About this Research Topic
Lignin is one of the major components of lignocelluloses and the most abundant aromatic polymer on earth. It is an irregular aliphatic-aromatic heteropolymer synthesized from phenylpropane monomeric units with various carbon-oxygen and carbon-carbon interunit linkages. It is separated as waste in the pulp and biorefining industries. The value-added utilization of lignin is critical to the economical success of cellulose-based biorefining processes. Lignin shows great potential as a source for alternative fuels and chemicals. Its highly functionalized and aromatic nature allows its direct conversion to aromatic specialty and fine chemicals. Higher carbon content and lower oxygen content compared to the carbohydrate fractions in the biomass render it a promising feedstock for fuel and chemical production.
For the pulp and biorefining industries, lignin should be removed from hemicelluloses and cellulose. Various fractionation processes cause condensation of lignin, and this poses many difficulties for its valorization. Particularly, depolymerization of condensed lignin leads to low yields of monomers, and we have limited information about the structures of separated lignin. Therefore, other than developing viable valorization methods for separated lignin, structures of separated lignin deserve attention in order to elucidate the exact mechanisms by which it hydrolyzes and condenses during fractionation. This could open the way towards new fractionation and valorization methods.
Degradation of lignin plays an important role in many lignin valorization strategies. Recently, diverse degradation methods, including biological degradation, thermochemical pyrolysis, and catalytic depolymerization have been investigated for effective lignin utilization. However, the industrialization of these methods is still restricted by some critical issues such as low yields and product separation cost. Therefore, new degradation methods and catalysts are still needed for economically-feasible and effective valorization. Biological valorization of lignin is promising but shows low efficiencies and selectivities, so this subfield also requires further studies.
The Topic Editors encourage submissions of original research articles, perspectives and review articles that cover the following topics:
· New biomass fractionation methods for improving lignin quality
· Structural elucidation of native and separated/technical lignins
· Chemocatalytic depolymerization of lignin
· Biological degradation of lignin
· Upgrading of lignin to fuels and chemicals
· Lignin-based materials
Keywords: Lignin, Structure, Fuels, Chemicals, Materials
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