Investigation of N transfer during coal pyrolysis and combustion by using ReaxFF molecular dynamics
Summary¶
ReaxFF MD on a ~26k-atom coal model with diverse nitrogen functionalities follows N partitioning during pyrolysis and combustion. The abstract reports that >65% N remains in char after pyrolysis, ~25% enters tar, and combustion with 10,000 O2 molecules yields trends for NH3, HCN, HNCO, NO and radicals (CN, NH2/NH, COxN, HOxN), with pyrrolic-N highlighted as especially active. The extended abstract ties fuel-N tracking to NOx control in clean coal conversion: because experiments struggle to resolve radical populations during fast pyrolysis and combustion, ReaxFF trajectories are presented as a complement for atomic-scale N migration and gas-phase product evolution.
Methods¶
MD application (ReaxFF). Reactive MD uses GMD-Reax (GPU-oriented ReaxFF implementation named in the conference PDF) with the Mattsson coal/char ReaxFF parameterization referenced there. Coal supercell: stoichiometry C₁₄₁₈₈H₁₁₄₆₁N₁₂₂O₆₅₈S₅₈ (26,487 atoms) built from a Liulin coal skeleton; N is partitioned among pyrrolic, pyridinic, quaternary, and –NH₂ motifs using XPS-motivated fractions quoted in the text. Equilibration: both pyrolysis and combustion geometries are NPT-relaxed at 500 K, 1 atm. Combustion setup: a ~204.6 Å cubic PBC cell containing the coal model plus 10,000 O₂ molecules. Heating ramps: 500–2500 K (pyrolysis) and 1000–3000 K (combustion) at 2 K/ps; velocity–Verlet integration with Δt = 0.25 fs and a Berendsen thermostat (as stated in the PDF). Reaction mining uses VARxMD.
Force-field training and standalone static QM are N/A for the headline workflow.
Barostat details after 500 K equilibration, total simulated time per ramp stage, post-ramp production segments, pyrolysis-only cell vectors, electric fields, and replica exchange are not transcribed numerically from the indexed conference pages—see the PDF for any additional timing tables.
Findings¶
Pyrolysis partitioning: trajectory analysis reports >65% of N retained in char and ~25% migrating to tar-range fragments (percentages as stated in the abstract). Temperature trends: N in C₄₀⁺ fragments changes slowly 500–1300 K, then redistributes rapidly ~1300–1900 K with growth of N in C₅–C₄₀ species (qualitative description in the PDF). Combustion gases: tracks NH₃, HCN, HNCO, NO and radicals/intermediates (CN, NH₂/NH, COₓN, HOₓN) with only minor N₂, NO₂, N₂O generation in the summarized runs. Mechanism hooks: NO tied to NH oxidation and subsequent HOₓN/COₓN pathways; HNCO feeds COₓN species that influence NOₓ evolution; pyrrolic-N highlighted as most active, with O₂ H-abstraction on N–H promoting combustion chemistry.
Limitations¶
Conference proceedings extended abstract (no DOI in front matter); claims should be checked against any peer-reviewed follow-on publication. Hardware/runtime remarks in the PDF are illustrative, not transferable performance benchmarks.
Relevance to group¶
Corpus coal + ReaxFF snapshot complementary to combustion and hydrocarbon ReaxFF applications.
Citations and evidence anchors¶
- No DOI in front matter; cite conference abstract PDF path above.