Aluminum-enhanced Ca-based CO2 sorbents: Core-shell assembly and the impact of stabilizer precursors

Abstract

Lately, Ca-based sorbents with a core–shell structure have been effectively produced to augment the sorbent’s capabilities. However, modifying the pristine core of Ca-based pellets with a core–shell structure notably influences the performance of the synthesized sorbent, and research in this domain remains scarce. Here, two categories of Al-stabilized, Ca-based pristine cores were produced using Ca(OH)₂ mixed with Al-based stabilizer precursors of insoluble aluminum oxide and soluble aluminum nitrate, respectively, through the extrusion-spheronization technique. Due to the impact of mechanical extrusion, soluble aluminum nitrate can accumulate in-homogeneously in the Ca-based pristine core, leading to its expansion and rupture during the high-temperature calcination stage because of the decomposition of aluminum nitrate. The oxide-form aluminum stabilizer precursor can be uniformly distributed throughout the Ca-based pristine core pellets, demonstrating notably superior cyclic CO₂ sorption capability and mechanical strength. The Al-fortified, core–shell structured Ca-based sorbent pellets demonstrated a peak CaO carbonation conversion rate of 54.8 % after 100 cycles when the Ca:Al molar ratio was precisely set to 85:15, which is about 2.1 times higher compared to the core–shell Ca-based sorbent pellets composed of a pure CaO core. This is primarily due to the formation of an evenly distributed inert Ca₁₂Al₁₄O₃₃ within the pristine core, which effectively reduces high-temperature sintering. Hence, core–shell Ca-based sorbent pellet assembled with an Al-stabilized pristine core, could be a promising candidate for application in the CaL process for CO₂ capture.