Co-reporter:H. Stotz;L. Maier;O. Deutschmann
Topics in Catalysis 2017 Volume 60( Issue 1-2) pp:83-109
Publication Date(Web):2017 February
DOI:10.1007/s11244-016-0717-5
A kinetic modeling study on methane oxidation over reduced Pd for various fuel-rich conditions around the stoichiometric point of the partial oxidation at high temperatures (900–1100 K) is presented. A thermodynamically consistent detailed surface reaction mechanism is developed within the mean field approximation. The proposed kinetic model consists of 54 elementary-step based reactions including seven gas-phase species and 15 surface intermediates. Three different methane activation paths are implemented, comprising pyrolytic C–H bond dissociation steps, oxygen-assisted and dual-oxygen-assisted CH4 activation. In situ experimental measurements in a quasi-autothermally operated flow reactor, using the capillary sampling technique, are performed for model evaluation. The provided experimental data includes spatially resolved temperature and concentration profiles within a single catalytic channel of a Pd/Al2O3-coated monolith. Supplementary numerical simulations based on literature data for fuel-lean and fuel-rich conditions at high temperatures extend the model’s capability to predict a wide range of different experimental conditions.
Co-reporter:Andreas Gremminger, Patrick Lott, Menno Merts, Maria Casapu, Jan-Dierk Grunwaldt, Olaf Deutschmann
Applied Catalysis B: Environmental 2017 Volume 218(Volume 218) pp:
Publication Date(Web):5 December 2017
DOI:10.1016/j.apcatb.2017.06.048
•Rapid deactivation of Pd based catalysts due to generation of sulfates.•Pre-turbo positioning enhances activity due to higher temperature.•Rich treatment at higher temperature regenerates SO2 poisoned catalysts.•Regeneration was successfully demonstrated during operation on lean-burn gas engine by changing to λ < 1.The influence of SO2 on the total oxidation of methane over Pd-Pt/Al2O3 and Pd‐Pt/La2O3‐Y2O3‐CeO2-ZrO2 catalysts under typical lean burn gas engine conditions was investigated and compared to engine-aged samples. Differences in deactivation rate and in stability of poisoning species were identified at 400 °C and 450 °C. A positive effect of higher pressure, related to pre-turbo positioning of the catalyst, on the activity was observed. Realistic pre- turbo conditions including high temperature (600 °C) and high pressure (4 bar) were found to favor methane conversion but even under these conditions some deactivation took place due to formation of strongly bound sulfur species and probably due to sintering of the noble metal particles. Engine aged samples were obtained after 60 h on an SO2 containing exhaust-gas of a lean‐burn gas engine at 450 °C. Laboratory tests with these samples revealed high accumulation of sulfur species with a higher concentration at the catalyst inlet than the outlet. Different regeneration strategies for SO2 poisoned catalysts were successfully applied. Rich conditions led to very pronounced regeneration at 550 °C of a poisoned Pd‐Pt/La2O3‐Y2O3‐CeO2-ZrO2 catalyst. Short rich pulses were even able to regenerate the catalyst during operation at the gas engine. Periodic switches to λ < 1 finally stabilized a methane conversion above 65% for several hours demonstrating the good transferability of lab test data to the engine tests.Download high-res image (83KB)Download full-size image
Co-reporter:Julian N. Bär, Mauro Iurk Rocha, Edimilson Jesus de Oliveira, Olaf Deutschmann
International Journal of Hydrogen Energy 2016 Volume 41(Issue 5) pp:3701-3711
Publication Date(Web):9 February 2016
DOI:10.1016/j.ijhydene.2015.12.015
•The CPOX of unmodified jet fuels and its sulfur-containing surrogates were investigated.•The influence of the main hydrocarbon structure of a jet fuel and the role of sulfur on the syngas selectivity is discussed.•Sulfur addition leads to a loss in hydrogen selectivity, whereas the carbon-based main product selectivity is not affected.•The results support a two-staged deactivation process, caused by sulfur addition at lean conditions.Jet-fuel surrogates with varying composition and sulfur content were partially oxidized over a Rh/Al2O3 honeycomb catalyst. The surrogates consisted of a blend of n-dodecane, 1,2,4-trimethylbenzene, and benzothiophene to represent model mixtures of the main chemical properties of jet fuels. The experiments were performed under quasi-autothermal conditions for three different C/O-ratios in a set-up, specifically designed for fuels with high boiling points. The product distribution significantly changes with sulfur addition showing increased water formation, undesired by-products and a decline in fuel conversion. A steady increase of by-product formation over time on stream leads to coke deposition for fuels with ≥50 mg S per kg fuel. The interplay between sulfur and coke, caused deactivation and its impact on syngas selectivity, fuel conversion, and by-product formation is discussed.
Co-reporter:H. Gossler, O. Deutschmann
International Journal of Hydrogen Energy 2015 Volume 40(Issue 34) pp:11046-11058
Publication Date(Web):14 September 2015
DOI:10.1016/j.ijhydene.2015.06.125
•Numerical study on hydrogen production in internal combustion engines.•Simulation: Single-zone model with global heat transfer, detailed reaction mechanism.•Numerical optimization to determine optimal operating conditions for max. H2 yield.•Reaction flow analysis provides detailed insight into chemical conversion process.The production of hydrogen is studied numerically under uncatalyzed partial oxidation and homogeneous charge compression ignition (HCCI) conditions in an internal combustion engine fueled by natural gas. The HCCI process is modeled by a single-zone variable volume reactor using a global heat transfer model and elementary-step reaction mechanisms. Numerical optimization is applied to maximize the hydrogen yield at the end of the expansion stroke by varying the equivalence ratio, engine speed and initial pressure for a fixed initial temperature. Suitable constraints were defined, including peak pressure and bounds to the optimization variables. From these results, maximum hydrogen yield profiles and the associated operating parameter profiles as functions of initial temperature were obtained. The profiles exhibit strong linear dependency with initial temperature. Reaction flow analysis was performed to gain detailed insight into the chemical processes involved when the engine is run under optimal conditions for a maximum hydrogen yield. The integral reaction flow analysis shows that substantial amounts of hydrogen are produced from precursors, which are also valuable products, such as methanol, formaldehyde and ethylene.
Co-reporter:Claudia Diehm, Olaf Deutschmann
International Journal of Hydrogen Energy 2014 Volume 39(Issue 31) pp:17998-18004
Publication Date(Web):22 October 2014
DOI:10.1016/j.ijhydene.2014.06.094
Co-reporter:Claudia Eßmann, Lubow Maier, Aijun Li, Steffen Tischer, and Olaf Deutschmann
Industrial & Engineering Chemistry Research 2014 Volume 53(Issue 31) pp:12270-12278
Publication Date(Web):2017-2-22
DOI:10.1021/ie5015525
Natural gas steam reforming (SR) over technically used rhodium/alumina (Rh/Al2O3) honeycomb catalysts is studied experimentally at temperatures between 923 and 1073 K and steam-to-carbon ratios (S/C) of unity, with regard to coke deposition caused by the decomposition of the product species ethylene (C2H4) and carbon monoxide (CO). Furthermore, the process is modeled using detailed reaction mechanisms, and numerical simulations are carried out to describe the coke formation on Rh/Al2O3 catalysts quantitatively. The amount of deposited carbon was detected and analyzed for varying feed mixtures of the products CO and C2H4 diluted in N2. During the decomposition of CO, the saturation of the amount of coke is monitored by feeding CO in high concentrations. No saturation occurs for the same amounts of coke resulting from the decomposition of C2H4. The coking rate caused by the decomposition of C2H4 is found to be ∼25 times higher than the coking rate caused by the decomposition of CO. The differences in coking behavior caused by C2H4 and CO, respectively, are described by coking models.
Co-reporter:Alexer Zellner; Rainer Suntz; Olaf Deutschmann
Chemie Ingenieur Technik 2014 Volume 86( Issue 4) pp:538-543
Publication Date(Web):
DOI:10.1002/cite.201300140
Abstract
Die katalytische Reduktion von NO wurde in einem optisch zugänglichen Strömungskanal mittels planarer laserinduzierter Fluoreszenz (PLIF) in situ und nicht-invasiv untersucht. Der Aufbau des Versuchsreaktors und dessen Adaption an die PLIF-Methode werden präsentiert. Die Ergebnisse zeigen die zweidimensionalen Fluoreszenzverteilungen von NO über einer Katalysatorscheibe sowohl unter reaktiven als auch nicht-reaktiven Bedingungen. Ein Pt/Al2O3-beschichteter Monolith eines Dieseloxidationskatalysators diente dabei zur Herstellung selbstgefertigter Katalysatorscheiben.
The catalytic reduction of NO inside an optically accessible channel reactor has been investigated using in situ and non-invasive planar laser-induced fluorescence (PLIF). The construction of the experimental reactor as well as an effective implementation of PLIF is presented. Two-dimensional maps of the NO fluorescence above a catalytic surface are obtained under both reactive and non-reactive conditions. NO reduction in a Diesel oxidation catalyst consisting of a Pt/Al2O3 coated monolith is studied exemplarily.
Co-reporter:Lea C. S. Kahle, Thomas Roussière, Lubow Maier, Karla Herrera Delgado, Guido Wasserschaff, Stephan A. Schunk, and Olaf Deutschmann
Industrial & Engineering Chemistry Research 2013 Volume 52(Issue 34) pp:11920-11930
Publication Date(Web):July 29, 2013
DOI:10.1021/ie401048w
Catalytic dry reforming over a platinum-based catalyst is described experimentally and numerically in a laboratory pilot-plant flow reactor. The results reveal that coking in the upper part of the catalyst bed and at the entrance of the reactor occurs, depending on the composition of the reaction mixture and the respective temperature. To a significant extent, gas-phase reactions play a role as being the cause for the observed coking behavior in the reforming of methane in the presence of carbon dioxide at high temperatures of 1123–1273 K and at 20 bar. Hydrogen addition can inhibit coke formation better than water addition. The reactor is modeled by a one-dimensional description of the reacting field using elementary-step reaction mechanisms of up to 4238 gas-phase reactions among 1034 species and 58 heterogeneous reactions among 8 gas-phase species and 14 surface-adsorbed species. The study leads an optimized positioning of the catalyst in a technical reformer tube.
Co-reporter:L. C. S. Kahle, T. Roussière, L. Maier, K. Herrera Delgado, G. Wasserschaff, S. A. Schunk, and O. Deutschmann
Industrial & Engineering Chemistry Research 2013 Volume 52(Issue 41) pp:14727-14727
Publication Date(Web):2017-2-22
DOI:10.1021/ie4028473
Co-reporter: Dr. Olaf Deutschmann; Dr. Jan-Dierk Grunwaldt
Chemie Ingenieur Technik 2013 Volume 85( Issue 5) pp:595-617
Publication Date(Web):
DOI:10.1002/cite.201200188
Abstract
Eine ganzheitliche Betrachtungsweise von Abgasnachbehandlungssystemen ist derzeit der attraktivste Ansatzpunkt für die weitere Verminderung der Schadstoffemissionen und um auf neue Herausforderungen durch strengere Emissionsgrenzwerte, neue Rohstoffbasis und effektivere Motorkonzepte schneller zu reagieren. Dieser Artikel gibt einen Überblick zu gegenwärtigen Abgasnachbehandlungssystemen. Heutige und zukünftige Herausforderungen und Ansätze zu deren Bewältigung werden diskutiert. Bei den vorgestellten Lösungsansätzen spielen hierarchische Modellierung von DFT-Berechnungen bis zur CFD-Simulation des kompletten Abgasstranges, realitätsnahe Abgasprüfstände und Alterungsverfahren sowie On-board-Diagnostik ebenso wie die Charakterisierung von Katalysatoren insbesondere unter Reaktionsbedingungen sowie möglichst alle Längenskalen eine wichtige Rolle. In Zukunft werden wissensbasierte roboter-kontrollierte Präparation und dynamische Modelle, gekoppelt mit Informationen aus dem realen Betrieb, Forschung und Entwicklung maßgeblich unterstützen.
Looking at exhaust-gas after-treatment systems in its entirety leads to further improvement of emission control devices and to the accomplishment of future challenges such as lower legislative emission limits, new fuels, and more efficient engine concepts. This article provides an overview on the state-of-the art mobile exhaust-gas after-treatment devices. Current and future challenges are discussed in the light of present approaches such as hierarchical modeling reaching from DFT computations of molecular processes to CFD simulation of entire lines of exhaust-gas cleaning devices, close-to-reality emission control test benches and aging procedures, on-board diagnostics, and catalyst characterization at operating conditions and preferentially all length scales. In future, knowledge-based robot-controlled preparation and dynamic models coupled with information from real operation will significantly support research and development.
Co-reporter:Vikram Menon, Vinod M. Janardhanan, Steffen Tischer, Olaf Deutschmann
Journal of Power Sources 2012 Volume 214() pp:227-238
Publication Date(Web):15 September 2012
DOI:10.1016/j.jpowsour.2012.03.114
This paper presents a novel approach to model the transient behavior of solid-oxide fuel cell (SOFC) stacks in two and three dimensions. A hierarchical model is developed by decoupling the temperature of the solid phase from the fluid phase. The solution of the temperature field is considered as an elliptic problem, while each channel within the stack is modeled as a marching problem. This paper presents the numerical model and cluster algorithm for coupling between the solid phase and fluid phase. For demonstration purposes, results are presented for a stack operated on pre-reformed hydrocarbon fuel. Transient response to load changes is studied by introducing step changes in cell potential and current. Furthermore, the effect of boundary conditions and stack materials on response time and internal temperature distribution is investigated.Highlights► Novel approach to model solid-oxide fuel cell (SOFC) stacks in two and three dimensions. ► Hierarchical model developed. ► Results presented for a stack operated on pre-reformed hydrocarbon fuel. ► Transient response to load changes studied.
Co-reporter:Torsten Kaltschmitt, Claudia Diehm, and Olaf Deutschmann
Industrial & Engineering Chemistry Research 2012 Volume 51(Issue 22) pp:7536-7546
Publication Date(Web):January 12, 2012
DOI:10.1021/ie201712d
Catalytic partial oxidation (CPOX) is a promising technology for reforming of liquid hydrocarbon fuels to hydrogen or synthesis gas for use in fuel cells. The addition of a certain amount of the tail gas of the fuel cell stack to the reformer inlet feed can increase overall efficiency and lead to higher H2 and CO selectivities and reduce coke formation. The effect of carbon dioxide or steam addition (1, 5, 10, 20, and 30 vol% of the total flow) on the performance of a CPOX reformer operated with isooctane as fuel surrogate is systematically studied over a wide range of C/O feed ratios (0.72–1.79) using a Rh/alumina honeycomb catalyst. The specific impact of the coreactants H2O and CO2 on reformer behavior can be interpreted by the water gas shift (WGS) chemistry. Production of H2 and CO2 increases with H2O addition at the expense of CO and H2O. Opposite trends are observed in case of CO2 addition. Tail gas recycling reduces formation of soot precursors up to 50% compared to the corresponding fuel feed without coreactants. However, tail-gas recycling shifts the formation of soot precursors toward lower C/O ratios.
Co-reporter:O. Deutschmann;C. Diehm;D. Livio
Chemie Ingenieur Technik 2012 Volume 84( Issue 8) pp:
Publication Date(Web):
DOI:10.1002/cite.201250242
No abstract is available for this article.
Co-reporter:Dr. Nikolay M. Mladenov;Dr. Steffen Tischer ; Olaf Deutschmann
Chemie Ingenieur Technik 2011 Volume 83( Issue 10) pp:1688-1696
Publication Date(Web):
DOI:10.1002/cite.201100136
Abstract
Die exotherme chemische Umsetzung des Abgases verursacht in der monolithischen Struktur technischer Dreiwegekatalysatoren einen lokal und zeitlich variierenden Wärmeeintrag, der zu charakteristischen radialen und axialen Temperaturprofilen führt. Auf einem Motorprüfstand gemessene Temperaturprofile für stationär und dynamisch mit Realabgasen sowie homogen mit heißem Inertgas gealterte Dreiwegekatalysatoren werden mit denen frischer Katalysatoren verglichen. Die experimentell ermittelten Temperaturprofile können mittels numerischer Simulation des Wärme- und Stofftransportes und der chemischen Umsätze durch Variation der lokalen Dispersion der katalytischen Aktivkomponente ohne Kenntnis der konkreten Alterungsgeschichte des Katalysators wiedergegeben werden. Damit kann man aus dem lokalen Wärmeeintrag, bestimmbar durch Messung von Temperaturprofilen, direkt auf die lokale Katalysatordeaktivierung, ausgedrückt durch die verminderte lokale Dispersion, schließen.
The exothermic chemical conversion of exhaust gases leads to a spatially and temporarily varying heat source in the monolithic structure of three-way catalytic converters which results in characteristic radial and axial temperature profiles. In an engine-test bench, temperature profiles are measured and compared for fresh and aged catalysts, the latter ones aged by real exhaust gases at steady-state and transient real conditions as well as by a hot inert gas. Numerical simulations of the heat and mass transport and chemical conversion are used to reproduce the measured temperature profiles assuming locally varying dispersion of the catalytic components due to aging without knowing the aging history. Hence, the local chemical heat source, observed by the measurement of temperature profiles, can directly be used to estimate the local catalyst deactivation, expressed by the reduction of the local catalyst dispersion.
Co-reporter: Olaf Deutschmann
Chemie Ingenieur Technik 2011 Volume 83( Issue 11) pp:1954-1964
Publication Date(Web):
DOI:10.1002/cite.201100133
Abstract
Heterogen katalysierte Gasphasenreaktionen bei hohen Temperaturen werden seit langem bei Energieumwandlungsprozessen eingesetzt, um effizient chemische Energieträger in Wärme, Strom und wertvollere chemische Energieträger zu wandeln. Aufgrund der hohen Temperaturen und kurzen Verweilzeiten sind die verwendeten Apparate durch komplexe, nichtlineare Wechselwirkungen zwischen Massen- und Wärmetransport sowie heterogene und mitunter auch homogene und elektrokatalytische chemische Reaktionen charakterisiert, deren Verständnis für Optimierung von Reaktordesign und Betriebsbedingungen Voraussetzung ist. Der Beitrag diskutiert die aktuellen Herausforderungen der Hochtemperaturkatalyse sowohl in der Grundlagenforschung als auch der Technologieentwicklung anhand von mit logistischen Kraftstoffen betriebenen Reformern zur Erzeugung wasserstoffreicher Reformate.
Heterogeneously catalyzed gas phase reactions at high temperatures have been used for energy conversion for a long time to convert chemical energy carriers into heat, electricity, and more valuable chemicals. Due to high temperatures and short residence times, the used devices exhibit complex, non-linear interactions between mass and heat transport as well as heterogeneous and sometimes homogeneous and electrocatalytic reactions. Optimization of reactor design and operating conditions calls for a better understanding of those interactions. This article discusses the current challenges in high temperature catalysis from fundamental and technological perspectives. The thematic focus is on the catalytic reforming of logistic fuels for the production of hydrogen-rich reformates.
Co-reporter:L. Maier;B. Schädel;K. Herrera Delgado;S. Tischer;O. Deutschmann
Topics in Catalysis 2011 Volume 54( Issue 13-15) pp:
Publication Date(Web):2011 September
DOI:10.1007/s11244-011-9702-1
A detailed multi-step reaction mechanism is developed for modeling steam reforming of methane over nickel-based catalysts. The mechanism also includes partial and total oxidation reactions, water–gas shift reactions, formation of carbon monolayers, and methanation reactions. A method is presented for ensuring thermodynamic consistency in the development of surface reaction mechanisms. The applicability of the mechanism is tested by simulating experimental investigations of SR of methane on a Ni-coated monolithic cordierite catalyst as well as experimental studies from literature. The reactive flow in the channels of the experimentally used monolithic structures is modeled by a two-dimensional flow field analysis of a single monolith channel coupled with the reaction mechanism developed. The gas composition and surface coverage with adsorbed species are calculated as function of the position in the channel. The model developed is able to properly describe steam reforming of methane over the nickel catalysts for wide ranges of temperature and steam/methane ratio.
Co-reporter:Willi Boll, Steffen Tischer, and Olaf Deutschmann
Industrial & Engineering Chemistry Research 2010 Volume 49(Issue 21) pp:10303-10310
Publication Date(Web):June 24, 2010
DOI:10.1021/ie100516j
Abatement of pollutant emissions over platinum-containing catalytic converters of lean operated engines is studied. Several close-to-production model catalysts with varying platinum loading and hydrothermal aging procedures are characterized by BET, HR-SEM, HR-TEM, and CO-TPD. Pollutant conversion is numerically investigated in an isothermal flat bed reactor using varying lean exhaust-gas mixtures and temperatures. The performance of the monolithic catalysts is modeled by a two-dimensional flow field description of a single channel coupled with models for washcoat diffusion and multistep reaction mechanisms. An optimizing procedure is presented which allows adaption of kinetic parameters for slightly different catalysts. The catalytic active surface area of the catalyst determined by CO-TPD can serve as parameter to model the varying noble metal loading and consequences of hydrothermal aging without any adaption of the kinetic data included in the reaction mechanism.
Co-reporter:M. Votsmeier Dr.;O. Deutschmann Dr.
Chemie Ingenieur Technik 2010 Volume 82( Issue 9) pp:
Publication Date(Web):
DOI:10.1002/cite.201050694
No abstract is available for this article.
Co-reporter:A. Banerjee, O. Deutschmann
Journal of Catalysis (February 2017) Volume 346() pp:30-49
Publication Date(Web):1 February 2017
DOI:10.1016/j.jcat.2016.11.035
•Oxygen reduction on LSM-YSZ is described by elementary kinetics.•Three mechanisms are tested against several sets of experimental data.•The mechanism proposing the chemisorption of O2 on LSM is the most tenable.•The thermodynamically consistent kinetics is intrinsic.•A model-based sensitivity analysis elucidates the rate-limiting steps.A multi-physics based transient, continuum model of a solid oxide half-cell comprising of a porous LSM-YSZ composite cathode sintered to a dense YSZ electrolyte was developed to investigate the oxygen reduction reaction kinetics. The model coupled species, electron and ion transport through the porous cathode to surface and electro-chemistry. The electrochemical reduction of O2 was modeled using three candidate elementary kinetic mechanisms. Each mechanism included parallel surface and bulk pathways for O2 reduction and was driven by three different electric phase potentials. The mechanisms were compared against three sets of electrochemical impedance spectra and polarization curves measured by Barbucci et al. (2009), Cronin et al. (2012) and Nielsen and Hjelm (2014) over a wide range of operating temperatures (873–1173 K), inlet O2 concentrations (5–100%) and overpotentials (−1 V to +1 V). Two of the three mechanisms were able to quantitatively reproduce the three sets of experiments by only tweaking the microstructural parameters for each individual set. Yet on analyzing their kinetic and thermodynamic parameters, the mechanism postulating the chemisorption of gas-phase O2 on LSM to form the superoxo-like adsorbate O2- was determined to be the most realistic. A model-based sensitivity analysis revealed that ionic transport in the YSZ phase, O2 dissociation in conjunction with surface to bulk charge transfer in the LSM phase and charge transfer at the three phase boundary were the rate limiting steps throughout the operating space. Additionally, the bulk pathway was found to be insignificant.Download high-res image (92KB)Download full-size image
Co-reporter:Julius Rischard, Claudia Antinori, Lubow Maier, Olaf Deutschmann
Applied Catalysis A: General (5 February 2016) Volume 511() pp:
Publication Date(Web):5 February 2016
DOI:10.1016/j.apcata.2015.11.026
•High yields of 1,3-butadiene from n-butane produced over Mo-V-MgO catalysts.•Direct oxydehydrogenation and catalyst regeneration integrated in one vessel.•Optimization of inlet position in two-zone fluid bed reactor.•Calcination temperature affects catalyst performance.The oxidative dehydrogenation of n-butane has been studied in a two-zone fluidized bed reactor using two Mo-V-MgO catalysts. Both catalysts have been prepared by incipient wetness impregnation and were calcinated at different temperatures. The operating conditions temperature, flow velocity, n-butane inlet height and oxygen/n-butane molar ratio were varied to maximize 1,3-butadiene yield. At suitable conditions, the two-zone fluidized bed reactor can be operated at steady state performing chemical conversion and catalyst regeneration in a single vessel. The regeneration zone at the bottom of the fluidized bed was used to burn coke depositions as well as to fill up lattice oxygen of the catalyst. After regeneration the catalyst particles can reach the reaction zone due to particle mingling inside the fluidized bed. Different behaviors for both catalysts, despite equal metal content, were observed. The catalyst calcinated at lower temperature tends more to coke formation. Raman spectroscopy, XRD, and BET were used to identify the reason for this. With Raman spectroscopy, small graphite particles were identified on the low temperature calcined catalyst surface. These graphite particles seem to be precursors for coke deposition. The Mo-V-MgO catalyst calcinated at 720 °C leads to an improved selectivity to 1,3-butadiene being 51% and a 1,3-butadiene yield of 32.7% at steady state.Download high-res image (95KB)Download full-size image
Co-reporter:Vikram Menon, Vinod M. Janardhanan, Olaf Deutschmann
Chemical Engineering Science (3 May 2014) Volume 110() pp:83-93
Publication Date(Web):3 May 2014
DOI:10.1016/j.ces.2013.10.025
•A numerical model is developed for Solid Oxide Electrolysis Cells.•The model couples kinetics at the micro-scale level with macro-scale phenomena.•Model is validated with experimental data for SOEC running on H2–H2O.•Electrochemical behavior and irreversible losses during SOEC operation are reported.•Efficiency analysis and limiting current behavior of the SOEC system are studied.In this analysis, we report an in-house model to describe the complex fundamental and functional interactions between various internal physico-chemical phenomena of a SOEC. Electrochemistry at the three-phase boundary is modeled using a modified Butler–Volmer approach that considers H2 as the electrochemically active species. Also, a multi-step elementary heterogeneous reaction mechanism for the thermo-catalytic H2 electrode chemistry, dusty-gas model to account for multi-component diffusion through porous media, and plug flow model for flow through the channels are used. Results pertaining to detailed chemical processes within the cathode, electrochemical behavior and irreversible losses during SOEC operation are demonstrated. Furthermore, efficiency analysis is performed and limiting current behavior of the SOEC system is investigated.
Co-reporter:Hüseyin Karadeniz, Canan Karakaya, Steffen Tischer, Olaf Deutschmann
Chemical Engineering Science (27 September 2014) Volume 117() pp:
Publication Date(Web):27 September 2014
DOI:10.1016/j.ces.2014.06.007
Co-reporter:Julian N. Bär, Canan Karakaya, Olaf Deutschmann
Proceedings of the Combustion Institute (2013) Volume 34(Issue 2) pp:2313-2320
Publication Date(Web):1 January 2013
DOI:10.1016/j.proci.2012.06.115
The ignition (light-off) temperatures of catalytic oxidation reactions provide very useful information for understanding their surface reaction mechanism. In this study, the ignition behavior of the oxidation of hydrogen (H2), carbon monoxide (CO), methane (CH4), ethane (C2H6), and propane (C3H8) over Rh/alumina catalysts is examined in a stagnation-point flow reactor. The light-off temperatures are identified by means of the sudden increase of the catalyst temperature when linearly heating the catalyst for various fuel/oxygen ratios. For hydrogen and all hydrocarbons studied, the results show a rise of ignition temperature with increasing fuel/oxygen ratio, whereas the opposite trend is observed for the light-off of CO oxidation. Hydrogen oxidation, however, shows an opposite trend compared to previous investigations, performed on platinum [1,2].
Co-reporter:A. Li, S. Zhang, B. Reznik, S. Lichtenberg, ... O. Deutschmann
Proceedings of the Combustion Institute (2011) Volume 33(Issue 2) pp:1843-1850
Publication Date(Web):1 January 2011
DOI:10.1016/j.proci.2010.06.037
Synthesis of pyrolytic carbon as a matrix for carbon fiber reinforced carbon composites by chemical vapor infiltration (CVI) is studied experimentally and numerically using the oxygen-containing precursor ethanol. The effects of residence time on microstructure and deposition rate of pyrolytic carbon are investigated. A short residence time is found to favor the formation of high-textured pyrolytic carbon. The evolutions of microstructure and deposition rate of pyrolytic carbon are compared with those of carbon deposited from methane. Compared to methane, ethanol exhibits a much higher deposition rate of pyrolytic carbon with similar microstructures. Pyrolysis of ethanol is modeled using a two-dimensional flow model coupled with a detailed gas-phase reaction mechanism involving 261 species taking part in 1177 reversible reactions. Reaction rate analysis reveals that C3-hydrocarbons are the most important intermediate species contributing to the maturation of gas-phase composition. A comparison of the kinetic predictions with equilibrium calculations demonstrates that the CVD reactor applied is operated far away from equilibrium.
