Removal of HCl from gases using modified calcined Mg-Al-CO3 hydrotalcite: Performance, mechanism, and adsorption kinetics

Abstract

To achieve carbon neutrality, it is essential to remove HCl resulting from the extensive use of alternative fuel feedstock in thermochemical plants. In this work, the HCl removal performance of modified calcined Mg-Al hydrotalcite (Mg-Al-CO3) on gaseous stream was investigated. The layered structure of Mg-Al-CO3 intercalated with CO32– was successfully prepared using the coprecipitation method with a molar ratio of Mg/Al equal to 3.1. The optimal performance of Mg-Al-CO3 for HCl removal was observed at 300 °C, and the breakthrough chlorine capacity was 102.7 mg g−1. Among calcined Mg-Al samples, only Mg-Al-400 exhibited better HCl removal performance than Mg-Al-CO3. The specific surface area of Mg-Al-400 was 183.73 m2 g−1, which was 2.8 times greater than that of Mg-Al-CO3. The average HCl removal rate was 90.11 % within the first 120 min, which was 1.12 times higher than that of Mg-Al-CO3. Moreover, the breakthrough chlorine capacity of Mg-Al-400 was increased by 16.9 %, reaching 120.1 mg g−1. Two reaction paths were identified for Mg-Al-400, first Mg2+ reacts with Cl− to generate MgCl2, and then Cl− acted as a new interlayer anion of hydrotalcite. According to the results of adsorption kinetics, the pseudo-second-order and the Bangham model were found to fit well with the HCl removal process of Mg-Al-400.