模擬氣態二氧化碳和液態乙醇胺的分子界面

Abstract

隨著溫室效應加劇，近年與降低溫室氣體排放與捕捉的相關研究愈來愈盛行，其中又以二氧化碳的研究最為常見。化學家利用與化學相關方式進行二氧化碳捕捉，並以醇胺類分子作為主要的捕捉劑。 本論文欲利用分子動力學模擬實驗，針對氣態Carbon dioxide系統與液態Monoethanolamines系統的氣液界面進行討論。使用Gaussian 09計算軟體中BYLP-D2和MP2方法，並以aug-cc-pVTZ作為計算基組，此結果作為量子力學的比較基準；分子力學部分則是使用Tinker version 7.1計算軟體，以mm3參數檔作為基礎進行參數的調整。 利用所得力場分別計算兩個CO2分子和兩個MEA分子間的作用力，同時也使用BYLP-D2和MP2方法對相同分子系統做計算。接著利用分子動力學模擬實驗，獲得(CO2)13系統和(MEA)27系統達平衡狀態時的位能，進一步的計算出在不同溫度範圍下的Cv值，藉由Cv值的分布找出系統相變的溫度。所得熔點值與文獻Maillet 團隊所得的熔點值相當接近，MEA系統所得熔點和實驗上熔點雖有些差距，但相差值還在可接受的範圍內。接著固定單CO2分子和單MEA分子間CN的距離，沿著其吸附路徑計算我們所得力場的計算結果和BLYP-D2方法之間的能量差距，發現在物理吸附的範圍附近，以所得力場計算分子間能量和BLYP-D2方法計算的能量幾乎相同 建立好力場後，接著，藉由分子力學的模擬實驗對氣態CO2系統和液態MEA系統的反應介面進行探討。在反應的過程中，我們確實看見氣態的CO2分子進入MEA系統，且發現當表面上有較多MEA分子中的親水基團時，能捕捉到較多CO2分子的等有趣現象。As the global warming intensify, more and more studies that about reducing greenhouse gases emission and capture was developed recently. And the study about carbon dioxide is the most popular. Chemists utilize the chemical methods to capture carbon dioxide and regard the aminol amine as the major capturer. We utilize the molecular mechanics simulations to discuss the interface of gas carbon dioxide and liquid monoethanolamine. Using MP2 and BLYP-D2 methods from Gaussian 09 and adopted with aug-cc-pVTZ basis set. Regard the calculation results as the quantum mechanics datum. The molecular mechanics calculations were performed using Tinker version 7.1 and adopted mm3 parameters as groundwork for adjusting parameters. When the force field was decided we used it to work out the intermolecular interaction of CO2-dimer and MEA-dimer and used MP2 and BLYP-D2 method to calculated the same molecule system simultaneously. We obtained the potential energy of (CO2)13 and (MEA)27 system when these systems were achieved equilibrium during the molecular mechanics simulations. Further, we can calculate the heat capacity under different temperature and got a melting point of these systems. The solid-solid phase transition of (CO2)13 clusters was very close to the Maillet et al. that they got the melting point of (CO2)13 system. The other system of (MEA)27 was calculated by the same method. Even though there has a slight difference in melting point between experiment and the value we got, it was within the range that can accept. Then we fixed the distance between carbon and nitrogen atom from carbon dioxide and monoethanolamine, respectively. To calculate the difference of intermolecular interaction energy that used the BLYP-D2 method and our force field at molecular mechanics simulation. We found that the calculation result from our force field was fitting for the BLYP-D2 method within the scope of physical absorption. After setting up the force field, we started to run the molecular mechanics simulation and discuss the interface of gas carbon dioxide and liquid monoethanolamine. We saw the carbon dioxide molecule getting into the monoethanolamine system during the simulations and found interesting phenomenon was that more hydrophilic group could capture more carbon dioxide molecules on our surface of monoethanolamine system.