**4.1. Lignin valorisation**

ninolytic peroxidase enzymes or laccase enzymes have been exploited to oxidise aromatic

Yi-Lin Chung et al. developed a catalytic and solvent-free method for synthesis of a lignin-poly (lactic acid) copolymer. The g-type poly(lactic acid) (PLA) copolymer, synthesised from graft polymerisation of lactide onto lignin, is catalysed by triazabicyclodecene (TBD) as depicted in **Figure 4**. It displays a glass transition temperature range from 45 to 85°C with multiphase melting behaviour. It also can be used to enhance UV absorption and reduce brittleness with-

**Figure 4.** Ring-opening polymerisation of lactide (LA) on lignin using triazabicyclodecene (TBD) catalyst scheme.

**Figure 5.** Quantitative analysis of product streams from organosolv lignin substrate. Reprinted with permission from

Reprinted with permission from Ref. [45]. Copyright (2013) American Chemical Society.

Ref. [46]. Copyright (2014) American Chemical Society.

units within lignin complex molecules [44].

out sacrificing its elasticity [45].

**3.3. Examples of lignin to value-added materials**

296 New Advances in Hydrogenation Processes - Fundamentals and Applications

Lignin valorisation is an approach or strategy to convert lignin obtained from any sources, especially biomass, into value-added products as shown in **Figure 6** [47]. Scientists have studied this strategy for many decades through variation of thermal, catalytic and biological approaches in order to break lignin down into its constituent monomers and oligomers as well as upgrading the resulting monomers to fuels or chemicals [48].

The strategy usually involved one or more processes in order to achieve maximum lignin conversion. For example, Gianpaolo Chieffi et al. studied the efficiency of integrating smart recycle and upcycle of biomass-derived waste stream with strategies for the preparation of functional carbonaceous and composite materials using Fe and Ni (cheap and abundant metal precursors) [49].

Lignin valorisation can be roughly categorised into two sections: (1) upstream which involved separation and isolation process of lignin (e.g. pyrolysis, hydrogenolysis and hydrolysis) and (2) downstream, where valorised products are obtained through depolymerisation and chemical modification of the isolated lignin (e.g. hydrodeoxygenation, catalytic cracking, hydrogenation and dehydrogenation) [50]. In this section, we focus on the downstream process which is to convert the lignin monomers to the fuels and chemicals via hydrogenation.
