Experimental and theoretical insight into the effect of a novel composite dispersant on the properties of coal pitch water slurry

Abstract

To optimize the utilization efficiency of coal pitch (CP), an innovative composite dispersant was designed and employed in the preparation of coal pitch water slurry (CPWS) by effectively combining modified sodium lignosulfonate (MLS) and amphoteric polycarboxylate (AAD) based on the principle of complementary advantages. The effects of the proportion of MLS to AAD on the characteristics of CPWS were systematically analyzed and assessed by various technical methods, including apparent viscosity, rheological behavior, static stability, adsorption behavior, etc. Results indicated that the CPWSs utilizing distinct composite dispersants belonged to the category of yield pseudoplastic fluids and had a good correlation with the Herschel-Bulkley model. Among them, the CD-2, composite dispersant with a mass ratio of MLS:AAD = 1:1, exhibited superior performance in terms of viscosity reduction and stabilization properties. It demonstrated the maximum adsorption capacity (5.23 mg/g) and adsorption layer thickness (7.22 nm) compared to other dispersants. Meanwhile, it could significantly increase the wettability (with a contact angle of 74.5°) and the absolute Zeta potential value (32.5 mV) of CP. The density functional theory (DFT), molecular dynamics (MD) simulation, and extended Derjaguin-Landua-Verwey-Overbeek (eDLVO) theory were carried out to investigate the interaction mechanism of composite dispersant with CP and the interaction energy among CP particles. The differences in energy levels between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HUMO) of MLS and AAD were significantly smaller than that of H2O. The hydrophobic groups of composite dispersants were efficiently adsorbed onto CP, while the hydrophilic groups adsorbed water molecules, with an adsorption energy reaching −169.36 kcal/mol. The steric hindrance of composite dispersant exerted a crucial influence on the dispersion of CPWS, enabling CP particles to be stabilized in water. The present study offers a novel approach to enhance the characteristics of CPWS and establishes a theoretical foundation for the design of efficient composite dispersants.