Biomass type | Process type | Yield | Operating conditions | Main findings | Reference |
Olive mill waste water (OMW) | hydro thermal carbonization (HTC) | ~30% | ・ catalyst: citric acid; ・ temperature: 180˚C or 220˚C; ・ residence time: 14 h; ・ pressures: 9 bar (180˚C) and 24 bar (220˚C) | ・ the organic carbon content of the biochar is enhanced with increasing HTC temperature and pressure; ・ mass balance considerations confirm that the yield of biochar is associated with a low fraction of carbohydrates in OMW | [60] |
Two-phase olive mill waste (TPOMW) | TGA | ~22.4% | ・ pressure: 0.1 - 1.5 MPa; ・ peak temperature: 400˚C - 550˚C; ・ heating rate: 5 K∙min−1 | ・ biochar yield from pyrolysis of TPOMW decreased when both peak temperature and pressure increased; ・ an increase of both peak temperature and pressure results in a higher fixed-carbon yield and devolatilization rate | [58] |
Sunflower husks | thermochemical liquefaction | 574 gchar∙kg−1 husks | ・ temperature: 280˚C; ・ feed rate 30 g∙kg−1; ・ solvent: distilled water, methanol, ethanol, isopropanol and n-butanol | ・ HHV of the biochars were higher than that of the feedstock; ・ biochars compared favorably with coal on a Van Krevelen diagram; ・ at temperatures below 280˚C, the charring of the biomass is not complete, with some of the cell wall lignin still intact | [61] |
Vine shoots-derived biochar | laboratory-scale fixed-bed slow pyrolysis | na | ・ heating rate: ~5 K∙min−1; ・ pressure: 0.1 - 1.1 Mpa; ・ temperature: 400˚C - 600˚C | ・ particle size the most significant factor in determining the potential stability of biochars; ・ operating at higher peak temperatures leads to the production of more stable materials; ・ the absolute pressure decreased the tar content in the producer gas; ・ no statistically significant effects of increasing pressure on the aromaticity of biochar | [59] |