Thermal runaway prediction for impregnated activated carbons from isothermal DSC measurements

Abstract

Isothermal DSC measurements are used to extract the kinetics of the reaction between activated carbon, which has been impregnated with K 2CO 3, and air at elevated temperature. For the carbon studied here, the reaction takes place in two apparently independent processes. In the first process, the surface functional groups react with the carbon and with air, and in the second process the remaining carbon reacts with air. The impregnate causes the dramatic acceleration of the reaction compared to the reactivity of the pure base carbon in air. The reaction of the surface functional groups with air obeys the following reaction for the fractional degree of conversion, d α 1/d t= γ 1 exp(− E a1/ k B T) α 1 m (1− α 1) n , with m and n approximately equal to −0.95 and 0.5, respectively. The reaction of the remaining carbon with air follows zero-order reaction kinetics. The obtained reaction kinetics can fit the results of isothermal DSC measurements over a wide range of temperature and scanning DSC measurements over a wide range of sweep rates, without any adjustment of parameters. The reaction kinetics, among other experimentally-derived parameters, were then used to calculate the temperature–time profiles for samples of carbon held in stainless steel mesh cylinders of various diameters within a heated constant-temperature oven. These calculations are shown to agree well with experiments at numerous temperatures for two cylinder radii using the same set of kinetic parameters used to fit the DSC results. Some of the temperatures and radii were selected such that thermal runaway of the carbon sample would occur, and the simulations modeled the time and temperature of this runaway accurately. Therefore, it should now be possible to simulate the temperature–time response of this particular impregnated carbon to conditions of high-temperature storage, such as those of the IATA oven exposure test or to storage within a shipping container exposed to a particular thermal history.