Hydrogen production by supercritical water gasification of black liquor: Use of high temperatures and short residence times in a continuous reactor

Abstract

The Supercritical Water Gasification (SCWG) of black liquor (BL) to obtain hydrogen and dispose of organic waste simultaneously has been studied in a continuous reactor employing short residence times. The experiments were conducted at 600–700 °C, with times between 24.5–29.1 s, at 23 MPa and feedstock was diluted to different concentration levels (0.81–2.43 wt.%). Furthermore, different NaOH concentrations (0–1.2 wt.%) were added to maintain a basic medium and avoid the polymerization of the compounds. Hydrogen production and COD removal was conducted with short residence times. The best results regarding hydrogen yield were achieved at 700 °C, 24.5 s residence time and 0.9 wt.% NaOH concentration, with a production of 38.68 mol H2/kgsample. In contrast, and regarding COD removal, the best results were obtained at 700 °C, with 24.5 s residence time and the highest feed COD concentration used (2.43 wt.%). The COD removal levels reached were between 65–90 %.