Technological advancement in lignin recovery and valorization for sustainable and economic biorefinery developments

Abstract Lignin recovery from lignocellulosic material is a prominent solution to environmental concerns and problems and establishes more sustainable and competitive lignocellulosic biorefineries. Lignin has the potential to produce various commodity chemicals, biofuels, plastics, dyes, adhesives, concrete binders, foaming agents, lubricants, and nanomaterials, and is a commitment step for a safer and sustainable circular bioeconomy development. However, lignin valorization is hindered by a series of factors, i.e., heterogeneous nature, intrinsic recalcitrance, and the presence of strong intermolecular bonding and functionalities. Most of the lignin residue generated during cellulosic or pulp industries is combusted for electricity production in an uneconomic manner. Therefore, we have critically assessed and discussed the main constraints of novel strategies concerning lignin isolation and valorization, which is widely used in the landscape of lignocellulose biomass-based biorefining to reduce the dependency on fossil reserves and indirectly impacts the circular economy and lifestyle of people. Finally, this review highlights the integrated approach linked to enzyme-to-microbe, microbe-to-microbe interactions, or modified lignin fraction via employing metabolic engineering, discusses the commercial aspects of lignin in the market, and describes the future perspectives as well. Additionally, various advanced catalytic approaches under oxidative/reductive environments and hydrodeoxygenation are well explored, illustrating their influence on the selectivity of lignin depolymerization. The article will consolidate existing knowledge but also incorporate some novel perspectives for future advancement concerning lignin valorization in a sustainable way, which is a prerequisite objective for various biorefinery developments.