Indian PhD student Chetna Madan gives an insight into her stay as a visiting researcher at the Institute of Chemical Engineering and Environmental Technology at TU Graz.
People, TU Graz
Die Rolle von Wasserstoff im zukünftigen Energiesystem (V. Hacker). Die Energie- und Klimakrise macht eine dekarbonisierte Wirtschaft alternativlos. Wasserstoff kann als Energieträger einen wesentlichen Beitrag dazu leisten und seine chemische Anwendung in Brennstoffzellen ist bereits jetzt möglich.
Urania, Alte Technik 19-20:30 Uhr
Michaela Roschger, Sigrid Wolf, Kurt Mayer, Andreas Billiani, Boštjan Genorio, Selestina Gorgieva and Viktor Hacker
Determining the optimum layer thickness, for the anode and cathode, is of utmost importance for minimizing the costs of the alkaline direct ethanol fuel cell (DEFC) without lowering the electrochemical performance. In this study, the influence of layer thickness on the performance of the ethanol oxidation reaction (EOR) and oxygen reduction reaction (ORR) in an alkaline medium and resistance was investigated. The prepared gas diffusion electrodes (GDEs) were fully characterized, with scanning electron microscopy to determine the layer thickness and electrochemically in half-cell configuration. Cyclic voltammetry and polarization curve measurements were used to determine the oxidation and reduction processes of the metals, the electrochemical active surface area, and the activity towards the ORR and EOR. It was demonstrated that realistic reaction conditions can be achieved with simple and fast half-cell GDE measurements. Single cell measurements were conducted to evaluate the influence of factors, such as membrane or ethanol crossover. In addition, electrochemical impedance spectra investigation was performed to identify the effect of layer thickness on resistance. This successfully demonstrated that the optimal layer thicknesses and high maximum power density values (120 mW cm−2) were achieved with the Pt-free catalysts and membranes used.
Sustainable Energy & Fuels, 2023
Stoppacher B., Lonardi F., Bock S., Bele M., Bertucco A., Hacker V.
The utilization of real producer gases such as raw biogas or gasified wood for chemical looping hydrogen production implies the introduction of harmful contaminants into the process. Hydrogen sulfide represents one of the most challenging trace gases in the Reformer Steam Iron Cycle (RESC).
The aim of the present work was an in-depth investigation of steam reforming with pure methane and synthetic biogas contaminated with selective concentrations of 1, 5 and 10 ppm of hydrogen sulfide. To validate the experimental data, the fixed-bed reactor system was modelled as one‑dimensional pseudo‑homogeneous plug flow reactor by an adapted Maxted model. In a preliminary thermodynamic study, the dry equilibrium composition was determined within a deviation of 4% for SMR and 2% for synthetic biogas reforming compared to the experimental results.
The impact of hydrogen sulfide on the reactivity of the catalyst was discussed and quantified by the methane conversion. The deactivation rate and extent correlate directly to the concentration of H2S, as higher hydrogen sulfide concentrations lead to a faster deactivation and lower residual methane conversion. A comparison of the methane conversion as a function of sulfur coverage between experimental and simulated data showed good agreement. The predicted results are within <10% deviation for SMR and synthetic biogas reforming, except for sulfur coverages between 0.6 and 0.8. The temperature in the catalyst bed was monitored throughout the deactivation process to gather additional information about the reaction behavior. It was possible to visualize the shift of the reforming reaction front towards the bottom of the reactor caused by catalyst deactivation. The impact of sulfur chemisorption on the morphology of the steam reformer catalyst was analyzed by SEM/EDS and BET techniques. SEM images clearly indicated the presence of sulfur as a sort of dust on the surface of the catalyst, which was confirmed by EDS analysis with a sulfur concentration of 0.04 wt%.
Journal of Physics: Energy, 2023
CEET contributions to the MOOC "Dekarbonisierung & Nachhaltigkeitsmanagement: Der Weg zum klimaneutralen Unternehmen": https://imoox.at/course/dekarb
In kraft pulping, large quantities of biomass degradation products dissolved in the black liquor are incinerated for power generation and chemical recovery. The black liquor is, however, a promising feedstock for carboxylic acids and lignin. Efficient fractionation of black liquor can be used to isolate these compounds and recycle the pulping chemicals. The present work discusses the fractionation of industrial black liquor by a sequence of nanofiltration and bipolar membrane electrodialysis units. Nanofiltration led to retention of the majority of lignin in the retentate and to a significant concentration increase in low-molecular-weight carboxylic acids, such as formic, acetic, glycolic and lactic acids, in the permeate. Subsequent treatment with bipolar membrane electrodialysis showed the potential for simultaneous recovery of acids in the acid compartment and the pulping chemical NaOH in the base compartment. The residual lignin was completely retained by the used membranes. Diffusion of acids to the base compartment and the low current density, however, limited the yield of acids and the current efficiency. In experiments with a black liquor model solution under optimized conditions, NaOH and acid recoveries of 68–72% were achieved.
Paul Demmelmayer, Lena Steiner, Hansjörg Weber and Marlene Kienberger
Reactive liquid–liquid extraction has been widely investigated as a means of isolating carboxylic acids from fermentation broths. However, commonly applied fossil-based solvent phases should be replaced by green alternatives. In this work, we investigate a thymol-menthol-based deep eutectic solvent (tmDES) as a green alternative to the commonly applied modifier 1–octanol for the extraction of lactic acid, acetic acid, and oxalic acid from a model solution and pre-treated sweet sorghum silage press juice (pSPJ); tri–n–octylamine (TOA) was used as a reactive extractant. Additionally, NMR spectroscopy was used to detect interactions between menthol and thymol molecules, as well as among these and TOA and lactic acid. NMR measurements of tmDES revealed the existence of multiple intermolecular contacts between thymol and menthol. Furthermore, nuclear Overhauser effects (NOEs) between the tmDES, TOA, and lactic acid molecules were found. Extraction experiments showed that tmDES improves the extraction efficiency when using pSPJ as the feed phase. The maximum extraction efficiency for lactic acid increased from 35.0 ± 0.8 % to 48.7 ± 0.7 % and for acetic acid from 52.4 ± 0.2 % to 82.2 ± 0.6 % when using a tmDES instead of 1–octanol at 50 °C. Furthermore, the use of tmDES resulted in higher extraction efficiencies as compared to the use of 1–octanol at equilibrium pH values ranging from five to seven, which is a common pH range for fermentation. Besides having superior biocompatibility and extraction efficiency as compared to 1–octanol, tmDES allow carboxylic acid extraction processes to be carried out at higher pH levels.
Separation and Purification Technology, 2023
Spin-off Fellowships are an essential impulse to prepare the environment for future spin-offs and to accelerate the practical implementation of the research results of TU Graz. The project will develop and produce membrane electrode assemblies for fuel cells and electrolyzers using a newly developed catalyst system.
Press release (OTS Presseaussendung, 20.12.2022)
TU Graz news
Sigrid Wolf, Michaela Roschger, Boštjan Genorio, Daniel Garstenauer, Josip Radić and Viktor Hacker
Electrocatalyst development for alkaline direct ethanol fuel cells is of great importance. In this context we have designed and synthesized cerium-modified cobalt manganese oxide (Ce-CMO) spinels on Vulcan XC72R (VC) and on its mixture with reduced graphene oxide (rGO). The influence of Ce modification on the activity and stability of the oxygen reduction reaction (ORR) in absence and presence of ethanol was investigated. The physicochemical characterization of Ce-CMO/VC and Ce-CMO/rGO–VC reveals CeO2 deposition and Ce doping of the CMO for both samples and a dissimilar morphology with respect to the nature of the carbon material. The electrochemical results display an enhanced ORR performance caused by Ce modification of CMO resulting in highly stable active sites. The Ce-CMO composites outperformed the CMO/VC catalyst with an onset potential of 0.89 V vs. RHE, a limiting current density of approx. −3 mA cm−2 and a remaining current density of 91% after 3600 s at 0.4 V vs. RHE. In addition, remarkable ethanol tolerance and stability in ethanol containing electrolyte compared to the commercial Pt/C catalyst was evaluated. These outstanding properties highlight Ce-CMO/VC and Ce-CMO/rGO–VC as promising, selective and ethanol tolerant ORR catalysts in alkaline media.
RSC Advances, 2022
The current energy crisis could be a turbo for renewable energies. So-called "green hydrogen" plays an important role in the energy transition. It can generate, store and transport electricity highly efficiently and without greenhouse gas emissions. Green hydrogen" is not yet sufficiently available and therefore cannot replace fossil fuels in the short term, but in the long term it is seen as an important player on the road to an environmentally friendly, renewable energy system.
Interview mit Viktor Hacker (Ö1, Wissen Aktuell, 6. December 2022, 13:55)
Michaela Roschger, Sigrid Wolf, Boštjan Genorio and Viktor Hacker
In this work, the metal content of Pd85Ni10Bi5/C catalysts for the alkaline ethanol-oxidation reaction was reduced from 40 wt.% (PdNiBi/C (40/60)) to 30 wt.% (PdNiBi/C (30/70)), 20 wt.% (PdNiBi/C (20/80)) and 10 wt.% (PdNiBi/C (10/90)), while increasing performance. The synthesized catalysts were examined using physicochemical measurements and electrochemical measurements. The best performing catalysts were used to fabricate membrane electrode assemblies for carrying out single-cell tests and to determine the influence of the metal/carbon ratio of the electrode. The electrochemical surface area (695 cm2 mg−1) and activity were increased, resulting in high peak-current densities for the ethanol oxidation reaction (3.72 A mg−1) by the resulting more accessible metal particles. The electrode produced with the PdNiBi/C (30/70) catalyst reached a maximum power density of 34.8 mW mg−1 at 50 °C. This successfully demonstrated a doubling of the power density compared with the performance of the PdNiBi/C (40/60) electrode, while simultaneously reducing the costs.
Asep Samsudin, Michaela Roschger, Sigrid Wolf and Viktor Hacker
In recent years, there has been considerable interest in anion exchange membrane fuel cells (AEMFCs) as part of fuel cell technology. Anion exchange membranes (AEMs) provide a significant contribution to the development of fuel cells, particularly in terms of performance and efficiency. Polymer composite membranes composed of quaternary ammonium poly(vinyl alcohol) (QPVA) as electrospun nanofiber mats and a combination of QPVA and poly(diallyldimethylammonium chloride) (PDDA) as interfiber voids matrix filler were prepared and characterized. The influence of various QPVA/PDDA mass ratios as matrix fillers on anion exchange membranes and alkaline fuel cells was evaluated. The structural, morphological, mechanical, and thermal properties of AEMs were characterized. To evaluate the AEMs’ performances, several measurements comprise swelling properties, ion exchange capacity (IEC), hydroxide conductivity (σ), alkaline stability, and single-cell test in fuel cells. The eQP-PDD0.5 acquired the highest hydroxide conductivity of 43.67 ms cm−1 at 80 °C. The tensile strength of the membranes rose with the incorporation of the filler matrix, with TS ranging from 23.18 to 24.95 Mpa. The peak power density and current density of 24 mW cm−2 and 131 mA cm−2 were achieved with single cells comprising eQP-PDD0.5 membrane at 57 °C.
Nanomaterials 2022, 12, 3965.
The ElektroPower project of the Institute of Chemical Engineering and Environmental Technology was awarded the Austrian Start-up Prize PHÖNIX in the category "PROTOTYPE" by the Federal Minister Martin Kocher of the Ministry of Labour and Economy (BMAW) and the Federal Minister Martin Polaschek of the Ministry of Education, Science and Research (BMBWF). In total, there were over 200 submissions and four prizes were assigned.
Merit Bodner received the Young Scientist Award 2022 for the Hydrogen Usages Pillar, organized by Hydrogen Europe Research. The award ceremony took place on the 26th of October 2022 as part of the Hydrogen Week 2022 in Brussels.
Young Scientist Award 2022
The course Chemical Engineering of biobased products, held by Marlene Kienberger and the course ´Bioethanolveredelung´ held by Georg Rudelstorfer are nominated for the ´Price for Excellence in teaching´. Both courses are on the short list for the price.
As part of the cooperation Research and Innovation Ecosystem Graz (RIE Graz), the institute was visited on the initiative of the head of Siemens Technology Austria and the head of CCT Additive Manufacturing, organized by DI Christine Schichler.
Astrid Loder, Simone Santner, Matthäus Siebenhofer, Andreas Böhm, Susanne Lux*
Direct reduction of mineral iron carbonate with hydrogen is a CO2-lean technology for the production of elemental iron from iron carbonate ore. In this study, the reaction mechanism and reaction kinetics were investigated by thermogravimetric analysis and in a fixed-bed tubular reactor. The degree of metallization increases with increasing temperature from 773 to 1023 K. At 1023 K, the degree of metallization is 93 wt%, with the remaining iron species being wüstite. The reduction proceeds via two reaction pathways: calcination of iron carbonate to wüstite with consecutive reduction of wüstite to elemental iron and direct reduction of iron carbonate to elemental iron. The reaction steps occur simultaneously. During the first hour of reaction, which corresponds to the heat-up phase, calcination of iron carbonate to wüstite adopts the dominant reaction path. Then wüstite reduction and direct iron carbonate reduction with hydrogen to elemental iron, become dominant, facilitated by the increasing porosity of the ore due to the release of CO2. Towards the end of the reduction process the remaining wüstite is reduced to elemental iron. The kinetic triplet – solid phase reaction kinetic model, activation energy and frequency factor – was determined for each reaction step. The reaction kinetics can be described by a combination of an Avrami-Erofeyev model (A3 model for iron carbonate calcination to wüstite), and reaction-order models (F2 model for the reduction of iron carbonate to elemental iron and F3 model for the reduction of wüstite to elemental iron).
Chemical Engineering Research and Design 188 (2022) 575-589
During the Seminar RE4Industry Knowledge Transfer on 20-22 October 2022 at TU Graz, Inffeldgasse 25/D, i7, Prof. Hacker chaired the session ‘Green Hydrogen’ supported by Prof Lux as expert, and Prof. Kienberger moderated the panel on Circular Bioeconomy.
The ElektroPower project of the Institute of Chemical Engineering and Environmental Technology has been nominated in the category "PROTOTYPE" for the Austrian start-up prize PHÖNIX, which is awarded on behalf of the Federal Ministry of Education, Science and Research (BMBWF) and the Federal Ministry for Digital and Economic Affairs (BMDW).
Michaela Roschger, Sigrid Wolf, Kurt Mayer, Matthias Singer and Viktor Hacker
Alkaline direct ethanol fuel cells (DEFCs) represent an efficient energy conversion device for sustainable ethanol fuel. In this study, a design with new structural parameters for the anodic flow field of the alkaline DEFC was modeled with the aid of computational fluid dynamics and was then actually constructed. Single-cell tests were performed to evaluate the impact of the developed design on fuel cell performance. The results show that fuel cell performance significantly increased when using the improved design in the low-temperature range. The higher the temperature in the cell, the lower the influence of the flow field structure on performance. In addition, the influence of external factors, such as the orientation of the cell, the preheating of the fuel, and the direction of the two fuel flows relative to each other (co-current and counter-current), are shown.
For his PhD thesis “Modeling of Interfacial Mass Transfer in Liquid-Liquid Systems”, Roland Nagl received the MegaWATT award for the best annual PhD-thesis in the field of technical thermodynamics at a DACH university. In his thesis Roland Nagl established a modeling framework to investigate the fundamental phenomena which govern the mass transfer through liquid-liquid interfaces in industrial separation processes. The price was awarded by the WATT e.V. during the Thermodynamik-Kolloquium 2022 conference in Chemnitz.
TU Graz SciPix is a photo and video competition held at TU Graz, which focuses the spotlight on the diverse research being carried out. With three awarded contributions the institute was very successful this year. The photos and video contributions will first be displayed on the Campus Alte Technik, then moved on to the Campus Neue Technik and finally displayed at the Campus Inffeldgasse.
Winning photos and video:
Link to TU Graz SciPix: https://www.tugraz.at/en/research/research-at-tu-graz/tu-graz-scipix/
Rainbow column: This is the Taylor Couette Disc Contactor, which was used for CO2 purification of a gas stream with sodium hydroxide. The pH curve was visualized in the course of the chemical reaction with a universal indicator. © TU Graz
Taylor lava lamp: The eponymous vortex formations of the Taylor-Couette flow are used to bring immiscible phases into contact (gases, liquids and solids). The solid serves as a heterogeneous catalyst and the red colored solvent extracts the reaction product. © TU Graz
The beauty of the imperfect: During the production of a fuel cell, catalyst ink is ultrasonically sprayed onto the membrane. Perfect homogeneity is essential. Here, the aesthetic pattern was created by too much ink. The swollen membrane is unusable. © TU Graz
Mario Kircher, Georg Rudelstorfer, Michaela Roschger, Michael Lammer, Rafaela Greil and Susanne Lux (from left to right) © TU Graz
To learn about the CO2 problem, the fourth grade students of the Carneri BG/BRG visited the institute on 20 September 2022 and also gained insights into the research work in the field of hydrogen technology.
© TU Graz
Feedback on the visit:
The Summer School on Advanced Studies of Polymer Electrolyte Fuel Cells was organised for the fourteenth time in cooperation between Yokohama National University and Graz University of Technology.
The seven-day program was opened by Prof. Mitsushima and Prof. Hacker, where they placed an emphasis on the long-standing tradition of the summer school and the cooperation between the Universities. The 14th International Summer School on PEFCs attracted 63 participants from 16 different universities and companies.
The Interreg SI-AT H₂GreenTECH project has successfully reached its finish line! The project partners contributed to the establishment of a hydrogen ecosystem in the field of green hydrogen and hydrogen technologies in the cross-border area Slovenia-Austria. The developed Hydrogen Center, as a B2B web platform and One-stop-shop, is an integrative facilitator and motivator for finding common solutions with its existing and future members that contribute to the improvement of the regional hydrogen ecosystem. It serves companies, researchers, and students by providing information, encouraging research and business networks and collaboration opportunities, sharing knowledge, and improving the flow of innovation in the cross-border area. Two strategic documents to support and guide the further development of the Hydrogen Center were prepared.
Asep Samsudin, Merit Bodner and V. Hacker
Anion exchange membrane fuel cells have unique advantages and are thus gaining increasing attention. Poly(vinyl alcohol) (PVA) is one of the potential polymers for the development of anion exchange membranes. This review provides recent studies on PVA-based membranes as alternative anion exchange membranes for alkaline fuel cells. The development of anion exchange membranes in general, including the types, materials, and preparation of anion exchange membranes in the last years, are discussed. The performances and characteristics of recently reported PVA-based membranes are highlighted, including hydroxide conductivity, water uptake, swelling degree, tensile strength, and fuel permeabilities. Finally, some challenging issues and perspectives for the future study of anion exchange membranes are discussed.
Polymers, MDPI 2022
Silvia Maitz, Matthäus Siebenhofer and Marlene Kienberger
Black liquor, a side stream of the kraft pulping process, contains valuable low molecular weight carboxylic acids and carbohydrates. Hydrothermal treatment and wet oxidation of black liquor with a dry matter content of 43 % were investigated as an approach to convert these carbohydrates to carboxylic acids to increase their concentration. Wet oxidation with H2O2 or O2 at 115–185 °C led to partial degradation of carbohydrates, but no significant formation of the investigated carboxylic acids, glycolic, lactic, formic and acetic acid, was detected. Treatment under N2 atmosphere at 185 and 220 °C finally led to an increase of the hydroxy acid concentration. After two hours of heat treatment at 220 °C, 90 % of the carbohydrates were degraded, coupled with a high carbon conversion efficiency of 32 % based on the formation of lactic acid and glycolic acid, of which the concentrations increased by 51 and 73 %, respectively.
Bioresource Technology Reports, Volume 19, 2022, 101148, ISSN 2589-014X https://doi.org/10.1016/j.biteb.2022.101148.
Roland Nagl, Sandrina Stocker, Patrick Zimmermann and Tim Zeiner
This work examines the mass transfer in reactive liquid-liquid systems applying the dynamic concentration gradient theory (CGT). The CGT is based on a square gradient approach delivering an expression for the Gibbs energy of an inhomogeneous system as basis for the mass transfer in a two-phase system. For this work, the CGT was combined for the first time with a reaction kinetics model to model the reactive mass transfer. The model was validated by experiments. As model reaction the reversible diacetone alcohol formation in a water-toluene system was chosen. To parameterize the Gibbs excess energy model, phase equilibria were measured and furthermore, the predictive power of the model to calculate interfacial tension in equilibrium was also checked by own experiments. To analyze the mass transfer in liquid-liquid systems the model prediction was compared to experimental data from Nitsch-cell experiments. It was found that the model predictions are in excellent agreement to the forward reaction predictions as well as to the backward reaction.
Adrian Drescher and Marlene Kienberger
In today’s linear economy, waste streams, environmental pollution, and social–economic differences are increasing with population growth. The need to develop towards a circular economy is obvious, especially since waste streams are composed of valuable compounds. Waste is a heterogeneous and complex matrix, the selective isolation of, for example, polyphenolic compounds, is challenging due to its energy efficiency and at least partially its selectivity. Extraction is handled as an emerging technology in biorefinery approaches. Conventional solid liquid extraction with organic solvents is hazardous and environmentally unfriendly. New extraction methods and green solvents open a wider scope of applications. This research focuses on the question of whether these methods and solvents are suitable to replace their organic counterparts and on the definition of parameters to optimize the processes. This review deals with the process development of agro-food industrial waste streams for biorefineries. It gives a short overview of the classification of waste streams and focuses on the extraction methods and important process parameters for the isolation of secondary metabolites.