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

Abstract

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 (1–3 wt%), 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.