Publikationen über den Einsatz der SOPAT Technologie

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Steinhoff, J., Charlafti, E., Leleu, D.  Reinecke, L., Franken, H.
Becker, K., Kalem, M., Sixt, M., Braß, M., Borchardt, D., Bäcker, W., Wegener, M., Maaß, S., Weber, M., Acher, T., Matten, C., Pfennig, A., Kraume, M. und Bart, H.*
Onyshchenko, O., Kohanuk, O.

Evaluation of the effectiveness of phot-optical measurement methods was carried out for optimization of the dewatering of fine classes of enrichment products from the coal factory. According to existing scheme dewatering step (centrifuge) feed consists of hydrosizers concentrate, flotation concentrate and hydrocyclones concentrate.

The photo-optical SOPAT measuring technique for particle sizing was applied to process and measure the sizes by means of automated image analysis.

Coal sludge dewatered in filtration centrifuges is a fine material, the average particle diameter of which is 306-21 µm (according to testing), which predetermines its high water holding capacity.

Using the data of the technical specifications, a variant of the technology for the dewatering of enrichment products (hydrosizer concentrate, flotation concentrate and product of the hydrocyclone) was considered. Based on the studies and performed calculations, the requirements of the process for ash content (12%) and humidity (12%) of the sediment in existing process are not met.

Ali, H., Solvsvik, J.
Physics of Fluids (link)
Mass transfer is a crucial phenomenon in designing and scaling up chemical and biochemical stirred tanks. The literature lacks a pilot-scale study on investigating mass transfer in non-Newtonian fluids. A pilot-scale study is a prerequisite step before scaling up the process from laboratory to industrial-scale. Thus, a study using pilot-scale stirred tank was conducted to investigate bubble hydrodynamics and mass transfer in non-Newtonian fluids. This work is a scale-up study from laboratory to pilot-scale. Axial distributions of bubble–liquid mass transfer coefficient and interfacial area were obtained using dedicated in situoptical endoscope probes (oxygen and bubble size) simultaneously. Volumetric mass transfer coefficient was determined by recording local dissolved oxygen concentrations in liquid. Interfacial area was estimated by measuring local bubble size and global gas holdup. Bubble–liquid mass transfer coefficient was then deduced by combining the obtained values of volumetric mass transfer coefficient and interfacial area. Effects of operating conditions, fluid rheology, and probe axial positions (liquid height) on bubble–liquid mass transfer coefficient were considered. The operating conditions (power inputs and superficial gas velocities) were in the range of 30–250 W/m3 and 3.10–4.70 mm/s, respectively. Bubble–liquid mass transfer coefficient increased with an increase in operating conditions, whereas it decreased with an increase in fluid rheology and liquid height. Scale-up effects on mass transfer were higher for water than viscous fluids, as suggested by large deviation (9.6%) in values of bubble–liquid mass transfer coefficient.
Kempin, M. V., Drews, A.
Chemie Ingenieur Technik (link)
Pickering emulsions have received increasing interest in many fields of application recently. In designing Pickering emulsion properties, focus is typically laid on composition whereas the preparation process as another possible leverage is not considered in detail. Here, Pickering emulsions of constant composition were prepared using two dispersing heads of a rotor‐stator homogenizer and compared in terms of Sauter mean diameters and rheology. It was found that the ratio of tip speed and gap width between rotor and stator is a better correlating parameter than tip speed only.
Stehl, D., Skale, T., Hohl, L.,Lvov, Y., Koetz, J., Kraume, M., Drews, A., von Klitzing, R.
American Chemical Society (link)
Unmodified natural clay particles, halloysite nanotubes (HNTs; l = 800 nm, douter = 50 nm, dinner = 15 nm), are used to stabilize oil-in-water Pickering emulsions (PEs). The hydrophilic HNTs are laterally attached to the oil/water interface and accumulate in bundles because of capillary forces. The nanotubes cover the oil droplets and prevent them from coalescing. The influence of HNT concentration on the oil droplet size and stability of the emulsions is investigated. An increase in the HNT concentration results in a nonmonotonous decrease in the droplet size, which can be attributed to changes in the packing parameter. The high mechanical stability of PEs allows for the separation of the oil droplets from the continuous phase by membrane filtration, and the emulsion phase could be highly concentrated up to around 90 vol % oil phase fraction. This study facilitates an accurate and more efficient application of HNT-stabilized PEs, e.g., for recyclable or continuous liquid/liquid reaction systems.
Seidel, S., Maschke, R. W., Werner, S., Jossen, V., Eibl, D.
Chemie Ingenieur Technik (link)
Oxygen supply in aerobic bioprocesses is of crucial importance. For this reason, this paper presents the oxygen demand of different cells and summarizes experimental and numerical possibilities for the determination of oxygen transfer in bioreactors. The focus lies on the volumetric oxygen mass transfer coefficient (kLa) calculation using computational fluid dynamics and state‐of‐the‐art models for surface‐aerated and forced‐aerated bioreactors. In addition, experimental methods for the determination of the kLa value and the gas bubble size distribution are presented.

Ali, H., Solsvik, J. 

Physics of Fluids (link)

Splitting of the volumetric mass transfer coefficient into a bubble–liquid mass transfer coefficient and interfacial area is essential to quantify the mass transfer rate of stirred tanks precisely. Axial distributions of the bubble–liquid mass transfer coefficient were determined in viscous Newtonian and non-Newtonian fluids using a laboratory-scale stirred tank. A detailed knowledge of the bubble–liquid mass transfer coefficient was obtained by using dedicated in situ oxygen and bubble size endoscope probes simultaneously. The volumetric mass transfer coefficient was estimated from recorded local dissolved oxygen concentrations in liquids. The interfacial area was calculated by measuring the bubble size and gas hold-up. The bubble–liquid mass transfer coefficient was then obtained by combining the estimated volumetric mass transfer coefficient and interfacial area. The bubble–liquid mass transfer coefficient was evaluated with effects of fluid rheology (concentrations of fluids), operating conditions (power input and superficial gas velocity), and axial liquid height. Bubble breakage is higher close to the stirrer due to intensive turbulence. The bubble–liquid mass transfer coefficient depended directly on operating conditions and indirectly on fluid rheology and liquid height.

Niño, L., Gelves, R., Ali, H., Solsvik, J., Jakobsen, H. 

Chemical Engineering Science (link)

A generalized model for bubble breakage and coalescence is proposed using Computational Fluid Dynamics – CFD for considering the complete energy spectrum. An eulerian model and balance equations are simultaneously used to simulate the multiphase flow and bubble size distribution, respectively. The turbulent kinetic energy and its dissipation are calculated using the standard turbulence model k-ε. A semi-empirical model that solves the second-order longitudinal structure function based on an interpolation function is coupled to CFD via UDF (User Defined Functions) code. CFD results are compared with experimental data obtained from Sauter mean diameter measurements at different bioreactor positions and stirred by a Rushton turbine. A reasonable prediction is obtained in comparison with the original Coulaloglou and Tavlarides (Break up) and Prince and Blanch (Coalescence) model. Further, the generalized model was extended to other stirring and aeration geometries using the same 10 litter tank bioreactor. The latter for evaluating strategies for overcoming gas-liquid mass transfer problems commonly found in bioreactors and a significant effect of the energy spectrum is reached in the geometries studied. The above, explained by the kLa oxygen transfer rate and bubble size determinations. It is numerically demonstrated that flow patterns and bubble size significantly influence the average kLa mass transfer in a bioreactor.

Pesch, S., Knopf, R., Radmehr, A., Paris, C. B., Aman, Z. M., Hoffmann, M., Schlüter, M.

Multiphase Science and Technology (link)

To accurately model the subsea distribution of accidentally released crude oil as a result of deep-sea oil well blowouts, the initial droplet size distribution is one of the most important input parameters. To date, only a very limited number of datasets contain results from large-scale experiments. Hence, a vast extrapolation to the field scale is often required, causing uncertainty when applying model correlations for the prediction of the ensuing droplet sizes, which have been tuned by means of lab-scale experimental results, to the field scale. In this paper, we present two-phase oil-in-water jet experiments conducted in two differently sized facilities with optical access. Lab-scale experiments with nozzle pipe diameters of 1-7.5 mm are compared to pilot-plant-scale experiments with nozzle pipe diameters of 32-74 mm. For the 32 mm nozzle pipe, additional cases with built-ins upstream of the nozzle exit are run for comparison, in order to simulate the influence of irregular blowout geometries. Endoscopic imaging is employed for the investigation of the droplet sizes. For the validation of the expected velocities and levels of the turbulent kinetic energy dissipation rate, particle image velocimetry is used. The resulting droplet size distributions are approximately log-normal. A model correlation for the prediction of droplet sizes based on existing literature correlations using the energy dissipation rate is deduced. Scale-up from lab to large scale is carried out on the basis of this correlation. The large-scale experimental results deviate significantly from the model correlation tuned by means of the small-scale results, which is referable to an upper limit of droplet stability. Considering the respective equation for this limit, in conjunction with the presented model correlation, provides a reasonable prediction of expectable droplet sizes for any scale of experiments.

Tang, Q., Zhang, J., Wu, Y., Wang, Y. and Liu, Z.

Chinese Journal of Chemical Engineering (link)

Drop size distribution (DSD) or mean droplet size (d32) and liquid holdup are two key parameters in a liquid–liquid extraction process. Understanding and accurately predicting those parameters are of great importance in the optimal design of extraction columns as well as mixer–settlers. In this paper, the method of built-in endoscopic probe combined with pulse laser was adopted to measure the droplet size in liquid–liquid dispersions with a pump-impeller in a rectangular mixer. The dispersion law of droplets with holdup range 1% to 24% in batch process and larger flow ratio range 1/5 to 5/1 in continuous process was studied. Under the batch operation condition, the DSD abided by log-normal distribution. With the increase of impeller speed or decrease of dispersed phase holdup, the d32 decreased. In addition, a prediction model of d32 of kerosene/deionized system was established as d32/D = 0.13(1 + 5.9φ)We−0.6. Under the continuous operation condition, the general model for droplet size prediction of kerosene/water system was presented as d32/D = C3(1 + C4φ)We−0.6. For the surfactant system and extraction system, the prediction models met a general model as d32/D = n We−0.6.

Rusli, S.; Grabowski, J.; Drews, A.; Kraume, M.

Advanced Chemical Reaction Kinetics of Pharmaceutical Processes (link)

The enzymatic hydrolysis of triglycerides with lipases (EC involves substrates from both water and oil phases, with the enzyme molecules adsorbed at the water-oil (w/o) interface. The reaction rate depends on lipase concentration at the interface and the available interfacial area in the emulsion. In emulsions with large drops, the reaction rate is limited by the surface area. This effect must be taken into account while modelling the reaction. However, determination of the interfacial saturation is not a trivial matter, as enzyme molecules have the tendency to unfold on the interface, and form multi-layer, rendering many enzyme molecules unavailable for the reaction. A multi-scale approach is needed to determine the saturation concentration with specific interfacial area so that it can be extrapolated to droplet swarms. This work explicitly highlights the correlation between interfacial adsorption and reaction kinetics, by integration of the adsorption kinetics into the enzymatic reaction. The rate constants were fitted globally against data from both single droplet and drop swarm experiments. The amount of adsorbed enzymes on the interface was measured in a single drop with a certain surface area, and the enzyme interfacial loading was estimated by Langmuir adsorption isotherm.

Kempin, M. V., Stock, S., von Klitzing, R., Kraume, M., Drews, A.

Separation and Purification Technology (link)

In recent years, Pickering emulsions (PE) have become of increasing interest for their application in (bio-) catalytic multiphase processes. To design an economically feasible process, an efficient and effective catalyst recovery is necessary. Ultrafiltration of PE has been shown to be a promising procedure. In this work, the influence of drop size distributions and rheology on the ultrafiltration of water-in-oil and oil-in-water PE stabilized by different nanoparticles as well as organic solvent-nanoparticle suspensions was studied.

Particles with higher hydrophobicity led to larger Sauter mean diameters. Depending on the ability of silica particles to form three-dimensional network structures, shear thinning or Newtonian rheological behavior was obtained. When suspensions of particles with gelling properties were filtered, an increase in flux compared to the filtration of the pure organic solvent was observed. Water-in-oil PE showed – regardless of investigated particle type and concentration – a disproportionate increase of flux with pressure. However, adjusting the membrane pre-treatment procedure led to a linear dependency between flux and pressure, which was also observed for oil-in-water PE (without special pre-treatment).

This work shows that the ultrafiltration of PE made from various nanoparticles is possible and contributes to a better understanding of PE characteristic properties and their influence on the ultrafiltration behavior.

Panckow, R. P., McHardy, C., Rudolph, A., Muthig, M., Kostova, J., Wegener, M., Rauh, C.

Journal of Food Engineering (link)

Regardless of whether the occurrence of foams in industrial processes is desirable or not, the knowledge about the characteristics of their formation and morphology is crucial. This study addresses the measuring of characteristics in foam and the trailing bubbly liquid that result from air bubble entrainment by a plunging jet in the environment of industry-like bottling processes of non-carbonated beverages. Typically encountered during the bottling of fruit juices, this process configuration is characterized by very fast filling speeds with high dynamic system parameter changes. Especially in multiphase systems with a sensitive disperse phase like gas bubbles, the task of its measurement turns out to be difficult. The aim of the study is to develop and employ an image processing capability in real geometries under realistic industrial conditions, e.g. as opposed to a narrow measurement chamber. Therefore, a typically sized test bottle was only slightly modified to adapt an endoscopic measurement technique and to acquire image data in a minimally invasive way. Two convolutional neural networks (CNNs) were employed to analyze irregular non-overlapping bubbles and circular overlapping bubbles. CNNs provide a robust object recognition for varying image qualities and therefore can cover a broad range of process conditions at the cost of a time-consuming training process. The obtained single bubble and population measurements allow approximation, correlation and interpretation of the bubble size and shape distributions within the foam and in the bubbly liquid. The classification of the measured foam morphologies and the influence of operating conditions are presented. The applicability to the described test case as an industrial multiphase process reveals high potential for a huge field of operations for particle size and shape measurement by the introduced method.

Skjefstad, H. S., Dudek, M., Øye, G. and Stanko, M.

Journal of Petroleum Science and Engineering: p. 106971. (link)

This paper reports the effect of inlet choking and addition of surfactant on the performance of a parallel pipe oil–water separator. These two issues can have a strong effect on oil–water separation in real hydrocarbon production systems.

Experiments were performed with Exxsol\textsc {TM} D60 and salt water. Three choke settings were tested for flow rates in the range 300–500 L/min, with three inlet water cuts and three water extraction rates. The test matrix was run with and without added surfactant. The oil–water distribution and behaviour within the separator is also studied. Droplet size measurements were performed at the separator inlet for droplet size distribution generation in the form of cumulative volume plots.

The study shows that inlet choking has an overall negative effect on separator performance, especially for water-continuous inlet regimes. The maximum decrease in performance due to choking was 14 pp, while it was 4 pp due to addition of surfactant.

Kempin, M. V., Kraume, M. and Drews, A

Journal of Colloid and Interface Science, 573: p. 135-149. (link)

Pickering emulsions (PE) are becoming of increasing interest for catalytic multiphase processes. Ultrafiltration of PE is a promising procedure for catalyst recovery to enable continuous processes. Dispersing conditions during production of PE are expected to significantly influence PE characteristics, and control of these properties is essential for robust process design. However, while the impact of PE composition has been studied before, knowledge on dispersing conditions is surprisingly scarce.

Heyse, A., Kraume, M. & Drews, A.

Colloids and Surfaces B: Biointerfaces, 185 (link)

The use of Pickering emulsions for biocatalytical applications has recently received increased attention in cases where hydrophobic reactants are involved. For process applications, knowledge of the emulsion’s rheology is crucial for the fluid dynamical design of equipment and selection of operating conditions. Colloidal silica nanoparticle stabilized Pickering emulsions usually exhibit shear-thinning behavior caused by a complex particle-particle network. While this has been observed by many authors, no publication has yet dealt with the rheology of silica nanoparticle stabilized Pickering emulsions containing enzymes. Thus, the aim of this study was to investigate the impact of the commonly used biocatalyst lipase (type and concentration), the dispersed phase volume fraction and the silica particle concentration on the rheological behavior of water-in-oil Pickering emulsions. For this purpose, the impact of the named parameters on the viscosity curves were measured. Lipases reduced the viscosities and transferred the rheological behavior from shear-thinning to Newtonian, which might be due to interactions of the lipase molecules via the formation of intermolecular disulfide bonds, which disturb the hydrogen-bond based silica particle-particle network. However, by increasing the dispersed phase volume fraction or the silica particle concentration the rheological behavior of emulsions became again shear-thinning. This work will help to produce bioactive Pickering emulsions with tailor-made characteristics.

Qiao Tang; Sishi Ye; Yundong Wang

State Key Laboratory of Chemical Engineering, Department of Chemical Engineering, Tsinghua University (link)

The scale-up of the industrial mixer is always based on operation experience, and lacks theoretical basis. In this paper, effects of scale-up criteria on the mixing time and flow characteristic in the intermittent pump-mixer with single-phase has been studied. Three-dimensional time-dependent mixing prediction has been carried out using multi reference frames(MRF) method and standard k-ε model embodied by computational fluid dynamics(CFD) package FLUENT6.3. The results indicated that the calculated mixing time was depended on detecting location, but the dependency became weaker by increasing the impeller speed. The power number was obtained at different Reynolds number, and it tended to be a constant as 1.3 under the condition of sufficient turbulence. Geometric similarity ensured the axial flow characteristics in the mixer. The criterion of equal impeller tip speed and equal Reynolds number demanded a longer mixing time and obtained a lower suction pressure head than the benchmark mixer. The criterion of equal circulation time and geometrical similarity could obtain the same mixing time as the benchmark and high suction pressure head, but the power consumption per unit volume sharply increased to 24 times as the benchmark. The criterion of equal power consumption per unit volume and geometrical similarity could obtain a better balance of all the parameters considered, and was considered to be the best one compared with other three criteria.

Castellano, S.

Phd-thesis, Université de Lyon (link)

This thesis project focuses on the study of the hydrodynamics of dispersions in liquid-liquid extractors used in the nuclear recycling industry. In the first part of the project, a homogeneous population balance model (0D-PBM), based on the evaluation of volume-average coalescence and rupture rates, is proposed. The method takes into account spatial inhomogeneities in the mixture, including the probability density function of the dissipation of turbulent kinetic energy in the device. The model is capable of reproducing low-viscosity turbulent liquid-liquid dispersion experiments. In the second part of this study, a generalized model for rupture and coalescence nuclei, valid for the whole spectrum of turbulence, is proposed and validated. Most of the cores available in the literature are based on the Kolmogorov second-order structure function, which is valid only in the inertial domain. However, in many industrial situations, most of the drops can have a size in the dissipative domain, where the Kolmogorov second-order structure function does not apply. The generalized model is based on Davidson’s second-order structure function, which is valid across the entire spectrum of turbulence. In the last part of the study, a model to simulate the hydrodynamic behaviour of a pulsed column is proposed. The model is based on a 1D population balance, the source terms of which were modelled using generalized Coulaloglou and Tavlarides nuclei. Turbulent inhomogeneities in the pulsed column were taken into account by the probability density function of the turbulent dissipation rate.

Marbà-Ardébol, A. M., Emmerich, J., Muthig, M., Neubauer, P. & Junne, S.

Journal of Visualized Experiments, 154, S. 1-9 (link)

In situ monitoring in microbial bioprocesses is mostly restricted to chemical and physical properties of the medium (e.g.,pH value and the dissolved oxygen concentration). Nevertheless, the morphology of cells can be a suitable indicator for optimal conditions, since it changes with dependence on the growth state, product accumulation and cell stress. Furthermore, the single-cell size distribution provides not only information about the cultivation conditions, but also about the population heterogeneity. To gain such information, a photo-optical in situ microscopy device1 was developed to enable the monitoring of the single-cell size distribution directly in the cell suspension in bioreactors. An automated image analysis is coupled to the microscopy based on a neural network model, which is trained with user-annotated images. Several parameters, which are gained from the captures of the microscope, are correlated to process relevant features of the cells, like their metabolic activity. Until now, the presented in situ microscopy probe series was applied to measure the pellet size in filamentous fungi suspensions. It was used to distinguish the single-cell size in microalgae cultivation and relate it to lipid accumulation. The shape of cellular particles was related to budding in yeast cultures. The microscopy analysis can be generally split into three steps: (i) image acquisition, (ii) particle identification, and (iii) data analysis, respectively. All steps have to be adapted to the organism, and therefore specific annotated information is required in order to achieve reliable results. The ability to monitor changes in cell morphology directly in line or on line (in a by-pass) enables real-time values for monitoring and control, in process development as well as in production scale. If the off line data correlates with the real-time data, the current tedious off line measurements with unknown influences on the cell size become needless.

Böhm, L., Hohl, L., Bliatsiou, C. & Kraume, M. 

Chemie Ingenieur Technik, 91(12), S. 1724-1746 (link)

Mainly with respect to biotechnological cases, current developments in the field of impeller geometries and findings for multistage configurations with a specific view on aerated stirred tanks are reviewed. Although often the first choice, in the given case the 6‐straight blade disc turbine is usually not the best option. Furthermore, quantities usable for scale‐up, specifically applicable in this field are discussed. Only quantities taking local conditions into account appear to be able to actually compare different stirrer types and scales.

Murasiewicz, H. und Esteban, J.

Industrial & Engineering Chemistry Research, 58 (16), S. 6933-6947 (link)

Glycerol carbonate has gained attention as a value-added product from reacting glycerol and dimethyl carbonate. This work studies the dispersion in nonreacting conditions of the two compounds under conditions relevant to the production of glycerol carbonate. Images were acquired to obtain droplet size distributions and Sauter mean diameters (d3,2), which increased with dispersed phase volume fraction and viscosity, whereas the difference of interfacial tension with changing conditions could be neglected as its value remained very similar at all conditions. d3,2 was correlated with available theoretical models based on the Weber number and energy dissipation rate, and two further correlations were proposed for high and moderate viscosities to describe the effect of viscosity, concentration of dispersed phase, and hydrodynamic parameters. The predicted value of d3,2 correlated well with experimental data, with the accuracy of both correlations reaching at least 93%.

Röhl, S., Hohl, L., Kempin, M., Enders, F., Jurtz, N. und Kraume, M.

Chemie Ingenieur Technik (link)

The impact of different silica nanoparticles on rheology, interfacial tension and drop size distributions in liquid‐liquid systems is determined experimentally. The particles vary in wettability and specific surface area. In contrast to commonly used high‐energy devices for Pickering emulsion preparation, low energy input by stirring allows to quantify drop breakage and coalescence in steady state and dynamic conditions. The experiments can provide essential information for drop size model development in nanoparticle‐stabilized emulsions.

Makarov, A., Klishchenko, R., Egurnov, A. und Kornienko, I

Ukrainian Chemistry Journal, 85 (3) (link)

Industrial and domestic waste water containing waste lubricants, cooling suspensions, waste from the food, alcohol and pulp and paper industries contain fuel residues, solvents, fats, dyes and other organic compounds. Large volumes and multi-component composition of such waste complicate and cost more water purification. Disinfection of such waters using adsorption, membrane or catalytic technologies requires the cost of scarce materials and expensive equipment, as well as leading to the formation of secondary man-made wastes in the form of waste adsorbents, catalysts, membranes, etc.

A promising option is the use of organ-containing sewage in formulations of composite water-coal fuel. At the same time, organic substances of sewage during the combustion of technological equipment allocate additional heat, which allows improving the energy characteristics of the fuel. The possibility of using plasmochemical technology for the stabilization of composite aqueous-coal fuel on the basis of organ-containing wastewater has been investigated. Organic dispersion media used waste after purification of fusel oil and wastewater after the washing of parts for technical purposes. Electrokinetic and rheological properties of composite aqueous-coal fuel have been studied. It has been established that the previous plasmochemical conversion of organo-containing wastewater, which is used as a dispersion medium for composite water-coal fuel, makes it possible to improve its operational properties. The growth of sedimentation stability and the optimization of effective viscosity are achieved both by increasing the electrostatic repulsion of the suspension particles with an increased ξ-potential and by achieving the bimodal composition of the disperse phase.

There is also a significant increase in the absolute values of ξ – the potential reached in the alkaline medium (pH = 10) 55-64 mV for anthracite coal. Accordingly, electrostatic repulsion of coal particles increases and improves in the viscosity in the modified samples is (1.1-1.25 Pa·s) and sedimentation stability (28-36 hours). The sedimentation stability of the fuel obtained is significantly improved in comparison with conventional suspensions of coal in organ-containing wastewater and reaches 28 to 36 hours without the addition of stabilizers. In addition, highly dispersed additives increase the reactivity of the composite aqueous-coal fuel contributes to increasing the caloricity and completeness of the burning of slurry fuel.

Da Costa Basto, R. M., Casals, M. P., Mudde, R. F., van der Wielen, L. A. M. und Cuellar, M. C.

Chemical Engineering Science: X, 3 (link)

Multiphasic fermentations where an organic phase is spontaneously formed or when it is added for product removal are commonly used for production of valuable compounds. The turbulent conditions and the presence of surface-active compounds (SACs) during fermentation create a stable emulsion difficult to separate. A gas bubble/oil droplet separation method has been proposed to break such emulsion. In this paper, we propose a mathematical model to describe oil/bubble interaction in a region of high oil droplet concentration. Model validation was performed using a synthetic emulsion and an emulsion from a fermentation broth. By applying the optimal parameters predicted by the model, a 6- and 3-times oil recovery improvement was reached for the synthetic emulsion and the fermentation broth, respectively. In conclusion, the proposed mechanistic model allowed to improve oil recovery in the existing laboratory set-up, and can be used to optimize the separation and recovery method at large scale.

Castellano, S., Carrillo, L., Sheibat-Othman, N., Marchisio, D., Buffo, A. und Charton, S.

Chemical Engineering Journal (374), S. 1420-1432 (link)

A generalized model for breakage and coalescence kernels valid for the entire spectrum of turbulence is proposed and validated. Most of the available kernels in the literature indeed assume that in a turbulent liquid-liquid dispersion, the dispersed droplets have dimension in the inertial subrange, and are affected by eddies with size in the same subrange. These kernels are based on the Kolmogorov second-order structure function, which is valid only in the inertial subrange. However, in most industrially encountered situations, many droplets may have a size in the dissipation range, where the Kolmogorov second-order structure function does not apply. Therefore, a more general description of the energy transferred between these droplets and the turbulent eddies is needed to properly model breakage and coalescence events.

In this work, the Coulaloglou and Tavlarides (1977) breakage and coalescence kernels have been modified through the implementation of the second-order structure function proposed by Davidson (2004), along with the Pope (2000) energy spectrum. Turbulent liquid-liquid dispersion experiments at high continuous phase viscosity are performed to test and validate the model. The generalized model is able to predict the experimental Sauter mean diameters at different viscosities, turbulent conditions and dispersed-phase volume fraction without any adjustment of the kernel parameters.

Steinhoff, J., Charlafti, E., Reinecke, L., Kraume, M. und Bart, H.-J.

The Canadian Journal of Chemical Engineering (link)

Note: Accepted, unedited articles published online and citable. The final edited and typeset version of record will appear in the future.

This contribution presents a standardized experimental setup for the development of gravity separators. Two different optical measurement techniques for the characterization of the inlet and outlet dispersion with a droplet spectrum of 20–2000 μm are used. The settling behaviour in a standardized batch settling test (ERICAA cell) serves as a basis for predicting the drop diameter resolved separation efficiency of a horizontal continuous separator. The latter (DN150, length 0.65 m) was operated and monitored with a phase fraction of up to 15 % and a load of up to 17.0 m3m–2h–1. A paraffin oil with a viscosity of 10 mPas was the dispersed and water the continuous phase. Sauter mean diameters of dispersions measured inline show a good agreement with those calculated from batch settling tests. Additionally, the modelled separation efficiencies are compared to the experimental results produced with the continuous separator.

Sinha, S., Mishra, D., Agrawa, A. und Sahu, K. K.

Journal of Cleaner Production (176), S. 452-462 (link)

Intensification of chemical processes has surfaced many challenging but promising areas. Enhancement of Oxygen Mass Transfer (OMT) is one such area in aqueous chemical processes. Several attempts made to alleviate OMT limitation, however, remains futile in lowering energy and material requirement. In this regard, the use of n-Dodecane, an Oxygen Vector, could be a radically promising route for enhancing OMT. The present work explores the use of n-Dodecane (Oxygen Vector) for the enhancement of OMT, corroborated with the Classical Molecular Dynamic (MD) simulations. The results showed that 2.5% (v/v) n-Dodecane addition in aqueous systems (‘Na2SO3 solution – n-Dodecane’ and ‘H2O – n-Dodecane’) would lead to enhancement up to 750%. MD simulation results confirm the transfer of oxygen from n-Dodecane-to-aqueous medium with diffusivity of 10−8 m2/s, thus becomes the dominating route for the enhancement in OMT. In addition, it has been found that n-Dodecane fraction, temperature and the rate of oxygen consumption reaction are the dictating parameters for enhancement. The concept of Oxygen Vector for enhancing OMT has been successfully exploited for cleaner leaching of metals (>95 % Cu, Ni and Co) from refractory complex sulfides at moderate temperature-pressure conditions (T∼ 95 °C and pO2∼3 Bar), which would have otherwise been possible at T > 200 °C and pO2 > 10 Bar. In addition, recyclability of n-Dodecane, Oxygen Vector, in leaching system is an added advantage. Thus, this study offers a promising route in enhancing kinetics of oxidative aqueous processes and provides suggestive insights for lowering the material and energy requirements.

Hohl, L.

Dissertation (link)

Mikroemulsionssysteme bestehend aus Wasser, 1-Dodecen und nicht-ionischen Tensiden bilden je nach Zusammensetzung und Prozessbedingungen bis zu drei füssige Phasen aus. Da diese Systeme vielversprechende Reaktionsmedien für die Hydroformylierung langkettiger Olefne und vergleichbare Prozesse sind, wurde der Einfuss der dritten Phase auf Dispersion und Phasentrennung untersucht. Beide Phänomene sind entscheidend für den Gesamtprozess, da sie sowohl die Reaktionsraten als auch die Efzienz des Katalysatorrecyclings und die Reinheit des Reaktionsproduktes beeinfussen. Mittels einer in-situ Endoskopmesstechnik und Bildanalyse wurde in dieser Arbeit eine Methode entwickelt, um die füssigen Phasen in gerührten Systemen zu identifzieren. Durch eine Kombination dieser Methodik mit einer Analyse des Phasenverhaltens und der physikalischen Eigenschaften wurden des Weiteren relevante Einfussgrößen auf Tropfenbruch und Koaleszenz unter zwei- und insbesondere dreiphasigen Bedingungen bestimmt. Die Vorhersage von Tropfengrößen mittels Populationsbilanzen verläuft erfolgreich in zweiphasigen Mikroemulsionssystemen, jedoch ist die Vorhersagekraft unter dreiphasigen Bedingungen nur in eingeschränkten Prozessparametern sowie in vergleichbar einfachen Systemen ausreichend. 

Um eine weitere Optimierung der Vorhersage zu ermöglichen wurden unter anderem Bedingungen für die Bildung multipler Emulsionen sowieso zu erwartende Trends der Tropfengrößen als Funktion der Prozessbedingungen dargestellt. Darüber hinaus konnte der Einfuss der dreiphasigen Dispersionen auf die Phasentrennung aufgeklärt und quantifziert werden. Dazu wurde ein bestehendes Modell zur Phasentrennung auf den dreiphasigen Zustand erweitert. Ein Vergleich der Experimente und Simulationen zeigt ein hohes Potenzial dieses Modells für die Beschreibung dreiphasiger füssig/füssig Systeme.

Malone, K., Aman, Z. M., Pesch, S., Schlüter, M. und Krause, D.

Deep Oil Spills, S. 43 – 64 (link)

The size distribution of oil droplets and gas bubbles forming at the exit geometry of a deep-sea blowout is one of the key parameters to understand its propagation and fate in the ocean, whether with regard to rising time to the surface, drift by ocean currents, dissolution or biodegradation. While a large 8 mm droplet might rise to the sea surface within minutes or hours, microdroplets <100 μm may take weeks or months to surface, if at all. On the other hand, a microdroplet or bubble dissolutes faster due to its larger surface to volume ratio and is also more available for biodegrading bacteria. To be able to properly model these effects, it is necessary to understand the drop formation processes near the discharge point and to predict the evolving droplet size distribution (DSD) for the specific conditions.

Banaei, M., Dellaerta, R., Deen, N. G., Kuipers, J. A. M. und van Sint Annaland, M. 

Particuology 43, S. 66-75 (link)

In this work, the borescopic particle image velocimetry (BPIV) technique was applied to a bubbling gas–solid fluidized bed, and the results were compared with published positron emission particle tracking (PEPT) measurement data. Before performing the experiments, the sensitivity of the BPIV results to the illumination power, light reflectivity of the particles, and location of the borescope was also investigated. The BPIV and PEPT results were in fair agreement; however, some discrepancies were observed. The difference between the two sets of results were mainly caused by the intrusiveness of BPIV, the fact that the local solids volume fraction was not accounted for in the BPIV analysis, and the intrinsic differences of these two methods. Therefore, measurement of the local solids volume fraction with the borescope is highly recommended for further development of the BPIV method, which will also enable measurement of the local solids mass fluxes inside dense gas–solid fluidized beds.

Hohl, L., Röder, V. und Kraume, M. 

Chemical Engineering & Technology (link)

Drop size distributions and phase separation behavior of water‐oil‐nonionic amphiphile systems are investigated using an in situ endoscope measurement technique and an external camera in stirred tanks in batch mode. The fitting procedure and the simulation results of a phase separation model are analyzed under the condition that either the swarm sedimentation speed or the mean drop size during sedimentation is known. The steady‐state drop size distributions are self‐similar over the whole range of process parameters, but not in the decaying turbulence field after agitation stop. The coalescence rate in the first seconds after agitation stop clearly affects the separation behavior, so that a prediction of the separation time based on the initial conditions in steady state is not trivial.

Villwock, J.

Dissertation online abrufbar (link)

Prozesse, in denen zwei nicht ineinander lösliche Flüssigkeiten verwendet werden, spielen eine wichtige Rolle in der industriellen Anwendung. Eine besonders wichtige die Prozesseffizienz bestimmende Größe ist dabei die Tropfengrößenverteilung, die sich aus den beiden simultan ablaufenden und sich überlagernden Phänomenen Tropfenbruch und -koaleszenz ergibt. Vor allem die Tropfenkoaleszenz ist aufgrund der komplexen Interaktionen und der Vielzahl an Einflussparametern schon lange Gegenstand der Forschung, aber dennoch nicht vollständig verstanden. So ist z. B. der Einfluss von grenzflächenaktiven Substanzen wie Salzen bzw. Ionen bisher noch unzureichend experimentell untersucht worden. Innerhalb der vorliegenden Forschungsarbeit wurde im Rahmen eines Kooperationsprojektes systematisch der Einfluss von Ionen auf Koaleszenzvorgänge in Systemen von zwei nicht ineinander löslichen Flüssigkeiten untersucht. Die experimentellen Untersuchungen umfassten Versuche mit unterschiedlichem Detail- und/bzw. Komplexizitätsgrad mit drei Stoffsystemen und fünf Ionenarten. In Einzeltropfenuntersuchungen wurde die dynamische Interaktion zweier Tropfen bei Variation verschiedener Prozessparameter – mit dem Fokus auf Ionenstärke und -art – untersucht. Zunächst wurde die Reproduzierbarkeit und Vergleichbarkeit der Ergebnisse mittels Messungen von Einzeltropfenaufstiegsgeschwindigkeiten an beiden Projektstandorten evaluiert. Die Aufstiegsgeschwindigkeiten wurden ebenfalls bei der Zugabe von Ionen untersucht. In den anschließenden systematischen Experimenten mit Ionenzugabe wurde der Einfluss der Ionenstärke und -art auf die Koaleszenzeffizienz (Reihenuntersuchungen) und die Koaleszenzzeit (Detailuntersuchungen beim Projektpartner) bestimmt. In standardisierten Absetzversuchen wurde, ebenfalls an beiden Projektstandorten, die Beeinflussung des Phasenseparationsverhaltens durch Ionenzugabe vermessen. Damit waren eine qualitative und quantitative Bestimmung des Ioneneinflusses in einem polydispersen System möglich. Während beim Projektpartner für die Untersuchungen in einem turbulenten System eine DN150-Kühni-Kolonne verwendet wurde, erfolgte die Durchführung in dieser Arbeit in einem DN150-Rührkessel. Für die drei Stoffsysteme sowohl ohne als auch mit Ionenzugabe wurden die stationären Tropfengrößenverteilungen bzw. Sauterdurchmesser in Abhängigkeit vom Leistungseintrag und weiterführend das Koaleszenzverhalten anhand von Sprungversuchen bestimmt. Zum Abschluss wurden mögliche Korrelationen der Ergebnisse mit parallel gemessenen Stoffgrößen bzw. ionenspezifischen Eigenschaften überprüft, die Ergebnisse aus den drei Versuchsarten miteinander verglichen und sowohl Zusammenhänge als auch Unterschiede herausgestellt. Die in dieser systematischen Arbeit erhaltenen Ergebnisse und Zusammenhänge der drei Versuchskomplexe bilden eine gute Basis für weiterführende Untersuchungen sowie zur Modellierung der Koaleszenzeffizienz unter Berücksichtigung von Ionenstärke und -art in Flüssig/flüssig-Systemen.

Emmerich, J., Tang Q., Wang, Y., Neubauer, P., Junne, S. und Maaß, S.

Chinese Journal of Chemical Engineering 27 (2), S. 257-277 (link)

Particles occur in almost all processes in chemical and life sciences. The particle size and shape influence the process performance and product quality, and in turn they are influenced by the flow behavior of the particles during production. Monitoring and controlling such characteristics in multiphase systems to obtain sufficient qualities will greatly facilitate the achievement of reproducible and defined distributions. So far, obtaining this information inline has been challenging, because existing instruments lack measurement precision, being unable to process overlapping signals from different particle phases in highly concentrated multiphase systems. However, recent advances in photo-optics made it possible to monitor such features (particle size distribution (PSD), aspect ratio and particle concentration) with advanced image analysis (IA) in real-time. New analysis workflows as well as single feature extractions from the images using multiple image analysis algorithms allowed the precise real-time measurements of size, shape and concentration of particle collectives even separated from each other in three phase systems. The performances, advantages and drawbacks with other non-photo-optical methods for assessing the particle size distribution are compared and discussed.

Bliatsiou, C., Malik, A., Böhm, L. und Kraume, M.

Industrial & Engineering Chemistry Research 58 (7), S. 2537-2550 (link)

Hydromechanical stress is a crucial parameter for a broad range of multiphase processes in the field of (bio)chemical engineering. The effect of impeller type and geometry on hydromechanical stress in stirred tanks is important. The present study aims at characterizing conventional and new impeller types in terms of particle stress. A two-phase liquid/liquid noncoalescing dispersion system is employed, and the drop breakage is monitored in-line in a stirred tank. The published effects of agitation on drop deformation are confirmed and expanded significantly for five modified new impeller types. Radial impellers are advantageous for applications where low shear conditions are desired. A modified propeller with a peripheral ring and the developed wave-ribbon impellers present remarkable results by producing significantly low and high hydromechanical stress, respectively. The results obtained are correlated in terms of mean and maximum energy dissipation rate, as well as circulation frequency in the impeller swept volume.


Riegler, P., Chrusciel, T., Mayer, A., Doll, K. und Weuster-Botz, D.

Biochemical Engineering Journal 141, S. 89-101 (link)

A retrofit approach enables the non-invasive and reversible modification of a commercially available stirred-tank bioreactor into a gas-lift bioreactor within a few minutes. The gas-lift bioreactor configuration was characterised using a non-coalescent medium at working volume-specific volumetric gas flow rates of up to 20 L L−1 h−1, showing mean gas bubble diameters of up to 0.57 mm, volumetric power inputs of up to 23 W m-3, gas-liquid mass transfer coefficients of up to 153 h−1 (CO) and up to 122 h−1 (H2), mixing times (θ90) of down to 0.5 min and gas hold-ups of up to 1.2%. A comparison of autotrophic batch processes with Clostridium aceticum and Clostridium carboxidivorans in the stirred-tank (2.0 L) and the retrofitted gas-lift bioreactor (2.5 L) at identical operating conditions showed differences in the cell dry weight and product concentrations (acetate, ethanol, butyrate, 1-butanol, hexanoate, 1-hexanol) due to gas-liquid mass transfer limitations caused by the reduced power input in the gas-lift bioreactor. CO limitation was demonstrated by a myoglobin-protein assay for CO measurement in the liquid phase. The simple retrofitting of a stirred-tank bioreactor for gas-lift operation thus provided comparative data on process performances of acetogenic bacteria that convert synthesis gas in gas-lift and stirred-tank bioreactors on a lab-scale.

Banaei, M., Dellaert, R., Deen, N. G., van Sint Annaland, M. und Kuipers, J. A. M.

AIChE Journal (64), Issue 9, S. 3303-3311 (link)

A borescopic technique was used for finding the effect of pressure on the hydrodynamics of gas‐solid fluidized beds. The results showed that solids radial distribution may become more or less uniform with increasing pressure depending on the superficial gas velocity. Moreover, it is found that the solids volume fraction of the emulsion phase may decrease at relatively high pressures, only in the central region of the bed. Additionally, it is observed that with increasing pressure the bubble size generally decreased in the central regions and increased near the wall regions. This trend was more complicated at low excess gas velocities. The number of bubbles increased for the central regions and near the walls for all the performed experiments. However, this parameter showed a different trend at other radial positions. 

Steinhoff, J.

Chemie Ingenieur Technik, 90 (12 – Special Issue ACHEMA Nachberichte), S. 1983 – 1985 (link)

Als ein wichtiges Teilgebiet der Verfahrenstechnik war die Extraktionstechnik auf der diesjährigen ACHEMA wieder mit zahlreichen Neuerungen und Innovation vertreten. Neben bekannten Firmen präsentierten auch Universitäten und Hochschulen ihre neuen Konzepte zur Stofftrennung. Eine Auswahl der gezeigten Innovationen wird hier vorgestellt.

Stehl, D., Milojević, N., Stock, S., Schomäcker, R. und von Klitzing, R.

Industrial & Engineering Chemical Research (online) (link)

Hydrophilic silica nanoparticles (100 nm in length and of 20 nm diameter) and larger hollow Halloysite nanotubes (HNTs; 800 nm in length with an outer diameter of 50 nm and an inner diameter of 15 nm) are used to stabilize an oil-in-water emulsion. These particle-stabilized Pickering emulsions (PEs) are used for the hydroformylation of a long-chain olefin (1-dodecene). Rhodium (Rh) and the water-soluble ligand sulfonated 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene are used as catalyst. The emulsions are prepared by sonication and Ultra-Turrax in a specially designed vessel to protect the catalyst from oxygenation and to control the temperature of each sample during the preparation process. The Rh catalyst shows interfacial active behavior and strongly influences the mean droplet size of the emulsions, stability, wettability, and energy of detachment. Further, the Rh catalyst stabilizes an emulsion even in the absence of particles. In a mixture of Rh catalyst and particles, both attach at the interface if the droplet size is in a magnitude of micrometers. These PEs show a monotonous droplet decrease with increasing particle concentration. It is shown that hydroformylation is possible in all emulsions stabilized by the Rh catalyst, silica nanoparticles, or HNTs. However, the conversions in the emulsions are different. The highest conversion is observed in silica-stabilized emulsions with above 40 wt % after a reaction time of only 5 h. Further, high selectivity for aldehyde was observed for all emulsions. A model for the behavior of the emulsions in the reactor is postulated. Interestingly, the emulsions stabilized by the Rh catalyst and silica nanoparticles are destroyed after the reaction, but the HNTs-stabilized PEs remained stable.

Emmerich, J., Tang, Q., Wang, Y., Neubauer, P., Junne, S. und Maaß, S.

Chinese Journal of Chemical Engineering (in press) (link)

Particles occur in almost all processes in chemical and life sciences. The particle size and shape influence the process performance and product quality, and in turn they are influenced by the flow behavior of the particles during production. Monitoring and controlling such characteristics in multiphase systems to obtain sufficient qualities will greatly facilitate the achievement of reproducible and defined distributions. So far, obtaining this information inline has been challenging, because existing instruments lack measurement precision, being unable to process overlapping signals from different particle phases in highly concentrated multiphase systems. However, recent advances in photo-optics made it possible to monitor such features (particle size distribution (PSD), aspect ratio and particle concentration) with advanced image analysis (IA) in real-time. New analysis workflows as well as single feature extractions from the images using multiple image analysis algorithms allowed the precise real-time measurements of size, shape and concentration of particle collectives even separated from each other in three phase systems. The performances, advantages and drawbacks with other non-photo-optical methods for assessing the particle size distribution are compared and discussed.

Pedraza‐de la Cuesta, S., Knopper, L., van der Wielen, L. A. M., und Cuellar, M. C. 

Modeling and Analysis (link)

Sesquiterpenes are a group of versatile, 15‐carbon molecules with applications ranging from fuels to fine chemicals and pharmaceuticals. When produced by microbial fermentation at laboratory scale, solvents are often employed for reducing product evaporation and enhancing recovery. However, it is not clear whether this approach constitutes a favorable techno‐economic alternative at production scale. In this study empirical correlations, mass transfer and process flow sheeting models were used to perform a techno‐economic assessment of solvent‐based processes at scales typical for flavors and fragrances (25 MT year−1) and the fuel market (25 000 MT year−1). Different solvent‐based process options were compared to the current state of the art, which employs surfactants for product recovery. The use of solvents did reduce the sesquiterpene evaporation rate during fermentation and improved product recovery but it resulted in costs that were higher than, or similar to, the base case due to the additional equipment cost for solvent‐product separation. However, when selecting solvents compatible with the final product formulation (e.g. in a kerosene enrichment process), unit costs as low as $0.7 kg−1 can be achieved while decreasing environmental impact. 

Hohl, L., Schulz, J. M. und Kraume, M. 

Journal of Chemical Engineering of Japan 51 (4), S. 383-388 (link)

Microemulsion systems consisting of water, oil and non-ionic surfactants can develop up to three liquid phases as a function of composition and temperature. Under three phase conditions, Population Balance Equations (PBEs) derived from two phase systems need to be extended to account for the influence of the third phase on the droplet size distributions. PBE fitting parameters can not be simply transferred from two phase to three phase conditions, which is attributed to the changing composition of the liquid phases induced by solubility variation. A method to derive PBE fitting parameters for the three phase conditions and describe the droplet sizes in these systems is presented herein.

McHardy, C., Rudolph, A., Panckow, R., Kostova, J.,  Wegener, M. und Rauh, C. 

Fachtagung “Experimentelle Strömungsmechanik” (Full Article)

Undesired foaming during high-speed filling of non-carbonated beverages is often observed in practice. To reduce foam formation, the filling dynamics must be adapted to the foaming capacity of the product which in turn reduces the output and economic efficiency of the filling line. The macroscopic stability of these undesired foams is determined by morphological properties of the foam, e.g. the bubble size distribution. At the same time, the entrainment and dispersion of the gas phase in the product is affected by the filling dynamics and the product’s material properties. The present contribution deals with the measurement of the morphology of foams arising during the bottling of fruit juices. For this, industrial bottling pro-cesses are reproduced in the lab and the forming foams are characterized in real-time with an inline measurement technique which yields 2D photo optical visuals. Automatic image analysis is applied to analyze the shape and size of foam bubbles and determine size distri-butions with respect to space and time. The results allow conclusions concerning the effect of the volume flow and product properties on the morphology of the foam and provide a basis for the development of actuators for the active control of foaming.

Castellano, S., Sheibat-Othman, N., Marchisio, D., Buffo, A. und Charton, S.

Chemical Engineering Journal (354), S. 1197-1207 (link)

A zero-dimensional homogenous Population Balance Model (PBM) based on the evaluation of the volume-averaged coalescence and breakup rates is here adopted for the first time to fit the model parameter values through experiments carried out on a water-oil emulsion. The method accounts for the spatial inhomogeneities in mixing, namely for the probability density function of the turbulent kinetic energy dissipation in the apparatus, but avoids the use of coupling the PBM with computational fluid dynamics (CFD) or compartmentalization, thus ensuring fast computational time. In order to demonstrate the advantage of the proposed model over traditional ones based on the volume-averaged turbulent kinetic energy dissipation rate, the operating conditions were varied, including the mixing rate, the disperse phase fraction as well as considering inverse emulsions (water in oil and oil in water). The new model was found to be more generalizable to different operating conditions.

Marbà Ardébol, A. M.

Technische Universität Berlin (link)

Die Zellmorphologie wird nicht nur durch den Zellzyklus, die Alterungs- oder individuelle Eigenschaften beeinflusst, sondern auch durch Umweltbelastungen, wie sie z.B. im großen Maßstab auftreten. Die Zellmorphologie kann ein geeignete Parameter für eine in situ Messung sein, da sie sich dynamisch verändert und dabei oft mit der Zellphysiologie zusammenhängt. Um Beziehungen zwischen der Zellphysiologie und Morphologie identifizieren zu können, müssen statistisch repräsentative Datenmengen gemessen werden. Zu Berücksichtigen ist, dass das Verhalten der Zellen dabei nicht nur extrem dynamisch ist, sondern auch sehr sensibel gegenüber Umweltveränderungen. Daher können off line Messungen ungeeignet sein, kleinere Änderungen in den morphologischen Eigenschaften zu detektieren. Die Probenahme und in der Regel die Probenvorbereitung würde diese überdecken, abgesehen von einer oft nicht ausreichenden Anzahl von Daten oder eines nicht vertretbaren Aufwandes. 

Unter den Techniken, die in der Lage sind, morphologische Merkmale von Zellen zeitnah zu erfassen, sind automatisierte Bildgebungstechnologien vielversprechend, da sie über die Größe hinaus weitere Informationen über zelluläre Strukturen, Form und Zellaggregation liefern. Die photo-optische in situ Mikroskopie (ISM) und die drei-dimensionale holographische Mikroskopie (DHM) wurden in dieser Studie zur Messung der morphologischen Dynamik in eukaryontischen Kulturen auf Einzelzellbasis eingesetzt, die exemplarisch an heterotrophen Algen und Hefe untersucht wurde. 

Die intrazelluläre Konzentration der mehrfach ungesättigten Fettsäure Docosahexaensäure (DHA) in der heterotrophen Alge Cryptecodinium cohnii wurde überwacht. Eine Korrelation zweiter Ordnung zwischen dem DHA-Gehalt, wie er off line chromatographisch gemessen wurde, und der Vorhersage unter Verwendung des Durchschnitts des Sauter-Durchmessers konnte gefunden werden. Eine unterschiedliche Medienzusammensetzung beeinflusste nicht nur die Zellgröße, sondern auch die Zirkularität und Phasenhomogenität der Algenzellen. Folglich wurden verschiedene Chloridionenersatzstoffe hinsichtlich des Zellwachstums und der Lipidakkumulation in C. cohnii getestet. 

Mehrkompartimenten-Reaktoren wurden eingesetzt, um den Einfluss von Gradienten, wie sie im großen Maßstab auftreten, auf die morphologische Heterogenität innerhalb von Saccharomyces cerevisiae Kulturen zu untersuchen. Insbesondere wurden die Auswirkungen von Sauerstofflimitierungen auf die Zellheterogenität untersucht. Entgegen den Erwartungen wurde die Sterolsynthese durch die oszillatorische Sauerstoffverfügbarkeit positiv beeinflusst (die Ergosterolesterkonzentrationen stiegen um 75 %), obwohl sich das mikrobielle Wachstum verlangsamte (die Biomassekonzentration war um 20 % erniedrigt). 

Darüber hinaus wurde die Knospung der Hefe mit Hilfe der ISM auf Einzelzellebene in Batchkultivierungen überwacht. Die Größenverteilung wurde während der Wachstumsphase enger, so dass die Populationshomogenität zunahm. War die Glukose verbraucht, blieb der Prozentsatz der Nicht-knospenden Zellen aufgrund einer stark verminderten Wachstumsaktivität nahezu konstant. Anhand des Anteils knospender Zellen konnte zwischen den verschiedenen Kultivierungsstadien unterschieden werden. 

Die gezeigten Methoden erwiesen sich als geeignet zur Überwachung morphologischer Eigenschaften über einen relevanten Konzentrationsbereich hinweg. Eine schnellere Partikelidentifizierung, auch von überlappenden Partikeln, und weitere Untersuchungen zu einem besseren Verständnis der Zusammenhänge zwischen Form und Zustand einer Zelle wird den Einsatz der Technologie zur Kontrolle einer Vielzahl an Bioprozessen erlauben.

Panckow, R. P., Röhm, P., Junne, S. und Kraume, M.

Chemie Ingenieur Technik 90 (9), S. 1301 (link)

Der Einsatz von Single-Use-Bioreaktoren zum Erzielen hoher Ausbeuten in Zellkulturen gewinnt zunehmend an Bedeutung. Die r den schnellen rme- und Stoffaustausch tigen Energieeinträge nnen die zelluläre Phase durch zu hohe Scherbeanspruchung schädigen.

Zur Beschreibung dieser Beanspruchung wurde ein Flüssig/flüssig-Modellstoffsystem [1] in einem wellendurchmischten Single-Use-Bioreaktor der Fa. Celltainer Biotech BV eingesetzt. Dessen patentiertes Durchmischungskonzept basiert auf der Kombination einer rotatorischen mit einer translatorischen Bewegung. Die am Reaktor befestigte und kontinuierlich mitbewegte foto-optische Endoskopmesstechnik der Fa. SOPAT GmbH erfasst hrend des Prozesses 2D-Bilddaten und misst Größe und Form der fluiden Partikel durch automatische Bildanalyse [2] (Abb.). 


Die aufgezeichnete Zerstörungskinetik der dispersen Phase gibt Aufschluss über deren Beanspruchung. Die Erkenntnisse aus dem Modellstoffsystem über die Scherbeanspruchung dienen als Grundlage r den Bezug auf das reale System mit einer zellulären Phase. Die Vermessung der durch Oberflächenbegasung eingetragenen Luftbläschen dient neben kLa als Kennwert r die Beschreibung des Stofbergangs zwischen flüssiger und gasrmiger Phase.

[1] S. Wollny, R. Sperling, Chem. Ing. Tech. 2007, 79 (3), 199 208.
[2] R. P. Panckow et al., Chem. Eng. Technol. 2015, 38 (11), 2011 2016.

Heyse, A., Plikat, C., Grün, M., Delaval, S., Ansorge-Schumacher, M. und Drews, A. 

Process Biochemistry (n/a) (link)

The technical application of biocatalysts is commonly realized in aqueous media limiting the range of reactants to hydrophilic compounds. The use of Pickering emulsions (PEs), where biocatalysts are immobilized in water droplets stabilized by nanoparticles and surrounded by solvent containing the substrates, presents an alternative for reactions involving hydrophobic reactants.

While batch PE biocatalysis has been demonstrated for a variety of reactions and enzymes, no continuous process at industrially relevant residence times has been reported yet.

Here, a continuous membrane reactor is proposed to retain the aqueous drops containing the enzymes in the reactor while the product containing permeate is continuously filtered through the membrane. To identify main influencing factors on membrane operation, the impact of enzyme properties and concentration of nanoparticles on drop size distribution (DSD) and filterability was investigated.

It was found that enzyme properties have a strong impact on both DSD and filtration. With lipases, PEs showed an improved filterability and reproducibility. Higher particle concentrations lowered the flux through the membrane due to unbound particles forming the filter cake. Thus, particle concentration should be kept as low as possible. The concept was proven by a continuous lipase catalyzed transesterification with the enzyme remaining active in the PE.

Grafschafter, A., Rudolstorfer, G. und Siebenhofer, M.

Chemie Ingenieur Technik 90 (6): 864 – 871 (link)

The Taylor‐Couette disc contactor (TCDC) uses the hydrodynamic advantages of the rotating disc contactor (RDC) and Taylor‐Couette reactor. Drop size distribution, dispersed phase holdup and residence time distribution (RTD) of the TCDC in 0.1 m and 0.3 m diameter scale were determined. A correlation for the prediction of the Sauer mean diameter was validated experimentally for 0.3‐m scale. Analysis of RTD suggests application of the tank‐in‐series model. The number of vessels in series rises with increasing hydraulic load and decrease with increasing rate of rotation. The axial dispersion coefficient was determined in order to evaluate backmixing.

Malone, K., Pesch, S., Schlüter, M., und Krause, D.

Environmental Science Technology (link)

To date, experimental investigations to determine the droplet size distribution (DSD) of subsea oil spills were mostly conducted at surface conditions, i.e. at atmospheric pressure, and with dead, i.e. purely liquid, oils. To investigate the influence of high hydrostatic pressure and of gases dissolved in the oil on the DSD, experiments with a downscaled blowout are conducted in a high-pressure autoclave at 150 bar hydrostatic pressure. Jets of “live”, i.e. methane-saturated, crude oil and n-decane are compared to jets of “dead” hydrocarbon liquids in artificial seawater. Experiments show that methane dissolved in the liquid oil increases the volume median droplet diameter significantly by up to 97%. These results are not in good accordance with state-of-the-art drop formation models, which are based on oil-only experiments at atmospheric pressure, and therefore show the need for a modification of such models which incorporates effects of hydrostatic pressure and dissolved gases for the modeling of deep-sea oil spills and blowouts.

Marbà-Ardébol,  M.-A., Emmerich, J., Muthig, M., Neubauer, P. und Junne, S.

Microbial Cell Factories (link)


The morphology of yeast cells changes during budding, depending on the growth rate and cultivation conditions. A photo-optical microscope was adapted and used to observe such morphological changes of individual cells directly in the cell suspension. In order to obtain statistically representative samples of the population without the influence of sampling, in situ microscopy (ISM) was applied in the different phases of a Saccharomyces cerevisiae batch cultivation. The real-time measurement was performed by coupling a photo-optical probe to an automated image analysis based on a neural network approach.


Automatic cell recognition and classification of budding and non-budding cells was conducted successfully. Deviations between automated and manual counting were considerably low. A differentiation of growth activity across all process stages of a batch cultivation in complex media became feasible. An increased homogeneity among the population during the growth phase was well observable. At growth retardation, the portion of smaller cells increased due to a reduced bud formation. The maturation state of the cells was monitored by determining the budding index as a ratio between the number of cells, which were detected with buds and the total number of cells. A linear correlation between the budding index as monitored with ISM and the growth rate was found.


It is shown that ISM is a meaningful analytical tool, as the budding index can provide valuable information about the growth activity of a yeast cell, e.g. in seed breeding or during any other cultivation process. The determination of the single-cell size and shape distributions provided information on the morphological heterogeneity among the populations. The ability to track changes in cell morphology directly on line enables new perspectives for monitoring and control, both in process development and on a production scale.

Rohm, H., Böhme, B. und Skorka, J. 

LWT: 92, 564-568 (link)

Comminution of the solid contents during chocolate manufacture is an important process that affects physical and sensory properties of the final product. In this study, size reduction was achieved either by multiple passages through a roller refiner, or by agitated ball milling. Particle analysis revealed that size distributions but also particle size geometry and surface is affected by refining intensity and refiner type. The current results demonstrate that it is especially refining intensity that can be used to target rheological properties of chocolate.

Kacker, R., Maaß, S., Emmerich, J. und Kramer, H.

AIChE Journal (link)

In this study, an in-situ imaging system has been analysed to characterize the crystal size, the shape and the number of particles during a continuous crystallization process in a COBC. Two image analysis approaches were examined for particle characterization in the suspension containing both small nuclei and larger grown crystals (non-spherical and irregular in shape). The pattern matching approach, in which the particles are approximated to be spherical, did result in an overestimation of the size. Alternatively, a segmentation based algorithm resulted in reliable crystal size and shape characteristics. The laser diffraction analysis in comparison to the image analysis overestimated the particle sizes due to the agglomeration of particles upon filtration and drying. The trend in the particle counts during the start of crystallization process, including nucleation, determined by the image analysis probe was comparable with the one measured by FBRM, highlighting the potential of in-situ imaging for process monitoring.

Jun Zhu, Chanyuan Tao

Chongqing University, Chemical Engineering and Technology, 2017, PhD

D. Thesis Database, China (link)

As one of the core equipment of fluid mixing, stirred reactor is widely applied in many fields such as metallurgy, chemical industry, petroleum, which directly influences the efficiency of the whole production process of production and corporate profits. Therefore, stirred reactor is one of major research hotspotsfor fluid mixing. High efficientand energy saving stirred reactor contributes to promote chemical process intensification, energy conservation and emission reduction, while the breakthrough lies in the reasonable impeller design, strengthen development of chaotic mixing theory…

Heyse, A., Plikat, C., Ansorge-Schumacher, M. und Drews, A.

Catalysis Today: 12/2017 (link)

Pickering emulsions are currently receiving increased attention as a promising alternative to dispersions or surfactant stabilized emulsions in two-phase biocatalysis. In order to design a continuous membrane reactor using water-in-oil Pickering emulsions for biocatalysis, knowledge on the filterability of the Pickering emulsion is required. This can be influenced by a number of factors, e.g. type and size of stabilizing nanoparticles, applied solvent, and used membrane. In a previous application of water-in-oil Pickering emulsions for continuous biocatalysis in a membrane reactor, spherical silica particles were used to stabilize the emulsion. This resulted in densely packed filter cakes due to unbound residual particles and decreasing flux over time. Furthermore, rather large droplet sizes with small specific interfacial areas were achieved. In this work, the use of colloidal silica nanoparticle for the stabilization of bioactive Pickering emulsions was studied. The filterability of bioactive water-in-oil Pickering emulsions stabilized by spherical or colloidal silica nanoparticles was compared. Using colloidal silica nanoparticles was found to result in smaller emulsion drop sizes, higher filterability and better reproducibility of drop size distribution and flux. An increase in water volume fraction decreased the flux level, but filtration was still possible at industrially relevant fluxes. With the selected nanoparticles, continuous biocatalysis in a membrane reactor at constant flux, i.e. constant residence time, was performed twice for 30 h. Substrate and product concentrations were constant and reproducible and the enzyme was still active after 30 h. The productivity was higher than that obtained with spherical silica nanoparticles and the process duration is the longest so far reported for continuous biocatalysis in PE at industrially relevant residence times.

 Hohl, L. und Kraume, M.

Chemical Engineering Research and Design: 89 (11), 1561–1573 (link)

The phase behavior of microemulsion systems consisting of oil, water and non-ionic surfactants can lead to emulsions with unique properties: by adjusting temperature and composition a system with three liquid phases is obtained. These systems can be used as solvent systems for reactions such as the hydroformylation of long-chained olefins. Knowledge of the occurring dispersion and coalescence processes is crucial for process optimization and control. Using an endoscope measurement technique in a stirred tank, relevant criteria that determine the formation of complex droplets by the two dispersed phases such as multiple emulsions are defined. The influence of the third phase on dispersion and coalescence is discussed by analyzing the drop sizes of the dispersed phases in agitated systems in situ. Furthermore, the impact of the third liquid phase on the slope of sedimentation and coalescence curves is analyzed in subsequent phase separation experiments.

Petzold, M., Röhl, S., Hohl, L., Stehl, D., Lehmann, M., von Klitzing, R. und Kraume, M.

Chemie Ingenieur Technik, 89 (10) (link)

Mass transfer in stirred liquid-liquid systems with and without silica nanoparticles is investigated for the saponification of benzoyl chloride. The mass transfer area is positively affected by the nanoparticles which lead to an increase of the liquid-liquid interfacial area due to droplet coalescence hindrance. However, an additional mass transfer resistance induced by particles at the liquid-liquid interface was observed for all particle concentrations, since the high occupancy diminishes the available area for mass transfer. The ratio of the two oppositional effects needs to be determined to identify suitable nanoparticle reaction systems.

Hohl, L., Knossalla, M. und Kraume, M.

Chemical Engineering Science, 171: 76-87 (link)

The phase separation of liquid/liquid systems consisting of oil, water and amphiphilic molecules is a function of temperature and composition. The phase separation is fastest in liquid three phase systems, where the organic and aqueous excess phases are separated by a microemulsion middle phase. In this work, a detailed analysis of the relevant physical properties (density, rheology, interfacial tension) of the phases in combination with drop size distribution measurements and image analysis of the droplet interactions is performed using an endoscope measurement system. This methodology enables to directly quantify influencing effects of droplet size and droplet interactions on dispersion and phase separation processes. The duration and character of the separation process strongly depends on the droplet interactions (e.g. formation of multiple emulsions) of the dispersed phases.

Schmidt, M., Pogrzeba, T., Hohl, L., Weber, A., Kielholz, A., Kraume, M. und Schomäcker, R.

Molecular  Catalysis, 439: 1-8 (link)

The palladium catalyzed methoxycarbonylation of long-chain olefin 1‐dodecene in a liquid/liquid biphasic system composed of methanol as polar phase and the substrate/product as nonpolar phase is reported. The immobilization of the palladium based catalyst in the methanol phase is affected by the use of the watersoluble ligand SulfoXantPhos and methanesulfonic acid as co‐catalyst. We investigated these systems with respect to reaction performance and catalyst recycling by variation of the type and amount of co-solvent in both existing phases. By modifying these systems with a co-solvent, catalyst recycling could be improved compared to the benchmark system without co-solvents to a palladium and phosphorous leaching <1 ppm. The applied homogeneously dissolved palladium catalyst could be quantitatively recycled four times via a simple phase separation without any loss in activity and selectivity.

Cocke, J. und Maaß, S.

Macromolecular Reaction Engineering, DOI: 10.1002 (link)

Recent studies have revealed unexpected developments in drop size by only small changes in the geometrical constraints of batch vessels used for suspension polymerization. The effect of the dispersed phase fraction, surfactant concentration, as well as baffle length on the evolving drop size distribution in different low viscous liquid–liquid systems is investigated. The analysis is focused on the drop-dominated systems by hindering the coalescence by polyvinyl alcohol (PVA) concentrations up to three times higher than the critical micelle concentration. The influence of PVA on drop size in breakage-dominated systems is well reproduced with population balance equation simulations. The Drops are measured using a photo-optical system with automated image analysis. The measured drop sizes increase with increasing dispersed phase fraction. As coalescence is completely hindered, all observed coalescence effects are connected to phase inversion, a catastrophic phenomenon during suspension polymerization for industrial production processes. Phase inversion can be reproduced for all studied solvents with and without the use of surfactants. In particular, the influence of the baffles can be reproduced. The system is adapted and trained to detect phase inversion as a warning system to make the suspension polymerization process more stable and robust.

Panckow, R., Reinecke, L., Cuellar, M. C. und Maaß, S.

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles, 74 (3) (link)

The exact knowledge of Drop Size Distributions (DSD) plays a major role in various fields of applications to control and optimise processes as well as reduce waste. In the microbial production of advanced biofuels, oil droplets are produced under turbulent conditions in an aqueous medium containing many surface active components, which might hinder the recovery of the product. Knowledge of DSD is thus essential for process optimisation. This study demonstrates the capability of a photo-optical measurement method for DSD measurement in fermentation broth and in plate separators aimed at cost reduction in the microbial production of advanced biofuels. Measurements were made with model mixtures in a bioreactor, and at the inlet and outlet of a plate separator. In the bioreactor, the method was effective in detecting a broad range of droplet sizes and in differentiating other disperse components (e.g. microbial cells and gas bubbles). In the plate separator, the method was effective in determining the influence of the varied parameters on the separation Efficiency.

Li, X.

University of Twente (link)

Solvent extraction is one of the main separation techniques and has been developed for a wide range of industrial applications. Ionic liquids (ILs) are often considered as environmentally friendly solvents and have been studied widely in various laboratory applications. Aiming to design effective extraction processes, in this work ILs have been employed for fractionation of pyrolysis oil, for demulsifying oil-in-water emulsions to recover surfactant, and for the design of a novel smart separation process type: fixed liquid extraction.
Pyrolysis oil, the liquid product of fast pyrolysis of lignocellulosic biomass, is a complex mixture containing hundreds of components. For the valorization of pyrolysis oil, value-added chemicals are required to be separated. A study on aromatics removal from pyrolytic sugar streams was described in chapter 2 and 3, and a study on fractionation of oxygenates (acetic acid, glycolaldehyde and acetol) from pyrolysis oil cuts in chapter 4.
In chemical enhanced oil recovery (CEOR), surfactant together with alkali and polymer are injected in the reservoir to enhance oil recovery yield. The surfactant is usually blended with water and oil in stable emulsions. Therefore, the first step for surfactant recovery is to destabilize these oil emulsions which is called demulsification. In chapter 5, in total 13 ILs were evaluated as demulsifiers for a model oil-in-water emulsion, and the efficiency and mechanism of demulsification were discussed.
Application of ILs at industrial scale is restricted by their major drawbacks, such as high viscosity and corrosivity. IL-based emulsion systems that make use of stabilizers can potentially overcome these drawbacks. In chapter 6 the formation of several IL-based emulsions stabilized by microgel particles was studied, including the parametric influences on the drop size distributions. The influence of microgel particles on the extraction capacity and kinetics were investigated as well. In chapter 7, a novel separation process concept was explored for the processes, referred to as fixed liquid extraction, aiming for the design of separation process for extremely small S/F.
ILs can effectively remove aromatics from pyrolytic sugar streams. Value-added oxygenates can be fractionated by a two-step extraction process. The studied halogenide ILs and P666,14[N(CN)2] can demulsify heptane-in-water emulsions and the mechanism of demulsification is anion exchange. Several IL-based emulsions stabilized by microgel particles has been prepared, and the concept of fixed liquid extraction has been demonstrated for the first time.

Grafschafter, A. und Siebenhofer, M.

Chemie Ingenieur Technik, 89 (4): 409-415 (link)

The Taylor-Couette disc contactor (TCDC) is a stirred liquid-liquid phase contactor which is suitable for applications in bioseparations. For liquid-liquid reactor design, information about the specific mass transfer area is inevitable. Therefore, the drop size distribution and holdup in the TCDC were investigated under various operating conditions and appropriate correlations for the prediction of these parameters have been determined. Experimental data of drop size distributions were correlated with lognormal, Gaussian, and Weibull drop size distribution functions.

Skale, T., Hohl, L., Kraume, M. und Drews, A.

Journal of Membrane Science (link)

This study shows the possibility of separating w/o Pickering emulsions (PE) via ultrafiltration and consequently enables a continuous process concept for catalysed L/L reactions in Pickering emulsions which are currently receiving increased attention. In two types of filtration experiments, the stability of PE against coalescence caused by the applied filtration pressure and stirring was shown. The PE could be concentrated up to 80% water phase fraction. In pressure stepping experiments, permeabilities between 3 and 10 L/(m2 h bar) could be achieved depending on the drop size distribution of the PE. For the used 1 kDa PVDF membrane, an unexpected overproportional behaviour of the fluxes at higher pressures was observed. The presented results show that Pickering emulsions can be regarded as a promising alternative to conventional dispersions also in continuous L/L catalysis.

Marbà-Ardébol, A.-M., Emmerich, J., Neubauer, P. und Junne, S.

Process Biochemistry, 52: 223-232 (link)

To date, on line monitoring in bioprocesses is restricted to conventional parameters. Presently, advances in microscopy allow the monitoring of single-cell size distributions in a bypass or in situ. These data provide information regarding population heterogeneity, substrate conversion, or product synthesis as these parameters are related to the size of the cells. In this study, changes in the single-cell size distribution of the heterotrophic microalgae Crypthecodinium cohnii were tracked with holographic microscopy and a photo-optical microscopy probe, which is applicable in situ. This algae produces the polyunsaturated fatty acid docosahexaenoic acid (DHA). On the basis of the cell size and broadness of the size distribution, the applied methods enabled to distinguish between cells in the growth and production phase. Under conditions of low growth and high fatty acid accumulation, the cell size kept concomitantly changing. The correlation between cell size measurements and the intracellular DHA content was confirmed by regression analysis. The phase heterogeneity, which was measured by holographic microscopy, changed simultaneously with the DHA synthesis. The amount of information obtained by both digital holographic and in situ microscopy is similar to that obtained by flow cytometry but with reduced effort for a real-time Analysis.

Pogrzeba, T., Schmidt, M., Hohl, L., Weber, A.,  Buchner, G., Schulz, J., Schwarze, M., Kraume, M. und Schomäcker, R.

Industrial and Engineering Chemistry Research, 55 (50): 12765 – 12775 (link)

The first applications of aqueous surfactant-free multiphase emulsions as reaction media for rhodium-catalyzed hydroformylation of 1-dodecene and Suzuki coupling reaction of 1-chloro-2-nitrobenzene and 4-chlorobenzeneboronic acid are herein reported. The reaction systems were formulated from oil (reactant and solvent), aqueous catalyst solution, and diethylene glycol butyl ether [C4H9(C2H4O)2OH]. We investigated these multiphase systems with respect to reaction engineering and catalyst recycling to evaluate their application potential for new chemical processes based on switchable solvents. For the hydroformylation, conversion of 23.4% after 4 h reaction time could be achieved at mild reactions conditions of 95 °C and 15 bar syngas pressure. The applied Rhodium-SulfoXantPhos catalyst could be successfully recycled for four times, maintaining its very high linear-to-branched selectivity of 99:1. For the Suzuki coupling reaction yields up to 90% were achieved within a single run. The Pd/SPhos catalyst could be recycled three times, but activity decreased at almost stable selectivity due to higher ligand leaching during the separation steps.

Stehl, D., Hohl, L., Schmidt, M., Hübner, J., Lehmann, M., Kraume, M., Schomäcker, R. und von Klitzing, R. 

Chemie Ingenieur Technik, 88 (11): 1806 – 1814 (link)

Emulsions stabilized by solid particles are so called Pickering emulsions which are characterized by their high stability against coalescence. This type of emulsion can be used for a lot of applications. Very little is known about how reaction conditions affect their properties. In this study the influence of important reaction conditions like shear stress, pressure, temperature, and the influence of synthesis gas on Pickering emulsions is investigated. It is shown that the emulsions remain stable in terms of coalescence in a broad range of the reaction conditions and are suitable as reaction media for industrial processes and for a reaction optimization with a subsequent separation step.

Heeres, A. S., Heijnen, J., van der Wielen, L. A. M. und Cuellar, M. C.

Chemical Engineering Science, 145: 31-44 (link)

In the search for advanced biofuels, microorganisms have been developed that make and secrete long chain hydrocarbons, resulting in a four phase fermentation mixture (cells, aqueous liquid, organic product, and (produced) gas). The product immiscibility offers the potential for a straightforward recovery, but surface active components in the fermentation broth emulsify the product droplets. In the current process, multiple centrifugation steps with chemical de-emulsifiers are used for product recovery, posing economic and environmental burdens on the process. In this paper, an alternative separation method is presented, in which gas bubbles induce coalescence of the emulsified oil droplets, obtaining a continuous oil layer. The oil layer formation was influenced by the gas flow rate, nozzle diameter, column geometry, and emulsion properties, offering the possibility for process optimisation. The developed gas bubble induced oil recovery method does not require chemical additives, uses mild process conditions, and can potentially be integrated with the fermentation, giving a low cost alternative for the conventional recovery method. Using this technology, another step can be made towards economically feasible production of advanced biofuels.

Hohl, L., Schulz, J., Paul, N. und Kraume, M.

Chemical Engineering Research and Design, 108: 210-216 (link)

Tunable multiphase systems can be applied for the hydroformylation of long-chained olefins. These reaction systems enable highest yields and fastest separation processes under three phase operating conditions. However, little is known about the characteristic properties of these complex dispersions. In this study, a simplified model system consisting of water, 1-dodecene and a solvo-surfactant was analysed. The minimum aggregation concentration, interfacial tension, density and viscosity were determined. Additionally, the phase behaviour was investigated using conductivity measurements. The phase volume fractions under three phase conditions were analysed. An endoscope measurement technique was applied to determine the dispersion conditions and drop size distributions in a stirred tank as a function of composition and stirrer speed.

Fries, T., Dittler, I., Blaschczok, K. , Löffelholz, C., Dornfeld, W., Schön, R., Drews, A. und Eibl, D.

Chemie Ingenieur Technik, 88(1-2): 177-182 (link)

Zur Quantifizierung der Beanspruchung durch die Zentrifugalpumpe PuraLev® 200SU wurde der mittlere Sauter-Durchmesser des Modellsystems Emulsion in Abhängigkeit des massenspezifischen Leistungseintrages ermittelt. Anschließend wurde mit ausgewählten Parametern die Absterberate von CHO-Zellen untersucht und mit den Ergebnissen der Emulsionsversuche verglichen. Es konnte gezeigt werden, dass für das biologische System neben dem Leistungseintrag weitere Parameter wie die Impellerumfangsgeschwindigkeit Einfluss auf die Partikelbeanspruchung haben.

Amokrane, A., Maaß, S., Lamadie, F., Puel, F. und Charton, S.

Chemical Engineering Journal, 296: 366–376 (link)

The pulsed column is one of the most used contactors in solvent extraction processes, especially in the nuclear fuel treatment industry and for hydrometallurgical applications. The optimisation of solvent extraction operations needs a thorough understanding of the diphasic flow’s properties inside the apparatus, especially that of the dispersed phase. For the first time, in-situ measurements of the drop size distribution (DSD) were achieved in a small diameter pulsed column (lab scale), by using the SOPAT-VF light reflectance video probe on two water-in-oil (W/O) systems exhibiting low and high viscosities of the oil phase. Separate effects of the pulse amplitude and frequency on the DSD and the phase hold-up were evidenced for both O/W systems, despite their different viscosity levels. This technique allowed very precise measurements of droplet-diameters in quite a confined space, three orders of magnitude, which is remarkable. Experimental findings allowed the validation of a computational fluid dynamics (CFD)–population balance equation (PBE) coupled model and the improvement of breakage and coalescence kernel parameters. Rupture and coalescence mechanisms were correctly captured. The dependence of emulsion’s properties on the column hydrodynamics could then be illustrated over one period of the pulsed flow. Incidence of higher levels of pulsation intensity, hardly achievable experimentally, and separate investigation of the effects of viscosity and surface tension are presented.

Hohl, L., Paul, N., und Kraume, M.

Chemical Engineering and Processing, 99: 149–154 (link)

Micellar multiphase systems can be applied to enable reactions like the hydroformylation of long-chained olefins. These liquid/liquid systems combine advantages of homogenous catalysis like high and specific yield or mild reaction conditions with a fast phase separation process. In previous studies highest yields were observed in systems under three phase operation conditions whereby the reaction rate was a function of stirrer speed. Hence, dispersion conditions and drop size distributions need to be taken into consideration. In this study, micellar three phase systems were analysed using an endoscope measurement technique and image analysis in a stirred tank. A methodical approach to identify the respective phases and to clarify the dispersion conditions was found. The mean Sauter diameters were quantified as a function of the system composition. By applying abrupt changes of the stirrer frequency, the dynamic behaviour and coalescence effects were investigated.

Aksamija, E., Weinländer, C., Sarzio, R. und Siebenhofer, M.

Separation Science and Technology 50(18):2844-2852 (link)

In the present project, the design of the Rotating Disc Contactor (RDC) has been fundamentally simplified and optimized in terms of separation efficiency, load capacity, and suitability for downstream processing of bio-based materials. Optimized performance was obtained when the stator discs were abandoned and their function was adopted by enlarged rotor discs. Mass transfer experiments showed improved separation efficiency in the novel apparatus, while the operating range was simultaneously increased. Due to recurring drop formation and re-coalescence in every compartment, large droplets were not observed, resulting in a narrower drop size distribution compared to the RDC.

Hofmann, A., Schembecker, G. und Merz, J.

Colloids and Surfaces A: Physicochemical and Engineering Aspects (473), S. 85-94 (link)

The surface activity of amphiphilic molecules such as proteins lead to an affine adsorption at gas–liquid interfaces. Using this physicochemical property for separation like in foam fractionation these amphiphilic molecules can be separated and/or concentrated via the adsorption on gas bubbles out of aqueous solutions. Hence, in foam fractionation the bubble size plays a fundamental role on the performance as it influences the foam structure and determines the available surface area for the adsorption of surface active molecules. Therefore, the bubble size constitutes a key parameter in foam fractionation and thus, needs to be characterized and investigated experimentally in more detail. In this study, a method for optically measuring the bubble size in a device for continuous foam fractionation is introduced which is based on the detection and subsequent analysis of spherical bubbles in digital images using an ideal circle for the template matching technique. With the help of the implemented bubble size measurement method a performance study for the model system β-casein was performed to point out the role of bubble size on the performance of a foam fractionation process in stripping mode. The crosslink between process parameters like the superficial feed and gas velocity with the bubble size and the separation efficiency is presented and discussed. For the first time, the validity to use a single mean bubble diameter for characterization of a whole foam bed in continuous foam fractionation operated in stripping mode was shown for two different gas spargers. It was shown that the foam fractionation performance is directly adjustable via bubble size by changing the ratio of superficial feed to gas velocity.

Panckow, R., Comandè, G., Maaß, S. und Kraume, M.

Chemical Engineering & Technology, 38(11): 2011-2016 (link)

The presented results are obtained by means of an automated image analysis software capable of measuring particle diameters in photographs taken in situ by a 2D photo-optical measurement device. Initially, the applicability of this measurement method must be proven for fluid particle systems on the basis of spherical-shaped particles. As a first approach in targeting the issue of irregularly shaped fluid particles, a pure gas-liquid system is analyzed to investigate the influence of the variation of operating parameters. In the second step, the spherical shape is changed by reducing the surface-active auxiliaries. The usage of shape factors helps to interpret the appearance of the 2D projected objects. By examining the capabilities and limitations, it is demonstrated that the size of fluid particles can be detected online and in situ in order to analyze and control the particular chemical process.

Dittler, I., Dornfeld, W., Schöb, R., Cocke, J., Rojahn, J., Kraume, M. und Eibl, D.

Journal of Visualized Experiments, (102): 10.3791/53052 (link)

NEU! Übersetzung auf Hindi verfügbar

Pumps are mainly used when transferring sterile culture broths in biopharmaceutical and biotechnological production processes. However, during the pumping process shear forces occur which can lead to qualitative and/or quantitative product loss. To calculate the mechanical stress with limited experimental expense, an oil-water emulsion system was used, whose suitability was demonstrated for drop size detections in bioreactors1. As drop breakup of the oil-water emulsion system is a function of mechanical stress, drop sizes need to be counted over the experimental time of shear stress investigations. In previous studies, the inline endoscopy has been shown to be an accurate and reliable measurement technique for drop size detections in liquid/liquid dispersions. The aim of this protocol is to show the suitability of the inline endoscopy technique for drop size measurements in pumping processes. In order to express the drop size, the Sauter mean diameter d32was used as the representative diameter of drops in the oil-water emulsion. The results showed low variation in the Sauter mean diameters, which were quantified by standard deviations of below 15%, indicating the reliability of the measurement technique.

Heeres, A., Schroën, K., Heijnen, J., van der Wielen, L. und Cuellar, M.

Biotechnology Journal, 10(8): 1206-1215 (link)

Developments in synthetic biology enabled the microbial production of long chain hydrocarbons, which can be used as advanced biofuels in aviation or transportation. Currently, these fuels are not economically competitive due to their production costs. The current process offers room for improvement: by utilizing lignocellulosic feedstock, increasing microbial yields, and using cheaper process technology. Gravity separation is an example of the latter, for which droplet growth by coalescence is crucial. The aim of this study was to study the effect of fermentation broth components on droplet coalescence. Droplet coalescence was measured using two setups: a microfluidic chip and regular laboratory scale stirred vessel (2 L). Some fermentation broth components had a large impact on droplet coalescence. Especially components present in hydrolysed cellulosic biomass and mannoproteins from the yeast cell wall retard coalescence. To achieve a technically feasible gravity separation that can be integrated with the fermentation, the negative effects of these components on coalescence should be minimized. This could be achieved by redesign of the fermentation medium or adjusting the fermentation conditions, aiming to minimize the release of surface active components by the microorganisms. This way, another step can be made towards economically feasible advanced biofuel production.

Aksamija, E.

Dissertation | Technische Universität Graz (link)

In the present work the design of the RDC extractor, a well-established apparatus in solvent extraction, has been fundamentally simplified and optimized in terms of separation efficiency, load capacity and applicability for extraction of bio-based raw materials. Based on the Rotating Disc Contactor (RDC), a novel design of internals was discovered in the interaction of CFD simulation with Ansys Fluent and experimental validation (Particle Image Velocimetry, DSD measurements, sedimentation, tracer, load and mass transfer experiments). Being a hydrodynamic hybrid of a RDC and a Taylor-Couette reactor, the novel apparatus, therefore named TCDC, promises a wide range of applicability apart from solvent extraction. Experimentally validated simulation series show optimized hydrodynamic operating parameters (axial mixing, drop size distribution, vorticity, etc.) when the stator rings are abandoned and their function is adopted by rotor disks with increased diameter. Mass transfer experiments showed improved separation efficiency over the RDC, the HTU-value was decreased by ~ 35% while the operating/flooding limits were simultaneously increased. The elimination of the stator rings simplifies manufacturing and operation as well as cleaning and maintenance. Empirical design rules from literature, still state-of-the-art for the geometric design of RDCs, have been updated, simplified and theoretically consolidated.

Dittler, I., Kaiser, S., Blaschczok, K., Löffelholz, C., Bösch, P., Dornfeld, W., Schöb, R., Rojahn, J., Kraume, M. und Eibl, D.

Engineering in Life Sciences, 14(3): 311-317 (link)

The suitability of oil–water emulsions to predict shear forces in stirred bioreactors under cost-effective and time-saving conditions has been demonstrated several times, but no application to pumps has been described so far. In this report, the drop sizes in a model oil–water system were determined for the Levitronix PuraLev® multiuse (MU) series (PuraLev® 200MU and PuraLev® 600MU), a peristaltic pump (Masterflex® I/P Easy Load), and 4-piston diaphragm pump (Quattroflow 1200-SU, where SU is single-use) using inline endoscopy. It was determined that the Sauter mean diameter could be used as a comparison criterion to estimate mechanical stress in pumps. The investigation showed that PuraLev® MU pumps are characterized by up to 59% larger Sauter mean diameters than their counterparts at comparable operational conditions. This indicates lower hydrodynamic stress in the PuraLev® MU pumps. Using computational fluid dynamics, a well-streamlined fluid flow and low turbulent energy dissipation rates were found in the PuraLev® MU pumps, which correlated well with experimental results. A calculation model was used to predict the Sauter mean diameter by combining both experimental and computational fluid dynamics data. Good agreement with deviations below 13% was determined between model predictions and experimental data.

Ngo, T. H.

Dissertation | Technische Universität Carolo-Wilhelmina zu Braunschweig (link)

Gas-liquid-liquid systems, in which a gas is absorbed into an oil-water emulsion with or without chemical reaction, are of scientific, technical and commercial importance due to their wide industrial application.

Through the development of the aqueous biphasic technique in homogeneous catalysis, gasliquid-liquid systems have gained increasing attention in various chemical processes, e.g. hydroformylation, carbonylation, hydrogenation and oligomerization (Cornils, 1999). This aqueous biphasic technique involves using water-soluble ligands to solubilize the metal complex catalyst in an aqueous phase, which is easily separated from reactants and reaction products by decantation. Hydroformylation of propene to n-butyraldehyde is a typical example for important industrial applications of gas-liquid-liquid reaction systems. In this process, the reactive gas mixture of carbon monoxide, hydrogen and propylene is converted to n-butyraldehyde in an aqueous solution of rhodium catalyst (Cents et al., 2004).  Three different phases therefore exist in the reactor: the gas phase containing CO, H2, and propylene; the aqueous catalyst phase (water phase); and the dispersed organic butyraldehyde phase (oil phase).

Panckow, R., Maaß, S., Emmerich, J. und Kraume, M.

Chemie Ingenieur Technik, 85(7): 1036-1045 (link)

Die exakte Bestimmung der Phasengrenzfläche in Gas/flüssig-Systemen ist unabdingbar für die optimierte Prozessführung verfahrenstechnischer Anlagen. Die experimentelle Studie zeigt Untersuchungen an einem Luft/Wasser-System mittels dreier Messtechniken hinsichtlich der Bestimmung der Veränderung der Blasengröße in Abhängigkeit von der Rührerdrehfrequenz. Die äußerst präzise und selbstreferenzielle Methode der foto-optischen Analyse wird bzgl. der Bildverarbeitung näher betrachtet. Es wird gezeigt, dass die neuesten Entwicklungen im Bereich der Foto-Optik und der Bildverarbeitung wertvolle Grundlagen zur Etablierung einer präzisen Echtzeitgrößenmesstechnik geliefert haben. Dies ist notwendig, da laserbasierte Methoden nur unzureichende Prozessdaten liefern.

Schilder, L., Maaß, S. und Jess, A.

Industrial & Engineering Chemistry Research, 52(5): 1877-1885 (link)

The kinetics of the IL-catalyzed reaction of isobutane with 2-butene and the size distribution of the dispersed IL droplets were investigated in a stirred tank reactor. The results were used to calculate the intrinsic reaction rate constant with a model accounting for the interplay of external and internal mass transport and chemical reaction. The intrinsic reaction rate was found to be very high, leading to a low effectiveness factor of the IL catalyst. The used fraction of the IL droplets with a diameter of about 400 μm was very small, and the actual reaction took place only in a thin spherical shell with a thickness of about 5 μm.

Emmerich, J., Maaß, S., Rojahn, J., Kraume, M. and Neubauer, P.

Chemie Ingenieur Technik, 84(8): 1189 (link)

No abstract is available for this article. Full article available under this link.

Ngo, T. H. und Schumpe, A.

International Journal of Chemical Engineering, 2012 (link)

Absorption of pure oxygen into aqueous emulsions of n-heptane, n-dodecane, and n-hexadecane, respectively, has been studied at 0 to 100% oil volume fraction in a stirred tank at the stirring speed of 1000 min−1. The volumetric mass transfer coefficient, , was evaluated from the pressure decrease under isochoric and isothermal (298.2 K) conditions. The O/W emulsions of both n-dodecane and n-hexadecane show a maximum at 1-2% oil fraction as reported in several previous studies. Much stronger effects never reported before were observed at high oil fractions. Particularly, all n-heptane emulsions showed higher mass-transfer coefficients than both of the pure phases. The increase is by upto a factor of 38 as compared to pure water at 50% n-heptane. The effect is tentatively interpreted by oil spreading on the bubble surface enabled by a high spreading coefficient. In W/O emulsions of n-heptane and n-dodecane increases with the dispersed water volume fraction; the reason for this surprising trend is not clear.

Maaß, S., Rojahn, J., Hänsch, R. und Kraume, M.

Computers and Chemical Engineering, 45: 27-37 (link)

Image analysis has become a powerful tool for the work with particulate systems, occurring in chemical engineering. A major challenge is still the excessive manual work load which comes with such applications. Additionally manual quantification also generates bias by different observers, as shown in this study. Therefore a full automation of those systems is desirable. A MATLAB® based image recognition algorithm has been implemented to automatically count and measure particles in multiphase systems.

A given image series is pre-filtered to minimize misleading information. The subsequent particle recognition consists of three steps: pattern recognition by correlating the pre-filtered images with search patterns, pre-selection of plausible drops and the classification of these plausible drops by examining corresponding edges individually. The software employs a normalized cross correlation procedure algorithm. The program has reached hit rates of 95% with an error quotient under 1% and a detection rate of 250 particles per Minute depending on the System.

Maaß, S. und Kraume, M.

CIT Plus, 6: 31-33 (link)

CITplus – Das Sopat-System (Smart On-line Particle Analysis Technology) ist die Kombination einer photo-optischen Messtechnik und einer Bildverarbeitungs-Software. Diese analysiert im Gegensatz zu herkömmlichen inline-Sonden auch in hochkonzentrierten Dispersionen Größe und Konzentration von festen oder fluiden Partikeln in Echtzeit. Dies findet – anders als bei offline Methoden – direkt im Reaktor statt, wodurch erstmals eine Prozesssteuerung auf Basis der Partikelgröße möglich wird.

Maaß, S., Paul, N. und Kraume, M.

Chemical Engineering Science, 76: 140-153 (link)

The effect of the dispersed phase fraction on the evolving drop size distribution in different low viscous agitated liquid/liquid systems was investigated. The analysis focused on the drop breakage phenomena by hindering the coalescence completely. Therefore, polyvinyl alcohol concentrations were used around three times higher than the critical micelle concentration.

The measured drop sizes were increasing with increasing dispersed phase fraction. As coalescence was completely hindered and also the measured dispersion viscosity showed no influence on the dispersed phase hold-up, the size increase is proposed to be a result of turbulence hindering.

The influence of the dispersed phase fraction on the drop sizes in breakage dominated systems was well reproduced with population balance equation (PBE) simulations. The used breakage models require a turbulence damping factor (1+φd), which is used in most of the common models. Summarizing the various PBE simulations we can conclude that drop sizes in systems with different dispersed phase fractions can be easily predicted, if the model parameters are fitted to one set of experiments studying the same physical system. The change of the solvent was successfully simulated with outstanding results for two of the three further investigated organics.

The used Weber correlations were also able to reproduce the linear interdependency between the drop size and the dispersed phase fraction. Unfortunately, every change in the dispersed phase needed new parameter estimation. As at least three out of four different liquid/liquid systems were predicted with excellent results, the PBE is proposed as a more robust tool which gives additionally information about the transient behavior of the system. Therefore, PBE should be used rather than the classical correlations widely used in academics and industries.

Maaß, S. und Kraume, M.

Chemical Engineering Science, 70: 146-164 (link)

An evaluation of several breakage rates from the literature based on single drop experiments was carried out. This data was collected in a single drop breakage cell under turbulent conditions, comparable to those in a stirred tank. For a constant initial diameter and flow velocity at least 750 single drops have been investigated to measure the breakage time and probability, using high-speed imaging. These results were used for the determination of breakage rates by the product of the inverse of breakage time and the breakage probability. The same subdivision was carried out for the literature models. These differentiations in the analysis showed that published models for the breakage probability are more or less similar and in good agreements with the experimental results. Proposed approaches for the breakage time are contrary. The experiments support the assumption of some researchers that the breakage time rise with increasing drop diameter. The magnitude of the predicted values of the breakage time for all kind of models is one or more magnitudes higher than experimental results in this study and from literature. Furthermore the influence of the physical properties, like viscosity or interfacial tension, is only poorly reflected in the available models. These analysis results lead to an improved breakage time model, which takes into account different breakage mechanisms and the influence of viscosity and interfacial tension. Combined with a breakage probability from literature, this new model leads to an excellent prediction of the breakage rate for the investigated single drops.

Maaß, S., Buscher, S., Hermann, S. und Kraume, M.

Biotechnology Journal, 6(8): 979-992 (link)

Understanding of particle strain and drop breakage is relevant for various technical applications. To analyze it, single drop experiments in a breakage cell and evolving drop size distributions in an agitated system are studied. The mechanisms for particle strain and drop breakage are assumed to be comparable for the investigated turbulent flow regime. The agitation process is simulated using a population balance model. This model provides transient prediction capacities at different scales and can be used for scale-up/down projects. The number and the size distributions of daughter fragments for single drops have been studied. The results clearly support the assumption of binary breakage. The most common assumption of a Gaussian distribution for the daughter drop size distribution could not be supported. The evolution of a breakage-dominated toluene/water system was then simulated using different daughter drop size distributions from literature. The computational results were compared with experimental values. All simulations were able to predict the transient Sauter mean diameter excellently but varied strongly in the results on the shape of the distribution. In agreement with the experimental single drop results, the use of a bimodal or a very broad bell-shaped distribution of the daughter drops is proposed for the simulations. Although these results were obtained in a particular vessel for a specific phase system, it can be applied to simulate transient multiphase systems at different scales. We would expect that the general trends observed in this study are comparable to various applications in multiphase bioreactors.

Maaß, S., Rehm, T. und Kraume, M.

Chemical Engineering Journal, 168(2): 827–838 (link)

Based on the successful predictions of transient drop sizes in the first part of this research (Maaß et al., Prediction of drop sizes for liquid–liquid systems in stirred slim reactors—part I: single stage impellers. Chem. Eng. J., 162 (2010) 792–801), this part is a straight continuation and extension of the earlier work. The predictive capabilities of the used population balance equation model are increased for single stage impellers and transferred to scale-up procedures of such applications. Therefore different scale-up rules for liquid–liquid systems are tested experimentally and by simulations in two different sized, geometrically similar vessels. The multi stage impellers are tested against comparable single stage impellers in terms of power consumption, mixing time and minimum impeller speed. Especially for high aspect ratios (larger than three), multi stage impellers successfully compete with the single stage ones. The measured drop size distributions in slim reactors with multi stage impellers showed no dependency on the local position, although the dispersion process is tedious due to the compartmentalization. The simulations are not able to reflect this initial phase of the dispersion process, but are in close agreement with the experiments after complete dispersion is fulfilled. Based on these experiences the aspect ratio is increased up to five and the resulting drop size can be predicted with reasonable deviations (lower than 10%). The results of the scale-up of this multi stage impeller liquid–liquid system do not lead to a clear conclusion. Although the simulations recommend the use of constant power input, the experiments could not support this. None of the other traditional scale-up rule are supported by the experiments. Overall, the results of power consumption, mixing time and dispersion behavior show the great potential of multi stage impellers for process optimization and intensification in slim reactors.

Maaß, S., Wollny, S., Voigt, A. und Kraume, M.

Experiments in Fluids, 50(2): 259-269 (link)

An online measurement technique for drop size distribution in stirred tank reactors is needed but has not yet been developed. Different approaches and different techniques have been published as the new standard during the last decade. Three of them (focus beam reflectance measurement, two-dimensional optical reflectance measurement techniques and a fiber optical FBR sensor) are tested, and their results are compared with trustful image analysis results from an in situ microscope. The measurement of drop sizes in liquid/liquid distribution is a major challenge for all tested measurement probes, and none provides exact results for the tested system of pure toluene/water compared to an endoscope. Not only the size analysis but also the change of the size over time gives unreasonable results. The influence of the power input on the drop size distribution was the only reasonable observation in this study. The FBR sensor was not applicable at all to the used system. While all three probes are based on laser back scattering, the general question of the usability of this principle for measuring evolving drop size distributions in liquid/liquid system is asked. The exterior smooth surface of droplets in such systems is leading to strong errors in the measurement of the size of the drops. That leads to widely divergent results. A different measurement principle should be used for online measurements of drop size distributions than laser back scattering.

Maaß, S., Metz, F., Rehm, T. und Kraume, M.

Chemical Engineering Journal, 162 (2): 792 – 801 (link)

Although investigations in the field of stirred liquid/liquid dispersions have a long history, new questions are still emerging in dealing with the different aspects of industrial applications, such as suspension polymerizations. In this study the influence of physical parameters on drop size and power consumption, like liquid level, stirrer speed, stirrer height and baffle length, were experimentally analyzed. The results were used to determine modeling approaches which are capable of displaying the influence of the named parameters. It was shown that the energy law (dp ∼ ɛ−0.4; Shinnar, 1961 [1]) using the average energy dissipation only roughly predicts the Sauter mean diameter. The population balance equation (PBE) used with a one-zone modeling approach is slightly better in its prediction of results. Very satisfying predictions were obtained by using the PBE with a two-zone model. The overall deviations between calculated and predicted Sauter mean diameter was less than 10% using this approach. Only the successful prediction of the influence of the baffle length remained unattainable, even with the PBE two-zone model.