Computation of plate columns for NOx absorption by a new stage-to-stage method

A new stage-to-stage method has been developed for the calculation of NX_x absorption columns. Each stage of the absorption column is simulated as a combination of a bubble column reactor (absorption) and an adiabatic plug for reactor (oxidation). The bubble column reactor is modelled as two single stirred tank reactors, one as a gas-phase and one as a liquid-phase reactor, both coupled by mass and heat transfer. In this hydrodynamic model, a dynamic approach is adopted, in which the gas-phase transport of N₂O₄ is the limiting step for the absorption. A gas-phasepseudo-enhancement for factor for N₂O₄ is therefore introduced. The balance equations for a single phase of the bubble column are solved with a Newton-Raphson algorithm. The entire column calculation is divided into a gas and a liquid side. On both sides, the stage-to-stage method is applied in such way that the overall calculation is performed as a loop process. The direction of the loop calculation follows that of the flow: gas-side upwards and liquid-side downwards.     

Interfacial chemistry of cobalt(II) during sol–gel synthesis of cobalt-containing mesoporous materials

Co-MCM-41 and Co-MCM-48 with cobalt amounts from about 3 wt.% to 9 wt.% have been synthesized under various conditions, and the samples were characterized by XRF, XRD and N₂-sorption. EXAFS least-squares curve fitting detected only oxygen and silicon backscattering shells, which verified the incorporation of cobalt into the silica framework both for as-synthesized and calcined samples. XANES profiles showed that the oxidation state of cobalt in the samples is unaltered during synthesis. It has been shown that the cobalt is precipitated as cobalt hydroxide during synthesis, and this hydroxide is in equilibrium with aqueous cobalt ions in the synthesis gel. The precipitated cobalt hydroxide precursors are incorporated into the mesoporous silica framework, while the aqueous cobalt ions remain dissolved in the aqueous phase. The cobalt amount in the final samples is therefore pH dependent. This equilibrium is also important in the formation of the mesoporous structure. Addition of increasing amounts of cobalt salt to a MCM-48 synthesis gel causes a change in the mesoporous structure from cubic Ia3d to hexagonal, which is suggested to be a consequence of the charge density matching process. The increased amounts of the divalent cobalt(II) ions in the gel screen the negatively charged silica precursors, which decreases the total surface charge density of the silica, and thus causes the surfactants to self-assemble into the hexagonal structure.     

Modelling of alcohol and water diffusion in fuel cell membranes—Experimental validation by means of in situ Raman spectroscopy

In this work a multi-component transport model has been set up to describe the diffusion driven mass transport of water and methanol in fuel cell membranes. For a membrane in contact with liquid methanol and water on one side and conditioned air on the other, the corresponding differential equations and boundary conditions were derived in a polymer-related coordinate system taking into account the polymers three-dimensional swelling. Phase equilibrium parameters and unknown diffusion coefficients for Nafion^® 117 were obtained by comparing the simulation results to water and methanol concentration profiles measured with confocal Raman spectroscopy. The influence of methanol concentration, temperature and air flow rate was predicted by the model with a maximum relative mean deviation between measurement and simulation of 8.6% for methanol and 3.4% for water.     

Bemerkungen zu der Arbeit von Lauersen und Orth: Die Verteilung der Ascorbins?ure in der Kartoffelknolle

Ohne ZusammenfassungDiese Z.83, 193 (1942).     

Die Wärmeübertragung in zylindrischen Gasschichten bei natürlicher Konvektion

Ohne Zusammenfassung Schlu? von Heft 5, S. 178. Inhaltsübersicht s. Heft 5, S. 165