TY - JOUR
T1 - Highly efficient lignin depolymerization and enhanced bio-oil upgrading via in-situ hydrogenation
T2 - Impact of lignin structure
AU - Gao, Jie
AU - Cao, Yang
AU - Zhang, Yitian
AU - Luo, Gang
AU - Fan, Jiajun
AU - Clark, James H.
AU - Zhang, Shicheng
N1 - Publisher Copyright:
© 2024 Elsevier B.V.
PY - 2024/10/15
Y1 - 2024/10/15
N2 - The inherent structural rigidity of lignin poses a significant challenge to its direct hydrogenation to produce aromatic compounds, requiring harsh reaction conditions. In this study, microwave-assisted hydrothermal liquefication was employed to rapidly generate raw bio-oil under mild conditions, coupled with an in-situ hydrogenation strategy to upgrade its quality. A series of lignin substrates were characterized to establish the relationship between lignin characteristics and aromatic products. Grass lignin can produce low molecular weight bio-oil in high yields (50.4–60.7 %) within 30 min at 180 °C, which is attributed to the abundance of cleavable β-O-4 linkages in its uniform structure. In contrast, softwood lignin with abundant guaiacyl (G) units possessed a robust thermal stability, resulting in a low monomer yield, but a high selectivity to G-type products (97 %). The raw bio-oil was further upgraded through in-situ hydrogenation with Pd catalysts. Low reaction temperatures (60–100 °C) favored the hydrogenation of aromatic aldehydes and ketones to their alcohol products, while high temperatures (100–220 °C) promoted the deep hydrogenation of aromatic side chains to alkyl products. Besides, an upgraded bio-oil with a higher heating value (29.8 MJ/kg) was obtained. Furthermore, the hydrogenation mechanism was investigated through the kinetics of simulated bio-oils. The activation energy follows the order: dimer β-O-4 linkage < monomer aldehyde group < ketone group < C[dbnd]C linkage, which is consistent with the hydrogenation kinetics observed in real lignin bio-oil. Overall, this study highlights the impact of lignin characteristics on subsequent conversion and also enhances our understanding of the complex depolymerization/hydrogenation mechanisms during lignin upgrading.
AB - The inherent structural rigidity of lignin poses a significant challenge to its direct hydrogenation to produce aromatic compounds, requiring harsh reaction conditions. In this study, microwave-assisted hydrothermal liquefication was employed to rapidly generate raw bio-oil under mild conditions, coupled with an in-situ hydrogenation strategy to upgrade its quality. A series of lignin substrates were characterized to establish the relationship between lignin characteristics and aromatic products. Grass lignin can produce low molecular weight bio-oil in high yields (50.4–60.7 %) within 30 min at 180 °C, which is attributed to the abundance of cleavable β-O-4 linkages in its uniform structure. In contrast, softwood lignin with abundant guaiacyl (G) units possessed a robust thermal stability, resulting in a low monomer yield, but a high selectivity to G-type products (97 %). The raw bio-oil was further upgraded through in-situ hydrogenation with Pd catalysts. Low reaction temperatures (60–100 °C) favored the hydrogenation of aromatic aldehydes and ketones to their alcohol products, while high temperatures (100–220 °C) promoted the deep hydrogenation of aromatic side chains to alkyl products. Besides, an upgraded bio-oil with a higher heating value (29.8 MJ/kg) was obtained. Furthermore, the hydrogenation mechanism was investigated through the kinetics of simulated bio-oils. The activation energy follows the order: dimer β-O-4 linkage < monomer aldehyde group < ketone group < C[dbnd]C linkage, which is consistent with the hydrogenation kinetics observed in real lignin bio-oil. Overall, this study highlights the impact of lignin characteristics on subsequent conversion and also enhances our understanding of the complex depolymerization/hydrogenation mechanisms during lignin upgrading.
KW - Aromatic compounds
KW - In-situ hydrogenation
KW - Lignin biorefinery
KW - Renewable energy
UR - http://www.scopus.com/inward/record.url?scp=85204067211&partnerID=8YFLogxK
U2 - 10.1016/j.cej.2024.155837
DO - 10.1016/j.cej.2024.155837
M3 - Article
AN - SCOPUS:85204067211
SN - 1385-8947
VL - 498
JO - CHEMICAL ENGINEERING JOURNAL
JF - CHEMICAL ENGINEERING JOURNAL
M1 - 155837
ER -