Xylene Mixture Research Articles

Environmental Assessment and Eco-Efficiency Analysis of the Dividing Wall Distillation Column for Separating a Benzene–Toluene–Xylene Mixture

The benzene–toluene–xylene (BTX) system represents an energy-intensive petrochemical process with various industrial applications. Global climate changes have forced modern industry to act toward environmental safety, which requires technological changes. Thus, the divided wall column (DWC) represents a significant advancement in multicomponent mixture separation. To assess the impact of the conventional BTX process and its intensification proposal based on DWC technology, it is necessary to integrate an eco-efficiency approach that jointly analyzes the economic and environmental variables influencing the system, such as water consumption, CO2 emissions, and utility costs. An auxiliary utility plant was also considered for more realistic results in terms of energy and water consumption, which was identified as a lack in many research studies that performed an overall sustainability analysis. The results showed that the DWC scheme is 37.5% more eco-efficient than the conventional counterpart, mainly due to a 15.6% and 30.3% savings on energy and water consumption, respectively, which provided a 15.5% and 16.7% reduction on CO2 emissions and utility costs, respectively. In addition, all other environmental and safety indicators based on the waste algorithm reduction (WAR) were reduced by approximately 16%. Thus, the DWC proved to be a convenient technology with economic attractiveness and environmental friendliness.

Highly Efficient Separation of Intermediate-Size m-Xylene from Xylenes via a Length-Matched Metal-Organic Framework with Optimal Oxygen Sites Distribution.

Xylene separation is crucial but challenging, especially for the preferential separation of the intermediate-size m-xylene from xylene mixtures. Herein, exploiting the differences in molecular length and alkyl distribution among xylenes, we present a length-matched metal-organic framework, formulated as Al(OH)[O2C-C4H2O-CO2], featuring an effective pore size corresponding to m-xylene molecular length combined with multiple negative O hydrogen bond donors distribution, can serve as a molecular trap for efficient preferential separation of the intermediate-size m-xylene. Benchmark separation performance was achieved for separating m-xylene from a ternary mixture of m-xylene/o-xylene/p-xylene, with simultaneous record-high m-xylene uptake (1.3 mmol g-1) and m-xylene/p-xylene selectivity (5.3) in the liquid-phase competitive adsorption. Both vapor- and liquid-phase fixed-bed tests confirmed its practical separation capability with benchmark dynamic m-xylene/p-xylene and m-xylene/o-xylene selectivities, as well as excellent regenerability. The selective and strong m-xylene binding affinity among xylene molecules was further elucidated by simulations, validating the effectiveness of such a pore environment for the separation of intermediate-size molecules.

Highly Efficient Separation of Intermediate‐Size m‐Xylene from Xylenes via a Length‐Matched Metal–Organic Framework with Optimal Oxygen Sites Distribution

AbstractXylene separation is crucial but challenging, especially for the preferential separation of the intermediate‐size m‐xylene from xylene mixtures. Herein, exploiting the differences in molecular length and alkyl distribution among xylenes, we present a length‐matched metal–organic framework, formulated as Al(OH)[O2C−C4H2O−CO2], featuring an effective pore size corresponding to m‐xylene molecular length combined with multiple negative O hydrogen bond donors distribution, can serve as a molecular trap for efficient preferential separation of the intermediate‐size m‐xylene. Benchmark separation performance was achieved for separating m‐xylene from a ternary mixture of m‐xylene/o‐xylene/p‐xylene, with simultaneous record‐high m‐xylene uptake (1.3 mmol g−1) and m‐xylene/p‐xylene selectivity (5.3) in the liquid‐phase competitive adsorption. Both vapor‐ and liquid‐phase fixed‐bed tests confirmed its practical separation capability with benchmark dynamic m‐xylene/p‐xylene and m‐xylene/o‐xylene selectivities, as well as excellent regenerability. The selective and strong m‐xylene binding affinity among xylene molecules was further elucidated by simulations, validating the effectiveness of such a pore environment for the separation of intermediate‐size molecules.

Harnessing aerial oxygen as an oxidant for dehydrogenation of 2, 3-dihydroquinolones: An application to synthesis of 4-quinolone alkaloids

Reagent and catalyst-free dehydrogenation (aromatization) of 2, 3-dihydroquinolones under aerobic oxidation is reported. This protocol involves metal-free synthesis of 4-quinolones from easily accessible stating materials in mixture of xylenes as solvent at 130 °C for 3–6 days. No chromatography purification and workup procedures are not needed. The product solidified in pure state from the reaction mixture and unreacted starting material remain in solution. The yields are up to 95 %. This methodology will be accessible to synthesize some 4-quinolone alkaloids.

Estimation of catalytic cracking of vacuum gas oil by ZSM-5- and β-zeolite-containing two-layered and novel three-layered hierarchical catalysts using Curie point pyrolyzer

ZSM-5- and β-zeolite-containing two-layered hierarchical catalysts (2 L-Z and 2 L-β) were prepared using a template of malic acid and novel three-layered hierarchical catalysts were also prepared combining mesoporous silica derived from the gel skeletal reinforcement (GSR) method with hexamethyldisiloxane (HMDS) - acetic anhydride (AA) as reinforcing agents. 2 L-Z and 2 L-β catalysts contained mesoporous silica of 50 wt% and microporous zeolite of 50 wt% and were called 2 L-Z-(Z50) and 2 l-β-(Z50) in which the amount of zeolite is shown in parenthesis. 3 L-co-gel and 3 L-mix, two types of three-layered hierarchical catalysts, were prepared by making GSR-silica in the presence of a 2 L catalyst for the former and by combining GSR-silica-gel with 2 L catalyst for the latter. 3 L catalysts contained 50 wt% of the 2 L catalyst and 50 wt% large-mesoporous GSR-silica and revealed three layered properties of microporous zeolite, small mesoporous silica and large mesoporous silica. Signals of zeolite crystals and amorphous phase were observed in XRD measurement for 3 L catalysts. Both smaller size of mesopores and larger size of mesopores were observed in N2 adsorption-desorption measurement. Vacuum gas oil (VGO) was catalytically cracked using 2 L and 3 L hierarchical catalysts with the use of Curie point pyrolyzer (CPP) method. ZSM-5-containing 3 L catalysts exhibited the lower conversions than corresponding 2 L catalyst, kaolin-mixed catalyst and ZSM-5 single while 3 L-co-gel-β-(Z25), which included 25 wt% of β-zeolite, exhibited the highest activity among β-zeolite-containing catalysts. The higher selectivity for p-xylene in xylene mixture was detected in catalytic cracking using 3 L-co-gel-Z-(Z25) and 3 L-mix-Z-(Z25) catalysts. When the relative activity against XRD integral intensity and amounts of acid sites was plotted against average pore diameter derived from N2 adsorption-desorption measurement, the strong correlation was observed, suggesting that the intrinsic activity of active sites of zeolite could be related to the pore size of the whole catalyst.

EFFECT OF AN ALKYL SUBSTITUTE ON HYDROCONVERSION OF INDIVIDUAL AROMATIC HYDROCARBONS ON Co/HZSM-5/SO42-–ZrO2 COMPOSITE CATALYST

A systematic study of the hydrogenation of individual aromatic hydrocarbons (benzene, toluene, xylene) and their mixtures was carried out at 1800C, H2/Ar=7, WHSV = 2h-1 and atmospheric pressure on a composite catalyst 0.4%Co/HZSM-5/SO42-(2.0%)–ZrO2. It has been established that the developed catalyst has a high hydrogenating ability with respect to aromatic hydrocarbons at low hydrogen pressures. Alkyl-substituted benzenes turned out to be more active. It was found that alkyl substituents increase the activity of hydrogenation of the benzene ring of an aromatic hydrocarbon. According to their conversion, benzene, toluene and xylene form the following sequence: benzene<toluene<xylene. It was found that the optimal temperature for the process of hydroconversion of aromatic hydrocarbons on a composite catalyst is 1800C. The influence of the concentration of the hydrogenating component of the catalyst – Co on the hydroconversion was also investigated. It was found that the optimal concentration of Co is 0.4wt %. It has been established that in a benzene:toluene:xylene mixture, the conversion of benzene in comparison with its separate hydroconversion increases by more than 10%. The hydroconversion of aromatic hydrocarbons is accompanied by the formation of high-octane naphthenic hydrocarbons - cyclohexane, methylcyclohexane and methylcyclopentane. The antibatic change in the yield of CH and MCP with the duration of the experiment shows that the hydrogenation of the aromatic ring is primary and the isomerization of C6H10 to MCP is secondary, i.e. MCP is the result of a sequential transformation. The absence of dimethylcyclohexane (DMCH) in the benzene:toluene:xylene mixture conversion products suggests that the benzene and xylene conversions additionally involve transalkylation

Xylene adsorption behaviors of Co-MOF-74(X) synthesized from Co(II) salt with different anions

Xylene, a typical volatile organic compound (VOC) and primary raw material in the chemical industry, has been found to be a key component in ozone formation. Metal organic frameworks (MOFs) containing open metal sites are capable of binding to xylene. To recover xylene from waste solvent and to mitigate the environmental risks associated with it, three 1D coordination polymers (CPs), Co-MOF-74(X) (X = OAc–, Cl–, or NO3–), were synthesized using various cobalt salts of Co(OAc)2·4H2O, CoCl2·6H2O and Co(NO3)2·6H2O to investigate the influence of anions. Moreover, the liquid phase adsorptive performance for xylene was evaluated. The morphology features and structure differences of the resulting Co-MOF-74(X) were determined by SEM-EDS, XRD, N2/CO2 adsorption, FTIR and XPS. In situ DRIFT was applied to further distinguish the adsorption performance of Co-MOF-74(X) for xylene. The results indicated that Co-MOF-74(X) exhibits a different morphology. Co-MOF-74(OAc–) is flaky and agglomerated severely, while both Co-MOF-74(Cl–) and Co-MOF-74(NO3–) are hexagonal rod–like crystals. All of Co-MOF-74(X) showed microporous structures with high specific surface areas. A small amount of Cl– was retained in Co-MOF-74(Cl–), forming a Co–Cl bond with Co(II), and the active site of adsorption increased. Co-MOF-74(Cl–) shows the highest adsorption capacity of 1317.65 mg/g for the xylene mixture with excellent cyclic stability reported so far, which is 2.17 or 2.78 times more than Co-MOF-74(NO3–) or Co-MOF-74(OAc–). Therefore, it is anticipated to be a highly efficient adsorbent for removal or recovery of xylene.

Co-exposure of petrochemical workers to noise and mixture of benzene, toluene, ethylbenzene, xylene, and styrene: Impact on mild renal impairment and interaction

Epidemiological evidence concerning effects of simultaneous exposure to noise and benzene, toluene, ethylbenzene, xylene, and styrene (BTEXS) on renal function remains uncertain. In 2020, a cross-sectional study was conducted among 1160 petrochemical workers in southern China to investigate effects of their co-exposure on estimated glomerular filtration rate (eGFR) and mild renal impairment (MRI). Noise levels were assessed using cumulative noise exposure (CNE). Urinary biomarkers for BTEXS were quantified. We found the majority of workers had exposure levels to noise and BTEXS below China's occupational exposure limits. CNE, trans, trans-muconic acid (tt-MA), and the sum of mandelic acid and phenylglyoxylic acid (PGMA) were linearly associated with decreased eGFR and increased MRI risk. We observed U-shaped associations for both N-acetyl-S-phenyl-L-cysteine (SPMA) and o-methylhippuric acid (2-MHA) with MRI. In further assessing the joint effect of BTEXS (β, −0.164 [95% CI, −0.296 to −0.033]) per quartile increase in all BTEXS metabolites on eGFR using quantile g-computation models, we found SPMA, tt-MA, 2-MHA, and PGMA played pivotal roles. Additionally, the risk of MRI associated with tt-MA was more pronounced in workers with lower CNE levels (P = 0.004). Multiplicative interaction analysis revealed antagonisms of CNE and PGMA on MRI risk (P = 0.034). Thus, our findings reveal negative dose-effect associations between noise and BTEXS mixture exposure and renal function in petrochemical workers. With the exception of toluene, benzene, xylene, ethylbenzene, and styrene are all concerning pollutants for renal dysfunction. Effects of benzene, ethylbenzene, and styrene exposure on renal dysfunction were more pronounced in workers with lower CNE.

A CHARGE-ASSISTED HYDROGEN-BONDED ORGANIC FRAMEWORK FOR SELECTIVE SEPARATION OF p-XYLENE

A charge-assisted hydrogen-bonded organic framework (HOF) FJU-201 is constructed by N,N’-bis(5-isophthalic acid)naphthalimide divalent anion (H2L2-), p-xylene and dimethylammonium. FJU-201 can only crystallize in solutions containing p-xylene, and cannot crystallize in both o-xylene and m-xylene. FJU-201 can also crystallize in xylene mixtures with the content of p-xylene is not less than 50%, which can be used for separating and purifying p-xylene, and it has good recyclability.

Confinement of p‐Xylene in the Pores of a Bilanthanide Metal–Organic Framework for Highly Selective Recognition

AbstractThe rapid and accurate sensing of p‐xylene, an essential raw material with a multi‐billion‐dollar market, in xylene mixture is of great significance in industry; however, the highly similar molecular structures, energy levels, and spectral characteristics of xylene isomers make the selective recognition extremely challenging. Metal–organic frameworks (MOFs) exhibiting tailorable pores and potential binding sites provide prospects for xylene sensing but a comprehensive understanding of the pore effect is still elusive, primarily due to the intricacies involved in the sensing process. Herein, we reported a robust bilanthanide MOF NKU‐999‐EuTb with precisely engineered pores to accommodate p‐xylene, of which the binding sites were confirmed by single crystal X‐ray diffraction and dynamic magnetic susceptibilities. NKU‐999‐EuTb exhibits high‐performance in selective recognition for p‐xylene towards its isomers. Through a systematical study, it was revealed that absorbing p‐xylene into the pores governs the sensing performance. This work provides insights for developing advanced sensing materials for complex isomers.

Confinement of p-Xylene in the Pores of a Bilanthanide Metal-Organic Framework for Highly Selective Recognition.

The rapid and accurate sensing of p-xylene, an essential raw material with a multi-billion-dollar market, in xylene mixture is of great significance in industry; however, the highly similar molecular structures, energy levels, and spectral characteristics of xylene isomers make the selective recognition extremely challenging. Metal-organic frameworks (MOFs) exhibiting tailorable pores and potential binding sites provide prospects for xylene sensing but a comprehensive understanding of the pore effect is still elusive, primarily due to the intricacies involved in the sensing process. Herein, we reported a robust bilanthanide MOF NKU-999-EuTb with precisely engineered pores to accommodate p-xylene, of which the binding sites were confirmed by single crystal X-ray diffraction and dynamic magnetic susceptibilities. NKU-999-EuTb exhibits high-performance in selective recognition for p-xylene towards its isomers. Through a systematical study, it was revealed that absorbing p-xylene into the pores governs the sensing performance. This work provides insights for developing advanced sensing materials for complex isomers.

Human Health Risk Assessment of the Photocatalytic Oxidation of BTEX over TiO2/Volcanic Glass.

This study demonstrates rapid photocatalytic oxidation of a benzene, toluene, ethylbenzene, and xylene (BTEX) mixture over TiO2/volcanic glass. The assessment of the photocatalytic oxidation of BTEX was conducted under conditions simulating those found in indoor environments affected by aromatic hydrocarbon release. We show, under UV-A intensities of 15 mW/cm2 and an air flow rate of 55 m3/h, that low ppmv levels of BTEX concentrations can be reduced to below detectable levels. Solid-phase microextraction technique was employed to monitor the levels of BTEX in the test chamber throughout the photocatalytic oxidation, lasting approximately 21 h. Destruction of BTEX from the gas phase was observed in the following sequence: o-xylene, ethylbenzene, toluene, and benzene. This study identified sequential degradation of BTEX, in combination with the stringent regulatory level set for benzene, resulted in the air quality hazard indexes (Total Hazard Index and Hazard Quotient) remaining relatively high during the process of photocatalytic oxidation. In the practical application of photocatalytic purification, it is crucial to account for the slower oxidation kinetics of benzene. This is of particular importance due to not only its extremely low exposure limits, but also due to the classification of benzene as a Group 1 carcinogenic compound by the International Agency for Research on Cancer (IARC). Our study underscores the importance of taking regulatory considerations into account when using photocatalytic purification technology.

Three-Dimensionally Ordered Silicalite-1 Membrane for Separation of the Xylene Mixture with High Permeance and Separation Factor

Three-Dimensionally Ordered Silicalite-1 Membrane for Separation of the Xylene Mixture with High Permeance and Separation Factor

Chemical Delamination Applicable to a Low-Energy Recycling Process of Photovoltaic Modules

This work follows the current trend and need to ensure the best recyclability of retired materials. This paper focuses on experiments with chemical delamination of polymer layers on crystalline silicon photovoltaic cells. The aim of the study is to separate individual components of a PV module so that the components can be subsequently recycled with low energy demand. The ultimate goal is to separate whole silicon cells for reuse rather than for recycling. Several solvents (e.g., toluene, cyclohexane, tetrahydrofuran, and the commercial solvent U 6002 (a mixture of xylene and 2-ethoxyethylacetate)) were used to disrupt the polymer layers. The results showed toluene to be the most effective solvent, which acted the fastest and was able to disrupt the EVA (ethylene-vinyl acetate) film structure the most. The main problem of the investigated chemical delamination was the concurrent solvent absorption by the EVA film. This phenomenon was observed for all solvents. The absorption prevented the dissolution of the EVA film and changed its dimension, causing the adhering silicon cells to crack. While, as the final experiment shows, chemical delamination is, as done, a more energy-intensive process in terms of total energy consumption than the current chemical mechanical processes, we propose in the next development the recapture of toluene from the swollen EVA.

Liquid–Liquid Equilibrium in Xylene Solubles (XS) Analysis of Polypropylene

AbstractA multicomponent Flory‐Huggins model is implemented and utilized to describe the liquid–liquid equilibrium phenomenon in mixtures of polypropylene and xylene, in the context of the well‐known xylene solubles (XS) test. The XS experiment is a common procedure in many polymer laboratories, used to determine the percentage of xylene solubles in samples of polypropylene, which provides an approximate measure of the atactic and oligomeric chains. Despite the importance of the test, the literature lacks a thermodynamic perspective regarding the description of this extraction phenomenon. In the present study, the Flory‐Huggins interaction parameter is adjusted in a multicomponent framework to ensure that equilibrium chain length distributions calculated with the proposed model best match experimental distributions. It is shown that the experimental data obtained from XS analyses can be accurately fitted by the proposed model and that the estimated Flory‐Huggins interaction parameter is more sensitive to the polymer average molar mass than to the degree of tacticity, when a particular catalyst is considered.

Thermodynamic approach for hydrogen production from the steam reforming reaction of aromatic hydrocarbons (BTX)

This study investigates the preferred reaction conditions through thermodynamic analysis to produce hydrogen from the steam reforming of BTX, a mixture of benzene (C6H6), toluene (C7H8), and xylene (C8H10). A thermodynamic equilibrium analysis employing the minimization of Gibbs free energy was used to investigate the effects of temperatures (200–1000 °C), S/C ratios (0.5–4.0), and pressure (1–20 atm) on the molar fraction at equilibrium, conversion (C6H6, C7H8, C8H10), selectivity (C, CO, CO2, CH4), moles (H2 and CH4), and H2 yield. The steam reforming of BTX is a complex process that involves various reactions such as steam reforming, cracking, carbon formation, and water-gas shift reactions. It was confirmed that cracking does not occur above 700 °C, and carbon deposition does not form with S/C ratio higher than 3.0. In addition, the steam reforming reaction of BTX was found to be favorable at low pressure. To minimize undesirable reactions, such as cracking and carbon deposition, and enhance hydrogen production, the optimal conditions were identified as S/C ratio of 3.0, temperature of at least 700 °C, and atmospheric pressure. This research contributes valuable insights into the steam reforming of BTX, highlighting the optimal conditions that maximize hydrogen production while minimizing unwanted reactions. By identifying these conditions, the study underlines the importance and innovation in the hydrogen production field, potentially guiding future research and industrial applications.

Behavior of C70 Fullerene in a Binary Mixture of Xylene and Tetrahydrofuran

The self-organization properties of C70 fullerene molecules in a xylene/tetrahydrofuran binary mixture were studied for the first time by optical absorption, refractometry, and dynamic light scattering. A correlation has been established between the change in the refractive index of the C70/xylene/tetrahydrofuran solution and the degree of self-organization of C70 molecules in the medium at various concentrations and storage periods of the solution. It is shown that the features of the optical absorption spectrum of C70/xylene/tetrahydrofuran at a fixed low concentration of fullerene are sensitive to its storage time. It was determined that the beginning time of the formation of C70 nanoclusters and their final size depend on the degree of concentration of fullerene and the time spent keeping the solution. The observed nature of the C70 fullerene solution in a binary mixture may help to elucidate its mechanism of self-organization in the future.

Controllability and Energy‐Saving Ability of the Dividing‐Wall Column for Batch Distillation

AbstractThe batch distillation is significant and flexible to separate liquid mixtures. However, it is usually energy intensive. The dividing‐wall column (DWC) is a promising and practical energy‐saving process intensification technology. The DWC for batch distillation (batch DWC) to separate benzene, toluene, and xylene mixtures was examined with composition and temperature control structures to verify its controllability. Besides, the batch DWC outperforms the conventional single‐column batch distillation and middle‐vessel batch distillation in terms of distillation time and energy consumption under the same conditions. In terms of more practical temperature control results, the batch DWC saves 63 % of energy compared with the conventional single‐column batch distillation and 47 % of energy compared with the middle‐vessel batch distillation.

Process Optimization of Para-xylene Crystallization Separation Process via Morphology Approach, Multi-dimensional Population Balance Equation, and Equation-Oriented Models.

An activity coefficient-based model was proposed to predict pertinent saturated concentrations in organic solid-liquid equilibrium, and the binary parameters of xylene mixtures were experimentally obtained. Also, a novel monocular 3D reconstruction technique was developed to measure crystal size and applied to derive the kinetics of nucleation and growth of para-xylene crystals. Subsequently, a multi-dimensional population balance equation was used to predict the particle size distribution in the crystallizer and an algorithm was designed to simulate and optimize the economic benefit of the crystallization separation process. Consequently, it became possible to predict the optimal coolant flowrate and inlet temperature, as well as the feed flowrate for a crystallization process with given operating conditions and device parameters.

Synthesis of an IMF zeolite membrane for the separation of xylene isomer

The synthesis of a continuous IMF zeolite membrane was fabricated on tubular substrates by seeded growth for the first time. The straight channels of IMF zeolite with diameters of 0.53–0.59 nm are distinguishable for p-xylene from o-xylene molecules. Pure IMF-phase high-silica IM-5 zeolite seeds with uniform and fine crystal size were fabricated by a new sonication-assisted aging process. The seeds were coated on the support by dipcoating and induced the formation of continuous membrane. Separation performance in p-/o-xylene mixture was investigated at various temperature and pressure. The typical IM-5 zeolite membrane had p-/o-xylene separation factor of 3.7. Our results suggest that IM-5 zeolite is a potentially good membrane material for the separation of xylene mixtures.