The Research On Construction And Performance Optimization Of Calcium-based Sorbent Derived From Metal Organic Framework

CO₂ emission is considered as the main source for global warming.As a promising CO₂ capture technology,calcium looping has attracted wide attention.Although calcium oxide possesses a high theoretical sorption capacity,it is easy to quickly lose its sorption capacity after repea ted cycles.In order to deal with this issue,the main solutions consist of inert carrier doping and microstructure control.Metal organic framework materials（MOF s）derived solid materials exhibit unique microstructure and controllable preparation,which is a pathway to develop ideal calcium-based sorbents.Toward this end,this paper intends to use the homolog ous MOF-derived calcium-based sorbent to explore the effect of synthetic parameters,inert carrier types and loading modes on the sorption performance of the MOF-derived sorbent.By the combination of the multiple characterization methods,the structure-performance relationship for the MOF-derived sorbent is revealed.The results provide new ideas for rational design of high-performance calcium-based sorbents.In order to develop a calcium-based sorbent with high activity and high stability,a simple MOF template synthesis route was proposed to prepare an inert alumina supported calcium-based sorbent with superior performance.The cyclic performance experiments and structural characterization techniques were applied to explore structure-performance relationship for the MOF-derived sorbents.The results show that the calcium-aluminum solid solution and its uniform mixing with Ca O on the nanometer scale improve d the thermal stability.Al₂O₃ can be as low as4.44wt%,and still maintains good thermal stability.Synthetic factors（solvothermal reaction temperature,metal salts and orga nic ligands）contribute to a certain influence on the crystallization rate and coordination mode between metal ions and organic ligands,which in turn affect the sorption performance of the MOF-derived sorbents.The optimal MOF-derived sorbent showed a sorption capacity up to 0.64 g _CO2g^-1_sorbent and a retention rate of 94.95%after 10 cycles of reaction.Compared with limestone-derived sorbent,the optimal MOF-derived sorbent still reach 0.53 g _CO2g^-1_sorbent after 30 cycles,which is 500%times of the former.In order to clarify the effect of inert support type on the performance of the MOF-derived calcium-based sorbents,the calcium-based sorbents supported by different inert carrier types were prepared.Using the identical loading content,the alumina-based sorbent showed a better performance than that of the magnesium-based sorbent.The sorption capacity of the former was still 0.55 g _CO2g^-1_sorbent and the conversion rate can be maintained at about 70%after 10 cycles.Magnesium-based sorbent exhibits better sorption performance when the mass ratio increases to15wt%,the sorption capacity is 0.49 g _CO2g^-1_sorbent and the retention rate is as high as 90.89%after 10 cycles.The superior sorption performance for the calcium-based sorbents can be attributed to the following factors:inert carrier as a physical protection barrier,the uniform mixing of the active component and the inert carrier on the nanometer scale,and the synergy effect of Ca（OH）₂.Since the influence mechanism of the inert carrier loading mode on the physico-chemical properties of the modified calcium-based sorbents should be identifed,the relationship between loading modes and the cyclic characteristics for the MOF-derived sorbents was explored.For the Ca Al-based sorbent synthesized by"one-step method",the initial sorption capacity can reach 0.60 g _CO2g^-1_sorbent and the conversion rate decreases to 61.88%after 10 cycles.Through adopting the"two-step method",the initial sorption capacity was only 0.52 g _CO2g^-1_sorbent,but the conversion rate increases to 71.78%after 10 cycles.Similarly,the Ca Mg-based sorbent synthesized via"one-step method"obtains a higher sorption capacity while lower retention rate than that of the sorbent prepared by"two-step method".The"one-step method"MOF precursor forms a new molecular structure,the sorbent contains high Ca（OH）₂content to increases the sorption contact surface,thereby increase the sorption capacity,while the"two-step method"can significantly improve the stability due to the inert carrier using physical loading way and higher content.