660 Technische Chemie
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Microcrystalline cellulose pellets for oral drug delivery are often produced by a combined wet extrusion-spheronization process. During the entire process, the cylindrical as well as the spherical pellets are exposed to various stresses resulting in a change of their shape and size due to plastic deformation and breakage. In this work, the effect of moisture content of pellets on their mechanical behavior is studied. In static compression tests, the strong influence of water content on deformation behavior of pellets is confirmed. Moreover, impact tests are performed using a setup consisting of three high-speed cameras to record pellet-wall collisions. Material properties, such as stiffness, restitution coefficient, breakage force, and displacement, were analyzed depending on the water content.
Ein Bioraffineriekonzept für (Bier-)Treber wird vorgeschlagen, bei dem im Gegensatz zu bestehenden Konzepten wasserlösliche Komponenten durch Pressen abgetrennt und als Grundlage für eine Milchsäurefermentation mit Lactobacillus delbrueckii subsp. lactis verwendet werden. Die verbleibenden strukturellen Kohlenhydrate des Treberrückstandes werden durch hydrothermale und enzymatische Vorbehandlung in fermentierbare Zucker überführt. Es entstehen deutlich weniger Nebenprodukte, die das Wachstum von Mikroorganismen inhibieren können, als bei der Nutzung von nicht abgepresstem Treber.
This contribution presents a novel approach to investigate entrainment in distillation and absorption columns. An image-based probe allows precise droplet detection at various radial and axial positions above trays. Validations achieve an aver-age error of 6.4 % (monospheres 9.2–114.4mm) and 3 % (monodisperse droplet stream up to 19 m s–1and 74.5mm).Experiments in a DN 450 cold flow test rig show an increasing (decreasing) share of larger droplets with higher gas (liq-uid) loads. Locally measured droplet sizes depend on probe position as well as tray design and enable an extrapolation tointegral entrainment rates.
Organic solutions of lithium bis(fluorosulfonyl)imide (LiFSI) are promising electrolytes for Li-ion batteries. Information on the diffusion coefficients of the species in these solutions is needed for battery design. Therefore, the self-diffusion coefficients in such solutions were studied experimentally with the pulsed-field gradient nuclear magnetic resonance technique. The self-diffusion coefficients of the ions Li+ and FSI− as well as those of the solvents were measured for LiFSI solutions in pure dimethyl carbonate and ethylene carbonate as well as in mixtures of these solvents at 298 K and ambient pressure. Despite the Li+ ion being the smallest species in the solution, its self-diffusion coefficient is the lowest as a result of its strong coordination with the solvent molecules.
The influence on the mass transfer in liquid-liquid extraction was investigated during droplet formation in a quiescent aqueous continuous phase for the two transition components, acetone and acetonitrile, in toluene. Both transition components have similar characteristics. However, an approximately eight times slower mass transfer of a droplet hanging on a capillary in relation to a rising droplet could be observed. The droplet formation time and the initial solute concentration are decisive for the mass transfer behaviour. A lower volumetric flow leads to slower droplet formation and a higher specific mass transfer area enhancing mass transfer, which is visualized via laser induced fluorescence (LIF). Additionally, as expected, higher initial solute concentrations promote Marangoni turbulences and thus mass transfer, which is measured via confocal Raman spectroscopy inside a fixed hanging droplet.
Bacterial cell appendix formation supports cell-cell interaction, cell adhesion and cell movement. Additionally, in bioelectrochemical systems (BES), cell appendages have been shown to participate in extracellular electron transfer. In this work, the cell appendix formation of Clostridium acetobutylicum in biofilms of a BES are imaged and compared with conventional biofilms. Under all observed conditions, the cells possess filamentous appendages with a higher number and density in the BES. Differences in the amount of extracellular polymeric substance in the biofilms of the electrodes lead to the conclusion that the cathode can be used as electron donor and the anode as electron acceptor by C. acetobutylicum. When using conductive atomic force microscopy, a current response of about 15 nA is found for the cell appendages from the BES. This is the first report of conductivity for clostridial cell appendices and represents the basis for further studies on their role for biofilm formation and electron transfer.
Reactive absorption with amines is the most important technique for the removal of CO2
from gas streams, e.g. from flue gas, natural gas or off-gas from the cement industry.
In this work a rigorous simulation model for the absorption and desorption of CO2 with
an amine-containing solvent is validated using data from pilot plants of various sizes.
This model was then coupled with a detailed simulation of a coal-fired power plant.
The power generation efficiency drop with CO2 capture was determined and process
parameters in the power plant and separation process were optimized. It was shown
that the high energy demand of CO2 separation significantly reduces power generation
efficiencies, which underlines the need for improvements. This can be achieved by better
solvents or by advanced process designs. In this work such improved CO2 separation
processes are described and evaluated by detailed simulation studies.
In order to develop detailed rigorous simulation models for reactive absorption with novel
solvent systems, a precise knowledge of the liquid phase reaction kinetics is necessary.
There are well established techniques for measuring species distributions in equilibirated
aqueous amine solutions by NMR spectrosopy. However, the existing NMR techniques
cannot be used for monitoring fast reactions in these solutions. Therefore, in this work
a novel temperature-controlled micro-reactor NMR probe head was developed which
enables studying reaction kinetics with time constants in the range of seconds.
On this basis, modern solvent systems for CO2 absorption can be characterized and
the scale-up of separation process for future plants can be accompanied using rigorous
process simulation.
A new class of amines that are promising solvents for reactive CO2-absorption processes was thoroughly investigated in a comprehensive experimental study. The amines are all derivatives of triacetoneamine and differ only in the substituent of the triacetoneamine ring structure. These amines are abbreviated by the acronym EvA with a consecutive number that designates the derivatives. About 50 EvAs were considered in the present study, from which 26 were actually synthesized and investigated as aqueous solvents. The investigated properties were: solubility of CO2, rate of absorption of CO2, liquidliquid and solid-liquid equilibrium, speciation (qualitative and quantitative), pK-values, pH-values, foaming behavior, density, dynamic viscosity, vapor pressure, and liquid heat capacity. All 26 EvAs were assessed in an experimental screening. The results were compared with the results of two standard solvents from industry: aqueous solvents of monoethanolamine (MEA) and a solvent blend of methyl-diethanolamine and piperazine (MDEA/PZ). Detailed studies were carried out for two EvAs that revealed significantly improved performance compared to MEA and MDEA/PZ: EvA34 combines favorable properties of MEA and MDEA/PZ in one molecule. EvA25 reveals a liquid-liquid phase split that reduces the solubility of CO2 in the solvent and shifts the CO2 into the aqueous phase. This allowed the design of a new CO2-absorption process, that takes advantage of the liquid-liquid phase split. Finally, the chemical speciation in 16 EvAs was investigated by NMR spectroscopy. From the results, relationships between the chemical structure of the EvAs and the observed speciation, basicity, and application properties were established. This enabled giving guidelines for the design of new amines and proposing new types of amines, which were called ADAMs.
Molecular simulation is an important tool for investigating the behavior of fluids and solids. Nanoscopic processes and physical properties of the material can be studied predictively based on the description of the molecular interactions by force fields. This is used in the present work to tackle engineering questions that are hard to answer with other methods. First, mass transfer at fluid interfaces was investigated on the nanoscopic level. Therefore, two distinct simulation methods were developed and used to systematically investigate the mass transfer in mixtures of simple model fluids, described by the ‘Lennard-Jones truncated and shifted’ (LJTS) potential. The research question was whether the adsorption of components at the interface, which is observed also in many simple fluid mixtures, has an influence on the mass transfer. Such an influence was indeed found in the studies with both scenarios. Furthermore, explosions of nanodroplets caused by a spontaneous evaporation of the liquid phase were investigated with non-equilibrium molecular dynamics (NEMD) simulations. In these simulations, the interior of an LJTS droplet was superheated by a local thermostat, so that a vapor bubble nucleated inside of the droplet. Depending on the degree of superheating, different phenomena were observed, ranging from a simple evaporation of the droplet over oscillatory behavior of the bubble to an immediate droplet explosion. For molecular simulations of real mixtures, suitable force fields are needed. In this work, a set of molecular models for the alkali nitrates was developed and systematically compared to experimental data of thermophysical and structural properties of aqueous alkali nitrate solutions from the literature. Lastly, the structure and clustering of 1:1 electrolytes in aqueous solution was investigated for a broad concentration range starting from near infinite dilution up to high supersaturation. Based on the simulation results, an empirical rule was proposed to provide estimates of the solubility of salts with standard molecular dynamics simulations without the need of elaborate calculation schemes or significant additional computational effort.
Thermodynamic Modeling of Poorly Specified Mixtures using NMR Fingerprinting and Machine Learning
(2023)
Poorly specified mixtures, i.e., mixtures of unknown or incompletely known composition,
are common in many fields of process engineering. Dealing with such mixtures in process
design is challenging as their properties cannot be described with classical thermodynamic
models, which require a full specification. As a workaround, pseudo-components
can be introduced, which are generally defined using ad-hoc assumptions. In the present
thesis, a new framework is developed for the thermodynamic modeling of such mixtures
using nuclear magnetic resonance (NMR) experiments in combination with machine-learning
(ML) methods. In the framework, a characterization of a mixture in terms of
structural groups (“NMR fingerprint”) is obtained by using the ML concept of support
vector classification. Based on the group-specific fingerprint, quantum-chemical descriptors
of the unknown part of the mixture as well as activity coefficients can already be
predicted. Furthermore, a meaningful definition of pseudo-components is achieved by
clustering the structural groups into pseudo-components with the K-medians algorithm
based on their self-diffusion coefficients measured by pulsed-field gradient (PFG) NMR.
It is demonstrated that the characterization of poorly specified mixtures in terms of
pseudo-components can be combined with several thermodynamic group-contribution
methods. The resulting thermodynamic models were applied to various poorly specified
mixtures and used for solving two typical tasks from conceptual fluid separation process
design: the solvent screening for liquid-liquid extraction processes and the simulation
of open evaporation processes. The predictions with the methods developed here show
very good agreement with the results obtained for the fully specified mixtures.