This study utilized oil-rich coal as a material to achieve the effective preparation of organophosphorus-rich tar with enhanced value through co-pyrolysis in combination with different phosphorus-bearing substances. Through a comprehensive analysis of its chemical composition, the organic phosphine compounds were systematically studied and classified. Possible reaction pathways were proposed, laying a solid experimental foundation for the high-value conversion and application of coal tar. The molecular architecture and constituent profiles of valuable compounds within organophosphorus-rich tar were primarily analyzed using nuclear magnetic resonance (NMR) and gas chromatography coupled with mass spectrometry (GC-MS). Various phosphorus-containing reagents were introduced to explore the range of structures and types of organophosphorus species generated during co-pyrolysis. Under co-pyrolysis conversion conditions, various phosphorus sources are reacted with oil-rich coal to construct carbon-phosphorus (C-P) bonded molecules via a free radical-mediated chain reaction mechanism. This study establishes a green and efficient route to the high-value utilization of oil-rich coal, and a novel strategy for constructing C-P bonds was proposed.
The co-combustion of methanol and dimethyl ether (DME) presents a promising approach for achieving efficient and low-emission combustion in engines. To comprehensively evaluate the applicability of detailed chemical kinetic mechanisms for methanol/DME blends, six existing mechanisms from the literature were systematically assessed using an integrated approach combining numerical simulation and experimental measurement. The analysis focused on various key parameters, including ignition delay times (IDT), laminar burning velocity (LBV), and concentrations of different critical intermediate species. For the first time, LBV data for methanol/DME blends at various mixing ratios were experimentally measured using the heat flux method in the present work, providing critical data for mechanism validation. In terms of IDT prediction, the Yan mechanism demonstrated the highest accuracy across different pressures, equivalence ratios, and blend ratios, while the Aramco 2.0 mechanism also performed well under most conditions. For LBV prediction, the Yan mechanism provided the most reliable predictions for methanol and DME under high-pressure conditions, whereas the Aramco 2.0 mechanism yielded the smallest overall prediction error for blended fuels under atmospheric pressure. Species concentration simulations revealed that both the Aramco 2.0 and Yan mechanisms captured the variation trends of CO, CO2, and CH2O with temperature reasonably well. However, discrepancies can be observed in CH2O predictions around 800 K, indicating variations in the configuration of reaction pathways. Overall, the Yan and Aramco 2.0 mechanisms show high reliability in characterizing the combustion behavior of methanol/DME blended fuels. The choice between these mechanisms should be guided by the specific pressure conditions in practical applications.
This study employs Reactive force field molecular dynamics (ReaxFF MD) simulations to probe ammonia pyrolysis and oxidation across temperatures and equivalence ratios, revealing accelerated combustion with temperature and key species variations. Based on the analysis of combustion mechanisms through molecular dynamics simulations and reaction pathway analysis derived from six published combustion mechanisms, this study has established a relatively comprehensive combustion pathway for ammonia. A detailed kinetic model for ammonia combustion, comprising 41 species and 351 reactions, is developed using a hierarchical construction method. The model demonstrated excellent agreement with a wide range of experimental data, including ignition delay times (IDTs), laminar burning velocities (LBVs), and species concentrations under diverse conditions, thereby validating its predictive capability. Reaction path analysis and sensitivity analysis revealed that the ammonia combustion process involves two major pathways: N2 generation and NOx generation from NH2. Key reactions affecting performance include NH3, NH2, NH, and H. The reaction NH2 + NO = N2 + H2O exhibits the most significant inhibiting effect on ammonia combustion. Meanwhile, H + O2 = O + OH remains a strong promoter for LBVs and key species formation in ammonia, whereas its promoting effect on ammonia ignition performance becomes considerably weaker. In contrast, the reaction NH2+ HO2 = H2NO + OH shows the strongest promoting influence on IDTs. Additionally, NH2-involved reactions that generate radicals such as OH and O, as well as those yielding N2 and H2O, also substantially enhance the ignition performance of ammonia.
The co-pyrolysis of bamboo (BB) and waste tires (WT) is a promising waste-to-energy strategy; however, a fundamental understanding of its reaction kinetics and real-time volatile interactions remains limited. This study addresses this gap by employing an integrated TG-FTIR-GC/MS approach to elucidate the synergistic mechanisms, kinetics, and product evolution of BB/WT co-pyrolysis. Marked synergy was observed between 300-500 degrees C for blends of 5:5, and 3:7 (BB : WT). At the 5:5 ratio, the phenolic, ketone, and alkene contents decreased to 12.42%, 13.37%, and 51.91%, respectively. At the 3:7 ratio, the phenolic and ketone contents further decreased to 2.65% and 5.96%, respectively, with alkenes accounting for 61.18%. The activation energies for BB, WT, and their 1:1 blend, determined using the KAS, FWO, and Friedman methods, were 101.91, 117.04, and 113.67 kJ/mol, respectively. The Coats-Redfern method identified A2/3 for BB, F3/2 for WT, and D3 for the 1:1 blend as the most suitable reaction models. These findings provide crucial insights for optimizing the co-pyrolysis process, and enhancing the efficient utilization of biomass and WT.
Ca-doped and Ca-loaded LaMnO3 (CLMO and CaO-LMO) were derived from LaMnO3 (LMO) and synthesized by coprecipitation and doping. Batch adsorption tests revealed that CLMO exhibited superior adsorption capabilities for phytic acid in acidic water, with an adsorption capacity of 86.54 mg P/g at pH 3, representing 63% and 130% increases over those of LMO and CaO-LMO, respectively. Conversely, CaO-LMO demonstrated an enhanced adsorption performance in neutral to alkaline water with an adsorption capacity of 83.20 mg P/g at pH 10, which was 810% and 111% higher than those of LMO and CLMO, respectively. The adsorption of phytic acid by all three perovskites was characterized as monolayer chemical adsorption, involving mechanisms such as ligand exchange, inner sphere complexation, and electrostatic attraction. X-ray diffractometry, X-ray photoemission spectroscopy, and Fourier transform infrared spectroscopy confirmed that the primary adsorption sites for phytic acid were the La/Ca sites and oxygen vacancies in CLMO, the La/Ca sites in CaO-LMO, and the La sites in LMO. Ca doping/loading enriched the active sites for phytic acid adsorption and enhanced the structural stability of the materials. CLMO and CaO-LMO exhibited excellent performance in recovering different forms of organic phosphorus from various real wastewater sources under dynamic adsorption conditions. The results suggest that CLMO should be prioritized for organic phosphorus removal in acidic waters, whereas CaO-LMO should be prioritized for the same in alkaline waters. This research provides a technical solution for the efficient recovery of organic phosphorus from water bodies.
The electrochemical reduction of nitrate (NO3RR) presents an environmentally viable strategy for simultaneously mitigating nitrogen-based water pollution and synthesizing green ammonia (NH3). Nevertheless, the overall efficacy of this process is severely hindered by the sluggish kinetics inherent to its multielectron transfer steps, coupled with intense competition from the hydrogen evolution reaction (HER). Metal-based single-atom catalysts (SACs) with low-spin effects, such as Cu and Ru, exhibit great performance in the NO3RR. However, this study demonstrates that nitrogen-doped carbon-supported cobalt nanoparticles (Co NPs) significantly outperform Co SACs in NO3RR. Under alkaline conditions, the Co NPs architecture achieved a remarkable Faradaic efficiency of 98.1%, alongside an exceptional NH3 yield rate of 31.9 mgNH3 h-1 mgcat-1. In-situ electrochemical spectroscopy reveals that Co NPs promote a direct nitrate-to-ammonia pathway involving rapid deoxygenation and hydrogenation intermediates, whereas Co SACs favor indirect routes with sluggish *NH2OH formation. Density functional theory calculations uncover that Co NPs exhibit high-spin electronic states, elevated near-Fermi-level electron density, and stronger Co-3d/NO3--2p orbital hybridization, leading to enhanced nitrate adsorption, lower potential-determining energy barriers, and weakened hydrogen adsorption that suppresses HER. Notably, these high-spin states are further enhanced by the nitrogen-doped carbon substrate, which increases the near-Fermi-level electron density and boosts catalytic activity. These controllable high-spin structures and the electronic synergistic effect enable accelerated nitrate activation, efficient proton-electron transfer, and improved ammonia selectivity. This work establishes high-spin cobalt nanoparticle ensembles as a superior active-site motif for NO3RR, and provides a fundamental design principle for next-generation electrocatalysts that integrate wastewater denitrification with sustainable ammonia synthesis.
China has vast reserves of agricultural straw resources. The high-value utilization of agricultural straw through biomass gasification technology holds significant importance for China to achieve 'carbon neutrality' and 'carbon peaking'. This work systematically investigated the effects of equivalence ratio (ER) and gasification temperature (GT) on the properties of the gasified gaseous, solid, and liquid products of corn stover (CS), which was conducted in a home-made and lab-scale fixed-bed gasifier. Results showed that with the increase in GT and ER, the mass yield of bio-gas gradually increased, while the mass yield of bio-char gradually decreased. Higher GT and lower ER were beneficial for improving the lower heating value (LHV) of bio-gas. Specifically, the LHV of bio-gas reached its maximum value of 11.26 MJ/Nm3 at the GT of 900 degrees C and the ER of 0.05, along with the contents of H2, CO, CH4, and CnHm being 22%, 25.91%, 13.59%, and 1.12%, respectively. Furthermore, the contents of H and volatiles in bio-char significantly decreased, while the ash content significantly increased at higher GT and ER. Regarding the tar product, the contents of phenols, alcohols, acids, and aldehydes decreased at higher GT, while the contents of aromatics and ethers increased. In addition, the contents of aromatics and phenols in tar decreased at higher ER, while that of ethers increased.
The pyrolysis kinetics of octamethylcyclotetrasiloxane (D4) at high temperatures, crucial for silicon-based material synthesis and waste-to-energy applications are not fully understood. This work carries out this research by combining flow tube experiments (803-843 K), with ReaxFF molecular dynamics (MD) simulations (1,500-2,600 K). Experimentally, a significant increase in methane (CH4) production at 843 K-compared to its absence at 803 K-suggests a high activation energy barrier for CH4 formation, which is overcome via Si-C bond cleavage, and methyl radical (& centerdot;CH3) chain reactions. ReaxFF MD simulations indicate that D4 decomposition follows first-order kinetics at high temperatures, with an apparent activation energy of 81.3 +/- 4.2 kJ/mol, much lower than the 273.2-320 kJ/mol reported at lower temperatures. This difference arises from the enhancement of the D4 decomposition channel in which radicals participate in at high temperatures. Both experiments and simulations confirm that hydrogen abstraction by & centerdot;CH3 radicals (& centerdot;CH3 + R-H -> CH4 + R & centerdot;) is the primary route for CH4 production. The developed multi-scale kinetic model offers crucial insights for optimizing silicon-based material synthesis and simulating silicon-containing gas combustion.
In contrast to the extensive research on polycyclic aromatic hydrocarbons (PAHs), the reaction chemistry of oxygenated PAHs (OPAHs) during combustion has received little attention, despite their highly detrimental effects. Among OPAHs, anthraquinone, a tricyclic ring structure with two ketone groups, was selected for focus in this study due to its confirmed production in various combustion processes, and no study on its formation chemistry is available in the literature. To elucidate its reaction chemistry, a multifaceted investigation (experimental, theoretical, and modeling) was employed. Fuel-rich oxidation of toluene and the pyrolysis of anisole and 4-methylanisole using a flow reactor were performed to quantify anthraquinone experimentally. Theoretical calculations were conducted for the rate parameters of molecular growth reactions from p-benzoquinone/p-naphthoquinone via Hydrogen-Abstraction-Carbon-Addition (HACA), and a combination of small oxygenated aromatics-benzaldehyde and its radicals. The sub-mechanism involving anthraquinone formation and consumption was developed and integrated with the existing model. The developed model could satisfactorily replicate both the measured data in a flow reactor and the literature data in a flame. To inspect anthraquinone reaction chemistry, kinetic analysis was conducted, demonstrating that three pathways were important for anthraquinone formation: (1) combination of small oxygenated aromatics; (2) HACA mechanism from small quinones, and (3) oxidation of PAHs. However, the predominant formation pathways varied with conditions and fuel. In a flow reactor, combination and oxidation pathways were the primary contributors to anthraquinone formation during pyrolysis and oxidation. Under flame conditions, the relative importance of these three pathways varied dynamically with the height-above-burner.
The high cost associated with hydrogen storage and transportation pose a significant barrier to the widespread adoption of hydrogen energy. Utilising ammonia as a hydrogen carrier offers a promising solution but the development of an efficient catalyst is critical in reducing the costs of the process. In the present work, a new La(1-x)SrxCoO3 (x = 0, 0.2, 0.4, 0.6, 0.8) perovskite composite catalyst was synthesised via the sol-gel method for ammonia decomposition. The effect of the strontium (Sr) doping in the perovskite on ammonia's thermal decomposition was examined. The results show that Sr2+ doping can effectively enhance the catalytic activity of the catalyst, in which La0.4Sr0.6CoO3 catalysts exhibited the highest catalytic activity at 650 degrees C with a decomposition rate of 98.89% and a gas hourly space velocity of 37,500 mL & centerdot;h-1 & centerdot;g-1. Density functional theory calculation reveals that the La0.4Sr0.6CoO3 exhibits a unique balance of structural, electronic and catalytic properties that optimises NH3 cracking performance with favourable N2 desorption characteristics. The enhanced redox activity from the optimal Co4+concentration in La0.4Sr0.6CoO3 reduces the rate-limiting N-H cleavage barrier.
This study employs ReaxFF MD simulations to systematically investigate the pyrolysis behaviors of six lignin monomer model compounds with varying methoxy group numbers and C4-position substituents over 2,000 to 4,000 K. The results indicate that methoxy groups are the key structural units governing initial reactivity, lowering activation energies, and accelerating the fragmentation of parent molecules. While alkyl groups increase activation energies and hinder decomposition. As temperature rises, dominant reaction pathways undergo significant shifts. At lower temperatures (2,000-2,500 K), reactions primarily involve homolytic cleavage and removal of methoxy groups, leading to oxygen-containing products; under high-temperature conditions, ringopening reactions of aromatic structures are markedly enhanced, promoting the substantial formation of C1-C5 hydrocarbons. Among oxygen-containing products, carbon monoxide gradually evolves into the dominant stable product above 3,000 K, and its generation is synergistically promoted by both elevated temperature and higher methoxy group abundance. Formaldehyde exhibits distinct dynamic evolution patterns at 3,000 and 4,000 K. Regarding hydrocarbon products, acetylene emerges as the predominant stable end-product with continuous accumulation, facilitated by both high-temperature conditions and hydrocarbon side-chain structures. These results clarify, at the atomic scale, the intrinsic relationships among 'molecular structure-reaction pathway-temperature effects' during the pyrolysis of lignin monomer model compounds, providing theoretical foundations for the in-depth understanding of lignin pyrolysis mechanisms and the optimization of thermochemical conversion processes.
The unsym-dimethylhydrazine ((CH3)2NNH2,UDMH)/nitrogen tetroxide (N2O4) combination is a widely used high-energy propellant in liquid propulsion systems, and understanding its combustion kinetics is essential to optimize ignition and combustion properties. In this work, the unimolecular decomposition and H-abstraction reactions of UDMH were comprehensively and theoretically investigated. Their potential energy surfaces (PESs) were calculated at the CCSD(T)/CBS//M06-2X/def2-TZVP level of theory. The minimum energy path (MEP) of barrierless bond dissociation reactions was obtained using the multi-reference method of MRCISD/CBS//CASPT2/cc-pVDZ. Pressure-dependent rate constants at 300-2,500 K were obtained by RRKM/Master Equation calculations. For the unimolecular decomposition of UDMH, the dissociation energies of the NH2 and CH3 groups are relatively low among the bond dissociation channels, resulting in NH2 and CH3 group dissociation reactions dominating the unimolecular decomposition of UDMH, while the elimination reactions have less contribution caused by their high energy barriers. For the H-abstractions by NO2, reactions involving cis-HONO formation occur more easily at all three sites of UDMH. Additionally, the H-abstraction reactions at the NH2 group possess the greatest rate constants because of lower energy barriers. Both the H-abstraction reactions initiated by H atoms and CH3 radicals at the amine group, play important roles under low temperature conditions, and those at the primary carbon sites are dominant at high temperatures. Additionally, the H-abstraction reactions of UDMH and monomethylhydrazine initiated by NO2 and H, are compared. The detailed kinetic parameters of unimolecular decomposition, and H-abstraction reactions of UDMH obtained in this work aid model development, and enhance the understanding of its combustion chemistry.
Oxymethylene ethers (OMEs) are promising alternative fuels. A comprehensive evaluation of the prediction accuracy of their chemical kinetic models is essential for their computational fluid dynamics simulations. Thus, this study evaluates comprehensively the performance of ten recently proposed kinetic models of OME1-4 against 43 experimental datasets, including ignition delay times, laminar burning velocities, and species concentrations. The investigated models are different in terms of their development methods and chemical natures. While all ten models include the chemistry of OME1, seven, five, and three models of them can describe the combustion of OME2, OME3, and OME4, respectively. For OME1, the models of Liet al. (2021), Cai et al. (2020), and Jacobs et al. (2019) demonstrate prediction advantages over other models. The model of Shrestha et al. (2022) provides the lowest prediction uncertainties for the combustion of OME2, while the reduced model of Dinelli et al. (2024) matches the data of OME3 and OME4 best. However, none of these models achieves very high prediction accuracy for all considered targets and, more importantly, for all interested OMEs. The results of sensitivity and reaction flux analyses reveal that, for all OMEs, the fuel decomposition reactions via unimolecular H-transfer influence their auto-ignition at high temperatures and pyrolysis behaviors significantly. The auto-ignition behavior of long-chain OMEs over a wide temperature range is highly sensitive to the reactions of smaller OMEs, as their primary fuel radicals are produced via the beta-scission of radicals of longer OMEs. These findings provide insights into improved chemical models of OMEs.
Recent years have witnessed major advances in heated tobacco products. However, optimizing the aroma release and smoke generation of these products remains a formidable challenge. Alkali metal salts have emerged as effective catalysts for pyrolysis, demonstrating the dual benefits of enhanced catalytic efficiency and alleviating coke deposition. To effectively illustrate the effect of adding salt on the low-temperature catalytic pyrolysis performance of reconstituted tobacco sheets, thermogravimetric analysis and pyrolysis gas chromatography-mass spectrometry analyses were carried out, and the Flynn-Wall-Ozawa method and the Kissinger method were also applied to calculate reaction kinetics. The addition of the sodium (Na) salt or potassium (K) salt in reconstituted tobacco sheets was observed to significantly decrease the temperature corresponding to the maximum weight loss rate and increase the total weight loss with the range of 100-300 degrees C. Meanwhile, the content of key components in the pyrolysis gas gradually increased, indicating that the ability to catalyze cellulose and lignin pyrolysis improved. The results of dynamic analysis show that the apparent activation energy of reconstituted tobacco sheets decreased by an average of 80.95 or 49.12 kJmol-1 after adding Na or K salt when the conversion rate was 0.1-0.8. The approach reported herein not only exhibits a fundamental advance in the low-temperature pyrolysis of reconstituted tobacco sheets for heated tobacco products but also increases the concentration of pyrolysis gas and aromatic substances.
This study focuses on methods to correct the non-ideal behaviors of a gas following a reflected shock wave, as applied in chemical kinetic modeling. These non-ideal behaviors of gas were experimentally observed through an increase in the pressure (P5) of the inert argon gas behind the reflected shock wave. The impact of the initial temperature in the driven section (T1) and the concentration of a diatomic gas, O2, in argon on the P5 pressure trace is discussed. The experimental results show a negligible dependence between the rise in P5 pressure and both the initial temperature T1 (40-80 degrees C) and significant concentrations of O2, up to 25%. To account for facility-related non-ideal effects in chemical kinetic models, two methods found in the literature were analyzed, as well as the commonly used assumptions of constant volume or constant internal energy. Updated approaches are proposed to improve the prediction of both the ignition delay times and the evolution of pressure during fuel combustion by using pressure traces of argon as the test gas. The updated methods yielded promising results regardless of the fuel/O2/Ar mixtures for temperatures ranging from 825 to 1,700 K at 20 bar in a 50 mm internal diameter shock tube, especially below 1,200 K.
As a major type of agricultural waste, bagasse is rich in volatile matter and low in ash, making it an ideal raw material for thermochemical conversion to hydrogen-rich gas. In this study, an ex-situ microwave-assisted catalytic pyrolysis technique was used. CaO and Na2CO3 and their mixed catalysts in different ratios were selected for the experiments at 550 degrees C. The aim is to optimize both the hydrogen yield and concentration of the components to produce high-quality fuel. Thermogravimetric analysis (TG/DTG) revealed the influence of the catalysts: Na2CO3 significantly promotes low-temperature deoxygenation, and CaO can effectively adsorb CO2. Molecular dynamics simulations showed that elevated temperatures promote carbon chain breakage, but too high a temperature (2,500 K) may lead to a carbonization cascade reaction, which inhibits bond breakage. The gas-phase products indicate that the mixed catalyst is most effective at a ratio of CaO : Na2CO3 of 1:3, achieving the highest H2 yield (maximum 17.26%) along with significant hydrocarbon generation inhibition (24.90%), and CO content reduction (23.45%). Catalyst characterization confirmed the presence of CaCO3 in the mixed catalysts after pyrolysis. The CaO: Na2CO3 = 1:3 catalyst was found to have a unique fibrous structure and a microporous network. Raman spectroscopy reveals the ordering of the carbon structure and differences in functional groups under the action of different catalysts. This study provides a theoretical basis for further optimizing the pyrolysis process of bagasse, and helps improve the conversion efficiency of biomass energy.
Despite their importance in the chemistry of aromatic compounds and as platform molecules from lignin decomposition, cresol isomers (ortho, meta, and para) are currently only considered as a single lumped species in detailed kinetic models. Furthermore, there are no experimental results available on the combustion of cresol isomers due to their extremely low volatility. This paper presents a recently developed detailed kinetic mechanism for the combustion of cresol isomers, driven by theoretically calculated rate constants for H-abstractions from the three isomers and for the decomposition of the addition products of the resulting radicals with O2. It also presents the first-ever quantification of species during the oxidation of the cresol isomers in a jet-stirred reactor, as well as the first measurements of the laminar burning velocity of cresol isomers using a flat flame burner, with a different behavior for p-cresol compared to the other two. The new detailed kinetic model produces accurate predictions of mole fractions of fuel, CO, CO2, ethylene, and more deviations for heavier products. Experimental data showed similar reactivity but significant differences in the nature and distribution of products depending on the position of hydroxy and methyl groups. Satisfactory burning velocity predictions were obtained for o-cresol and fair ones for m-cresol in lean mixtures. However, the large deviations observed for p-cresol suggest the need for further model improvement. Flow rate analyses revealed significant differences in the primary fuel consumption steps between the three isomers, explaining the observed differences in the products.
Unsym-dimethylhydrazine (UDMH) is an important nitrogen-containing liquid propellant fuel commonly combined with nitrogen tetroxide (NTO) in hypergolic systems. In this work, theoretical calculations were performed on the decomposition reactions of critical UDMH radical, HNN(CH3)2 to get insight into its combustion chemical kinetics. Specifically, reactions of its isomerization,beta-scission, and H-abstraction reactions attacked by NO2 and NO, as well as the subsequent decomposition reactions of formed NN(CH3)2 were investigated. Potential energy surfaces (PESs) for these reactions were obtained by employing the CCSD(T)/CBS(D+T)//M06-2X/def2-TZVP method. The RRKM/Master Equation approach was used to calculate the temperature-and pressure-dependent rate constants. Comparisons with monomethylhydrazine (MMH) radicals were made to elucidate the effect of CH3-group substitution on the kinetic characteristics of UDMH-radical decomposition. For isomerization and beta-scission reactions of HNN(CH3)2, it undergoes beta-N-C scission reaction more readily than H-migration isomerization to H2NN(CH3)CH2. Additionally, the rate constants for beta-scission reactions of UDMH radicals are close to those of MMH radicals. For the H-abstraction reactions of HNN(CH3)2 by NO2, the reaction forming NN(CH3)2 and cis-HONO from the decomposition of cis-ONON(H)N(CH3)2 has the highest rate constants, which differ significantly from the H-abstraction of MMH radical (HNN[H]CH3). HNN(CH3)2 primarily undergoes H-abstraction at the terminal nitrogen site, forming NN(CH3)2, whereas HNN(H)CH3 prefers H-abstraction from the central nitrogen atom. The H-abstraction reaction of HNN(CH3)2 by NO also easily produces NN(CH3)2. Subsequently, NN(CH3)2 dissociates via a low-barrier pathway to produce N2 and C2H6. The calculated rate constants provide important parameters for the kinetic modeling development of UDMH/NTO combustion.
