Metal-Al layered double hydroxides synthesized from aluminum slags as efficient CO2 adsorbents at pre- and post-combustion temperature
L. Santamaría, S.A. Korili, A. Gil
Abstract
Layered double hydroxides (LDH) have been proposed as the materials that offer the best performance in the moderate-temperature range, between 200 and 450 °C, for CO 2 adsorption, so the effect of some synthesis parameters and surface modification on their adsorption capacities is herein investigated. This work reports the use of M 2+ (Co, Mg, Ni and Zn)/Al layered double hydroxides synthesized with a 3:1 molar ratio by the co-precipitation method and using aluminum extracted from saline slags as source of this metal as CO 2 adsorbents. The synthesis and use of Zn/TiAl is also reported considering several proportions of Al-Ti. Structural characterization and comparison of the series has been achieved using powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), nitrogen physisorption at 196 °C and thermogravimetry measurements (TGA). The performance of calcined LDH as CO 2 adsorbents was evaluated in the 50 – 400 °C temperature range and 80 kPa and results show that Ni 6 Al 2 and Mg 6 Al 2 samples present a significant adsorption capacity at low temperature (0.382 and 0.292 mmol CO2 /g, respectively). At 400 °C only Mg 6 Al 2 maintains its high adsorption capacity (0.275 mmol CO2 /g) compared to the other calcined LDH. Its adsorption capacity at moderate-temperature range was proven to be better than that of a commercial Mg 6 Al 2 sample. In all materials the CO 2 adsorption capacity at 200–450 °C increased by incorporating potassium (K 2 CO 3 and KOH as sources) up to 0.58 mmol CO2 /g for Mg 6 Al 2 +K 2 CO 3 . The addition of the amine TEPA in the low-temperature range worked for Co 6 Al 2 and Mg 6 Al 2 (increment > 40 %). In the case of Zn 6 Al 2 , the partial substitution of Al by Ti also increased the CO 2 adsorption capacity from 0.177 to 0.244 mmol CO2 /g, finding isosteric heats between 17.07 and 23.30 kJ/mol using the Clausius-Clapeyron equation. ● Aluminum saline slags were used to prepare layered double hydroxides (LDH). ● LDH synthesized by the co-precipitation and aluminum extracted from a waste as CO 2 adsorbents. ● Ni- and Mg-LDH samples present a significant adsorption capacity of CO 2 at low temperature. ● In all materials the CO 2 adsorption capacity at 200–450 °C increased by incorporating of K.