Evolution Of Calcium,Magnesium And Aluminum Oxides At High Temperature And Their Effects On CO₂ Capacity Of CaO

The Calcium-looping process based on the carbonation/calcination cycle reaction of Ca O-based adsorbents has the advantage of efficiently on capturing CO₂ in flue gas.Since the activity of ordinary Ca O adsorbents was significantly attenuated in the multi-cycle reactions,the development of highly performance Ca O adsorbents was very important.This paper proposes that Mg and Al oxides were used together as atomic frameworks to enhance the activity of the adsorbent,and the high-temperature phase evolution of Ca-Mg-Al-O and the CO₂ capture performance of the composite adsorbent are studied in detail.As Chinese grovement approving the carbon neutrality and peak CO2 emissions plan,the widespread use of carbon reduction technology has become an important means to realize it.Ca-looping progress is an effective technology to reduce CO2 emissions from human activities.It has the advantage of efficiently capturing CO2 in flue gas.However,due to the attenuation of Ca O activity in the multi-cycle reaction process,the preparation of high-performance Ca O-based adsorbents is very important for Ca-looping.Firstly,wet-mixing method was used to prepare a single-frame Ca-based adsorbent doping with MgO and Al2O3.It was found that the phase composition of MgO-stabilized adsorbent did not change as the calcination temperature changes.And the addition of Mg²⁺would make the adsorbent have a higher cyclic reactivity.The CO2 capacity of Ca O/MgO calcined at 700℃could be 0.69g CO2/g sorbent in the initial cyclic reaction.While for the precursor mixture of the Ca-Al adsorbent calcined at 700 or 800℃for 3 h,the reaction products were Ca O and Ca12Al14O33.The adsorbent of Ca O/Ca3Al2O6 calcined at 900℃got highly cyclic stability.and its CO2 capacity was 0.54 g CO2/g sorbent after 26 cycles,it was 127%higher than that of pure Ca O under the same reaction conditions.Secondly,thermodynamic simulation and XRD characterization was used to find out the components of Mg-Al-O as the composite framework of the adsorbent.It was found that the remaining amount of Ca O in the thermal equilibrium state of the MgO-Al2O3-Ca O was more than that of the Al2O3-Ca O single framework system.At the same time,the addition of MgO in the system could make MgO and Al2O3 reacted to form Mg Al2O4,which consumes Al³⁺,so that it would effectively impede the formation of Ca12Al14O33.As for XRD characterizations,it was found that the mixed precursors were calcined at 700°C,the system products were Ca O,MgO,and Ca3Al2O6;when calcined at 800-1000°C,the system products are Ca O,MgO,Ca3Al2O6,and Mg Al2O4.Finally,the CO₂ capacity of the Ca-Mg-Al composite adsorbent and its multi-cycle reaction performance were also explored.It is found that the multi-cycle CO2 capacity of the Ca-Mg-Al composite adsorbent was higher than that of the Ca-Al single framework adsorbent under the same proportion.When the Ca-Mg-Al composite adsorbent was calcined at 900°C,its CO2 adsorption capacity was 0.56 g CO2/g sorbent after 26 cycles.When the multi-skeleton composite adsorbent is calcined under severe conditions,it still maintains high reactivity and cyclic stability.The CO2 adsorption capacity of the 23rd cycle were still 0.53 g CO2/g sorbent.Moreover,the adsorbent had a sponge-like structure composed of spherical Ca O particles,which was beneficial to maintain the pore structure of the adsorbent during the multi-cycle reaction process,so as to maintain the cyclic reaction stability of the adsorbent.