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.

Progress of Dispersants for Coal Water Slurry

“…These typically comprise linear and comb structures to cater to the polar groups of coal [21,22]. The hydrophobic end and the hydrophilic end of the one-dimensional linear structure dispersant are in a straight line, such as naphthalene sulfonate formaldehyde condensate (NSF) [23,24], sodium dodecyl benzene sulfonate, and sodium dodecyl sulfate (SDS) [25], while the two-dimensional structure dispersant contains a large number of hydrophobic and polar groups, such as comb polymer sodium polystyrene sulfonate (PSS) [26]. The latter is formed by copolymerization of polymer monomer, polyethylene glycol acrylate monoester, sodium p-Phenylethane sulfonate, and acrylamide [27,28].…”

“…This suggests that the enhancement of electrostatic repulsion between coal particles is not the sole determining factor contributing to particle dispersion, and the synergistic effect of other factors must also be considered [11,14]. In a study by Chen et al [23] on the dispersion mechanism of naphthalene sulfonate formaldehyde (NSF) in CWS, it was discovered that the apparent viscosity and yield stress of CWS significantly decreased with the addition of 1.5% NSF, aligning with the saturated adsorption value of NSF on superfine coal. Furthermore, the zeta potential and contact angle of finely pulverized coal decreased with increasing NSF dosage, indicating that the coal surface experienced greater electrostatic repulsion force and improved wetting ability after NSF addition.…”