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  • Wiley-Blackwell  (5)
  • American Geophysical Union (AGU)
  • American Association of Petroleum Geologists (AAPG)
  • 1995-1999  (2)
  • 1965-1969  (3)
  • 1
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 148-158 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Rules are presented for the startup of an adiabatic tubular reactor, based on a qualitative analysis of the dynamic behavior of continuously-operated vapor- and liquid-phase processes. The relationships between the process dynamics, operating criteria, and operating constraints are investigated, since a reactor startup cannot be isolated from an entire plant startup. Composition control of the process material is critical to speed up plant startup operations and to minimize the amount of offgrade materials. The initial reactor conditions are normally critical for a successful startup. For process conditioning, a plant should have an operating mode at which the reactor can be included in a recycle loop together with its feed system and downstream process section. Experimental data of an adiabatic tubular reactor startup and thermal runaway demonstrate some operational problems when such an intermediate operating stage is missing. The derived rules are applied to an industrial, highly heat-integrated reactor section, and the resulting startup strategy is summarized in an elementary-step diagram.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 503-515 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The safeguarding methodology of chemical plants is usually based on controlling the instantaneous values of process state variables within a certain operating window, the process being brought to shutdown when operating constraints are exceeded. This method does not necessarily prevent chemical reactors suffering from a runaway during dynamic operations because (a) excessive amounts of unreacted chemicals can still accumulate in the process, and (b) no means are provided to the operating personnel to identify hazardous process deviations. A model-based startup and safeguarding procedure is developed for an industrial adiabatic tubular reactor to improve process safety during startup. The trajectories of manipulated variables are calculated by minimizing the amount of one of the main reactants in the reactor effuent. It is concluded that proper control of the initial reactor temperature profile is critical for a safe startup while the impact of other manipulated variables is relatively smaller than that of the initial reactor temperature profile.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 5 (1967), S. 61-68 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrochemical possibilities for investigation of nucleic acids with high molecular weight are restricted to the determination of the adsorption behavior. According to our experience the alternating current polarography (Breyer-polarography) is mainly appropriate for the characterization of changes in the secondary structure of DNA. The Breyer-polarogram shows the alternating current of the dropping electrode in dependence on their potential which varied from 0-2 v. negative against the normal calomel electrode (NCE). By addition of native DNA to the supporting electrolyte (buffer solution) the current drops down in the range of adsorption between 0 and 1 v. At 1.16 v. against NCE the desorption takes place together with the formation of a rounded desorption peak. The investigation was carried out in phosphate buffer solution 0.1m with 0.075m NaCl or in a phosphate buffer 0.18m with 0.03m NaCl. In the pH range above pH 8 NaOH was added to realize the higher pH values. A calf thymus DNA sample having a mean molecular weight of about 18 million was used. The concentration of DNA was 5 × 10-3-1 × 10-1 wt.-%. The polarographic measurements were performed with an a.c./d.c.-polarograph “GWP 564” from Akademiewerkstätten für Forschungsbedarf der Deutschen Akademie der Wissenschaften zu Berlin (DAW). The denaturation of the double helix causes a sharp desorption peak at negative potentials of the alternating current polarogram. This new criterion for the helix-coil transition is due to formation of unpaired bases. These nearly free bases undergo a specific adsorption and the desorption takes place within a narrow potential range. Nevertheless, at present time an electron transfer to particular bases cannot be excluded at special conditions. The increase of the sharp peak permits to estimate: (a) the melting curve of the double helix in agreement with spectroscopic measurements; (b) the photolysis of the double helix; (c) the strand separation in acid and alkaline solution. In the alkaline range the sharp peak increases and reaches its maximum at pH 〉 12. In the acid range, however, no sharp peak is observed and the rounded desorption peak decreases. Therefore, the best way of following the conformation changes is to measure the current difference between the curves of the solutions with and without DNA at electrocapillary-zero-potential. On the classical d.c.-polarogram one can measure small current steps only, which may be caused mainly by capacity changes. Moreover, the scission of the molecule by ultrasonic action can be followed. In this case the rounded peak of DNA increases but the sharp peak does not appear. Similar alternating current polarograms are obtained with poly-A in the native state, because helical and unordered regions coexist in the same molecule. The very rapid indication of these structure changes allows one to carry out kinetic measurements at a fixed potential with this method.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 80 (1968), S. 565-566 
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0570-0833
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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