多孔洞型鈣鋁複合材料之合成、分析與應用於二氧化碳的吸附之研究

Abstract

在本研究中，提出了兩種鈣鋁複合二氧化碳吸附材料的合成方式。第一部分為利用將先行合成的均勻中孔洞氧化鋁以微波加熱的含浸法方式形成含奈米氧化鈣的中孔洞鈣鋁氧化物，接著以XRD、BET進行結構鑑定與結晶型態分析，並藉由TEM觀察微結構，再利用TGA測量二氧化碳之吸附量。由含浸法合成出的鈣鋁複合材料在低溫600oC燒結就可形成Ca12Al14O33的鈣鋁氧相，隨著含浸的鈣量增加，二氧化碳的吸附量也增加，但相對的擴散造成的吸附效應就比較少。在多次吸脫附迴圈中，二氧化碳吸附量有顯著的自活化效應，其吸附量會隨著迴圈次數增加而增加。第二部分為利用溶膠-凝膠法形成多孔洞具有層狀水滑石結構的鈣鋁氧化物，亦以XRD、BET、TEM進行組成與結構分析，再利用TGA測量二氧化碳之吸附量及吸附/脫附迴圈。由於此合成方法製備出的鈣鋁氧化物微條狀結構，具有高表面積，也可讓二氧化碳快速擴散到材料內部因此具有快速吸脫附的現象。由於溶膠-凝膠法會在室溫就讓鈣鋁兩種金屬產生作用，產生鈣鋁的層狀水滑石結構，經600oC熱處理, 可形成鈣鋁氧複合物與氧化鈣均勻散佈其中的材料，因為鈣鋁氧相的生成,其具有極優異的高溫熱穩定性，因此大為提升此二氧化碳吸附材料的抗燒結性質，故其在吸脫附迴圈中呈現相當穩定，在多次高溫迴圈後的吸附量也幾乎沒有損失。同時由於此材料具有多孔洞的結構，並也有高穩定的鈣鋁氧產物保持其高表面積的特性，自活化作用的特性也在此系列吸附材料中顯現。

In this study, two series of porous-structured carbon dioxide sorbents were synthesized. These sorbents could be successfully applied to carbon dioxide capture at high temperature, and also show stable performances for carbonation/ calcination cycles. In the first series sorbents are fabricated by wet impregnation method, using a pre-synthesized ordered mesoporous alumina as a porous matrix with calcium acetate via microwave-assisted hydrothermal process to obtain the mesoporous Ca-Al-O composite sorbents. The mesoporous structures have been characterized by small-angle XRD, N2 adsorption-desorption isotherms, SEM, and TEM. The crystallinity was determined by HRTEM and large-angle XRD. Since the microwave energy might highly enhance the activity of alumina, the phase of Ca12Al14O33 can be obtained at 600oC calcination. With more CaO-loaded, the CO2 uptake-capacity can also increase; which makes the adsorption kinetics becomes majorly chemisorption domain. Sorbents produced by wet impregnation have the unique characterization, the self-reactivation that induces CO2 capture capacity increasing during carbonation/calcination cycles. And in the second series of sorbents synthesized by sol-gel method, via the oligomerization and polymerization of aluminum isopropoxide, reactions between Ca and Al occur and thus rendering the scaffold-like LDH structure. After 600oC calcination, the already interacted Ca-Al-O materials transform into the highly stable form that can also improve the mechanical strength of the sorbent structure and enhance the sintering-resistant nature over cycles as well. Due to the network skeleton, the sorbents are composed of high BET surface area with worm-like porous structure which makes CO2 can quickly diffuse into the interior material and cause the fast adsorption/desorption characteristic. Additionally, the self-reactivation effect also occurs in these sorbents that the CO2-uptake capacity is increased during carbonation/calcination cycles.