ReaxFF MD simulations of petroleum coke CO2 gasification examining the S/N removal mechanisms and CO/CO2 reactivity
Scope
ReaxFF NVT molecular dynamics of CO₂ gasification of a high-sulfur petroleum coke model at 3000 K, tracking sulfur and nitrogen speciation alongside CO/CO₂ reactivity including Boudouard-type chemistry.
Summary¶
Petroleum coke used as fuel or gasification feedstock retains sulfur and nitrogen in thermally stable moieties that participate in high-temperature conversion. The article examines removal and transformation pathways for those heteroatoms during CO₂ gasification using reactive force field molecular dynamics, explicitly addressing overlap between slow pyrolysis and gasification kinetics under the chosen hot, short trajectories.
Methods¶
Reactive MD (ReaxFF). Simulations use the reactive force field formalism cited in the article to follow bond rearrangement in a high-sulfur petroleum coke atomistic model at combustion/gasification-relevant temperature.
System. The petcoke structure is the Qingdao high-sulfur model with composition C₁₆₄₈H₇₇₂O₅₉N₂₄S₄₇ (2550 atoms) from prior work, built to capture curvature, stacking, length distribution, and O/N/S functional-group content; the same model was used in related pyrolysis and combustion ReaxFF studies at 2000–4000 K for comparison.
Integration and conditions. Runs are NVT at 3000 K for 250 ps, bracketing conditions where the abstract notes overlap between slower pyrolysis and slower gasification so both contribute to overall behavior. The paper contrasts regimes described as pyrolytic, reducing, and oxidizing with respect to CO₂ exposure (contribution of petcoke self-pyrolysis, CO₂ oxidation, and CO reduction is evaluated in the Methods narrative).
Analysis. Trajectories track S and N redistribution into gas-phase and condensed fragments and follow C oxidation sequences involving CO and CO₂, including stepwise interpretation of Boudouard-type chemistry. PBC and 3D periodic supercells are used as in the cited ReaxFF pet-coke work; N/A — integration timestep, thermostat name, and QEq/electrostatic update interval not copied from the local PDF to this page (see Fuel article and SI). N/A — barostat / pressure control: constant-volume NVT; no NPT production stage reported for these runs. N/A — static or oscillating electric field. N/A — replica exchange, umbrella, or metadynamics; production is standard NVT time evolution.
Force-field training (block 2). N/A — the paper applies an existing Reaxff CHONS parameterization for high-temperature coke/CO₂ chemistry rather than reporting a new fit in this work.
Static QM (block 3). N/A — central claims are from ReaxFF MD, not a standalone DFT study.
Findings¶
Sulfur. The abstract summarizes transformation sequences such as thiophenic S toward COS, C₁₋₂S-type fragments toward CₙOₙS-class species, further toward H₂S and SO₂ under the modeled oxygen inventory.
Nitrogen. Pyrrolic and pyridinic N are reported to evolve through CON, CN, and NO₁₋₂-containing intermediates toward C₁₋₂O₁₋₂N, COₙN, and HNO₁₋₂-type species and ultimately toward products such as HCN and nitrogen oxides depending on local oxygen (0 < n < 5 in the abstract’s shorthand).
CO/CO₂ reactivity. ReaxFF captures Boudouard chemistry as a two-step picture: one O from CO₂ bonds to a coke C, then the O–C bond in CO₂ breaks after CO release; the coke C that bound O is subsequently removed as a second CO, matching the abstract’s disassembly of the overall C + CO₂ ⇌ 2CO stoichiometry into atomistic events.
Interpretation. The authors argue that such trajectories help relate feedstock structural diversity (the “scale challenge”) to coke consumption chemistry beyond a single effective Boudouard rate. The KB should treat S/N removal and CO/CO₂ chemistry as coupled observables from the same NVT runs, not as independent post-processing metrics.
Limitations¶
Simulations use a single high-temperature window and short real time; quantitative rates and yields should not be extrapolated to industrial gasifiers without additional validation. The petcoke structural model is necessarily a single atomistic realization; compositional diversity in real feedstocks means pathway statistics should be read as illustrative rather than exhaustive.
Relevance to group¶
Companion study to other Zhong et al. petcoke ReaxFF papers in the corpus, emphasizing CO₂ gasification chemistry rather than hydrogen or ammonia reductants.
Citations and evidence anchors¶
- https://doi.org/10.1016/j.fuel.2019.116051