Assessment of Iron(III) chloride as a catalyst for the production of hydrogen from the supercritical water gasification of microalgae

Alkali metal salts and supported transition metals have been the dominant catalysts used to maximise hydrogen production from supercritical water gasification (SCWG). Recently, FeCl3 has emerged as an alternative to these that has been found to be more effective in some cases reported in literature. However, to these authors’ knowledge, few studies exist that study this catalyst with none that involve microalgae as the feedstock. Investigation is reported into the effect of FeCl3 on the SCWG of Chlorella vulgaris for a range of temperatures (400–600°C) and biomass concentrations (1–3wt%), with comparisons made to other catalysts (KOH, Ru/C and their combinations). A significant decrease in hydrogen yield, carbon conversion and energy efficiency was observed with the addition of FeCl3, due to a reduced pH which suppressed the water gas shift reaction and catalysed of char forming reactions. This was in contrary to Ru/C and KOH catalysts, where those outcomes increased. Additionally, when FeCl3 was used with Ru/C, the ruthenium was poisoned, nullifying its positive effects. Consequently, FeCl3 is not a suitable catalyst for hydrogen production from microalgae, either alone or in conjunction with a ruthenium catalyst. [Display omitted] •FeCl3 significantly reduces hydrogen yield, carbon conversion and efficiency.•Lewis acid nature of the catalysts is the likely cause of negative effects.•Measurement of TIC is important for accurate gasification efficiency evaluation.•FeCl3 poisons ruthenium catalysts if used together.•The pH of the solution must be considered when considering new catalysts.