A review of the fractionation and properties of lignin derived from pulping black liquor and lignocellulose pretreatment

The pulp and paper industry generates large quantities of Pulping Black Liquor (BL). Minimizing the chemical content in BL through effective and environmentally friendly treatment methods is therefore essential. BL contains a substantial amount of highly heterogeneous lignin, which has a complex chemical structure and a broad molecular weight distribution. Only a small fraction of this lignin is used as a dispersant, concrete additive, or binder in mining operations, while the majority is used as a fuel source. Solvent fractionation of this inhomogeneous lignin with solvents offers a promising solution to overcome these limitations. The fractionated lignin has a more controlled molecular weight and a more uniform structure, facilitating its high-value applications and reducing the environmental impact of BL. This paper reviews the conversion of lignin in BL, various methods for lignin separation, and recent advances in the use of commonly used solvents such as methanol, ethanol, acetone, dichloromethane, ethyl acetate, and ionic liquids for lignin fractionation. A novel and effective solvent-based approach for lignin fractionation from BL is proposed.