Recent advances in catalytic conversion of lignin to value-added chemicals using ionic liquids and deep eutectic solvents: a critical review

Abstract

Lignin is an amorphous, heterogeneous, aromatic biopolymer that is obtained from nature. The scientific community is very interested in how lignin might be converted into compounds with added value in order to support a sustainable future and biobased economy. Ionic liquids (ILs) and deep eutectic solvents (DESs) are emerging as important kinds of comparatively greener solvents, and have been used for the catalytic transformation of different kinds of lignin and its model compounds into a wide variety of useful chemicals. The catalytic transformation processes can be carried out more quickly and possibly with less negative environmental effects by utilizing the unique qualities of these green solvents (ILs and DESs) with various functions. Catalytic systems that use ILs and DESs as media or catalysts may also yield a new product line. The catalytic chemical conversion of lignin to value-added chemicals and fuel products using ILs and DESs as reaction medium is the subject of this review. Several studies have been carried out on lignin solubility and extraction using these solvents; therefore, herein we have reviewed the advances in lignin valorization to fine chemicals using ILs and DESs.