Chemie Ingenieur Technik最新文献

The understanding of deactivation processes in heterogeneous catalysis is key for the development of new materials and exploration of new operation windows. In this contribution, the periodic transient kinetic method (PTK) is used to identify and separate catalyst deactivation processes for the first time. The PTK method is applied for a standard Ni/Al₂O₃ catalyst in CO and CO₂ methanation for 24 h and compared to steady-state experiments. For the example reactions, the study exhibits different deactivation behavior for CO and CO₂ methanation. The results demonstrate that the PTK method delivers an insight into the deactivation process and furthermore gives evidence for the underlying mechanism.

With the aid of structured catalysts and reactors, such as monoliths, solid foams, and 3D printed structures, the limitations of conventional slurry and packed-bed reactors can be surmounted. Multiphase mathematical models were presented for solid foam structures and the models were verified for the hydrogenation of arabinose, galactose, and xylose to the corresponding sugar alcohols. High product selectivities were obtained in batch and continuous experiments. Three kinetic models were considered: a competitive adsorption model, a semi-competitive adsorption model as well as a non-competitive adsorption model for sugar monomers and hydrogen. The models gave a good reproduction of the data, but the semi-competitive adsorption model was the most plausible one because of the size difference between adsorbed sugar and hydrogen molecules.

The objective of this paper is to investigate possible strategies for applying nonlinear frequency response (NFR) analysis based on the concept of higher-order frequency response functions to distributed parameter systems. Three approaches are presented and compared: one based on applying the existing procedure directly to the partial differential model, and two based on approximation of the distributed parameter system with a series of lumped parameter segments. One of them treats the complete series of segments integrally, while the other treats it segment by segment, so it uses only the model of a single segment. A simple example, an isothermal plug-flow reactor with a simple reaction mechanism, is used as a case study. Pros and cons for all three approaches are given.

In the present contribution, the historical development of dimensionless numbers describing axial mixing effects in chemical reactors is analyzed. While the Bodenstein number has become established in Europe, the American literature often uses the Péclet number for this purpose. A journey through the historical reaction engineering literature shows that the development was complex and that Langmuir's decisive role in particular has hardly been acknowledged to date. Unfortunately, despite decades of using dimensionless numbers for mass and heat transport in chemical reactors, no consensus has yet been reached on a uniformly accepted nomenclature. To remedy this shortcoming, a proposal for consistently defined numbers at the molecular and the reactor level is made.

Fouling in continuous reactors presents a significant challenge in the process intensification of specialty polymers. While in continuous stirred tank reactors (CSTRs) fouling is minimal, tubular reactors experience severe fouling, sometimes leading to complete blockage. Therefore, it is crucial to understand process and design conditions contributing to deposit formation. In this work, the impact of geometry, mixing elements, novel coatings, and ultrasonic waves are tested on tubular reactors for the polymerization of polyvinylpyrrolidone.

Diastereomeric cocrystals are used in chiral separations. Cocrystal solubility of the diastereomers is necessary for process design. Here, we extend our cocrystal solubility prediction to diastereomeric cocrystals. In this work, cocrystals of malic acid and tartaric acid were studied in four different solvents. Results showed qualitative agreement with experimental data. Hence, the shortcut method can be applied for preliminary estimation of suitable solvents for resolution. The predicted solubility lines can also serve as a tool to identify the stability between diastereomeric cocrystals.

The impact of gelation temperature and starting composition (solvent, silica, and polymer content) on the pore structure of silica xerogels with bimodal meso-/macropore structure is explored. Using statistical regression models, precise control over the pore structure is demonstrated, a challenge in previous studies. Higher gelation temperatures and increased polyethylene oxide (PEO) content enhance the mesopore volume, while higher solvent content and reduced polymer content increase the macropore volume. The ratio of mesopore to macropore volume can be effectively adjusted, facilitating the design of xerogels with tailored properties. These findings optimize silica xerogels with bimodal pore structure for applications in catalysis, thermal insulation, and other advanced technologies.

Verfahrenstechnische Apparate realisieren einen Prozess in einer konkreten Anwendungsumgebung. Oft sind dabei problematische Stoffsysteme zu prozessieren oder Betriebsbedingungen zu beherrschen, die besondere Herausforderungen an das verfahrenstechnische Design und den Betrieb der Apparate stellen. Beispiele sind schäumende Systeme in Verdampfungs- oder Desorptionsprozessen, Mulmbildung in Extraktoren, Tropfenmitriss aus Verdampfern, Flashbehältern oder an Kolonnenzuläufen oder Fouling, d. h. die unerwünschte Belagbildung auf wärme- und/oder stoffübertragenden Oberflächen. Für alle diese Phänomene gilt die Strategie Vermeiden – Vermindern – Beherrschen. Um dafür geeignete prozesstechnische, apparative oder betriebliche Maßnahmen zu testen und zu bewerten, sind einheitliche experimentelle Methoden erforderlich, die es erlauben, die Schaumneigung oder die Foulinganfälligkeit eines Stoffsystems, eines Apparates oder einer Betriebsweise unter definierten Bedingungen reproduzierbar zu quantifizieren. Erst dann können potentielle Abhilfemaßnahmen verlässlich bewertet und qualifiziert werden. Das vom Bundesministerium für Wirtschaft und Klimaschutz über den Projektträger Jülich geförderte Verbundprojekt „Entwicklung einer standardisierten Methodik für Design und Bewertung von Apparaten und Equipment in foulinggefährdeten Trennprozessen – SAMARA“ hat eine solche Methodik für Kristallisations- und organisches Fouling an metallischen und polymeren Wärmeübertragungsoberflächen sowie in Kolonnenpackungen entwickelt. Als Ergebnis stehen Standardapparaturen für Kolonnen und Wärmeübertrager sowie eine standardisierte Vorgehensweise mit empfohlenen Modellstoffsystemen zur Verfügung, die eine reproduzierbare Quantifizierung der Foulinganfälligkeit von Stoffsystemen oder Apparate- bzw. Equipmentausführungen erlauben. Die Standardisierung von Bewertungsmethoden erlaubt die Setzung von reproduzierbaren Referenzpunkten und unterstützt damit die Innovation und Einsatz neuer, besserer Produkte und Prozesse. Zur Unterstützung des Transfers dieser Ergebnisse liegt eine neue VDI-Richtlinie im Entwurf vor, die demnächst der interessierten Fachöffentlichkeit zur Kommentierung vorgelegt werden wird. Weitere Arbeiten in diesem Heft befassen sich mit Gestrickabscheidern zur Tropfenabscheidung sowie Verdampfung und Kondensation an komplexen Strukturen. Ich wünsche Ihnen Freude und die eine oder andere Inspiration bei der Lektüre der Beiträge.

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