Catalytic Supercritical Water Gasification: Continuous Methanization of <i>Chlorella vulgaris</i>

Abstract

Continuous catalytic supercritical water gasification (CSCWG; 400 °C, 28 MPa) of microalgal biomass (Chlorella vulgaris) was carried out at the microalgae production site of ZHAW in Wädenswil (Switzerland) nonstop over a period of 100 h. Microalgae slurries (3–15 wt %) were successfully gasified to a methane-rich gas for 55 h. The low total organic carbon of the reactor effluent (<400 mg L–1) recorded during that period demonstrated the high catalytic activity of the Ru/C catalyst for converting microalgae to the gaseous products. The addition of a sulfur removal step with a commercial zinc oxide adsorbent was essential for protecting the catalyst against sulfur poisoning. A brine effluent rich in nutrients (N, K, S, P, Na) was withdrawn continuously from a salt separator. In summary, the use of a zinc oxide adsorbent upstream of the catalyst bed, together with a higher ruthenium loading of the catalyst, improved the long-term performance of the CSCWG process significantly.