Molecular mechanism of the degree of influence of ethoxy and alkyl structures on the wettability of low-rank coal

Abstract

The mechanisms of the effects of decyl polyoxyethylene ether (DEO6), decyl polyoxyethylene ether (DEO8), and aliphatic alcohol polyoxyethylene ether (AEO6) on the wettability of coal dust from low-rank coal have been investigated in this study. The aim is to reveal the difference in the degree of influence of the structure of the alkyl and ethoxy groups. The surface tension test showed that AEO6, which can form a soft chain structure, could reach the critical micelle concentration (CMC) the fastest, followed by DEO6, and DEO8, which has the strongest polar effect, the slowest. The contact angle, settling time, and water retention experiments revealed that the AEO6-treated coal dust had the strongest wettability and water retention, which could effectively inhibit the coal dust and weaken the possibility of its secondary dust. Fourier transform infrared (FTIR) spectroscopy reveals that AEO6 with long alkyl chains can produce strong nonpolar effects, and in the process of adsorption with coal dust, it can produce strong hydrophobic bonding with nonpolar groups on the surface of low-rank coal, and finally form a directional adsorption conducive to the enhancement of wettability. Scanning electron microscope (SEM) showed a trend from DEO6-coal, DEO8-coal, and AEO6-coal appearing to have surfaces that sequentially become flatter and denser, with a gradual decrease in the number of loose particles and a weakening of the pore structure. Molecular dynamics (MD) simulations agree with the above experimental results. That is, the interaction between water molecules is stronger in the AEO6-modified coal system, followed by the DEO8 system and weakest in the DEO6 system. And the advantage of DEO8-coal is weaker than that of AEO6-coal but better than that of DEO6-coal. Based on the above experimental and simulation results, it can be concluded that the ability of the alkyl structure to influence the wettability of surfactant-modified coal dust is higher than the structure of the ethoxylate group, which will provide theoretical guidance for coal dust management and dust suppression.