ReaxFF MD Simulations Research Articles

Enhancing burning rate of ammonium nitrate by ammonia borane: Mechanism from reactive molecular dynamics simulation.

The development of ammonium nitrate (AN)/ammonia borane (AB) as a green propellant is crucial for their applicability in different engines. This study investigates the release patterns of small products, particularly nitrogen-containing molecules, during the initial pyrolysis of AN/AB at low and high pressures using ReaxFF MD simulations. Compared with pure AN, the addition of AB gives the hybrid system enhanced reactivity, leading to faster decomposition and higher energy release. The results show that the consumption of AN in the S13 system (AB with a mass ratio of 12.6 %) is accelerated at 1.47 MPa. NO2 and NO are produced through HNO3 and NO3. At 6.89 MPa, AN exhibits the fastest decomposition rate in the S15 system. The high pressure enhances more reactions of NO with free radicals such as NH and accelerates the release of N2. As the percentage content of AB increases to 15.3%, more H2O while more NO2 is generated. The effect of AB on the generation of radicals such as H2 and H, is analyzed. AB not only promotes the initial pyrolysis of AN but also accelerates the conversion of intermediates.

Insight into the mechanism of H2O promoted CaCO3 decomposition in CO2 atmosphere

Calcium looping is one of the most promising CO2 capture technology. The flus gas during the calcination stage of the calcium looping contains both CO2 and H2O. However, the effect of H2O on the decomposition of carbonation in the CO2 atmosphere remains inconclusive. This study employed the Reactive Force Field molecular dynamics (ReaxFF-MD) simulations to investigate the influence of H2O on the decomposition of calcium carbonate in a CO2 atmosphere. The TGA experiments demonstrated that H2O increases the decomposition rate of calcium carbonate and also reduces the reaction temperature. Subsequently, the effects of varying CO2 and H2O concentrations on the decomposition of calcium carbonate were examined using ReaxFF-MD simulations. The simulation results for calcium carbonate decomposition, with the addition of CO2 and H2O, aligned with the experimental trends, verifying the reliability of the models. By tracking and labeling carbon, oxygen and hydrogen atom sources in the simulation, the decomposition, carbonation and hydrolysis reaction network for the CaCO3 decomposition in CO2 atmosphere was systematically constructed. Analysis of the chemical reactions and atomic distribution indicated that H2O primarily facilitates calcium carbonate decomposition by generating HCO3− through surface hydrolysis, which reduces the activation energy of the reaction. Moreover, the hydroxyl groups formed by hydrolysis compete with atmospheric CO2 for active sites on CaO, further inhibiting the carbonation reaction and increasing the calcination rate.

Analysis of the nanostructure evolution of soot in n-heptane/iso-octane with 2,5-dimethylfuran addition: A combined experimental study and ReaxFF MD simulations

The soot formation of n-heptane/iso-octane doped 2,5-dimethylfuran (DMF) with different ratios was experimentally investigated through laminar diffusion flame and numerically simulated by using the pyrolysis simulations method of reactive force field molecular dynamics (ReaxFF MD). The results showed that the laminar diffusion flame height of n-heptane/iso-octane increased with increasing DMF doping ratio. At a consistent sampling height, the primary soot particle sampling numbers collected were first decreasing and then increasing, and the size of the primary soot particle was first increasing and then decreasing accompanied by the DMF doping ratio increasing. Furthermore, the transmission electron microscope (TEM) analysis provided that DMF initially inhibited and subsequently promoted the primary soot particle growth in the n-heptane/iso-octane flame. The core-shell ratio increased and then decreased with the increase of the DMF doping ratio, which indicated that the maturity of soot decreased and then increased. In n-heptane/iso-octane doped with DMF ReaxFF MD pyrolysis simulation, it was divided into three stages 0–0.5 ns (the first stage), 0.5–3 ns (the second stage), and 3–4.5 ns (the third stage). Fuel decomposed in the first stage and reacted violently in the second stage. The soot precursors continued to react, molecule size kept to increase, and the polycyclic aromatic hydrocarbons (PAHs) continued to grow. In the third stage, the carbon number of the largest molecules were slowly increasing, and the development of soot entered mature stage, where the H/C ratio was slowly decreasing. Through ReaxFF MD simulations, it was found that the maturity of soot exhibited decreasing and then increasing trend with the increase of DMF doping ratio. The graphene-like structures were mainly concentrated around the H/C ratio of 0.297 region.

Mechanistic insights into the pyrolysis of pine resin sludge based on experiments and ReaxFF-MD simulation: High-value bio-oil production, nitrogen conversion, kinetics and environmental risk assessment

Forestry and agro-industrial waste conversion into high-value chemicals and fuels is considered one of the hottest ongoing research and industrial topics toward sustainable development. As one of the forestry and agro-industrial waste, pine resin sludge (PRS) with amino acids, pine resin residues and their derivatives such as abietic acid and 4-Epidehydroabietal, have ecological toxicity and require environmentally friendly treatment. Herein, a thermal process of PRS that generates high-value biofuels while reducing environmental pollution was reported. The results of the experiment and simulation reveal that the N of bio-oil is the major evolution direction of N, and the nitrogenous gas product is mainly NH3, a useful synthesis gas. ReaxFF-MD simulations elucidated the migration and conversion mechanism of nitrogen in amino acids. The main products of amino acid pyrolysis are 3-oxo-2-Propenenitrile, 2,4-Cyclopentadien-1-ylidenemethanone and 4R)-4-amino-5,5-dihydroxypentanoic acid. PRS's thermal weightlessness was divided into three phases, and the average activation under non-isothermal conditions was calculated at 78.17, 85.68, 206.42 kJ/mol (thermal decomposition) and final 117.78, 149.31, 195.54 kJ/mol (thermal oxidation). Thermal decomposition and oxidation process followed Avrami-Erofeev model (n=2), three-dimensional diffusion model (n=3) and mampel power (n=1). PY-GC/MS analysis shows that pyrolysis at different temperatures recovered mainly 4-Epidehydroabietal (37.15–89.67 %) for potential use as the biosynthesis of dehydrofolate. The bio-oil from PRS pyrolysis shows an excellent yield (31.43 %) and a high calorific value (37.21 MJ/kg), which is comparable to biodiesel. This work focused on offering an appealing and instructive guide for the logical treatment of sludge from pine resin production.

Insights into the dynamics of supported Au nanoparticles in the wet environments from first-principles and ReaxFF MD simulations

The interactions between metal and oxide supports have been widely studied, where the size effect of metal nanoparticles (NPs) and the gas environment play critical roles in catalytic performance. We employed density functional theory and ReaxFF reactive force field to investigate the size dependent properties of gold NPs supported on cerium dioxide, such as structural dynamics, adsorption, and electronic properties under wet environments. Distinct dynamic behaviors were observed in wet environments compared to vacuum conditions. In the wet environments, the hydroxide (OH) species preferentially adsorbs on the low coordination sites, such as edge sites, of NPs. This selective absorption induces a reconstruction effect on small NPs. Moderate-sized NPs exhibit significant surface reconstruction due to abundant OH adsorption at interface sites. However, this effect is negligible in larger NPs. A high interfacial population of OH significantly contributes the high catalytic performance of moderate-sized NPs. Moreover, OH adsorption modulates the charge distribution within the NPs, leading to their stabilization through OH-induced charge transfer. These findings provide insights into understanding and optimizing reactions in wet environments, offering a foundation for the development of more effective catalyst.

Atomic effect and mechanism of different hydrogen content on superlubricity properties of H-DLC films

Hydrogen atoms play a pivotal role in achieving superlubricity in DLC films. Nevertheless, the inherent limitations in analytical testing techniques obscure the mechanisms by which hydrogen atoms achieve superlubricity in DLC films. Furthermore, direct evidence supporting the widely accepted mechanism of hydrogen passivation remains elusive. Therefore, we used ReaxFF MD simulations to investigate the effects of different hydrogen content on the tribological and wear properties of hydrogen-doped H-DLC films. Hydrogen atoms diffuse from the DLC films and gradually accumulate on the friction surface during the sliding, effectively passivating and inhibiting the C–C bonds at the interface. This reduces cross-linking between H-DLC films, consequently loweringfrictiontemperature significantly during the sliding. A significant release of hydrogen atoms during the friction process weakens the strength of machinery of H-DLC films, potentially causing structural failures under hydrogen-rich conditions, with the released hydrogen atoms subsequently occupying structural voids within films. At the microscopic scale, the friction of H-DLC film decreases with the increase of hydrogen content, but when the hydrogen content reaches 40 % or above, the local collapse of the system will be caused, resulting in the failure of superlubricity. Finally, the friction and wear of H-DLC film under high hydrogen conditions will rebound.

Micropore effects on coal pyrolysis process investigated by using reactive molecular dynamics

The micropore structure can serve as the diffusion channels for intermediates and light tar products during coal pyrolysis, which is very important for modulating the desired tar or char products. In this work, the micropore effects on product distribution and the reaction mechanisms during Hailaer coal pyrolysis was explored for the first time from the atomistic simulation point of view by using large-scale ReaxFF MD simulation and the reasonable model with the artificially adding micropore strategy. The results suggest that the micropore structure indeed has a significant impact on the major tar product distribution and competitive reactions during coal pyrolysis process at high temperature. The micropore can promote decomposition reactions through accelerating C–C bond breaking significantly and inhibit the recombination reactions accompanied with the char formation with more carbon in sp2 structure. Based on the oxygen-containing bond behaviors in char products obtained from coal pyrolysis process, it is unraveled that the more micropore exits in coal structure, the more Csp3-O bonds and less Csp2-O bonds in char precursors. Particularly, the light tar products with ring groups are more influenced by micorpore structures than those chain products. Considering that the limitation of current experimental techniques in micropore detection, the strategy sheds new light on the depth investigation of micropore effects on reactions, which can provide complement for experimental observations and tar product modulation.

Room-temperature solution processed silicon nanocluster: Theory prediction and experiment achievement

We have presented in this work that silicon nanoclusters (Si NCs) embedded in silicon nitride (▪) can be synthesized by vacuum ultra-violet irradiation of perhydropolysilazane (PHPS) at room temperature. The formation of Si NCs is first predicted by reactive molecular dynamics (ReaxFF-MD) simulations based on a self-developed Si/N/H force field. Then the existence of Si NCs is further verified by photoluminescence (PL) spectroscopy and Raman spectroscopy characterization. Additionally, the photochemical conversion mechanism of PHPS is examined. Moreover, it has been found based on Fourier transform infrared (FT-IR) measurements that ▪ samples prepared with an intermediate irradiation time are the most readily to be oxidized, which can be attributed to the high concentration of the active group -▪, being consistent with the reaction mechanism. We have demonstrated that ReaxFF-MD simulation can be a powerful complement to experimental investigations in revealing the conversion mechanism of polymer precursor to ceramics at the atomic level.

Insights into hydro thermal gasification process of microplastic polyethylene via reactive molecular dynamics simulations

Microplastics have become a pressing environmental issue due to their widespread presence in our ecosystems. Among various plastic components, polyethylene (PE) is a prevalent and persistent contaminant. Hydrothermal gasification (HTG), a promising technology for converting PE into syngas, holds great promise for mitigating the microplastic problem. In this study, we employ ReaxFF molecular dynamics simulations to investigate the HTG process of PE, shedding light on the intricate relationships between temperature, water content, carbon conversion efficiency, and product distributions. The results reveal that hydrothermal gasification of PE is a complex process involving multiple reaction pathways. Consistently with experimental findings, the calculations indicate that the gas phase exhibits a substantial hydrogen fraction, reaching up to 70%. Interestingly, our simulations reveal a dual role of water content in the HTG process. On one hand, water enhances hydrogen production by promoting the gas formation. On the other hand, it elevates the activation energy required for PE decomposition. Depending on the water content, the calculated activation energies range from 176 to 268 kJ/mol, which are significantly lower than those reported for thermal gasification (TG). This suggests that HTG may be a more efficient route for PE conversion. Furthermore, this study highlights the importance of optimizing both temperature and water content in HTG systems to achieve high yields of hydrogen-rich syngas. The results obtained from our ReaxFF MD simulations demonstrate the robustness of this computational methodology in elucidating complex chemical reactions under extreme conditions. Our findings offer critical insights into the design of advanced waste management strategies for microplastics and contribute to the development of sustainable practices for resource recovery. This work underscores the potential of HTG as a key technology for addressing the global challenge of plastic pollution.

Rational utilization of the size and electronic effect of inhibitors enabling high polishing rate with minimum corrosion in copper chemical mechanical polishing

Chemical mechanical polishing (CMP) relies on corrosion to remove excess materials, while also on corrosion inhibitors to ensure post-polished surface quality. The robust adsorption of inhibitors onto metal surfaces typically improves inhibition effectiveness but significantly reduces the polishing rate. In this study, we propose and validate a novel strategy that focuses on the utilization of large-sized physisorption-type inhibitors to address this inherent conflict. By incorporating disproportionated rosin (DR) as the inhibitor, the developed slurry facilely obtained a balance between polishing efficiency and quality for copper CMP. The inhibition mechanism of DR was elucidated through electrochemical characterization, adsorption isotherms, and reactive forcefield molecular dynamics (ReaxFF MD) simulations. The weak physisorption of the inhibitors facilitated their easy removal, resulting in minimal impact on the polishing rate. Additionally, the large-size structure of DR effectively hindered corrosive substances from reaching concave areas not under external force, thereby demonstrating superior inhibition efficacy. The adsorption mode of DR on copper was simultaneously determined through adsorption isotherms and ReaxFF MD simulations, marking the first instance of linking classic adsorption theory with MD simulations. The advantage of the ReaxFF MD simulations over classic MD simulations and density-functional-theory calculations for the metal-inhibitor adsorption systems was also discussed and demonstrated.

A comprehensive experimental and theoretical study of thermal response mechanisms of TKX-50 and HMX

TKX-50 and HMX, as two highly promising energetic materials, are widely used in rocket propellants. TKX-50/HMX cocrystal can also improve the defects of TKX-50 and HMX and vastly expand their application scope. Their response mechanisms to the same thermal stimulation, including reactivity and decomposition and combustion behavior, are important in understanding their combustion characteristics and engine performance. This study systematically investigates the thermal response mechanisms of TKX-50 and HMX under the same thermal stimulations based on experimental measurements and theoretical analysis. Ignition delay times and burn times of TKX-50 and HMX with different particle sizes at various temperatures and pressures are measured in shock tube experiments. ReaxFF MD simulations are performed to analyze the thermal decomposition of TKX-50 and HMX in terms of potential energy evolution, intermediate and final products, and possible reaction pathways. Ab initio kinetics of hydrogen atom abstraction reactions of TKX-50 and HMX with three highly active species, Ḣ, ȮH, and NO2, are studied. The barrier heights, reaction enthalpies and rate coefficients for all reactions are further analyzed. The results show that: (1) the ignition delay time and burn time of TKX-50 (128, 138, and 55 µm) are measured to be 200–600 µs and 40–400 µs respectively, which are almost the same as those of HMX (6 and 0.8 µm) in the same temperature range; (2) the burn time of TKX-50 is less affected by pressure but more affected by particle size, whereas both pressure and particle size have a significant effect on the burn time of HMX; (3) TKX-50 is shown to be readily decomposed and less affected by temperature changes than HMX under the same conditions; (4) ȮH is generated more rapidly in the TKX-50 system, but more persistently in the HMX system; (5) H atom abstraction reactions from TKX-50 by all species are less endothermic but more exothermic than those from HMX.

Impact of mixing low-reactivity gases on the mechanism of hydrogen spontaneous combustion: A ReaxFF MD study

The phenomenon of spontaneous combustion during the release of high-pressure H2 is critical to the safe storage and transportation. Besides physical methods to suppress self-ignition, the approach of mixing low-reactivity gases has gained increasing attention. Previous work has mainly focused on the flow, physical heating effects, and boundary conditions of self-ignition in mixed gases, while the intrinsic chemical reaction mechanisms of spontaneous combustion remain underexplored. To clear this issue, this work uses the ReaxFF MD simulation method to study the spontaneous combustion process of H2/CO and H2/CH4 mixtures with various concentrations. The results indicate that: (1) in pure H2, H2/CO, and H2/CH4 systems, the primary initial reaction mechanism is H2+O2HO2+H. Additionally, in some mixed systems, CO + O2CO2+O and CH4+O2CH3+HO2 may also serve as initial reaction mechanisms. (2) Under fuel-lean combustion conditions, the RIDTs of the systems decrease, supporting the viewpoint that self-ignition typically occurs first in fuel-lean regions. The addition of CO and CH4 increases the RIDTs, which helps inhibit the development of self-ignition. (3) In H2-rich environments, CO combusts to CO2 through the formation of HOCO, while CH4 undergoes dehydrogenation and oxidation processes through intermediates such as CH3, CH3O, and HCHO, leading to the formation of CO and CO2. The combustion of H2 is also influenced by these processes. (4) The addition of CO and CH4 increases the activation energy of H2 combustion, raising the reaction energy barrier that must be overcome for spontaneous combustion. This effectively helps to suppress the occurrence and development of self-ignition during the release of high-pressure gases.

Atomic oxygen erosion mechanism of polyimide via reactive molecular dynamics simulation and density functional theory calculation

Atomic oxygen (AO) causes serious oxidative degradation on polymeric materials in the space environment, yet understanding its reaction mechanism is a challenging task. Herein, we primarily investigate the reaction sites and reaction paths of pure polyimide material to AO erosion and propose a modification strategy involving electron-withdrawing groups to enhance the material's resistance to AO with density functional theory (DFT) and reactive force field molecular dynamics (ReaxFF MD). DFT calculations reveal that AO erosion is an electrophilic reaction, which preferentially interacts on the benzene ring with pronounced electron density distribution on the third part of the polyimide molecule. ReaxFF MD simulations validate this finding and provide additional reaction pathways that are divided into the early-stage reactions and later secondary reactions. In the early stage, only small number of AOs take part in the reactions that include the formation of CO bonds and ring opening processes. These reactions are relatively slow and majorly determine the AO resistance of the material. In the subsequent stage, AO predominantly reacts with reactive species and radicals generated from earlier reactions, leading to fast degradation. With these findings, we propose a strategy to enhance the AO resistance by introducing electron-withdrawing functional groups in the polyimides. As exemplified, the polyimide with -CF3 group shows 21.1% lower erosion yield than unmodified polymer. The present study gives a deep insight for the mechanism of AO erosion on polyimide by exploring its reaction sites and provides valuable theoretical guidance for improving the material's resistance to erosion.

Reaction Dynamics of CO2 Hydrogenation on Iron Catalysts Using ReaxFF Molecular Dynamics Simulation.

The conversion of CO2 to hydrocarbons using catalysts is a promising route to utilize CO2 and produce more valuable chemicals in a sustainable manner. Recent studies have shown that iron-based catalysts perform well for the hydrogenation of CO2. While the hydrogenation reaction mechanism in the gas phase is straightforward, when catalyzed by iron it has been demonstrated to involve various chemical transformations, and the selectivity and conversion are strongly dependent on the particle size. To further investigate the dependence of the reactivity of iron catalysts on cluster size, we performed reactive molecular dynamics simulations using the ReaxFF force field (ReaxFF-MD) for iron nanoclusters of various sizes in a CO2 and H2-rich environment. We demonstrated that the homogeneous hydrogenation of CO2 was correctly described by this ReaxFF model. The dissociation mechanism of CO2 on the Fe4, Fe16 clusters, and the bcc(100) Fe slab agrees with previous DFT results. The ReaxFF-MD simulations suggest a strong dependence of reactivity on the cluster size, with the Fe4 cluster having the highest reactivity. We show that ReaxFF-MD provides a route to understand reaction mechanisms in these nonequilibrium reactive processes where fast processes and local minima are important.

Anisotropic Effects in Local Anodic Oxidation Nanolithography on Silicon Surfaces: Insights from ReaxFF Molecular Dynamics.

Fully understanding the anisotropic effect of silicon surface orientations in local anodic oxidation (LAO) nanolithography processes is critical to the precise control of oxide quality and rate. This study used ReaxFF MD simulations to reveal the surface anisotropic effects in the LAO through the analysis of adsorbed species, atomic charge, and oxide growth. Our results show that the LAO behaves differently on silicon (100), (110), and (111) surfaces. Specifically, the application of an electric field significantly increases the quantity of surface-adsorbed -OH2 while reducing -OH on the (111) surface, and results in a higher charge on a greater number of Si atoms on the (100) surface. Moreover, the quantity of surface-adsorbed -OH plays a pivotal role in influencing the oxidation rate, as it directly correlates with an increased formation rate of Si-O-Si bonds. During bias-induced oxidation, the (111) surface appears with a high initial oxidation rate among three surfaces, while the (110) surface underwent increased oxidation at higher electric field strengths. This conclusion is based on the analysis of the evolution of Si-O-Si bond number, surface elevation, and oxide thickness. Our findings align well with prior theoretical and experimental studies, providing deeper insights and clear guidance for the fabrication of high-performance nanoinsulator gates using LAO nanolithography.

Experimental and simulation study on the thermal decomposition of Xishan coal and the pyrolysis of coal with Na2SO4

ABSTRACT Based on the Thermal Decomposition of Xishan coal Experiments and ReaxFF MD Simulations, the study investigated the processes and product changes in the thermal decomposition of coal and the pyrolysis of coal with Na2SO4. The results indicate that the initial temperature of thermal decomposition of Xishan coal is around 300 °C in experiments and approximately 1600 K in molecular simulations. The addition of Na2SO4 advances the initial pyrolysis temperature and promotes the generation of total number and types of products. Xishan coal pyrolysis generates a large number of small molecular gases and free radicals, and the addition of Na2SO4 promotes the generation of CO, CH4, and H2S, as well as the accumulation of a significant number of free radicals. Free Na mainly affects the evolution of N elements, promoting the formation of N into amino groups, and Na easily combines with sulfur-containing intermediates. Through the extraction of sulfur-containing intermediates and the analysis of the influence of free radicals, it was found that S elements Xishan coal ultimately forms H2S. This study microscopically confirms that in the coal with Na2SO4 system, H2S originates from the hybridised sulfur atoms in the carbon chain and free SO 4 2 − .

Automated Skeleton Network Generation for ReaxFF Molecular Dynamics Simulations of Hydrocarbon Fuel Pyrolysis and Oxidation via a Rate-Based Algorithm.

In this study, we present an automated approach of rate-based skeleton network generation for ReaxFF MD simulation (RxMD-SN) for deriving the reaction kinetic mechanism of large hydrocarbon fuels in pyrolysis and oxidation from large-scale ReaxFF MD simulations. The approach contains the statistical calculation of reaction rate constants and the generation of skeleton reaction networks using a rate-based algorithm. The RxMD-SN method takes advantage of reaction flux ranking at a small time interval in terms of temporal reaction rate to extract the core reaction networks, which allows for keeping the rare reaction events that may be dominant in a certain period of the reaction network. The kinetic models derived from ReaxFF MD simulation in CH4 oxidation can reproduce what was obtained in the ReaxFF MD simulation, which demonstrates the capability of RxMD-SN in capturing the global reaction kinetics. An evaluation of reaction rate constants indicates that close kinetic parameters are shared for n-octane oxidation of similar reaction classes, shared oxidation reactions of CH4 against n-heptane, and shared pyrolysis reactions of the RP-3 surrogate fuel against n-heptane. This capability of RxMD-SN is particularly beneficial in meeting the challenges in characterizing the oxidation reaction kinetics of large hydrocarbon molecules. RxMD-SN approach is potentially a general approach in chemical kinetics modeling on the basis of ReaxFF MD simulations.

Revealing the mechanism of hydration on the CO2 kinetic adsorption of CaO surface via ReaxFF MD simulations with experiments

Hydration has been regarded as an effective method to improve the cyclic activity of CaO during the Calcium looping CO2 capture process, but its mechanism remains unclear. In this work, the hydration reaction of CaO surface and its underlying mechanism was studied by ReaxFF molecular dynamics simulation combing with TGA experiments. The effect of hydration on the initial CO2 adsorption rate showed a trend of promoting at low H2O degree and inhibiting at high H2O concentration. The CaO surface was easily passivated, and it can maintain its crystal structure and begin to distort at about 1.0 H2O monolayer contents. Hydration failed to promote the CO2 adsorption rate, inversely the CO2 adsorption process accelerated the diffusion of H ions inward the CaO lattice·H2O dissociation produced two hydroxyl groups: direct OwH and indirect OsH. Atomic density profiles showed that the direct hydroxyl pairs were always, and indirect OsH groups can consume surface oxygen active sites, reducing the initial rapid CO2 adsorption activity. On the pre-hydrated CaO surface, CO2 molecules were more likely to bind to solid oxygen active sites than OH groups. The H free radical diffused inside the lattice in the form of transition HO2 state, promoting the slow CO2 adsorption amount.

Evolution and generation mechanism of retained oil in lacustrine shales: A combined ReaxFF-MD and pyrolysis simulation perspective

To accurately investigate the evolution characteristics and generation mechanism of retained oil, the study analyzed organic-rich lacustrine shale samples from the Paleogene Kongdian Formation in Cangdong Sag, Bohai Bay Basin. This analysis involves Rock-Eval pyrolysis, pyrolysis simulation experiments, Gas Chromatograph Mass Spectrometer (GC–MS), and reactive molecular dynamics simulations (ReaxFF). The results revealed the retained oil primarily consisted of n-alkanes with carbon numbers ranging from C14 to C36. The generation of retained oil occurred through three stages. A slow growth stage of production rate was observed before reaching the peak of oil production in Stage I. Stage II involved a rapid increase in oil retention, with C12–C17 and C24–C32 serving as the primary components, increasing continuously during the pyrolysis process. The generation process involved the cleavage of weak bonds, including bridging bonds (hydroxyl, oxy, peroxy, imino, amino, and nitro), ether bonds, and acid amides in the first stage (Ro =0.50%–0.75%). The carbon chains in aromatic ring structures with heteroatomic functional groups breaks in the second stage (Ro =0.75%–1.20%). In the third stage (Ro =1.20%–2.50%), the ring structures underwent ring-opening reactions to synthesize iso-short-chain olefins and radicals, while further breakdown of aliphatic chains occurred. By coupling pyrolysis simulation experiments and molecular simulation technology, the evolution characteristics and bond breaking mechanism of retained oil in three stages were revealed, providing a reference for the formation and evolution mechanism of retained oil.

Sintering Mechanism of Fe2O3 Particles during Iron-Based Chemical Looping Combustion by Using ReaxFF MD Simulation and Experiments

Sintering Mechanism of Fe₂O₃ Particles during Iron-Based Chemical Looping Combustion by Using ReaxFF MD Simulation and Experiments