Pressured carbon dioxide hydrothermal leaching of catalytic gasification ash for dealkalization of solid waste, sodium catalyst recovery and carbon dioxide utilization

Abstract

Abstract The alkali catalysts are easy to deactivate, causing low catalysts recovery. Meanwhile, the alkali in the gasification residue also poses potential hazard to the environment if improperly handled. So alkali recovery and alkali residue dealing hinder the progress of catalytic gasification. In this study, pressured carbon dioxide (CO2) hydrothermal leaching catalytic gasification ash to recover sodium (Na) catalyst as sodium carbonate (Na2CO3) and CO2 mineralization was studied, and the re-catalytic performance of recovered Na was evaluated as well. When gasified at 900 °C, the catalytic gasification ash is composed of sodium aluminum silicates [(Na2O)0.33NaAlSiO4]. By hydrothermal leaching at 180 °C with 2 MPa of CO2, 93.6% of Na can be leached, and the leaching residue is composed of amorphous Si and Al matters. At the same time, 138 g of CO2 can be mineralized by dealing with 1 Kg of catalytic gasification ash. Moreover, the recovered Na even shows better catalytic performance than fresh Na2CO3 with the same Na loaded amount, due to calcium (Ca) in the recovered Na can also enhance gasification reactivity. By pressured CO2 hydrothermal leaching, the catalyst can be recovered, the alkali in the gasification residue can be dealkalized, and CO2 can be mineralized as well, thus making catalytic gasification cleaner. Therefore, it is an economical and environmental-friendly way for alkali recovery and CO2 utilization.