanes using 1-butyl-1-methylmorpholinium tricyanomethanide and 1-butyl-3-methylimidazolium tricyanomethanide ionic liquids

Liquid – liquid experimental data for four ternary systems {1-butyl-1-methyl-morpholinium tricyanomethanide, [BMMOR][TCM], or 1-butyl-3-methylimidazolium tricyanomethanide, [BMIM][TCM] + p-xylene + octane, or decane} were determined at T = 298.15 K and atmospheric pressure. The separation of p-xylene from alkanes (octane, or decane) is performed by extraction with the tricyanomethanide - based ionic liquids. Good miscibility of p-xylene and practical complete immiscibility of alkanes in ionic liquids have been observed. Selectivity, S and solute distribution ratio, β at constant temperature for these mixtures were calculated and discussed. These parameters derived from the experimental equilibrium data were compared with the values for other ionic liquids available in the literature. The NRTL and UNIQUAC models were used to correlate experimental LLE data. Agreement between experimental and correlated data was satisfactory. The influence of the cation structure of the ionic liquid on the phase equilibrium and the separation ability of these ionic liquids was discussed. Additionally, the water content and basic physicochemical properties, such as: density, ρ and dynamic viscosity, η were determined for pure ILs at wide temperature range at ambient pressure.

Separating Xylene Isomers by Commensurate Stacking of p‐Xylene within Channels of MAF‐X8

The development of energy-efficient processes for selective separation of p-xylene from mixtures with its isomers is of vital importance in the petrochemical industries. Current industrial practice uses BaX zeolite that has high adsorption selectivity for p-xylene. Finding para-selective structures is challenging. With state-of-the-art simulation methodologies we systematically screened a wide variety of zeolites and metal-organic frameworks (MOFs). Our investigations highlight the crucial importance of the channel dimension on the separation. MAF-X8 is particularly noteworthy because the channel dimensions and geometry allow "commensurate stacking" which we exploit as a separation mechanism at saturation conditions. Due to a significantly improved capacity compared to BaX, the cycle times for p-xylene with MAF-X8 are found to be about a factor of 4.5 longer. This is expected to result in significant process improvements.

Separation and effect of residual moisture in liquid phase adsorption of xylene on y zeolites

The separation of p-xylene and m-xylene from C8 aromatic hydrocarbon feed using Y zeolites is investigated. Effect of residual moisture on p-xylene adsorption on BaY was measured in order to optimize the activation temperature of the adsorbent. The results show that with an increase in temperature the moisture on the adsorbent decreases. An optimum loading of moisture is required for adsorption of xylene on the adsorbents. The Everett equation is used to determine the adsorption capacity and selectivity. It has been found that the adsorbents best suited for the separation of p-xylene, m-xylene, o-xylene and ethyl benzene from the mixture of C8 aromatics are NaY, NaY, BaY and KY, respectively. The XRD results show that the crystallinity of the adsorbent decreases upon exchanging the zeolites to K+ and Ba2+ ions.