Study On Spontaneous Combustion Risk Of Activated Carbon

Activated carbons (AC) are used in industry, agriculture, national defense, aerospace and many other fields due to the well-developed pore structure, large surface area, tunable surface properties and strong adsorption ability. However, if not handled in proper manner during the transportation, storage and application, they take the risk of spontaneous combustion, which as a consequence would induce fire and explosion. Although a great deal of researches have been put onto the self-ignition behavior of AC and a considerable progress has been made so far, a regular law for revealing the underlying principles within the self-ignition of AC is still in demand. Hence it’s of great importance from the perspective of practical use, risk prediction and assessment to unravel the key factors for the AC self-ignition and the kinetics and the plausible mechanisms within the exothermal process of AC oxidation.It’s the contribution of this work to systematically analyze the factors that exert an influence over the AC self-ignition and the probable mechanisms that lie in the process. The primary work is presented as follow:(1) The AC (activated carbon) samples were successfully prepared with cottonwood powder as raw material, zinc chloride and phosphorous acid as activated agents by controlling impregnation ratios and activation temperatures. The surface topography, surface functional groups and adsorption property of the AC samples were tested and analyzed. The different factors which influenced the spontaneous ignition property of AC samples were tested by Self-Ignition Temperature Testing Instrument and Simultaneous Thermal Analyzer449C (STA449C). The results revealed that impregnation ratios, activation temperatures and activated agents have different influences on the spontaneous combustion behavior, among which the activation temperatures may play a key role.(2) The kinetic parameters, such as the initial exothermic temperature, the pre-exponential factor, the apparent activation energy and so on, were determined by heat flow curves of the AC samples which were obtained at different heating rates of2℃/min,5℃/min,10℃/min and20℃/min. By the comparison and analysis of the kinetic parameters in the process of oxidation reaction with the three nonisothermal dynamics analysis methods, namely, Kissinger, Flynn-Wall-Ozawa and Friedman-Reich-Levi, the optimal analyzing method was obtained and the spontaneous combustion reaction mechanism of AC was finally deduced. (3) The reaction progress curves of AC samples under the isothermal condition and temperature programming condition and time to maximum rate under adiabatic condition (TMRad)were predicted with the software AKTS on the basis of the kinetic parameter of AC. The temperature effects, the runaway border conditions and the nature of security for AC were further analyzed and ultimately, the prediction and evaluation of the risk of ignition spontaneous combustion of AC were accomplished.