Hydrothermal carbonization: Process water characterization and effects of water recirculation

- Poplar wood was treated hydrothermally at 220 °C and process water was analyzed.
- Polar, aromatic compounds, and substances of higher molecular weight were detected.
- Accumulated organic acids in the liquid phase catalyze dehydration reactions.
- Recirculated reactive compounds polymerize and form additional solid substance.
- Overall process performance is greatly enhanced by recirculation.