Experimental and molecular dynamics of corn straw char high-temperature steam gasification: Effects on char structure, temperature and steam mass concentration

Clarifying the micro-mechanism of corn straw char (CSC) in steam gasification is crucial for optimizing biochar conversion into clean syngas. To investigate the steam gasification characteristics and reaction mechanism of CSC under different preparation conditions and gasification parameters, and high-temperature steam gasification system for CSC was designed and constructed. The study examined the gas product release rate, carbon conversion rate, and changes in the residual surface structure of CSC under different preparation conditions, gasification temperatures, and times. The chemical structure of CSC was characterized using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), and ¹³C NMR, leading to the construction of the CSC molecular structure model. Reaction Force Field molecular dynamics (ReaxFF-MD) simulations were employed to investigate the effects of different temperatures (2000–4000 K) and steam mass concentrations (28–50 %) on gas production and to reveal the mechanism of high-temperature steam gasification of CSC. Results revealed that CS-900-5 exhibited the highest reactivity, achieving 90.73 % conversion rate and peak H₂ release rate of 95.2 ml/min at 1100 ℃ in 60 s. The primary CO generation pathway was identified as: C₂H· + OH· → C₂OH· → C₂O· + OH· → CHO· → CO, with reaction frequencies of 21, 119, 510, 603, and 608 in the range of 2000–4000 K. At 3000–4000 K, secondary reactions of CH₄ and CO₂ were enhanced. The secondary reaction pathways of CH₄ and CO₂ are CH₄ + OH· → CH₃· + OH· → CH₄O· → CH₂O· → CO + H₂, and CO₂ + C₂H· → C₃HO₂· → C₂OH· → C₂O₂H· → CO + H₂, respectively. Reducing steam mass concentrations decreased CSC gasification ability, as reflected by the reduction in CO and H₂ yields. Meanwhile, the number of C₂–C₄ increased progressively, from 16 to 97. This study provides theoretical support for improving biochar gasification efficiency and optimizing biomass conversion processes.