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    Title: 胺基表面修飾中孔氧化矽在二氧化碳捕捉之應用
    Other Titles: Amine-modified mesoporous silicas for CO2 capture
    Authors: 楊竣斐;Yang, Chun-Fei
    Contributors: 淡江大學化學工程與材料工程學系碩士班
    張裕祺;Chang, Yu-Chi
    Keywords: 中孔矽材;胺官能基;mesoporous;amine
    Date: 2011
    Issue Date: 2011-12-28 18:50:37 (UTC+8)
    Abstract: 大氣中二氧化碳含量的 增加被認為是造成地球暖化現象的主要元兇之一。因此,高效能且符合經濟效益的二氧化碳捕捉或隔離技術的研發是一重要且刻不容緩的議題。在本研究中,吾人利用中孔洞氧化矽所具備的高比表面積、高孔體積、可調控孔徑以及豐富的表面氫氧基可供官能化修飾等特點,探討並比較以後合成法或一步合成法製備不同胺基表面修飾中孔洞氧化矽樣品,並利用各種物化光譜與分析實驗技術,如傅立葉紅外線光譜、氮氣等溫吸附/脫附、粉末x-ray繞射、元素分析及掃描式/穿透式電子顯微鏡等,對各種樣品之物化特性詳加鑑定。隨後利用熱重分析法測試並比較各種樣品之二氧化碳吸附效能,並利用固態核磁共振光譜探討可能的CO2吸附機理。
    在後合成修飾法方面,吾人首先合成中孔洞二氧化矽SBA-15做為擔體,而後將各種胺官能基修飾在其孔璧上,並探討不同胺基結構、鏈長與負載量之聚乙烯聚胺類,如二乙烯三胺(DETA;含3N)、三乙烯四胺(TETA;含4N)、四乙烯五胺(TEPA;含5N)、五乙烯六胺(PEHA;含6N)等對CO2吸附效能之影響。實驗結果發現,所合成修飾之吸附劑在未去除模板劑時(樣品以PSxN命名; x = 3 ~ 6命名),由PS3N、PS4N、PS5N、PS6N所測得之CO2吸附量分別為40、200、200和182 mg-CO2/g-adsorbent。後三者之吸附效能遠超過一般公認商業化所需的最低標準(~ 88 mg/g)。其中,PS3N之吸附效能較低,推估應是因為其鏈長較短,因而可利用來捕捉CO2的胺官能基也較少之故。吾人並探討利用微波加熱輔助以一步合成法直接製備胺基表面修飾之孔洞氧化矽吸附劑。同樣的,在未去除模板劑條件下(樣品以MWxN; x = 3 ~ 6表示),由MW3N、MW4N、MW5N以及MW6N吸附劑所測得之CO2吸附量分別為10、149、195和110 mg/g。後三者之CO2吸附效能雖略遜於前述以後合成法所合成修飾之吸附劑,但是整體效果仍然不差,尤其是此舉有效地縮短了吸附劑樣品合成的時間。
    進一步的物化鑑定分析顯示:經煅燒去除模板劑之後的樣品,一步合成法相較於後合成法所得到之SBA-15擔體本身的比表面積明顯降低,而孔體積則無明顯變化。據此,吾人推估擔體之比表面積並非影響吸附效能的主因,而其孔體積大小才是決定可負載胺官能基數量,進而影響CO2吸附量的關鍵。此外,在探討比較四種不同胺基表面修飾SBA-15吸附劑在經過多次重複吸/脫附之後,發現含較高碳數胺基吸附劑之CO2吸附效能並無明顯衰退,反之,含較低碳數者因鏈長較短,在經多次吸/脫附後,其胺官能基團容易從SBA-15擔體上脫落,因而造成CO2吸附效能的衰退。在CO2吸附機理方面,吾人由碳-13交叉極化魔角旋轉固態核磁共振光譜實驗證實擔體中P123模板劑的存在與否,並不影響二氧化碳吸附效能,此一結果顯然與現有文獻所推論之吸附機制相違背,就此而論,類此固態吸附劑系統之詳細CO2吸附機理仍有待進一步研究闡明。
    The progressive increase in atmospheric carbon dioxide (CO2) content has been held responsible for the global warming phenomena, which has becoming a vital ecological issue. Thus, the R&D of highly efficient and cost-effective technologies for CO2 capture and separation is a demanding task in carbon sequestration. Utilizing the unique characteristics possessed by mesoporous silicas, viz. high surface areas, high total pore volume, controllable pore sizes, and enriched surface hydroxyls available for functionalizations etc., this study aims to use porous silicas as supports to fabricate various amine-functionalized adsorbents for CO2 capture. The amine-functionalized porous adsorbents prepared by either post-synthesis modification or microwave-assisted direct (one-step) synthesis methods were characterized by a variety of different analytical and spectroscopic techniques, such as Fourier-transformed infrared (FT-IR), N2 adsorption/desorption isotherm, powdered x-ray diffraction (PXRD), elemental analysis (EA), and scanning/transmission electron microscopy (SEM/TEM). The CO2 uptake capacities and adsorption/desorption kinetics of various solid adsorbents were examined by a home-built thermogravimetic apparatus. The adsorption mechanism was also explored by solid-state nuclear magnetic resonance (SS-NMR) spectroscopy.
    For samples prepared by post-synthesis modification method, various polyethylenepolyamines, viz. diethylenetriamine (DETA; 3N), triethylenetetramine (TETA; 4N), tetraethylenepentamine (TEPA; 5N), and pentaethylenehexamine (PEHA, 6N) were grafted onto the as-synthesized mesoporous SBA-15 silica support. The amine-functionalized adsorbents so fabricated without removing the surfactant (P123) template (denoted as PSxN; x = 3-6), namely PS3N, PS4N, PS5N, and PS6N were found to have a maximum CO2 uptake capacity of 40, 200, 200, and 182 mg-CO2/g-adsorbent, respectively; the latter three being surpassing the minimum benchmark value (ca. 88 mg/g) commonly proposed for commercialization. That the PS3N adsorbent showed a lower CO2 uptake capacity is attributed to the shorter chain length and less amine functional group available by the DETA compared to its counterparts. Likewise, for samples fabricated by microwave-assisted direct synthesis method without removing the surfactant template (denoted as MWxN, x = 3-6), namely MW3N, MW4N, MW5N, and MW6N were found to have a maximum CO2 uptake capacity of 10, 149, 195, and 110 mg/g, respectively. While the adsorbents so fabricated appear to have a somewhat lower CO2 uptake capacity than those prepared by post-synthesis grafting method, the time required for obtaining the former samples (12 hours) was shorten as much as 6 folds.
    By comparing the physicochemical properties of PSxN and MWxN samples after removing their surfactant templates (by calcination) revealed that while the latter series samples exhibit notably lower surface areas than the former, their pore volumes remained nearly unchanged after the calcinations treatment. Thus, it is indicatives that pore volume (rather than surface area) of the adsorbent, which dictates the available amine functional group loading, is the controlling factor of CO2 uptake. Additional durability tests further revealed that adsorbents modified by polyethylenepolyamines with longer carbon chain lengths (and hence more amines) show superior durability than those with shorter carbon chain lengths (less amines). Further investigation by 13C cross-polarization magic-angle-spinning (CP-MAS) SS-NMR also verified that the presence of the P123 surfactant template has negligible effect on CO2 uptake. This result clearly contradicts the adsorption mechanism proposed in the literatures, as such, genuine mechanism related to adsorption of CO2 in these solid porous adsorbents demands further investigations.
    Appears in Collections:[化學工程與材料工程學系暨研究所] 學位論文

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