The work described in this paper is part of Department of Defense-Industry-University collaboration to develop fundamental understanding of the effects of alternative fuels on emissions from military ...gas turbine engines. The study was conducted in an axisymmetric, co-flow, laminar flame configuration at atmospheric pressure to determine the effects of fuel structure on aromatic species and soot. Five fuels with varying molecular structure were investigated: pure n-dodecane and four binary mixtures: m-xylene/n-dodecane, n-heptane/n-dodecane, iso-octane/n-dodecane, and methylcyclohexane/n-dodecane. Flames with non-premixed and partially-mixed fuel jets were studied. This paper describes the results of flames with non-premixed fuel jets; a companion paper describes the results for the partially pre-mixed fuel jets. In all of the experiments, the total carbon flow rate and the fraction of carbon from the two components in the binary mixtures were kept constant to facilitate comparison among the fuels. A laser-induced fluorescence technique was used to obtain spatially-resolved information on the aromatic species. Signals from aromatic species were collected in two wavelength ranges corresponding to species with one or two rings and three–five rings. Laser-induced incandescence and laser extinction were applied to obtain two-dimensional soot volume fraction for all flames. The flames of the paraffin fuels are non-smoking and have similar spatial distributions of aromatic species and soot as well as maximum soot volume fractions. The flame from the m-xylene fuel is smoking and has spatial distributions of aromatic species and soot that are distinctly different than for the paraffin fuels. Maximum soot volume fraction produced by the m-xylene fuel is approximately three times that of the paraffin fuels.
Multi‐resonant thermally activated delayed fluorescent (MR‐TADF) materials are blooming for high‐resolution organic light‐emitting diodes (OLEDs). However, boron/nitrogen (B/N)‐integrated MR‐TADF ...emitters suffer severe efficiency roll‐off from their strong inter‐molecular π–π interactions. Herein, versatile narrowband pure blue emitters (mono‐mx‐CzDABNA and tri‐mx‐CzDABNA) are demonstrated featuring a ring‐fused extended π‐skeleton: a classic steric hindrance and rigidity accessed by integrating with meta‐xylene (mx) rotors. tri‐mx‐CzDABNA shows a narrowband (FWHM, 26 nm) pure blue emission (λmax, 462 nm) with substantial hypsochromic shift (12 nm) while maintaining MR‐TADF characteristics. The key solid‐state analyses conclude that they conceivably suppress the non‐radiative energy loss, thus improving the photoluminescence quantum yield (PLQY > 90%) and rate of reverse intersystem crossing (RISC) (kRISC ≈2.85 × 105 s−1). The integration of tri meta‐xylene significantly leads to an enhanced horizontal dipole ratio (HDR) from 65% to 85%. Hyperfluorescent‐OLEDs are fabricated using designed MR‐TADF as terminal emitter, achieving a narrowband (FWHM, 34 nm) pure blue electroluminescence (λmax, 472 nm) and maximum external quantum efficiency (EQEmax) of 26.97% with magnificently suppressed efficiency roll‐off (7.8%) at 1000 cd m−2. So, it is believed that regulation of internal efficiencies and high color purity can amplify the route to achieving a narrowband pure blue emission through new synthetic MR‐TADF approaches.
The architecture of the ring fuses and extends π‐skeleton based on high‐order B/N‐embedded steric rooted and structurally rigid hypsochromic‐shifted narrow‐band pure blue multi‐resonant thermally activated delayed fluorescent emitter for efficient and ultralow‐efficiency roll‐off hyperfluorescent‐organic light‐emitting diodes.
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.
Come on xylene: Through chemical modification of the Al2O3 support by bio‐inspired polydopamine, a highly selective and stable MIL‐160 membrane was developed for separation of p‐xylene from its isomers by pervaporation. Attributed to its suitable pore size (0.5≈0.6 nm), the MIL‐160 membrane selectively allows p‐xylene to pass through, while excluding the bulkier o‐xylene and m‐xylene.
Assessing the role of volatile organic compounds (VOCs) in production of ozone and secondary organic aerosol (SOA) is especially important in light of ongoing policy goals. Here, we estimated the ...ozone formation potential (OFP) and SOA formation potential (SOAP) of anthropogenic and biogenic VOC emissions to evaluate (1) anthropogenic VOCs and associated sectors that dominate OFP and SOAP and (2) the potential impacts of enhanced biogenic VOCs from urban greening programs on air quality in Los Angeles county. In the present-day scenario, ethylene had the largest OFP followed by m & p-xylene, toluene, propylene, and formaldehyde. The top five contributors to SOAP were toluene, mineral spirits, benzene, heptadecane, and hexadecane. Mobile and solvent sources were the dominant VOC sources for both OFP and SOAP. The potential increases in biogenic VOC emissions due to future urban greening had significant effects on urban air quality that offset the benefits of reducing anthropogenic VOC emissions. This study demonstrates that urban greening programs in Los Angeles county, and likely other cities as well, need to account for both anthropogenic and biogenic VOC contributions to secondary pollution, and greening cities should consider using vegetation types with low VOC emissions to avoid further degradation to urban air quality.
This study investigated mathematical modeling and optimization of the xylene isomerization reaction in a commercial adiabatic reactor. The proposed model, consisting of a set of algebraic and ...ordinary differential equations, is based on a heterogeneous one‐dimensional steady‐state formulation. To verify the proposed model, the simulation results have been compared to available data from an industrial reactor. A good agreement has been found between the simulation and plant data. The genetic algorithm (GA) method is applied to optimize the reactor operating conditions considering the para‐xylene (p‐xylene) mole fraction in reactor outlet as the main objective function. According to the simulation results, there is an optimum initial temperature for maximizing the objective function. In the optimization process, the p‐xylene mole fraction was enhanced by 3.0% at an optimized feed temperature of 678.04K.
The wavelength-dependence of the complex refractive indices (RI) in the visible spectral range of secondary organic aerosols (SOA) are rarely studied, and the evolution of the RI with atmospheric ...aging is largely unknown. In this study, we applied a novel white light-broadband cavity enhanced spectroscopy to measure the changes in the RI (400–650 nm) of β-pinene and p-xylene SOA produced and aged in an oxidation flow reactor, simulating daytime aging under NO x -free conditions. It was found that these SOA are not absorbing in the visible range, and that the real part of the RI, n, shows a slight spectral dependence in the visible range. With increased OH exposure, n first increased and then decreased, possibly due to an increase in aerosol density and chemical mean polarizability for SOA produced at low OH exposures, and a decrease in chemical mean polarizability for SOA produced at high OH exposures, respectively. A simple radiative forcing calculation suggests that atmospheric aging can introduce more than 40% uncertainty due to the changes in the RI for aged SOA.
With the aim to solve the serious problem of white plastic pollution, we report herein a low-cost process to quantitatively convert polyethylene terephthalate (PET) into p-xylene (PX) and ethylene ...glycol (EG) over modified Cu/SiO
catalyst using methanol as both solvent and hydrogen donor. Kinetic and in-situ Fourier-transform infrared spectroscopy (FTIR) studies demonstrate that the degradation of PET into PX involves tandem PET methanolysis and dimethyl terephthalate (DMT) selective hydro-deoxygenation (HDO) steps with the in-situ produced H
from methanol decomposition at 210 °C. The overall high activities are attributed to the high Cu
/Cu
ratio derived from the dense and granular copper silicate precursor, as formed by the induction of proper NaCl addition during the hydrothermal synthesis. This hydrogen-free one-pot approach allows to directly produce gasoline fuels and antifreeze components from waste poly-ester plastic, providing a feasible solution to the plastic problem in islands.
Unlike homogeneous catalysts that are often designed for particular reactions, zeolites are heterogeneous catalysts that are explored and optimized in a heuristic fashion. We present a methodology ...for synthesizing active and selective zeolites by using organic structure-directing agents that mimic the transition state (TS) of preestablished reactions to be catalyzed. In these zeolites, the pores and cavities could be generated approaching a molecular-recognition pattern. For disproportionation of toluene and isomerization of ethylbenzene into xylenes, the TSs are larger than the reaction products. Zeolite ITQ-27 showed high disproportionation activity, and ITQ-64 showed high selectivity for the desired para and ortho isomers. For the case of a product and TS of similar size, we synthesized a catalyst, MIT-1, for the isomerization of endo-dicyclopentane into adamantane.
Taking into account that the transformation of biomass-derived 2,5-dimethylfuran (DMF) to
p
-xylene involves Diels-Alder (DA) cycloaddition as the limiting step, the use of an ITQ-2 zeolite obtained ...by direct synthesis (DS-ITQ-2) as a catalyst for this reaction is proposed based on the fact that the organic molecule employed for its synthesis mimics the size and shape of the DA oxanorbornene cycloadduct intermediate. Periodic Density Functional Theory (DFT) calculations reveal a better stabilization of the oxanorbornene intermediate within the external hemicavities or "cups" of the DS-ITQ-2 zeolite (MWW-framework) than in other zeolites employed for this reaction, such as FAU and Beta. Interestingly, experimental results also show improved catalytic conversion values for the DS-ITQ-2 zeolite compared to FAU and Beta, in good agreement with the stabilization energies calculated by DFT. The "
ab initio
" catalyst design presented here to enhance the catalytic performance for the transformation of biomass-derived products is a valuable example that could be employed for the rationalization of other chemical processes catalyzed by zeolites.
DS-ITQ-2 has been proposed as catalyst for the Diels-Alder (DA) reaction between 2,5-dimethylfuran and ethylene to produce
p
-xylene based on the fact that the organic molecule employed for its synthesis mimics the DA intermediate cycloadduct.
Single-molecule imaging is challenging but highly beneficial for investigating intermolecular interactions at the molecular level
. Van der Waals interactions at the sub-nanometre scale strongly ...influence various molecular behaviours under confinement conditions
. Inspired by the traditional compass
, here we use a para-xylene molecule as a rotating pointer to detect the host-guest van der Waals interactions in the straight channel of the MFI-type zeolite framework. We use integrated differential phase contrast scanning transmission electron microscopy
to achieve real-space imaging of a single para-xylene molecule in each channel. A good correlation between the orientation of the single-molecule pointer and the atomic structure of the channel is established by combining the results of calculations and imaging studies. The orientations of para-xylene help us to identify changes in the van der Waals interactions, which are related to the channel geometry in both spatial and temporal dimensions. This work not only provides a visible and sensitive means to investigate host-guest van der Waals interactions in porous materials at the molecular level, but also encourages the further study of other single-molecule behaviours using electron microscopy techniques.
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