Franz Winter

Hydrogen-based direct reduction is a promising route to reduce CO2 emissions from primary ironmaking. However, the effect of elevated pressure on phase evolution and microstructural development of iron ore fines is not fully understood. This study investigates three iron ore fines with varying mineralogies and iron grades: a high-grade hematitic iron ore (A), a gangue-rich magnetitic iron ore (B) and its oxidized hematitic derivative (C). Reduction experiments were conducted in 100 % H2 at pressures of 5, 7 and 9 bar using a heating rate of 60 K/min. Phase transformations were monitored by time-resolved in-situ XRD and heat-map analysis, while microstructural changes were characterized by SEM/EDX. The pressure response depended on the iron ore type. For hematitic iron ore A, the first detectable metallic iron (Fe0) reflection shifted from 260 °C at 5 bar to 240 °C at 7 and 9 bar, representing a 40 °C decrease compared with 1 bar. Magnetitic iron ore B showed no shift above 3 bar, with Fe0 formation at 280 °C across 5 to 9 bar. Similarly, oxidized iron ore C exhibited Fe0 formation at 280 °C for 5-9 bar, indicating a pressure-induced shift compared to lower pressures but no further acceleration beyond 5 bar. SEM/EDX analysis revealed reduction-induced cracking, formation of Fe-rich domains and locally compacted regions. Overall, elevated pressure promotes earlier metallic iron formation, although these effects depend on iron ore mineralogy and microstructural accessibility.

Thermally activated biochar catalysts from straw, eucalyptus, and sewage sludge were prepared under eight gasification conditions and evaluated for catalytic toluene decomposition relevant to syngas reforming. Steam treatment and high burn off levels promoted pore widening, whereas CO2 activation preserved the microporous structure of the samples. Notably, mesopore formation was influenced more by the precursor than by the gasification conditions. High-temperature gasification improved thermal oxidation stability as well as thermal and electrical conductivity. Sewage sludge-derived biochars, characterized by high inorganic content and low total porosity, exhibited stable but moderate toluene conversion (0.6–0.3 over 60 min). In contrast, lignocellulosic biochars achieved higher initial conversion (up to 0.9) but deactivated more rapidly due to pore accessibility limitations. Multivariate statistical analysis (principal component analysis and Spearman’s correlation) identified microporosity, electrical and thermal conductivity as key parameters governing initial catalytic activity, while mesoporosity became critical during prolonged reaction, highlighting structure–performance relationships in biochar-based catalysts.

A radiotracer-supported investigation was carried out on the measurement of residence time distribution (RTD) of a continuously operated suspension reactor for thermochemical energy storage. In the continuously stirred tank reactor (CSTR) copper sulfate pentahydrate (CuSO4∙5H2O) was dehydrated and (re)hydrated. Radiocopper (64Cu) in the form of neutron-activated copper sulfate was used as the radiotracer for the RTD experiments at different operating conditions. With the radiotracer being in identical physicochemical form like the thermochemical material used for energy storage, an in-operando RTD measurement was archived using 64CuSO4 as a radiotracer compound. The results showed that the particle mean residence time, calculated from the RTD, indicates that there is no direct correlation to the oil mean residence time. The strongest influence on the particle mean residence time holds the oil viscosity, where the particle residence time increases with higher oil viscosity. The impact of the particle size on the particle mean residence time could be neglected, due to the same range in size of the used particles during the hydration and dehydration experiments. No influence of the steam bubbles during dehydration could be observed, however, the use of a nitrogen flow from the bottom of the reactor prolonged the particle mean residence time. The results of the investigation can be used to optimize the reactor design and process parameters not only for oil suspended thermochemical reactors but also in other reactors where 64Cu in the form of CuSO4 can be applied.

The environmental impacts from fossil fuel use have accelerated the global transition to sustainable energy sources. Hydrogen has become a promising alternative due to its high energy density and clean combustion. However, hydrogen production streams are frequently contaminated with methane, which needs efficient, durable, and cost-effective purification technologies such as pressure swing adsorption (PSA). The present study provides a comparative evaluation of biomass-derived activated carbons and a commercial activated carbon for hydrogen–methane separation. High-surface-area activated carbons were synthesized from sustainable pine and birch precursors via chemical activation using potassium hydroxide (KOH, impregnation ratio 3:1) at 800 °C. Their dynamic adsorption performance was systematically assessed in a fixed-bed setup under a PSA system operating at pressures of 25, 35, and 50 bar, using a of hydrogen–methane gas mixture, where methane feed concentrations ranging from 10 to 30 vol%. This work focuses on the behavior of the adsorbent material and does not constitute a complete PSA process evaluation. The biomass-derived activated carbons showed well-developed textural characteristics, with specific surface areas up to 1416 m² g⁻¹, which exceeded that of the commercial reference material (1023 m² g⁻¹). This improved pore structure was reflected in their adsorption behavior at an operating pressure of 50 bar; the birch-derived carbon achieved a methane uptake of 10.5 mol kg⁻¹, more than twice the capacity of 5.30 mol kg⁻¹ measured for the commercial adsorbent. Beyond initial adsorption capacity, the study emphasizes operational durability and reusability. Cyclic adsorption–desorption experiments, supported by Raman spectroscopy, revealed pronounced structural changes in the commercial activated carbon under repeated operational stress, as indicated by an increase in the I_D/I_G ratio from 1.08 to 1.24. In contrast, the biomass-derived activated carbons preserved their morphological integrity and adsorption efficiency over successive cycles. These findings demonstrate that pine- and birch-derived activated carbons are not only sustainable alternatives but also operationally stable adsorbents capable for hydrogen purification processes.

The environmental impacts from fossil fuel use have accelerated the global transition to sustainable energy sources. Hydrogen has become a promising alternative due to its high energy density and clean combustion. However, hydrogen production streams are frequently contaminated with methane, which needs efficient, durable, and cost-effective purification technologies such as Pressure Swing Adsorption (PSA). The present study provides a comparative evaluation of biomass-derived activated carbons and a commercial activated carbon for hydrogen–methane separation. High surface-area activated carbons were synthesized from sustainable pine and birch precursors via chemical activation using potassium hydroxide (KOH, impregnation ra-tio 3:1) at 800 °C. Their adsorption performance was systematically assessed in a fixed-bed PSA system operating at pressures of 25, 35, and 50 bar, with a gas mixture of hydrogen-methane, where methane feed concentrations was ranging from 10 to 30 vol%. The biomass-derived activated carbons showed well-developed textural characteristics, with specific surface areas up to 1416 m² g⁻¹, exceeding that of the commercial reference material (1023 m² g⁻¹). This improved pore structure was reflected in their adsorption behavior at an operating pressure of 50 bar, the birch-derived carbon achieved a methane uptake of 10.5 mol kg⁻¹, more than twice the capacity measured for the commercial adsorbent of 5.30 mol kg⁻¹. Beyond initial adsorption capacity, the study emphasizes operational durability and reusability. Cyclic adsorption–desorption experiments, supported by Raman spectroscopy, revealed pronounced structural degradation in the commercial activated carbon under repeated operational stress, as indicated by an increase in the ID/IG ratio from 1.08 to 1.24. In contrast, the biomass-derived activated carbons preserved their morphological integrity and adsorption efficiency over successive cycles. These findings demonstrate that pine- and birch-derived activated carbons are not only sustainable alternatives but also operationally stable adsorbents capable for hydrogen purification processes.

Potassium carbonate sesquihydrate is a promising thermochemical energy storage material in the low- to mid-temperature range < 150°C, but its practical implementation is often limited by agglomeration and deliquescence during hydration. To address these challenges, this study investigates the reversible dehydration of K2CO3·1.5H2O in a multi-phase suspension reactor, aiming to prevent agglomeration and improve reaction performance compared to conventional reactor concepts, by suspending the salt in an inert liquid phase that maintains efficient heat and mass transfer. Up to ten dehydration-hydration cycles were conducted in a lab-scale suspension reactor using mineral oil, silicone oil, and mixtures thereof as suspension media. Results show that silicone oil effectively prevents agglomeration and enables stable cycling over ten cycles, achieving dehydration conversions of up to 93% at 145°C. A mixture containing 20 wt% silicone oil in mineral oil provided comparable stability and performance in five dehydration-hydration cycles while reducing silicone oil demand and therefore material costs significantly. Hydration experiments performed in a Dewar reached consistent temperature lifts of 23-27 K and maximum temperatures between 51°C and 85°C across varying silicone oil contents and starting temperatures. The results demonstrate good cycle stability of K2CO3·1.5H2O in the multi-phase suspension reactor and further confirm this reactor concept as a scalable approach for mitigating agglomeration in salt hydrate-based thermochemical energy storage systems.