The Effect of Operational Parameters on the Catalytic Combustion of n-Butane/Air Mixtures on Platinum Wire

Abstract

The effect of mixture composition, total pressure and catalyst temperature on the kinetics of the catalytic combustion of n-butane/air or n-butane/oxygen mixtures on isothermally heated platinum wire is reported. The catalyst temperature was changed from 680 to 1,130 K for mixtures containing n-butane between 1 and 4.5% at total pressures between 10 and 100 kPa. The measurements allowed the determination of different kinetic properties like reaction rate, turnover frequency, overall and partial reaction orders and activation energy. The pressure dependence of the reaction rate offered the possibility to make a critical analysis of the kinetic equations frequently utilized in the literature.

Heterogeneous catalytic ignition of n-butane/air mixtures on platinum

“…After ignition, the activation energy has a sudden jump to typical diffusion controlled values, as can be seen from the analysis of quasi steady-state values using the regression Ln(dQ r /dt) = f(1/T w ). This is also in agreement with the model of the ignition process as a sudden transition from kinetic to mixed or diffusion control [2,29,30].…”

“…with M F the molar mass of the fuel [30]. The ratio r R /ν F is of the order 2×10 -4 , indicating the existence of significant controlling factors, characteristic for surface processes.…”

Kinetics of isothermal ignition and combustion of some oxygenated VOCs on platinum wire

“…The general trend was similar with that found for hydrocarbon-air mixtures [5][6][7][8][9][10][11][12][13][14][15][16][17] , with some characteristics induced by the specificity of system.…”

“…The discharge of the condenser C, previously charged to a suitable voltage (established by trial and error) across the wire in less than 1 ms ensures the temperature jump, while the integrated circuit IC senses the bridge and adjust the feed voltage through the power transistor T. The voltage Ust across the standard resistor is monitored with a Tektronix TDS 210 oscilloscope. All experiments were carried out in an explosion cell previously 8,10,11 described, supplemented with a Si PIN S 123 photodiode (from Hamamatsu) connected to the second channel of oscilloscope.…”

“…This was achieved using a quasi-rectangular temperature profile applied on the wire, obtained by discharging a condenser and heating it subsequently by using a specially designed feeding circuit and measuring its characteristic properties. 5 This technique has been subsequently applied to different hydrocarbon-air mixtures, obtaining valuable kinetic and mechanistic information [6][7][8][9][10][11][12][13][14] and is supplemented here with oxygenated VOCsair mixtures. From the measured characteristic of the heating circuit and using calibration diagrams, a number of properties of the system like the critical ignition temperature, critical ignition energy, thermal flux emitted by the combustion reactions and the induction period as functions of the gaseous mixture pressure, fuel concentration or platinum catalyst temperature could be measured.…”