Construction Of Metal-organic Framework Derived Calcium-based Bifunctional Material And Its Reactvity For Chemical Looping CO₂ Capture And In Situ Conversion

Excessive emissions of the greenhouse gas CO2 in the atmosphere are the main cause of global warming.CO2 capture,utilization and storage(CCUS)technology is considered to be one of the most feasible ways to solve this problem.Due to the advantages of low exergy destruction,low cost and easy product separation,CO2 capture and in-situ conversion technology based on chemical looping is known as a CCUS method with industrial application prospects.However,as the key to realizing this technology,calcium-based bifunctional materials are highly susceptible to high temperature deactivation leading to performance deactivation.Based on this,this study synthesized highly efficient calciumbased sorbents and calcium-iron bifunctional materials via a metal-organic framework selftemplate method,and discussed the influence of different loading methods and calcium-iron proportions(Ca/Fe=0-100%)on the sorption capacity,CO yield and cycle stability of chemical looping CO2 capture and in situ reverse water-gas conversion process via performance experiments and material characterizations,which provides an important reference for achieving efficient CO2 capture and in situ conversion.The sorbents derived from the physical coupling method has a larger adsorption capacity,better adsorption stability and adsorption-desorption rate than that prepared from chemical coupling method.Comparing these two methods,the initial adsorption capacity,retention rate and the highest adsorption and desorption rate of physical and chemical coupling methods are as follows:0.65 gCO2/gsorbent vs.0.71 gCO2/gsorbent,59%vs.63%,0.105 gCO2·min-1·g-1sorbent vs.0.11 gCO2·min-1·g-1sorbent and 0.098 gCO2·min-1·g-1sorbent vs.0.102 gCO2·min-1·g-1sorbent,which is attributed to the sorbent obtained from the former method has a larger specific surface area,total pore volume,more intensive distribution in the 20-60 nm pore size,more obvious calcium zirconate crystal phase diffraction peaks,smaller crystal size and lower degree of sintering phenomenon.The double-exponential and zero-order kinetic models revealed that the chemical coupling method has more excellent adsorption dynamics characteristics but the physical coupling method has a better characteristic of desorption dynamics.For calcium-iron bifunctional materials,the increase of calcium content is beneficial to improve its CO2 adsorption performance due to the high active calcium oxide content,specific surface area and pore volume.Thanks to the formation of calcium zirconate,all bifunctional materials have good cycle stability in cycling experiments.The bifunctional material with iron oxide mass fraction of 30%shows the most excellent reduction rate due to its good oxygen transporting ability(the lowest temperature-programmed reduction onset temperature of 325℃).The CO2 sorption performance of the bifunctional material determines the conversion of CO in the H2 reduction stage,and the selectivity of CO production close to 100%.The catalytic property of iron can increase the conversion rate of bifunctional material.As the iron content increases,the rate of CO production in the CO2 oxidation stage is slower and less(the maximum CO space time yield decreases from 0.99 mol·kg-1·s-1 to 0.40 mol·kg-1·s-1).