Effects of molecular weight of grafted sulfonated lignin on its dispersion and adsorption properties as a dispersant for coal water slurries

A series of grafted sulfonated lignin-based dispersants, GCL3J series with different molecular weight, were prepared by graft copolymerization, sulfonation and polycondensation reactions using alkali lignin as the main raw material. The effects of molecular weight of GCL3J on its adsorption behaviors and dispersion properties in coal water slurry were investigated. Rheological property investigations show that GCL3J series are better than FDN in reducing the viscosities of coal water slurry, especially for GCL3J-3 which M_w and inherent viscosity are 31 500 Da and 8.06 mL/g, respectively. Adsorption results show that all the adsorption isotherms of GCL3J on coal surface are belonging to Langmuir monolayer adsorption. With the increase of molecular weight, the adsorption amounts on coal surface decrease. Zeta potential results show that the adsorption forces between GCL3J and coal surface increase with the increase of molecular weight.