A review on lignin extraction processes at different production scales

Lignin is the world’s second most plentiful natural polymer and most abundant source of aromatics, but it is heavily underutilized in value-added products due to its complex, heterogeneous structure. As the demand for sustainable materials and energy grows, the potential for lignocellulosic biomass biorefineries is increasingly being explored. The successful implementation of biorefineries depends on the effective valorization of all components of lignocellulosic biomass, including lignin. The success of lignin extraction technologies depends on achieving economic and technological feasibility for scale-up and successful commercialization. Following extraction, the structural characteristics of the produced lignin are important for its potential valorization into value-added products. For different extraction methods, potential benefits and downfalls, level of scale-up achieved, as well as lignin recovery and its quality, are highlighted throughout this paper. It was observed that lignin extraction technologies integrated into existing pulp mill operations for producing kraft lignin and lignosulfonates have seen the greatest scale-up activities due to the benefit of reduced capital costs compared to greenfield developments. However, the generated lignin suffers from a degraded lignin structure caused by the pulping operation. Solvent-based processes can produce high-purity lignin, and with the diversity of available solvents, along with lignin extraction conditions, novel processes can be fabricated to target desired lignin characteristics. However, their success is heavily dependent on the ability to recover and recycle solvents economically. • Many lignin production technologies have been researched, but scale-up beyond pilot scale is limited. • Lignin recovered from pulp mills is more mature than other biorefining operations. • Solvent-based processes are diverse but rely on high solvent recovery and recyclability. • Production methods heavily influence lignin structure.