Search Results (27)

The oxidative coupling of methane (OCM) is a promising process for converting methane directly into more valuable ethane and ethylene. In this work, high time resolution online mass spectrometry was employed to track the OCM reaction over a commercial La₂O₃ catalyst, focusing on the effects of methane to oxygen ratio, gas hourly space velocity (GHSV), and the presence of H₂O and CO in the feed gas on methane conversion and C₂ yield. The results demonstrated that an optimized GHSV (44,640 to 93,000 mL·g⁻¹·h⁻¹) and methane to oxygen ratio (CH₄/O₂ = 3) would achieve the highest methane conversion and C₂ yield at 740 °C. Furthermore, at a GHSV of 44,640 mL·g⁻¹·h⁻¹, the introduction of 1% H₂O into the reaction mixture resulted in a twofold increase in C₂ yield at 650 °C, while the addition of 1% CO led to a threefold increase in C₂ yield at 550 °C. A model in which only the front-end catalyst is active was also developed to show excellent agreement with the experimental data. The relationship between catalytic performance and the effective catalyst position in the catalyst bed provides important insights into optimizing reactor design and operating conditions to maximize C₂ yield and selectivity in the OCM reaction. Full article

A three-dimensional numerical investigation using ethylene–oxygen was conducted to examine the characteristics of detonation waves in a non-premixed rotating detonation engine (RDE) across three equivalence ratio conditions: fuel-lean, stoichiometric, and fuel-rich. The study aims to identify the distinct timescales associated with detonation wave propagation within the combustor and to analyze their impact on detonation wave behavior, emphasizing the influence of equivalence ratio and injector behavior on detonation wave characteristics. The results indicate that the wave behavior varies with mixture concentration, with the ethylene injector demonstrating greater stiffness compared to the oxygen injector. In lean mixtures, characterized by excess oxidizer, waves exhibit less intensity and slower progression toward equilibrium, resulting in prolonged reaction times. Rich mixtures, with excess fuel, also show a delayed approach to equilibrium and an extended chemical reaction timescale. In contrast, the near-stoichiometric mixture achieves efficient combustion with the highest thermicity, rapidly reaching equilibrium and exhibiting the shortest chemical reaction timescale. Overall, the induction timescale is generally 2–3 times longer than its respective chemical reaction timescale, while the equilibrium timescale spans a broad range, reflecting the complex, rapid dynamics inherent in these chemical processes. This study identifies the role of the characteristic chemical timescale in influencing the progression of pre-detonation deflagration in practical RDEs. Prolonged induction times in non-ideal conditions, such as those arising from equivalence ratio variations, promote incomplete reactions, thereby contributing to pre-detonation phenomena and advancing our understanding of the underlying flow physics. Full article

Ethylene glycol (EG) is a contaminant in the wastewater of airports because it is commonly used in aircraft deicing fluids during the cold season in northern regions. Ethylene glycol by itself has relatively low toxicity to mammals and aquatic organisms, but it can lead to a substantial increase in chemical and biological oxygen demands. The contamination of water with EG facilitates the rapid growth of microbial biofilms, which decreases the concentration of dissolved oxygen in water and negatively affects overall biodiversity. The development of a simple method to decompose EG with high efficiency and low operating costs is important. This study revealed that ethylene glycol can be completely oxidized using UV-C activated hydrogen peroxide (H₂O₂/UV-C) at a high rate (up to 56 mg L⁻¹ h⁻¹) at an optimum EG:H₂O₂ molar ratio of 1:10–1:15. Air purging the reaction mixture at 1000 cm³ min⁻¹ increases the EG mineralization rate up to two times because the simultaneous action of UV-activated H₂O₂ and O₂ (H₂O₂ + O₂/UV-C) leads to a synergistic effect, especially at low EG:H₂O₂ ratios. The kinetics and mechanism of EG degradation are discussed on the basis of the concentration profiles of ethylene glycol and intermediate products. Full article

The main weakness of non-silicone hydrogel contact lenses is their low oxygen permeability (Dk). Hence, we have tried to optimize their Dk using various concentrations and lengths of the poly (ethylene glycol) dimethacrylate crosslinker in a mixture of N,N-Dimethylacrylamide and Cyclohexyl methacrylate monomers. After synthesizing the different contact lenses, we evaluated their chemical, optical, and mechanical properties. The resultant non-silicone hydrogel contact lenses presented similar high water contents (75.69–80.60%) and adequate optical (e.g., a transmittance ranging from 85.91% to 99.91% and a refractive index between 1.3630 and 1.3740) and elongation at break (178.95–356.05%) characteristics for clinical applications. Conversely, they presented high contact angles (81.00–100.00°) and a low Young’s modulus (0.066–0.167 MPa). Regarding the impact of the crosslinking modifications, the water content, contact angle, refractive index, transmittance, and Young’s modulus of the synthesized lenses were slightly affected by crosslinker conditions. In contrast, the elongation at break (178.95–356.05%) and, more importantly, the oxygen permeability, which reached values of up to 73.90 Fatt units, were considerably impacted by the crosslinker conditions. To our knowledge, this study demonstrates for the first time that, in addition to water, other usual hydrogel components, like crosslinkers, can modulate the Dk of non-silicone contact lenses. It also provides a simple and scalable method to fabricate more permeable non-silicone lenses. Full article

Methylene blue dye in water sources can pose health risks to humans, potentially causing methemoglobinemia, a condition that impairs the blood’s ability to carry oxygen. Hence, the current study investigates the synthesis of novel magnesium borate/magnesium oxide (Mg₃B₂O₆/MgO) nanostructures and their efficiency in removing methylene blue dye from aqueous media. The nanostructures were synthesized using the Pechini sol–gel method, which involves a reaction between magnesium nitrate hexahydrate and boric acid, with citric acid acting as a chelating agent and ethylene glycol as a crosslinker. This method helps in achieving a homogeneous mixture, which, upon calcination at 600 and 800 °C, yields Mg₃B₂O₆/MgO novel nanostructures referred to as MB600 and MB800, respectively. The characterization of these nanostructures involved techniques like X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, N₂ gas analyzer, and field-emission scanning electron microscope (FE-SEM). These analyses confirmed the formation of orthorhombic Mg₃B₂O₆ and cubic MgO phases with distinct features, influenced by the calcination temperature. The mean crystal size of the MB600 and MB800 samples was 64.57 and 79.20 nm, respectively. In addition, the BET surface area of the MB600 and MB800 samples was 74.63 and 64.82 m²/g, respectively. The results indicated that the MB600 sample, with its higher surface area, generally demonstrated better methylene blue dye removal performance (505.05 mg/g) than the MB800 sample (483.09 mg/g). The adsorption process followed the pseudo-second-order model, indicating dependency on available adsorption sites. Also, the adsorption process matched well with the Langmuir isotherm, confirming a homogeneous adsorbent surface. The thermodynamic parameters revealed that the adsorption process was physical, exothermic, and spontaneous. The MB600 and MB800 nanostructures could be effectively regenerated using 6 M HCl and reused across multiple cycles. These findings underscore the potential of these nanostructures as cost-effective and sustainable adsorbents for methylene blue dye removal. Full article

A 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-based derivative (PN-DOPO) combined with aluminium phosphates-coated sepiolite (Sep@AlPO₄) was used to improve the flame retardance, thermal stability and mechanical performances of poly (ethylene oxide) (PEO)/poly (butylene adipate-co-terephthalate) (PBAT) blends. The synergistic effects of PN-DOPO and Sep@AlPO₄ on flame-retarded PEO/PBAT composites were systematically discussed. Results indicated that introducing 5 wt% Sep@AlPO₄ with 10 wt% PN-DOPO into PEO/PBAT achieved a V-1 rating for the UL-94 test and increased the limiting oxygen index value to 23.7%. Moreover, the peak heat release rate (p-HRR), average HRR and total heat release values of PEO/PBAT/PN10%/Sep5% composites decreased by 35.6%, 11.0% and 23.0% compared with those of PEO/PBAT, respectively. Thermogravimetric analysis (TGA) results confirmed that PN-DOPO/Sep@AlPO₄ enhanced the initial thermal stability and char yield of PEO/PBAT matrix, and TGA/Fourier transform infrared spectrometry results revealed that the composites exhibited the characteristic absorption peaks of phosphorous-containing groups and an increase in gas-phase volatiles during thermal degradation. The morphological structures of the residues indicated that PN-DOPO and Sep@AlPO₄ mixtures produced a more dense and continuous char layer on the composite surface during burning. Rheological behaviour revealed that higher complex viscosity and modulus values of PEO/PBAT/PN-DOPO/Sep@AlPO₄ sample could also promote the crosslinking network structure of condensed phases during combustion. Furthermore, the PEO/PBAT/PN-DOPO/Sep@AlPO₄ composites exhibited superior elongation at break and flexural performance than the PEO/PBAT system. All results demonstrated that the PEO/PBAT system modified with PN-DOPO/Sep@AlPO₄ showed remarkable flame retardance, and improved thermal stability and mechanical properties, indicating its potential application in areas requiring fire safety. Full article

Rotating detonation engines (RDEs) are considered to be promising thrusters for aerospace propulsion. Detonation initiation in RDEs can be accompanied by a destructive explosion of an excess volume of the fuel mixture in the combustor. To exclude this phenomenon, a “mild” rather than “strong” initiation of detonation is required. For the mild initiation of detonation in RDEs, it is necessary to ignite a mixture of a certain minimum volume sufficient for deflagration-to-detonation transition (DDT). In this study, the critical conditions for detonation initiation through DDT in a semiconfined slit combustor simulating the RDE combustor with a separate supply of ethylene and oxygen diluted with nitrogen (from 0 to 40%) were obtained experimentally. It turned out that for the mild initiation of detonation, it is necessary to ignite the mixture upon reaching the critical (minimum) height of the combustible mixture layer. Thus, for the mild initiation of detonation in the undiluted C₂H₄ + 3O₂ mixture filling such a slit combustor, the height of the mixture layer must exceed the slit width by approximately a factor of 12. In terms of the transverse size of the detonation cell λ the minimum layer height of such mixtures in experiments is ~150λ. Compared to the experiments with the premixed composition, the critical height of the layer is 20% larger, which is explained by the finite rate of mixing. As the degree of oxygen dilution with nitrogen increases, the critical height of the layer increases, and the role of finite rate mixing decreases: the results no longer depend on the method of combustible mixture formation. Full article

Systematic three-dimensional numerical simulations of flame acceleration and deflagration-to-detonation transition (DDT) in a semi-confined flat slit combustor are performed. The combustor is assumed to be partly filled with the stoichiometric ethylene–oxygen mixture at normal pressure and temperature conditions. The objective of the study is to reveal the conditions for DDT in terms of the minimum height of the combustible mixture layer in the slit, the maximum dilution of the mixture with nitrogen and the maximum slit width. The results of the calculations are compared with the available experimental data. The calculation results are shown to agree satisfactorily with the experimental data on the slit-filling dynamics, flame structure, the occurrence of the preflame self-ignition center, DDT, and detonation propagation. DDT occurs in the layer at a time instant when the flame accelerates to a velocity close to 750 m/s. DDT occurs near the slit bottom due to the formation of the self-ignition center ahead of the leading edge of the flame as a result of shock wave reflections from the walls of injector holes at the slit bottom and from the corners of the conjugation of the slit bottom and side walls. The decrease in the height of the mixture layer, the dilution of the mixture with nitrogen, and the increase in the slit width are shown to slow down flame acceleration in the slit and increase the DDT run-up distance and time until DDT failure. The obtained results are important for determining the conditions for mild initiation of detonation via DDT in semi-confined annular RDE combustors. Full article

In this work, dimethoxyethane (DME) and 1,3-dioxolane (DOL) are studied as the co-solvent of an advanced electrolyte for fast charging of Li-ion batteries by using lithium bis(fluorosulfonyl)imide (LiFSI) as a salt and fluorinated ethylene carbonate (FEC) as an additive. It is shown that even when used with LiFSI and FEC, neither DME nor DOL constitute a suitable electrolyte for Li-ion batteries, either because of their inability to form a robust solid-electrolyte interphase (SEI) with graphite (Gr) anodes or because of their oxidative instability against oxygen released from the delithiated LiNi_0.80Co_0.10Mn_0.10O₂ (NCM811) and LiNi_0.80Co_0.15Al_0.05O₂ (NCA), respectively. However, using 30% FEC as the co-solvent can make 1:1 DME/DOL mixture compatible with high-voltage Li-ion batteries and combining it with conventional ethylene carbonate (EC) and ethyl methyl carbonate (EMC) significantly enhances the fast charging capability of Li-ion batteries. As a result, an advanced electrolyte composed of 1.2 m (molality) LiFSI 1:1:1:2 DME/DOL/EC/EMC + 10% FEC (all by wt.) offers much improved fast-charging performances in terms of capacity and capacity retention for a 200 mAh Gr/NCA pouch cell, compared with a 1.2 m LiFSI 3:7 EC/EMC baseline electrolyte. AC impedance analysis reveals that the significant improvement is attributed to a much reduced charge transfer resistance, while the advanced electrolyte has little effect on the bulk and SEI resistances. Full article

The joint American–Russian Space Experiment Flame Design (Adamant) was implemented on the International Space Station (ISS) in the period from 2019 to 2022. The objectives of the experiment were to study the radiative extinction of spherical diffusion flames (SDF) around a porous burner (PB) under microgravity conditions, as well as the mechanisms of control of soot formation in the SDF. The objects of the study were the normal and inverse SDFs of gaseous ethylene in an oxygen atmosphere with nitrogen dilution at room temperature and pressures ranging from 0.5 to 2 atm. The paper presents the results of transient 1D and 2D calculations of 24 normal and 13 inverse SDFs with and without radiative extinction. The 1D calculations revealed some generalities in the evolution of SDFs with different values of the stoichiometric mixture fraction. The unambiguous dependences of the ratio of flame radius to fluid mass flow rate through the PB on the stoichiometric mixture fraction were shown to exist for normal and inverse SDFs. These dependences allowed important conclusions to be made on the comparative flame growth rates, flame lifetime, and flame radius at extinction for normal and inverse SDFs. The 2D calculations were performed for a better understanding of the various observed non-1D effects like flame asymmetry with respect to the center of the PB, flame quenching near the gas supply tube, asymmetrical flame luminosity, etc. The local mass flow rate of fluid through the PB was shown to be nonuniform with the maximum flow rate attained in the PB hemisphere with the attached fluid supply tube, which could be a reason for the flame asymmetry observed in the space experiment. The evolution of 2D ethylene SDFs at zero gravity was shown to be oscillatory with slow alterations in flame shape and temperature caused by the incepience of torroidal vortices in the surrounding gas. Introduction of the directional microgravity, on the level of 0.01$g$, led to the complete suppression of flame oscillations. Full article

In the present work, the two-phase mixture (HTLc) of hydrotalcite and its oxide were used to improve the barrier properties, UV resistance and antimicrobial activity of Poly(ethylene terephthalate) (PET) for their application in liquid milk packaging. Firstly, CaZnAl-CO₃-LDHs with a two-dimensional layered structure were synthesized by hydrothermal method. CaZnAl-CO₃-LDHs precursors were characterized by XRD, TEM, ICP and dynamic light scattering. A series of PET/HTLc composite films were then prepared, characterized by XRD, FTIR and SEM, and a possible mechanism of the composite films with hydrotalcite was proposed. Barrier properties to water vapor and oxygen have been studied in PET nanocomposites, as well as their antibacterial efficacy by the colony technique and their mechanical properties after exposure to UV irradiation for 24 h. By the presence of 1.5 wt% HTLc in the PET composite film, the oxygen transmission rate (OTR) was reduced by 95.27%, the water vapor transmission rate was reduced by 72.58% and the inhibition against Staphylococcus aureus and Escherichia coli was 83.19% and 52.75%. Moreover, a simulation of the migration process in dairy products was used to prove the relative safety. This research first proposes a safe technique for fabricating hydrotalcite-based polymer composites with a high gas barrier, UV resistance and effective antibacterial activity. Full article

The conditions for the mild initiation of the detonation of homogeneous stoichiometric ethylene-oxygen mixtures diluted with nitrogen up to ~40%vol. in a planar semi-confined slit-type combustor with a slit 5.0 ± 0.4 mm wide, simulating the annular combustor of a Rotating Detonation Engine (RDE), are determined experimentally using self-luminous high-speed video recording and pressure measurements. To ensure the mild detonation initiation, the fuel mixture in the RDE combustor must be ignited upon reaching a certain limiting (minimal) fill with the mixture and the arising flame must be transformed to a detonation via deflagration-to-detonation transition (DDT). Thus, for mild detonation initiation in a C₂H₄ + 3O₂ mixture filling the slit, the height of the mixture layer must exceed the slit width by approximately 10 times (~50 mm), and for the C₂H₄ + 3(O₂ + 2/5 N₂) mixture, by approximately 60 times. The limiting height of the mixture layer required for DDT exhibits a sharp increase at a nitrogen-to-oxygen mole ratio above 0.25. Compared to the height of the detonation waves continuously rotating in the RDE combustor in the steady-state operation mode, for a mild start of the RDE, the fill of the combustor with the explosive mixture to a height of at least four times more is required. Full article

Biomass is a material that can be potentially used as a natural fiber resource. Rice husk (RH) and sugarcane bagasse (SB), respectively containing 36.6% and 60% cellulose, are fibers that have the potential for biocomposite formation. In this study, an amine magnetic biocomposite (B-MNH₂) was prepared by a one-step solvothermal reaction. Delignified RH and SB fibers at a ratio of 1:1 were added to a mixture of ethylene glycol, iron chloride, and 1,6-hexanediamine, and kept in a stainless steel autoclave reactor at 200 °C for 6 h. The obtained B-MNH₂ contained 64.5% of Fe and 2.63 mmol/g of amine. Its surface area increased significantly from 9.11 m²/g to 25.81 m²/g after amine functionalization, and its optimum adsorption for Pb(II) ions was achieved within 360 min at 596.82 mg/g and pH 5. Moreover, the pseudo-first-order mechanism fitted well to the adsorption model. Other parameters, such as chemical oxygen demand (COD), total suspended solid (TSS), and dye during adsorption were also reduced by about 67.7%, 95.6%, and 89%, respectively. B-MNH₂ showed a slight decrease in performance by only 8% after the fourth repeated use. The amine magnetic biocomposite led to the development of a potential adsorbent due to the high surface area, stable material, and easy separation, and was capable of absorbing contaminants from an aqueous solution. Full article

Nowadays, N-functionalized carbon nanomaterials attract a growing interest. The use of melamine as a functionalizing agent looks prospective from environmental and cost points of view. Moreover, the melamine molecule contains a high amount of nitrogen with an atomic ratio C/N of 1/2. In present work, the initial carbon nanofibers (CNFs) were synthesized via catalytic pyrolysis of ethylene over microdispersed Ni–Cu alloy. The CNF materials were pretreated with 12% hydrochloric acid or with a mixture of concentrated nitric and sulfuric acids, which allowed etching of the metals from the fibers and oxidizing of the fibers’ surface. Finally, the CNFs were N-functionalized via their impregnation with a melamine solution and thermolysis in an inert atmosphere. According to the microscopic data, the initial structure of the CNFs remained the same after the pretreatment and post-functionalization procedures. At the same time, the surface of the N-functionalized CNFs became more defective. The textural properties of the materials were also affected. In the case of the oxidative treatment with a mixture of acids, the highest content of the surface oxygen of 11.8% was registered by X-ray photoelectron spectroscopy. The amount of nitrogen introduced during the post-functionalization of CNFs with melamine increased from 1.4 to 4.3%. Along with this, the surface oxygen concentration diminished to 6.4%. Full article

This paper reports the optimization of a two-step atmospheric pressure plasma process to modify the surface properties of a polyurethane (PU) foam and, specifically, to prepare a superhydrophobic/superoleophilic absorbent for the removal of oils and nonpolar organic solvents from water. In particular, in the first step, an oxygen-containing dielectric barrier discharge (DBD) is used to induce the etching/nanotexturing of the foam surfaces; in the second step, an ethylene-containing DBD enables uniform overcoating with a low-surface-energy hydrocarbon polymer film. The combination of surface nanostructuring and low surface energy ultimately leads to simultaneous superhydrophobic and superoleophilic wetting properties. X-ray photoelectron spectroscopy, scanning electron microscopy and water contact angle measurements are used for the characterization of the samples. The plasma-treated PU foam selectively absorbs various kinds of hydrocarbon-based liquids (i.e., hydrocarbon solvents, mineral oils, motor oil, diesel and gasoline) up to 23 times its own weight, while it completely repels water. These absorption performances are maintained even after 50 absorption/desorption cycles and after immersion in hot water as well as acidic, basic and salt aqueous solutions. The plasma-treated foam can remove mineral oil while floating on the surface of mineral oil/water mixtures with a separation efficiency greater than 99%, which remains unaltered after 20 separation cycles. Full article