Different seaweed species were gasified in supercritical water as biomass feedstock. The experimental conditions were 500°C of temperature and 1 h of reaction time. The coke yields were found to be significantly lower than those obtained with lignocellulosic and protein contained wastes. The gaseous species detected contained mainly hydrogen, methane, and carbon dioxide. Hydrogen yields ranging between 11.8 and 16 g H2 kg-1 seaweed have been obtained. On the other hand, the methane yields were found to be in the range of 39 and 104 g CH4 kg-1 seaweed. Dissolved organic carbon (DOC) values of aqueous phase show the extent of higher gasification (Schumacher et al., 2011).

Guan et al. reported results from a systematic study of the gasification of the alga Nannochloropsis sp. in supercritical water at 450-550°C. The gaseous products were mainly H2, CO2, and CH4, with lesser amounts of CO, C2H4, and C2H6. Higher temperatures, longer reaction times, higher water densities, and lower algae loadings provided higher gas yields. The algae loading strongly affected the H2 yield, which more than tripled when the loading was reduced from 15 wt% to 1 wt%. The water density had little effect on the gas composition. The temporal variation of intermediate products indicated that some (e. g., alkanes) reacted quickly, whereas others (aromatics) reacted more slowly (Guan et al., 2012).