Molecular mechanism of influence of alkyl chain length in ionic surfactant on the wettability of low rank coal

The surfactant can effectively improve the wetting effect of the solution on coal and improve the dust removal efficiency of coal dust, which is of great significance to mine dust control. To investigate the effect of alkyl chain length of surfactants on the wettability of low rank coal, ionic surfactants with different chain length structures were selected, and molecular dynamics and quantum chemistry simulation methods were used to reveal the effect of alkyl chain length on the wettability of low rank coal at the molecular level. The simulation results show that with the increase of alkyl chain length, the absolute value of coal-water interface formation energy increases gradually, and reaches the maximum when the chain length is 16. The wetting effect of anionic surfactant is better than that of cationic surfactant. Surfactants C16SNa and C16TAB show isotropy at the coal-water interface, which is beneficial to increase the adsorption thickness between coal and water and improve the wettability of low rank coal. The alkyl chain length mainly affects the hydrophobic interaction between surfactants and coal molecules, and then regulates the wettability of low rank coal surfaces. When the alkyl chain is longer than 16, the steric hindrance of surfactant molecules is large, which is not conducive to improving the wettability of low rank coal surface. The settlement experiment and contact angle experiment show that C16SNa and C16TAB have the best wetting effect on low rank coal, which is basically consistent with the simulation results. This study provides a basis for the molecular structure design of new high-efficiency surfactants.