Activation Strategies for Calcium-Based Sorbents for CO2 Capture: A Perspective

The chemical looping process (CLP) using calcium-based sorbents to capture CO2 through cyclic carbonation–calcination reaction (CCR) before, during, or after the conversion of carbonaceous fuel occurs, is a viable CO2 control technology. With extensive past and current research efforts, the basic process concept has been found to be attractive at larger scales. Additionally, process simulations based on experimental results indicate that the parasitic energy consumption for this high temperature process is relatively low compared to low temperature processes such as the amine-based process. The ability of the calcium-based sorbents to maintain stable reactivity and physical integrity in cyclic reaction under severe operating conditions is one of the most important criteria for the success of the calcium looping technology. Despite being abundant and cheap, calcium-based sorbents derived from naturally occurring precursors, such as limestone and dolomite, suffer from rapid reactivity deterioration after high-temperature calcination and/or several CCR cycles. This deactivation is attributed to the morphological change at both macroscopic and microscopic levels, including pore pluggage, surface area reduction, and alteration of crystallographic plane distribution on the CaO surface. Much attention has recently been placed on sustaining and/or retaining the sorbent reactivity through sorbent modifications and/or reactivation. This paper provides an overview of the optimization and reactivation strategies of calcium-based sorbents with focus on three methodsmodification of precursors, addition of dopants and/or supports, and reactivation through steam/water hydration.