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91.
Steady state analysis of a combined hybrid process consisting of a reactive distillation column, pervaporation unit, and a
distillation column is presented. This process configuration was first presented by Steinigeweg and Gmehling (2004) for the
transesterification of methyl acetate and butanol to butyl acetate and methanol. This system is characteristic for its low
reaction rate and complex phase equilibrium. Steinigeweg and Gmehling (2004) have shown that the combination of reactive distillation
and pervaporation is favourable since conversions close to 100 % can be reached with a reasonable size of the reactive section
in the reactive distillation column. The aim of this paper is to show that although high conversion can be achieved, very
complicated steady state behaviour must be expected. The presented analysis is based on mathematical modelling of a process
unit, where the steady-state analysis, including continuation and bifurcation analyses, was used. Multiple steady states were
predicted for the studied system; three steady states with conversions higher than 98 %. However, not all predicted steady
states met the maximal allowed temperature condition in the reactive section (catalyst maximal operation temperature of 393
K). The presence of multiple steady states reduces the operability and controllability of the reactive distillation column
during its start-up and during the occurrence of any variation of operating parameters because the system can be shifted from
one steady state to another one (concurrent exceeding the maximal allowed temperature) with unwanted consequences, e.g. production
loss. Therefore, design and subsequent operation of such a complicated system is an ambitious task requiring knowledge of
any possible system behaviour. 相似文献
92.
Josef Šlapal 《Mathematica Slovaca》2011,61(5):717-732
We study neighborhoods with respect to a categorical closure operator. In particular, we discuss separation and compactness
obtained from neighborhoods in a natural way and compare them with the usual closure separation and closure compactness. We
also introduce a concept of convergence based on using centered systems of subobjects, which naturally generalizes the classical
filter convergence in topological spaces. We investigate behavior of the convergence introduced and show, among others, that
it relates to the separation and compactness in natural ways. 相似文献
93.
Věra Najmanová Lukáš Rambousek Kamila Syslová Věra Bubeníková Romana Šlamberová Karel Valeš Petr Kačer 《Chromatographia》2011,73(1):143-149
A rapid and precise LC-ESI-MS-MS method for the parallel identification and quantification of dopamine, serotonin and their metabolites (homovanillic acid, 3-methoxytyramine, 3,4-dihydroxyphenylacetic acid and 5-hydroxyindolacetic acid) from rat brain tissue without any pre-analysis adjustment of the sample such as pre-concentration or derivatization has been developed. In particular, the reaction-monitoring mode was selected for its extremely high degree of selectivity and the stable-isotope-dilution assay for its high precision of quantification. Alternation the ionization polarity in the course of mass spectrometry detection enabled to determine substances susceptible to various ionization modes in only one analysis run. This fact, in combination with an easy pre-treatment step, constitutes the method straightforward and time undemanding. The developed method was characterized with a high precision (≤19.5%, determined as RSD), an acceptable accuracy (≥82.0%, determined as recovery), a low limit of detection (≤0.40 ng/100 mg brain tissue) and a low limit of quantification (≤0.42 ng/100 mg brain tissue). The method has been applied in a recent animal study. The levels of the studied neurotransmitters have been determined in the rat brain hippocampus, prefrontal cortex, and striatum in an animal model of schizophrenia induced by an acute dose of a dizocilpine. 相似文献
94.
Haas W Rath T Pein A Rattenberger J Trimmel G Hofer F 《Chemical communications (Cambridge, England)》2011,47(7):2050-2052
Cu(2)ZnSnSe(4) nanoparticles have high potential to be used as ink for printable solar cells. Using transmission electron microscopy we show that these nanoparticles exhibit a broad range of chemical heterogeneity. These results are contrary to the interpretation of previous experimental work and will have considerable impact on the development of these nanoparticles. 相似文献
95.
Ma Z Rissner F Wang L Heimel G Li Q Shuai Z Zojer E 《Physical chemistry chemical physics : PCCP》2011,13(20):9747-9760
Density functional theory calculations are used to investigate the electronic structure of pyridine-based self-assembled monolayers (SAMs) on an Au(111) surface. We find that, when using pyridine docking groups, the bonding-induced charge rearrangements are frequently found to extend well onto the molecular backbone. This is in contrast to previous observations for the chemisorption of other SAMs, e.g., organic thiolates on gold, and can be explained by a pinning of the lowest unoccupied states of the SAM at the metal Fermi-level. The details of the pinning process, especially the parts of the molecules most affected by the charge rearrangements, strongly depend on the length of the molecular backbone and the tail-group substituent. We also mention methodological shortcomings of conventional density functional theory that can impact the quantitative details regarding the circumstances under which pinning occurs and highlight a number of peculiarities associated with bond dipoles that arise from Fermi-level pinning. 相似文献
96.
Vid Agrež Ferdinand Bammer Boštjan Podobnik Rok Petkovšek 《Applied physics. B, Lasers and optics》2013,112(1):73-81
We present an experimental and numerical analysis, how deviations of the multiplexer-retardation influence the output power of a time-multiplexed dual channel laser. The laser has two different channels, each one with its own gain medium. The channels are time-multiplexed by a single crystal photo-elastic modulator. It enables to double the repetition rate and output power of the laser. However, as multiplexing is based on polarization-switching, the retardation of the modulator should be kept within certain limits. By experimental measurement and theoretical analysis, we determine the operational window within which the retardation should be kept to avoid additional losses into the resonator. The analysis was done for two configurations of the laser setup, namely with and without a quarter-wave plate. 相似文献
97.
W. Alexejew E. Gottlieb Ferdinand Fischer Stohmann und von Rechenberg 《Fresenius' Journal of Analytical Chemistry》1887,26(1):68-70
Ohne Zusammenfassung 相似文献
98.
Dr. Ferdinand v. Arlt 《Monatshefte für Chemie / Chemical Monthly》1901,22(2):144-150
Ohne Zusammenfassung 相似文献
99.
100.
Ohne ZusammenfassungAus dem Laboratorium des k. k. technologischen Gewerbe-Museums in Wien. 相似文献