Effect of CO₂ on HCl removal from syngas using normal and modified Ca-based hydrotalcites: A comparative study

MSW pyrolysis and gasification technologies have been recognized as effective means to enhance the resource utilization of MSW and promote a circular economy. However, the presence of HCl gas can significantly impact the quality and application of syngas. To maximize syngas resource utilization, develop highly efficient HCl adsorbent, this study investigates the performance and mechanism of HCl removal from syngas using a conventional hydrotalcite (Mg-Al-CO3) and modified Ca-based hydrotalcite (Ca-Mg-Al-CO3). The impact of CO2, a component naturally presents in syngas, on the performance of both materials, were also investigated. Characterization techniques, including XRD, TGA, SEM, and analysis of pore properties and specific surface area, were employed to understand the underlying reaction mechanism. The results demonstrated that the performance of Ca-Mg-Al-CO3 was significantly superior to that of conventional Mg-Al-CO3 sorbents, particularly in the presence of CO2 However, the presence of CO2 had a detrimental impact on the performance of Ca-Mg-Al-CO3 in HCl removal, and this effect became increasingly pronounced with higher concentrations of CO2. TGA results revealed a competitive relationship between HCl and CO2 during the adsorption process. Additionally, the fitting results of adsorption kinetics suggested that the adsorption reaction of HCl and CO2 by Ca-Mg-Al-CO3 followed multiple rate-controlling mechanisms.