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In-situ investigation of separation instabilities during sedimentation in the centrifugal field
Titus Sobisch, Dietmar Lerche, Torsten Detloff, Raúl Montalvo, Nelson Quintas
LUM GmbH, Rudower Chaussee 29 (OWZ) 12489 Berlin info@lum-gmbh.de, www.lum-gmbh.com
Abstract:
Only in some selected cases classification and clarification processes in thickeners and centrifuges can be described fairly well based on Stokes law. Normally, accelerating and hindering effects have to be accounted for. Furthermore, in real systems other irregular phenomena have been observed as sedimenting clusters, stratification of dispersions and the formation of an interlayer between supernatant and sedimenting particle collective. The latter is caused by the preferential floatation of fines and light particles due to liquid displaced by sedimenting particles. The demixing of dispersions containing lose agglomerates is even more complex.
These phenomena lead to an undesirable remixing and a loss of separation efficiency.
Instability phenomena during separation in a centrifugal field were characterized in-situ using multisample analytical centrifugation with photometric detection. In more detail instability phenomena in carbon black dispersions are investigated as function of centrifugal acceleration, temperature, viscosity and density of the dispersion media and of surfactant concentration during preparation.
separation instabilities, analytical centrifugation, carbon black dispersions, asymmetric aggregates
As a general feature it was noticed that the more instable the dispersion or the faster separation occurs (due to centrifugal acceleration, preparation conditions, viscosity or density difference) the earlier the appearance of back folding.
A possible explanation for the back folding is a change in orientation of asymmetric aggregates. At high particle concentration asymmetric particle aggregates are supposed to have a preferential orientation ‘broadsideon’, which is the orientation leading to minimal light attenuation. After reaching a critical lower concentration larger aggregates are settled out and small asymmetric aggregates will be able to rotate resulting in an increased light attenuation.
A close link between time of appearance of back folding and quality of carbon black dispersions exists. Namely, the more stable the dispersion the less pronounced and later the back folding effect. Varying the surfactant concentration during dispersion preparation a considerable termination of the effect was observed when increasing the surfactant concentration from 3 to 5 %. However, a further increase in surfactant concentration did not change the quality of dispersion.
Titus Sobisch, Dietmar Lerche, Torsten Detloff
LUM GmbH, Rudower Chaussee 29 (OWZ) 12489 Berlin info@lum-gmbh.de, www.lum-gmbh.com
Abstract:
Unit processes using centrifugal fields are often applied for separation and classification of fine grained materials. Modelling of these processes requires information about the separation behaviour of the suspensions to be processed. To this end direct measurements in centrifuges are obligatory for the dimensioning of the separation units to obtain the desired cut-off size and residual effluent turbidity. Moreover, these measurements have to gather kinetic information as function of the processing conditions, particle interaction and particle concentration. Results of measurements at earth gravity cannot be scaled up to reflect the situation in a centrifugal field.
A multisample analytical centrifugation technique with photometric detection is presented which allows a comprehensive characterization of separation processes in the centrifugal field with high sample throughput. In particular the type of sedimentation behaviour (free sedimentation of individual particles, hindered settling, zone settling) can be deduced from the progression of the transmission profiles. Even more it can determine the critical residence time as function of feed concentration for a desired effluent clarity and allows measuring the velocity distribution of particles inside the centrate in-situ.
The photometric detection enables to determine the velocity distribution of dispersions down to very low feed concentrations. This is especially important for clarification processes.
Colloidal stable quartz suspensions revealed a broad velocity distribution as expected.
fine particle slurries, analytical centrifugation, sedimentation, velocity distributions, clarification
Conclusions
Multisample analytical centrifugation with photometric detection allows a comprehensive characterization of separation processes in the centrifugal field with high sample throughput. In particular the type of sedimentation behaviour (free sedimentation of individual particles, hindered settling, zone settling) can be deduced from the progression of the transmission profiles. Even more it can determine the critical residence time as function of feed concentration for a desired effluent clarity and can measure the velocity distribution of particles inside the centrate in-situ.
The separation behaviour of quartz suspensions as function of concentration of solids and centrifugal acceleration was characterized and the velocity distributions inside the centrate were determined time-dependently (i.e. the composition after different times of centrifugation) and as function of location (i.e. the composition at different distances from the centre of rotation). Both informations are essential for design of separation processes (residence time, weir height).
The photometric detection enables to determine the velocity distribution of dispersions down to very low feed concentrations. This is especially important for clarification processes.
Colloidal stable quartz suspensions revealed a broad velocity distribution as expected.
L.U.M. GmbH, Stability & Particle Analysis,
F. Aguilar, G. G. Badolato, H. P. Schuchmann
The development of emulsion based products as well as process development/monitoring and quality assurance require efficient and objective analytical tools for shelf life evaluation and stability determination. Destabilisation processes in emulsions are very complex. Aging and
breaking of emulsions are the result of several processes – creaming or sedimentation, flocculation, coalescence, Ostwald ripening, phase inversion – which can occur separately or simultaneously. This is the main reason why the development of reasonable procedures for shelf life prediction is very difficult and always depends on the product which is subject to evaluation.
The multisample approach applied using analytical centrifugation allows an accelerated characterisation of any demixing processes (creaming, sedimentation, phase separation) as well as the quantification of time dependent structural alterations (e.g. flocculation, coalescence). The analytical centrifugation is very sensitive to small changes in the inherent stability, but also alterations due to slow aging can be revealed far faster than by simple visual assessment.
Model emulsions were designed exhibiting creaming, coalescence, flocculation or Ostwald ripening as the dominating mechanism for instability. Results obtained are compared with rheological measurements, particle size analysis by light scattering and common accelerated stability tests like freeze/thaw cycling and storing at 45 °C.
see google.docs
Evaluation of long term stability of model emulsions by multisample analytical centrifugation
Application of multisample analytical centrifugation for fast evaluation of long term stability and freeze/thaw stability of emulsions
L.U.M. GmbH, Stability & Particle Analysis,
The development of emulsion based products as well as process development/monitoring and quality assurance require efficient and objective analytical tools for shelf life prediction and stability determination. Freeze/thaw stability is often used as measure of long term stability. On the other hand high freeze/thaw stability is often required as property of the final product. To this end the potential of multisample analytical centrifugation was evaluated as an accelerated test procedure.
A new multisample approach is presented using analytical centrifugation, which allows for an accelerated characterization of destabilization processes (creaming, sedimentation, coalescence, phase separation). The kinetics of these destabilizing processes can be traced simultaneously for up-to 12 different samples with temperature control in the range between 4 and 45 °C. No dilution is necessary, which otherwise could lead to changes of dispersion properties.
Analytical centrifugation measures in a rapid way the inherent stability of the samples. Therefore, alterations due to slow aging may be investigated combining first a shorted common accelerated stability test like freeze/thaw cycling and second a rapid evaluation by analytical centrifugation.
The wide application potential of this approach is demonstrated by examples of measurements on cosmetic creams and on beverages.
see google.docsRapid emulsifier selection and evaluation of emulsion stability by analytical centrifugation
L.U.M. GmbH, Stability & Particle Analysis,
Selection of emulsifiers and evaluation of emulsion stability is a frequent task. This relates to practical issues like formulation of emulsions, optimization of manufacturing, quality control, shelf life prediction and breaking of emulsions.
Results of investigations on emulsion stability behaviour as function of polarity of nonionic emulsifiers and preparation conditions are presented.
The investigations revealed that the method applied is very suitable for screening purposes, optimization of emulsion manufacturing and that time of investigation and centrifugal acceleration can be adapted to avoid conditions were centrifugal forces are the determining factor for phase separation.
SHELF LIFE PREDICTION OF LIQUID FOOD PRODUCTS BASED ON MULTISAMPLE ANALYTICAL CENTRIFUGATION (MAC)
Dietmar Lerche, Titus Sobisch and Stefan Kuechler
L.U.M. GmbH, Stability & Particle Analysis,
Rudower Chaussee 29, 12489
Many dispersions in industry and daily life are colloidal systems based on emulsions, partly containing additional solid particles to improve their performance. The long term stability of the “quality” of emulsion based products is crucial, as between the production date and the time of their use or consumption often weeks, month and even years are passed by. Shelf life depends directly on physical stability besides other phenomena like structural alterations due to aging or degradation phenomena by light. Centrifugation is the only method truly to accelerate physically sedimentation or creaming processes of emulsions and suspensions. In addition, analytical photocentrifugation is a very efficient tool to determine the separation/demixing velocity (SDV). In this paper we demonstrate that based on experimentally obtained SDV by MAC the shelf life may be determined directly. We present a SOP, how the influence of the elevated g-forces may be evaluated based on the analysis of a velocity versus g-force (centrifugal acceleration) dependency. Shelf life at gravity (1 g) can be confidently calculated based on linear or non-linear regression. Besides shelf life these studies reveal additional information regarding the structural (rheological) stability of emulsion based products.
Carbon nanotubes enlisted to reduce waste in cleanup of toxic chemicals
"Researchers at Pacific Northwest National Laboratory have demonstrated a new, environmentally friendly process for treating water contaminated by perchlorate ....
The conventional method for treating perchlorate-contaminated water employs an ion exchange resin. Regenerating the resin requires flushing with an acidic solution, which results in large quantities of secondary waste.
The PNNL method is an electrically controlled anion exchange process. The technology is unique in that it uses an electric current to regenerate the resin and release the perchlorate without producing a lot of secondary waste ...To create the new process, Lin and his colleagues induced a positive charge to an electrically conducting polymer, such as a polypyrrole, that selectively attracts the negatively charged perchlorate ions. Application of an electric current releases the trapped perchlorate ions for disposal. Now neutral, the polymer can be reverted to a positively charged surface and re-used.
The scientists increased the amount of perchlorate that can be captured by depositing the polymer as a polypyrrole thin film on a matrix of carbon nanotubes, creating a porous conductive nanocomposite."
Und die Palästinenser in Gaza und der Westbank? Für sie gilt derzeit ohne Ausnahme die Regel des unheilvollen Nahostspiels: Keine Hoffnung. Die Perspektivlosigkeit und das Elend der besetzten Gebiete verweisen auf das völlige Versagen und die Doppelmoral der internationalen Gemeinschaft.
Inter arma silent musae – wo Kanonen donnern, setzt das Hirn aus. Frieden im Nahen Osten verlangt internationale Verhandlungen, kein militärisches Diktat, kein taktisches Stückwerk. Es geht um gleiche Rechte für alle und gegenseitige Anerkennung und Sicherheit. Frieden braucht aber auch eine demokratische Zivilgesellschaft, die national geschürtem Hass entgegensteht, die jeweiligen Fundamentalismen bekämpft und jeden "Kampf der Kulturen", jeden "Heiligen Krieg" offensiv zurückweist.
Die Partner von medico international im Libanon, in Israel und Palästina stehen für säkulare Kulturinitiativen im schiitischen Südbeirut, Gesundheitsausbildung palästinensischer Flüchtlinge im Libanon, arabische Frauenhäuser in Israel, israelisch-palästinensische Kliniken in der Westbank und Trauma-Arbeit in Gaza. Für die Hoffnung eines gleichberechtigten Zusammenlebens im Nahen Osten.
Die libanesisch-palästinensischen Hilfsorganisationen AMEL, PARD und NAMSC bitten um Geldspenden für Milchpulver, Babynahrung, Hygieneartikel, Decken, Notunterkünfte, Erste-Hilfe-Sets. Auch im Gaza-Streifen fehlt weiterhin das Allerlebensnotwendigste: Medikamente, Nahrung, Wasser. medico international stellt 10.000 Euro Soforthilfe bereit und ruft gemeinsam mit dem ATTAC-Koordinierungskreis und medico international schweiz zu Spenden auf.
