BIOBTX

Lignin is the key constituent of the lignocellulosic biomass and responsible for the structural and mechanical integrity of plants. Lignin is a polymer with wide variability in structure. Its components depend on the biomass source and are most often combined with cellulose and hemicelluloses. It is considered the recalcitrant to chemical and biotransformation treatments. Therefore, lignin often becomes a low-value waste product of biomass processing technologies, such as in the conventional paper and pulp industry and in the modern bioethanol-fuel-production industry. Structurally, lignin is a three-dimensional amorphous phenolic polymer that consists of monomers such as phenyl-propane unit, C3-C6 including p-coumaryl, sinapyl, and coniferyl alcohol. It contains β-O-4 (40% to 60%), biphenyl (3.5% to 25%), α-O-4 (3% to 5%), and β-5 (4% to 10%) linkages. The different structural and chemical properties of lignin lead to the production of a wide variety of aromatic chemicals. Therefore, lignin is observed as the major aromatic source of the bio-based economy.

Lignin valorisation can be roughly categorised into two sections:

(1) upstream which involves separation and isolation process of lignin from biomass (e.g., pulping and pyrolysis)

(2) downstream, where valorised products are obtained through depolymerisation and chemical modification of the isolated lignin (e.g., hydrogenolysis and hydrolysis)