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Molecular size evaluation of linear and branched paraffins from the gasoline pool by DFT quantum chemical calculations

机译：通过DFT量子化学计算评估汽油库中直链和支链烷烃的分子大小

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摘要

A good approach of the critical molecular dimensions of 35 linear and branched C5-C8 paraffins by DFT quantum chemical calculations at B3LYP/6-31G** level of theory in gas phase is described. In this context, we found that either the determined molecular width or width-height average values can be used as critical measures in the analysis for selection of molecular sieves materials, depending on their pore size and shape. The molecular width values for linear and monosubstituted paraffins are 4.2 and 5.5 A, respectively. In the case of disubstituted paraffins, the values are 5.5 A for 2,3-, 2,4-, 2,5- and 3,4-disubstituted and for 2,2- and 3,3-disubstituted are 6.7-7.1 A. The values for ethyl-substituted are 6.1-6.7 A and for trisubstituted isoparaffins are 6.7. In order to select a porous material for selective separation of isoparaffins and paraffins, the zeolite diffusivity can be correlated with the critical diameter of the paraffins according to the geometry-limited diffusion concept and the effective minimum dimensions of the molecules. The calculated values of CPK molecular volume of the titled paraffins showed a good discrimination between the number of carbons and molecular size. Keywords:
机译：描述了通过气相色谱理论水平为B3LYP / 6-31G **的DFT量子化学计算，对35个直链和支链C5-C8链烷烃的临界分子尺寸的一种很好的方法。在这种情况下，我们发现，根据分子筛材料的孔径和形状，确定的分子宽度或宽度-高度平均值可以用作分析分子筛材料的关键措施。直链和单取代链烷烃的分子宽度值分别为4.2和5.5A。对于二取代的石蜡，对于2,3-，2,4-，2,5-和3,4-二取代的值为5.5 A，对于2,2-和3,3-二取代的值为6.7-7.1 A乙基取代的值为6.1-6.7A，三取代的异链烷烃的值为6.7。为了选择用于选择性分离异链烷烃和链烷烃的多孔材料，可以根据几何形状限制的扩散概念和分子的有效最小尺寸，将沸石的扩散率与链烷烃的临界直径相关联。标题石蜡的CPK分子体积的计算值显示出碳数和分子大小之间的良好区别。关键字：

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