Aluminiumchlorid‐katalysierter Organosolv‐Aufschluss von Buchenholz

The Organosolv pulping is a process to separate lignocellulosic biomass into its components cellulose, hemicellulose and lignin. Usually this process is catalyzed by Brønsted acids. In this work the Brønsted acid is replaced by the Lewis acid aluminum chloride. Much less aluminum chloride is needed to achieve similar pulp properties like high cellulose recovery, high hemicellulose and lignin removal. Also aluminum chloride catalyzes the degradation of xylose to the important basic chemicals furfural and lactic acid.     

Bewertung des Nutzens von Cold‐Flow‐Versuchen bei der Charakterisierung von Kolonneneinbauten

Cold flow experiments with air and water as model fluids can make an important contribution to the characterization of column internals. They can be performed with comparatively low effort, however, on the other hand serve as an essential base for fluid dynamic model approaches, which in turn provide a bridge to technically relevant systems and operating conditions. In combination with other valuation methods, such as test mixture analyses or mathematical models, they can make a very important contribution to the safe and pinpoint design of column internals. Possibilities, but also limits of cold flow experiments are shown and related to tests with organic systems.     

Gasfluss‐Sputtern von Katalysatorschichten für Polymer‐Elektrolytmembran‐Brennstoffzellen

Gas flow sputtering (GFS) at increased pressures results in the formation of nanoscale particles of the sputtered material. This process has been evaluated regarding its applicability for synthesizing Pt catalysts for polymer electrolyte membrane fuel cells (PEMFCs). Catalyst layers of varying Pt‐loadings were deposited directly onto carbon fiber paper (gas diffusion layers, GDLs). Immediately after deposition, the catalytic activity of the resulting particulate deposits was tested by H₂‐oxidation at predefined ratios of H₂/O₂. The Pt deposits were subsequently evaluated regarding their applicability in a PEMFC environment.     

Synthese von porösen Voll‐ und Core‐Shell‐Glaskugeln zur Trennung von chiralen Anästhetika

For the separation of chiral anesthetic gases suitable support materials for the selectors are necessary. Due to the controlled texture properties porous glass shows a high potential for such applications. In this study porous glass beads with particle diameters of 40 – 400 µm and 2 – 4 mm could be obtained via a special fluidized‐bed reactor and the method of ionotropic gelation. Furthermore, the first core‐shell beads on the basis of porous glasses could be synthesized via the combination of an ion‐exchange induced phase separation and a selective leaching step. The new materials are characterized by a defined mesoporous shell and a non‐porous glass core.     

Reaktion von Acetophenonmonomethyl‐ und ‐dimethylhydrazonen mit dem Vilsmeier‐Reagenz; Bildung von Pyrazol‐4‐carbiminiumsalzen: ein Beitrag zum Mechanismus

Reactions of Acetophenonmonomethyl‐ and ‐dimethylhydrazones with the Vilsmeier‐Reagent; Formation of Pyrazol‐4‐carbiminium Salts: A Contribution to the Mechanism Kira discovered the formation of ( 4e ) N,N‐Dimethyl‐N‐[1,3‐diphenylpyrazol‐4‐ylmethylen]ammonium perchlorat by the reaction from acetophenonphenylhydrazone 1e with the Vilsmeier‐Reagent 2 . On the example of the Acetophenonmonomethylhydrazone 1a we represent the mechanism of this reaction. 1a reacts with the Vilsmeier‐Reagent 2 firstly to 3a (scheme 1). 3a is formylated in the secondary step by 2 on the methyl group of the acetophenon part followed of a ring conclusion to the pyrazol 4a containing a carbiminium group in position 4 as substituent. 3a doesN′t react to 6a directly. Hydrolysis of 4a gives 5a . We found moreover, that acetophenondimethylhydrazones 8 react with 2 to 4 , too (scheme 2, eq 2). But here the proton of the methylamino group in 1 is occupied by the methyl group in 8 . Therefore, the reaction starts in this case with an attack on the methyl group of the acetophenon part followed of the ringconclusion to the intermediate 6 accompanied of the eli‐mination of the methyl group. In the last step the not isolated pyrazol 6 is formylated by 2 in 4‐position to 4 . In a secondary reaction from 8 with 2 the compounds 9 are formed (scheme 2, eq. 3). 9 are intermediates in the reaction from 8 to 4 only in a small extent.     

Adsorptionshysterese von Phosphorsäure in Polybenzimidazol‐Hochtemperatur‐Polymerelektrolytmembran‐Brennstoffzellen

During thermal cycling investigations on polybenzimidazole high temperature polymer electrolyte membrane fuel cells a stationary hysteresis behavior of the cell current was observed. With the Tafel equation a correlation to the surface oxygen concentration on the platinum is given. Because no such hysteresis of oxygen adsorption on platinum is known a new theory is proposed. This theory is based on the thermal dependence of the surface coverage of phosphoric acid on platinum. The resulting adsorption hysteresis is confirmed as being the reason for the observed cell current hysteresis by the results of a Monte Carlo simulation. This is validated through a qualitative comparison with measured data from aged test cells.     

Untersuchung von Kraftstoffdampf‐Rückhaltesystemen bei Einsatz von ethanolhaltigen Biokraftstoffen

Fuel vapor restraint systems are used in vehicles to avoid discharge of volatile hydrocarbons from fuel tanks. Until 2020 nearly 10 % of all fossil fuels shall be replaced by biofuels upon which bioethanol plays an important role. The topic of this article is the proper operation of fuel vapor restraint systems depending on the composition of bioethanol‐fuel blends. As a first step, activated carbons commonly used in fuel restraint systems are tested. Received results and measured data serve as input for a mathematical model with the intention to simulate the performance of fuel vapor restraint systems depending on bioethanol‐fuel composition.