CAREER: Molecular Transport Theory for Nanoporous Solids

CTS-9734153奥尔巴赫最环保的技术依赖于从无害材料中去除污染物的分离。沸石分子筛由如下所示的规则间隔的分子大小的笼子组成，非常适合于这些分离。尽管人们对沸石了解很多，但还没有简单的理论来准确预测分子如何在沸石中扩散。这是因为很难对偶发事件动力学和强吸附-吸附相互作用进行建模。此外，分子筛被物理科学中最重要的一门课--大学一年级化学--忽视了。为了解决这些问题，首席研究员将开发新的教育技术和分子传输理论，旨在加速新兴化学技术的材料和工艺筛选。在工业上重要的沸石中，许多碳氢化合物的流动性极其缓慢，这排除了直接的分子动力学模拟的使用，因此需要专门针对罕见事件的建模技术。以往分子筛中扩散的过渡态模拟是在低负载下进行的，因此可以忽略吸附-吸附相互作用。这些条件与工业过程无关，工业过程基本上是在满载碳氢化合物的情况下进行的。为了模拟工业条件下沸石中的传输，首席调查员将开发三种不同精度和速度的新技术。一种加速的分子动力学算法增加了一种新的降低位置到位置激活能的增强势，如果这种增强避免了过渡态，那么它将基本上预测准确的扩散系数。将开发一个晶格蒙特卡罗模拟，其中包括一种新的处理吸附-吸附相互作用修改的活化能的方法。最后，将得到一个完整的解析理论，首次用流体平均场理论合成起伏活化能。这种新的层次结构提供了根据工艺优化中对速度或精度的需求来选择模型的机会。这些模型将被合并到一年级化学模块中，名为“工业中的沸石”，涉及新的基于网络的交互软件，模拟这些系统的物理和化学性质。这项研究将在多个层面上影响科学和社会。首先，将沸石科学和技术融入到大学一年级的化学中，将使成千上万的学生兴奋并了解工业化学和工程的现实世界的好处。其次，化学反应动力学和平均场理论的这种新的结合将产生第一个真正的分子理论在沸石中的传输，阐明了主-客体和客体-客体相互作用之间的竞争是如何控制这些传输过程的。这将指导和补充新的扩散测量，并将加快筛选新的化学工艺。第三，当应用于大孔沸石中的芳烃分离和氢氟烃分离时，这些计算将有助于指导科学家和工程师选择最佳的沸石硅铝比、沸石通道结构、温度和压力来进行高效和经济的分离。

CTS-9734153 Auerbach Most environmentally friendly technologies rely on separations that remove pollutants from benign materials. Zeolite molecular sieves, consisting of regularly spaced, molecular-sized cages shown below, are ideally suited for these separations. Although much is known about zeolites, no simple theory exists for accurately predicting how molecules diffuse through them. This is because of the difficulty in modeling infrequent event dynamics coupled with strong adsorbate-adsorbate interactions. Furthermore, zeolites are ignored by the single most important class in physical science: freshman chemistry. To address these issues, the Principal Investigator will develop novel educational techniques and molecular transport theories aimed at accelerating material and process screening of emerging chemical technologies. The mobility of many hydrocarbons in industrially important zeolites is exceedingly sluggish, precluding the use of straightforward molecular dynamics simulations, and hence requiring modeling techniques specialized for infrequent events. Previous transition state simulations of diffusion in zeolites were performed at low loadings, so that adsorbate-adsorbate interactions could be neglected. These conditions are irrelevant to industrial processes, which are carried out at essentially full hydrocarbon loading. To model transport in zeolites under industrial conditions, the Principal Investigator will develop a hierarchy of three new techniques with varying accuracy and speed. An accelerated molecular dynamics algorithm that adds a novel boost potential for reducing site-to-site activation energies will predict essentially exact diffusivities provided that the boost avoids transition states. A lattice Monte Carlo simulation will be developed that includes a new treatment of activation energies modified by adsorbate-adsorbate interactions. Finally, a completely analytical theory will be derived that synthesizes for the first time fluctua ting activation energies with the mean field theory of fluids. This new hierarchy provides the opportunity of choosing a model based on the need for speed or accuracy in process optimization. These models will be incorporated into a freshman chemistry module entitled: "Zeolites in Industry," involving new Web-based, interactive software that mimics the physical and chemical properties of these systems. This research will impact science and society on many levels. First, incorporating zeolite science and technology into freshman chemistry will excite and inform thousands of students about real-world benefits of industrial chemistry and engineering. Second, this novel combination of chemical reaction dynamics and mean field theory will yield the first truly molecular theory for transport in zeolites, elucidating how the competition between host-guest and guest-guest interactions controls these transport processes. This will guide and complement new diffusion measurements, and will accelerate screening of new chemical processes. Third, when applied to aromatic separations and hydrofluorocarbon separations in large-pore zeolites, these calculations will help guide scientists and engineers in choosing optimal zeolite Si:Al ratios, zeolite channel structures, temperatures and pressures for carrying out efficient and cost-effective separations.