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Isomer Mixtures (isomer + mixture)

Distribution by Scientific Domains

Chemistry	80%

Selected Abstracts

Understanding Adsorption and Interactions of Alkane Isomer Mixtures in Isoreticular Metal,Organic Frameworks

CHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2007
Li Zhang Dr.
Abstract Novel metal,organic frameworks (MOFs) may lead to advances in adsorption and catalysis owing to their superior properties compared to traditional nanoporous materials. A combination of the grand canonical Monte Carlo method and configurational-bias Monte Carlo simulation was used to evaluate the adsorption isotherms of C4,C6 alkane isomer mixtures in IRMOF-1 and IRMOF-6. The amounts of adsorbed linear and branched alkanes increase with increasing pressure, and the amount of branched alkanes is larger than that of the linear ones. The locations of the alkane isomer reveal that the Zn4O clusters of the IRMOFs are the preferential adsorption sites for the adsorbate molecules. The interaction energy between the Zn4O cluster and the adsorbate is larger than that between the organic linker and the adsorbate. It was further confirmed that the Zn4O cluster plays a much more important role in adsorption by pushing a probe molecule into the pore at positions closer to the Zn4O cluster. It is difficult for branched alkane molecules to approach the Zn4O cluster of IRMOF-6 closely owing to strong spatial hindrance. In addition, the adsorption selectivity is discussed from the viewpoints of thermodynamics and kinetics, and the diffusion behavior of n -butane and 2-methylpropane were investigated to illustrate the relationship between diffusion and adsorption. [source]

Auslegung und Optimierung von hybriden Trennverfahren,

CHEMIE-INGENIEUR-TECHNIK (CIT), Issue 3 2004
M. Franke Dipl.-Ing.
Abstract Unter hybriden Trennverfahren versteht man die Verschaltung von mindestens zwei verschiedenen, apparativ getrennten Grundoperationen, die zur Trennaufgabe beitragen. Hybride Trennverfahren werden bei schwierigen Trennungen, wie bei engsiedenden oder azeotropen Gemischen, eingesetzt, wenn eine einzelne Grundoperation, z.,B. Rektifikation, Extraktion, Kristallisation, Membranverfahren oder Chromatographie, gar nicht oder nur mit sehr großem Aufwand zum Ziel führt. Aufgrund der Struktur des Hybridprozesses, die das Vorhandensein mindestens zwei verschiedener Grundoperationen und eine entsprechende Anzahl von Rückführungen impliziert, ist die Auslegung komplex, sie wird deshalb z.,Z. systematisch in der Forschung untersucht. In dieser Arbeit werden die Anforderungen an eine Auslegungsmethodik für hybride Trennverfahren dargestellt. Es wird eine Methodik vorgestellt, die auf einer detaillierten Modellierung der Grundoperationen und einer simultanen Mehrvariablen-Optimierung beruht. Die Anwendbarkeit dieser Methodik wird anhand einer Isomerentrennung gezeigt. Design and Optimization of Hybrid Separation Processes Hybrid separation processes are defined as the combination of at least two different unit operations in different apparatus which contribute to the separation task. Hybrid processes are used for difficult separations, e.g., close-boiling mixtures and azeotropes, if a single unit operation, e.g., distillation, membranes, extraction, crystallization or chromatography, is not efficient or even not feasible. Because of the structure of a hybrid process which implies two or more unit operations and recycle streams, the design is not straightforward and therefore subject of today's research. In this work general criteria for such a consistent design method are described and a design approach for hybrid separation processes is presented. It bases on rigorous modeling of the unit operations and simultaneous multivariable optimization. The approach feasibility is demonstrated by the separation of an isomer mixture. [source]

Boron-substituted ZSM-5 membranes: Preparation and separation performance

AICHE JOURNAL, Issue 6 2000
Vu A. Tuan
ZSM-5 zeolite membranes with boron substituted into the framework for silicon were prepared on porous stainless-steel and ,-alumina tubular supports. These membranes had higher n-C4H10/i-C4H10 separation selectivities, and effectively separated these isomer mixtures to higher temperatures than membranes with aluminum substituted into the framework. Membranes were prepared with Si/B ratios as low as 12, and the best membranes were prepared from alkali-free gels. The highest n-C4H10/i-C4H10 permselectivity at 473 K was 60, and the highest at 527 K was 24. For most alkali-free membranes, the n-C4H10/i-C4H10 permselectivities and separation selectivities increased with boron content, and membranes on ,-alumina supports had both higher permeances and separation selectivities. Membranes with the same permeances and selectivities can be reproducibly prepared, and they are stable at elevated temperatures. [source]

Understanding Adsorption and Interactions of Alkane Isomer Mixtures in Isoreticular Metal,Organic Frameworks

Synthesis and thermal crosslinking of oxazolidine-functionalized polyurethanes

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2007
Robert Andreu
Abstract A new oxazolidine derivative was obtained from phenol, 2-amino-2-methylpropane-1,3-diol and paraformaldehyde. The reaction of this novel oxazolidine diol with phenylisocyanate lead to a urethane model compound which can be polymerized thermally by oxazolidine ring opening to give a Mannich bridge structure. Linear segmented polyurethanes were prepared by reaction of different ratios of oxazolidine diol and commercial polyethylenglycol (Mw , 400) with 4,4,-methylenbis (cyclohexylisocyanate) (HMDI, 90% isomers mixture). The polyurethanes were thermally characterized and crosslinked by oxazolidine ring opening to obtain materials which showed improved thermal stability. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4965,4973, 2007 [source]