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Water-in-oil emulsion foaming by thiourea nitrosation: Reaction and mass transfer

Authors

  • Gabriel da Silva,

    1. Process Safety and Environment Protection Research Group, School of Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia
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  • Bogdan Z. Dlugogorski,

    Corresponding author
    1. Process Safety and Environment Protection Research Group, School of Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia
    • Process Safety and Environment Protection Research Group, School of Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia
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  • Eric M. Kennedy

    1. Process Safety and Environment Protection Research Group, School of Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia
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Abstract

A study has been undertaken into the chemical production of gas bubbles within a concentrated water-in-oil emulsion, typical of those used as emulsion explosives. Chemical foaming was initiated by the introduction of a concentrated sodium nitrite solution to the emulsion, and the measurement of the decreasing emulsion density with time served to estimate the rate of nitrogen production. A conversion of emulsion density to nitrite ion concentration facilitated a kinetic analysis of the data. The change in nitrite ion concentration follows a rate equation which indicates that the rate-limiting reaction step corresponds to the N-nitrosation of thiourea by ON+, with an apparent rate constant of 0.22 M−1 s−1 at 25 °C. Tests over a temperature range of 25 to 50 °C yielded an activation energy of 59 kJ mol−1. A mass-transfer model describing the rate of diffusion between aqueous droplets is presented. This model suggests that chemical kinetics, rather than molecular diffusion, is the rate-limiting phenomenon in the foaming of emulsions. Supporting this finding, the kinetic experiments in emulsion returned very similar results to previous experiments performed in aqueous media under similar conditions. © 2006 American Institute of Chemical Engineers AIChE J, 2006

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