Organic Chemistry in Microreactors

Reactor model for fast reactions in the micro-bubble column and validation

A simple reactor model for predicting conversions in a micro-bubble column is described. It assumes fast reactions so that the gaseous component is readily consumed at the gas-liquid interface. Then, gas-liquid mass transfer becomes determining. As input parameters for the model, the hydrodynamics, specific interfacial area, and mass transport need to be described. Two fast model reactions, the catalytic oxidation of butyraldehyde and the absorption of CO2 in aqueous NaOH, show the applicability of the model but also its limits. The model was used for predicting reaction performance in dependence of operating conditions, in particular to get maximum conversion with the antagonistic paramete…

Microreactor processing for the aqueous Kolbe-Schmitt synthesis of hydroquinone and phloroglucinol

Hydroquinone and phloroglucinol were used as substrates for the aqueous Kolbe-Schmitt synthesis, using a novel processing methodology, termed high-p,T processing, recently demonstrated for the carboxylation of resorcinol. By the high-p,T approach, the temperature limitations of classical batch synthesis, e.g., set by reflux conditions (solvent boiling point), can be overcome by simple technical expenditure, e.g., the use of a few microstructured components, a capillary, and a needle valve at very low internal holdup. In this way, favorable speed-up of chemical reaction is achieved at temperatures normally outside the useful range for organic synthesis. While the hydroquinone synthesis gave …

Polymerisationen in mikrostrukturierten Reaktoren: Ein Überblick

Polymerisationen sind in jüngster Zeit als neue Anwendung für die Mikroverfahrenstechnik und Mikrofluidik erschlossen worden. Neben homogenen Polymerisationen im Bulk oder in Lösung gibt es mittlerweile auch Ansätze für heterogene Polymerisationen mittels Miniemulsionstechnik. Zudem können Polymerpartikel mit definierter Größe, Form und Morphologie hergestellt werden. Der Beitrag stellt erste Nutzungen der neuen Technik durch die polymerproduzierende Industrie im Labor- und sogar im Produktionsmaßstab unter Einsatz mikroverfahrenstechnischer Apparate vor.

Addition of Secondary Amines to α,β-Unsaturated Carbonyl Compounds and Nitriles by Using Microstructured Reactors

Several additions of amines to a,ß-unsaturated carbonyl compounds (Michael additions) were performed in a continuous-flow microstructured reactor rig and compared to the respective batch reaction. Dimethylamine/diethylamine/piperidine and acrylic acid ethyl ester/acrylonitrile were employed as two sets of reactants, giving six reactions. Some of these reactions are highly exothermal. Using the traditional batch procedure the olefin must be added quite slowly to the diluted amine to ensure temperature control and safe operation; especially this is necessary for the addition of dimethylamine (40 mass % aqueous solution) to acrylonitrile. Good yields (>85%) are achieved in this way; however…

Monolayers of Bolaform Amphiphiles: Influence of Alkyl Chain Length and Counterions

We have prepared self-assembled monolayers of novel cationic bolaform amphiphiles on negatively charged substrates. Most of these amphiphiles form smooth, defect-free monolayers which can be used to reverse the substrate surface charge and thus allow subsequent adsorption of anionic molecules and construction of multilayers. Atomic force microscopy, surface force measurement, and surface plasmon spectroscopy were combined to probe the molecular orientation and ordering, mechanical properties, and surface electrical properties of the monolayers. In addition, the amphiphile aggregation behavior at an air-water interface was studied by surface tension measurement, and lyotropic phase behavior …

Preferential CO oxidation over catalysts with well-defined inverse opal structure in microchannels

Catalyst supports of CeO 2 /SiO 2 and Al 2 O 3 with three-dimensionally ordered macroporous structure were fabricated in microchannels by application of PMMA opals as templates. Pt-Rh supported on CeO 2 /SiO 2 showed high efficiency for CO removal in preferential CO oxidation in the presence of excess hydrogen. Pt-Rh supported on Al 2 O 3 with an inverse opal structure showed higher reactivity than that supported on wash-coated Al 2 O 3 layers in microchannel reactor.

Micellar and lyotropic behavior of three isomeric bola-amphiphiles with pyridinium groups

The micellar and lyotropic phase behavior of three isomeric bola-amphiphiles 1, 2 and 3 based on para-, meta- and ortho-phenylene derivatives with hydrophilic pyridinium headgroups was investigated. The micellar behavior was characterized by surface-tension and conductivity measurements: while the para-substituted amphiphile 1 and the ortho isomer 3 aggregated to micelles, the meta-substituted amphiphile 2 exhibited stepwise, but discontinous self-association. This is explained by the mass-action and phase-separation model. The existence of “premicellar” aggregates and the discontinous aggregation of 2 is evidenced in addition by a difference-spectro-photometric measurement. The low surface…

Low temperature catalytic combustion of propane over Pt-based catalyst with inverse opal microstructure in microchannel reactor

A novel Pt-based catalyst with highly regular, periodic inverse opal microstructure was fabricated in a microchannel reactor, and catalytic testing revealed excellent conversion and stable activity for propane combustion at low temperatures.

The synthesis and the thermotropic phase behavior of the dipolar amphiphiles C 5 H 5 N + (CH 2 ) m OCOPhPHCOO(CH 2 ) m N + C 5 H 5 and the polymeric amphiphile [(CH 2 ) 6 OPhPhO(CH 2 ) 6 OCOCH([CH 2 ] 6 N + C 5 H 5 )COO] n are described

Industrial Microreactor Process Development up to Production

This chapter is about industrial applications of microprocess technology. Industry is not very active in publishing not only because of confidentiality reasons but also because of the absence of direct need for a corresponding profile. Thus, one cannot expect that the ongoing developments can be shown with a similar degree of completeness, clarity and detailedness, as this is possible for reviewing scientific contributions from academy with a wealth of peer-reviewed papers. Especially, the information of major interest of what has been transferred to production and how do the companies make profit with the new technology is usually kept secret. Thus, it has to be accepted that some informat…

α, ω-Dipolar amphiphiles: Influence of rigid and flexible units on aggregation behavior

Mono- and α,ω-dipolar amphiphiles with hydrophilic pyridinium head groups, and flexible and rigid hydrophobic parts have been synthesized. Surface tension and conductivity measurements proved that micellar aggregates for amphiphiles 1–4 are formed. The incorporation of rigid units leads to a decrease in the critical micellar concentration (CMC): the rigid monopolar amphiphile 2 aggregates at lower concentration than the flexible monopolar amphiphile 1. A similar decrease was observed when chain ends were connected: the flexible α,ω-dipolar amphiphile 3 has a lower CMC than the flexible monopolar amphiphile 1. The more flexible amphiphiles 1–3 allow the formation of micelles of different sha…