Reaction Channels Research Articles

Toward Reducing the Energy Cost of NOx Formation in a Spark Discharge Reactor through Pinpointing Its Mechanism

Interest in sustainable nitrogen fertilizer production using plasma technology is rapidly growing, and this method is a promising way to decentralize fertilizer synthesis and achieve carbon-free production. However, improving efficiency remains a major challenge for the industrial application of this technology. Herein, we present comprehensive experiments using spark discharge to pinpoint the key factors affecting the efficiency of this process and provide technical approaches to improve the energy usage. We found that applying a bipolar voltage at high frequencies greatly benefited the NOx yield and its efficiency via the utilization of residual species. Measurements using active cooling for the reactor and electrodes revealed that the chemical loss process was not significant, but the energy loss during the heating of the electrode was the dominant loss process, particularly at high frequencies (>20 kHz) where an anchor state of the spark was reached. However, the beneficial effects of higher frequencies compensated for and mitigated the higher power loss resulting in slowing the increase of the energy cost with the energy density. Moreover, enlarging the plasma zone (reaction channel) by increasing the electrode gap was an effective approach for enhancing the energy usage for the desired reaction. Further, the limitations of enlarging the gap were resolved by inserting a floating electrode in the large gap, yielding higher NOx production (1.8%–3.0%) at a lower energy cost (1.9–4.4 MJ/mol), and further enhancements could be achieved by optimizing the reactor configuration. Therefore, the results provide an important basis for the further development and optimization of plasma reactors for efficient chemical reactions.

Experimental and Updated Kinetic Modeling Study of Neopentane Low Temperature Oxidation.

Neopentane is an ideal fuel model to study low-temperature oxidation chemistry. The significant discrepancies between experimental data and simulations using the existing neopentane models indicate that an updated study of neopentane oxidation is needed. In this work, neopentane oxidation experiments are carried out using two jet-stirred reactors (JSRs) at 1 atm, at a residence time of 3 s, and at three different equivalence ratios of 0.5, 0.9, and 1.62. Two different analytical methods (synchrotron vacuum ultraviolet photoionization mass spectrometry and gas chromatography) were used to investigate the species distributions. Numerous oxidation intermediates were detected and quantified, including acetone, 3,3-dimethyloxetane, methacrolein, isobutene, 2-methylpropanal, isobutyric acid, and peroxides, which are valuable for validating the kinetic model describing neopentane oxidation. In the model development, the pressure dependencies of the rate constants for the reaction classes Q̇OOH + O2 and Q̇OOH decompositions are considered. This addition improves the prediction of the low-temperature oxidation reactivity of neopentane. Another focus of model development is to improve the prediction of carboxylic acids formed during the low-temperature oxidation of neopentane. The detection and identification of isobutyric acid indicates the existence of the Korcek mechanism during neopentane oxidation. Regarding the formation of acetic acid, the reaction channels are considered to be initiated from the reactions of ȮH radical addition to acetaldehyde/acetone. This updated kinetic model is validated extensively against the experimental data in this work and various experimental data available in the literature, including ignition delay times (IDTs) from both shock tubes (STs) and rapid compression machines (RCMs) and JSR speciation data at high temperatures.

Kinetic Properties Study of H Atom Abstraction by CH3Ȯ2 Radicals from Fuel Molecules with Different Functional Groups.

The detailed kinetic properties of hydrogen atom abstraction by methylperoxy (CH3Ȯ2) radicals from alkanes, alkenes, dienes, alkynes, ethers, and ketones are systematically studied in this work. Geometry optimization, frequency analysis, and zero-point energy corrections were performed for all species at the M06-2X/6-311++G(d,p) level of theory. The intrinsic reaction coordinate calculation was consistently performed to ensure that the transition state connects the correct reactants and products, and one-dimensional hindered rotor scanning results were performed at the M06-2X/6-31G level of theory. The single-point energies of all reactants, transition states, and products were obtained at the QCISD(T)/CBS level of theory. High-pressure-limit rate constants of 61 reaction channels were calculated using conventional transition state theory with asymmetric Eckart tunneling corrections over the temperature range of 298.15-2000 K. Reaction rate rules for H atom abstraction by CH3Ȯ2 radicals from fuel molecules with different functional groups are constructed, which can be used in the development of combustion models of these fuels and fuel types. In addition, the influence of the functional groups on the internal rotation of the hindered rotor is also discussed.

Dual Photochemistry of Benzimidazole.

Monomers of benzimidazole trapped in an argon matrix at 15 K were characterized by vibrational spectroscopy and identified as 1H-tautomers exclusively. The photochemistry of matrix-isolated 1H-benzimidazole was induced by excitations with a frequency-tunable narrowband UV light and followed spectroscopically. Hitherto unobserved photoproducts were identified as 4H- and 6H-tautomers. Simultaneously, a family of photoproducts bearing the isocyano moiety was identified. Thereby, the photochemistry of benzimidazole was hypothesized to follow two reaction pathways: the fixed-ring and the ring-opening isomerizations. The former reaction channel results in the cleavage of the NH bond and formation of a benzimidazolyl radical and an H-atom. The latter reaction channel involves the cleavage of the five-membered ring and concomitant shift of the H-atom from the CH bond of the imidazole moiety to the neighboring NH group, leading to 2-isocyanoaniline and subsequently to the isocyanoanilinyl radical. The mechanistic analysis of the observed photochemistry suggests that detached H-atoms, in both cases, recombine with the benzimidazolyl or isocyanoanilinyl radicals, predominantly at the positions with the largest spin density (revealed using the natural bond analysis computations). The photochemistry of benzimidazole therefore occupies an intermediate position between the earlier studied prototype cases of indole and benzoxazole, which exhibit exclusively the fixed-ring and the ring-opening photochemistries, respectively.

Multichannel experimental and theoretical approach to the C12(O18,F18)B12 single-charge-exchange reaction at 275 MeV: Initial-state interaction and single-particle properties of nuclear wave functions

Background: Single-charge-exchange reactions are appropriate tools to study the nuclear response to one-particle/one-hole isospin probes, gaining additional interest from the connection to beta decay. This analogy has been recently extended to second order, connecting double-charge-exchange reactions and double beta decays. Nowadays, the availability of powerful experimental setups and advanced nuclear theories and models allows one to access precious information on key nuclear structure aspects embedded in the widely sought neutrinoless double beta decay. Purpose: We intend to bring to light the main nuclear structure and reaction features involved in the O18+C12 collision at 275 MeV incident energy. In this paper, the main focus is on the role of the initial- and final-state interactions in the overall reaction dynamics and on the single-particle nuclear structure properties accessed via the study of single-nucleon transfer reactions. Forthcoming articles will be devoted to go into the details of the response to one- and two-particle/hole isospin probes. Methods: Cross-section energy spectra and angular distributions were measured in a unique experimental setup for the C12(O18,O18)C12 elastic and inelastic scattering, the C12(O18,O17)C13 one-neutron stripping, the C12(O18,F19)B11 one-proton pickup, and the C12(O18,F18)B12 single-charge-exchange nuclear reactions. A unique comprehensive and coherent theoretical calculation, able to describe the whole network of direct reactions using state-of-the-art nuclear structure and reaction theories, was performed, and it is presented for the first time in this article. This holistic approach, applied both to the experimental and theoretical analysis, is the main feature and worth of the work here presented. Results: The energy and angular resolutions achieved in each reaction channel allowed us to isolate specific transitions and to map the diffraction patterns in the angular distributions. The cross-section calculations describe well the experimental data, both in terms of the absolute values and diffraction patterns. Although the distorted wave Born approximation (DWBA) calculations prove to be accurate in describing all the studied channels, better results are achieved when the couplings to inelastic transitions in both the incoming and outgoing partitions are introduced, as done in the coupled channels Born approximation (CCBA) calculations. Otherwise, no real improvement is found when the coupling effects among different partitions are explicitly taken into account in the coupled reaction channels (CRC) calculations. Conclusions: The multichannel approach proposed in this paper is a promising method for accurate investigations of direct reactions originating in heavy-ion collisions. This is quite appealing for the precise spectroscopy of heavy nuclei proposed in many areas of nuclear physics. An example is the NUMEN project with its challenging commitment to provide valuable information on neutrinoless double beta decay nuclear matrix elements from single- and double-charge-exchange cross-section measurements.1 MoreReceived 18 July 2022Accepted 23 January 2023DOI:https://doi.org/10.1103/PhysRevC.107.024605©2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCharge-exchange reactionsCollective modelsDirect reactionsNuclear many-body theoryOptical, coupled-channel & distorted wave modelsShell modelSpectroscopic factors & electromagnetic momentsTransfer reactionsProperties6 ≤ A ≤ 19TechniquesNuclear data analysis & compilationNuclear reactionsSpectrometers & spectroscopic techniquesNuclear Physics

Computational Investigation of Substituent Effects on the Alcohol + Carbonyl Channel of Peroxy Radical Self- and Cross-Reactions

Organic peroxy radicals (RO2) are key intermediates in atmospheric chemistry and can undergo a large variety of both uni- and bimolecular reactions. One of the least understood reaction classes of RO2 are their self- and cross-reactions: RO2 + R'O2. In our previous work, we have investigated how RO2 + R'O2 reactions can lead to the formation of ROOR' accretion products through intersystem crossings and subsequent recombination of a triplet intermediate complex 3(RO···OR'). Accretion products can potentially have very low saturation vapor pressures, and may therefore participate in the formation of aerosol particles. In this work, we investigate the competing H-shift channel, which leads to the formation of more volatile carbonyl and alcohol products. This is one of the main, and sometimes the dominant, RO2 + R'O2 reaction channels for small RO2. We investigate how substituents (R and R' groups) affect the H-shift barriers and rates for a set of 3(RO···OR') complexes. The variation in barrier heights and rates is found to be surprisingly small, and most computed H-shift rates are fast: around 108-109 s-1. We find that the barrier height is affected by three competing factors: (1) the weakening of the breaking C-H bond due to interactions with adjacent functional groups; (2) the overall binding energy of the 3(RO···OR'), which tends to increase the barrier height; and (3) the thermodynamic stability of the reaction products. We also calculated intersystem crossing rate coefficients (ISC) for the same systems and found that most of them were of the same order of magnitude as the H-shift rates. This suggests that both studied channels are competitive for small and medium-sized RO2. However, for complex enough R or R' groups, the binding energy effect may render the H-shift channel uncompetitive with intersystem crossings (and thus ROOR' formation), as the rate of the latter, while variable, seems to be largely independent of system size. This may help explain the experimental observation that accretion product formation becomes highly effective for large and multifunctional RO2.

Mechanistic Insights into the Oxidative Degradation of Formic and Oxalic Acids with Ozone and OH Radical. A Computational Rationale

Gas-phase and aqueous oxidations of formic and oxalic acids with ozone and OH radicals have been thoroughly examined by DFT methods. Such acids are not only important feedstocks for the iterative construction of other organic compounds but also final products generated by mineralization and advanced oxidation of higher organics. Our computational simulation unravels both common and distinctive reaction channels, albeit consistent with known H atom abstraction pathways and formation of hydropolyoxide derivatives. Notably, reactions with neutral ozone and OH radical proceed through low-energy concerted mechanisms involving asynchronous transition structures. For formic acid, carbonylic H-abstraction appears to be more favorable than the dissociative abstraction of the acid proton. Formation of long oxygen chains does not cause a significant energy penalty and highly oxygenated products are stable enough, even if subsequent decomposition releases environmentally benign side substances like O2 and H2O.

Sooting tendency of isopropanol-butanol-ethanol (IBE)/diesel surrogate blends in laminar diffusion flames

Recent advancements in metabolic engineering have demonstrated the cost-effective production of isopropanol-butanol-ethanol (IBE) from switchgrass biomass. As such, IBE is seen as a viable future fuel to transition the transportation sector towards renewable biofuels. In this study, an atmospheric co-flow diffusion flame burner was used to examine the sooting tendency of IBE when mixed with a diesel surrogate for blend ratios varying from 0% to 100% by volume. Experimental measurements of soot volume fraction were obtained by implementing a color-ratio pyrometry technique and reporting the variation of sooting tendency in terms of the Yield Sooting Index (YSI). Measurements demonstrated soot formation and hence YSI decreased nonlinearly with increasing IBE content. To gain further insight into the kinetics affecting soot formation, numerical modeling studies were carried out using laminarSMOKE++ and a comprehensive kinetic mechanism with soot chemistry. From a reaction path and rate of production analysis, IBE demonstrated that it can perturb OH and HO2 radical pools and enhance CO and CO2 reactive channels from IBE oxygenated intermediates to suppress the formation of soot precursors. Studies were also extended to examine the role of CO2 dilution on soot formation. It was shown that further soot reduction can be attained by lowering the rate of overall soot formation kinetics, perturbing reaction intermediates leading to soot formation by the depletion of H-atom radical pool, while enhancing the oxidation through enhanced OH-radical production.

Reactions of 3d transition metal hydride cations with CO2

Quantum chemical calculations were conducted to study reactions between cationic 3d transition metal hydride and carbon dioxide. The calculated results reveal that there are mainly-two reaction channels, which are to form HCOO− (Path A) and [M(CO)(OH)]+ (Path B), respectively. Path A is always kinetically more favorable than Path B except for Zn. However, only Path A of Sc-Cr could occur under ambient conditions in the gas phase. According to the analyses of charges and spin populations along the reaction pathways, Path A was found to be a hydride transfer mechanism, and Path B is a hydrogen atom transfer mechanism except for Zn, which should be a proton-coupled electron transfer mechanism.

Analytical potential energy surface and dynamics for the OH + CH3OH reaction.

Using as functional form a combination of valence bond and mechanic molecular terms a new full-dimensional potential energy surface was developed for the title reaction, named PES-2022, which was fitted to high-level ab initio calculations at the coupled-cluster singles, doubles, and perturbative triples-F12 explicitly correlated level on a representative number of points describing the reactive system. This surface simultaneously describes the two reaction channels, hydrogen abstraction from the methyl group [(R1) path] and from the alcohol group [(R2) path] of methanol to form water. PES-2022 is a smooth and continuous surface, which reasonably describes the topology of this reactive system from reactants to products, including the intermediate complexes present in the system. Based on PES-2022 an exhaustive dynamics study was performed using quasi-classical trajectory calculations under two different initial conditions: at a fixed room temperature, for direct comparison with the experimental evidence and at different collision energies, to analyze possible mechanisms of reaction. In the first case, the available energy was mostly deposited as water vibrational energy, with the vibrational population inverted in the stretching modes and not inverted in the bending modes, reproducing the experimental evidence. In the second case, the analysis of different dynamics magnitudes (excitation functions, product energy partitioning, and product scattering distributions), allows us to suggest different mechanisms for both (R1) and (R2) paths: a direct mechanism for the (R2) path vs an indirect one, related with "nearly trapped" trajectories in the intermediate complexes, for the (R1) path.

Transparent Cross-Flow Platform as Chemiluminescence Detection Cell in Cross Injection Analysis.

This work presents the use of a transparent 'Cross Injection Analysis' (CIA) platform as a flow system for chemiluminescence (CL) measurements. The CL-CIA flow device incorporates introduction channels for samples and reagents, and the reaction and detection channels are in one acrylic unit. A photomultiplier tube placed above the reaction channel detects the emitted luminescence. The system was applied to the analysis of (i) Co(II) via the Co(II)-catalyzed H2O2-luminol reaction and (ii) paracetamol via its inhibitory effect on the catalytic activity of Fe(CN)63- on the H2O2-luminol reaction. A linear calibration was obtained for Co(II) in the range of 0.002 to 0.025 mg L-1 Co(II) (r2 = 0.9977) for the determination of Co(II) in water samples. The linear calibration obtained for the paracetamol was 10 to 200 mg L-1 (r2 = 0.9906) for the determination of pharmaceutical products. The sample throughput was 60 samples h-1. The precision was ≤4.2% RSD. The consumption of the samples and reagents was ca. 170 µL per analysis cycle.

Nepenthes-inspired hierarchical ZnIn2S4/Ru nanotubes with chemical bond-mediated interface enable efficient photocatalytic benzyl alcohol oxidation

In nature, Nepenthes has a unique tubular structure for harvesting and preserving goals. Herein, inspired by Nepenthes, we report the selective photocatalytic oxidation of benzyl alcohol by using the hierarchical ZnIn2S4/Ru nanotubes. The tubular chamber with abundant active sites not only facilitates enriching the target molecules but also shortening the bulk-to-surface distance, and the Zn-S-Ru interfacial bonds creates direct charge transfer channels for the activating O2 to generate •O2– species boosting the benzyl alcohol selective conversion to benzaldehyde. The photocatalytic benzyl alcohol oxidation reaction has a high conversion rate of 68.2 % as well as a benzaldehyde selectivity of 99 % under visible light irradiation. The effects of Zn-S-Ru interfacial bonds on modulating the carrier transfer dynamics for the selective catalytic oxidation reaction are investigated by electrochemical characterization and density functional theory simulation. This work offers an inspiration on regulating the interfacial charge transfer channel for the photo-driven selective oxidation reaction.

Development of a practical soot model for diesel surrogate fuels and oxygenated fuels with specific soot precursor tracking and uniform model structure

Soot formation and oxidation involve several complex processes, which are driven by gas-phase chemistry and soot particle dynamics. An effective soot model for diesel surrogate and practical oxygenated fuels is necessary for predicting the soot emissions to meet the emission regulations in engines. To develop a practical and universal soot model for various fuels without tuning any model parameters under wide operating conditions, it is important to reproduce the soot behaviors for different fuels with distinct molecular structures. In this work, a practical soot model was developed to describe the soot behaviors for diesel surrogate fuels comprising large n-alkane, isoalkane, cycloparaffin, and aromatic hydrocarbon, as well as oxygenated fuels including alcohol and ether. The influence of the fuel molecular structures on the soot behaviors was emphasized by utilizing the specific reaction pathways of polycyclic aromatic hydrocarbon (PAH) production and the specific reaction channels of the soot formation including soot nucleation and PAH condensation for different fuels. An efficient method named the moment projection method (MPM) was employed to describe the soot particle dynamics by directly solving the moment transport equations and track the number of soot particles. By coupling a reduced chemical reaction model for describing the fuel oxidation chemistry and PAH formation, it is found that the soot volume fraction and number density are well predicted for iso-octane, n-heptane, toluene, methanol, n-butanol, dimethyl ether, their mixtures, and diesel surrogate in shock tubes and laminar premixed flames without tuning any model parameters. The effects of equivalence ratio, temperature, and fuel type on soot production are analyzed through the rates of soot nucleation, surface growth, PAH condensation, and oxidation. The computational results indicate that the present model can satisfactorily reproduce the soot characteristics of different fuels with distinct soot formation and oxidation processes.

The reactions of 2-furfuryl alcohol with hydrogen atom: A theoretical calculation and kinetic modeling analysis

The rate constants for H-initiated reactions of 2-furfuryl alcohol (2FFOH) were calculated for the first time by a high-level quantum chemical method combined with the Rice–Ramsperger–Kassel–Marcus (RRKM) theory/Master equation method. A detailed potential energy surface was constructed by the CCSD(T)/CBS//M06–2X/def2-TZVP method, involving H-abstraction, initial H-addition, adduct-subsequent pathways and interconnected conversion pathways. The H-addition reaction on the β-carbon and δ-carbon sites to form bimolecular products 2-methylene-2,3-dihydrofuran plus OH and 2-methylene-2,5-dihydrofuran plus OH were found to be the major product channels at high temperatures. No significant pressure dependence is observed for the total rate constants of 2FFOH + H. However, the overall kinetics behavior does not reflect the site characteristics, i.e., the site-specific rate constants for each reaction channel show different temperature and pressure dependences. The total rate constants via the H-addition mechanism are higher by factors of 3.3–10 than those via H-abstraction channels under all studied conditions. The present updated kinetic model obtained by applying these new calculated rate constants can better predict 2FFOH decomposition, especially at 30 Torr, and it can also lead to good predictions of the speciation profiles (e.g., vinyl ketene) during 2FFOH pyrolysis. The data calculated in the present work can provide valuable information for the development of combustion models of furan-based biofuels.

Mechanistic model of MAPK signaling reveals how allostery and rewiring contribute to drug resistance

BRAF is prototypical of oncogenes that can be targeted therapeutically and the treatment of BRAFV600E melanomas with RAF and MEK inhibitors results in rapid tumor regression. However, drug‐induced rewiring generates a drug adapted state thought to be involved in acquired resistance and disease recurrence. In this article, we study mechanisms of adaptive rewiring in BRAFV600E melanoma cells using an energy‐based implementation of ordinary differential equation (ODE) modeling in combination with proteomic, transcriptomic and imaging data. We develop a method for causal tracing of ODE models and identify two parallel MAPK reaction channels that are differentially sensitive to RAF and MEK inhibitors due to differences in protein oligomerization and drug binding. We describe how these channels, and timescale separation between immediate‐early signaling and transcriptional feedback, create a state in which the RAS‐regulated MAPK channel can be activated by growth factors under conditions in which the BRAFV600E‐driven channel is fully inhibited. Further development of the approaches in this article is expected to yield a unified model of adaptive drug resistance in melanoma.

High-temperature mid-IR absorption and reaction kinetics of 2-methyl-1,3-dioxolane: An experimental and theoretical study

This work reports the mid-IR spectroscopy and reaction kinetics of 2-methyl-1,3-dioxolane (2M13DO). We carried out spectroscopic measurements to deduce temperature-dependent absorption cross-sections of 2M13DO over a broad wavelength range of 8.4–10.5 μm (950–1190 cm−1). For these measurements, we employed a rapidly tuning MIRcat-QT™ laser that can be operated either at a fixed wavelength or scanned mode over wide wavelength regions. By operating the laser at a fixed wavelength, we monitored the decay of 2M13DO behind reflected shock waves over T5 = 1050–1400 K and P5 = 0.7 and 2.6 bar. Our measured concentration time-histories of 2M13DO allowed us to directly extract the overall rate coefficients for the unimolecular decomposition of 2M13DO using the first-order rate law. We did not observe any pressure dependence in the measured rate coefficients, indicating that the reaction is close to the high-pressure limit. By employing the W1U composite method, we explored the important pyrolysis reaction pathways of 2M13DO in the reactive potential energy surface. Three important reaction channels, namely, 2M13DO → CH2CHOCH2CH2OH (IM1), 2M13DO → 2CH3CHO (P3), 2M13DO → CH3 + 1,3-dioxolan-2-yl (P4) were identified. Below 700 K, IM1 forming channel is dominant, whereas CH3CHO formation is dominant under our experimental conditions. Above 1500 K, the radical forming channel (CH3+P4) takes over other channels. At higher temperatures, the contribution of the radical forming channel continually increases, accounting for ∼ 99% at 2000 K. We used the stochastic RRKM-ME model to predict the pressure and temperature dependence of the rate coefficients, k(T, P), and time-resolved species profiles. Our theory showed excellent agreement with the measured rate coefficients. These are the first direct determination of the rate coefficients of the unimolecular decomposition of 2M13DO.

Facets of reaction mechanism in 6Li+181Ta system

More focused investigations are required to better understand the different modes of fusion phenomena in weakly bound projectiles. In order to comprehend the reaction mechanism of weakly bound projectiles, a new measurement of the evaporation residue cross sections from the 6Li-induced reaction on 181Ta in the 4.5–7.1 MeV/nucleon energy range has been reported in this article. The γ-ray spectrometry has been employed to identify the 183m,g Os, 182Os, 183Re, and 183,182m2,180Ta residues produced in the reaction via different evaporation channels. The EMPIRE-3.2.2 code, which houses both the equilibrium and pre-equilibrium models in its framework, and PACE4 have been tasked to analyze the measured excitation functions. Out of the two, EMPIRE-3.2.2 demonstrates better agreement with the data. A systematic analysis of the measured data and theoretical background indicates that the complete and incomplete fusion of 6Li contribute to the residual cross sections. Thus, the strength of the partial fusion has been inferred. Further, the neutron transfer channels have been found to contribute significantly to the reaction dynamics; hence they are investigated using the coupled reaction channel calculations and discussed in detail. The isomeric cross section ratio obtained from the measured residual cross sections of the isomeric pair of 183Os highlights the significance of angular momentum and relative spins of the ground and isomeric states as a function of projectile incident energy.

Enhancing the dechlorination of CuCl residue using a microwave sulfation-roasting method: Process optimization and mechanism investigation

Spent CuCl residue produced from zinc hydrometallurgy is a typical toxic and hazardous solid waste as well as a secondary resource owing to its high contents of chlorine and valuable metals (Pb, Cu, Zn). The removal of chlorine from the CuCl residue and recycling of valuable metals are critical issues for the copper slag resource treatment process. In this study, a novel method of microwave sulfation-roasting under an oxygen atmosphere is used to improve the dechlorination process, and various parameters, such as roasting temperature, duration, sulfuric acid concentration, and liquid/solid ratio, are optimized. First, according to thermodynamic calculations, the addition of H2SO4 can significantly decrease both the roasting temperature and time needed for microwave oxidation-roasting. The dechlorination experimental results reveal that the dechlorination rate of the CuCl residue is as high as 91.91% under a temperature of 250 °C, holding time of 120 min, sulfuric acid concentration of 70%, and liquid-solid ratio of 1.42. The microstructure, chemical composition, and phase changes of the CuCl residue before and after roasting are characterized using scanning electron microscopy coupled with energy-dispersive spectroscopy, X-ray fluorescence and X-ray diffraction; further, the mass contents of the main elements in the roasting product and tail gas absorption solution are determined by chemical analysis, Evidently, the selective heating property of microwaves produces more holes and cracks in the copper slag, which can provide a new reaction channel for H2SO4 and CuCl slag reactions, and almost all CuCl in the copper slag is completely removed by transformation into CuO, CuSO4 and Cu2O(SO4). Simultaneously, a large number of gas by-products produced in the dechlorination process, such as SO2 and Cl2, can be absorbed by the NaOH solution. Therefore, no pollution is generated in the environment. These findings illustrate that microwave sulfation-roasting is an effective method for promoting the treatment and recycling of CuCl waste residues.

Pyrolysis of Methyl Formate and the Reaction of Methyl Formate with H Atoms: Shock Tube Experiments and Statistical Rate Theory.

Methyl formate (MF) is the smallest carboxylic ester and currently considered a promising alternative fuel. It can also serve as a model compound to study the combustion chemistry of the ester group, which is a typical structural feature in many biodiesel components. In the present work, the pyrolysis of MF was investigated behind reflected shock waves at temperatures between 1430 and 2070 K at a nominal pressure of 1.1 bar. Both time-resolved hydrogen atom resonance absorption spectroscopy (H-ARAS) and time-resolved time-of-flight mass spectrometry (TOF-MS) were used for species detection. Additionally, the reaction of MF and perdeuterated MF-d4 with H atoms was investigated at temperatures between 1000 and 1300 K at nominal pressures of 0.4 and 1.1 bar with H-ARAS. In the latter experiments, ethyl iodide served as precursor for H atoms. Rate coefficients of seven parallel unimolecular decomposition channels of MF and five parallel reaction channels of the MF + H reaction were calculated from statistical rate theory on the basis of molecular and transition state data from quantum chemical calculations. These calculated rate coefficients were implemented into an MF pyrolysis/oxidation mechanism from the literature, and the experimental concentration-time profiles of H (from ARAS) as well as MF, CH3OH, HCHO, and CO (from TOF-MS) were modeled. It turned out that the literature mechanism, which was originally validated against flow-reactor experiments, ignition delay times, and laminar burning velocities, was generally able to fit also the concentration-time profiles from the shock tube experiments reasonably well. The agreement could still be improved by substituting the original rate coefficients, which were estimated from structure-reactivity relationships, by the values calculated from statistical rate theory in the present work. Details of the channel branching are discussed, and the updated mechanism is given, also in machine-readable form.

Fragmentation dynamics of acetylene in collision with highly charged ions: Concerted and sequential breakage of CH and CC bonds

The three-body fragmentation of ${\mathrm{C}}_{2}\mathrm{H}{{}_{2}}^{3+}$ to ${\mathrm{H}}^{+}+{\mathrm{C}}^{+}+{\mathrm{CH}}^{+}$ as a consequence of one CH and one CC bond breaking is investigated by 50-keV/u ${\mathrm{Ne}}^{8+}$ impact. All three fragments are detected in coincidence with a scattered projectile (either ${\mathrm{Ne}}^{7+}$ or ${\mathrm{Ne}}^{6+}$) employing a reaction microscope, and their momentum vectors as well as the kinetic energies were obtained. Four distinguished structures are observed in the energy correlation spectra, indicating that abundant fragmentation mechanisms contribute to the ${\mathrm{H}}^{+}+{\mathrm{C}}^{+}+{\mathrm{CH}}^{+}$ channel. The Newton diagrams and Dalitz plots are employed to trace fragmentation mechanisms. We found that both the concerted fragmentation and the sequential pathway with CH bond breaking prior to CC contribute to this channel. The possible electronic states of the ${\mathrm{C}}_{2}\mathrm{H}{{}_{2}}^{3+}$ precursor that may contribute to the identified fragmentation mechanisms are analyzed with the help of quantum chemical calculations. Furthermore, the influence of the collision dynamics between the projectile and the target to the dissociation mechanisms is discussed by comparing the contributions from the reaction channel with transferring one electron while ionizing the other two, i.e., T1I2, and the reversed channel T2I1. The T2I1 channel is observed to be more efficient to initiate fragmentation mechanisms leading to higher kinetic-energy release.