化學迴圈燃燒程序中，使用碳氫化合物當作燃料常造成嚴重的積碳現象，會造成載氧體的失活。本研究探討鎳基載氧體經碳氫燃料還原後，金屬鎳催化碳氫燃料裂解造成之積碳現象。
使用光輔助固定床反應器(Photo-assisted packed-bed reactor，PPBR)、熱重分析儀(Thermogravimetric analyzer，TGA)及流體化床反應器(Fluidized-bed reactor，FBR)進行反應性測試。實驗中探討鎳含量對積碳之效應，實驗結果發現鎳含量超過30 wt%後，載氧體在合成氣氣氛下還原30分鐘後，鎳金屬會催化CO氣體，產生積碳現象。在不同鍛燒溫度製備載氧體，以探討晶相組成及反應性之差異，氧化鎳與二氧化鈦在700度以上形成鎳鈦氧尖晶石結構，鍛燒溫度提高，氧化鎳的初始還原溫度也提高，且低溫鍛燒的載氧體在氮氣升溫過程中，有輕微(6 wt%)釋氧的情況發生，是因氧吸附及鍵結於載氧體的晶格缺陷中，而在升溫過程釋出。將載氧體擔載於六種不同擔體，在PPBR中進行反應性測試，發現金屬鎳容易催化一氧化碳產生二氧化碳及碳沉積，可由實驗結果推測積碳之機制及影響因素。TGA實驗顯示積碳趨勢與PPBR結果相反，主要原因為TGA及PPBR中使用的氣體流率不同，造成氣體於載氧體中擴散效果不同。進一步將反應性與抗積碳較佳的載氧體大量製備且造粒，在TGA下進行15次氧化還原迴圈測試，載氧體具有良好的反應活性且無明顯聚集現象，於FBR下進行流體化及反應性測試，以冷模及理論計算推測載氧體的最小流體化速度，使載氧體達到流體化。載氧體在FBR中展現出良好的反應性，在還原段能產生純度接近100%的CO2，且連續操作10小時後，載氧體並沒有明顯燒結、聚集以及去流體化的現象。
上述實驗所篩選出來的NSi5-9載氧體，具有抗積碳效果且反應性佳，多次循環後仍具有良好反應性。價格低廉且反應性佳的SiO2將可作為具實用性之載氧體。

In chemical looping combustion process, the reaction of carbon deposition often results in the inactivation of oxygen carriers. In this work, we investigated the cracking reaction of hydrocarbon fuels in the presence of metallic nickel, which was the Ni-based oxygen carrier reduced by fuel.
Reactivities of oxygen carriers were evaluated in three different reactors, photo-assisted packed-bed reactor, thermogravimetric analyzer, and fluidized bed reactor. To figure out the effect of nickel content on carbon deposition, oxygen carriers with different loading amount of nickel was prepared. According to the results, the obvious carbon deposition was occurred after 30 minutes of reduction in syngas atmosphere as the nickel content was more than 30 wt%. The calcination temperature in the preparation procedure affected on the structure and reactivity of oxygen carriers. NiTiO3 spinel structure was formed at 700 oC with using titanium dioxide as supporting material. The reduction temperature of nickel oxide was increased with the increase in calcination temperature. The release of 6 wt% of oxygen gas from oxygen carriers was observed during the heating process under inert atmosphere. It is probably due to some oxygen was adsorbed or bonded in lattice defects of oxygen carriers. The oxygen carriers with six kinds of supports were evaluated in PPBR reactor under syngas and carbon monoxide atmospheres, respectively. Carbon monoxide was converted to carbon dioxide and coke with reacting with Ni-based oxygen carriers. The rational reaction mechanism was clarified according to these experiments. The carbon deposition results obtained from TGA was in contrary to those from PPBR, resulting from the different diffusion rates in these two reactors. The mass production of the optima OC with good redox reactivity and carbon-depositing resistance, NSi5-9, was further carried out for FBR. Fifteen redox-cycles of redox reactions in TGA demonstrated this OCs had good activity and agglomeration resistance. The minimum fluidization velocity was determined by cold model of FBR and theoretical calculations. NSi5-9 exhibited excellent reactivity and produced almost 100% CO2 during the reduction period in FBR. No significant sintering, agglomeration, and defluidization phenomena were observed after 10 h of continuous operation.
In summary, NSi5-9 had high reactivity and carbon-depositing resistance after multiple redox cycles in TGA and FBR. The SiO2 can be practical supporting material in CLC process due to its cheap cost and good reactivity.

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