Variations of apparent activation energy based on thermodynamics analysis of zeolitic imidazolate frameworks including pyrolysis and combustion

Abstract

Thermodynamics of zeolitic imidazolate frameworks (ZIFs) in pyrolysis and combustion processes at different heating rates were analyzed and kinetic parameters were calculated using thermogravimetric tests. Related results show that TG curves of both pyrolysis and combustion processes shift to the high-temperature zone with the increase of heating rates. Differences of DTG curves reaction intensity of the pyrolysis process are not evident with the increase of heating rates, while the reaction intensity of DTG curves of the combustion process is reduced gradually. The pyrolysis process can be divided into the dehydration (30–230 °C) and the pyrolysis reaction (430–950 °C). The combustion process can also be divided into the dehydration (30–250 °C) and the combustion reaction (331–449 °C). Three stages of the pyrolysis process are carried out by dynamical analysis due to changes of slopes, while the combustion process has only one stage. Dynamical parameters, such as the most probable mechanism, the pre-exponential factor and the apparent activation energy, are acquired by the way of comparison using two methods of Coats-Redfern (CR) model based on integral form and Achar-Brindley-Sharp-Wendworth (ABSW) model based on the differential form. Some interesting phenomena are also presented that effects of heating rates on the thermal decomposition and the kinetic analysis.