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  • 1
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Reversed-flow technique ; Rate constants ; Bimolecular gaseous reactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Rate constants for bimolecular reactions in the gas phase, under diffusion controlled conditions, can easily be determined by the reversed-flow gas chromatography (RF-GC) technique. The analysis of the diffusion band by means of a simple PC programme gives directly an apparent, second-order rate constant for gaseous reactions. By varying the amounts of the reactants, one can calculate the true order of the reaction and the true non-first-order rate constant of gaseous reactions. The calibration problem of the analytical techniques in non-first-order reaction kinetics is absent as are other disadvantages connected with carrier gas flow, peak shape and their instrumental spreading. The method can be used for atmospheric reactions and was applied in the gaseous reaction systems: SO2+NO2, SO2+Br2, C6H6+NO2, C6H5CH3+NO2 and C3H6+NO2 with various concentrations of reactants in nitrogen. The effect of the NO2 concentration on the apparent second-order rate constant of C2H4+NO2 at 333.2 K was also studied. Finally, the effect of sun light pre-irradiation of C2H2+NO2 in nitrogen was investigated.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Reversed-flow technique ; Catalysis ; Ring opening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Kinetic parameters for the ring opening of cyclohexane over modified ZSM-5 zeolites can be measured simultaneously under non-steady state conditions using reversed-flow gas chromatography. At relatively low temperatures, the main product detected and measured was propene. The mathematical relations used for the calculation of adsorption-desorption rate constants, surface reaction rate constants and adsorption equilibrium constants for the reactant cyclohexane are different from previously studied catalytic reactions, owing to the different experimental arrangement for feeding the catalytic bed. The diffusion bands obtained experimentally for reactant or product are described by the sum of two or three exponential functions of time, respectively. From the exponential coefficients of time and the pre-exponential factors, all determined by simple PC programs, the above kinetic parameters are calculated.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' Zeitschrift für analytische Chemie 352 (1995), S. 639-642 
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract When an analyte can be chromatographed on a HPLC column using a suitable solvent, the diffusion coefficient of this analyte into the solvent can easily and accurately be determined, together with the calibration factor of the detector for this analyte. The experimental arrangement needed is based on a slight modification of the HPLC valve so that the analyte is introduced into the chromatographic column via a short diffusion column filled with the solvent. The new method is theoretically developed and the required mathematical relations have been derived. As an example, the diffusion coefficient of liquid benzene in chloroform, together with its calibration factor, are measured, under various experimental conditions, and the values found compare very well with that calculated by Wilke-Chang formula. Diffusivities and calibration factors of ions in aqueous liquid systems can also be determined by the new method.
    Type of Medium: Electronic Resource
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