A parametric study on supercritical water gasification of Laminaria hyperborea: A carbohydrate-rich macroalga

• L. hyperborea was gasified to produce substantial yields of hydrogen and methane.
• Gas yields and CGE increased with temperature, catalyst loading and reaction hold time.
• Ru/Al2O3 catalyst produced highest yields of methane and with CGE up to 98%.
• Sodium hydroxide produced highest yields of hydrogen up to 30 mol/kg.

The potential of supercritical water gasification (SCWG) of macroalgae for hydrogen and methane production has been investigated in view of the growing interest in a future macroalgae biorefinery concept. The compositions of syngas from the catalytic SCWG of Laminaria hyperborea under varying parameters including catalyst loading, feed concentration, hold time and temperature have been investigated. Their effects on gas yields, gasification efficiency and energy recovery are presented. Results show that the carbon gasification efficiencies increased with reaction temperature, reaction hold time and catalyst loading but decreased with increasing feed concentrations. In addition, the selectivity towards hydrogen and/or methane production from the SCWG tests could be controlled by the combination of catalysts and varying reaction conditions. For instance, Ru/Al2O3 gave highest carbon conversion and highest methane yield of up to 11 mol/kg, whilst NaOH produced highest hydrogen yield of nearly 30 mol/kg under certain gasification conditions.