HCl removal performance of Mg-stabilized carbide slag from carbonation/calcination cycles for CO2 capture
Mg-stabilized carbide slag (MSCS) was fabricated with carbide slag, magnesium nitrate hydrate and a by-product of biodiesel from transesterification by combustion, and was used as a CO2 sorbent in calcium looping cycles. The cycled MSCS containing a ratio of CaO to MgO of 80:20 from the calcium looping cycles (i.e. carbonation/calcination cycles) for CO2 capture was subsequently used as an HCl sorbent. The HCl capture performance of the cycled MSCS which had experienced repetitive CO2 capture cycles using calcium looping was investigated in a triple fixed-bed reactor. The reaction products of the cycled MSCS after HCl absorption are CaClOH, CaO, and MgO. MgO is an inert support. The cycled MSCS reaches the highest HCl capture capacity at 750 °C. The number of CO2 capture cycles increases the effect of chlorination temperature on the HCl capture capacity of the cycled MSCS. The HCl capture capacity of the cycled MSCS drops slightly with the number of CO2 capture cycles. The HCl capture capacity of the MSCS which has undergone 10 CO2 capture cycles can retain 0.21 g HCl/g sorbent, which is about 1.7 times as high as that of the carbide slag. The presence of CO2 leads to a reduction in the HCl capture capacity of the cycled MSCS. MSCS can maintain a more stable microstructure due to the presence of MgO during the repetitive CO2 capture cycles. The cycled MSCS from the CO2 capture cycles exhibits a more porous structure than the cycled carbide slag, especially in the pore size range of 2–10 nm in diameter, which benefits HCl capture. Therefore, the cycled MSCS from CO2 capture cycles using calcium looping appears promising to remove HCl.