Core-in-Shell CaO/CuO-Based Composite for CO₂ Capture

Abstract

This paper describes the preparation of composite materials containing both CaO as a reversible CO2 sorbent and CuO, serving as an oxygen carrier, which allows the spent Ca sorbent to be regenerated in a fuel gas stream after it has been used for CO2 capture. Calcium aluminate cement is used as a support to enhance pellet strength. The pellets were prepared in a mechanical pelletizer for granulation of powdered materials with addition of spray water. Three types of pellets were prepared: (i) core-in-shell with 50% CuO and 50% CaO (75% CuO and 25% CaO in the core), (ii) core-in-shell with 50% CuO, 40% CaO, and 10% cement (75% CuO and 25% CaO in the core), and (iii) homogeneous pellets with 50% CuO, 40% CaO, and 10% cement addition as a binder. CO2/O2 carrying activity of the pellets was then tested in a thermogravimetric analyzer (TGA). The attrition resistance of the obtained material was examined during attrition tests in a bubbling fluidized bed (i.d. 50 mm). The oxygen carrying capacity of pellets indicates that 25% CaO in the core is sufficient to support the CuO and prevent decay of its activity as an oxygen carrier during reduction/oxidation cycles. To demonstrate that the pellets produced actually have a core-in-shell pattern, larger cross-sectioned particles were analyzed using the scanning electron microscope/energy dispersive X-ray method (SEM/EDX). The SEM/EDX analyses clearly showed different morphology and elemental composition of the core and shell, with a higher content of CuO in the core. The results of attrition tests showed that after fluidization for 2 h, particle size distribution changed negligibly and high temperature did not cause significantly more pronounced attrition. These tests clearly showed that the procedure employed is suitable for large-scale preparation of core-in-shell CaO/CuO-based pellets which have numerous benefits.