Feasibility and mechanism of an amine-looping process for efficient CO2 mineralization using alkaline ashes

Amine-looping-based CO2 mineralization is a promising technology for simultaneous CO2 absorption, mineralization, and carbonate crystallization in a single step. This paper performed a detailed investigation of the feasibility and underlying mechanism of the amine-looping process using industrial alkaline solid wastes, including one biomass ash (BA) and two coal-fired fly ashes named FA1 and FA2. The CO2 sequestration capacity and CO2 removal efficiency of selected ashes were investigated in five typical amine solutions, including monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), 2-amino-2-methy-1-propanol (AMP), and piperazine (PZ). The physicochemical property of ashes before and after carbonation and the dissolution of alkaline minerals in various amine solutions were systematically determined to explore the underlying mechanism involved in the amine-looping process. Results show that greater improvement in CO2 removal efficiencies and CO2 sequestration capacities were obtained by selected ashes in amine solutions compared to the traditional CO2 mineralization in the water-ash-CO2 system. It also revealed that amines played important roles in promoting CO2 mass transfer, enhancing Ca2+ leaching, and producing small-sized CaCO3. The largest CO2 sequestration capacity (102.9 g/kg) was achieved by FA1 in PZ solution which was suggested as the preferred solvent for the amine-looping process. In addition, the environmental risk of carbonated ashes for agricultural application in terms of amine loss and phytotoxicity was evaluated. Results implied that the phytotoxicity of carbonated BA could be neglected when a simple centrifugal wash was used to remove the absorbed amine on the surface of carbonated BA whilst the phytotoxicity of selected ashes can be significantly reduced after carbonation reactions.