Combining residual iron dust and biomass fly ash as in-situ waste-based catalysts to promote tar reduction and enhance producer gas quality from biomass steam gasification

Abstract

This work explored the potential of industrial biomass fly ash (BFA) and residual iron dust (RID) as novel in-situ catalysts for steam gasification of residual forest biomass. Three catalysts were developed using these materials. First, G_BFA was granulated with water and self-hardened to form a chemically and mechanically stable material, which was afterwards calcined. G_BFA + RID was prepared using the same method but incorporating both BFA and RID as raw materials. Finally, a fraction of the latter was reduced in a 10 %vol.H₂/N₂ atmosphere – G_{BFA + RID reduced}. The catalytic performance of these materials was assessed using toluene cracking and biomass steam gasification experiments. All catalysts exhibited potential for toluene cracking, particularly G_{BFA + RID reduced}, which increased gas yield by 45-fold and H₂ yield by 126-fold. All catalysts demonstrated catalytic activity when applied in bench-scale fluidised bed gasification experiments. G_{BFA + RID reduced} exhibited the highest activity, reaching a 93 % tar conversion and enhancing hydrogen production by 174 % compared to the reference condition (inert alumina granules), demonstrating the synergistic effects of Fe⁰ and CaO. This catalyst improved producer gas quality, leading to H₂ concentration over 55 %vol._{dry, and inert (N2, Ar) free gas}. Another key strength of this work is the in-situ application of catalysts directly inside the gasifier, which leverages the thermal inertia of the reactor, offering a more energy-efficient and simplified process design. Additionally, the catalysts were produced at costs between 3.4 and 13.5 €·kg⁻¹_catalyst, substantially lower than conventional catalysts, further supporting their potential as cost-effective and sustainable alternatives. Overall, this study demonstrated that waste-derived materials can repurpose industrial residues while enhancing clean energy production.