Lignin Fractionation Methods: Can Lignin Fractions Be Separated in a True Industrial Process?

Lignin is among one of the largest natural resources in the world, with aromatic structures that can serve as a raw material in the synthesis of high value-added chemicals, the production of bioenergy, and the development of carbon-based products, among others. A better understanding of the chemical structure of lignin and its valorization methods is necessary to overcome current technological challenges for industrial scale applications. The main challenge found to provide the most abundant source of aromatics in the world is the fractionation of lignin. Current studies propose a way to fractionate lignin to obtain more homogeneous and less complex fractions, because of the fact that aromatic compounds are essential intermediates in the manufacture of polymers, and lignin is the main source of biologically aromatic-based substrates. Numerous review articles have addressed research aimed at understanding the structure of lignin, however, a limited focus has been given to its fractionation methods. This article aims to review papers published in recent years using different lignin fractionation techniques, focusing on the four main types of fractionations: in organic solvents, gel permeation chromatography in preparatory scale, ultrafiltration and precipitation by varying acid gradient. This a Review summarizes the most recent innovations in the area of biorefineries for the chemical valorization of lignin derived from various botanical sources through different fractionation methods.