Molecular dynamics simulations and experimental study of the modification mechanisms of a quaternary amphoteric polycarboxylate dispersant on the rheology of petroleum coke water slurry

Petroleum coke, as a byproduct of delayed coking in oil refineries, can be used as a raw material for gasification to meet the demand for hydrogen in oil refining processes, which can significantly reduce the cost of oil refining while efficiently and cleanly utilizing solid waste. Due to the low ash content of petroleum coke, the feedstock used for gasification is usually petroleum coke water slurry (PWS). However, the rheology of PWS needs to be improved before gasification. In this paper, a quaternary amphoteric polycarboxylate dispersant (PC-4) was synthesized by free radical polymerization with methylallyl polyoxyethylene ether (HPEG-1000), sodium styrene sulfonate (SSS), acrylic acid (AA) and trimethylallyl ammonium bromide (TAB), and for studying the influence of -N(CH3)4+, a ternary polycarboxylate dispersant (PC-3) was also prepared without the -N(CH3)4+ cationic group. The adsorption capacity of PC-4 is about 1.6 times higher than that of PC-3, and PC-4 also leads to an increased zeta potential and stronger hydrophilic modification performance when used to modify Lanqiao petroleum coke (LQ). Therefore, PC-4 is more suitable for enhancing the slurryability and rheological behavior of PWS. Molecular dynamics simulation (MD) was employed to reveal the adsorption mode of PC-4 on the surface of LQ particles. The cation-pi interaction between the -N(CH3)4+ ions of the PC-4 molecules and the aromatic structure of the petroleum coke were directly observed in images obtained from the MD simulation. The introduction of -N (CH3)4+ optimizes the adsorption configuration, resulting in a relatively dense and uniform dispersant layer on the LQ particle surface. Finally, the experimental results and MD simulation were integrated to reveal the PWS modification mechanism of PC-4.