Molecular dynamics simulation study on the effect of SDS and AEO3 complex on the wettability of lignite

In order to explore the micro-mechanism of the influence of anionic surfactant and nonionic surfactant on the wettability of low-rank coal, the molecular dynamics simulation method (MD) was used to study the influence of anionic surfactant (SDS), nonionic surfactant (AEO3) and their complex system on the wettability of lignite. The results show that when SDS is compounded with AEO3, the thickness of coal/water adsorption layer is 36.35×10−10 m, which wets 58.83% of lignite molecular layer. At this time, the diffusion coefficient of water molecules increases significantly, thus increasing the probability of collision between coal and water molecules, and further enhancing the wettability of water on lignite. In SDS/ AEO3 compound system, the interaction energy between lignite and water and between surfactant and water is greater than that of SDS and AEO3 alone. The interaction energy between coal and water, surfactant and water are all provided by non-bond energy, and the electrostatic energy accounts for more than 82.28% of the non-bond energy, while the contribution of Van der Waals’ force energy is very small, even inhibiting the interaction between surfactant and water. There is little difference in the length of hydrogen bonds between SDS, AEO3 and SDS/ AEO3, but the number of hydrogen bonds between SDS/ AEO3 and water is more than that SDS and AEO3 separated produced with water.