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 g_char∙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]