Experimental and DFT study on the mechanism of inorganic chlorine to organic chlorine during pyrolysis of high chlorine lump coal

High-chlorine coal thermal utilization triggers severe equipment corrosion, yet the fundamental mechanisms governing the anomalous low-temperature transformation of inorganic to organic chlorine remain elusive. This study systematically investigated chlorine migration pathways during the pyrolysis of Xinjiang Shaerhu coal, utilizing both experimental characterization and density functional theory (DFT) calculations. Results reveal that the inorganic-to-organic chlorine conversion rate in lump coal peaks at 90 % at 750℃, significantly exceeding the 54 % observed for fine coal. Concurrently, the mass-transfer-limited lump coal tar yield peaks at 650℃ before rapidly declining, with chlorinated organics dominated by long-chain chlorinated hydrocarbons rather than the multi-component aromatics found in fine coal. Mechanistically, nanoconfinement within lump coal internal pores weakens Na-Cl ionic bonds to induce sub-melting-point dissociation. DFT calculations confirm that the binding energy of Cl· radicals at in-plane central vacancies (−853.5 kJ/mol) is far higher than at edge sites (−451.9 kJ/mol), while oxygen-containing functional groups lower the reaction barrier via electron-withdrawing inductive effects to facilitate stable covalent C-Cl cross-linking.This study elucidates the transformation mechanism of inorganic-to-organic chlorine from the perspectives of confined mass transfer and electronic structure regulation, providing a theoretical foundation for parameter optimization and anti-corrosion control in industrial vertical furnace lump coal pyrolysis dechlorination processes.