Gasification of alga Nannochloropsis sp. in supercritical water

We report 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. On the basis of this observation and the complete set of experimental results, we propose a global reaction network for algae SCWG that includes parallel primary pathways to each of these two types of intermediate products. The intermediate products then produce gases.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► We report results for the gasification of the alga Nannochloropsis sp. in supercritical water. ► We propose a reaction network with two intermediates for algae SCWG. ► High temperature, long time, high density, and low algae loading give high gas yields. ► The H2 yield more than tripled as the algae loading decreased from 15 to 1 wt%. ► The activation energies show that H2, CH4, and CO2 form in independent reaction paths.