High-Temperature Capture of CO2 by Strontium Oxide Sorbents

This article reports on the use of strontium oxide (SrO)-based sorbents for chemical sorption of carbon dioxide (CO2) at high temperatures (>1000 °C). Two different sizes of the SrO granules were tested as potential sorbent materials through cycles of carbonation and calcination at high temperature in a fixed-bed reactor, under flux of argon (Ar) and Ar/CO2. Thermogravimetric analysis (TGA) assessed their carrying capacity and effectiveness at increasing numbers of cycles. Further investigation was dedicated to the SrO granules in combination with alumina or hydroxyapatite to prevent the material from sintering under high-Temperature conditions and to improve the sorbent durability. A simple kinetic analysis was also performed on the basis of TGA data. The sorbent materials, before and after the cycling steps, were characterized through mercury intrusion porosimetry, environmental scanning electron microscopy, and X-ray diffraction analysis to evaluate any change in the microstructure, thus including the pore-size distribution, material morphology, and crystallographic phases, which can influence the CO2 flowing ability and capture. The results showed that fine granules of SrO are not totally effective, owing to their tendency to break down and consolidate into a compact agglomerate for high-Temperature carbonation. Coarse granules of SrO and SrO/Al2O3, contrarily, maintained open architectures during cycling and allowed one to obtain a similar CO2 carrying capacity of around 9.4% by weight, although showing a different compaction degree. Kinetic analysis confirms the better performance of the sorbent in the form of coarse granules.