Athabasca油砂沥青中重组分的分子模拟

MOLECULAR MODELLING OF HEAVY COMPONENTS PRESENT IN ATHABASCA BITUMEN PITCH

利用分子模拟技术对加拿大Athabasca油砂沥青超临界萃取分馏残渣组分的化学分子结构进行了研究 ,首先选用长度不同的桥链构建了其三维平均结构 ,然后采用分子力学 (MM)和分子动力学 (MD)方法得到能量最低也即最稳定的构象 .研究发现 ,即使分子的二维结构相同 ,其三维结构差别也很大 ,由此可见仅用二维模型来表征重质油大分子的结构和物理化学性质远远不够 .另外 ,分子模拟还可以预测沥青质残渣中最有可能存在的桥链长度 .Athabasca沥青残渣组分中长度为C5到C7的桥链存在的可能性最大 ,而C1和C2桥链则由于其总能量相对较高 。

Abstract Based on the postulated 2D average molecular unit structures proposed by Zhao et al, 3D conformations for the end-cuts of Athabasca bitumen pitch in Canada were created using polymethylene bridges with different lengths by the Computer Aided Molecular Design (CAMD) method. Molecular Mechanics (MM) and Molecular Dynamics (MD) computations were carried out on these conformations to determine the lowest energy structures and hence the most stable conformations. The 3D conformations and the total energy of the target molecules were intimately related. It was found that the equivalent conformations in three dimensions were quite varied even though the two-dimensional structure remained exactly the same. This meaned that simple 2D structures of macromolecules could not adequately represent their structural, physical and chemical properties. The most likely polymethylene bridge lengths within the pitch end-cut molecules were estimated from the CAMD results; a value in the range of C4 to C6 was most likely. The probability of Cl and C2 bridges was less because their total energies were comparatively high.