High temperature CO2 sorption using mixed oxides with different Mg/Al molar ratios and synthesis pH

Several hydrotalcites were prepared by the co-precipitation method with different Mg/Al molar ratios (from 2 to 20) and synthesis pH (8.5 and 10); upon calcination, the hydmtalcite-derived mixed oxides (HDMOs) were obtained, to be used as CO2 sorbents at high temperature, for instance in post- or pre-combustion CO2 capture processes. The sorption equilibrium isotherms were determined for screening purposes of all materials prepared using a magnetic suspension microbalance (static experiments) at 300 degrees C, along with a detailed physicochemical characterization (TG-DTG, ICP OES, XRD, FTIR, physical sorption-desorption of N-2 at -196 degrees C and TPD-CO2). In addition, the most promising HDMOs, in terms of CO2 sorption capacity, were submitted to successive CO2 sorption-desorption cycles (dynamic experiments) in a packed column at 300 degrees C, with and without water in the feed, to assess their potential in a sorption-desorption cyclic operation. The results indicate that a synthesis pH of 8.5 provides samples with better CO2 sorption capacities and that there is an optimum Mg/Al molar ratio (between 4 and 10). The sample with a synthesis pH of 8.5 and a Mg/Al molar ratio of 7 (called 8.5HT7) provided an outstanding CO2 sorption capacity (1.62 mmag(-1) at 1 bar of CO2 and 300 degrees C) when compared with the other samples herein prepared, but also when compared with commercial (MG63 and MG70) and with other similar materials found in the literature. Finally, an average working capacity of 1.04 mmag(-1) and 2.11 mmag(-1) was obtained after repeated sorption-desorption cycles at 0.4 bar of CO2 and 300 degrees C for the 8.5HT7 HDMO under dry and wet conditions (45 vol.% H2O), respectively.

Automated summary

Hydrotalcites were prepared by co-precipitation with different Mg/Al molar ratios and synthesis pH, and the derived mixed oxides were used for CO2 sorption at high temperature. Samples with a synthesis pH of 8.5 and an optimum Mg/Al molar ratio between 4 and 10 showed outstanding CO2 sorption capacities. Repeated sorption-desorption cycles for 8.5HT7 HDMO under wet conditions significantly improved its working capacity.