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Table 1 Summary of thermochemical and catalytic technologies for lignin conversion [25]

From: Development of Rhodococcus opacus as a chassis for lignin valorization and bioproduction of high-value compounds

Technology Main product Product application Process notes
Gasification Syngas (gas) Production of energy, hydrogen, and methanol (methanol synthesis); alkanes (Fischer–Tropsch); isobutane (isosynthesis); ethanol (fermentation and catalysts); aldehydes and alcohols (oxosynthesis) Performed under high temperatures (> 700 °C); can involve the addition of water and catalyst
Fast pyrolysis/hydrothermal liquefaction (HTL) Bio-oil (liquid) Production of energy and various liquid fuels (e.g., biogasoline) by catalytic upgrading Performed at 250 to 700 °C; can involve the addition of water (HTL), hydrogen (hydropyrolsis) and catalyst (catalytic pyrolysis)
Torrefaction/slow pyrolysis Biochar (solid) Used as a more optimized solid fuel for combustion Performed at 200 to 350 °C
Solvolysis Soluble lignin fragments (liquid) Phenolics and alkyl phenolics Two main categories
(A) Acid- and base-catalyzed depolymerization
(B) Supercritical solvent depolymerization
Hydrogenolysis Soluble lignin fragments (liquid) Phenolics and alkyl phenolics Hydrogen donor (e.g., hydrogen gas, alcohol, or acid) and a catalyst can be used to cleave linkages
Oxidative cracking Soluble lignin fragments (liquid) Aromatic aldehyde, ketones, and carboxylic acids Linkages in lignin can be cleaved by an oxidant (e.g., air and hydrogen peroxide) and a catalyst