After cellulose, lignin is the second most common biopolymer on earth. It is a major component of trees and grasses and is produced in large quantities as a waste product in paper, pulp and bioethanol production. However, as this complex biopolymer is difficult to break down, the residual material is usually incinerated. An international research team led by the Leibniz Institute for Catalysis (LIKAT) is now showing how lignin can be efficiently utilised.

Together with Chinese partners, the LIKAT team has developed a process that converts the plant material into aromatic amides. Amides are organic compounds derived from ammonia (NH3) and are important raw materials for medicines and pesticides, for example.

Development of an innovative catalyst

The development focuses on a catalyst in which cobalt atoms are individually anchored in a carbon matrix. It is said to be extremely active and enables precise, selective conversion of lignin. The key factor is that the new catalytic process does not require toxic reagents and runs under mild conditions.

Amides from lignin

The conversion of lignin therefore takes place in two steps, which can be carried out in a reaction vessel: First, lignin is broken down into carboxylic acids with the aid of oxygen, which then react with ammonia or amines to form aromatic amides. ‘Instead of disposing of this valuable raw material, we can now convert it into useful chemical products,’ explains Zhuang Ma, one of the study's lead authors.

An important step towards sustainable circular chemistry

It is also noteworthy that the process works not only with processed lignin, but also with ordinary pine wood chips. Here, yields were achieved that almost reached the ‘theoretically possible maximum values’. In addition, the catalyst can be used multiple times without losing performance. ‘Our research lays the foundation for truly renewable production of important chemical building blocks,’ says LIKAT researcher Jagadeesh Rajenahally. ‘This is an important step towards sustainable circular chemistry.’ 

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