Engineering Functionalized Mesoporous Materials for Selective Separations

爱德华·J·马金努。该项目涉及对环境应用至关重要的基于吸附分离的功能化介孔二氧化硅材料的合成、表征和评价。具体地说，我们寻求开发高性能的吸附剂，用于两个应用：修复受重金属污染的水蒸气，以及分离石蜡/烯烃气体混合物。严重的金属污染是环境问题的主要来源，现有技术并不总是足以满足严格的监管限制。最近，人们对开发高选择性的吸附剂以去除水溶液中的汞等重金属产生了新的兴趣，但大多数注意力集中在优化材料的选择性上。许多实际工程问题，如稳定性、再生能力和传质问题，在很大程度上被忽略了。烯烃/烷烃分离是先进吸附剂在环境保护中发挥重要作用的另一个机会。由于与蒸馏这些混合物相关的高资本成本，许多化工生产设施燃烧回收含有有价值的烯烃物种的吹扫气流。这导致了原料的大量浪费和排放的增加。一种低成本的基于吸附的过程可以分离这些混合物是非常可取的，但需要开发新型的吸附材料。以分子模拟为指导，我们将遵循这样的策略，即来自M41S材料家族的介孔二氧化硅通过用配体功能化孔壁来定制用于重金属修复或烯烃/石蜡分离的策略。配体的选择是为了调节目标物种与配体之间的孔径和相互作用强度，以获得理想的分离性能。这意味着相互作用的强度必须足够大，以实现高选择性和容量，但必须足够弱，以便材料可以很容易地再生。我们还将对材料进行改造，以实现最佳的传质特性。我们的合成策略将建立在我们最近的一些工作基础上，在这些工作中，我们将有机硅烷配体连接到介孔二氧化硅的孔壁上。这些材料可以用传统技术制成粉末状。我们也已经能够使用乳液过程来合成自支撑的功能化“宏观结构”。该项目包括三个主要组成部分。将使用蒙特卡罗和分子动力学技术进行详细的分子模拟研究，以探索与配体与客体物种相互作用的方式有关的基本问题，以改变系统的吸附热力学和扩散性质。以这些结果为指导，我们将在介孔二氧化硅中引入不同的配体，并使用一系列技术对材料进行表征，包括X射线衍射、扫描电子显微镜、透射电子显微镜和氮气吸附。对于重金属吸附剂，我们将初步研究端胺基烷氧基硅烷配体和磺化阳离子配体的使用情况。对于烯烃/烷烃吸附剂，我们将测试金属阳离子，如银，是否可以与磺化配体一起选择性地吸附烯烃。然后，将通过测量混合物等温线来评估材料的性能，以获得选择性和吸附容量。重要的是，我们还将使用填充床进行突破曲线分析和再生测试。这些测试将有助于确定将这些材料用于工业和消费应用的可行性。

ABSTRACTCTS-0086777Edward J. MaginnU. of Notre Dame This project concerns the synthesis, characterization and evaluation of functionalized mesoporous silica-based materials for adsorption-based separations critical to environmental applications. Specifically, we seek to develop high performance adsorbents for two applications: the remediation of aqueous streams contaminated with heavy metals, and the separation of paraffin/olefin gas mixtures.Heavy metal contamination is a major source of environmental concern, and existing technologies are not always adequate for meeting stringent regulatory limits. There has been renewed interest recently in developing highly selective adsorbents for the removal of heavy metals such as mercury from aqueous streams, but most of the attention has focused on optimizing the selectivity of materials. Many practical engineering concerns such as stability, regeneration capability and mass transfer issues have been largely ignored.Olefin/paraffin separation represents another opportunity where advanced adsorbents can play a large role in environmental protection. Due to the high capital costs associated with distillation of these mixtures, many chemical production facilities flare recycle purge streams containing valuable olefin species. This results in a significant waste of feedstock as well as increased emissions. A low capital adsorption-based process that could separate these mixtures is highly desirable, but requires the development of new types of adsorbent materials.Using molecular modeling as a guide, we will follow a strategy in which mesoporous silicas from the M41S family of materials are tailored for either heavy metal remediation or olefin/paraffin separation by functionalizing the pore walls with ligands. The ligands will be chosen so as to tune the pore diameter and interaction strength between the target species and the ligand to achieve desirable separation performance. This means that the interaction strength must be great enough to achieve high selectivity and capacity, but weak enough so that the material can be easily regenerated. We will also engineer the material to achieve optimum mass transfer characteristics. Our synthetic strategy will build on some of our recent work in which we have attached organosilane ligands onto the pore walls of mesoporous silica. These materials can be made in powdered form using conventional techniques. We have also been able to synthesis self-supporting functionalized "macrostructures" using an emulsion process.The project involves three main components. Detailed molecular modeling studies using Monte Carlo and molecular dynamics techniques will be conducted to probe fundamental issues pertaining to the way in which ligands interact with guest species to change the adsorption thermodynamics and diffusion properties of the system. Using these results as a guide, we will then incorporate different ligands into mesoporous silica and characterize the materials using a range of techniques, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption. For the heavy metal adsorbents, we will initially investigate the use of amine-terminated alkoxysilane ligands and sulfonated ligands with exchangeable cations. For the olefin/paraffin adsorbents, we will test whether metal cations such as silver can be used with the sulfonated ligands to selectively adsorb olefins. The performance of the materials will then be evaluated by measuring mixture isotherms to obtain selectivities and adsorption capacity. Importantly, we will also perform breakthrough curve analyses and regeneration tests using a packed bed. These tests will help determine the feasibility of using these materials for industrial and consumer applications.