Hydrogen production by supercritical water gasification of food waste using nickel and alkali catalysts

Abstract

Supercritical water gasification (SCWG) of food waste was carried out with nickel and alkali catalysts (NaOH, KOH, Ca(OH)2, Na2CO3, NaHCO3 and K2CO3). The food waste was comprised of a variety of food items. The experiment was performed in a batch reactor at supercritical water (SCW) conditions of 400°C and 22.1MPa for 10mins. Hydrogen (H2) gas yield regarding the use of the catalysts was in the sequence; Ni-K2CO3 > Ni-NaOH > Ni-KOH > Ni-NaHCO3 > Ni > Ca(OH)2 > Ni-Na2CO3 > No catalyst. The results of this study indicate that using Ni was effective to support the steam reforming reaction. However its effects on the water gas shift reaction (WGSR) was little. Also carbon dioxide (CO2) was the predominant gas product in the presence of metal carbonates and bicarbonate. As a result, H2 selectivity was in the sequence, Ni-NaOH > Ni-KOH > Ni-K2CO3 > Ni-Ca(OH)2 > Ni > Ni-Na2CO3 > Ni-NaHCO3 > No catalyst. Furthermore, using 4g of NaOH was effective to shift the WGSR forward to produce a higher H2 yield and selectivity than when 4g of Ni was used. However, when equal amounts of Ni and NaOH were used, the conversion of food waste into gaseous products was necessary to produce more H2 during the WGSR. © 2014 WIT Press.