Enhanced Dispersion and Stability of Petroleum Coke Water Slurries via Triblock Copolymer and Xanthan Gum: Rheological and Adsorption Studies

The rheology of petroleum coke (petcoke) water slurries was investigated with a variety of nonionic and anionic dispersants including poly(ethylene oxide) (PEO)-b-poly(propylene oxide) (PPO)-b-PEO triblock copolymers (trade name: Pluronic, BASF), poly(vinyl alcohol) (PVA), polyvinylpyrrolidone (PVP), poly(ethylene oxide) (PEO), poly(carboxylate acid) (PCA), sodium lignosulfonate (SLS), and poly(acrylic acid) (PAM. Each effective dispersant system shared very similar rheological behavior to the others when examined at the same volume fraction from its maximum petcoke loading. Triblock copolymer, Pluronic F127 (F127), was found to be the best dispersant by comparing the maximum petcoke loading for each dispersant. The yield stress was measured as a function of petcoke loading and dispersant concentration for F127, and a minimum dispersant concentration was observed. An adsorption isotherm and atomic force microscopy (AFM) images reveal that this effective dispersion of petcoke particles by F127 is due to the formation of a uniform monolayer of brushes where hydrophobic PPO domains of F127 adhere to the petcoke surface, while hydrophilic PEO tails fill the gap between petcoke particles. F127 was then compared to other Pluronics with various PEO and PPO chain lengths, and the effects of surface and dispersant hydrophilicity were examined. Finally, xanthan gum (XG) was tested as a stabilizer in combination with F127 for potential industrial application, and F127 appears to break the XG aggregates into smaller aggregates through competitive adsorption, leading to an excellent degree of dispersion but the reduced stability of petcoke slurries.