Catalyst-Free Depolymerization of Methanol-Fractionated Kraft Lignin to Aromatic Monomers in Supercritical Methanol

Shubho Ghosh, Masud Rana and Jeong-Hun Park ()
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Shubho Ghosh: Department of Environment and Energy Engineering, Chonnam National University, Gwangju 61186, Republic of Korea
Masud Rana: Department of Environment and Energy Engineering, Chonnam National University, Gwangju 61186, Republic of Korea
Jeong-Hun Park: Department of Environment and Energy Engineering, Chonnam National University, Gwangju 61186, Republic of Korea

Energies, 2024, vol. 17, issue 24, 1-19

Abstract: Lignin is considered a renewable source for the production of valuable aromatic chemicals and liquid fuel. Solvent depolymerization of lignin is a fruitful strategy for the valorization of lignin. However, Kraft lignin is highly prone to produce char (a by-product) during the hydrothermal depolymerization process due to its poor solubility in organic solvents. Therefore, the minimization of char formation remains challenging. The purpose of the present study was to fractionate Kraft lignin in methanol to obtain low-molecular-weight fractions that could be further depolymerized in supercritical methanol to produce aromatic monomers and to suppress char formation. The results showed that the use of methanol-soluble lignin achieved a bio-oil yield of 45.04% and a char yield of 39.6% at 280 °C for 2 h compared to 28.57% and 57.73%, respectively, when using raw Kraft lignin. Elemental analysis revealed a high heating value of 30.13 MJ kg −1 and a sulfur content of only 0.09% for the bio-oil derived from methanol-soluble lignin. The methanol extraction process reduced the oxygen content and increased the hydrogen and carbon contents in the modified lignin and bio-oil, indicating that the extracted lignin fraction had an enhanced deoxygenation capability and a higher energy content. These findings highlight the potential of methanol-soluble Kraft lignin as a valuable resource for sustainable energy production and the production of aromatic compounds.

Keywords: Kraft lignin; methanol-soluble lignin; hydrothermal liquefaction; bio-oil; phenolic monomer (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2024
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