ReaxFF MD Simulations Research Articles

Factors governing wear of soda lime silicate glass: Insights from comparison between nano- and macro-scale wear

Previous studies demonstrated the macroscale wear behavior of soda lime silicate (SLS) glass in humid air was governed by the mechanochemical reactivity of sliding interfaces, which is a function of relative humidity (RH). In this study, it was observed that no disenible nanowear of SLS glass surface in dry conditions because the contact is elastic. In humid conditions, nanowear occurred due to water-induced mechanochemical reactions and the RH dependence above 20% was relatively weak. Nanowear of SLS glass decreased at the sodium ions enriched region, which was revealed with ReaxFF-MD simulations. Further analyses revealed that the wear behavior of SLS glass surface depends on both the mechanochemical reactions occurring at the sliding interface and the transport of the mechanochemical reaction products.

Reactive molecular dynamics simulations on thermal decomposition of 3-methyl-2,6-dinitrophenol.

In this paper, we simulated the decomposition mechanism of 3-methyl-2,6-dinitrophenol (MDNP) based on reaction molecular dynamics using ReaxFF force field. In addition, the evolution of some main products over time at different heating rates (10, 15, and 20K·ps-1) was studied. As indicated by the simulation results, with the elevation at different heating rates, the time required for the system to reach equilibrium was shortened, and more products were obtained. At three heating rates, C7H7O5N2, C7H6O4N2, C7H5O5N2, C7H5O4N2, HON, NO, and NO2 were the main intermediate products, and N2, CO2, H2O, H2, and NH3 were the primary final products. To be specific, C7H5O5N2 was the first produced intermediate product, and H2O was the first produced final product with the largest abundance. The intermediate products first increased and then decreased to zero. Moreover, the primary chemistry reactions in the MDNP pyrolysis were simulated through ReaxFF MD simulations.

Exploration on the steam gasification mechanism of waste PE plastics based on ReaxFF-MD and DFT methods

Steam gasification of plastics is a promising way to deal with the increasing waste plastics as well as produce H2-rich syngas. In this paper, ReaxFF-MD simulation and DFT calculation methods were combined to study the reaction process of the PE steam gasification and the formation mechanisms of syngas especially hydrogen. According to the main reaction, the gasification process has two overlapping stages: PE thermal depolymerization followed by H2O reforming reaction. The depolymerization stage is mainly the terminally or intermediately breaking process of C–C bond, during which different R· radicals and ·R· double radicals fragments continuously dissociated into smaller hydrocarbons until C1-C4. The free H· radicals released through dehydrogenation and H-transfer reaction in depolymerized stage can highly reduce the energy barrier of subsequent H2O reforming reaction. The production of H2 mainly comes from the reforming reaction of H2O with free H· radicals and the accompanying ·OH radical actively participates in the formation process of CO. Besides, the effects of temperature and water content on product distributions are analyzed. Increasing temperature and water content can promote the steam reforming consumption of hydrocarbons and thus a rise in H2 and CO yields, but the improvement effects gradually decrease. The revelation of radical transformation and integration in this article can be a guide in later reaction adjustment as well as catalyst selection.

Study on the atomic scale of thermal and thermo-oxidative degradation of polylactic acid via reactive molecular dynamics simulation

The reactive force field molecular dynamics (ReaxFF-MD) simulations were performed on polylactic acid (PLA) for the first time to understand its thermal and thermo-oxidative degradation mechanisms. The main degradation products of PLA observed in actual experiments were well reproduced by ReaxFF-MD simulations. The results showed that the initial thermal degradation pathway for the PLA was the homolytic cleavage of CO bond next to the ester group, followed by CO bond breaking in the ester group and CC bond cleavage. Carbon monoxide, carbon dioxide and acetaldehyde were the major volatile products generated following the thermal degradation after being initiated by the homolytic scission. In thermo-oxidative degradation simulation, the alkyl peroxide and hydroperoxide were formed, which degraded into alkoxyl and hydroxyl radicals, resulting in the increase of the lower carbon fraction (C1–4). This study would provide meaningful theoretical guidance for the mechanisms of thermal and thermo-oxidative degradation of PLA.

Insight into Pyrolysis Behavior of Silicone-Phenolic Hybrid Aerogel Through Thermal Kinetic Analysis and Reaxff Md Simulations

Insight into Pyrolysis Behavior of Silicone-Phenolic Hybrid Aerogel Through Thermal Kinetic Analysis and Reaxff Md Simulations

Thermal Decomposition Mechanisms of Insensitive High Energy qy-HMX Using ReaxFF MD Simulation Supported with TG-DSC and Pyro-GC/MS Experiments

Thermal Decomposition Mechanisms of Insensitive High Energy qy-HMX Using ReaxFF MD Simulation Supported with TG-DSC and Pyro-GC/MS Experiments

Combined ReaxFF and Ab Initio MD Simulations of Brown Coal Oxidation and Coal-Water Interactions.

In this manuscript, we use a combination of Car–Parrinello molecular dynamics (CPMD) and ReaxFF reactive molecular dynamics (ReaxFF-MD) simulations to study the brown coal–water interactions and coal oxidation. Our Car–Parrinello molecular dynamics simulation results reveal that hydrogen bonds dominate the water adsorption process, and oxygen-containing functional groups such as carboxyl play an important role in the interaction between brown coal and water. The discrepancy in hydrogen bonds formation between our simulation results by ab initio molecular dynamics (CPMD) and that by ReaxFF-MD indicates that the ReaxFF force field is not capable of accurately describing the diffusive behaviors of water on lignite at low temperatures. The oxidations of brown coal for both fuel rich and fuel lean conditions at various temperatures were investigated using ReaxFF-MD simulations through which the generation rates of major products were obtained. In addition, it was observed that the density decrease significantly enhances the generation of gaseous products due to the entropy gain by reducing system density. Although the ReaxFF-MD simulation of complete coal combustion process is limited to high temperatures, the combined CPMD and ReaxFF-MD simulations allow us to examine the correlation between water adsorption on brown coal and the initial stage of coal oxidation.

Chemical interplay between components in overall thermolysis of CL-20/N2O revealed by ReaxFF molecular dynamics simulations

Understanding of the interplay reactions between components in CL-20 bicomponent crystals is fundamental for synthesis and applications of new CL-20 cocrystals and host-guest materials. This paper reports the thermal decomposition of CL-20/N2O host-guest crystal investigated using ReaxFF MD simulations under both isothermal and adiabatic conditions. The isothermal thermolysis simulation at low temperature of 800 ​K and adiabatic decomposition simulation initiated at 800 ​K were performed to reveal as much as the real and overall scenario of CL-20/N2O thermolysis. Two reference systems of ε-CL-20 and CL-20/H2O were employed for clear depiction of reaction mechanism. Permitted by VARxMD for reaction details and facilitated by the three-stage classification, the overall scenario of CL-20/N2O thermolysis and deep insight about the interplay reaction details between host CL-20 and guest N2O were obtained. The dominating of host CL-20 decomposition during entire thermolysis of CL-20/N2O is similar with that of CL-20/HMX and CL-20/TNT. However, the branching ratios of major reaction pathways of CL-20 initial decomposition were altered. The decomposition kinetics in initial thermolysis of CL-20/N2O was found significantly slowed when compared with ε-CL-20, which is caused by the guest N2O molecules that capture the NO2 intermediates generated from host CL-20 decomposition and prevent NO2 from their active participation in further decomposition of the system. It should be noted that the early formation of N2 from guest N2O in CL-20/N2O decomposition accelerates self-heating at certain extent and provides extra oxidative NO3, which slightly compensates to the slowed kinetics in the initial stage. The acceleration effect of guest oxidant N2O on CL-20/N2O decomposition will sustain through the ​oxygen migration of guest N2O in later secondary reactions to form more NOx than that of CL-20/H2O, consequently reducing the reaction zone of CL-20/N2O thermolysis. What was obtained in this work demonstrates that ReaxFF MD simulations combined with the analysis scheme of three-stage classification can facilitate the depiction of thermolysis mechanism of CL-20 bicomponent crystals and be useful in searching for leading candidates of guest molecules for CL-20 host-guest materials.

Kinetic characteristics and reactive behaviors of HSW vitrinite coal pyrolysis: A comprehensive analysis based on TG-MS experiments, kinetics models and ReaxFF MD simulations

Currently it is highly desired to study coal pyrolysis based on weight loss behavior, mathematical model of pyrolysis kinetics and advanced multi-scale molecular simulations to realize clean utilization of coal. This work presents a comprehensive analysis of HSW vitrinite coal pyrolysis based on thermogravimetric mass spectrometry (TG-MS) experiments, kinetics models and reactive force field molecular dynamics (ReaxFF MD) simulations. The weight loss and gas release behavior of HSW vitrinite coal at different heating rates was investigated by TG-MS. The kinetic parameters of coal pyrolysis were analyzed by Coats-Redfern model and distributed activation energy model (DAEM). The pyrolysis reactive behaviors and thermal decomposition process of HSW vitrinite coal was observed and analysis with ReaxFF MD simulations at atomic scale. The results show that the weight loss rate of pyrolysis decreased with increased heating rate. The trend of higher heating rate delayed the release of pyrolysis gas was consistent with TG results. The pyrolysis activation energy increases from 12.30 to 25.83 kJ/mol with further pyrolysis stage by Coats-Redfern model, and from 59.85 to 328.24 kJ/mol with higher carbon conversion hate by DAEM model. The results of ReaxFF MD simulations give complex initial chemical process of coal pyrolysis process, which agrees with the actual and expected coal pyrolysis process. Also the secondary reaction of tar in later stage of pyrolysis is observed clearly via ReaxFF MD simulations.

A theoretical study of aluminium doping in silicon anode based lithium‐ion batteries using ReaxFF molecular dynamics simulation

Silicon and Aluminium are abundant elements in nature. Silicon materials have higher capacity that can be used as a replacement for the graphite anode. However, due to mechanical failure and self-degradation during battery operation, Si is not suitable to be used as an anode in LIBs. The cycle performance of LIBs depends on the diffusion of Li within anode material. The high energy barrier of the Si structure results in lesser kinetic transport of Li, hence Si anode is not feasible to be used in LIBs. In the past, many approaches were proposed to improve the rate performance of Si anode that includes doping, porosity, amorphicity, and geometry tailoring. In this paper, the ReaxFF interatomic potential and MD simulations were conducted to study the kinetic behavior of aluminium doped amorphous lithiated silicon (a-LixSiAly) compounds. The results suggest that by doping of aluminium, the coefficient of diffusion improves, although there is no relation found between the amount of dopant and diffusivity. We replaced dopant aluminium with alumina and studied the structural and kinetic behavior of silicon anode based lithium-ion batteries (LiSi). Our results show that the specific amount of alumina can improve diffusivity but is not as significant as in the case of aluminium. We used hybrid GCMC/MD simulations to compute the open-voltage profiles during the cell discharge operation. These simulation results provide an interesting relation between Li and Al content in the compound for voltage discharge profile. Doping of aluminium and its amphoteric oxide can increase the diffusion coefficient of Li in LiSi batteries. A specific amount of doping improves the battery discharge voltage profile. To the best of the authors understanding, not much research has been carried out on this idea. The present research results suggest the improved capacity and cycle performance of batteries. The voltage profile diagrams suggest an exponential relation between aluminium and lithium content while doping, and this can be used in the industrial manufacture of LiSi batteries. The Al2O3 doping results in a parabolic curve, which clarifies the specific amount of dopant that can lead to the highest performance.

A comprehensive understanding of the synergistic effect during co-pyrolysis of polyvinyl chloride (PVC) and coal

In this work, the co-pyrolysis behaviors of polyvinyl chloride (PVC) with coal were investigated using the reactive molecular dynamics (ReaxFF MD) simulations. The weight loss characteristics of PVC and coal pyrolysis obtained from ReaxFF MD simulations were in good agreement with the thermo-gravimetric (TG) experimental results. The synergistic effect on the production of inorganic gas, organic gas, and tar were investigated via co-pyrolysis simulations. The results showed that coal promoted HCl release by providing extra H for Cl radicals. It led to more H being retained in the de-HCl PVC, resulting in an increase of C2H4 yield and a decrease of C2H2 yield. PVC promoted the generation of CO2, CO and CH2O, while inhibited the generation of H2O. PVC had little effect on coal pyrolysis tar yield because little H radicals were generated from PVC pyrolysis. However, large amount of H and OH radicals were generated from coal pyrolysis, leading to a promoting effect on the decomposition of PVC and the secondary reactions of PVC pyrolysis tars. Kinetic results suggested that the synergistic effect reduced the activation energy by 13% at low temperature stage, while reduced the activation energy by 36% at high temperature stage during PVC/coal co-pyrolysis.

Molecular insights into the role of char-bound hydrogen in char-NO reactions under high pressures: A reactive molecular dynamics simulation study

In the present work, the role of char-bound hydrogen in char-NO reaction under pressurized oxy-fuel combustion (POFC) conditions was studied using the reactive molecular dynamics (ReaxFF MD) simulations. The effects of char-bound hydrogen on the chemisorption of NO, formation of N2, kinetics of char-NO reaction, and structure of char at different pressures and temperatures were investigated. The results show that the char-bound hydrogen hindered the chemisorption of NO, and inhibited the generation of CN. The role of char-bound hydrogen in the chemisorption of NO weakened with the increase in pressure. Considerable amount of H2O was generated during the reaction of NO with H-containing char, which proves that char-bound hydrogen provided another channel for the conversion of NO to N2, especially at high pressures. The activation energies of the chemisorption of NO and the formation of N2 during the reaction of NO with H-containing char were determined to be 174 and 126 kJ/mol, respectively. The ReaxFF MD simulation results were in good agreement with previous experimental and DFT values. The char-bound hydrogen increased the activation energies of the chemisorption of NO and the formation of N2 by 40% and 29%, respectively. The role of char-bound hydrogen in char gasification and char structure were also examined. The char-bound hydrogen reduced the consumption of char, and CO was the main product from char gasification. The results of the O/C and N/C ratios of char indicate that char-bound hydrogen had little effect on the desorption of CO. By analyzing the dynamic evolution of char structure, it is found that char-bound hydrogen inhibited N-down chemisorption of NO.

Unraveling the surface behavior of amino acids on Cu wiring in chemical mechanical polishing of barrier layers: A combination of experiments and ReaxFF MD

Amino acids, as basic chemical additives, promote the development of novel chemical mechanical polishing (CMP) slurries and have been widely applied in microelectronic industries because of their high efficiency, nonpolluting nature and low cost. In this work, the surface action mechanisms of glycine, sarcosine, and L-glutamic acid on copper were studied by combining electrochemical measurements, morphological characterization, and ReaxFF MD simulations. The results show that these three amino acids can complex copper ions effectively and generate complexes, which can form a composite film with amino acid molecules and copper oxides to adsorb on the Cu surface to prevent the local attack of a corrosion medium on the copper. In particular, the processed slurry containing sarcosine has the best balance between the complexation ability and the corrosion inhibition effect, by which a better surface morphology of Cu can be obtained while complexing with Cu ions effectively. Additionally, ReaxFF MD simulations provide atomic insight into the removal of Cu atoms under the synergetic action of chemical and mechanical effects. The removal of Cu atoms by amino acids mainly occurs through the synergetic effects of Cu-N binding and mass transfer, while the corrosion inhibition efficiency mainly comes from the strong adsorption ability caused by the binding and intercalation of Cu-O bonds on the Cu substrate.

Influence mechanism of Nano-Fe2O3 on amorphous carbon graphitisation in molecular view via ReaxFF MD simulation

ABSTRACT Nano-Fe2O3/C composites are widely used in the electrochemical energy storage field. Preparing nano-Fe2O3/C composites via graphitising the amorphous carbon inserting nano-Fe2O3 particles is potential if the influence mechanism of nano-Fe2O3 on the graphitisation of amorphous carbon is explored in-depth. Here, an amorphous carbon model (a-C model) and a nano-Fe2O3-inserting model (C\\Fe2O3 model) were built via the liquid-quench method, and the reaction of Fe2O3 and C during graphitisation was explored via the reactive force field (ReaxFF) simulation. The results showed that nano-Fe2O3 could inhibit the graphitisation of amorphous carbon, and the mechanism was revealed. The Fe2O3 molecules collided with the aromatic carbon layer because of the thermal motion, which caused the breaking of the carbon layer and the generation of CO2 and Fe. Certain Fe reduced from Fe2O3 destroyed the aromatic carbon layers by the strong affinity between Fe and C atoms and generated intercalation compounds (FeCx). Furthermore, the regularisation and stacking of large carbon layers were impeded. Thus, the graphitisation of amorphous carbon was inhibited.

ReaxFF Molecular Dynamics Simulations of Thermal Reactivity of Various Fuels in Pyrolysis and Combustion

The methodology development and applications of ReaxFF molecular dynamics (ReaxFF MD) in unraveling the complex reactions and kinetics for pyrolysis and oxidation of organic systems are reviewed. Particular attention is given to the large-scale ReaxFF MD simulation method of similar to 10,000 atoms and practical simulation strategies to overcome the temporal-spatial limits as much as possible. High-performance computing codes running on CPU cluster/supercomputers and on GPU were overviewed. GPU-enabled code like GMD-Reax is revolutionizing large-scale ReaxFF MD simulations to run mainly on a single GPU. A step-forward for reaction analysis was achieved in the code of VARxMD to reveal detailed reactions based on the identification of bond types and unique species that allows for categorization of reaction species and pathways through structure searching of reaction sites and reactants/products. Efforts for extracting rate constants and kinetics modeling from unperturbed kinetics of ReaxFF MD simulations are reviewed, and challenges remain. The important factors of model scale effects, elevated simulation temperature, and possible validation of ReaxFF MD reaction simulation results theoretically and experimentally are illustrated and discussed. The novel hybrid simulation strategies proposed recently that may expand applications of ReaxFF MD to connect with realistic scenarios of engine combustion and relevant chemical effects on aerospace vehicle materials are briefed. The simulation practices of large-scale ReaxFF MD in understanding the similarities and differences of reactivity and reaction mechanisms in pyrolysis of liquid hydrocarbon fuels, solid fuels (coal, biomass, polymer), and energetic materials of CL-20 and its cocrystals are briefly described, which indicates that large-scale ReaxFF MD simulations are a feasible and straight means to capture the dynamics of an almost entire reaction process and to evaluate reactivity of organic systems computationally. There is still a great deal of work to be done to push the boundaries of ReaxFF MD simulations forward. With the constant improvement of the ReaxFF force field and reaction analysis capability, ReaxFF MD playing a key role in understanding reaction mechanisms and its potential in kinetics modeling of pyrolysis and oxidation of various fuels can be expected.

Investigation of recycled phenol effects on supercritical water gasification of coal using ReaxFF MD simulation

Simulation investigation of coal gasification in supercritical water is fundamentally important since experimental approaches are limited in summarizing the transient response of coal gasification for the complexity of coal molecules. In this paper, recycling technology of intermediate phenol is applied to the coal gasification which is investigated by experiment and ReaxFF molecular dynamics simulations. The experimental results show that carbon gasification efficiency and hydrogen yield increase by 54% and 59%, respectively. The simulation results agree well with experiments. Trajectory analysis of the overall scenario shows that additional phenol promotes more active free radicals, reduces the potential energy and prevents the char formation effectively. A deeper insight into the aromatic ring opening indicates that the reaction energy carrier of aromatic ring opening is lowered enormously with phenol added. Further investigation by frontier molecular orbitals (FMO) and energy decomposition analysis (EDA) is conducted, the interaction energy of dual-ring to phenol is higher and its stability decreases from 6.17 to 2.32 kJ/mol, in which the ΔEorb provides the main contribution. In a word, the positive effects of phenol on coal gasification in supercritical water are discussed theoretically, which provides a theoretical basis for the large-scale continuous industrial application.

Elucidating multiple-scale reaction behaviors of phenolic resin pyrolysis via TG-FTIR and ReaxFF molecular dynamics simulations

Phenolic resin is a matrix material widely used in ablative thermal protection systems (TPS) and its pyrolysis behavior is crucial for the analysis and prediction of TPS thermal response. However, it still remains a huge challenge to elucidate the involved reaction mechanisms due to the process complexity and unpredictability. Herein, a combination of TG-FTIR and ReaxFF MD simulation method was adapted to explore phenolic resin pyrolysis mechanism. Experiment results indicate that the pyrolysis process of phenolic resin can be divided into three stages, and the activation energy of each stage increases gradually. Heating rate affects the initial pyrolysis temperature of phenolic resin, but has no obvious effect on the types of pyrolysis products. Additionally, an accurate and reasonable decomposition kinetic model is established based on 30 kinds of kinetic function models, involving diffusion, random nucleation and nuclei growth, phase interface reaction and chemical reaction. The cook-off simulations results suggest that the major pyrolysis products of phenolic resin at high temperature include H2, CO, C2H2, and H2O, which formation mechanisms are also discussed according to the simulation trajectories. The reaction model and the activation energy of phenolic resin pyrolysis based on simulations are in good agreement with the experimental results, contributing to the deep understanding of phenolic resin pyrolysis behaviors at atom scale. This study may provide theoretical data basis for the establishment of thermal response calculation model of resin-based composite thermal protection materials.

Construction of a coal char model and its combustion and gasification characteristics: Molecular dynamic simulations based on ReaxFF

In present work, an atomistic coal char representation is constructed through the pyrolysis of the classical Given bituminous coal model using the reactive molecular dynamics (ReaxFF MD) simulation. The combustion and gasification characteristics of the char are also investigated via ReaxFF MD simulations. The coal pyrolysis activation energy obtained from ReaxFF simulation is 403 kJ/mol, which is in good agreement with recent experimental data. The char fragments are extracted from the pyrolysis products and the 3D representation of the char model is constructed. The chemical properties of the char examined are the H/C and O/C ratio; aromaticity; distribution of oxygen and nitrogen; aromatic and aliphatic ring structures; and the physical features of char model including the helium density, radial distribution function of carbon atoms, and pore size distribution. The char combustion and gasification simulation results show that the activation energy for char-O2 oxidation, char-CO2 gasification, and char-H2O gasification are 129, 320, and 283 kJ/mol, respectively. By analyzing the distribution of the products and radicals as well as the evolution of char molecular structure, the char combustion and gasification mechanisms are revealed. It is also found that char-H2O gasification leads to the generation of large amounts of C2 species.

Mechanism analysis and simulation of methyl methacrylate production coupled chemical looping gasification system

Nowadays, the efficient and cleaner utilization of coal have attracted wide attention due to the rich coal and rare oil/gas resources structure in China. Coal chemical looping gasification (CCLG) is a promising coal utilization technology to achieve energy conservation and emission reduction targets for highly pure synthesis gas. As a downstream product of synthesis gas, methyl methacrylate (MMA), is widely used as raw material for synthesizing polymethyl methacrylate and resin products with excellent properties. So this paper proposes a novel system integrating MMA production and CCLG (CCLG-MMA) processes aiming at “energy saving and low emission”, in which the synthesis gas produced by CCLG and purified by dry methane reforming (DMR) reaction and Rectisol process reacts with ethylene for synthesizing MMA. Firstly, the reaction mechanism of CCLG is investigated by using Reactive force field (ReaxFF) MD simulation based on atomic models of char and oxygen carrier (Fe2O3) for obtaining optimum reaction temperature of fuel reactor (FR). Secondly, the steady-state simulation of CCLG-MMA system is carried out to verify the feasibility of MMA production. The amount of CO2 emitted by CCLG process and DMR reaction is 0.0028 (kg CO2)−1·(kg MMA)−1. The total energy consumption of the CCLG-MMA system is 45521 kJ·(kg MMA)−1, among which the consumption of MMA production part is 25293 kJ·(kg MMA)−1. The results show that the CCLG-MMA system meets CO2 emission standard and has lower energy consumption compared to conventional MMA production process. Finally, one control scheme is designed to verify the stability of CCLG-MMA system. The CCLG-MMA integration strategy aims to obtain highly pure MMA from multi-scale simulation perspectives, so this is an optimal design regarding all factors influencing cleaner MMA production.

Dynamic migration mechanism of organic oxygen in Fugu coal pyrolysis by large-scale ReaxFF molecular dynamics

Organic oxygen accounts for essential constituents of the chemical coal structure and makes significant contributions to the reactivity of coal in pyrolysis. The dynamic migration mechanism of organic oxygen during coal pyrolysis was explored by heat-up ReaxFF molecular dynamics simulations. A multicomponent molecular model for Fugu subbituminous coal was simulated in the temperature range of 300−2500 K with a heating rate of 1 K/ps using the GMD-Reax software. The difference between the pyrolysis products yields and their oxygen content indicates that organic oxygen in Fugu coal migrates preferentially into gas-phase oxygen during pyrolysis. Molecules of CO2, H2O, CH2O, and CO are identified as major O-containing gas products and their generation sequence shows consistency with reported experimental observations. CH2O molecules are produced mainly from cleavage of alkyl-alkyl ethers and their secondary cracking reactions will lead to their decrease trend and contribute partially to the rapid production of CHO radicals at high temperatures. The phenolics and carbonyl groups are found as the dominant functionalities in asphaltene and tar. The cleavage of alkyl-aryl and aryl-aryl ethers contributes to the production of phenolics that transform into carbonyl groups at higher temperatures through isomerization of aromatic rings. The decrease of phenolics and increase of carbonyl groups in the fast pyrolysis stage should be attributed mainly to the structure transformation reactions rather than migration among different pyrolyzate lumps of gas, tar, and asphaltene. This work suggests that ReaxFF MD simulation is useful for exploring the comprehensive dynamic migration mechanism of organic oxygen in coal pyrolysis.