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  • Polymer and Materials Science  (3)
  • Oxoniobates  (1)
  • 1
    ISSN: 0009-286X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Minimum Reflux Calculation for Nonideal Distillations. The minimum reflux ratio is the lower limit of operation for a distillative separation. Due to rising energy costs one is increasingly forced to approach this thermodynamically defined minimum energy consumption. This paper presents an overview of the important methods of calculation published to date. First, a concise physical and mathematical description of the problem is given to introduce the concept of pinch points. These are characteristic regions in separation profiles of distillation columns where an infinite number of stages would be required under minimum reflux conditions. Then, shortcut and rigorous problem solutions for both ideal and non-ideal mixtures are reported. Ideal mixtures can be computed using the well-known Underwood equations, which also cover complex column designs (multiple feeds/products, sidestream strippers and enrichers). However, pronouncedly non-ideal systems still require time-consuming simulations of columns with a large number of stages. Hence, recent developments attempt to avoid column simulations and to compute pinch points directly.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0009-286X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Discontinuous Rectification of Azeotropic Mixtures with Use of Auxiliary Substances. Batchwise rectification is one of the most commonly used thermal separation operation in the production of fine chemicals and pharmaceiticals, where small amounts of mixtures containing several product or auxiliary components are generally separated. Greater plant flexibility with regard to mixture composition, throughput, and separation specification often also favours batchwise over continuous processing. This publication discusses process engineering possibilities of batchwise rectification of azeotropic mixtures with the aid of various examples. It gives a detailed presentation of two industrial batch rectifications with additional feed of auxiliary substances, viz. azeotropic rectification with entrainment agent and extractive rectification. In both cases the set goal is to minimise charge times and to maximise the quantities processed in plant operation, with time-optimised control of auxiliary substance throughput being of critical importance in both cases.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie Ingenieur Technik - CIT 61 (1989), S. 16-25 
    ISSN: 0009-286X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Design of distillative separation with due consideration of thermodynamic aspects. This article presents a method for development of advantageous distillative separation equipment by starting from the ideal case of a thermodynamically loss free separation and applying simplifications. Process engineering boundary conditions can serve for clear divisions into individual areas. Possibilities of process integration by a direct thermal and mass linkage are indicated, and promising thermal networking measures are mentioned. The procedure is illustrated by examples.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 31 (1992), S. 1437-1456 
    ISSN: 0570-0833
    Keywords: Oxoniobates ; Cluster compounds ; Niobium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metal clusters, discrete or condensed, are characteristic of the structures of many compounds which contain transition metals in low oxidation states. The highly reduced oxoniobates support the concept of condensed clusters. They contain Nb6O12 clusters which are either isolated or linked at the apices of the Nb6 octahedra to form oligomeric chains or networks. The analysis of the bonding relationships allows the identification of different types of Nb atoms and thus the quantitative prediction of valence electron concentrations for finite or infinite structures composed of these condensed M6X12 clusters.
    Additional Material: 39 Ill.
    Type of Medium: Electronic Resource
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