Mechanism of enhancing the injectability of coal with the chelating wetting agent by molecular dynamics simulation

Abstract

The wetting effect of water injection is of crucial importance for preventing geological disasters during the exploitation of deep coal seams. In this work, the promotion mechanism of the chelating wetting agent composed of the anionic surfactant sodium dodecyl benzene sulfonate (SDBS) and the chelating agent amino trimethylene phosphonic acid (ATMP) on the wetting effect of coal was explored through molecular dynamics simulations, surface tension tests, contact angle tests, scanning electron microscopy, and field tests. The electrostatic potential distribution of each molecule was analyzed by using the method of quantum chemical calculation, and the adsorption process of water molecules on the coal surface was simulated by adopting molecular dynamics. The results showed that the structures such as aromatic rings and alkane chains on the coal molecule surface had a small difference in electronegativity and were not easily combined with water molecules. The carbon chains of SDBS and ATMP molecules could adsorb at these sites, and their polar groups were exposed in water and formed hydrogen bonds with H₂O molecules with relatively strong interaction forces, thus increasing the hydrophilicity of the coal surface, significantly reducing the surface tension and contact angle of the aqueous solution, and enhancing the wetting effect of water on coal. In addition, it could also dissolve the minerals on the coal surface, connect the pores, and increase the contact area. When the chelating wetting agent solution was applied in the on-site coal seam water injection test, the water injection rate and volume increased significantly, creating a safer and more reliable environment for coal mine production.