Pyrolysis kinetics of ZnAl LDHs and its calcined products for H2S removal

Abstract

This paper reports the calcined products of the hydrotalcite-based ZnAl-layered double hydroxides (LDHs) for H2S removal. The thermal behavior of ZnAl LDHs was investigated by thermogravimetry–differential scanning calorimetry (TG–DSC) and thermogravimetry–mass spectrum (TG–MS). The activation energies were estimated by the Kissinger method and Flynn–Wall–Ozawa (FWO) method. To clarify the physical and chemical transformation during pyrolysis, the initial sample (ZnAl LDHs) and its pyrolysis products calcined at several different temperatures were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscope. The results show that there are two major stages of the thermal decomposition of ZnAl LDHs: Stage I with an intense endothermic peak at 196 °C in DSC curve is ascribed to the removal of water (both the physically absorbed water and the interlayer water) and a small loss of CO2. Stage II with a broad endothermic peak is due to the decomposition of the carbonate anions and a little part of dehydroxylation from brucite-like sheets. The activation energies calculated by the Kissinger and FWO method are 110.7 and 112.8 kJ mol−1 of stage I and 94.3 and 98.1 kJ mol−1 of stage II, respectively.