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 13.5 MPa 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.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights▶ Subcritical water gasification of model food waste compounds showed that production of hydrogen gas increased when NaOH was added in the presence of Ni catalysts. NaOH also reduced the amount of CO2, and tar produced and decreased the amount of carbon deposited on the Ni/SiO2 and Ni/Al2O3 catalyst surface.