COSMO-SAC模型氫鍵描述之修正及其在離子液體之應用

Abstract

本作共分為兩部分，第一部份修正COSMO-SAC活性係數模型的氫鍵作用力描述。近期(2017)有文獻指出，如將氫鍵的方向性考慮至COSMO-SAC模型當中，則在耦合系統之熱力學性質的預測上會有顯著的進步。將氫鍵方向性納入考量的方法之一為透過價殼層電子對互斥理論(Valence Shell Electron Pair Repulsion Theory, VSEPR)，推測孤電子對(Lone pair, LP)的位置，進而得到孤電子對與質子形成氫鍵的方向。然而，這種基於分子構型以推得孤電子對的方法在一些分子上會有所侷限，例如：氫氟酸(HF)以及二甲基亞碸(DMSO)。在這兩個分子中，即無法透過其分子內部的鍵結關係得到孤電子對之位置。為了將氫鍵的方向性有效地引入至所有種類之系統，本論文利用分子電位分布(Molecular Electrostatic Potential Map, MESP)尋找分子局部電位的低點，並將該局部低點視為孤電子對的位置。以此方法決定氫鍵的方向後，除了不須再依靠分子結構取得氫鍵的方向之外，所有中性分子系統在無限稀釋下的活性係數、汽液相平衡、液液相平衡、辛醇-水分配係數等熱力學性質的預測上亦有所進步(中性分子之汽液相平衡預測準確度取得約5-7%之進步)。本作第二部份則將第一部分所提及的新方法用在離子液體系統中，並且搭配新提出之符合熱力學一致關係式模型，也在稀薄離子液體的系統中取得了顯著的進步(滲透係數之預測準確度改善約10%)，成功將氫鍵作用力的方向性更廣泛的應用至離子液體等帶電系統中。

A new approach for determining directional hydrogen bonding interactions in the COSMO-SAC model is proposed for both neutral and charged species. In a recent work, Chen and Lin showed that the consideration of directional hydrogen bonding in the COSMO-SAC model significantly improves the description of solvation properties of associating fluids. In their method, the direction of a hydrogen bond was determined based on the VSEPR theory; however, this geometric approach does not reflect the local electronic environment of the lone pairs and cannot be applied to certain molecules such as DMSO and HF. In this work, we adopt a new scheme that determines the hydrogen bond acceptors of a molecule based on the minima in the molecular electrostatic potential (MESP). The hydrogen bonding directions thus determined result in improvements (about 5-7% for VLE) in the prediction of the COSMO-SAC model for a variety of thermodynamic properties and phase equilibria of neutral species, such as vapor-liquid equilibrium (VLE), liquid-liquid equilibrium (LLE), infinite dilution activity coefficient (IDAC), octanol-water partition coefficient (Kow). We also apply this new approach on charged species, such as ionic liquids (ILs), and apply with a new proposed extended PDH model. The improvement on IL-diluted region (about 10% for osmotic coefficient) is also reported.