Ask Sødahl Lysne defended his PhD on NTNU Friday 8 March 2024.
Thesis title: Steam reforming of biomass gasification tar impurities with Ni-Co/Mg (Al)O catalysts - Experimental studies using model tar components. His project is part of Bio4Fuels Work Package 4.2.
Summary of thesis
Hydrotalcite-derived Ni-Co/Mg(Al)O catalysts with a range of different Ni-Co ratios, Ni+Co loading, calcination temperatures and noble metal promotion (Pt/Pd/Rh) were prepared, targeting low-coking steam reforming of biomass gasification tar impurities. Fresh catalysts were characterized by XRD, ICP-MS, XRF, N2-physisorption, H2-chemisorption and TPR. All catalysts were tested through experimental studies with model tar components. The effects of key operating parameters, including temperature, steam concentration, tar loading and model tar composition, were additionally investigated. The benefits of the bi-metallic Ni-Co/Mg(Al)O catalyst was demonstrated, with intermediate Ni-Co ratios providing a suitable compromise between coke formation resistance associated with low Ni-Co ratios and the higher initial activity of high Ni-Co ratio catalysts. Post-run coke characterization by TGA-TPO-MS, Raman spectroscopy and STEM/EDS contribute to the understanding of the highly attractive resistance towards deactivation by coke formation associated with Ni-Co catalysts.
A coke classification system (based on characteristic TPO-MS coke combustion temperatures) was proposed, including soft coke A (undeveloped surface carbon), hard coke B1.1 (initial scattered carbon filaments), B1.2 (strongly deactivating metal particle encapsulating coke), B2 (carbon filament clusters and fused filaments) and B3 (strongly deactivating bulk encapsulating coke). Critical low-temperature (around 650 °C) and tar loading limits (below 20 g/Nm3) were identified, below/above which rapid deactivation by coke formation was observed (20-20 wt% Ni-Co sample). Noble metal promotion was shown to enhance bio-syngas in situ activation performance (with Rh > Pt > Pd), but did not considerably affect deactivation by coke formation. A critical Ni+Co loading limit was found (above 30 wt% Ni+Co), below which high dispersion metal particles were obtained. Strong deactivation by high-coordination active site tar inhibition and coke formation effects were observed with the high-dispersion samples. High-temperature calcination (800 °C) was found to reduce the strong deactivation effects associated with small-diameter metal particles, proposed to result from increasing coke and/or coke precursor gasification rates assisted by Mg(Al)O support basic sites.
The potential of the Switch-SRCG (cyclic steam reforming and coke gasification) dual-bed design was demonstrated, reducing overall coke deposition with both Ni and Ni-Co catalysts. The concept provides continuous on-stream catalyst regeneration by coke gasification, representing a novel approach to net low-coking biomass gasification tar reforming.
More information about the defence at NTNU's website.