Combined environmental exposures to the volatile organic compounds (VOCs) Benzene, Toluene, Ethylbenzene, and Xylene (BTEX) pose clear risks to public health. Research into these risks is ...under-studied even as BTEX levels in the atmosphere are predicted to rise. This review focuses on the available literature using single- and combined-BTEX component inhaled solvent exposures in animal models, necessarily also drawing on findings from models of inhalant abuse and occupational exposures. Health effects of these exposures are discussed for multiple organ systems, but with particular attention on neurobehavioral outcomes such as locomotor activity, impulsivity, learning, and psychopharmacological responses. It is clear that animal models have significant differences in the concentrations, durations and patterns of exposure. Experimental evidence of the deleterious health and neurobehavioral consequences of exposures to the individual components of BTEX were found, but these effects were typically assessed using concentrations and exposure patterns not characteristic of environmental exposure. Future studies with animal models designed appropriately to explore combined BTEX will be necessary and advantageous to discovering health outcomes and more subtle neurobehavioral impacts of long-term environmental exposures.
5-Hydroxymethylfurfural (HMF) is a platform chemical derived from C6 sugars, which can be transformed into various important chemicals and fuels because of the presence of C&z.dbd;O, C-O and furan ...ring functional groups. In this review, the selective tailoring of these groups in HMF to form 2,5-dimethylfuran, 2,5-dihydromethylfuran, 2,5-dihydromethyltetrahydrofuran, 5-ethoxymethylfurfural, 1,6-hexanediol, long-chain alkanes, 3-(hydroxy-methyl)cyclopentanone,
p
-xylene, 2,5-diformylfuran, 2,5-furandicarboxylic acid and maleic anhydride will be described to gain more insight into the transformation of HMF under various conditions. The focus of this review is on the mechanisms of the catalytic processes and potential design strategies for future catalysts. The activation of the functional groups and the key challenges involved in the precise design of bifunctional catalysts are highlighted. Some examples of "one-pot" transformations of fructose into various chemicals using the HMF platform are also presented.
The catalytic mechanisms and catalyst design strategies for 5-hydroxymethylfural conversion are summarized.
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•Spinel-type NiCr2O4 based chemiresistive gas sensors were rarely reported for VOC gas detection working at moderate temperatures.•NiO/NiCr2O4 nanocomposites were successfully ...synthesized through a simple hydrothermal route and used as sensing materials.•The NiO/NiCr2O4 based gas sensor showed 37.2 times higher xylene response of 66.2–100 ppm compared with unmodified NiO sensor.•Superior xylene selectivity against other interfering gases such as ethanol (Sxylene/Sethanol = 11.8) and acetone (Sxylene/Sacetone = 10.2).•Ppb-level detection limit with a response of 1.2–50 ppb xylene indicated the potential use on the trace xylene detection.
Xylene is a harmful and hazardous volatile organic compound (VOC) indoors, thus selective and sensitive detection for subppm-level xylene is crucial, however a remained challenge. In this work, p-NiO/p-NiCr2O4 nanocomposites were successfully synthesized through a simple hydrothermal route and used as sensing materials. In the comparative gas sensing test, the sensor fabricated from NiO/NiCr2O4 (Cr/Ni = 25 at%) nanocomposite exhibited the highest response (66.2–100 ppm) to xylene, which was 37.2 times higher than that of the pure NiO sensor. Moreover, the NiO/NiCr2O4 nanocomposite gas sensor showed not only superior xylene selectivity with low cross-responses to interfering gases such as ethanol (Sxylene/Sethanol = 11.8) and acetone (Sxylene/Sacetone = 10.2) but also ppb-level detection limit (1.2–50 ppb xylene) at 225 °C. The synergistic catalytic effect between NiO and NiCr2O4, optimized structural parameters and marked resistive variation due to the formation of nanoscale p-p heterojunctions were regarded as the main reasons for the ultrasensitive and selective xylene detection.
The separation and purification of xylene isomers is an industrially important but challenging process. Developing highly efficient adsorbents is crucial for the implementation of simulated moving ...bed technology for industrial separation of these isomers. Herein, we report a stacked one-dimensional coordination polymer {Mn(dhbq)(H
2
O)
2
, H
2
dhbq = 2,5-dihydroxy-1,4-benzoquinone} that exhibits an ideal molecular recognition and sieving of xylene isomers. Its distinct temperature-adsorbate–dependent adsorption behavior enables full separation of
p
-,
m
-, and
o
-xylene isomers in both vapor and liquid phases. The delicate stimuli-responsive swelling of the structure imparts this porous material with exceptionally high flexibility and stability, well-balanced adsorption capacity, high selectivity, and fast kinetics at conditions mimicking industrial settings. This study may offer an alternative approach for energy-efficient and adsorption-based industrial xylene separation and purification processes.
Using polymers to separate xylene isomers
Each of the three xylene isomers is a valuable feedstock for many chemical processes. However, because they have similar boiling points, separation by distillation or other evaporative methods is energy intensive and inefficient. Li
et al
. developed an alternative separation process using a manganese-based, stacked, one-dimensional coordination polymer with an interchain distance that varies with temperature and the content of the adsorbed hydrocarbons. At 393 kelvin, only
p
-xylene can access the voids, whereas
m
-xylene can enter at temperatures between 333 and 393 kelvin and
o
-xylene only below 333 kelvin. Through a sequence of separations, each isomer can be extracted with high selectivity. The material is simple, cost-effective, and easily scalable, and it exhibits remarkable water and air stability and excellent recyclability. —MSL
Controlling the interchain spacing of a flexible one-dimensional coordination polymer enables separation of three xylene isomers.
The oriented conversion of CO2 into target high‐value chemicals is an effective way to reduce carbon emissions, but still presents a challenge. In this communication, we report the oriented ...conversion of CO2 into value‐added aromatics, especially para‐xylene, in a single pass by combining core–shell structured Zn‐doped H‐ZSM‐5 (Zn‐ZSM‐5@SiO2) and a Cr2O3 component. Through precise regulation of the acidity of Zn‐ZSM‐5@SiO2, high para‐xylene selectivity (38.7 % in the total products) at a CO2 conversion of 22.1 % was achieved. Furthermore, a CO2‐assisted effect in the synthesis of aromatics during the tandem process has been clarified through a control experiment. The CO2 reactant can act as a hydrogen acceptor to accelerate the dehydrogenation of alkenes, intermediates in the synthesis of aromatics, thereby increasing the driving force towards aromatics in the tandem reaction process.
Tandem CO2 conversion: A capsule catalyst with Zn‐doped H‐ZSM‐5 (Zn‐ZSM‐5) as core and amorphous SiO2 as shell (Zn‐ZSM‐5@SiO2) has been prepared and combined with Cr2O3 as a methanol synthesis catalyst to realize the direct conversion of CO2 into value‐added aromatics, especially para‐xylene, in a tandem process (see figure).
Abstract
Transformation of greenhouse gas CO
2
and renewable H
2
into fuels and commodity chemicals is recognized as a promising route to store fluctuating renewable energy. Although several C
1
...chemicals, olefins, and gasoline have been successfully synthesized by CO
2
hydrogenation, selective conversion of CO
2
and H
2
into aromatics is still challenging due to the high unsaturation degree and complex structures of aromatics. Here we report a composite catalyst of ZnAlO
x
and H-ZSM-5 which yields high aromatics selectivity (73.9%) with extremely low CH
4
selectivity (0.4%) among the carbon products without CO. Methanol and dimethyl ether, which are synthesized by hydrogenation of formate species formed on ZnAlO
x
surface, are transmitted to H-ZSM-5 and subsequently converted into olefins and finally aromatics. Furthermore, 58.1%
p
-xylene in xylenes is achieved over the composite catalyst containing Si-H-ZSM-5. ZnAlO
x
&H-ZSM-5 suggests a promising application in manufacturing aromatics from CO
2
and H
2
.
Spray combustion of Jet A-1 and a Jet A-1/10% m-xylene blend was investigated to assess the influence of m-xylene addition on the spray characteristics and soot formation in a swirl-stabilized model ...combustor with dimensions of 94 mm × 94 mm cross-section and 188 mm length. Keeping the thermal power output constant at 10 kW, globally fuel lean flames were established for the neat Jet A-1 and 10% m-xylene blend fuels. The velocity field of the model combustor, spray characteristics, and soot volume fraction and primary particle size were measured, respectively, using stereoscopic particle image velocimetry, a Fraunhofer diffraction based droplet sizer, and auto-compensating laser-induced incandescence. Addition of m-xylene to Jet A-1 caused measurable differences in the flow field and the spray characteristics under identical air and fuel flow rates. Soot concentrations were modified throughout the flame by the addition of m-xylene, resulting in significant alterations in the cumulative soot loading within the spray flame envelope. In both flames, peak soot volume fractions were detected in the lower central portion of the combustor at the base of the inner recirculation zone and in the upper portion of the combustor in the fuel shear layer. Our results demonstrate the nontrivial influence of altered distillation characteristics (and other physical properties) of the fuel, induced by m-xylene addition, on flow field structure and spray properties. Potential mechanisms for the influence of changing flow field and spray characteristics, in addition to m-xylene doping of the Jet A-1, on soot processes are discussed.
The heterogeneous metal‐organic framework Bi‐BTC successfully catalyzed the synthesis of para‐xylene from bio‐based 2,5‐dimethylfuran and acrylic acid in a promising yield (92 %), under relatively ...mild conditions (160 °C, 10 bar), and with a low reaction‐energy barrier (47.3 kJ mol−1). The proposed reaction strategy also demonstrates a remarkable versatility for furan derivatives such as furan and 2‐methylfuran.
The heterogeneous metal‐organic framework Bi‐BTC can catalyze the conversion of bio‐based 2,5‐dimethylfuran and acrylic acid into para‐xylene with a promising yield (92 %) under relatively mild conditions (160 °C, 10 bar).
Large volumes of wastewater are generated during petroleum refining processes. Petroleum refinery wastewater (PRW) can contain highly toxic compounds that can harm the environment. These toxic ...compounds can be a challenge in biological treatment technologies due to the effects of these compounds on microorganisms. These challenges can be overcome by using ozone (O
3
) as a standalone or as a pretreatment to the biological treatment. Ozone was used in this study to degrade the organic pollutants in the heavily contaminated PRW from a refinery in Mpumalanga province of South Africa. The objective was achieved by treating the raw PRW using ozone at different ozone treatment times (15, 30, 45, and 60 min) at a fixed ozone concentration of 3.53 mg/dm
3
. The ozone treatment was carried out in a 2-liter custom-designed plexiglass cylindrical reactor. Ozone was generated from an Eco-Lab-24 corona discharge ozone generator using clean, dry air from the Afrox air cylinder as feed. The chemical oxygen demand, gas chromatograph characterization, and pH analysis were performed on the pretreated and post-treated PRW samples to ascertain the impact of the ozone treatment. The ozone treatment was effective in reducing the benzene, toluene, ethylbenzene, and xylenes (BTEX) compounds in the PRW. The 60-min ozone treatment of different BTEX pollutants in the PRW resulted in the following percentage reduction: benzene 95%, toluene 77%, m + p-xylene 70%, ethylbenzene 69%, and o-xylene 65%. This study has shown the success of using ozone in reducing the toxic BTEX compounds in a heavily contaminated PRW.
Carbon molecular sieve (CMS) membranes are candidates for the separation of organic molecules due to their stability, ability to be scaled at practical form factors, and the avoidance of expensive ...supports or complex multi‐step fabrication processes. A critical challenge is the creation of “mid‐range” (e.g., 5–9 Å) microstructures that allow for facile permeation of organic solvents and selection between similarly‐sized guest molecules. Here, we create these microstructures via the pyrolysis of a microporous polymer (PIM‐1) under low concentrations of hydrogen gas. The introduction of H2 inhibits aromatization of the decomposing polymer and ultimately results in the creation of a well‐defined bimodal pore network that exhibits an ultramicropore size of 5.1 Å. The H2 assisted CMS dense membranes show a dramatic increase in p‐xylene ideal permeability (≈15 times), with little loss in p‐xylene/o‐xylene selectivity (18.8 vs. 25.0) when compared to PIM‐1 membranes pyrolyzed under a pure argon atmosphere. This approach is successfully extended to hollow fiber membranes operating in organic solvent reverse osmosis mode, highlighting the potential of this approach to be translated from the laboratory to the field.
The pyrolysis of PIM‐1‐derived carbon molecular sieve membranes in an H2‐included environment results in well‐defined “mid‐sized” micropores and a drastic increase in p‐xylene permeability with a little loss in p‐xylene/o‐xylene selectivity.
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