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Component Separation (component + separation)

Distribution by Scientific Domains

Chemistry	60%
Physics and Astronomy	40%

Selected Abstracts

Compositional effects accompanying near equilibrium vapour growth of solid solution crystals of the types IV-VI and II-VI

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2010
A. Szczerbakow
Abstract Near equilibrium evaporation-condensation in a sealed ampoule leads to almost full compositional reproduction of a solid solution if it consists of components having comparable vapour pressures; this can be qualitatively interpreted by domination of entropy increase. Nevertheless, even vestigial separation requires closer characteristics, since it may prove crucial , particularly for properties of semiconducting solid solutions. Maximum component separation allowed by a small temperature difference is described here in terms of thermodynamics and kinetics of solid-vapour and vapour-solid phase transitions. Theoretical models of the determining effects having different character are shortly described, and their applicability areas are determined. Experimental data collected for crystal growth of numerous semiconducting solid solutions of the II-VI and IV-VI type support the conclusion drawn from the models that the near equilibrium crystal growth from the vapour in a closed system ensures the highest degree of compositional uniformity. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Characteristics of ammonia permeation through porous silica membranes

AICHE JOURNAL, Issue 5 2010
Masakoto Kanezashi
Abstract A sol,gel method was applied for the preparation of silica membranes with different average pore sizes. Ammonia (NH3) permeation/separation characteristics of the silica membranes were examined in a wide temperature range (50,400°C) by measurement of both single and binary component separation. The order of gas permeance through the silica membranes, which was independent of membrane average pore size, was as follows: He > H2 > NH3 > N2. These results suggest that, for permeation through silica membranes, the molecular size of NH3 is larger than that of H2, despite previous reports that the kinetic diameter of NH3 is smaller than that of H2. At high temperatures, there was no effect of NH3 adsorption on H2 permeation characteristics, and silica membranes were highly stable in NH3 at 400°C (i.e., gas permeance remained unchanged). On the other hand, at 50°C NH3 molecules adsorbed on the silica improved NH3 -permselectivity by blocking permeation of H2 molecules without decreasing NH3 permeance. The maximal NH3/H2 permeance ratio obtained during binary component separation was ,30 with an NH3 permeance of ,10,7 mol m,2 s,1 Pa,1 at an H2 permeation activation energy of ,6 kJ mol,1. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]

The German Lignocellulose Feedstock Biorefinery Project

BIOFUELS, BIOPRODUCTS AND BIOREFINING, Issue 3 2010
Jochen Michels
Abstract Well-known wood-pulping processes are optimized on the generation of cellulose while other constituents like hemicelluloses and lignin become denatured during treatment excluding their higher valuable utilization as compounds. The main objective of the joint project Lignocellulose Feedstock Biorefinery (2007,2009) was the development of a sustainable, integrated process for treatment and component separation of domestic lignocellulosic raw material, such as beech and poplar. All components (extracts, cellulose, hemicelluloses, and lignin) should be fractionized and conserved in a form, which allows further processing (biotechnological and/or chemical) for the generation of added-value products from each fraction. Pre-treatment and component separation on the basis of the OrganoSolv pulping process could be optimized in 1-kg-scale for the demands of the biorefinery and successfully transferred to a continuous process in 10-kg-scale with solvent recovery. Pre-treatments and component separations in ionic liquids are possible, but economically they are not competitive. The results of the techno-economic and ecological assessment showed that it is possible to run a lignocellulose feedstock biorefinery with a capacity of about 400 000 t/a wood in an economically and environmentally sound way. A conceptual design of a pilot plant was generated. Its realization and operation will become part of a follow-up project proposal. Copyright © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd [source]

On the properties of young multiple stars

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2004
E. J. Delgado-Donate
ABSTRACT We present numerical results on the properties of young binary and multiple stellar systems. Our analysis is based on a series of smoothed particle hydrodynamics (SPH) +N -body simulations of the fragmentation of small molecular clouds, which fully resolve the opacity limit for fragmentation. These simulations demonstrate that multiple star formation is a major channel for star formation in turbulent flows. We have produced a statistically significant number of stable multiple systems, with component separations in the range ,1,103 au. At the end of the hydrodynamic stage (0.5 Myr), we find that ,60 per cent of stars and brown dwarfs are members of multiples systems, with about a third of these being low-mass, weakly bound outliers in wide eccentric orbits. Our results imply that in the stellar regime most stars are in multiples (,80 per cent) and that this fraction is an increasing function of primary mass. After N -body integration to 10.5 Myr, the percentage of bound objects has dropped to about 40 per cent, this decrease arising mostly from very low-mass stars and brown dwarfs that have been released into the field. Brown dwarfs are never found to be very close companions to stars (the brown dwarf desert at very small separations), but one case exists of a brown dwarf companion at intermediate separations (10 au). Our simulations can accommodate the existence of brown dwarf companions at large separations, but only if the primaries of these systems are themselves multiples. We have compared the outcome of our simulations with the properties of real stellar systems as deduced from the infrared colour,magnitude diagram of the Praesepe cluster and from spectroscopic and high-resolution imaging surveys of young clusters and the field. We find that the spread of the observed main sequence of Praesepe in the 0.4,1 M, range appears to require that stars are indeed commonly assembled into high-order multiple systems. Similarly, observational results from Taurus and , Ophiuchus, or moving groups such as TW Hydrae and MBM 12, suggest that companion frequencies in young systems can indeed be as high as we predict. The comparison with observational data also illustrates two problems with the simulation results. First, low mass ratio (q < 0.2) binaries are not produced by our models, in conflict with both the Praesepe colour,magnitude diagram and independent evidence from field binary surveys. Secondly, very low-mass stars and brown dwarf binaries appear to be considerably underproduced by our simulations. [source]