Novel Regenerable Magnesium Hydroxide Sorbents for CO2 Capture at Warm Gas Temperatures

A novel sorbent consisting of Mg(OH)2 was developed for carbon dioxide (CO2) capture at 200−315 °C suitable for CO2 capture applications such as coal gasification systems. Thermodynamic analysis conducted with the FactSage software package indicated that the Mg(OH)2 sorbent system is highly favorable for CO2 capture up to 400 °C at 30 atm. MgCO3 formed during sorption decomposes to release CO2 at temperatures as low as 375 °C up to 20 atm. MgO rehydroxylation to form Mg(OH)2 is possible at temperatures up to 300 °C at 20 atm. The experimental data show that the sorbent is regenerable at 375 °C at high pressure and that steam does not affect the sorbent performance. A multicycle test conducted in a high-pressure fixed-bed flow reactor at 200 °C with 28% CO2 showed stable reactivity during the cyclic tests. The capture capacity also increased with increasing pressure. The sorbent is unique because it exhibits a high CO2 capture capacity of more than 3 mol/kg at 200 °C and also is regenerable at a low temperature of 375 °C and high pressure. High-pressure regeneration is advantageous because the CO2 compression costs required for sequestration can be reduced.