Thöming, Jorg
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Thöming, Jorg
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Thöming, Jorg
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Item-typ:Veröffentlichung, Gradierte poröse Strukturen zur Optimierung verfahrenstechnischer Prozesse : Anwendung in der Autothermen Dampf-Reformierung(2010-11-05); ; ; Many applications in chemical and process engineering are based primarily on the characteristics of porous materials. Therein, properties as pore size or porosity strongly affect mechanisms like mass transfer, heat transfer or catalytic efficiency. Against this background, this work investigates the possibility of using materials with properties distributed over space instead of using homogenous structure. The target of this investigation was to develop optimization tools for designing graded porous structures optimized for the use in process applications. As an example, this method was developed for reducing the temperature peak in the entrance of an autothermal steam-reformer by optimizing two porous elements. In the first case, an oxygen feed membrane was designed that on each position inside the reformer the right amount of oxygen is fed to the reaction such that the heat production by exothermic oxidation and the heat consumption by reforming reactions is always balanced. The result was a membrane with exponentially decreasing permeability leading to an almost constant temperature profile over the length of the reformer. This was true for simulation results as well as for experimental results in a lab scale reformer. For the other element, the structure of the catalyst support and therefore the total activity of the catalyst via the volumetric surface were on focus of the optimization. Also with this porous element, it was possible to reduce the temperature peak. The latter gives the big advantage to not only put the temperature profile on target but as well more financial values like conversion rate or selectivity.Dissertation291 448 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Rückgewinnung zweiwertiger Kationen aus Komplexmedien durch prozessintegrierte Nanofiltration(2014-01-21); ; ; In the present work, the nanofiltration for effective wastewater treatment of process bath wastewater from surface treatment plants contaminated with heavy metals was studied. The primary aim was to recover divalent ions from complex solutions and to reuse the nanofiltration permeat. A mathematical model for describing the nanofiltration was used and in a simulation model for the entire rinsing process involved. Since the separation behavior of nanofiltration membranes depends on the solution composition and its concentration as well as on the alkaline-acidic conditions, several mono- and divalent aqueous electrolyte solutions at different pH values were investigated. The most important parameter for the separating capacity is the membrane charge that changes strongly depending on the solution properties. The use of nanofiltration in the acidic pH range allowed even with an effective pressure of 5 bar the retention till 98 - 99R0of valuable process bath components and at the same time environmentally hazardous heavy metal ions such as nickel and zinc as it was shown in good agreement between simulation and experiment. The validated nanofiltration model was integrated in a rinsing cascade and so allowed the simulation of a circulating the nanofiltration permeat. The permeate quality was found to be sufficiently good to reduce the drag-out from the last rinsing bath so that the heavy metal concentrations were below the limits of direct discharge.Dissertation315 133 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Recovery of Ionic Liquids from aqueous solution by NanofiltrationThe T-SAR methodology was combined with membrane characterization methods. An application of the combined approach was demonstrated with two commercial nanofiltration membranes and it was possible to successfully predict their performance for the recovery of ionic liquids from aqueous solution. Using model solutions of Pyr16 (CF3SO2)2N, it could be evidenced the formation of a new phase of ionic liquid during the concentration process. In this case, 66% of the ionic liquid was separated and the effective recovery rate was duplicated up to 30% by using a coalescence filter. Hydrophobic ionic liquids from wastewaters produced in biotransformations of 2-octanone to 2-octanol, could be recovered as a separate phase, but hydrophilic ionic liquids which are used for the dissolution of cellulose and its subsequent regeneration could be only recovered as an aqueous solution. Recommendations for the systematic recovery of ionic liquids from industrial wastewaters were also introduced.Dissertation335 165 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, ECO-OPTIMIZATION OF RINSING AND RECYCLING NETWORKS IN METAL FINISHING(2009-01-23); ; ; Targeting sustainable production processes is a question of achieving more cost effective and environmental friendly material balances than being only an economic and environment orientated aim. For optimization approach this means solution of multi-objective problems. Therefore, the aim of this work is developing a general applicable optimization method, which enables the design of economic and ecological better processes and provides an instrument for eco-process design. With this motivation development of an ECO-optimization method, which is based on a superstructure that can consider both ecological and economic aspects simultaneously during process synthesis, comes out to be the central question of this work. This presented work provides a tool for decision making and strategically planning in systematic analysis of process flow diagrams assessing a system's environmental relevance as well as eco-eco trade off.Dissertation270 156 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Solid sponges as support for heterogeneous catalysts in gas-phase reactions(2017-12-07); ; ; Solid sponges combine large specific surface areas and low pressure losses with excellent heat transport properties. Thus, they are promising catalyst supports for endo- and exothermic processes. Nevertheless, design tradeoffs regarding the porosity and window diameter of solid sponges with respect to high catalyst densities, low pressure losses, and high effective thermal conductivities remain unsolved. Therefore, a 2-d pseudo-homogeneous multi-scale reactor model for solid sponges is developed in this work. The model is validated against polytropic lab-scale experiments for the methanation of carbon dioxide in a fixed-bed reactor. In order to quantify and analyze the design tradeoffs, the model is used to solve the outlined multi-objective optimization problem. Moreover, tailored graded solid sponges with an optimal porosity distribution in the radial direction are introduced to successfully resolve the existing design tradeoffs.Dissertation1004 457 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Validation of modeling approaches of heterogeneously catalyzed gas phase reaction processes by applying NMR imaging methods(2017-12-06); ; ; This thesis describes the first application of conventional magnetic resonance spectroscopic imaging (MRSI) as a validation tool for gas phase reactor models. For this purpose, techniques were developed that enable the in situ characterization of a model gas phase reaction process. These MRSI approaches allow concentration and temperature measurements inside operating catalyst beds which are considered difficult to measure by conventional, non-invasive methods. The system studied was the ethylene hydrogenation reaction catalyzed in a macroscopic nuclear magnetic resonance (NMR)-compatible fixed-bed flow reactor. Since NMR signals from the gas phase decay very rapidly, MRSI methods are required which allow fast data acquisition after NMR excitation. Thus, a multislice NMR spectroscopic imaging approach was optimized and implemented on a 7-Tesla NMR imaging system to realize ultrashort echo time TE. This method was used in a first approach to evaluate the applicability of MRSI to study gas phase concentrations within a packed bed reactor. The catalyst bed contained inactive Al2O3pellets and catalytically active Pt-Al2O3-pellets to enable the distinction of reactive and non-reactive zones. Spatial maps of the chemical composition could be extracted from the MRSI data sets and allowed the detection of single active catalyst pellets, as well as overall ethylene conversion. Simultaneous integral mass spectrometric (MS) measurements were in fairly good agreement with the MRSI measured concentrations. Building on these results, the multislice approach was extended and optimized to enable 3D MRSI measurements for the investigation of concentration distributions within opaque monolithic catalysts. The model reaction was catalyzed by a Pt-coated sponge packing or a honeycomb monolith (A : 25 mm; L: 50 mm). The 3D MRSI measurements allowed the determination of support structure depending concentration patterns and overall reaction progress. To prove the plausibility of the MRSI data, the experimental results were compared to a 1D model of the reactor based on kinetic data from the literature. Measured and simulated concentration profiles were in good agreement. Furthermore, a comparison with simultaneously performed integral MS concentration measurements demonstrated deviations below 5%. Finally, concentration mapping within the monolithic catalysts was combined with simultaneously detected temperature profiles. For this purpose, specially designed ethylene glycol filled NMR multipoint thermometers were inserted into the monolithic catalysts. The analysis of the ethylene glycol spectra enabled the detection of nearly continuous longitudinal temperature profiles. The results of the 3D MRSI measurements were compared to simulations of a predictive two dimensional model of the processes. Simulated and measured concentration and temperature profiles were in very good agreement, the deviations were below 9 %. Conventional MS measurements provided further evidence of the accuracy of the 3D MRSI measurements as well as of the 2D reactor model. These results demonstrate the great potential of 3D MRSI for studying heterogeneously catalyzed gas phase reactions within macroscopic tubular reactors, and supporting the development and validation of physically consistent reactor models.Dissertation596 313 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, The contribution of molecular interaction potentials to properties and activities of ionic liquid ions in solution(2012-04-23); ; ; Ionic liquids (ILs) have attracted significant interest due to their beneficial and tuneable physicochemical properties. To experimentally identify the IL structure(s) most suited for a certain technical purpose with no adverse effects to man and the environment, it would result in a nearly insurmountable number of trial and error experiments. Therefore, it is essential to understand their molecular interaction potentials. Thus, experiments were carried out with high performance liquids chromatography to estimate the molecular interaction potentials of 30 cations and 20 anions. An in silico method, i.e. COSMO-calculation, was employed to calculate the descriptors for more conventional and easily accessible approaches. Then using the measured and calculated molecular interaction potentials, it was established prediction models for the physicochemical and biological property of ILs in various environments.Dissertation309 92 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Continuous separation of microparticles in aqueous medium by means of dielectrophoresis(2016-11-11); ; There is a widespread need to separate microparticles suspended in liquid media. Dielectrophoresis (DEP), a technique for manipulating the motion trajectories of suspended particles, has enormous potential for solving difficult particle-particle separation problems. Nevertheless, the great majority of DEP applications have been limited so far to microchannels and lab-on-a-chip devices, with throughput typically in the A LA min-1 range. A promising, alternative solution to this problem is anticipated by upscaling DEP systems to enable high-throughput DEP separation on a clinical or industrial scale. To achieve this, a novel interdigitated electrode (IDE) design is proposed to meet the need for a high electric field when upscaling a DEP system. Numerical simulation using OpenFOAM demonstrated that, when replacing conventional plate IDE by cylindrical IDE (cIDE) in microchannel systems, the dielectrophoretic force field, represented by the gradient of the squared electric field, becomes stronger and more homogeneously distributed along the electrode array. The resulting particle DEP velocities were also higher for the cIDE. Simulations confirmed by experiments allow further predictions of particle motion in enlarged cIDE-DEP systems. Understanding how the interplay of channel geometry and electrode concept affects induced particle velocity is crucial when designing DEP separators having sufficiently high throughput to reach preparative scale. The objective of tailored design is to control particle motion trajectories predominantly by DEP while avoiding electrothermal interference in the form of fluid convection induced by a temperature gradient in the liquid phase due to Joule heating. One solution to this Joule heating problem in large-scale DEP systems is to tailor the ratios of electrode diameter, electrode distance and channel height. Based on model calculations, the influence on particle trajectories of both DEP force and drag force due to thermal convection was predicted for a case study involving a channel with rectangular cross section and an array of cIDEs at the bottom. The models were successfully verified by experimentally measuring and quantitatively analysing velocities of polyelectrolytic resin microparticles located at the subsurface of demineralized water. This allowed a qualitative sensitivity analysis of the impact of voltage input, particle size and medium properties on critical design parameters. From this, design criteria were deduced for the cIDE-DEP system that allow the influence of Joule heating to be minimised. There is still a need for continuous, contact-free fractionation of microparticles at high throughput. To achieve this, a sheath-flow-assisted dielectrophoretic continuous field-flow separator with a tailored arrangement of cIDE was developed, and size-dependent trajectories of dispersed particles were observed. Using a voltage input of 200 Veff at a frequency of 200 kHz, polystyrene particles (45, 25, and 11 Amicrometre in diameter) were levitated to different heights due to a negative DEP force. Experimental observations agree well with simulated particle trajectories that were obtained from by a modified Lagrangian particle tracking model in combination with Laplace's and Navier-Stokes equations. A theoretically calculated system throughput of up to 47 mLA min-1 was found to be possible by trading off design and operation parameters, enabling contact-free fractionation of sensitive microparticles with negligible shear stress. For further upscaling of the cIDE-DEP separation system, a new separation device with concentrically arranged cIDE configuration was proposed. Proof-of-concept is demonstrated by numerically predicting microparticle motion trajectories within the separator. Simulations show that a remarkable increment of suspension throughput can be achieved by the concentric cIDE separator compared to the cIDE separator under the same circumstances. From an evaluation of the impact of operating parameters on particle displacement, it can be deduced that continuous fractionation is possible even at system throughputs in the of hundreds of mLA min-1 range by using the concentric cIDE separator. These theoretical findings lay the foundation for continuous DEP-based microparticle separation on an industrial scale.Dissertation459 333 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, On the dielectrophoretic particle retention in porous media(2018-01-31); ; ; Dielectrophoresis (DEP) is a very suitable particle manipulation technique that is able to solve a range of separation problems because it is label-free, very sensitive and, if applied correctly, highly selective towards a specific target particle. DEP has mostly been researched and applied (bio-)analytical chemistry to solve separation problems on lab-on-a-chip devices at uL/min throughputs, which makes it incompatible for industrial scale processes. This thesis investigates a high-throughput method, DEP filtration, which is particle retention due to DEP in porous media. Particle retention dynamics in model porous media are scrutinized using simulative and experimental methods. Particle movement in transparent microchannels gives first-hand insight into DEP trapping dynamics. The results presented pave the way toward actual high-throughput DEP filtration that could tackle important separation problems, such as the separation of metal from scrap in recycling.Dissertation961 281 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, On gaseous microflows under isothermal conditions(2013-03-13); ; ; Flow processes of gases and related heat and mass transfer properties in smallest channels or porous structures are of utmost interest for many technical application in engineering science. This so-called microflows occur for instance in geometrically defined microchannels which are parts of Micro/Nano Electro Mechanical Systems (MEMS/NEMS) or in porous catalysts or filters. In such applications the heat transfer or the yield in gas phase reactions is crucially dependent on the flow behavior. In microflows the fluid gas phase is in a state called rarefied, when the distance of solid boundaries is on the same order of magnitude as the gaseous mean free path. The ratio of mfp to a characteristic length is defined as the Knudsen number which is reciprocally proportional to the gaseous pressure. Hence, also gases in larger structures can be rarefied if the pressure is sufficiently low. For instance in vacuum applications or high altitude aerodynamics gaseous rarefaction has to be taken into account. Depending on the dimensionless quantified rarefaction it is commonly known that continuum fluid dynamics fail for modeling gas flows in very small geometries. Rarefied flows behave totally different as continuum flows. Hence research on gaseous microflows can contribute to the general understanding of rarefaction effects.Dissertation668 353