Ulrich Kunz

PASSflow Syntheses Using Functionalized Monolithic Polymer/Glass Composites in Flow‐Through Microreactors

: A chemistapos;s wish finally becomes reality: microreactors for every synthetic laboratory! By precipitation polymerization various polymers are introduced into the irregular pore system of a porous glass rod. By embedding these rods into a housing, followed by functionalization and immobilization of reagents onto the polymer phase, versatile microreactors are obtained. With this apparatus, chemical transformations in solution can be performed, for example, a steroid derivatization.

Design, modeling and performance of a novel sonochemical reactor for heterogeneous reactions

Abstract We constructed a novel sonochemical reactor for heterogeneous solid fluid reactions which uses high intensity ultrasound from a concentrator horn. It can be shown that the concept of a conical funnel fits the demands for a nearly perfect radiation effectiveness and a good reaction management. Theoretical investigations concerning the sound field in both the sonotrode and the reactor for different cases give some insight in the fundamental relationship between consumed electrical power, converted mechanical energy in the transducer and radiated sound energy. The main energy conversion paths in the liquid are presented as well. A Grignard reaction was investigated in the reactor and showed extreme reaction rate enhancements which are due to a mechano chemical reaction kinetic caused by imploding bubbles and the thereby generated shock waves and microjets. A simulation of the particle size distribution during simultaneous reaction the fragmentation in an ultrasonic loop reactor was developed to correlate measured size distributions with model equations.

Zinc-air Batteries: Prospects and Challenges for Future Improvement

Abstract With the rising production of regenerative energy stronger focus on energy storage is necessary. One possibility to store electric energy is the use of battery technology. Especially high energy densities can be realized with metal-air batteries. Zinc-air batteries are known since more than 100 years, but have until now found use only in special markets. A well-known example is the battery for hearing aids. Many attempts have been undertaken to develop rechargeable zinc-based batteries, but only with limited success. Reasons for this fact and directions for future needs, applications and developments are discussed in the paper. Furthermore, first experiments for the use of ionic liquids as electrolytes in zinc-air-batteries are presented.

Enzyme-purification and catalytic transformations in a microstructured PASSflow reactor using a new tyrosine-based Ni-NTA linker system attached to a polyvinylpyrrolidinone-based matrix

The synthesis of a Ni-nitrilotriacetic acid (Ni-NTA) attached via a new tyrosine-based linker matrix on monolithic crosslinked poly(vinyl benzyl chloride)/poly(vinylpyrrolidinone) is described. This matrix is incorporated inside a microstructured PASSflow reactor which was used for automatic purification and immobilisation of His(6)-tagged proteins. These could be used as stable and highly active biocatalysts for the synthesis of (R)-benzoin (6), (R)-2-hydroxy-1-phenylpropan-1-one (7) and 6-O-acetyl-D-glucal (17) in a flow-through mode.

Polymer/carrier composites as materials and reactors for organic synthesis.

In this work new polymer/carrier composites are described which serve as novel materials in flow-through reactors for polymer-supported organic solution-phase synthesis. Monolithic polymer/carrier columns are prepared by a new precipitation polymerization process inside the void pore volume of megaporous glass carrier materials. Chemical functionalization of the internal polymer phase with chlorosulfonic acid or trimethylamine generates small, interconnected ion-exchange resin beads with a diameter of 1-3 microm which can be used for a large variety of organic syntheses. These monolithic rods are incorporated into an appropriate casing and can conveniently be operated in the flow-through mode. Important successful applications are polymer-assisted solution-phase reductions, oxidations and Horner-Emmons olefinations. Additionally, the use of these monolithic columns as catalytic microreactors and their performance in selected reactions are described.

Electrochemical reduction of oxygen at pyrolyzed iron and cobalt N4-chelates on carbon black supports

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.

Rate expression for THF synthesis on acidic ion exchange resin

Abstract The intrinsic kinetics for the liquid-phase cyclisation etherification of 1,4-butanediol (BD) to tetrahydrofuran (THF) and water were determined in a stirred batch reactor in the temperature range from 373 to 393 K . A sulphonic acid ion exchange resin powder with a particle size of 3–7 μm was manufactured and used as catalyst. The reaction can be regarded as irreversible and proceeds without diffusion limitations inside the catalytic microspheres. The formation of an intermediate containing 1,4-butanediol (BD) on an active site was determined to be the rate-determining step. The reaction product water acts as a strong inhibitor for the intermediate formation. The experimental results can be described by a three-parameter model based on Michaelis–Menten kinetics extended by an inhibition term for water. Within the developed rate equation, concentrations are expressed in liquid-phase activities from the UNIQUAC method in order to consider the nonidealities. The developed rate equation is valid in the whole range of possible concentrations and independent of the solvents used. During the experiments no formation of by-products was observed.

Polymer-assisted Horner-Emmons olefination using PASSflow reactors: Pure products without purification

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.

Activated solid–fluid reactions in ultrasound reactors

Abstract Reactions of solids with liquid reactants can be accelerated in ultrasound fields. Transient bubbles create liquid microjets and increase the amount of dislocations on metallic surfaces. Dynamic experiments and models for the activation of magnesium turnings in the Grignard reaction of chlorobutane and phenylchloride show a relation between the degree of activation and the local energy distribution in the ultrasound field. The local action of transient bubbles and microjets in cavitating sound fields was measured and calculated. This allows the prediction of reaction rates, optimum process parameters and the behavior of different metals in noncatalytic as well as catalytic solid–fluid reactions. A further optimization of reaction rates and safer production of organometallic compounds was reached by applying mixtures of calcium donated magnesium. These alloys are very brittle and can be cleaved under ultrasound. High reaction rates with a variety of organic chlorides and phenyl fluoride are observed with sonicated magnesium calcium alloys.

Electrochemical membrane reactors for sustainable chlorine recycling.

Polymer electrolyte membranes have found broad application in a number of processes, being fuel cells, due to energy concerns, the main focus of the scientific community worldwide. Relatively little attention has been paid to the use of these materials in electrochemical production and separation processes. In this review, we put emphasis upon the application of Nafion membranes in electrochemical membrane reactors for chlorine recycling. The performance of such electrochemical reactors can be influenced by a number of factors including the properties of the membrane, which play an important role in reactor optimization. This review discusses the role of Nafion as a membrane, as well as its importance in the catalyst layer for the formation of the so-called three-phase boundary. The influence of an equilibrated medium on the Nafion proton conductivity and Cl− crossover, as well as the influence of the catalyst ink dispersion medium on the Nafion/catalyst self-assembly and its importance for the formation of an ionic conducting network in the catalyst layer are summarized.