Insights into the Dispersion Mechanism of Microfine Coal Particles Modified with Naphthalene Sulfonate Formaldehyde Based on EDLVO Theory

Abstract

Coal water slurry (CWS) fuel prepared using microfine coal particles with a size distribution of 1–10 μm is a promising way to cleanly utilize solid resources in engines, even catering a popular application for clean coal technology. In an attempt to address the problems in coal aggregation in microfine coal water slurry (MCWS), dispersants are used to improve the dispersing status of microfine coal particles. Based on the experimental results and extended Derjaguin–Landau–Verwey–Overbeek (EDLVO) theory calculations, the role of naphthalene sulfonate formaldehyde (NSF) in MCWS performance was explored. The measurement of the slurry ability of microfine coals demonstrated that the apparent viscosity and yield stress of MCWS were decreased significantly with 1.5% NSF addition, which was consistent with the saturated adsorption value of NSF on microfine coals. Furthermore, the ζ-potential and contact angle of microfine coals were both decreased as a function of the NSF dosage, indicating that a larger electrostatic repulsion force and better wetting ability of the coal surface would be obtained in the presence of NSF. The thickness calculation results showed that the thickness is increased with NSF addition, which is attributed to that the NSF molecule extends into the surrounding solution to form a hydrophilic film. The EDLVO calculations illustrated that the total interaction was turned from an attractive force into a repulsive force in the case of NSF, noting that the better dispersion of microfine coals mainly resulted from the better hydrophilicity of the coal surface modified with NSF. The findings might provide guidance for MCWS preparation by revealing the interaction mechanism of microfine coals modified with NSF.