Catalytic depolymerisation of isolated lignins to fine chemicals using a Pt/alumina catalyst: part 1—impact of the lignin structure

Abstract

Catalytic depolymerisation of lignins with different β-O-4 linkage percentages affected both the yield and the nature of aromatic monomeric products.

Paving the Way for Lignin Valorisation: Recent Advances in Bioengineering, Biorefining and Catalysis

“…[194] Interestingly,t here is ag ood correlation between the relative yields obtained from the catalytic depolymerisation and analytical chemical degradation by thioacidolysis,w hich is based on b-ether bond cleavage.T his example suggests that the thioacidolysis method constitutes auseful, correlative approach for ranking lignin streams according to their potential for production of mono-aromatics products.R egarding the lignin residues, GPC traces after reaction were similar for each lignin, suggesting convergence to ah ighly condensed lignin that is resistant to further depolymerisation.…”

“…Thee ffectiveness of ac atalyst either for performing ap articular chemical transformation or for the cleavage of aspecific linkage can then be better assessed. [194] Such astrategy circumvents the difficulties associated with the limitations of simple model compounds. Indeed, these often offer ap oor representation of the actual lignin structure (reactions on model compounds are discussed in greater detail later in this review), and such results can thus typically only with difficulty be extrapolated to "real" lignins.…”

“…[194] By contrast, for lignins from chemical pulping processes (e.g., Kraft, soda lignins and lignosulfonates) b-O4linkages represent fewer than 10 %ofthe connections. [190] In addition, extensive condensation of lignin fragments yields strong and recalcitrant carbon-carbon bonds.A sac onsequence of the highly varied and complex chemical/bonding properties of different technical lignins,t here is,u nfortunately,no"one-size-fits-all" solution for catalytic downstream processing of these polymeric technical lignin streams.Nevertheless,contemporary methodologies for lignin utilisation and valorisation can be broadly divided into two primary categories:1 )convergent approaches,a nd 2) stepwise approaches (Scheme 9).…”

“…[188][189][190][191][192][193] Theabundances of different C À Oand C À C linkages in technical lignins,t herefore,a re likely to differ substantially from those determined for the native lignin, [190,194] ar ealisation that greatly impacts any choices made for further depolymerisation. An example of the impact of pretreatment severity on the nature of the lignin isolated is shown in Figure 3, in which mild acetolysis produces alignin high in b-ethers,w hereas almost no native lignin identity remains following the harshest pretreatment.…”

Structural Characterization of Lignin Isolated from Wheat-Straw during the Alkali Cooking Process

“…Lignin is a structurally complex polyphenolic biomacromolecule consisting primarily of three basic structural phenylpropane units: syringyl (S), guaiacyl (G), and p-hydroxyphenyl (H). Lignin is composed of different substructures, including the ether (β-O-4, α-O-4, and 4-O-5) and C-C linkages (β-β, β-5, β-1, and 5-5), and the proportion of β-O-4 linkages of the lignin obviously affects the distribution of degraded products and yield of depolymerized monomeric products (Bouxin et al 2015). Each of these substructures varies according to the biological species and the chemical method used for its extraction (Zhang et al 2016).…”