Sustainable hydrogen production via catalytic supercritical water gasification of microalgae biomass in glycerol-methanol mixture

Abstract

The reliance on fossil fuels has led to significant environmental issues, including greenhouse gas emissions and climate change. As global energy demand increases, the need for sustainable alternatives becomes crucial. Microalgae have emerged as a renewable and carbon-neutral source for hydrogen production through supercritical water gasification (SCWG) due to their rapid growth, minimal land requirements, and beneficial biochemical properties. This study examines hydrogen production from Dunaliella salina, Spirulina platensis, and Chlorella vulgaris through SCWG at 400°C, 242 bar, and a 45 min residence time. A 4 wt% glycerol/methanol mixture, simulating biodiesel byproducts, was used as the reaction medium with and without a 10 wt% cobalt catalyst at feed concentrations of 5, 10, and 15 wt%. Among microalgae, Dunaliella salina yielded the highest hydrogen mole fraction, reaching 65 % at 10 wt% feed concentration. The cobalt catalyst significantly enhanced hydrogen production (e.g., Dunaliella salina from 38.8 % to 58.5 % H₂ at 15 wt%), hydrogen selectivity (max 50.43 %), and gasification efficiency (max 14.5 %). Moreover, replacing deionized water with a glycerol/methanol medium proved highly beneficial. This substitution substantially increased hydrogen production, alongside notable improvements in selectivity and gasification efficiency, highlighting the synergistic effect of biodiesel byproducts as a reactive solvent in SCWG. These findings underscore the dual benefit of employing biodiesel-derived reaction media and cobalt catalysis in simultaneously enhancing the efficiency and performance of the gasification process. Among the studied species, Dunaliella salina showed the highest potential for clean hydrogen generation, confirming its promise as a strategic microalgal feedstock for future sustainable energy systems.