Ca-Mg-Al-oxide Sorbents Prepared from Hydrotalcite Precursors for CO2Capture at Realistic Calcium Looping Conditions

Abstract

The calcium looping (CaL) process, based on the cyclic carbonation/calcination of CaO sorbents, has been widely investigated recently as a potential technique to capture CO2 at reduced energy penalty. This process can be used in facilities such as power plants and produce a concentrated CO2 which is suitable for storage. In recent years, the hydrogen production processes become more important due to the development of sustainable energy. The CaL process can also be combined with reforming process to produce a concentrated stream of H2 >98 vol. % in a single step, which is known as sorption-enhanced reforming (SER) process, reducing the cost of H2 production effectively. The capture capacities and multicycle stabilities of sorbents are crucial in these uses. In this study, a series of CaMgAl oxide materials for CO2 capture, derived from layered-double hydroxides (LDHs), were prepared to test their performances at realistic calcium looping conditions, namely at high CO2 concentration in the calcination stage. A series of materials with different CaMgAl molar ratios were tested at different regeneration temperatures, regeneration times, and in different CO2 concentrations at the regeneration stage to find out the optimal treatment conditions. The multicycle capture capacities of these materials were examined and compared with that of limestone. Materials regenerated for 15 minutes at 930°C and 70∼100% CO2 had good performances. The Ca/Al = 7/1 materials possessed well capture capacity and multicycle stability compared with that of limestone. Addition of magnesium oxide can further improve its performance. In the 40 cycles test, although the initial capture capacity of the CaMgAl material was lower than that of the CaAl materials, because of the better stability of the former, its capture performance was better than that of the CaAl material at the end of the loop. These materials have the potential to be applied in hydrogen production and other related processes in the future.