Development and evaluation of polycarboxylic acid hyper-dispersant used to prepare high-concentrated coal–water slurry

High solid content coal–water slurries (abbreviated as CWS) with low viscosity and excellent stability are ideal for the combustion and storage, but it is very difficult to prepare the CWS with both properties in industry. In this study a new Polycarboxylic Acid (abbreviated as PC) hyper-dispersant containing fundamental chain, sulfonic groups, carboxyl and polyoxyethylene branches is designed and synthesized as additive to prepare the CWS with ideal solid content, viscosity and stability. The synthesized PC hyper-dispersant under optimized conditions can be used to prepare CWS with the 68.13 wt.% solid content and 645 mPa·s apparent viscosity at 0.4 wt.% dosage, and the CWS have no sediments during three days. The rheological property investigation shows that the CWS prepared using PC exhibit markedly shear-thinning characteristic, which is very advantageous to the static stability, pipe pumping and spray combustion under high-shear condition. Fundamental analysis considers that the carboxyl anchor on coal surface, exhibiting firm adsorption affinity. The sulfonic groups orient towards the solution, providing electronegativity on coal surface. The flexible polyoxyethylene branches orient towards the solution, forming a thick hydrophilic polyoxyethylene layer on coal surface. The excellent dispersing and stabilizing effects of PC hyper-dispersant for CWS are concluded to be due to the combined effects of steric hindrance, lubrication action and electrostatic repulsion force.

Graphical abstractThe COO¯ groups of PC Hyper-dispersant molecule anchor on the electropositive sites of coal surface, the SO3¯ groups and polyoxyethylene branches orient to the solution. The PC has strong adsorptive capacity on coal surface, and gives the coal particles strong electrostatic repulsion force and steric hindrance, which prevent aggregation during storage. Therefore, the PC can realize the CWS with both the low viscosity and desire stability.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A polycarboxylic acid is synthesized to act as hyper-dispersant of high solid content CWS. ► The inherent viscosity, SO3¯ and COO¯ groups of PC are optimized. ► The rheological behavior of CWS prepared using PC is systematically investigated. ► The adsorption mechanism of PC in coal–water interface is disclosed.