Viktor Hacker & D.J. Liu
On 10/11 November 2021, the Topical Meeting on Potential for cost reduction and performance improvement for PEMFC at component and system level took place at Graz University of Technology. Due to the prevailing Corona situation at the time, the event was geared largely towards online participation, but (additional) personal attendance was also possible. A video stream of the event and interactive discussion of questions, both via chat and directly, allowed for a lively meeting in the auditorium of Graz University of Technology and online.
M.G. Hosseini, V. Daneshvari-Esfahlan, S. Wolf & V. Hacker
Nitrogen-doped reduced graphene oxide-supported palladium–cobalt nanoparticles (PdCo NPs/NrGO NSs) are synthesized and used as a high-performance and low-cost anodic catalyst for direct hydrazine–hydrogen peroxide fuel cells. The SEM and TEM images of PdCo NPs/NrGO NSs show the uniform metal nanoparticle distribution on the NrGO NSs. The reduction of the oxygen functional groups and the doping of the nitrogen atoms in the GO framework are confirmed by FT-IR and XRD spectroscopic studies. The Pd catalysts modified by Co exhibit a higher catalytic activity, lower onset potential, better durability, and lower impedance values than unmodified Pd catalysts for the electro-oxidation of hydrazine. The kinetic studies show a first-order reaction with an activation energy of 12.51 kJ mol-1. A direct hydrazine–hydrogen peroxide fuel cell with PdCo NPs/NrGO NSs as anode and Pt/C as cathode provides an open circuit voltage of 1.76 V and a maximum power density of 148.58 mW cm-2 at 60 °C, indicating that the PdCo NPs/NrGO NSs are an economical, high performance and reliable anode catalyst for the direct hydrazine–hydrogen peroxide fuel cell.
RSC Adv., 2021, 11, 39223
Astrid Loder, Matthäus Siebenhofer, Andreas Böhm, Susanne Lux
Direct reduction of mineral iron carbonate with hydrogen is a high-potential candidate for carbon dioxide emission reduction in the iron and steel industry. This novel technology provides a new route for ‘clean’ iron production. For economic implementation, a sufficient supply of hydrogen is crucial. Up to now only highly pure hydrogen sources were used for the direct reduction. On the way to a sustainable, completely hydrogen-based iron production, low-grade hydrogen sources need to be considered. The effect of the hydrogen concentration and the impact of matrix constituents such as methane and carbon dioxide in the hydrogen source on the direct reduction of mineral iron carbonate with hydrogen at 873 K were investigated in this project. It was shown that complete iron carbonate conversion is possible at a metallization degree of 78 wt% with hydrogen concentrations as low as 55 vol%. Carbon dioxide in the feed gas (27–63 vol%) favors magnetite formation instead. Hydrogen is also consumed by the reverse water gas shift reaction in the formation of carbon monoxide. Methane in the feed gas (15–80 vol%) does not have a negative impact on the composition of the solid product. These results suggest that methane-rich hydrogen sources (e.g., coke oven gas) are viable options for direct iron carbonate reduction opening up a novel pathway for clean iron production from mineral iron carbonate with low-grade hydrogen sources.
Cleaner Engineering and Technology, Volume 5, December 2021
M. Bodner, Ž. Penga, W. Ladreiter, M. Heidinger, & V. Hacker
Fuel starvation is a major cause of anode corrosion in low temperature polymer electrolyte fuel cells. The fuel cell start-up is a critical step, as hydrogen may not yet be evenly distributed in the active area, leading to local starvation. The present work investigates the hydrogen distribution and risk for starvation during start-up and after nitrogen purge by extending an existing computational fluid dynamic model to capture transient behavior. The results of the numerical model are compared with detailed experimental analysis on a 25 cm2 triple serpentine flow field with good agreement in all aspects and a required time step size of 1 s. This is two to three orders of magnitude larger than the time steps used by other works, resulting in reasonably quick calculation times (e.g., 3 min calculation time for 1 s of experimental testing time using a 2 million element mesh).
Energies 2021, 14(23), 7929
G. Hosseini, V. Daneshvariesfahlan, H. Aghajani, S. Wolf & V. Hacker
In the present work, nitrogen-doped reduced graphene oxide-supported (NrGO) bimetallic Pd–Ni nanoparticles (NPs), fabricated by means of the electrochemical reduction method, are investigated as an anode electrocatalyst in direct hydrazine–hydrogen peroxide fuel cells (DHzHPFCs). The surface and structural characterization of the synthesized catalyst affirm the uniform deposition of NPs on the distorted NrGO. The electrochemical studies indicate that the hydrazine oxidation current density on Pd–Ni/NrGO is 1.81 times higher than that of Pd/NrGO. The onset potential of hydrazine oxidation on the bimetallic catalyst is also slightly more negative, i.e., the catalyst activity and stability are improved by Ni incorporation into the Pd network. Moreover, the Pd–Ni/NrGO catalyst has a large electrochemical surface area, a low activation energy value and a low resistance of charge transfer. Finally, a systematic investigation of DHzHPFC with Pd–Ni/NrGO as an anode and Pt/C as a cathode is performed; the open circuit voltage of 1.80 V and a supreme power density of 216.71 mW cm−2 is obtained for the synthesized catalyst at 60 °C. These results show that the Pd–Ni/NrGO nanocatalyst has great potential to serve as an effective and stable catalyst with low Pd content for application in DHzHPFCs.
Catalysts. 2021, 11, 22 p., 1372
Paul Demmelmayer and Marlene Kienberger
Fermentation of residues or side streams can be used to produce valuable products, such as carboxylic acids. Reactive solvent extraction is widely studied as isolation method for lactic acid from fermentation broths. Here, we investigate the reactive extraction of lactic acid from sweet sorghum silage press juice using different extractants, modifiers, and diluents. Besides a high extraction efficiency, a low crud formation with this highly complex raw material is targeted. Depending on the solvent phase composition, an extraction efficiency of up to 41.1 % was reached using DOA/ALIQ:1–octanol:n–nonane. The crud layer was highly influenced by the applied diluent and amounted to 2.6-42.3 vol% of the total mixture volume. The back-extraction experiments showed, that up to 98.2 % of lactic acid were recovered. Summarizing, the results show that reactive solvent extraction of lactic acid is applicable to highly complex process streams, and crud formation can be reduced by adjusting the solvent phase composition.
Separation and Purification Technology 2021, 120090
Sebastian Bock, Bernd Stoppacher, Karin Malli, Michael Lammer and Viktor Hacker
Decentralized hydrogen production is a promising pathway to use locally available, renewable resources and establish regional value chains. Besides the successful demonstration of hydrogen production from real producer biogas in at Ökostrom Mureck a techno-economic study was conducted to proof the economic viability of the technology.
The present study proofs the Reformer Steam Iron Process, conceptualized in the research group of Prof. Viktor Hacker at CEET, as an efficient and economically favorable option for decentralized high-purity hydrogen production.
The cold gas efficiency (CGE) for hydrogen production from biogas was estimated as 60–78%. An external recirculation was found to increase the CGE by +44%rel. for the predominant Fe–FeO conversion step. A pinch analysis proofed the full thermal integration of the process independent of the varied process parameters.
The economic feasibility was ascertained based on a case scenario for hydrogen production at a 3 MWth biogas plant. The system efficiency for hydrogen production was estimated at 62.5%, uncoupling the excess heat for district heating increased the overall system efficiency up to 84%. The costs for hydrogen production from biogas were estimated at 2.27 € kgH2.
Energy Conversion and Management 2021, 250, 114801
doi.org/10.1016/j.enconman.2021.114801 (Open Access)
Maximilian Grandi, Kurt Mayer, Matija Gatalo, Gregor Kapun, Francisco Ruiz-Zepeda, Bernhard Marius, Miran Gaberšček and Viktor Hacker
Electrochemical impedance spectroscopy is an important tool for fuel-cell analysis and monitoring. This study focuses on the low-AC frequencies (2–0.1 Hz) to show that the thickness of the catalyst layer significantly influences the overall resistance of the cell. By combining known models, a new equivalent circuit model was generated. The new model is able to simulate the impedance signal in the complete frequency spectrum of 105–10−2 Hz, usually used in experimental work on polymer electrolyte fuel cells (PEMFCs). The model was compared with experimental data and to an older model from the literature for verification. The electrochemical impedance spectra recorded on different MEAs with cathode catalyst layer thicknesses of approx. 5 and 12 µm show the appearance of a third semicircle in the low-frequency region that scales with current density. It has been shown that the ohmic resistance contribution (Rmt) of this third semicircle increases with the catalyst layer’s thickness. Furthermore, the electrolyte resistance is shown to decrease with increasing catalyst-layer thickness. The cause of this phenomenon was identified to be increased water retention by thicker catalyst layers.
Energies 2021, 14(21), 7299
Austrian researchers have demonstrated a chemical looping system can be retrofitted into biogas plants. It is said the new tech can produce high-purity hydrogen for fuel cells on an industrial scale. The scientists concerned said their system could produce hydrogen, on a decentralized basis, for €5/kg.
Verfahrenstechnik. Wasserstoff gilt als Energieträger der Zukunft. Ein Forschungsteam der Technischen Universität (TU) Graz fand heraus, wie man ihn umweltfreundlich aus Bioabfällen herstellen kann.
Die Presse, Wissen und Innovation
Fabian Zapf, Thomas Wallek
Instance selection aims at selecting model training data in a way that the performance of the trained models is maximized. In the context of modeling chemical processes by artificial neural networks, it can serve as an essential preprocessing step since measurement data of such processes are commonly highly clustered and thus far away from being ideally normally distributed. In this paper, four filter methods from literature and a newly proposed method for data selection are tested and combined with a convex hull data selection algorithm, which results in ten different selection approaches. These approaches are applied to five selected datasets by training feed-forward artificial neural networks with the produced split datasets. The final mean model deviation is used to quantify the algorithms’ performance and their standard deviation to provide information about their reproducibility. It is found that the convex hull extended algorithms self-organizing maps based stratified sampling with a proportional allocation rule and the newly proposed self-information-based subset selection perform best for real-world chemical engineering data.
Applied Soft Computing, Volume 113, Part B, December 2021, 107938
Wissenschaft gestaltet Zukunft. Am jährlichen interdisziplinären Wissenschaftstag TU Graz – Science for Future zeigen Forschende der TU Graz, wie sie über alle Disziplinen hinweg den gesellschaftlichen Herausforderungen mit innovativen Technologien begegnen und unsere Zukunft mitgestalten.
Viktor Hacker, Mobilität & Produktion: Volle Energie für den Klimaschutz
9:30 Begrüßung und Eröffnung des Wissenschaftstages der TU Graz
Horst Bischof, Vizerektor für Forschung der TU Graz
Harald Kainz, Rektor der TU Graz
Grußworte Karin Schaupp, Vorsitzende des Universitätsrates der TU Graz
Grußworte Peter Piffl-Percevic, in Vertretung des Bürgermeisters der Stadt Graz
Grußworte Barbara Eibinger-Miedl, Landesrätin für Wissenschaft und Forschung
Gast-Keynote Claudia KEMFERT:
Corona und Klimaneutralität: Wege aus der Krise
TU Graz Keynote Martin WILKENING: Designstrategien für neue Materialien zur Energiespeicherung
TU Graz Keynote Viktor HACKER:
Mobilität & Produktion: Volle Energie für den Klimaschutz
17:00 Podiumsdiskussion "Science for Future? Kann die Wissenschaft das Klima retten?"
Preisverleihung "TU Graz SciPix - Forschung im Fokus", Forschungsfoto-Wettbewerb der TU Graz
Ab 18:00 Abendessen und Networking
Moderation: Marlene Nowotny (Ö1 Wissenschaftsredaktion)
The Summer School on Polymer Electrolyte Fuel Cells and Hydrogen was successfully organised and held for the thirteenth time (Final Report).
Die Sommerakademie über Polymerelektrolytbrennstoffzellen und Wasserstoff wurde zum dreizehnten Mal erfolgreich organisiert und durchgeführt (Abschlussbericht)
Study Abroad Video by Dr. Barbara Lorber, Faculty of Technical Chemistry, Chemical and Process Engineering, Biotechnology.
Andreas Toth, Matthäus Siebenhofer, Susanne Lux
Emulsion-enhanced biphasic esterification has proven to be applicable for carboxylic acid recovery from dilute aqueous process streams. The carboxylic acid is esterified with 1-octanol in an emulsified regime with 4-dodecylbenzenesulfonic acid (4-DBSA) or Ni(DBSA)2 as catalyst. After phase separation, the laden solvent phase must be regenerated. This study presents a regeneration concept based on reactive distillation with transesterification of the octyl ester-laden solvent with methanol. The regenerated solvent is reused in the extraction step.
Chemie Ingenieur Technik (2021) 93,10, 1493-1501
Maitz, Silvia and Kienberger, Marlene
Black liquor (BL) from the kraft process is considered a promising feedstock for several biorefinery scenarios. Besides lignin and carboxylic acids, this liquor also contains hemicelluloses and their degradation products. A simple and reliable detection of those is of importance for further processing of the liquor. The present paper presents a thorough investigation of quantitative analysis of carbohydrates, by performing acid hydrolysis experiments with a concentrated BL sample of 44% total dry solids. The hydrolysates were then analysed for the four monosaccharides arabinose, xylose, galactose and glucose, by high performance ion chromatography (HPIC) with pulsed amperometric detection. The amount of sulphuric acid needed for complete hydrolysis of the carbohydrates was determined in the range of 3.5–5 mol kg−1 of BL. A lower acid concentration led to insufficient liberation of galactose and glucose, while higher acid concentrations led to degradation of arabinose and xylose. The carbohydrate degradation was also investigated over time for different dilutions and hydrolysis temperatures. These experiments confirmed that the hexoses require considerably harsher conditions for complete liberation compared to xylose and arabinose. The use of internal recovery standards (RSs) was tested; the highest recoveries were obtained by direct spiking of the samples with the RS prior to hydrolysis.
Holzforschung, vol. , no. , 2021, pp. 000010151520210047
Surrogate models of chemical processes can substitute rigorous models that are computationally expensive or of limited stability by simplified and typically solely data-driven models. In this work, gray-box surrogate models of classical process engineering unit operations comprising flash, distillation and compression units are developed to provide accurate models that allow for fast and stable predictions in view of later optimization of coupled models. The gray-box surrogates are first tested as individual models and then applied to model the cracked-gas compression of an ethylene plant, including a recycle stream. The process streams are hydrocarbon mixtures containing 50 components, which typically leads to significant convergence issues with rigorous approaches. A concluding comparison of the proposed surrogate models’ accuracies proves their robustness and computational efficiency and highlights the advantages of the proposed modeling methodology that complements and extends simple but physically meaningful white-box models with black-box models from the field of machine learning.
Computers & Chemical Engineering, Volume 155, 107510
Bernd Stoppacher, Sebastian Bock, Karin Malli, Michael Lammer, Viktor Hacker
Chemical looping with iron-based oxygen carriers enables the production of hydrogen from various fossil and biogenic primary energy sources. In applications with real producer gases, such as biogas or gasified biomass, hydrogen sulfide represents one of the most challenging contaminants. The impact of H2S on the reactivity of a Fe2O3/Al2O3 oxygen carrier material in chemical looping hydrogen production was investigated in the present work. Possible deactivation mechanisms of sulfur are discussed in detail on the basis of thermodynamic data. An experimental study in a fixed-bed reactor system gave experimental evidence on the fate of sulfur in chemical looping hydrogen systems. A profound interpretation was achieved through the fulfillment of the overall sulfur mass balance within a mean deviation of 3.7%. Quantitative investigations showed that hydrogen consumption in the reduction phase decreased by 12% at 100 ppm H2S in the feed gas.
Figure 1: Temperature profile (black), concentration for H2S (red) and SO2 (blue) of a redox cycle with reduction (grey background), steam oxidation (yellow) and air oxidation (blue background).
Fuel 307 (2022) 121677