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