Base-Catalyzed Depolymerization of Biorefinery Lignins

Abstract

Lignocellulosic biorefineries will produce a substantial pool of lignin-enriched residues, which are currently slated to be burned for heat and power. Going forward, however, valorization strategies for residual solid lignin will be essential to the economic viability of modern biorefineries. To achieve these strategies, effective lignin depolymerization processes will be required that can convert specific lignin-enriched biorefinery substrates into products of sufficient value and market size. Base-catalyzed depolymerization (BCD) of lignin using sodium hydroxide and other basic media has been shown to be an effective depolymerization approach when using technical and isolated lignins relevant to the pulp and paper industry. To gain insights in the application of BCD to lignin-rich, biofuels-relevant residues, here we apply BCD with sodium hydroxide at two catalyst loadings and temperatures of 270, 300, and 330 °C for 40 min to residual biomass from typical and emerging biochemical conversion processes. We obtained mass balances for each fraction from BCD, and characterized the resulting aqueous and solid residues using gel permeation chromatography, NMR, and GC–MS. When taken together, these results indicate that a significant fraction (45–78%) of the starting lignin-rich material can be depolymerized to low molecular weight, water-soluble species. The yield of the aqueous soluble fraction depends significantly on biomass processing method used prior to BCD. Namely, dilute acid pretreatment results in lower water-soluble yields compared to biomass processing that involves no acid pretreatment. Also, we find that the BCD product selectivity can be tuned with temperature to give higher yields of methoxyphenols at lower temperature, and a higher relative content of benzenediols with a greater extent of alkylation on the aromatic rings at higher temperature. Overall, this study shows that residual, lignin-rich biomass produced from conventional and emerging biochemical conversion processes can be depolymerized with sodium hydroxide to produce significant yields of low molecular weight aromatics that potentially can be upgraded to fuels or chemicals.

Continuous catalytic depolymerisation and conversion of industrial kraft lignin into low-molecular-weight aromatics

“…Studies on base-catalysed depolymerisation of lignin to produce phenolic compounds, in particular, have been conducted in various research efforts and are indeed current mainstay research [11][12][13][14][15][16][17]. The fact that soda is already adopted within the pulping processes promotes the potential of employing such homogeneous alkaline catalysis-from a process integration perspective.…”

“…The generated bio-oil solution was applied on wood and exhibited a good performance in improving its fungal resistance, introducing a new application for the produced reaction mixture from such process. In a very recent research effort by Katahira and co-workers [12], basecatalysed depolymerisation was applied on residual lignin- Fig. 1 Structures of the three primary building blocks of lignin (monolignols).…”

Promising Techniques for Depolymerization of Lignin into Value‐added Chemicals

“…Lignin‐based phenols come from many processes of thermal chemistry (pyrolysis, hydro/solvo‐thermal and combined methods such as catalytic pyrolysis and hydrogenolysis) ,,,,,,,,,,,,. Based on the standpoint in industrial vanillin production that not only yield but also selectivity or complexity of product mixture determine the production feasibility, the potential phenols that are generated with considerable yield and/or selectivity are collected in Figure .…”

Cooking with Active Oxygen and Solid Alkali: A Promising Alternative Approach for Lignocellulosic Biorefineries

“…[42] Lignin could be depolymerized into aromatic products with ac onversion of approximately 50 %a nd at otal selectivity of more than 90 %t hrough af ragmentation-hydrogenolysis process in alcoholo ver nickel-based catalysts. [44] Am ethod for the depolymerization of oxidized lignin to more than 60 wt %y ield of low-molecularmass aromatics was developed. [44] Am ethod for the depolymerization of oxidized lignin to more than 60 wt %y ield of low-molecularmass aromatics was developed.…”