Feasibility analysis of membrane reactors – discovery of reactive arheotropes

A feasibility analysis methodology adopted from reactive distillation is applied to membrane reactors. A model is formulated to depict the reactive liquid phase composition on the retentate side of a continuous type membrane reactor. The effects of both the chemical reaction kinetics and the membrane mass transfer kinetics on the feasible products are elucidated by means of retentate phase diagrams and bifurcation analysis. The proposed method can be applied to various membrane processes, independent of the specific structure of the membrane. Two quaternary reaction systems are considered to illustrate the methodology. In the first hypothetical system, it is shown how selective membranes can influence the sequence of effective volatilities which in turn affects the feasible products of the system. In the second example of practical importance, i.e. the heterogeneously catalysed synthesis of propyl acetate coupled with permeation through a porous polycarbonate membrane, the dusty gas model is applied to describe the component fluxes through the membrane. For the latter reaction system, the existence of reactive arheotrope is demonstrated. Arheotropes represent mass transfer controlled feasible products of membrane separation process.     

Damage and strain in pseudomorphic vs relaxed GexSi1−x layers on Si(100) generated by Si ion irradiation

We compare both the strain and damage that 100 keV Si irradiation at room temperature introduces in pseudomorphic and relaxed Ge_xSi_1−x films grown on Si(100) substrates. The ion range is such that the Si/Ge_xSi_1−x interface is not significantly damaged. The amount of damage produced in pseudomorphic and relaxed Ge_xSi_1−x layers of similar x for irradiation doses up to 2.5 × 10¹⁴ Si/cm² is the same, which proves that a pre-existing uniform strain does not noticeably affect the irradiation-induced damage. However, the irradiation-induced strain does depend on the pre-existing strain of the samples. Possible interpretations are discussed. On leave from Inst. voor Kern en Stralingsfysika, Catholic University of Leuven, Belgium.     

Reibungsversuche mit Krypton bei niedrigen Drücken

Tests of a linear Equation on the Evaluation of Krypton Friction Experiments at low Pressures and Connections to Viscosity Effects The coefficient of viskosity is nearly constant in the region with STP conditions and is independent of the pressure. This coefficient decreases with lowering the pressure until the region of molecular flow is reached. There we have free molecular‐ or vacuum viscosity. Experiments with the friction of gas have to take in the gas between surfaces which are movabel and parallel. Reactions of the gas with the moving surface cannot be neglected. We made our lab‐examinations of gas friction effects between two rotating cylinders. Generally there is a linear equation of the reciprocal values of viscosities and pressures. Our experiments show a region, where this linear relation is valid. This region has a low limit with coming to molecular flow and an upper limit if the gas is warmed up by friction at higher pressures.     

Wet-bulb temperature of binary mixtures

When binary mixtures are evaporated, a wet-bulb temperature does exist, provided that the evaporation is non-selective. The wet-bulb temperature can be calculated based on the energy balance, the kinetic equations for heat and mass transfer and the thermodynamic equilibrium. The calculated wet-bulb temperatures were found to be in good agreement with the experimental ones, obtained with mixtures of isopropyl alcohol and water.     

Fullerene-based ruthenium catalysts: a novel approach for anchoring metal to carbonaceous supports. I. Structure

The influence of fullerenes and related support materials on the structural and catalytic properties of ruthenium was investigated. Catalysts based on C₆₀, raw fullerene black, extracted fullerene black, cathode deposit and graphite were prepared by an impregnation/activation procedure with Ru₃CO₁₂. The local co-ordination sphere of the resulting highly dispersed X-ray amorphous ruthenium was investigated by means of EXAFS. The dominating role of the presence of non-six-membered carbon rings on the structure and the stability of the Ru particles will be illustrated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nachweis und Identifizierung von archäologischen Fetten

Indication and Identification of Archaeologic Fats In comparison to the food chemistry, the special tasks of fat indication in archaeologic discoveries consist in regarding possible changes of the fatty acid chains by soil storage. But changes of the composition expressed as percentages need not inevitably occur. There are many examples especially from zoologically determined subrecent bones that the total fat amount is indeed highly reduced, but the remaining residue seems unsignificantly altered. In case of alteration on an empiric basis a solution possibility can be achieved from two sides: pure fatty acid methylates are left to the effects of the natural environment. After some time the occurred changes are analysed. Since because of the relatively short period only introducing changes can be determined, you start from the other end: For archaeological findings enough time for changes has been available. Fats are extracted from objects which were identified by an archaeobotanist as seeds of certain plants or by an archaeozoologist as bones of certain animals and compared with recent fats. Ways of conversion get visible especially by a graduation of the findings according to the age.