Study on the influence of surfactants on the wetting of bituminous coal by halogen salt inhibitors: Molecular simulation and experimental characterization

Abstract

This study addresses the issues of poor wettability, inadequate water absorption, and short duration of halogen salt inhibitors by modifying them with four dodecyl-type anionic surfactsants:SDBS, MAPK, SDS, and ALSA. A combined approach of molecular simulation and experimentation was employed to investigate their wetting effects on bituminous coal. Molecular dynamics simulations revealed that polar groups of surfactants enhance solution wettability through hydrogen bonding. The ALSA system formed 1,338 hydrogen bonds, exceeding other surfactants by at least 9.09 %. The ALSA-modified inhibitor demonstrated the strongest water molecule infiltration intensity along the Z-axis, maximum penetration depth: 38.0318 Å, largest overlap area in relative concentration curves with coal, and highest isothermal water absorption, indicating optimal wetting. Quantum chemical simulations identified ALSA as having the best microreactivity. All four surfactants exhibited hydrophilic head groups and hydrophobic tail chains, functioning as “bridges” at the coal-inhibitor solution interface to enhance wettability. Experimental results showed that the ALSA-modified inhibitor achieved the most significant contact angle reduction 66.50 %, fastest settling rate, optimal water retention 32.71 %, and most complete oxygen-blocking film after drying. Both experiments and simulations consistently demonstrated that all four surfactants effectively enhance the wettability of halogen salt inhibitors on bituminous coal, with the improvement order being ALSA > SDS > SDBS > MAPK. The findings provide theoretical foundations and practical references for the application and optimization of inhibitors in coal spontaneous combustion prevention.