Flow Reactor Studies Research Articles

Combined Smog Chamber/Oxidation Flow Reactor Study on Aging of Secondary Organic Aerosol from Photooxidation of Aromatic Hydrocarbons.

Secondary organic aerosol (SOA) is a significant component of atmospheric fine particulate matter (PM2.5), and their physicochemical properties can be significantly changed in the aging process. In this study, we used a combination consisting of a smog chamber (SC) and oxidation flow reactor (OFR) to investigate the continuous aging process of gas-phase organic intermediates and SOA formed from the photooxidation of toluene, a typical aromatic hydrocarbon. Our results showed that as the OH exposure increased from 2.6 × 1011 to 6.3 × 1011 molecules cm-3 s (equivalent aging time of 2.01-4.85 days), the SOA mass concentration (2.9 ± 0.05-28.7 ± 0.6 μg cm-3) and corrected SOA yield (0.073-0.26) were significantly enhanced. As the aging process proceeds, organic acids and multiple oxygen-containing oxidation products are continuously produced from the photochemical aging process of gas-phase organic intermediates (mainly semi-volatile and intermediate volatility species, S/IVOCs). The multigeneration oxidation products then partition to the aerosol phase, while functionalization of SOA rather than fragmentation dominated in the photochemical aging process, resulting in much higher SOA yield after aging compared to that in the SC. Our study indicates that SOA yields as a function of OH exposure should be considered in air quality models to improve SOA simulation, and thus accurately assess the impact on SOA properties and regional air quality.

A study of CO2 hydrogenation over Ni-MgAlOx catalysts derived from hydrotalcite precursors

Ni/Mg/Al mixed oxides have been prepared by decomposing corresponding layered double hydroxides of the hydrotalcite family. XRD, FTIR and UV–vis–NIR analyses show that prepared materials are constituted by a rock-salt type Mg1−xNixO solid solution with Al3+ in tetrahedral interstices of the cube close packing of oxide anions. When activated at sufficiently high temperature, they convert into optimal size supported Ni metal catalysts which show very active and selective for CO2 methanation. Catalytic data show that these materials are more active at low temperature than Ni/γ-Al2O3 catalysts, with a comparable enhanced activity with respect to Ni/La2O3-Al2O3 ones. A role of basic oxides as activating components can be envisaged and related to the strength of the adsorption of CO2 on the “support” likely forming surface (bi)carbonates as active species. Activation energies and reactions orders have been calculated by flow reactor studies in differential reactor conditions. IR spectroscopy data show that carbon dioxide adsorbs on the reduced catalyst in the form of hydroxycarbonates, that convert at higher temperature in carbonates and strongly adsorbed linear and bridging carbonyl species on metallic nickel. The formation of surface CHx species is also evident.

Oxidation of linear and branched ethers: A comparative flow reactor study of OME2 and trimethoxymethane

Oxidation processes of a linear and a branched ether, oxymethylene ether 2 (OME2) and trimethoxymethane, also known as trimethyl orthoformate (TMOF), were investigated in two complementary atmospheric flow reactor setups coupled to electron ionization molecular-beam mass spectrometer (EI-MBMS). One with high mass resolution to measure speciation data and the second with photoionization MBMS (i2PEPICO) to gain isomer distribution. It can be shown that both ethers have different reactivity with trimethoxymethane reacting at lower temperatures. Furthermore, fuel decomposition and intermediate profiles can be analyzed by combining the results of isomer fractionation using i2PEPICO combined with the quantitative species profiles of EI-MBMS. The results show a huge number of oxygenated species. While the obtained species pool is similar, measured mole fractions differ. Isomers, as for example ethanol and dimethyl ether, are separated and quantified. Direct comparison of the oxidation intermediates of the linear and branched ether clarifies the different reactivity due to their given fuel structures.

On the diversity of fossil and alternative gasoline combustion chemistry: A comparative flow reactor study

Recent progress in molecular combustion chemistry allows for detailed investigation of the intermediate species pool even for complex chemical fuel compositions, as occur for technical fuels. This study provides detailed investigation of a comprehensive set of complex alternative gasoline fuels obtained from laminar flow reactors equipped with molecular-beam sampling techniques for observation of the combustion intermediate species pool in homogeneous gas phase reactions. The combination of ionization techniques including double-imaging photoelectron photoion coincidence (i2PEPICO) spectroscopy enables deeper mechanistic insights into the underlying reaction network relevant to technical fuels. The selected fuels focus on contemporary automotive engine application as drop-in fuels compliant to European EN 228 specification for gasoline. Therefore, potential alternative gasoline blends containing oxygenated hydrocarbons as octane improvers obtainable from bio-technological production routes, e.g., ethanol, iso-butanol, methyl tert‑butyl ether (MTBE), and ethyl tert‑butyl ether (ETBE), as well as a Fischer-Tropsch surrogate were investigated. The fuel set is completed by two synthetic naphtha fractions obtained from Fischer-Tropsch and methanol-to-gasoline processes alongside with a fossil reference gasoline. In total, speciation data for 11 technical fuels from two atmospheric flow reactor setups are presented. Detailed main and intermediate species profiles are provided for slightly rich (ϕ = 1.2) and lean (ϕ = 0.8) conditions for intermediate to high temperatures. Complementary, the isomer distribution on different mass channels, like m/z = 78 u fulvene/benzene, of four gasolines was investigated. Experimental findings are analyzed in terms of the detailed fuel composition and literature findings for molecular combustion chemistry. Influences of oxygenated fuel components as well as composition of the hydrocarbon fractions are examined with a particular focus on the soot precursor chemistry. This dataset is available for validation of chemical kinetic mechanisms for realistic gasolines containing oxygenated hydrocarbons.

Homogeneous catalyst modifier for alkyne semi-hydrogenation: systematic screening in an automated flow reactor and computational study on mechanisms

21 types of modifiers are screened for palladium catalysed semi-hydrogenation of alkynes with varying catalyst type, reaction time, and target substrate using an automated flow reactor system.

Comparison of Heterogeneous Hydroformylation of Ethylene and Propylene over RhCo3/MCM-41 Catalysts

The reaction mechanisms of heterogeneous hydroformylation of ethylene and propylene were compared at 413–453 K using RhCo3/MCM-41 as catalysts. The reaction rates of propylene for both hydroformylation and the undesired side reaction of hydrogenation were found to be about one order of magnitude lower than those for ethylene in flow reactor studies. The difference in the kinetic behavior between ethylene and propylene was investigated by measuring the reaction orders and apparent activation energies, and these macrokinetic observables were analyzed using the degree of rate control (DRC) method. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments were performed to characterize the surface intermediates formed during the reactions. When the reactant was changed from ethylene to propylene, the IR peak corresponding to adsorbed CO exhibited a significant increase, while the IR peaks of the alkyl group decreased in magnitude. Combined with the DRIFTS results, DRC analysis indicates that the first step of olefin hydroformylation, the formation of an alkyl group on the catalyst surface, plays a key role in the difference between ethylene and propylene. This step is kinetically nonrelevant when ethylene is the reactant, but it is one of the rate-controlling steps for propylene. The low concentration of the adsorbed propyl group, which is a common intermediate shared by both hydroformylation and hydrogenation of propylene, decreases the rates of both reaction pathways as compared to ethylene.

Bismuth Vanadate Encapsulated with Reduced Graphene Oxide: A Nanocomposite for Optimized Photocatalytic Hydrogen Peroxide Generation

The photocatalytic H2O2 production is a sustainable and eco-friendly process. Bismuth vanadate (BiVO4 or BVO) is a promising photocatalyst with a low band gap energy. Reduced graphene oxide (rGO) is known for promoting the transport of charges and preventing the recombination of photogenerated electron–hole pairs. This study proposes a synthesis method based on an electrostatic self-assembly approach for functionalizing BVO with GO for photocatalytic H2O2 generation. Different amounts of GO loading on BVO have been taken to assess and optimize the quality of xrGO–BVO (where x = 0.5, 1, 2, and 4 wt %) composites for effective H2O2 generation. H2O2 shows stability under acidic conditions; hence, the effectivity of the xrGO–BVO was tested using acids with different strengths. 1rGO–BVO exhibited efficient H2O2 generation in the presence of oxalic acid, promoting two-electron O2 reduction reaction with a good cyclic stability. A photocatalytic flow reactor study has also been presented to assess the feasibility of continuous H2O2 generation.

The effect of radial diffusion on nanoparticle formation in laminar flow reactors

The present work examines two-dimensional effects during nanoparticle formation in laminar flow reactors using two approaches: a 2D model and a simplified 1D model. The investigated cases consist of carbon nanoparticle synthesis via ethylene pyrolysis in laminar flow. The simplified 1D simulations are conducted using the 1D plug flow solver Nano PFR, while the 2D simulations have been performed using CoFlame in an axisymmetric configuration. Both models utilize a sectional population balance model coupled with gas-phase chemistry to simulate detailed particle formation processes.The effects of radial diffusion of the 2D approach are analyzed in a reference case of an isothermal reactor by comparing a diffusion model against a no-diffusion model. Results show that radial diffusion sufficiently mixes the gas phase species along the radius to approximate plug flow. While radial diffusion effects are apparent in particle formation, it is not nearly enough to develop a uniform radial profile for the primary particle and agglomerate number densities and volume fraction. Next, experimental data from the literature are simulated, examining the suitability, differences, and limitations between the 1D and 2D domains. Both models perform similarly in prediction accuracy for the gas-phase species, including fuel pyrolysis and PAH formation. Moreover, by integrating particle mass across several regions (i.e. radial integration approach), the 1D model can achieve accuracy on par with the 2D model for particle formation predictions. Both models can adequately capture SMPS measurements for particle volume fraction, number densities, and size distributions. Ultimately, within the range of experimental conditions typically found in current laminar flow reactor studies for carbon nanoparticle formation, a modified 1D approach can sufficiently describe the gas-phase chemistry and particle formation processes with lower computational costs than the 2D approach.

Interaction of NH3 and NO under combustion conditions. Experimental flow reactor study and kinetic modeling simulation

The interaction between ammonia and NO under combustion conditions is analyzed in the present work, from both experimental and kinetic modelling points of view. An experimental systematic study of the influence of the main variables for the NH3NO interaction is made using a laboratory tubular flow reactor installation. Experiments are performed at atmospheric pressure and variables analyzed include: temperature in the 700–1500 K range, air stoichiometry, from pyrolysis to very oxidizing conditions, and the NH3/NO ratio, in the 0.7–3.5 range. Nitrogen and argon have been used as diluent gas. A literature reaction mechanism has been used to simulate the present experimental results and discuss the main findings. Reaction path analysis has allowed the identification of the reaction routes under the studied conditions. The simulations reflect the main experimental trends observed. Main results show that NO reduction by NH3 occurs at any conditions studied, but is more intense under oxygen excess conditions. Interactions of NH3 and NO proceeds in a molar basis with optimum conversions of NO of up to almost 100%.

Combustion kinetics of alternative jet fuels, Part-I: Experimental flow reactor study

A comprehensive collection of technical aviation fuels enabled an experimental and numerical study on detailed combustion chemistry and pollutant formation presented in a series of 3 interlinking parts. Part-I: Experimental Flow Reactor Study focuses on the characterization of 42 technical jet fuels and provides experimental speciation data for model development presented in Part-II: Model and Surrogate Strategy. Model validation based on the presented technical fuels here is presented in Part-III: Model Application on Technical Jet Fuels.The fuels investigated in this study cover a broad range of approved SAFs (Sustainable Aviation Fuels), candidates for approval, and technical products outside the present ASTM-D7566 specification and is completed by reference fuels (ASTM-D1655). This includes SAF components such as HEFA (Hydroprocessed Esters and Fatty Acids), ATJ (Alcohol-To-Jet), SIP (Synthesized Iso-Paraffins), and Fischer-Tropsch-products as well as their blends.A systematic investigation of the soot precursor chemistry by analyzing the influence of the complex chemical fuel composition on the intermediate species pool is presented. The experimental set-up consists of an atmospheric flow reactor with coupled molecular-beam mass spectrometer (MBMS). Quantitative evolution of combustion reaction intermediates is recorded for fuel-rich (Φ = 1.2) and fuel-lean (Φ = 0.8) conditions at intermediate temperatures up to 1200 K including small intermediate species (e.g. ethylene, butene) and soot precursor species (e.g. benzene, naphthalene, phenanthrene).A general systematic dependency of the soot precursor concentration on the degree of unsaturation (Index of Hydrogen Deficiency) or the hydrogen content, respectively, is demonstrated. Furthermore, larger soot precursor concentrations depend on the naphthalene content of the fuel.

A Reusable Rgo/BiVO4 Photocatalyst for Hydrogen Peroxide Synthesis in Different Flow Systems

The photocatalytic H2O2 production is a sustainable and eco-friendly process, requiring mostly water, oxygen, and sunlight. In previous study, bismuth vanadate (BiVO4), a semiconductor with a low band gap energy (~2.4 eV) was encapsulated with reduced graphene oxide (rGO) to promote the separation and transport of charges, preventing the recombination of photogenerated electron-hole pairs in BiVO4. 1% GO loading on BiVO4 was found to deliver effective H2O2 synthesis. H2O2 shows stability in acidic pH (~3), hence the effectiveness of the rGO/BiVO4 was tested under different types of acids. The order of efficiency of the acids is as follows: oxalic acid > phosphoric acid > formic acid > perchloric acid. This study involves the stability and reusability aspects of rGO/BiVO4 exhibiting significant H2O2 synthesis in the presence of oxalic acid catalyzing two-electron O2 reduction reaction. The photocatalytic H2O2 synthesis reaction following a zero-order kinetics, while the photocatalytic H2O2 decomposition following a first-order kinetics has been proposed as a mechanistic insight. A photocatalytic flow reactor study has also been evaluated to assess the feasibility of H2O2 generation in different reactor systems. Photocatalytic performance of rGO/BiVO4 composite was analysed in batch as well as flow reactor conditions.

Modeling and Optimization of Multi-functional Ammonia Slip Catalysts for Diesel Exhaust Aftertreatment

Ammonia slip catalysts (ASC) are used downstream of the NH3-selective catalytic NOx reduction (SCR) system, to minimize ammonia slip from transport sector SCR units. The ASC may consist of an SCR active layer for NOx control, a layer with oxidation functionality for ammonia conversion, or a combination thereof, either as individual layers or as a single mixed layer. Mathematical models of such systems involve flow and mass transfer in the monolithic channels as well as coupled reaction/diffusion processes in the catalytic layers. In this work, we develop a single-channel 1D-1D (pseudo 2D) steady-state tank-in-series mathematical model for monolithic ammonia slip catalysts with up to two layers. Kinetics of relevant reactions over the Cu-Beta zeolite and the Pt/TiO2 layer, including SCR, ammonia oxidation, and the formation of N2O, were derived based on an extensive flow reactor study. The model was validated based on experiments using four different small-scale ASC monoliths, showing good agreement between the model predictions and the experimental results. Comparison of ten ASC configurations for the oxidation of 200 ppm NH3 at 300 °C shows that configurations with a pure layer of NH3 oxidation catalyst generate undesirable high N2O and NOx levels. The best ASC configurations feature fast diffusion in the catalytic layers (a high effective diffusion coefficient), a thin top layer loading with some ammonia oxidation catalyst, and a mixed layer of ammonia oxidation catalyst and the SCR catalyst to limit the formation of N2O and NOx.

Impact of Chemistry–Turbulence Interaction Modeling Approach on the CFD Simulations of Entrained Flow Coal Gasification

This paper examines the impact of different chemistry–turbulence interaction approaches on the accuracy of simulations of coal gasification in entrained flow reactors. Infinitely fast chemistry is compared with the eddy dissipation concept considering the influence of turbulence on chemical reactions. Additionally, ideal plug flow reactor study and perfectly stirred reactor study are carried out to estimate the accuracy of chosen simplified chemical kinetic schemes in comparison with two detailed mechanisms. The most accurate global approach and the detailed one are further implemented in the computational fluid dynamics (CFD) code. Special attention is paid to the water–gas shift reaction, which is found to have the key impact on the final gas composition. Three different reactors are examined: a pilot-scale Mitsubishi Heavy Industries reactor, a laboratory-scale reactor at Brigham Young University and a Conoco-Philips E-gas reactor. The aim of this research was to assess the impact of gas phase reaction model accuracy on simulations of the entrained flow gasification process. The investigation covers the following issues: impact of the choice of gas phase kinetic reactions mechanism as well as influence of the turbulence–chemistry interaction model. The advanced turbulence–chemistry models with the complex kinetic mechanisms showed the best agreement with the experimental data.

Impact of vitiation on flow reactor studies of jet fuel combustion chemistry

Flow reactors are commonly employed in investigations of the pyrolysis and oxidation chemistry of fuels. Typical flow reactors use either electrical heaters or vitiation heaters to provide the energy to preheat the reactants to the desired experimental conditions. The present study seeks to determine the impact of vitiation on flow reactor studies of fuel combustion chemistry by conducting both fuel pyrolysis and oxidation experiments in a flow reactor in which either an electrical heater or a vitiation heater is used as the energy source. Other than the heater all other aspects of the flow reactor are identical. Two fuels relevant to air-breathing propulsion systems were investigated – Jet A and JP-10. Profiles of the stable reaction products were measured using gas chromatography for a temperature of 1030 K at a pressure of 1 atmosphere, with residence times between 30 ms and 70 ms. The primary hydrocarbon products for Jet A pyrolysis and oxidation were C 2 H 4 , C 3 H 6 , CH 4 , C 4 H 8 , C 6 H 6 and C 7 H 8 . For JP-10, in addition to these species, cyclopentene (C 5 H 8 ) and cyclopentadiene (C 5 H 6 ) were measured. Under the conditions investigated, vitiation decreases the reaction times scales for both pyrolysis and oxidation. However, the product yields at a fixed fuel conversion were nearly identical for both the vitiated and non-vitiated experiments. Current kinetic models for Jet A and JP-10 pyrolysis and oxidation adequately captured the observed effects of vitiation on the stable species profiles.

Products and mechanism of thermal decomposition of chlorpyrifos under inert and oxidative conditions.

Chlorpyrifos (CPF) is a widely used pesticide; however, limited experimental work has been completed on its thermal decomposition. CPF is known to decompose into 3,5,6-trichloro-2-pyridinol (TCpyol) together with ethylene and HOPOS. Under oxidative conditions TCpyol can decompose into the dioxin-like 2,3,7,8-tetrachloro-[1,4]-dioxinodipyridine (TCDDPy). With CPF on the cusp of being banned in several jurisdictions worldwide, the question might arise as to how to safely eliminate large stockpiles of this pesticide. Thermal methods such as incineration or thermal desorption of pesticide-contaminated soils are often employed. To assess the safety of thermal methods, information about the toxicants arising from thermal treatment is essential. The present flow reactor study reports the products detected under inert and oxidative conditions from the decomposition of CPF representative of thermal treatments and of wildfires in CPF-contaminated vegetation. Ethylene and TCpyol are the initial products formed at temperatures between 550 and 650 °C, although the detection of HOPOS as a reaction product has proven to be elusive. During pyrolysis of CPF in an inert gas, the dominant sulfur-containing product detected from CPF is carbon disulfide. Quantum chemical analysis reveals that ethylene and HOPOS undergo a facile reaction to form thiirane (c-C2H4S) which subsequently undergoes ring opening reactions to form precursors of CS2. At elevated temperatures (>650 °C), TCpyol undergoes both decarbonylation and dehydroxylation reactions together with decomposition of its primary product, TCpyol. A substantial number of toxicants is observed, including HCN and several nitriles, including cyanogen. No CS2 is observed under oxidative conditions - sulfur dioxide is the fate of S in oxidation of CPF, and quantum chemical studies show that SO2 formation is initiated by the reaction between HOPOS and O2. The range of toxicants produced in thermal decomposition of CPF is summarised.

Carboxylic acids from limonene oxidation by ozone and hydroxyl radicals: insights into mechanisms derived using a FIGAERO-CIMS

Abstract. This work presents the results from a flow reactor study on the formation of carboxylic acids from limonene oxidation in the presence of ozone under NOx-free conditions in the dark. A High-Resolution Time-of-Flight acetate Chemical Ionisation Mass Spectrometer (HR-ToF-CIMS) was used in combination with a Filter Inlet for Gases and AEROsols (FIGAERO) to measure the carboxylic acids in the gas and particle phases. The results revealed that limonene oxidation produced large amounts of carboxylic acids which are important contributors to secondary organic aerosol (SOA) formation. The highest 10 acids contributed 56 %–91 % to the total gas-phase signal, and the dominant gas-phase species in most experiments were C8H12O4, C9H14O4, C7H10O4 and C10H16O3. The particle-phase composition was generally more complex than the gas-phase composition, and the highest 10 acids contributed 47 %–92 % to the total signal. The dominant species in the particle phase were C8H12O5, C9H14O5, C9H12O5 and C10H16O4. The measured concentration of dimers bearing at least one carboxylic acid function in the particle phase was very low, indicating that acidic dimers play a minor role in SOA formation via ozone (O3)/hydroxyl (OH) oxidation of limonene. Based on the various experimental conditions, the acidic compositions for all experiments were modelled using descriptions from the Master Chemical Mechanism (MCM). The experiment and model provided a yield of large (C7–C10) carboxylic acid of the order of 10 % (2 %–23 % and 10 %–15 %, respectively). Significant concentrations of 11 acids, from a total of 16 acids, included in the MCM were measured with the CIMS. However, the model predictions were, in some cases, inconsistent with the measurement results, especially regarding the OH dependence. Reaction mechanisms are suggested to fill-in the knowledge gaps. Using the additional mechanisms proposed in this work, nearly 75 % of the observed gas-phase signal in our lowest concentration experiment (8.4 ppb converted, ca. 23 % acid yield) carried out under humid conditions can be understood.

The effects of bimetallic interactions for CO2‐assisted oxidative dehydrogenation and dry reforming of propane

AbstractThe catalytic reduction of CO2 by propane may occur via dry reforming to produce syngas (CO + H2) or oxidative dehydrogenation to yield propylene. Utilizing propane and CO2 as coreactants presents several advantages over conventional methane dry reforming or direct propane dehydrogenation, including lower operating temperatures and less coke formation. Thus, it is of great interest to identify catalytic systems that can either effectively break the CC bond to generate syngas or selectively break CH bonds to produce propylene. In this study, several precious and nonprecious bimetallic catalysts supported on reducible CeO2 were investigated using flow reactor studies at 823 K to identify selective catalysts for CO2‐assisted reforming and dehydrogenation of propane.

Effects of oxide supports on the CO2 reforming of ethane over Pt-Ni bimetallic catalysts

Catalytic reduction of CO2 by ethane creates an opportunity to use the shale gas and CO2 as the raw materials to produce syngas via dry reforming. In the present work, Pt-Ni bimetallic catalysts were investigated on reducible (CeO2, TiO2) and irreducible (γ-Al2O3, SiO2) oxides. The results showed that catalysts supported on reducible oxides, especially CeO2, were more active than those supported on irreducible oxides. Pulse and flow reactor studies and infrared spectroscopy experiments revealed a bi-functional Mars-Van Krevelen redox mechanism on PtNi/CeO2 and a mono-functional Langmuir-Hinshelwood mechanism on PtNi/SiO2, providing insights into the effects of reducibility of oxide supports on the reaction kinetics. Additionally, compared with the non-reducible SiO2, in situ X-ray diffraction (XRD) and pulse reactor analysis revealed that CO2 could be effectively activated on the reducible CeO2 and formed surface oxygen species to promote ethane dissociation into active carbon species. Thermogravimetric analysis (TGA), Transmission electron microscopy (TEM) and Raman spectroscopy showed that cokes formed on PtNi/CeO2 were primarily disordered/amorphous carbon species that could be easily removed during reforming.

Exploration of the pyrolysis chemistry of 1,1-diethoxybutane: A flow reactor and kinetic modeling study

1,1-Diethoxybutane is a promising next-generation biofuel and this work reports the first study for its pyrolysis chemistry. Pyrolysis of 1,1-diethoxybutane was investigated in a flow reactor at 0.04 and 1 atm using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). A series of oxygenated and hydrocarbon products, including several radicals, were detected and their mole fractions were evaluated. A detailed kinetic model of 1,1-diethoxybutane, including 253 species and 1577 reactions, was developed and validated against the present experimental data. Modeling analyses including the rate of production analysis and sensitivity analysis were performed to reveal the crucial consumption pathways of 1,1-diethoxybutane, as well as the formation and consumption pathways of intermediates and products. The H-abstraction reactions of 1,1-diethoxybutane play a key role in fuel consumption. The intra-molecular elimination reactions and unimolecular CC or CO dissociation reactions of 1,1-diethoxybutane make minor contributions to fuel consumption. The sensitivity analysis also shows that the fuel consumption reactions have large sensitivities to 1,1-diethoxybutane. Further β-CC and β-CO scission reactions closely connect the consumption of six fuel radicals and the formation of most oxygenated products. The observation of high mole fractions of C1–C4 acids and aldehydes demonstrates the structural features of 1,1-diethoxybutane. Besides, several hydrocarbon products, such as C2–C4 alkenes, benzene and its precursors, were detected, some of which, such as propene, are also produced from the consumption reactions of fuel radicals. Besides, hydrocarbon products can also be produced from the combination reactions of small species, such as the combination reactions of C3 species to produce benzene and the combination reaction of allyl and methyl to produce 1-butene. The low benzene production ability of 1,1-diethoxybutane implies its low sooting tendency compared with fossil-derived transportation fuels.

Thermal Decomposition Mechanism of Aqueous Hydroxylammonium Nitrate (HAN): Molecular Simulation and Kinetic Modeling.

A detailed mechanism has been developed for thermal decomposition of hydroxylammonium nitrate (HAN) solutions, based on quantum mechanical calculations using the SMD-ωB97X-D method. The mechanism describes multiple kinetic processes, including nitration and nitrosation of hydroxylamine, HNO dimerization, and HONO-regeneration pathways involving H-abstraction reactions. Rate constants of elementary reactions were estimated using transition state theory with consideration of species' diffusion effect. Kinetic modeling was performed to predict species' evolutions in 0.1 m HAN in the temperature range of 463-523 K, and results show reasonable agreement with the experimental data from flow reactor studies. For more concentrated solutions, strong autocatalytic behaviors were predicted with the late emergence of NO2 and HONO, whose regeneration was previously considered as the major autocatalytic pathway. Sensitivity analysis results suggest an acid-catalyzed nitration-nitrosation pathway, based on which the autocatalysis should be caused by the rise of solution acidity. A linear correlation can be observed in the previously reported apparent Arrhenius parameters, which may be reconciled via a kinetic compensation effect.