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The influence of process parameters on the H2O2 yield of gas diffusion electrodes (GDE) are investigated. The investigated GDEs consist of Vulcan XC72 carbon black and PTFE on gold‐plated nickel wire cloth. An electrolysis cell is used to evaluate the influence of various process parameters, such as temperature, pH value, oxygen pressure and stoichiometric factor, electrolyte flow regime, current density and separator material at steady‐state conditions. It is found that the investigated GDE enables current efficiencies greater than 90 % at up to 2 kA m−2, whereby lower electrolyte temperatures and higher pH values contribute to higher H2O2 yields above 90 % current efficiency.

Regarding the treatment of (waste)water, electrochemical processes have various advantages over other methods. They are robust, easy to operate and flexible in case of fluctuating wastewater streams. In addition, a relatively broad spectrum of organic and inorganic impurities can be removed. This contribution provides an overview of electrochemical reactors for water, process water, and wastewater treatment, which are already in technical‐scale operation or subject of research. Some essential basics of electrochemical processes for the treatment of water are presented and examples for applications are given. This is followed by a description of the reactors.

The mechanical behavior of lithium-ion battery electrodes that undergo a severe capacity decrease are investigated by monitoring the out-of-plane displacement on the external surface of a pouch cell. The capacity degradation does not decrease gradually as a function of time but exhibits distinct behaviors with different causes. These are electrochemical aging during cycling and mechanical injury caused by manufacture failure. In the former case, both the permanent evolution and the anomalous distribution of the displacement accompanied with a consistent decrease of the capacity are correlated to the local deterioration of the adhesion of the material layers. The mechanical injury accelerates the capacity decrease by destroying the electrode structure, which results in a sudden decrease of the surface displacement. If the displacement reaches its limit, only a dynamic fluctuation remains, which reflects the remaining electrochemical process at a low level. As a result, we conclude that the loss of electrical connectivity between the active material layer and the current collector is responsible for the severe capacity degradation. This effect is more pronounced on the anode than the cathode. Both electrochemical cycling and mechanical injury can result in the weakening of the adhesion of the anode material on the current collector.

A continuous process to produce carbon-supported platinum catalysts by polyol reduction was examined. The reactant dispersion was rapidly heated up to reaction temperature while flowing through a directly electrically heated tube followed by a downstream isothermic tubular reactor. Appropriate inner diameters corresponding to the desired short heating-up times were calculated. A certain lower limit for the inner diameter is caused by temporary pluggings of particle agglomerates circumventing steady-state operation. Tube diameters were evaluated with respect to heating-up times and plugging. It was proved that with a tubular reactor a continuous preparation of carbon nanotube-supported platinum catalysts with a low particle size and evenly distributed particles is possible.

Platinum (Pt) nanoparticles show high activity as catalysts in various chemical reactions. The control of the morphology of Pt nanostructures can provide an opportunity to improve their catalytic properties. The preparation of Pt-loaded iron-oxide polyvinylbenzyl chloride nanocomposites was done in several stages: first by the formation of the core consisting of magnetite nanoparticles and second by the polymerization of vinylbenzyl chloride in the presence of the magnetic core particles. The third step is the amination of the chlorine group with ammonia, which leads to an ion exchange resin. Then, the Pt precursor (H2PtCl6) is attached by ion exchange. Finally, the Pt ions are reduced to Pt metal with NaBH4. The obtained material can be dispersed easily and be used as a catalyst which can be separated after the reaction by magnetic fields. Characterization of the resulting metallic nanocomposites is evaluated by atomic absorption spectroscopy, thermal gravimetric analysis, transmission electron microscopy, infrared spectroscopy, and gas chromatography. The activity of Pt at magnetic core/shell nanocomposites was measured for the reduction reaction of cinnamaldehyde to cinnamyl alcohol. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Im Rahmen des Projekts μ-Consortium wurde eine mobile Praktikumsanlage zur Einbindung der Mikroverfahrenstechnik in die Lehre realisiert. Zur Vermittlung von Kenntnissen in einer Vielzahl verfahrenstechnischer Operationen im Mikromasstab wurden Praktikumsversuche zu den Themengebieten Mischen und homogene Reaktion, heterogene Reaktionen, Warmeubertragung und Partikelsynthese entwickelt.

A multicomponent mass transfer model based on the generalized Maxwell-Stefan equations (GMS) for an extraction process with supercritical fluids is presented. The solution is obtained from the differential film model equations rather than from an explicit expression for the fluxes. The approach presented here also provides concentration profiles along the diffusion path length, which allow rigorous consideration of the dependence of mass transfer coefficients and thermodynamic factors on concentration, if desired. The volume translated Peng-Robinson equation of state is used along with a g E mixing rule (g E - molar excess Gibbs free energy) in order to account for strongly nonideal thermodynamics that necessarily arise in unstable liquid mixtures. The results show strong diffusional coupling effects for the system under consideration, propene (1)-isopropyl alcohol (2)-water (3). Finally, we demonstrate how diffusional coupling may provide options for process intensification.

The Fischer-Tropsch synthesis was discovered in Germany in the 1920s and has since been developed to industrial scale within a relatively short period of time. In the 21st century, the process is undergoing a renaissance, because an increasing fraction of liquid fuels will have to be produced from alternative raw materials like natural gas, coal or biomass in the future. On industrial scale, multitubular and bubble column reactors are used for this highly exothermic reaction. Due to several disadvantages of both reactor systems, new concepts are presently investigated. For intensification of mass transfer properties of multiphase reactors, alternative catalyst geometries like honeycombs, structured packings or foams are discussed. High catalyst utilization and isothermal operating conditions can be achieved in microstructured reactors. Furthermore, several membrane reactor concepts are under investigation. After an introduction to historical development and state of the art of Fischer-Tropsch reactors, chances and challenges of new reactor technologies will be discussed.

Palladium particles were generated by reduction of palladate anions bound to an ion exchange resin inside microreactors. The size and distribution of the palladium particles differed substantially depending on the degree of cross-linking and the density of ion exchange sites on the polymer/glass composites, the latter parameter having a larger influence than the former. The polymer phase of the composite materials was used for the loading with clusters composed of palladium particles which are 1 to 10 nm in diameter. The reactivity and stability of six different palladium-doped polymer/glass composite samples for transfer hydrogenations was investigated both under conventional and microwave heating in the batch mode as well as under continuous flow conditions using the cyclohexene-promoted transfer hydrogenation of ethyl cinnamate as a model reaction. Regarding the heating method it was found that catalysts that are composed of larger metal particles perform better under microwave irradiating conditions whereas samples with smaller particle sizes perform better under conventional heating. Comparing batch experiments with flow-through experiments the latter technique gives better conversion. Reusability was better in microwave heated experiments than in traditional heating.

Magnetische Funktionspartikel, sogenannte Magnetic Beads, die bereits in der analytischen Biotechnologie ihre Anwendung finden, werden auf Ihre Eignung als Katalysatormaterial untersucht. Die Ionentauscherfunktion der Magnetic Beads soll als katalytisch aktives Material in einer Transferhydrierungsreaktion genutzt werden. Fur die Herstellung der magnetischen Funktionspartikel wird ein neuer Syntheseweg eingesetzt, der nach einem Baukastenprinzip funktioniert. In einem Spruhprozess wird aus einer Dispersion/Losung, die magnetisierbare Nanopartikel, nanoskalige funktionale Ionentauscherpartikel und ein gelostes Matrixpolymer enthalt, in einem Schritt das Funktionspartikel hergestellt. Fur die Transferhydrierung wurden reaktionstechnische Untersuchungen unter Verwendung der magnetisierbaren Funktionspartikel in einem Ruhrkesselreaktor durchgefuhrt. Diese Daten werden mit in konvektiv durchstromten Komposit-Mikroreaktoren erhaltenen verglichen.

Die Fischer-Tropsch-Synthese wurde in Deutschland entdeckt und ab 1920 in kurzer Zeit zur technischen Reife entwickelt. Im 21. Jahrhundert erlebt das Verfahren eine Renaissance, da flussige Treibstoffe zukunftig auch aus alternativen Rohstoffen wie Erdgas, Kohle oder Biomasse hergestellt werden mussen. Fur die technische Durchfuhrung der stark exothermen Reaktion haben sich bisher Rohrbundelreaktoren und Blasensaulenreaktoren durchgesetzt. Da beide Reaktortechnologien Nachteile aufweisen, werden neue Reaktorkonzepte untersucht. Zur Intensivierung von Stofftransportvorgangen in mehrphasigen Reaktoren werden alternative Katalysatorgeometrien wie Wabenkorper, Packungen oder Schwamme entwickelt. Eine gute Katalysatorausnutzung bei isothermer Reaktionsfuhrung wird in mikrostrukturierten Reaktoren erreicht. Schlieslich wird auch die Eignung von Membranreaktoren fur die Fischer-Tropsch-Synthese betrachtet. Nach Darstellung der historischen Entwicklung und des erreichten Standes der Technik werden Chancen und Herausforderungen der neuen Reaktortechnologien diskutiert.

Zur okonomischen Bewertung der Mikroreaktionstechnik in der Spezialchemie und der pharmazeutischen Industrie wird unterschieden zwischen theoretischem, technischem, stofflichem und wirtschaftlichem Potenzial. Die Potenzialtheorie wird systematisch auf die Prozessentwicklung angewendet.

Besides platinum, various nonnoble metal compounds, when prepared appropriately, are suitable for the electrochemical reduction of oxygen in liquid electrolytes and PEM-fuel cells. Pyrolyzed N4-chelates, such as phthalocyanines, tetraazaannulenes and porphyrins with a central metal atom of iron or cobalt, are a very important group of compounds and have been investigated in the past. It was found that the catalytic activity, especially of phthalocyanines, was high when prepared on carbon black supports at high temperatures (400-900 °C). Investigations on tetraazaannulenes and porphyrins yielded similar results. Non-noble metal compounds of cyclame (1,4,8,11-tetraazacyclotetradecane), which are also N4-chelates, were not investigated as thoroughly. However, the catalytic activities of iron and cobalt cyclames were low, compared to those of phthalocyanines. With the (GC-MS) analysis of both decomposition products, it could be shown that the mechanism of the N4-chelate decomposition is of decisive importance for the catalytic activity.

Cf Article en Anglais dans Chemical Engineering & Technology, 1998, Vol 21 No 6, pp. 494-498

A PASSflow protocol for the Horner–Emmons olefination of aldehydes using polymer-bound hydroxide ions in flowthrough reactors is presented which allows preparation of alkenes in very high yield with minimal purification.

On etudie la reduction de NO avec NH 3 sur des catalyseurs d'oxyde de fer (3 catalyseurs non modifies: ERR-KAT, ENB-KAT, LN-KAT, et 1 catalyseur fer oxyde/chrome oxyde: HU-KAT) dans un reacteur a recirculation en utilisant des effluents gazeux simules dans un domaine de temperature compris entre 573 et 673 K et en faisant varier les concentrations de NO et NH 3 entre 0 et 1000 vpm et les concentrations de O 2 et H 2 O entre 0 et 9% vol

The reduction of nitric oxide with ammonia on an unsupported iron oxide catalyst has been studied in a continuous-flow recycle reactor using simulated flue gas. The responses of the employed reactor system to step and pulse inputs of tracer indicate that the system could be regarded as a continuous stirred tank reactor (CSTR). Preliminary tests were carried out to determine the effect of temperature and particle size on the measured reaction rates. Additional experiments were performed in order to study the influence of oxygen and water concentration on these rates. A gas chromatographic system has been developed to analyze the gas components NO, N2O, NO2, NH3, H2O, O2, CO2 and N2. In addition, the concentrations of NO and NO2 were measured with a nondisperse infrared (NDUV/NDIR) analyzer.

Jacobsen's cobalt-salen complex was covalently immobilized on polymer carriers that are part of different technical setups (polymer powder, composite Raschig rings, PASSflow microreactors) and employed for the enantioselective ring opening of terminal epoxides with water and phenols. The polymer-supported catalysts showed good activity and stereoselectivity and could be used repeatedly after a simple reactivation protocol in both batch as well as continuous-flow modes.

A new concept for noncovalent immobilization of a ruthenium olefin metathesis catalyst is presented. The 2-isopropoxybenzylidene ligand of a Hoveyda-Grubbs carbene is further modified by an additional amino group (7) and immobilization is achieved by treatment with sulfonated polystyrene forming the corresponding ammonium salt. In this novel strategy for the immobilization of ruthenium-based metathesis catalysts, the amino group plays a two-fold role, being first an active anchor for immobilization and second, after protonation, activating the catalysts (electron donating to electron withdrawing activity switch). The polymeric support was prepared by precipitation polymerization which led to small bead sizes (0.2-2 microm) and large surface areas. Compared to commercial resins this tailor-made phase showed superior properties in immobilization of complex 7. This concept of immobilization was applied to glass-polymer composite megaporous Raschig rings. Ru catalyst 7 on Raschig rings was used under batch conditions in various metathesis reactions, including ring-closing (RCM), cross- (CM) and enyne metathesis, to give products of high chemical purity with very low ruthenium contamination levels (21-102 ppm). The same ring can be used for up to 6 cycles of metathesis.

A new concept for immobilising Grubbs III catalyst by direct coordination of ruthenium to polyvinyl pyridine (PVP) is presented. PVP was prepared by precipitation polymerisation, which led lo small bead sizes (0.2-2 μm) and large surface areas. Compared to commercial resins, this phase showed superior properties when employed in model ring-closing metathesis (RCM) and in representative RCM. enyne and CM reactions with various substrates. The concept of immobilisation was also applied to Raschig rings made from a glass polymer composite material, which can be incorporated into devices for continuous flow processes.

Heterogeneous catalysis for organic synthesis under continuous-flow conditions becomes possible by a new reactor-based approach. Continuous-flow reactors with a monolithic glass/polymer composite interior are loaded with palladium particles by ion exchange followed by reduction. When incorporated into a continuous-flow setup (PASSflow) this reactor allows the transfer-hydrogenation of alkenes, alkynes, nitro-substituted aromatic compounds and benzyl ethers in the flow-through mode. In addition, the activity of the catalysts is well suited to achieve Suzuki, Sonogashira and Heck cross-coupling reactions in the absence of phosphanes or any other ligands, resulting in a greatly simplified purification. As an extension to this concept a bifunctional support was prepared inside the reactor consisting of Pd particles and an ion-exchange group (hydroxide form). In the Suzuki− Miyaura reaction the reactor serves as a base for immobilisation and activation of the boronic acid as boronate and as a catalyst for promoting the C−C coupling reaction under continuous-flow conditions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)