A Review on Eco-friendly Isolation of Lignin by Natural Deep Eutectic Solvents from Agricultural Wastes

Agricultural residues have attracted the attention of researchers in recent years due to their potential as a waste source that is abundantly available worldwide and can be used to create value-added products with economic and environmental benefits. Lignin is the second most inexhaustible natural biopolymer, delivering the most energetic material of all for the development of eco-friendly, biodegradable, and low-cost value-added products. Commonly lignin used as a macromolecule for the synthesis of low molecular weight chemical sand fuel. The present review article tries to present to fulfil research gap between extraction and isolation of lignin through natural deep eutectic solvents (NADES), green/sustainable methods which is fast-emerging techniques to extract valuable products. In this review article, we covered various methods on pre-treatment of lignocellulosic materials using NADES as exclusive and multifunctional solvents via the green integrated biorefinery approach. It also contains comparison between advantages and disadvantages of pre-treatment methods vs NADES of various biomass. Beside those various methods of sustainable synthesis of NADES and its properties; processing of lignin for production of value–added products, applications of lignin derived by green synthesis, and challenges to current state-of-the art technologies and future perspectives and current Markets are reviewed. We concluded that NADES can be effectively used for low-cost synthesis in the purification and isolation of lignin from agro wastes for attaining high yields which ultimately enhance economic value of lignocellulosic biomass.