Carboxyalkylated lignin derived coal wastewater slurry

Preparing coal water slurry from coal gasification wastewater as gasification/combustion feedstock offers a promising strategy for wastewater management and resource recovery. The primary challenge lies in optimizing slurry formulation to accommodate wastewater as the aqueous medium. This study demonstrated that carboxyalkylated lignin derivatives, i.e., biomass-based aromatic polymers, were effective dispersants for generating coal gasification wastewater slurry (CGWS). The alkyl chain lengths of carboxyalkylated lignin derivatives significantly influenced their molecular characteristics and, consequently, the physicochemical properties of the resulting slurry. Fundamentally, the dispersion performance of lignin derivatives and sodium methylene dinaphthalene sulfonate (NNO), as a commonly used dispersant for the slurry, was different. While NNO promoted dispersion via increasing electrostatic repulsion, the lignin derivatives promoted the slurry formulation primarily via grafting molecular structure. Among the tested lignin derivatives, CPr (carboxybutylated lignin) required the lowest dosage (0.20 wt%) and increased the solid concentration of the slurry from 50.42 wt% (NNO-CGWS) to 52.81 wt% (CPr-CGWS) at an apparent viscosity of 1000 mPa·s, while reducing its pseudo-plasticity. Additionally, lignin derivatives increased the calorific value of CGWS by 0.191 kcal/g using CPr at a dosage of 0.20 wt%. This work establishes carboxyalkylated lignin, particularly CPr, as a highly effective and eco-friendly dispersant for preparing value-added CGWS from industrial wastewater.