Reactions of Ethynyloxy Radical with Hydroperoxyl Radical: Bridging Theoretical Reaction Dynamics and Chemical Modeling of Combustion.

A detailed and accurate combustion reaction mechanism is crucial for understanding the nature of fuel combustion. In this work, a theoretical study of reaction HCCO+HO2 using M06-2X/6-311++G(d,p) for geometry optimization and combined methods based on spin-unrestricted CCSD(T)/CBS level of theory with basis set extrapolation from MP2/aug-cc-pVnZ (n=T and Q) for energy calculations were performed. The temperature- and pressure-dependent rate coefficients at 300-2000 K and 0.01-100 atm, suitable for combustion conditions, were derived using the Rice-Ramsberger-Kassel-Marcus/Master-Equation approach. Furthermore, temperature-dependent thermochemistry data of key species for the HCCO+HO2 system has also been studied. Finally, an updated ketene model is developed by supplementing the most recent theoretical work and the theoretical work in this paper. This updated model was tested to simulate the speciation of ketene oxidation in available experimental research. It is shown that the updated model for predicting ketene oxidation exhibits a high level of agreement with experimental data across a wide range of species profiles. An analysis was conducted to identify the crucial reactions that influence ketene ignition. This paper's research findings are essential for enhancing the combustion mechanism of ketene and other hydrocarbons and oxygenated hydrocarbon fuels.

Catalytic degradation of antibiotic sludge to produce formic acid by acidified red mud.

As complex and difficult-to-degrade persistent organic pollutants (POPs), antibiotics have caous damage to the ecological enused serivironment. Because of the difficult degradation of antibiotics, sewage and sludge discharged by hospitals and pharmaceutical enterprises often contain a large number of antibiotic residues. Therefore, the harmless and resourceful treatment of antibiotic sludge is very meaningful. In this paper, amoxicillin was selected as a model compound for antibiotic sludge. Acidified red mud (ARM) was used to degrade antibiotic sludge and produce hydrogen energy carrier formic acid in catalytic wet peroxidation system (CWPO). Based on various characterization analyses, the reaction catalytic mechanism was demonstrated to be the result of the non-homogeneous Fanton reaction interaction between Fe3O4 on the ARM surface and H2O2 in solution. Formic acid is the product of the decarboxylation reaction of amoxicillin and its degradation of various organic acids. The formic acid was produced up to 792.38 mg L-1, under the optimal conditions of reaction temperature of 90 °C, reaction time of 30 min, H2O2 concentration of 20 mL L-1, ARM addition of 0.8 g L-1, pH = 7, and rotor speed of 500 rpm. This research aims to provide some references for promoting red mud utilization in antibiotic sludge degradation.

Theoretical Prediction of Rate Constants for Hydrogen Abstraction by OH, H, O, CH3, and HO2 Radicals from Toluene.

Hydrogen abstraction from toluene by OH, H, O, CH3, and HO2 radicals are important reactions in oxidation process of toluene. Geometries and corresponding harmonic frequencies of the reactants, transition states as well as products involved in these reactions are determined at the B3LYP/6-31G(2df,p) level. To achieve highly accurate thermochemical data for these stationary points on the potential energy surfaces, the Gaussian-4(G4) composite method was employed. Torsional motions are treated either as free rotors or hindered rotors in calculating partion functions to determine thermodynamic properties. The obtained standard enthalpies of formation for reactants and some prodcuts are shown to be in excellent agreement with experimental data with the largest error of 0.5 kcal mol(-1). The conventional transition state theory (TST) with tunneling effects was adopted to determine rate constants of these hydrogen abstraction reactions based on results from quantum chemistry calculations. To faciliate its application in kinetic modeling, the obtained rate constants are given in Arrhenius expression: k(T) = AT(n) exp(-EaR/T). The obtained reaction rate constants also agree reasonably well with available expermiental data and previous theoretical values. Branching ratios of these reactions have been determined. The present reaction rates for these reactions have been used in a toluene combustion mechanism, and their effects on some combustion properties are demonstrated.

Temperature and pressure dependent rate coefficients for the reaction of C2H4 + HO2 on the C2H4O2H potential energy surface.

The potential energy surface (PES) for reaction C2H4 + HO2 was examined by using the quantum chemical methods. All rates were determined computationally using the CBS-QB3 composite method combined with conventional transition state theory(TST), variational transition-state theory (VTST) and Rice-Ramsberger-Kassel-Marcus/master-equation (RRKM/ME) theory. The geometries optimization and the vibrational frequency analysis of reactants, transition states, and products were performed at the B3LYP/CBSB7 level. The composite CBS-QB3 method was applied for energy calculations. The major product channel of reaction C2H4 + HO2 is the formation C2H4O2H via an OH(···)π complex with 3.7 kcal/mol binding energy which exhibits negative-temperature dependence. We further investigated the reactions related to this complex, which were ignored in previous studies. Thermochemical properties of the species involved in the reactions were determined using the CBS-QB3 method, and enthalpies of formation of species were compared with literature values. The calculated rate constants are in good agreement with those available from literature and given in modified Arrhenius equation form, which are serviceable in combustion modeling of hydrocarbons. Finally, in order to illustrate the effect for low-temperature ignition of our new rate constants, we have implemented them into the existing mechanisms, which can predict ethylene ignition in a shock tube with better performance.

Degradation of Isotianil in Water and Soil: Kinetics, Degradation Pathways, Mechanisms, and Ecotoxicity Assessments.

Pesticides are transported and transformed in soil and can enter surface water through various pathways. They undergo hydrolysis, oxidation, and photoconversion in surface water. Isotianil is a new fungicide that effectively controls rice blast. However, there are limited reports on its degradation. Herein, the hydrolysis and photolysis of isotianil in water and its degradation in soil samples from five provinces of China were investigated. The degradation products of isotianil were identified using ultrahigh-performance liquid chromatography-Q exactive hybrid quadrupole-orbitrap high-resolution accurate mass spectrometry, and four compounds were discovered for the first time. The degradation pathways of isotianil were inferred, and the reaction active site and degradation mechanism of isotianil were clarified based on density functional theory calculations. The ecotoxicity of the degradation product M118 (aminobenzonitrile) was found to be moderate toward Daphnia magna, which was predicted and confirmed by Ecological Structure Activity Relationships and the experiment, respectively. The results of this study will contribute to a better understanding of the fate of isotianil in the environment.

Structure characteristics and combustion kinetics of the co-pyrolytic char of rice straw and coal gangue.

Co-combustion is a technology that enables the simultaneous and efficient utilization of biomass and coal gangue (CG). Nevertheless, the factors that affect the combustibility of co-pyrolytic char, which represents the rate-determining step of the entire co-combustion process, remain unclear. This study investigates the impact of the physicochemical properties of co-pyrolytic char, including pore structure, carbon structure, and alkali metals, on the combustion characteristics. The TGA analysis indicates that the ignition and burnout temperatures of the co-pyrolytic char increase as the CG mixing ratio increases, resulting in a prolonged combustion. This is due to the fact that the carbon structure of the co-pyrolytic char becomes increasingly aromatic, accompanied by a reduction in aliphatic hydrocarbons and oxygen-containing groups as the CG mixing ratio increases. Furthermore, the high ash content of the CG is another significant factor contributing to the observed reduction in combustibility. The reaction between mullite, quartz in CG, and alkali metals in biomass results in the formation of aluminosilicate, which reduces the catalytic ability of alkali metals. Furthermore, the char combustion kinetics are analyzed by the KAS method, and the results indicate that the introduction of CG increases the activation energy of the entire char combustion process. The activation energy of the 80RS20CG is within the range of 102.22-164.99 kJ/mol, while the RS char is within the range of 89.87-144.67 kJ/mol.

Resource degradation of pharmacy sludge in sub-supercritical system with high degradation rate of 99% and formic acid yield of 32.44.

In response to the social goal of 'carbon peak and carbon neutral' in the 14th Five-Year Plan of China, this article used Enrofloxacin (ENR), a common antibiotic, as a model compound to study the method of efficiently degrading pharmaceutical sludge and simultaneously producing Formic Acid (FA), hydrogen storage energy, in a sub-supercritical system. The Ni/SnO2 bimetallic catalyst, which was prepared by the equal volume impregnation method, was used for the liquid phase catalysis. As shown by the results, when the reaction temperature was 330°C, and the addition amount of H2O2 was 0.38 mL, the degradation rate of antibiotics could reach 99% after the reaction proceeded for 6 h. In terms of the resource utilization, the yield of FA could reach up to 32.44%. The resource utilization efficiency with Ni/SnO2 catalyst in sub-/supercritical reaction was about 2.5 times higher than that without catalyst. The kinetic reaction model was established to explore the reaction rate of the antibiotic degradation process. In addition, the Ea and the frequency factor of the reaction were 6455 J/mol and 5.78, respectively. As shown by characterization, the prepared Ni/SnO2 bimetallic catalyst had good activity and has already passed repeated stability experiments. In short, this method has broad application prospects in antibiotic catalysis and resource degradation.

Study on Pyrolytic Mechanisms of n-Perfluorosilanes Si n F2n+2 (2 ≤ n < 6) and Perfluorocyclosilanes Si n F2n (3 ≤ n ≤ 6).

In this paper, the pyrolytic mechanisms of n-perfluorosilanes Si n F2n+2 (2 ≤ n < 6) and perfluorocyclosilanes Si n F2n (3 ≤ n ≤ 6) are studied in terms of kinetics and thermodynamics by theoretical calculation, and the pyrolytic reaction paths of Si n F2n+2 (2 ≤ n < 6) and Si n F2n (3 ≤ n ≤ 6) are obtained, which can be used to guide the experimental preparation research studies and separation operations of Si n F2n+2 (2 ≤ n < 6), Si n F2n (3 ≤ n ≤ 6), and their intermediate substances. The results of the kinetic analysis show that the pyrolytic mechanisms of Si n F2n+2 (2 ≤ n < 6) are as follows: first, the silicon-silicon bond breaking induces the generation of free radicals; then, in the chain transfer, the related free radicals participate in F-abstraction transfer with the molecules; and finally, the free radicals form the molecules, and the chain terminates. The F-abstraction transfer is the easiest process to initiate in the low-order silicon-fluorine substance during the chain transfer while releasing SiF2 at the same time, whereas the generation of double free radicals is the most difficult process. The pyrolytic mechanisms of Si n F2n (3 ≤ n ≤ 6) are as follows: first, the α-Si-Si bond breaking induces the generation of double free radicals; then, the α-Si-Si or ß-Si-Si bond breaks continually in the chain transfer; and finally, the double free radicals form the molecules, and the chain terminates. SiF2 is most easily formed by breaking during the chain transfer. In the pyrolytic processes of Si n F2n+2 (2 ≤ n < 6) and Si n F2n (3 ≤ n ≤ 6), the chain initiation of silicon-silicon bond breaking requires the highest bond breaking energy, which is the control step of the pyrolytic reaction. The results of the thermodynamic analysis show that the pyrolytic reactions of Si n F2n+2 (2 ≤ n < 6) and Si n F2n (3 ≤ n ≤ 6) are endothermic. When Si n F2n+2 (2 ≤ n < 6) undergoes a pyrolytic reaction and the temperature is higher, the main pyrolytic products are SiF4 and SiF2. When 600 K < T < 1200 K, the main pyrolytic products of Si4F10 are Si3F8 and SiF2, and when 900 K < T < 1400 K, Si5F12 can also convert to Si3F8 and SiF2. The main pyrolytic products of Si n F2n (3 ≤ n ≤ 6) are SiF2. When the temperature is higher, the pyrolytic order of Si n F2n (3 ≤ n ≤ 6) is as follows: Si3F6 (ring) < Si4F8 (ring) < Si5F10 (ring) < Si6F12 (ring). However, if the temperature is in the range of 1000 K < T < 1200 K, the pyrolytic order is the opposite.

Chemical structure stabilities of a Si x F y (x ≤ 6, y ≤ 12) series.

In this paper, we construct a Si x F y (x ≤ 6, y ≤ 12) series optimised at the B3LYP/6-31G(d,p) level. At the same level, we perform frontline molecular orbital (FMO), Mayer bond order (MBO), molecular surface electrostatic potential (MS-EPS) and natural population analysis (NPA) calculations to study the chemical structure stabilities of these Si x F y molecules. The FMO and MBO results demonstrate that the chemical structure stabilities of the Si x F y (x ≤ 6, y ≤ 12) series are ranked (from strong to weak) as SiF4 > Si2F6 > Si3F8 > Si4F10 > SiF2 > Si5F12 > Si3F6 (ring) > Si5F10 (ring) > Si6F12 (ring) > Si4F8 (ring). Furthermore, the chemical structure stabilities of the chains are stronger than those of the rings, while the number of silicon atoms is the same. In addition, infrared spectroscopy analysis shows that SiF4 is the most stable among the Si x F y (x ≤ 6, y ≤ 12) series, followed by Si2F6, and SiF2 is unstable. The experimental results are consistent with theoretical calculations. Finally, the MS-EPS and NPA results indicate that compounds in the Si x F y (x ≤ 6, y ≤ 12) series tend to be attacked by nucleophiles rather than by electrophiles; also, they show poor chemical structure stability when encountering nucleophiles.

Comprehensive Comparison of the Combustion Behavior for Low-Temperature Combustion of n-Nonane.

To meet the increasing need for clean combustion, improve the combustion efficiency of fuels, and reduce the pollutants produced in the combustion process, it is necessary to systematically study the combustion of hydrocarbon fuels. An accurate and detailed chemical kinetic model is an important prerequisite for understanding the combustion performance of hydrocarbon fuels and studying complex chemical reaction networks. Therefore, based on ReaxGen, new detailed mechanisms for the low-temperature combustion of n-nonane are proposed and verified in detail in this study. Meanwhile, some international mainstream combustion models such as the LLNL model and the JetSurf 2.0 model are compared with ours, showing that the proposed new mechanisms can better predict the ignition delay combustion characteristics of n-nonane, and they also hold in a wide range of conditions. In addition, the numerical simulation results of the concentration curve calculated for the new mechanisms, especially Model v2, are in good agreement with the experimental data, and the mechanisms can reproduce the performance of the negative-temperature-coefficient behavior toward n-nonane ignition. The numerical simulation results of the laminar flame propagation velocity varying with the equivalence ratio are also in good agreement with the available experimental data. Finally, the ignition delay sensitivity of n-nonane is analyzed by the sensitivity analysis method; the key reactions affecting the ignition mechanism are investigated; and the reaction path analysis is conducted to better understand the models' predicted performance. In a word, the new mechanisms are helpful to understand the ignition properties of large hydrocarbon fuels for high-speed aircrafts.

High-Sensitivity and Long-Life Microchannel Plate Processed by Atomic Layer Deposition.

As a key component of electron multiplier device, a microchannel plate (MCP) can be applied in many scientific fields. Pure aluminum oxide (Al2O3) as secondary electron emission (SEE) layer were deposited in the pores of MCP via atomic layer deposition (ALD) to overcome problems such as high dark current and low lifetime which often occur on traditional MCP. In this paper, we systematically investigate the morphology, element distribution, and structure of samples by scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS), respectively. Output current of different thickness of Al2O3 was studied and an optimal thickness was found. Experimental tests show that the average gain of ALD-MCP was nearly five times better than that of traditional MCP, and the ALD-MCP showed better sensitivity and longer lifetime.