Lehrstuhl Chemische Verfahrenstechnik

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Optimal design and operation of reactive extrusion processes: application to the production and scale-up of polyurethane rheology modifiers for paints
(2023-10-10) Cegla, Maximilian; Fage, Aleksandra; Kemmerling, Simon; Engell, Sebastian
In this work, the methodology for the optimal design, operation and scale-up of reactive extrusion processes in twin-screw extruders previously presented in Reference (Cegla and Engell, 2023). is applied to the production of hydrophobically ethoxylated urethanes (HEURs). The new process is a promising alternative to the current batch technology in large reactors with long residence times. We demonstrate the use of model-based design and scale-up for this case. A novel mechanistic finite volume twin-screw extruder model is used as the process model, which is adapted to the process at hand by embedding a detailed description of the HEUR chemistry and rheology. An economic cost function is used to examine the scale-up process from an 18 mm extruder to a 27 and 75 mm extruders, considering a selected range of products. The comparison between the optimization results obtained for the individual products with the optimization results for the production of multiple material grades using the same screw setup shows the high flexibility of the extruder-based process. Significant energy savings compared with the conventional batch process can be achieved using reactive extrusion. To quantify the effort for the transition to a purely continuous production in terms of flexibility and process logistics, product changeovers are investigated.
Entwicklung von Halogenierungsverfahren zur partiellen Oxidation von Schwefelwasserstoff und Biomasse
(2023) Wiesehahn, Maximilian; Agar, David W.; Vogt, Dieter
A computer vision sensor for the parallelization of actively regulated capillary slug flow microreactors
(2023-09-11) Gladius, Anoj Winston; Mylenbusch, Jonas A.; Agar, David William
In this work, a computer vision sensor for the extraction of slug length, slug velocity and phase ratio from capillary liquid–liquid slug flows from video feeds in real-time, including the necessary post-processing algorithms, is developed. The developed sensor is shown to be capable of simultaneously monitoring multiple capillaries and provides reasonable accuracy at less than 3.5% mean relative error. Subsequently, the sensor is used for the control of a parallelized and actively regulated dual-channel slug flow capillary microreactor setup. As a model reaction, the solvent-free epoxidation of methyl oleate with hydrogen peroxide and a phase-transfer catalyst based on tungstophosphoric acid and a quaternary ammonium salt to yield the product 9,10-epoxystearic acid methyl ester is conducted. A space–time yield of 0.679 kg L−1 h−1 is achieved.
Theoretical studies on a rotating film reactor for hydrogen production from methane
(2022-03-23) Becker, Tobias; Agar, David W.
A film of liquid metal can protect the reactor wall from carbon deposits during methane pyrolysis, discharge carbon from the reactor and prevent blocking. The film can be generated by rotation in a rotating film reactor. Parameters such as liquid volume flow, operating mode or the diameter of the reactor can have an influence on the reaction behavior. A design of experiments was used to investigate the rotating film reactor in more detail and to characterize the influence of various parameters.
Analysis and simplification of kinetic models for methane chlorination and pyrolysis
(2022-03-10) Keuchel, Florian; Heinlein, Moritz; Hohlmann, Jan; Agar, David W.
So far, no complete reaction mechanism has been proposed for high temperature chlorination and pyrolysis of methane. Various mechanisms for the description of this reaction pathway are combined and compared in this paper. This adaptation shows that the gas phase pyrolysis of methane and methyl chloride can be combined with surface reactions via nucleation from the gas phase or on the reactor wall to reproduce the product spectrum. In addition, kinetic parameters for a global simplified one-step mechanism focused on the formation of carbon are fitted to available experimental data.
Systematic simulation strategy of plasma methane pyrolysis for CO2-free H2
(2022-03-24) Magazova, Aliya; Böddeker, Simon; Bibinov, Nikita; Agar, David W.
Recently, the direct conversion of methane into hydrogen using cold plasma reactors has attracted increasing attention, since hydrogen has considerable potential as a future feedstock in the steel and chemical industries. However, the simulation of plasma pyrolysis reactors is extremely complex due to the vast temporal and spatial ranges of the variables involved and steep gradients. Previously, methane pyrolysis has been meticulously modeled by 0D simulations, and 3D plasma modeling has been largely confined to Argon systems. In this paper, a systematic methodology is presented, which provides an expedient and efficient hierarchy of 0D to 3D simulations, in order to approximate the methane pyrolysis simulation of a plasma reactor in its entirety. Various simulation tools are applied in a coordinated and pragmatic manner. The results show that the proposed synergy allows simplification of the reaction set and arc characteristics, significantly reducing the runtime required for the simulations.
Experimental splitting of hydrogen sulfide by halogens for application in reaction cycles
(2022-04-21) Wiesehahn, Maximilian; Zimmermann, Elodia Morales; Agar, David W.
Hydrogen sulfide is a toxic gas that is almost always present in the processing of crude oil or natural gas and must be removed. In addition, hydrogen can be used as an energy carrier if it can be separated from H2S. In this work, as the first step of a reaction cycle that could achieve just that, the bromination and chlorination of hydrogen sulfide are experimentally studied. It can be shown that both halogens are capable of completely converting hydrogen sulfide in a gas phase reaction. While the chlorination can produce byproducts, the bromination is free of such.
Filmreaktorkonzepte und Strategien zur Vermeidung und Entfernung von Kohlenstoffablagerungen bei der Methanpyrolyse
(2023) Becker, Tobias; Agar, David W.; Ehrhard, Peter
Der Weg zu einer klimafreundlicheren Zukunft führt unweigerlich über die Dekarbonisierung der wichtigsten Wirtschaftssektoren Energie, Bausektor, Verkehr, Industrie und Landwirtschaft. Wasserstoff leistet einen großen Beitrag auf diesem Weg, als alternativer Energiespeicher, Energieträger oder Treibstoff. Emissionsfreier Wasserstoff kann unter Nutzung regenerativer Energien via Methanpyrolyse produziert werden. Das Nebenprodukt Kohlenstoff erhöht durch Verkauf die Wirtschaftlichkeit des Prozesses, erzeugt aber auch verfahrenstechnische Herausforderungen. Akkumulation von Kohlenstoff endet unumgänglich mit einer Verblockung des Reaktors. Zur Vermeidung und Entfernung von Kohlenstoffablagerungen wurden verschiedene Reaktorkonzepte studiert. Im Fallfilmreaktor und im rotierenden Filmreaktor wird die Wand durch einen Film flüssigen Metalls vor Ablagerungen geschützt. Beide Reaktoren wurden experimentell, mit Schwerpunkten hinsichtlich der Ausbildung des Films, der Filmdicke und des Verweilzeitverhaltens, untersucht. Mit CFD-Modellen wurden die Pyrolysereaktion in den Reaktoren und die Abtrennung von Kohlenstoffpartikeln beleuchtet. In einem Fallfilmreaktor (L = 3 m, ⌀ = 26 mm) konnten bei 1600 K hohe Umsätze von > 90 % erzielt werden. Der Gleichstrombetrieb wurde als vorteilhaft identifiziert und mehr als 75 % des produzierten Kohlenstoffs konnten über den flüssigen Film abgetrennt werden. Der rotierende Filmreaktor wurde etwas kürzer (1,7 m) und breiter (. = 44 mm) ausgeführt. Umsätze > 83 % wurden bei gleichem formalen Reaktionsvolumen erreicht. Die Abtrennung des Kohlenstoffs wurde durch die Rotation des Reaktors verbessert. Ab Partikelgrößen von 5 µm konnte der Kohlenstoff nahezu vollständig über den Film abgetrennt werden. Neben den Filmreaktorkonzepten, wurden Bildung, Einfluss auf die Reaktion und Entfernung von Kohlenstoff in Rohrreaktoren untersucht. In kinetischen Untersuchungen wurde gezeigt, dass im Reaktor akkumulierender Kohlenstoff die Reaktion beschleunigt. Mit einem Modell aus Gasphasen- und Oberflächenreaktion konnten die Effekte gut beschrieben werden. Zuletzt wurden die Kohlenstoffverblockungen mit einer Pressvorrichtung mechanisch entfernt. Die zur Entfernung notwendige Kraft steigt mit der Kohlenstoffmenge im Reaktor und ist abhängig vom Reaktormaterial.
Novel adsorptive reactor configurations: fundamental conceptualisation for design and operation
(2023) Hussainy, Mamoon; Agar, David W.; Held, Christoph
There has been considerable interest in recent years in “intensified processes” that allow for the substantial amelioration of chemical processes in terms of equipment dimensions, costs, and safety. The integration of an additional separative functionality into chemical reactors can be used to manipulate the concentration and temperature profiles and thus dramatically enhance reactor performance. The resultant improvements in conversion and selectivity can, in turn, simplify or even eliminate the downstream processing necessary. Adsorptive reactors, in which adsorptive and reactive functionalities are combined, represent a promising example of the bifunctionality in industrial chemical reactors. In this research work, intensive yet comprehensive multiscale and multidimensional modelling and simulation studies have been conducted dealing systematically with the relations of the available degrees of freedom to one another and to the performance of adsorptive fixed bed reactors. The goal was to obtain know-how-oriented strategies to maximise the performance of adsorptive reactors. Amongst the several degrees of freedom available in design and operation of adsorptive reactors, it was found that the spatial distribution of the adsorptive and catalytic functionalities at the reactor level (macrostructuring) and the temperature profiling over the reactor length have been shown to be decisive factors for maximising adsorptive reactor performance. Considering the industrially-relevant Claus and Deacon reactions as test cases, two novel designs have been proposed, the multilevel isothermal and the central isothermal sandwich designs, by which a multi-fold performance improvement compared to the corresponding isothermal and adiabatic simple uniform structure adsorptive reactor designs could be attained even with incorporating the regeneration process necessary, where the cyclic steady state was calculated based on the direct substitution method. The improvements in space time yields obtained by the foresaid novel designs were respectively 700% and 650% for Claus reaction and 35-fold and 18.5-fold for Deacon reaction. The overall feasibility of these novel designs can be envisaged in the light of the considerable cost reduction, which compensate for the extra costs required for the technical realisation of the proposed designs, achieved by avoiding the expensive tail-gas treatment processes in case of Claus reaction or by simplified downstream processing in case of Deacon reaction.
Gas-consuming triphasic gas-liquid-liquid reactions in segmented slug flow
(2023) Vietinghoff-Scheel, Niclas von; Agar, David W.; Kockmann, Norbert
The chemical industry in Europe is transforming. Diversifying raw materials, an increased circular economy and a growing market of specialty chemicals require flexible and fast process development. Small-scale continuous reactors can contribute to these requirements. In particular, triphasic gas-liquid-liquid slug flows can perform complex multiphase systems at a laboratory scale. This work investigates strategies to counteract a gas shortage in gas-consuming reactions in such capillaries. On the one hand, gas permeation through the polymer capillary is investigated, and its influence on an existing slug flow is studied. On the other hand, individual gas bubbles are integrated into the slug flow using valves and an electrolysis cell. Both methods preserve the advantageous slug flow - however, they have advantages and disadvantages depending on the reaction applied. Moreover, they can be used in a scale-up of capillary reactors, contrary to established methods. For success in scale-up, inexpensive and robust sensors are necessary in addition to gas-feeding methods. For this purpose, non-invasive optoelectric sensors are developed for triphasic slug flows, which can detect the flow (velocity, phase ratios, segment lengths), but also determine local concentrations. Both light refraction and light absorption are exploited. Concentration sensors are used to study the homogeneously catalyzed hydrogenation of a dye to a colorless form. A change in hydrodynamic parameters had only minor effects compared to chemical parameters. However, the reaction was significantly intensified compared to a stirred tank reactor. Finally, selective fat hydrogenation in a triphasic slug flow is investigated. A suitable solvent selection can counteract unfavorable solid formation. The monounsaturated fatty acid could be selectively obtained from sunflower oil with a high content of polyunsaturated fatty acids.
Energetische Integration der CO2-Gewinnung direkt aus der Luft und seiner Methanisierung mit erneuerbarem Wasserstoff
(2022) Qiao, Yu; Agar, David W.; Tiller, Jörg C.
Global warming is posing a threat to our environment and our life. The major cause of global warming is the increase global atmospheric CO2 concentration from 280 ppm in the preindus-trial era to 415 ppm in 2020. The heavy reliance on fossil fuels as the primary energy sources results in globally over 30 Gt/year of energy-related CO2 emissions in this decade. To address the global issues of the threat of climate change, a common goal for limiting global warming was set in the Paris Agreement by the Intergovernmental Panel on Climate Change (IPCC) in 2015, which aims to restrict the global average increase in temperature to 1.5-2 °C by the end of this century. Moreover, the IPCC 2018 special Report restates the consensus of reducing the global net greenhouse gas emissions to zero by 2050. This indicates that a transition to net-zero CO2 emissions by 2050 is imperative. There are three main pathways for achieving the target of net-zero CO2 emissions. The first pathway is using renewable energy instead of fossil fuels as primary energy to reduce the sources of CO2 emissions. The second pathway is scaling up of carbon dioxide removal tech-nologies, namely the carbon capture and storage (CCS) technologies to lower current CO2 emis-sion rates from large stationary sources. The last pathway is applying the negative emissions technologies (NETs) to recapture the carbon dioxide previously released due to human activi-ties in the atmosphere. Among all the carbon dioxide removal (CDR) technologies, direct air capture (DAC) of CO2 with chemicals is the most promising NET with advantages such as a low demand of land and water use, high flexibility for location choosing, high technical feasibility, high scalability, and low risk. DAC faces the only significant challenge of decreasing its high costs. An attractive alternative to circumvent the intensive energy requirements for the regeneration of the adsorbents in the DAC is the coupling of the endothermic DAC process with an exother-mic process such as Power to Gas (Methane), i.e. the conversion of surplus renewable energy into chemical energy in the form of gas. The exothermic Sabatier reaction for the methanation of CO2 with renewable hydrogen is able to supply the heat to the DAC and thus reduce the cost for recapturing CO2 from ambient air. Based on this idea, a concept of an energetic integrated DAC-PtG system has been introduced in this work. The energetic integrated processes have been modeled and simulated with the software Aspen Custom Modeler® (ACM). The heat recovery system has been optimized by using a Pinch analysis. A systematic analysis of the energy demand and an economic evaluation have been made in order to evaluate the potential value of this concepts. Besides the energetic analysis of the integrated DAC-PtG system, the experimental studies for the DAC and methanation process were carried out separately in the laboratory. Lewatit® VP OC1065 has been selected from the adsorbent screening tests as the most suitable adsorbent for the DAC process. In order to identify its thermodynamic and kinetic performances during the ad- and desorption process, the adsorbent Lewatit® VP OC1065 has been examined in a mon-olithic and a fixed-bed adsorber. The methanation of CO2 has also been investigated with a parameter study using the method of statistical test planning on the 5 wt.% Ru/Al2O3 catalyst in an isothermal fixed-bed reactor. The results of this work present the possibility to integrate a DAC facility with a PtG device applying heat exchange to reduce the price of CO2 recovery from ambient air and to enhance the energy efficiency.
Kreuz-Gegenstrom-Verschaltung zum Numbering-up der Pfropfenströmung zu Extraktionszwecken
(2021-10-13) Schwarz, Christian Andreas; Mendelawi, Mehdy; Agar, David W.
In der Mikroverfahrenstechnik limitiert die Miniaturisierung den maximalen Durchsatz einer µ-Mixer-Settler-Einheit. Eine Steigerung der Produktion kann daher nur durch die Parallelisierung mehrerer Extraktionseinheiten erfolgen. Ein Strang aus n im Gegenstrom verschalteten Stufen benötigt dabei n + 1 Pumpen, der parallele Betrieb von m Strängen bereits m (n + 1) Pumpen. Ein neues Verschaltungskonzept wird vorgestellt, das die notwendige Pumpenzahl auf 2m + n – 1 reduziert. Das Konzept wird theoretisch diskutiert. Experimente belegen die prinzipielle Realisierbarkeit der Fluiddynamik.
Slug flow as tool for selectivity control in the homogeneously catalysed solvent-free epoxidation of methyl oleate
(2021-10-05) Gladius, Anoj Winston; Vondran, Johanna; Ramesh, Yashwanth; Seidensticker, Thomas; Agar, David W.
Catalytic oxidation of sustainable raw materials like unsaturated fats and oils, or fatty acids and their esters, lead to biobased, high-value products. Starting from technical grade methyl oleate, hydrogen peroxide as a green oxidant produces only water as by-product. A commercially available, cheap water-soluble tungsten catalyst is combined with Aliquat® 336 as a phase-transfer agent in solvent-free reaction conditions. In this study, we first report the transfer of this well-known batch system into continuous mode. The space–time yield is improved from 0.08 kg/L.h in batch to 1.29 kg/L.h in flow mode. The improved mass transfer and reduced back mixing of the biphasic liquid–liquid slug flow allows for selectivity control depending on physical parameters of slug flow namely volumetric phase ratio, volumetric flow rate, and slug length. Even though the product, methyl 9,10-epoxystearate is obtained at a maximum selectivity of only 58% in flow mode, higher space time yield combined with possible reactant recycling in flow mode offers a promising avenue of research. This work analyses the use of slug flow parameters as tools for controlling selectivity towards oxidation products of methyl oleate.
CFD modeling of reactor concepts to avoid carbon deposition in pyrolysis reactions
(2021-02-23) Becker, Tobias; Keuchel, Florian; Agar, David W.
Methane pyrolysis in an externally heated tubular reactor inevitably ends with clogging of the reactor. Thin molten metal wall films protect the walls from carbon depositions. A falling film reactor and a rotating film reactor are investigated by CFD simulation. The results show the considerable advantages of a rotating film reactor compared to the vertical film reactor. An alternative route for carbon production from methane is the implementation of an exothermic chlorination reaction. The tubular reactor concept involves the inflow of inert gas at the reactant inlet and through porous walls to ensure that the reaction takes place in the center, thus, largely reducing carbon deposits.
Ausarbeitung der Pfropfenströmung zum effektiven Extraktionswerkzeug in der Mikroverfahrenstechnik
(2021) Schwarz, Christian Andreas; Agar, David W.; Ehrhard, Peter
Der allgemeine Trend zur Prozessintensivierung lässt die Mikroverfahrenstechnik aufgrund ihrer charakteristischen kurzen Transportwege fürWärme- und Stoffströme in den Interessensfokus rücken. Speziell für rein transportlimitierte Prozesse wie die Extraktion kann eine Miniaturisierung erhebliche Verbesserungen hervorbringen. Im Rahmen dieser Arbeit wurde daher die flüssig-flüssig Pfropfenströmung als Extraktionswerkzeug weiterentwickelt. Zum einen wurde dabei die Beseitigung bisheriger Nachteile beim Einsatz der Pfropfenströmung fokussiert. Hierzu zählen die noch nicht abschließend erforschten Vorgänge bei der Phasentrennung, sowie der noch erhebliche Aufwand bei der Parallelisierung. Zum anderen wurde die Pfropfenströmung in Anwendungsgebieten untersucht, die für bisherige Extraktionsapparate noch große Herausforderungen darstellen. Die Vorgänge während der Phasentrennung wurden durch numerische Simulationen näher untersucht. Hierfür wurde als ein Hauptpunkt der Arbeit eine numerische Methode mit besonders geringen parasitären Strömungen entwickelt. Bei hohen Volumenströmen wurden dabei instationäre Beschleunigungsdruckverluste in den Fluidausgängen des Trennapparates als signifikanter Einfluss identifiziert. Daraufhin wurden experimentell Trennweisen untersucht, die derartige Beschleunigungseffekte auf das Volumen des Trennapparates begrenzen können. Die Reduzierung der Druckverluste und der Verzicht auf feinporige Membranen erlaubten den Einsatz von Ferrofluiden als disperse Phase, wodurch magnetische Spulen als Sensor eingesetzt werden konnten, die in Folgearbeiten gleichzeitig als Aktuator wirken können. Parallel wurde die Pfropfenströmung bei der Extraktion aus hochviskosen Medien heraus charakterisiert, da die bisher konventionell eingesetzten Extraktionskolonnen bei geringen Dichtedifferenzen, hohen Grenzflächenspannungen und viskosen Fluiden entweder keinen stabilen Gegenstrombetrieb mehr erlauben oder starke Einbußen im Stofftransport verzeichnen. Um die Pfropfenströmung unter diesen Bedingungen effektiv parallelisieren zu können, wurde ein Verschaltungskonzept erarbeitet und in kleinen Dimensionen experimentell plausibilisiert. Die Pfropfenströmung wird auf Basis der erarbeiteten Ergebnisse für die Anwendung auf herkömmliche Extraktionsaufgaben nicht als konkurrenzfähig bewertet. Stattdessen konnte die Pfropfenströmung als vielversprechendes Werkzeug überzeugen, wenn die Dichtedifferenz beider Phasen besonders klein ist, die Grenzflächenspannung hoch ist, oder derWertstoff aus einer hochviskosen Phase herausextrahiert werden soll.
Integrated adsorber concepts for use in direct air capture and power-to-gas applications
(2021) Drechsler, Carsten; Agar, David W.; Grünewald, Marcus
Die Anwendung technologischer Konzepte zur direkten Abtrennung des Treibhausgases Kohlenstoffdioxid (CO2) aus atmosphärischer Luft (Direct Air Capture, DAC) wird als einer der vielversprechendsten Ansätze zur Abschwächung des anthropogenen Treibhauseffekts betrachtet. Deren großtechnischer Einsatz wird jedoch durch verschiedene intrinsische Limitierungen erschwert, welche sich insbesondere aus dem stark verdünnten Zustand von CO2 in der Atmosphäre ergeben und in einen unzulässig hohen CO2-spezifischen Energiebedarf des Abtrennungsprozesses resultieren können. Durch Detailmodellierung und Simulationsstudien wird gezeigt, dass die in dieser Arbeit entwickelten Wärmeintegrationsstrategien und deren technische Realisierungen inner halb neuartiger Band- (MBtA) und Wanderbettadsorberkonzepte (MBdA) eine signifikante Reduktion des CO2-spezifischen Wärmebedarfs von thermischen Sorbentregenerationskonzepten ermöglichen. Die Problematik von Wasserkoadsorption auf DAC-Sorbentien, welche im Rahmen ausführlicher experimenteller Studien innerhalb dieser Arbeit bestätigt wird, kann jedoch zu einem zusätzlichen, signifikanten CO2-spezifischen Wärmebedarf innerhalb des Regenerationszyklus des Sorbents führen. Insbesondere eine Rückgewinnung der im desorbierten Wasserdampf gespeicherten Latentwärme durch mechanische Brüden- kompression (MVR) wird innerhalb dieser Arbeit als ein vielversprechender ingenieurtechnischer Ansatz zur Reduzierung der H2O-Koadsorption bedingten Energiestrafe identifiziert. Die entwickelten Konzepte werden innerhalb eines Power-to-Gas (PtG) Prozesses als wärmeeffiziente CO2-Quelle integriert. In diesem Zusammenhang zeigen durchgeführte Detailsimulationen und Pinchanalysen, dass durch eine gezielte Ausnutzung der Synergien innerhalb der Prozessstruktur ein hoch-ressourceneffizenter DAC-PtG Prozess realisiert werden kann. Dieser ermöglicht eine autotherme Produktion von Methan ausschließlich auf der Basis von erneuerbaren Energien und den Edukten Kohlenstoffdioxid und Wasser, welche aus atmosphärischer Luft gewonnen werden.
Fluiddynamik und Stofftransport der Gas-Flüssig-Flüssig-Pfropfenströmung in Mikrokanälen
(2021) Hellmann, David; Agar, David W.; Kockmann, Norbert
In der vorliegenden Arbeit wird die Gas-Flüssig-Flüssig-Pfropfenströmung als neues Mikroreaktorkonzept untersucht. Der Fokus liegt dabei auf der Nutzung des Kapillarreaktors für heterogen katalysierte Reaktionen mit in der Pfropfenströmung suspendiertem Katalysator. Zur Erzeugung der dreiphasigen Strömung wurde mit dem doppelten koaxialen Kontaktor ein neues Konzept entwickelt, welches den Strömungsbereich mit ähnlichen Phasenanteilen erschließt und dabei eine regelmäßige Pfropfenstruktur mit geringen Schwankungen in der Pfropfengröße aufweist. Mit der Entwicklung von miniaturisierten Membranelektrolysezellen wurde eine Möglichkeit zur pulsationsfreien Gaserzeugung entwickelt. Neben der Strömungserzeugung konnte auch eine Voraussage wichtiger Parameter wie Strömungsgeschwindigkeit, Druckverlust und Aufbau der Pfropfenströmung erreicht werden. Der Übergang von einer Pfropfenströmung mit Wandfilm zu einer Blockströmung ohne Wandfilm wurde für zwei- und dreiphasige Systeme untersucht und daraus Kriterien für die dreiphasige Strömung entwickelt, welche eine Voraussage der Wandfilmausbildung erlauben. Durch eine Modellierung einer heterogen katalysierten Konsekutivreaktion im dreiphasigen Suspensions-Kapillarreaktor und im Batchreaktor konnte gezeigt werden, dass der dreiphasige Suspensions-Kapillarreaktor eine dem Batchreaktor ähnliche Selektivität und Ausbeute ermöglicht und somit die Vorteile von Batchprozess und kontinuierlichem Betrieb kombiniert.
Coaxial flow contactors as alternative to double T-contactors for triphasic slug flow generation
(2020-04-06) Hellmann, David; Oliveira-Goncalves, Ícaro de; Agar, David W.
Triphasic gas-liquid-liquid slug flow systems have great application potential in flow chemistry and are normally generated with a double T-junction where the continuous phase and one disperse phase form a two-phase flow and the second disperse phase is added at the second junction. This design is limited to high disperse phase ratios when a regular and uniform flow is desired. The use of coaxial contactors allows overcoming most of these restrictions. The slug generation, stability, and regularity of the generated triphasic flow were experimentally characterized.
CO2-free energy from natural gas via BrOx cycle
(2020) González Rebordinos, Jesús; Agar, David W.; Grünewald, Marcus
In the present work a novel process for energy generation from natural gas without concomitant CO2 emissions, namely the Bromination-Oxidation (BrOx) cycle, is proposed and studied. This process consists of two exothermic reactions and an internal brominere cycle. Methane and bromine react in the first reaction step to yield solid carbon, that is separated by means of a cyclone or a filter, and hydrogen bromide. The latter is oxidised with oxygen in a second reactor yielding water and bromine. Bromine is separated and recycled to the first reaction step so that the energy is released in the process with solid carbon and water as only by-products. Firstly, the thermodynamics of the process were studied to assess its feasibility and simulations on both reaction steps in plug flow reactors were carried out in order to estimate suitable reaction conditions. A bench-scale plant was constructed to study experimentally methane bromination and determine temperatures and residence times that lead to complete reaction and carbon formation. Additionally, the carbon produced was characterised and its bromine content quantitatively determined. During methane bromination carbon deposition occurs, leading to inefficient operation. Two reactor concepts were proposed in this work, a vortex reactor that avoids deposition via the hydrodynamics of the system, and a sacrificial wall reactor in which deposition is not avoided but reactor cleaning is facilitated by means of a sacrificial coating on the inner walls. CFD simulation and optimisation of the vortex reactor was performed while sacrificial walls were studied experimentally. A catalyst for the second reaction step, hydrogen bromide oxidation, was synthesised and characterised, and experiments on both thermal and catalytic oxidation were carried out. Moreover, both operation modes were simulated and modelling was used to propose an optimal strategy for this reaction step. Finally, the flowsheeting of the BrOx cycle, including a preliminary economical analysis of the process, was performed and convenient separation units and operation parameters were selected based on the aforementioned data and simulation result.
Photoelectric sensor for fast and low-priced determination of bi- and triphasic segmented slug flow parameters
(2020-12-04) Vietinghoff, Niclas von; Lungrin, Waldemar; Schulzke, Raphael; Tilly, Jonas; Agar, David W.
Applying multiphase systems in microreactors leads to an intensification of heat and mass transport. Critical aspects of the well-studied segmented slug-flow, such as bubble generation and pump control, can be automated, provided a robust sensor for the reliable determination of velocity, phase lengths, and phase ratio(s) is available. In this work, a fast and low-priced sensor is presented, based on two optical transmission sensors detecting flow characteristics noninvasively together with a microcontroller. The resulting signal is mainly due to refraction of the bubble-specific geometries as shown by a simulation of light paths. The high performance of the processing procedure, utilizing the derivative of the signal, is demonstrated for a bi- and triphasic slug flow. The error of <5% is entirely reasonable for the purpose envisaged. The sensor presented is very fast, robust, and inexpensive, thus enhancing the attractiveness of parallelized capillary reactors for industrial applications.

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