天然礦物石灰石的改質分析與對二氧化碳捕獲之研究

Abstract

針對所有捕獲二氧化碳中高溫吸附材料研究中，利用氧化鈣與碳酸鈣之碳酸化/煅燒程序是一個有效之循環捕獲方法。本研究分為三大部分；第一部分為利用不同濃度醋酸改質天然礦物石灰石(Limestone)，並探討不同反應時間之影響。以XRD、SEM進行結構鑑定以及表面型態觀察，當acid/Limestone質量比為1.8/1、反應時間達5小時以上，便可成功將碳酸鈣(CaCO3)轉換成醋酸鈣(Ca(CH3COO)2)；再利用TGA進行多次吸/脫附循環測試；二氧化碳吸附量於第一次吸附可接近理論值，但於10次循環後因氧化鈣聚集而造成穩定性下降。 第二部分為於已改質之Limestone-acid中經由One pot或Two pot處理，加入適當比例之高溫抗劣化材料Al(NO3)3，使其可均勻分散在氧化鈣周圍。隨著鋁含量提升，雖然捕獲量會些許下降，但進行60個循環測試後其穩定性可高達90%以上；相較之下，未改質之天然礦物石灰石(Limestone)於30個循環後已劣化51.7%。最後將已改質之粉體經由造粒程序(Pellization)後實際應用於固定床反應器(Fixed-bed reactor)，實驗結果與於TGA進行二氧化碳捕獲相似，皆在同溫700℃進行吸/脫附循環具有較好之穩定性。

The Ca-looping process shows a considerable potential about reducing postcombustion CO2 emissions and CaO-based sorbents are promising materials for capturing CO2 at med-high temperature. The first experiment was investigated the different concentration of acetic acid to modified nature limestones, and discussed the influences under different reaction time. On the basis of X-ray diffraction analysis and SEM observation, when the mass ratio of acid to limestone is 1.8∶1 for 5 hours, the CaCO3 would turned into the Ca(CH3COO)2 successfully. Besides, after many times of carbonation-calcination cycles, the CO2 capture capacity could reach the maximum value at the first adsorption. But, its CO2 adsorption performance would decrease due to the sintering of CaO after 10 cycles. The second experiment was adding Al(NO3)3 into the modified Limestone-acid sorbent during the process of One pot/Two pot, it could distributed around the CaO uniformly to keep the compound stable and durable. With the content of Al increased, the CO2 capture capacity had a little degradation. However, after 60 cycles, the durability studies showed that the Limestone-acid-Al maintain more than 90% of the initial cycle capacity. By contrast, the limestone without modified which had decayed 51.7% after 30 cyclic runs. Finally, Limestone-acid-Al-pellets were applied in the fixed bed reactor, and the result in this experiment showed the same performance with TGA.