氧化鈣與碳酸鈣的碳酸化/鍛燒程序是一個有效率的捕捉二氧化碳的方法。本研究利用牡蠣殼與商用碳酸鈣所轉換得的氧化鈣粉末進行二氧化碳吸收量的測試。從牡蠣殼轉化得的氧化鈣粉末由平均粒徑53 nm的氧化鈣奈米顆粒所組成，在20% CO2/N2氣體環境下進行持溫650°C進行5小時的二氧化碳吸收，其轉化率可達84%。牡蠣殼所轉化得的氧化鈣粉末擁有9 wt%的雜質含量，與商用碳酸鈣轉化得的氧化鈣結晶粒徑比較，具有較大的氧化鈣結晶粒徑及較小的表面積。利用牡蠣殼所轉化的氧化鈣當吸收劑，在多循環二氧化碳吸收實驗中，於碳酸化與鍛燒程序間插入一個冷卻步驟，對整體的循環再生性與二氧化碳吸收量都有很大的改善。當吸收溫度為750°C時，牡蠣殼所轉化成的氧化鈣的在多循環二氧化碳吸收的總效能明顯優於商用碳酸鈣所轉化成的氧化鈣。利用X光繞射分析，本研究提出一個可能的機構，在牡蠣殼轉化得的氧化鈣內的雜質將在氧化鈣結晶晶界周圍形成過渡區，可抑制或減緩因為鍛燒而造成的晶粒成長以及封存二氧化碳所造成的晶格膨脹。插入的冷卻步驟將可以擴大過渡區的範圍，緩和因封存二氧化碳所造成的晶格錯亂及二氧化碳吸收量的衰退。除此之外，本研究亦將牡蠣殼與商用碳酸鈣所轉換得的氧化鈣粉末進行水合處理，發現到可大幅度增加吸收量與吸收速率，並利用吸收劑的結晶結構解釋其對吸收效率的影響。

The carbonation/calcination loop of CaO/CaCO3 is an efficient process for CO2 capture. This study investigated the CO2 capture capability of CaO powders derived from oyster shells and reagent-grade CaCO3. The CaO powder from oyster shells calcination consisted of nanoparticles of 53 nm and showed a CO2 absorption conversion as high as 84% at 650°C for 5 hours in 20% CO2/N2.The oyster shell-derived CaO powder had an oxide impurity content as high as 9 wt%, and a larger CaO crystal grain size and smaller specific surface area than the CaO derived from the reagent CaCO3. In cyclic CO2 capture tests, the cyclability and CO2 capacity of the oyster shell-derived CaO was significantly improved by inserting an intermediate cooling step between carbonation and calcination. At a carbonation temperature of 750°C, the overall performance of the oyster shell-derived CaO in cyclic carbonation was superior to that of the CaO from the reagent CaCO3. On the basis of X-ray diffraction analysis, it was suggested that the impurities contained in the oyster shell-derived CaO may have constituted transition zone on the CaO crystal grain boundary to suppress crystal growth in calcination as well as to ease up lattice expansion in CO2 fixation. The intermediate cooling enlarged the transition zone to mitigate lattice dislocations resulting from CO2 fixation and thus the decay in CO2 capacity. In addition, this study also investigated the CO2 capture capability of CaO powders derived from oyster shells and reagent-grade CaCO3 under deionized water hydration. The CO2 capacity and carbonation rate was significantly improved by the hydration of CaO powder. The correlation between the crystalline structure of the sorbents and the absorption performance will be explored.

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