Deactivation of Ca-Based Sorbents by Coal-Derived Minerals during Multicycle CO<INF>2</INF> Sorption under Elevated Pressure and Temperature

Deactivation of Ca-based sorbents by coal-derived minerals during multicycle CO<INF>2</INF> sorption reactions at elevated temperature and pressure was investigated using a laboratory-scale horizontal-tube reactor. The sorbents tended to undergo a solid−solid reaction with coal-derived ash components such as silicon (Si) and aluminum (Al) during multicycle CO<INF>2</INF> sorption with an intermediate hydration stage. This reaction formed complex inorganics, such as mayenite (Ca<INF>12</INF>Al<INF>14</INF>O<INF>33</INF>), calcium silicate (Ca<INF>2</INF>SiO<INF>4</INF>), and spurrite (Ca<INF>5</INF>(SiO<INF>4</INF>)<INF>2</INF>CO<INF>3</INF>), and substantially decreased the sorbents' CO<INF>2</INF> sorption ability. Interaction with the coal-derived minerals was significant during the multicycle calcination−carbonation reaction only when the sorbents were subjected to the intermediate hydration treatment. This result suggests that steam enhanced the solid−solid interaction between the minerals and the sorbents at elevated temperature (>873 K) and pressure (6.0 MPa) and that the interaction should be avoided by selecting proper reaction conditions for efficient utilization of the Ca-based sorbents.