醇胺化合物捕捉二氧化碳研究:從理論方法到分子動力學模擬
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2014
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自人類經濟活動蓬勃發展，石化燃料的大量使用，導致二氧化碳的排放量大增，進而引發極端氣候。在國際上目前提出的 碳捕捉與碳封存。乙基醇胺(mono-ethanolamine)、二乙基醇胺(diethanolamine)、三乙基醇胺(triethanolamine)為目前商用的碳捕捉劑，主要用於火力發電廠所產生出的二氧化碳。這類捕捉劑與二氧化碳的反應機制目前仍然未知，過去的研究透過理論計算的方法提出可能的反應機制，然而不同的理論方法對於反應路徑的預測有不同，故在本論文的研究起始於理論方法的分析，進而利用分子動力學的模擬，來提出新的捕捉劑設計策略。
在理論方法的研究中提出了一個含有12對幾何優化過後的C1資料庫以測試15個密度泛涵理論方程。這15個密度泛涵理論方程已被發表改善電子交換項針對遠距離凡德瓦力。測試的標準是利用∆CCSD(T) 並經過方均根(RMS)統計後判定。在這個階段的研究中發現，ωB97 、ωB97X、ωB97XD 系列很適合計算涵有強凡德瓦力的氫鍵系統。BLYP-D 適合用在胺類化合物與二氧化碳吸附的組合。所以在之後的研究中使用BLYP-D來計算分子動力學反應。
過去設計捕捉劑的策略是藉由提高胺的級數，來增加其親核性。工業製程是藉由環氧乙烷通入氨氣合成乙基醇胺、二已基醇胺、和三乙基醇胺，並藉由反應條件的控制而調整溶液中化合物的比例。然而三級胺類對二氧化碳的吸附能力並未優於二級胺類，因此重新思考朝向增長碳鏈來作為設計方向。正丙醇胺(n-propanolamine)在計算結合能和電荷分析上，都明顯優於乙醇胺。為了解二氧化碳與捕捉劑在動力學上的影響，分別利用分子動力學模擬乙醇胺、丙醇胺20%和50%的無水混合二氧化碳溶液，連續模擬12萬步。模擬中發現正丙醇胺在徑向分配含數上明顯優於乙醇胺，其中發現溶液中氫鍵環境有顯著的影響。氫鍵環境越高的乙醇胺系統，會不利於捕捉劑對二氧化碳的吸附；而氫鍵數量較低的丙醇胺系統對二氧化碳的吸附有顯著的提升。
在本篇研究中探討ωB97泛涵方程適用於強凡德瓦力的氫鍵系統，BLYP-D可用於捕捉劑與二氧化碳反應的計算。分子動力學的研究探討新的分子設計策略的有效性，吸附能力的提升以及其氫鍵對於碳捕捉的影響。
As large carbon emission is rapidly growing in recent years, the concentration of carbon dioxide in the air highly growing. CCS is an abbreviation for carbon dioxide capture and storage that the one of solution to decrease the concentration of carbon dioxide to compensate the effect of what global worming brings. MEA (monoethanolamine), DEA (diethanolamine), and TEA (triethanolamine) are commercial compounds for reducing carbon dioxide emission as post combustion methods in fire power plant. However, in the past research, many theoretical studies have different insight of capture mechanism. Especially the existence of zwitterion; therefore, the study is starting from how to choose DFT functional, and then to use the molecular dynamic method to find out the details of CO2 capture by alcoholamines; therefore, developing a new compounds for CO2 capture is our goal. First, A C1 database comprising 12 bounded complex is used for testing 15 dispersion improved DFT functionals including from GGA, hybrid-GGA, meta-GGA, GGA with empirical dispersion. The standard in the comparison is choosing the delta CCSD(T) scheme that the energy is extrapolated from aTZ to aQZ, and the small basis set is aDZ. The result shows that ωB97 series are good at the hydrogen bond with high dispersion system, and BLYP-D is an appropriate functional to calculate the alcohomolamine bounded carbon dioxide. Secondly, the traditional strategy of alcoholamine design is increasing the degree of amine that MEA, DEA, and TEA are the products of the reaction between ethylene oxide and ammonia in industry. MPA is another way to increase the carbon chain of alcoholamine compounds. In molecular dynamic study, the performance of new molecule has been improved that the binding energy and the proportion of CO2 absorbed by MPA on radial distribution function diagram. The first study conclude that ωB97 can be used in this system and the BLYP-D has top performance on absorption complex; moreover, the strategy of increasing carbon chain indeed improve the performance of the efficiency of CO2 capture.
As large carbon emission is rapidly growing in recent years, the concentration of carbon dioxide in the air highly growing. CCS is an abbreviation for carbon dioxide capture and storage that the one of solution to decrease the concentration of carbon dioxide to compensate the effect of what global worming brings. MEA (monoethanolamine), DEA (diethanolamine), and TEA (triethanolamine) are commercial compounds for reducing carbon dioxide emission as post combustion methods in fire power plant. However, in the past research, many theoretical studies have different insight of capture mechanism. Especially the existence of zwitterion; therefore, the study is starting from how to choose DFT functional, and then to use the molecular dynamic method to find out the details of CO2 capture by alcoholamines; therefore, developing a new compounds for CO2 capture is our goal. First, A C1 database comprising 12 bounded complex is used for testing 15 dispersion improved DFT functionals including from GGA, hybrid-GGA, meta-GGA, GGA with empirical dispersion. The standard in the comparison is choosing the delta CCSD(T) scheme that the energy is extrapolated from aTZ to aQZ, and the small basis set is aDZ. The result shows that ωB97 series are good at the hydrogen bond with high dispersion system, and BLYP-D is an appropriate functional to calculate the alcohomolamine bounded carbon dioxide. Secondly, the traditional strategy of alcoholamine design is increasing the degree of amine that MEA, DEA, and TEA are the products of the reaction between ethylene oxide and ammonia in industry. MPA is another way to increase the carbon chain of alcoholamine compounds. In molecular dynamic study, the performance of new molecule has been improved that the binding energy and the proportion of CO2 absorbed by MPA on radial distribution function diagram. The first study conclude that ωB97 can be used in this system and the BLYP-D has top performance on absorption complex; moreover, the strategy of increasing carbon chain indeed improve the performance of the efficiency of CO2 capture.
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二氧化碳捕捉, 計算化學, 密度泛函理論, 二乙基醇胺, carbon dioxide capture, computational chemistry, density functional theory, diethanolamine