Influence of NaOH, Ni/Al₂O₃ and Ni/SiO₂ catalysts on hydrogen production from the subcritical water gasification of model food waste compounds

The production of hydrogen via subcritical water gasification of model food waste compounds, glucose and glutamic acid representing carbohydrate and protein has been studied. The influence of NaOH additive, Ni/Al₂O₃ and Ni/SiO₂ catalysts and combinations of these catalysts in relation to hydrogen production was investigated at a temperature of 330°C and 13.5MPa pressure. Generally, glucose produced more hydrogen gas than glutamic acid even with NaOH. Hydrogen production from the model food waste compounds in the presence of NaOH was superior to that of the investigated nickel catalysts supported on SiO₂ and Al₂O₃. The production of hydrogen gas increased when NaOH was added, whereas other gases, CO, CO₂ and hydrocarbons (C₁-C₄) decreased with increasing concentration of NaOH. Combination of the catalysts Ni/SiO₂ or Ni/Al₂O₃ with NaOH alkali only slightly increased hydrogen production. The addition of NaOH reduced the amount of CO₂, and tar produced during subcritical water gasification of the model compounds, unlike when Ni/SiO₂ and Ni/Al₂O₃ catalysts were used. Furthermore NaOH decreased the amount of carbon deposited on the Ni/SiO₂ and Ni/Al₂O₃ catalyst surface. However the formation of dawsonite was confirmed and provided experimental evidence of the reaction of sodium hydroxide with alumina in Ni/Al₂O₃, with a potential for decreased catalytic activity.