Gasification of humic acid in subcritical and supercritical water.
Temperature, feed concentration, reaction time and catalyst affect H2 production.
High H2 yield at 600 °C with 15 wt% humic acid, 15 wt% FeCl3 in 75 min at 24 MPa.
H2 and total gas yields increased exponentially with rising FeCl3 concentration.
FeCl3 promotes ring-opening reaction to accelerate humic acid degradation.