Preparation And CO₂ Capture Performance Of Magnesium Based Adsorbents

As the major greenhouse gas,CO₂ has caused a series of environment issue,which has threatened human society development.To reduce the excessive emission of carbon dioxide,CO₂ capture have draw increasing attention in the world.Face to the emission of moderate temperature CO₂ issue,structure characteristic and CO₂ sorpersion performance of MgAl layered double hydroxides?LDHs?derived mixed oxides and multi-shelled hollow MgO microsphere adsorbens were studied.The porous MgAl-CO₃ LDHs-derived mixed oxides with Mg/Al molar ratios of 2:1,2.5:1,3:1,3.5:1 and 4:1 have been successfully prepared by a facile solvothermal method.With a 3D nanoflower-like structure,the MgAl-CO₃ LDHs-derived mixed oxides with Mg/Al molar ratio of 2 exhibit the best CO₂ sorption performance of about 0.9 mmol/g at the adsorption and desorption temperature of 200 oC and 400 oC.The addition of NaNO3 into the MgAl-CO₃ LDHs-derived mixed oxides?Mg/Al=2:1?can facilitate the sorption process by reducing the energy barrier between MgO and MgCO₃ in the reaction of MgO+CO₂?MgO···CO₂.Introducing methanol to the preparation process of LDHs prior to drying can effectively increase the specific surface area and improve the porosity of the sorbents by substituting the water molecules of MgAl-CO₃ LDHs.The sorbents co-modified by NaNO3 and methanol with Mg/Al molar ratio of 2 shows the favorable sorption performance with the CO₂ uptake of 1.70 mmol/g over 100 sorption/desorption cycles.Novel multi-shelled hollow MgO microspheres with different concentration of precursor were successfully prepared through a facile,green method by using carbonaceous microsphere as a template.The carbonaceous microsphere template was prepared via the emulsion polymerization reaction of sucrose under hydrothermal condition.The triple-shelled hollow microspheres structure with the smallest MgO crystal size,particle size and the slimmest thickness outermost shell was formed when the concentration of precursor was 2 mol/L.The increase of the numbers of shell can buffer mechanical stresses of volume change during the carbonation/calcination process.The decrease of the size of microsphere and the crystal size of MgO were conducive to the expose of adsorption sites.Meanwhile the thinner thickness of outermost shell can facilitate CO₂ diffusion and improve the initial CO₂ uptake eventually.Connected with sintering-resistance of inert Al-modification,the Al-doped MgO triple-shelled hollow microspheres sorbents can effectively disperse MgO and make more adsorption activity sites exposed,and eventually improve CO₂ adsorption capacity and MgO looping stability.The Al-doped MgO triple-shelled hollow microspheres sorbent exhibited a favorable moderate temperature CO₂ adsorption performance with the capacity of 0.82 mmolCO₂/g-ads after 30 carbonation/calcination cycles.