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26 results on '"Kareth, S."'

11. Influence of scCO(2), ultrasound, and quaternary ammonium salt on gelation time and structural characteristics of silica

Author

Hanu, A.M., Kareth, S., Puls, A., Ivanova, M., Mallick, B., Mudring, A.V., Petermann, M., and Publica

Abstract

In situ synthesis of silica gels via a one-step sol-gel process at ambient pressure or in supercritical CO2 was investigated. The influence of compressed gas, ultrasound irradiation, and quaternary ammonium salt (choline chloride) on the gelation time was determined. The obtained samples were characterized by N-2 adsorption/desorption measurements, scanning electron microscopy in combination with energy dispersive X-ray spectroscopy (SEM/EDX), and Fourier transform infrared-attenuated total reflection spectroscopy (FTIR-ATR). The retention capacity of the corresponding silica aerogels for Rhodamine B was evaluated as a model for organic water pollutants. The obtained results proved that scCO(2) has a beneficial effect, leading to a reduction of the gelation time. The obtained aerogels exhibit a higher surface area and larger pore diameter as well as a well-defined cylindrical pore structure.

Published
2014

12. Teilereinigung mit flüssigem CO2 bietet Rationalisierungspotenziale

Author

Mankiewicz, J., Bilz, M., Uhlmann, E., Petermann, M., Kareth, S., and Publica

Abstract

Technisches CO2 wird als Sekundärprodukt von vielen Lieferanten technischer Gase in unterschiedlicher Qualität angeboten. Es bietet viele grundsätzliche Vorteile und kommt bereits in unterschiedlichsten Industriebranchen zur Anwendung. Das deklarationsfreie CO2 wird in der Medizin- und Lebensmitteltechnik verwendet. Dort ist es als Strahlmittel, Kühlmedium, Prozess- oder Schutzgas weit verbreitet. So gehört die Extraktion von Koffein aus Kaffeebohnen zu den wohl bekanntesten Anwendungen. Die Teilereinigung mit komprimiertem CO2 hat ihren Ursprung in der Hochdruckextraktion zur Gewinnung von Naturextrakten. In der Metallbearbeitung befasste sich unter anderen das Forschungszentrum Karlsruhe mit der Öl- und Fettextraktion aus industriellen Schleifschlämmen, Spanabfällen sowie von Bauteilen. Die Öl- und Fettextraktion mit überkritischem CO2 erfolgte dort bei Prozessdrücken von weit über 74 bar und Temperaturen über 31 °C.

Published
2012

14. Phase equilibria of carbon dioxide + poly ethylene glycol + water mixtures at high pressure: Measurements and modelling

Author

Martín, Á., Pham, H.M., Kilzer, A., Kareth, S., Weidner, E., and Publica

Subjects
modelling, supercritical carbon dioxide, perturbed-chain statistical associating fluid theory, überkritisches Kohlendioxid, Trocknung, Modellierung, drying, particles from gas saturated solutions, Hochdrucksprühverfahren
Abstract

Phase equilibria of carbon dioxide + poly ethylene glycol (PEG) of average mol weight 6000 g/mol + water mixtures has been measured by the static method at conditions of interest for the development of Particles from Gas Saturated Solutions (PGSS)-drying processes (pressure from 10 MPa to 30 MPa, temperature from 353 K to 393 K). A thermodynamic model based on the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) equation of state has been developed for correlating experimental data. The model is able to predict the composition of the liquid phase with an average deviation of 8.0%. However, the model does not calculate correctly the concentration of PEG in the gas phase. The model is also capable of predicting VLE data reported in the literature of PEG + CO2 mixtures with PEGs of molecular weights ranging from 1500 g/mol to 18500 g/mol as well as solid-fluid equilibrium of carbon dioxide + PEG mixtures at pressures below 10 MPa.

Published
2009

25. Infrared laser triggered release of bioactive compounds from single hard shell microcapsules.

Author

Vöpel T, Scholz R, Davico L, Gross M, Büning S, Kareth S, Weidner E, and Ebbinghaus S

Subjects
Capsules, Transition Temperature, Water chemistry, Drug Carriers chemistry, Drug Liberation, Infrared Rays, Lasers
Abstract

Micro composites are commonly characterized in bulk. Here we study the temperature triggered release of a bioactive compound from single isolated microcapsules. We monitor the release process in real-time using a novel thermal microscopy method combining laser-induced heating and fluorescence imaging.

Published
2015
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26. Behavior of highly diluted electrolytes in strong electric fields-prevention of alumina deposition on grading electrodes in HVDC transmission modules by CO2-induced pH-control.

Author

Weber I, Mallick B, Schild M, Kareth S, Puchta R, and van Eldik R

Abstract

Alumina deposition on platinum grading electrodes in high voltage direct current (HVDC) transmission modules is an unsolved problem that has been around for more than three decades. This is due to the unavoidable corrosion of aluminum heat sinks that causes severe damage to electrical power plants and losses in the range of a million Euro range per day in power outage. Simple experiments in a representative HV test setup showed that aluminates at concentrations even below 10(-8) mol L(-1) can deposit on anodes through neutralization by protons produced in de-ionized water (κ≤0.15 μS cm(-1)) at 20-35 kV (8 mA) per electrode. In this otherwise electrolyte-poor aqueous environment, the depositions are formed three orders of magnitude below the critical precipitation concentration at pH 7! In the presence of an inert electrolyte such as TMAT (tetramethylammonium-p-toluenesulfonate), at a concentration level just above that of the total dissolved aluminum, no deposition was observed. Deposition can be also prevented by doping with CO2 gas at a concentration level that is magnitudes lower than that of the dissolved aluminum. From an overview of aqueous aluminum chemistry, the mystery of the alumina deposition process and its inhibition by CO2 is experimentally resolved and fully explained by field accumulation and repulsion models in synergism with acid-base equilibria. The extraordinary size of the alumina depositions is accounted for in terms of proton tunneling through "hydrated" alumina, which is supported by quantum chemical calculations. As a consequence, pulse-purging with pure CO2 gas is presented as a technical solution to prevent the deposition of alumina., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Published
2014
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