Oxidation Of Ethylene Research Articles

Theoretical study of H-abstraction reactions of di-n-propyl ether oxidation by H, CH3, HO2 and OH radicals

The H-abstraction reactions from di-n-propyl ether (DPE) by radicals are significant in the DPE oxidation process. However, corresponding rate constants only rely on either analogy from alcohols or estimation from alkanes due to the lack of experimental and theoretical studies. In current work, thermochemistry and kinetics of DPE oxidation by the H, CH3, HO2 and OH radicals have been studied using the composite methods (CBS-QB3 and G4). Four H-abstraction reaction systems have been discussed, all of them occur through energy barriers of −5.4–20.5 kcal/mol. The energy barriers increase in the order α < β < γ at CBS-QB3 and G4 levels. The hydrogen-bond reactant complexes, RCβHO2, RCαOH, RCβOH and RCγOH, are identified in the entrance channel for the H-abstraction by HO2 and OH radicals. The rate constants for target reactions are calculated with the transition state theory and canonical variational transition state theory over a broad temperature range of 400–1400 K. Rate constants and branching ratios show that the H-abstraction reaction from Cα is the dominant reaction over the investigated temperature range. The total rate constants of the DPE + OH system have been fitted as follows: k = 1105 × T 3.185 exp(1720/T) (cm3 mol−1 s−1). The G4 data well reproduce the available experimental rate constant for DPE + OH system. The rate constants of H-abstraction reactions in the kinetic model of Serinyel et al. [Fuel 263 (2020) 116554] are modified based on the current calculated results to obtain a revised model. A validation for the revised model against the jet-stirred reactor (JSR) measurements from the literature are also provided, and the modified mechanism shows good performances to predict the JSR data. Reaction pathway and sensitivity analyses are performed to identify the fuel consumption paths and key reactions in oxidation process of DPE.

Diverse Site-Selective Transformation of Benzylic and Allylic Silyl Ethers via Organocatalytic Oxidation

We herein report nitroxyl-radical catalyst 1a, which recognizes the electronic properties of silyl ethers, thus enabling selective oxidation of benzylic and allylic silyl ethers, despite steric factors. A subsequent one-pot reduction accomplishes the formal deprotection to the corresponding benzylic and allylic alcohols. This catalytic system allows the direct oxidative desymmetrization of bis-benzylic and bis-allylic silyl ethers to access synthetically useful monoprotected conjugated aldehydes, which can be applied to one-pot enantioselective transformations. Mechanistic studies revealed that the highly electron-accepting oxoammonium species from 1a as well as the trifluoroacetate form of phenyl iodonium bis(trifluoroacetate) (PIFA) play key roles for the selectivity-determining hydride transfer step.

Kinetic and thermodynamic studies on direct synthesis of methyl methacrylate from methyl propionate and methanol catalyzed by highly efficient cobalt complex at mild conditions

Methyl methacrylate (MMA) typically produced from the petroleum-based ethylene or isobutene selective oxidation route is a significantly important chemical widely used in industrial manufacture. Herein, an innovative and highly efficient liquid-phase catalytic system, cobalt complex catalyzed O2-interrupted hydrogen borrowing pathways, was developed for direct synthesis of MMA from methyl propionate and methanol at mild conditions, considering the problems of poor selectivity, rapid catalyst deactivation, and formaldehyde polymerization existed in one-step aldol reaction of methyl propionate with formaldehyde at 350–380 °C. The yield and selectivity of MMA could reach up to 50.2% and 81.8% at 60 °C and 1 atm. Thermodynamic calculations and analysis for this novel transformative process were conducted to confirm the feasibility and reasonability for MMA production at low temperature (below 100 °C). On the basis of the reaction networks proposed according to the experimentally detected products, studies on the kinetic informatics of this new process were conducted. The formaldehyde oxidation, aldol condensation of methyl/t-butyl propionate with formaldehyde and transesterification of t-butyl propionate/methacrylate with methanol are first-order dependent on their reactant concentrations. While the methanol dehydrogenation and transesterification of methyl propionate/methacrylate with t-BuOK are first-order dependent on the concentration of only methanol and t-BuOK. With the understanding of kinetic behavior of these reaction steps composed, the global kinetic model was established to describe this catalytic system and the corresponding parameters including pre-exponential factor and activation energy were calculated. The oxidative dehydrogenation of methanol to formaldehyde, with the highest activation energy of 84 kJ/mol, was the kinetic-relevant step, while the aldol condensation of methyl propionate with formaldehyde showed the lowest energy of 36 kJ/mol.

Investigating the Association Reactions of HOCH2CO and HOCHCHO with O2: A Quantum Computational and Master Equation Study

Glycolaldehyde, HOCH2CHO, is an important multifunctional atmospheric trace gas formed in the oxidation of ethylene and isoprene and emitted directly from burning biomass. The initial step in the atmospheric photooxidation of HOCH2CHO yields HOCH2CO and HOCHCHO radicals; both of these radicals react rapidly with O2 in the troposphere. This study presents a comprehensive theoretical investigation of the HOCH2CO + O2 and HOCHCHO + O2 reactions using high-level quantum chemical calculations and energy-grained master equation simulations. The HOCH2CO + O2 reaction results in the formation of a HOCH2C(O)O2 radical, while the HOCHCHO + O2 reaction yields (HCO)2 + HO2. Density functional theory calculations have identified two open unimolecular pathways associated with the HOCH2C(O)O2 radical that yield HCOCOOH + OH or HCHO + CO2 + OH products; the former novel bimolecular product pathway has not been previously reported in the literature. Master equation simulations based on the potential energy surface calculated here for the HOCH2CO + O2 recombination reaction support experimental product yield data from the literature and indicate that, even at total pressures of 1 atm, the HOCH2CO + O2 reaction yields ∼11% OH at 298 K.

Ethylene Oxide Catalysis Under Commercial Conditions – A Guide for Researchers

AbstractSelective oxidation of ethylene to ethylene oxide (EO) is performed industrially over catalysts comprised of silver particles supported on α‐Al2O3. In addition to various oxy‐anion and alkali promotors, alkyl chloride species (“chloride moderators”) are continuously introduced into commercial reactors. The effect and usage of chloride moderators is a key requirement for industrial ethylene epoxidation catalysts to reach optimal selectivity. While not an exhaustive review, the aim of this perspective is to provide guidance to academic researchers on the operation of EO catalysts under commercially relevant conditions with particular focus on the importance of performance optimization.

Extremely Low Temperatures for the Synthesis of Ethylene Oxide

The partial oxidation of ethylene in a methane atmosphere by pure oxygen is the most important industrial process for the synthesis of ethylene oxide. However, due to the high reactivity and exothermicity of the reaction system, the overall production is limited by kinetic and safety issues. The shift toward mild operative conditions can support the management of undesirable side reactions, enhancing the performance of the whole process. In the future, the direct use of liquefied ethylene and oxygen-enriched air, a low-cost waste in membrane-based nitrogen production, can provide convenient sources for heat removal as well as promote the use of innovative and more sustainable solutions. This work is focused on the experimental and numerical characterization of the oxidation of ethylene/methane/nitrogen/oxygen mixtures at different operative conditions, including extremely low temperatures, and oxidant compositions. To this aim, the laminar burning velocity and flammability limits were first measured utilizing the heat flux burner and compared with detailed kinetic mechanisms and experiments retrieved from the current literature. The reported data were adopted to identify the operational limits for innovative processes, paving the way to unlocking the potential of innovative chemistry at extreme conditions. Eventually, key performance indicators accounting for kinetic and safety aspects were defined to identify the most sustainable and convenient operative conditions.

Platinum nanoparticles supported on dendritic mesoporous silica nanoparticles with tunable size as ethylene scavengers for food preservation

Platinum-loaded dendritic mesoporous silica catalysts (Pt/DMS) with the size controlled by changing the molar ratio of NaSal/CTAB (φ) were successfully prepared using an incipient impregnating method. The resulting catalysts with high specific surface areas and distinctive central-radial pore channels exhibited excellent ethylene catalytic oxidation at low temperatures, enabling the complete ethylene conversion at 25 °C for 60 h and even at 0 °C for 200 min. The φ value plays an important role in controlling the DMS support structure and Pt activity. The high efficiency of low-temperature ethylene oxidation and long-term stability for Pt/DMS are attributed to high Pt dispersion, small Pt size, high Pt0 content and the rapid CO oxidation process. As an ethylene scavenger, Pt/DMS delayed the postharvest decay, deterioration, and storage quality loss of bananas and avocados, demonstrating the significant potential of as-prepared catalysts in the applications associated with fruit and vegetable (F&V) preservation.

A systematic analysis of chemical mechanisms for ethylene oxidation and PAH formation

Accurate prediction of soot formation and evolution remains a formidable challenge due to the complex interaction between gas-phase composition and solid-phase particles. Recent studies have shown that the choice of gas-phase mechanisms is of primary importance in affecting predictability. In this work, a systematic analysis of ethylene (C2H4) combustion mechanisms denoted as KAUST, Stanford, Aachen, Polimi, ABF, DLR/UT, Naples, Caltech, and SJTU, which have been widely used in the soot community, is performed to investigate their differences in fundamental chemistry, polycyclic aromatic hydrocarbon (PAH) chemistry, and soot prediction. It is found that the nine mechanisms exhibit large differences even in predicting canonical combustion properties (e.g., ignition delay time, laminar flame speed, and extinction strain rate), indicating significant variations in the fundamental chemistry. This is due to the fact that although most mechanisms share very similar dominant fuel-oxidation reactions, there are notable differences in the rate coefficients of sensitive reactions used in these mechanisms. Owing to the uncertainties in the fundamental chemistry, the predictions of C2H2 from the nine mechanisms show significant differences, which contributes to the differences in soot precursor prediction, in conjunction with the difference in benzene (A1) formation pathways demonstrated by the element flux analysis of the C atom. Furthermore, it is found that PAHs containing two rings play a dominant role in soot formation for most mechanisms. Moreover, it is observed that while Caltech and SJTU significantly under estimate soot formation, they reasonably reproduce its sensitivity to strain rate. These results indicate that despite substantial advances in the development of C2H4 oxidation and PAH formation chemistry, the various existing mechanisms lead to significant differences in predicting soot concentrations which can be traced back to considerable differences in both fundamental chemistry and PAH chemistry. This suggests that the fundamental chemistry should be calibrated or improved before further development of PAH chemistry and soot models.

Simultaneous oxidation of NO and acetaldehyde over bare and Fe-modified TiO2 under visible light irradiation

Photocatalytic behavior of bare and Fe-modified TiO2 (0.4 wt% and 1 wt% of Fe loading, respectively) in the rutile phase was studied for the oxidation of NO and acetaldehyde under visible light irradiation. 0.4 wt% Fe-TiO2 photocatalysts showed the highest activity towards oxidation of NO and acetaldehyde when pollutants were used individually. Boosted activity of 0.4 wt% Fe-TiO2 can be attributed to abundant Fe-oxide-TiO2 interface acting as active sites during reaction process. Moreover, when NO and acetaldehyde were used simultaneously, complex and mutual influential photocatalytic activity was evident, depending on reactants concentrations and photocatalysts structures. Bare TiO2 showed high selectivity towards NO oxidation. Such complexity in mutual interactions between different pollutants on the photocatalyst surface is a crucial factor, which should be considered in real-world application of photocatalysts.

Anthropogenic Pollutants Induce Changes in Peroxyacetyl Nitrate Formation Intensity and Pathways in a Mountainous Background Atmosphere in Southern China.

Mountainous background areas are typically considered to have a clean atmosphere where peroxyacetyl nitrate (PAN) can be decomposed. This study demonstrated that PAN was photochemically formed with a simulated production rate of 0.28 ± 0.06 ppbv h-1 in the Nanling mountains (1690 m a.s.l.) of South China and that net PAN formation was dependent on both volatile organic compounds (VOCs) and NOx precursors (transition regime). In contrast to dominated acetaldehyde oxidation in previous urban and rural research, PAN at Nanling was primarily formed by methylglyoxal (38%), acetaldehyde (28%), radicals (20%), and other oxygenated volatile organic compounds (OVOCs) (13%). Moreover, when polluted air masses invaded the Nanling mountains, the PAN production rate was altered, primarily because anthropogenic aromatics intensified PAN formation via the oxidized pathways of methylglyoxal, other OVOCs, and radicals. Finally, net PAN formation at Nanling reduced the hydroxyl radical level by consuming NOx, impaired local radical cycling, and thereby suppressed local O3 production. This suppressing effect was exacerbated on polluted days. The findings of this study deepen our understanding of PAN photochemistry and the impact of anthropogenic intrusions on the background atmosphere of mountainous regions.

Boosting Selective Oxidation of Ethylene to Ethylene Glycol Assisted by In situ Generated H2O2 from O2 Electroreduction

AbstractEthylene glycol is a useful organic compound and chemical intermediate for manufacturing various commodity chemicals of industrial importance. Nevertheless, the production of ethylene glycol in a green and safe manner is still a long‐standing challenge. Here, we established an integrated, efficient pathway for oxidizing ethylene into ethylene glycol. Mesoporous carbon catalyst produces H2O2, and titanium silicalite‐1 catalyst would subsequently oxidize ethylene into ethylene glycol with the in situ generated H2O2. This tandem route presents a remarkable activity, i.e., 86 % H2O2 conversion with 99 % ethylene glycol selectivity and 51.48 mmol gecat−1 h−1 production rate at 0.4 V vs. reversible hydrogen electrode. Apart from generated H2O2 as an oxidant, there exists ⋅OOH intermediate which could omit the step of absorbing and dissociating H2O2 over titanium silicalite‐1, showing faster reaction kinetics compared to the ex situ one. This work not only provides a new idea for yielding ethylene glycol but also demonstrates the superior of in situ generated H2O2 in tandem route.

Boosting Selective Oxidation of Ethylene to Ethylene Glycol Assisted by In-situ Generated H2O2 from O2 Electroreduction.

Ethylene glycol is a useful organic compound and chemical intermediate for manufacturing various commodity chemicals of industrial importance. Nevertheless, the production of ethylene glycol in a green and safe manner is still a long-standing challenge. Here, we established an integrated, efficient pathway for oxidizing ethylene into ethylene glycol. Mesoporous carbon catalyst produces H2O2, and titanium silicalite-1catalyst would subsequently oxidize ethylene into ethylene glycol with the in-situ generated H2O2. This tandem route presents a remarkable activity, i.e., 86% H2O2conversion with 99% ethylene glycol selectivity and 51.48 mmol gecat-1h-1production rate at 0.4 V vs. reversible hydrogen electrode. Apart from generated H2O2as an oxidant, there exists •OOH intermediate which could omit the step of absorbing and dissociating H2O2over titanium silicalite-1, showing faster reaction kinetics compared to the ex-situ one. This work not only provides a new idea for yielding ethylene glycol but also demonstrates the superior of in-situ generated H2O2in tandem route.

Micro-kinetics of ethylene and methane oxidation on platinum

The kinetics of ethylene (C2H4) and methane (CH4) on platinum (Pt) is investigated in an isothermal Pt microtube. A micro-kinetic model of C1 and C2 hydrocarbon oxidation on the Pt(111) surface established using density functional theory is tuned and validated based on experimental results obtained from the Pt microtube. Density functional theory (DFT) modelling is carried out to evaluate the Pt(111) surface coverage of selected species on the thermochemistry and kinetics. The model reasonably predicts the conversion temperature and carbon selectivity of C2H4 and CH4 oxidation under various fuel-oxygen ratios. Micro-kinetic analysis based on this model illustrates that the formation of hydrocarbon oxygenates intermediates is essential, which makes the activity of surface oxygen species decisive in the catalytic activity.

Effects of Palladium Precursors on the Activity of Palladium Nanocatalysts for the Oxidation of Volatile Organic Components.

To screen a suitable precursor, the effects of palladium salts on performance of Pd nanocatalysts for the oxidation of volatile organic components (VOCs) were investigated. A series of catalysts was prepared by impregnating Pd(NO3)2, PdCl2 and Pd(NH3)4Cl2 on alumina-coated cordierites. These catalysts were characterized by XRF, ICP-OES, XRD, N2 adsorption-desorption, TEM, EDS, Raman spectroscopy, pulse-CO chemisorption, H2-TPR, NH3-TPD, and XPS. Pulse-CO chemisorption and TEM showed that Pd species formed by Pd(NO3)2 have the highest metal dispersion (17.7%), while the other two were aggregating. For the same Pd loading, the higher the metal dispersion, the more the number of PdO species, so the number of PdO particles in the catalyst prepared from Pd (NO3) 2 is the largest. The catalytic oxidation activities of these catalysts were evaluated by ethane and propane. Based on a 99% conversion in the oxidation of ethane and propane at 598 K and 583 K, respectively, the catalyst prepared from Pd(NO3)2 was considered to be the best performing catalyst. The chloride species in precursors can promote the aggregation of Pd species and poison the catalysts. The results show that Pd(NO3)2 is more suitable as the precursor of VOC oxidation catalyst than PdCl2 and Pd(NH3)4Cl2.

Engineering Morphology and Ni Substitution of NixCo3–xO4 Spinel Oxides to Promote Catalytic Combustion of Ethane: Elucidating the Influence of Oxygen Defects

Transition metal oxides are potential alternatives to noble metal catalysts for oxidation reactions. Co-based spinel oxides, in particular, have attracted significant attention. Herein, NixCo3–xO4 catalysts were synthesized to elucidate the influence of oxygen vacancies on catalyst activities and reaction mechanisms for ethane combustion. A correlation between the activity and the population and properties of O defects was developed, with an increased number of O defects typically resulting in higher activity. Also, the shape-induced facet effect is related to the amount of Ni that is incorporated into the octahedral sites of Co oxide. The substituted Ni atoms altered the redox ability of NixCo3–xO4 by changing O vacancy formation and C–H bond dissociation. The NiCo2O4-TM catalyst (6.0 mmol mL–1 h–1) exhibits the highest activity for ethane oxidation compared with NiCo2O4-PC (0.5 mmol mL–1 h–1) and NiCo2O4-OL catalysts (1.3 mmol mL–1 h–1) at 330 °C, and its activation energy (Ea) is 70.9 kJ mol–1. No activity decay is observed after the initial transition stage of the reaction in a long-term stability test up to 500 h on the NiCo2O4-TM-coated monolith, either with or without water addition. A vacancy-mediated pathway was proposed according to in situ diffuse reflectance infrared Fourier transform (DRIFT) and density functional theory (DFT) calculations over the NiCo2O4(311) facet. Findings from this study expand our understanding of the facet-dependent catalytic behavior and ultimately enable the rational design of high-performance catalysts.

Strong relations of peroxyacetyl nitrate (PAN) formation to alkene and nitrous acid during various episodes

Peroxyacetyl nitrate (PAN) is one of the critical secondary pollutants in photochemical smog. This study investigated the relationship between PAN and PAN precursors with the Regional Atmospheric Chemical Mechanism version 2 model in six episodes recorded in Zhengzhou. In all episodes, peroxyacetyl radical (PA) was primarily produced by acetaldehyde oxidation, with more than 70% contributions. In photochemical episodes and photochemical-haze co-occurring episodes (combined episodes), methylglyoxal secondarily contributes 8.1%–10.6% to PA while in haze pollution, the propagation of other radicals to PA is the second most important source (12.0%–19.1%). Among anthropogenic non-methane hydrocarbons, alkene restricted PAN formation as first-generation precursors, with the relative incremental reactivity of PAN (RIRPAN) more than 0.6 during three-type episodes. Nitrous acid (HONO) also played important role in PAN formation. Especially during photochemical episodes, RIRPAN(HONO) reached 0.79, which was comparable to the RIRPAN value of alkene. Through sensitivity analysis of the relative formation of PAN to O3 (the amount of PAN generated when 100 ppb O3 formed), HONO was identified as the key precursor of PAN in haze pollution by promoting the oxidation of NMHC, while alkene predominated the relative formation of PAN to O3 in photochemical and combined pollution through producing acetaldehyde. The sensitivity of PAN to HONO is obviously enhanced with higher NOx/VOC ratios during photochemical and combined pollution.

Promotion Effects of Ce-Doping on Catalytic Oxidation of Ethane over Pt/CexTi1−xO2

The catalytic oxidation of VOCs is widely acknowledged as the most available technology to reduce air pollution. Among the catalysts for VOCs, 1 wt%-Pt/TiO2 catalysts using metal as a doping element have shown amazing potential in many fields. However, achieving high catalytic performance at relatively low temperatures based on the activation of molecules is still a formidable challenge owing to the catalytic activity being highly dependent on temperature. Here, the role of the rare earth metal Ce in the catalytic oxidation of ethane was studied by preparing Pt/CexTi1−xO2 (x = 0, 0.002, 0.005, 0.01, 0.02, and 0.05) catalysts. When the Ce/(Ce+Ti) molar ratio was 0.01, Pt/Ce0.01Ti0.99O2 achieved 90% ethane conversion at 436 °C. This reaction temperature is 15% lower than that for Pt/TiO2. The characterization results show that the doping of Ce caused lattice expansion of TiO2 and its distortion brought about by oxygen vacancies. Additionally, the appropriate amount of Ce-doping can alter the interaction between the active component Pt and the carrier TiO2, thereby improving the activity and concentration of the active surface lattice oxygen species of the catalyst. These results provide a foundation for the design of the catalytic oxidation of VOCs under mild operating conditions.

Evidence of Synergy Effects between Zinc and Copper Oxides with Acidic Sites on Natural Zeolite during Photocatalytic Oxidation of Ethylene Using Operando DRIFTS Studies

In this article, the role of surface sites of modified zeolites with semiconductor nanoparticles as alternative photocatalyts for protecting post-harvest foodstuff from the detrimental effects of ethylene is addressed. Two single and one double catalyst based on zinc and copper oxides supported over modified zeolite samples were prepared. Physical, chemical, and surface properties of prepared materials were studied by several characterization methods. UV-Vis absorption spectra show that the applied modification procedures increase the optical absorption of light in the UV and visible regions, suggesting that an increase in the photocatalytic activity could take place mainly in the obtained co-impregnated catalyst. An ethylene conversion around 50% was achieved when the parent natural zeolite support was modified with both transition metal oxides, obtaining higher removal efficiency in comparison to single oxide catalysts. Adsorption and photocatalytic oxidation experiments were also performed using single and double catalysts supported over fumed silica, attaining lower ethylene conversion and thus highlighting the role of zeolite surfaces as adsorption sites for ethylene during photocatalytic reactions. Operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies reveal that a synergistic mechanism occurs, involving ethylene adsorption at acidic sites of zeolite and its photocatalytic oxidation due to the generation of radicals by the light activation of nanoparticles of zinc and copper oxides.

Unimolecular Reactions of 2,4-Dimethyloxetanyl Radicals.

Alkyl-substituted oxetanes are cyclic ethers formed via unimolecular reactions of QOOH radicals produced via a six-membered transition state in the preceding isomerization step of organic peroxy radicals, ROO. Owing to radical isomer-specific formation pathways, cyclic ethers are unambiguous proxies for inferring QOOH reaction rates. Therefore, accounting for subsequent oxidation of cyclic ethers is important in order to accurately determine rates for QOOH → products. Cyclic ethers can react via unimolecular reaction (ring-opening) or via bimolecular reaction with O2 to form cyclic ether-peroxy adducts. The computations herein provide reaction mechanisms and theoretical rate coefficients for the former type in order to determine competing pathways for the cyclic ether radicals. Rate coefficients of unimolecular reactions of 2,4-dimethyloxetanyl radicals were computed using master equation modeling from 0.01 to 100 atm and from 300 to 1000 K. Coupled-cluster methods were utilized for stationary-point energy calculations, and uncertainties in the computed rate coefficients were accounted for using variation in barrier heights and in well depths. The potential energy surfaces reveal accessible channels to several species via crossover reactions, such as 2-methyltetrahydrofuran-5-yl and pentanonyl isomers. For the range of temperature over which 2,4-dimethyloxetane forms during n-pentane oxidation, the following are the major channels: 2,4-dimethyloxetan-1-yl → acetaldehyde + allyl, 2,4-dimethyloxetan-2-yl → propene + acetyl, and 2,4-dimethyloxetan-3-yl → 3-butenal + methyl, or, 1-penten-3-yl-4-ol. Well-skipping reactions were significant in a number of channels and also exhibited a markedly different pressure dependence. The calculations show that rate coefficients for ring-opening are approximately an order of magnitude lower for the tertiary 2,4-dimethyloxetanyl radicals than for the primary and secondary 2,4-dimethyloxetanyl radicals. Unlike for reactions of the corresponding ROO radicals, however, unimolecular rate coefficients are independent of the stereochemistry. Moreover, rate coefficients of cyclic ether radical ring-opening are of the same order of magnitude as O2 addition, underscoring the point that a competing network of reactions is necessary to include for accurate chemical kinetics modeling of species profiles for cyclic ethers.

Experimental and kinetic study on laminar burning velocities of ammonia/ethylene/air premixed flames under high temperature and elevated pressure

The laminar burning velocities (LBVs) of ammonia (NH3) blended with ethylene (C2H4) were measured at different blending ratios (α = 0–1), initial temperatures (Tu = 300–440 K), and initial pressures (Pu = 1–5 atm). The flame morphology showed that the NH3/C2H4/air flames suffer from cellular instability under elevated pressures (Pu = 5 atm). The Lewis number (Le) was used to evaluate the thermal diffusion instability. Le was insensitive to the initial pressure and positively correlated with the blending ratio. The hydrodynamic instabilities were investigated under various initial conditions, which were exacerbated by elevated initial pressures and large blending ratios. The LBVs and hydrodynamic instabilities of NH3 were enhanced by adding C2H4. The existing kinetic models can only accurately predict measured data within a narrow range. Based on Konnov Mech (2021), a new detailed kinetic model with 119 species and 1,365 reactions was developed, which could satisfactorily predict the LBVs of NH3/C2H4/air flames under current conditions. The analysis of reaction flux, sensitivity, and radical concentration in the pure and blended fuels provided deep kinetic insights. The consumption pathways of NH3 and C2H4 were diversified after blending. NH2, an important precursor of ammonia oxidation, adds a consumption channel with HO2, whereas HCCO, an important intermediate of ethylene oxidation, adds new channels with NO. H + O2 = OH + O, a chain branching reaction, significantly contributes to the LBVs of NH3/C2H4/air flames. The peak concentrations of H, O, and OH radicals increased as the C2H4 percentages increased. The relationship between the H radical concentration and blending ratio was virtually the same as that for the LBVs.