Challenges in industrial applications of technical lignins

TLDR

Lignin, a major by‑stream in lignocellulosic biorefineries, is largely incinerated for energy, and its modified structure and impurities limit its conversion into value‑added products. This review examines the limiting factors in utilizing technical lignins. The authors identify four major problem classes and propose approaches to overcome them.

Abstract

The primary aim of modern biorefineries is the efficient conversion of lignocellulosic materials into valuable products. Sugars and oils can be converted into valuable chemicals, but processing of lignin is still a challenge. A vast amount of lignin is incinerated to produce process steam and energy, and only a very small part is used for the production of value-added products. Technical lignins are isolated as by-streams in lignocellulosic refineries, e.g., as kraft, soda, organosolv, and hydrolysis lignins, as well as lignosulphonates. They have a modified structure and contain impurities that are dependent on the processing method. The structure and the composition of technical lignins restrict their subsequent applications. This paper reviews limiting factors in utilization of technical lignins. Four major classes of problems are identified, and approaches to overcoming these problems are suggested.