Lehrstuhl Fluidverfahrenstechnik

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Towards reliable characterization and model-based evaluation of organic solvent nanofiltration
(2021) Goebel, Rebecca; Vogt, Dieter; Skiborowski, Mirko
The interest in organic solvent nanofiltration (OSN) increased substantially in both academia and industry during the last decades, since it provides a great potential for energy savings. However, despite the advantages, there are still limitations, that lead to the fact that OSN is rarely considered as a competitive separation operation in process design. For a reliable evaluation of process design, the uncertainties in labscale measurements and the quantification of model parameter precision are major factors and the prediction of flux and rejection is additionally essential in order to reduce experimental effort for feasibility studies during process development. These challenges are addressed in this thesis. The evaluation of fluxes through multiple laboratory-scale membrane samples provides an accurate approximation of flux through an industrial- scale module. The results prove to be transferable to different membrane types. Furthermore, a collaborative study at different facilities demonstrates the comparability of experimental results obtained with a standardized procedure. Moreover, the consideration of experimental uncertainties in process design and membrane selection is proven to be as relevant as for the selection of an appropriate mass transfer model. In the second part of this work, a newly developed method for automatic development of predictive models for OSN shows promising results for prediction of solvent flux and solute rejection in pure and mixed solvents. The method derives the membranespecific model structure and discriminates automatically between potential, easily retrievable descriptors based on available data. For the prediction of solvent flux, a comparison with existing phenomenological models from literature points out that the new models are superior and cover effects that are not included in the fixed model structure of phenomenological models. Models developed for the prediction of rejection are more complex compared to those for solvent flux but are comparable accurate.
Model discrimination for multicomponent distillation
(2020-06-09) Waltermann, Thomas; Schlueter, Stefan; Benfer, Regina; Knoesche, Carsten; Górak, Andrzej; Skiborowski, Mirko
While rate-based models are available in commercial flowsheet simulation tools, packed distillation columns are still mostly designed based on the equilibrium stage model in combination with HETP values. In order to discriminate between both types of models in a simple way, this article proposes an algorithmic test, based on a geometric criterion for total reflux operation. Substantial differences are illustrated especially for wide-boiling mixtures, while component-specific mass transfer rates either increase or reduce the deviation. The derived results are validated by dedicated experiments.
Deaeration in Rotating Packed Beds
(2021) Groß, Kai Michael; Gorak, Andrzej; Kockmann, Norbert
Rotating packed beds (RPBs) overcome gravitational limitations as found in distillation or absorption columns by means of centrifugal force. The concept enables an intensified mass and heat transfer that leads to lower equipment volumes or increased performance. To impose centrifugal forces on gases or liquids the RPB consist of a motor-driven and packing equipped rotor in a static casing. An additional degree of freedom is offered due to the dependency of mass transfer performance and capacity on the rotational speed. Based on the equipment volume RPBs provide a very efficient mass transfer, enable large capacities and offer a high degree of flexibility. However, despite the high potential of the RPBs, their application in industry is limited. To facilitate the design process, a hydraulic and a mass transfer study was conducted. In the first step, a new prototype was designed and constructed together with an engineering partner to enable new investigation technologies and large-scale experiments. Changing geometries and an increasing centrifugal force along the radius of the rotor require a thorough understanding of the internal processes within the packing of an RPB. In the framework of the hydraulic study, the key characteristics were elucidated. For different packing types and packing geometries pressure drop and operating limits were investigated. For the first time, the liquid hold-up in the rotating packing was measured using the angle-resolved gamma-ray tomography. The information derived from the experimental studies was combined into design guidelines and a pressure drop model. The mass transfer of the RPB for liquid-side limited systems was investigated by the deaeration of water employing nitrogen as stripping gas. Lab-scale and pilot-scale equipment were investigated to generate a deeper understanding of the scaling effects. Co- and counter-current operations were evaluated for different packing-types and distributors. A model including literature correlations was developed and validated. Finally, cost models were included in a graphical user interface to quickly evaluate the costs of existing or potential RPB processes.
Liquid processing in Rotating Packed Beds
(2020) Wenzel, Dennis Alexander; Gorak, Andrzej; Schembecker, Gerhard
Rotating Packed Beds (RPBs) are one of the most promising concepts for intensified modular equipment in the chemical industry. Based on flexible design and by means of centrifugal force, their operation can be adjusted according to the respective process requirements. Despite the large potential of RPBs, many years of research, and although RPBs have been successfully applied to numerous processes on a pilot scale, their industrial implementation is still scarce. One of the key reasons is that the technology is often considered insufficiently mature, with a particular lack of knowledge in the field of liquid processing. Therefore, liquid processing in RPBs is investigated experimentally and analytically in this thesis, with respect to liquid phase reactive mixing, liquid-liquid extraction, and liquid-gas processing, in order to further develop the current RPB technology. The applicability of RPBs to these different processes is critically studied and rules of RPB design and operation are deduced. On this account, the current state of the art is analyzed, and the available methodology is adapted to RPBs. In experimental investigations, the role and importance of liquid distribution design, packing design, and residence time distribution in the apparatus are elucidated. These investigations are complemented by modeling results and a comparison to conventional devices and processes for each respective application. It is shown that RPBs are especially capable of providing fast liquid processing at high liquid flow rates and high viscosities and offer more operational degrees of freedom than their conventional counterparts. However, their utilization is also restricted based on limitations in the current design. Therefore, guidelines and recommendations for preferable RPB operation, RPB design, and the most reasonable industrial implementation of RPBs are presented, together with an alternative apparatus design.
Towards the development of advanced packing design for distillation in rotating packed beds
(2019-09-10) Qammar, Hina; Gladyszewski, Konrad; Górak, Andrzej; Skiborowski, Mirko
The growing demand for flexible and compact separation technologies has promoted the application of high‐gravity technology, like rotating packed beds (RPBs). Mass transfer characterization and packing design play an important role in the development of this technology. This article provides a systematic approach towards the evaluation of packing and the development of advanced packing design for distillation in RPBs. For the latter, an additive manufacturing approach is used to develop a new Zickzack packing for RPBs. The new packing provides better mass transfer at reduced pressure drop compared to available conventional packings, while being competitive in terms of mass transfer with the industrially applied rotating zigzag bed at significantly reduced pressure drop.
Application of organic solvent nanofiltration for multi-purpose production
(2017) Blumenschein, Stefanie; Górak, Andrzej; Schembecker, Gerhard
Due to increasing competitive pressure and a growing focus on environmentally friendly and sustainable production processes, energy-efficient and resource-saving processes are becoming more and more important. Organic solvent nanofiltration (OSN) is a relatively young membrane-based separation technology offering a high potential in process intensification compared to usual fluid separations. Despite the advantages application in industry still faces many challenges. The lack of predictability of separation performance of OSN membranes currently requires time-consuming, experiment-based process development. Contrarily, the pressure for accelerated process development is increasing, particularly in the specialty chemicals industry. In this work two different approaches are pursued to significantly accelerate the development of OSN processes. On the one hand, with regard to polymeric membranes a systematic investigation on the interactions between membrane, solvent and solute is carried out. From these results, an heuristic approach is developed which allows the identification of the best membrane for a given separation problem based on easily accessible or computable properties. Additionally, predictability and understanding of the complex separation performance is significantly improved. On the other hand, the separation behavior and the influence of diverse properties of ceramic membranes are investigated, in parallel to the development of new, narrow-pore separation layers for ceramic membranes, which are particularly suited to organic solvents. A transport model originally developed for aqueous nanofiltration is adapted and extended to an organic environment. The experimental results of rejection of the new membranes and the simulation are in very good accordance. Finally, the economic potential of organic solvent nanofiltration in a multi-purpose process environment is evaluated for a real production facility. Special terms and conditions in producing the high value and high purity substances, such as the application of a plant for several products at the same time with high yields and a good cleanability, are considered.
Analyse eines membranunterstützten Reaktivrektifikationsverfahrens zur Umesterung von Methylacetat mit Butanol
(2008-11-26T14:02:41Z) Bolivar, Wilda; Gorak, A.; Sadowski, G.
Die Kopplung von Reaktivrektifikation und Membrantrennung zu einem reaktiven hybriden Trennverfahren stellt einen weiteren Schritt auf dem Weg zu einem intensivierten Produktionsprozess in der chemischen Industrie dar. Bisherige Arbeiten auf diesem Gebiet beschränken sich bislang auf eine Betrachtung einzelner Teilaspekte des kombinierten Prozesses oder basieren auf Modellierungsansätzen, die keine Übertragung auf den industriellen Maßstab ermöglichen. In der vorliegenden Arbeit wird daher das Prozessverhalten eines reaktiven Hybridverfahrens mit Hilfe aktueller Modellierungswerkzeuge analysiert und ein Konzept zur Auslegung und Optimierung eines solchen Verfahrens entwickelt. Zur Erläuterung der einzelnen Schritte wurde als Beispielprozess ein Verfahren zur Umesterung von Methylacetat mit Butanol zu Butylacetat und Methanol ausgewählt, da sich dieses Verfahren zur Aufbereitung von Nebenprodukten aus der PVA-Herstellung eignet und damit eine technische Relevanz besitzt. Zudem stehen für diesen Prozess experimentelle Literaturdaten zur Bestimmung der notwendigen Modellparameter und Validierung der Simulationswerkzeuge zur Verfügung. Um der Komplexität des Verfahrens Rechnung zu tragen, wurden die einzelnen Prozessschritte Reaktivrektifikation und Membrantrennung zunächst getrennt untersucht. Dabei wurden geeignete physikalisch fundierte Modelle aus einer bestehenden Bibliothek ausgewählt und den veränderten Prozessbedingungen angepasst. Im Vordergrund stand dabei immer die getrennte Berücksichtigung von system-, prozess- und anlagenspezifischen Einflüssen, um eine Übertragung der Arbeitsergebnisse vom Labor auf den industriellen Maßstab zu ermöglichen. Die Arbeiten zu den einzelnen Verfahren umfassen dabei, neben der Modifikation bestehender Prozessmodelle, die Bestimmung der notwendigen Modellparameter sowie eine Validierung des Simulationswerkzeuges anhand von experimentellen Literaturdaten. Um eine Auslegung und Optimierung des Verfahrens zu ermöglichen, wurden die beiden Prozessschritte über die Definition einer Übergabereinheit entkoppelt. Auf diese Weise konnte das Prozessverhalten der einzelnen Verfahrensschritte getrennt analysiert und deren Wechselwirkungen dennoch berücksichtigt werden. Durch die Definition zusätzlicher Randbedingungen wurde auf der Basis von Prozesskosten sowohl die Auswahl eines geeigneten Membranmaterials als auch die Bestimmung der optimalen Übergabereinheit vorgenommen. Damit bietet sich die Möglichkeit, Prozesse, die auf einer Kombination von Reaktivrektifikation und Membrantrennung basieren, zuverlässig zu beschreiben und ihr Potenzial zur Intensivierung chemischer Produktionsprozesse zu beurteilen. Der in dieser Arbeit skizzierte Weg lässt sich auch auf andere integrierte Verfahren übertragen und leistet so einen Beitrag zur Intensivierung chemischer Produktionsprozesse.

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