Total utilization of lignin and carbohydrates in Eucalyptus grandis: an integrated biorefinery strategy towards phenolics, levulinic acid, and furfural

Abstract

Background: Lignocellulosic biomass, which is composed of cellulose, hemicellulose and lignin, represents the most abundant renewable carbon source with significant potential for the production of sustainable chemicals and fuels. Current biorefineries focus on cellulose and hemicellulose valorization, whereas lignin is treated as a waste product and is burned to supply energy to the biorefineries. The depolymerization of lignin into well-defined mono-aromatic chemicals suitable for downstream processing is recognized increasingly as an important starting point for lignin valorization. In this study, conversion of all three components of Eucalyptus grandis into the corresponding monomeric chemicals was investigated using solid and acidic catalyst in sequence. Results: Lignin was depolymerized into well-defined monomeric phenols in the first step using a Pd/C catalyst. The maximum phenolic monomers yield of 49.8 wt% was achieved at 240 °C for 4 h under 30 atm H 2. In the monomers, 4-propanol guaiacol (12.9 wt%) and 4-propanol syringol (31.9 wt%) were identified as the two major phenolic products with 90% selectivity. High retention of cellulose and hemicellulose pulp was also obtained, which was treated with FeCl 3 catalyst to attain 5-hydroxymethylfurfural, levulinic acid and furfural simultaneously. The optimal reaction condition for the co-conversion of hemicellulose and cellulose was established as 190 °C and 100 min, from which furfural and levulinic acid were obtained in 55.9% and 73.6% yields, respectively. Ultimately, 54% of Eucalyptus sawdust can be converted into well-defined chemicals under such an integrated biorefinery method. Conclusions: A two-step process (reductive catalytic fractionation followed by FeCl 3 catalysis) allows the fractionation of all the three biopolymers (cellulose, hemicellulose, and lignin) in Eucalyptus biomass, which provides a promising strategy to make high-value chemicals from sustainable biomass.

Unlocking Structure–Reactivity Relationships for Catalytic Hydrogenolysis of Lignin into Phenolic Monomers

“…Prolonging the reaction to 6 h led to decreased monomer yields (38.8 wt %). The results were in line with our previous reports …”

Development of ‘Lignin-First’ Approaches for the Valorization of Lignocellulosic Biomass

“…Softwood lignocellulose was effectively (77–98%) depolymerized in a mild lignin-first acidolysis process (140 °C, 40 min, entry 73 in Table 1 ) using dimethyl carbonate and ethylene glycol solvents/stabilization agent producing high yield (9 wt %) of aromatic monophenols (2020, second row in Figure 4 ) and preserving cellulose as evidenced by a 85% glucose yield after enzymatic digestion [ 92 ]. The total utilization of lignin and carbohydrates in eucalyptus towards phenolics, levulinic acid, and furfural was emphasized in another paper in 2020: Pd/C catalyst in methanol solvent was used in the hydrogenolysis step, 50 wt % maximum phenolic monomers yield was achieved (entry 74 in Table 1 ) [ 93 ]. Beech wood was directly converted into lignin derived monomers (20 wt % yield) and dimers and holocellulose derived light hydrocarbons in the presence of a sulfided NiMo/Al 2 O 3 catalyst in ethanol solvent at 260 °C (entry 75 in Table 1 ) [ 94 ].…”

Organosolv pretreatment assisted by carbocation scavenger to mitigate surface barrier effect of lignin for improving biomass saccharification and utilization

“…Biorefinery, an alternative technique to traditional petroleum refinery, aims at utilization of renewable lignocellulosic biomass to produce bio-based fuels, chemicals and materials [ 1 , 2 ]. In lignocellulosic biomass, cellulose and hemicellulose are considered as the economical constituents which are amenable to produce fermentable sugars and further be converted to biofuels and chemicals [ 3 , 4 ]. However, the presence of lignin in lignocellulosic biomass and the resulting complex lignocellulosic matrix make it highly resistant towards saccharification by microorganisms or enzymes to produce fermentable sugars [ 5 ].…”

“…After acid organosolv pretreatment and subsequent enzymatic hydrolysis, lignocellulosic biomass can be effectively fractionated into cellulosic sugars, hemicellulosic sugars and organosolv lignin [ 10 ]. As reported, the cellulosic and hemicellulosic sugars can be efficiently converted to bioethanol and value-added chemicals [ 3 , 4 ]. In the case of derived lignin, it offers promising opportunities to use lignin as antioxidants [ 11 ], adsorbents [ 12 ] and other bio-based materials [ 13 , 14 ].…”