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

Abstract

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.