Reactions of different food classes during subcritical water gasification for hydrogen gas production

The reactions of different food classes during alkaline subcritical water gasification have been investigated with a view on hydrogen gas production. Experiments were conducted with sub-stoichiometric amounts of H ₂O₂ for partial oxidation. NaOH was added to aid sample decomposition, reduce char/tar formation and to promote water-gas shift reaction. In general, hydrogen gas production depended on the class of food wastes including their chemical structure. Carbohydrate-rich food waste (glucose, molasses, tropical fruit mixture, whey powder) produced higher H ₂ gas yields than others (proteins and lipids). Lipid-rich samples were the most difficult to decompose into gasifiable intermediates and therefore produced the lowest H₂ yield. Generally, the addition of NaOH led to higher H₂ generation from all sample types. However, two separate side reactions namely, neutralization and saponification involving NaOH with protein- and lipid-rich samples, respectively were significant. Hydrogen production from carbohydrate-rich samples was most suited for the reaction conditions applied.