Engineering Functionalized Mesoporous Materials for Selective Separations

[摘要][cts -0086777]。该项目涉及用于吸附分离的功能化介孔硅基材料的合成、表征和评估，这对环境应用至关重要。具体来说，我们寻求开发两种应用的高性能吸附剂：重金属污染的水流的修复和石蜡/烯烃气体混合物的分离。重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管制限制。近年来，人们对开发高选择性吸附剂以去除含水流中的重金属（如汞）重新产生了兴趣，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视了。烯烃/石蜡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。由于与这些混合物的蒸馏相关的高资本成本，许多化学生产设施燃烧循环净化流含有有价值的烯烃物种。这导致了原料的大量浪费以及排放量的增加。一种低成本的基于吸附的方法可以分离这些混合物，这是非常可取的，但需要开发新型的吸附材料。以分子模型为指导，我们将遵循一种策略，其中来自M41S系列材料的介孔二氧化硅通过配体功能化孔壁，专门用于重金属修复或烯烃/石蜡分离。通过选择配体来调节靶种与配体之间的孔径和相互作用强度，从而达到理想的分离效果。这意味着相互作用强度必须足够大，以实现高选择性和高容量，但足够弱，使材料可以很容易地再生。我们还将设计材料以达到最佳的传质特性。我们的合成策略将建立在我们最近的一些工作上，其中我们将有机硅烷配体附着在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。我们还能够使用乳液工艺合成自支持的功能化“宏观结构”。该项目包括三个主要组成部分。使用蒙特卡罗和分子动力学技术进行详细的分子建模研究，以探索与配体与客体物质相互作用以改变系统的吸附热力学和扩散特性的方式有关的基本问题。以这些结果为指导，我们将在介孔二氧化硅中加入不同的配体，并使用一系列技术表征材料，包括x射线衍射、扫描电子显微镜、透射电子显微镜和氮吸附。对于重金属吸附剂，我们将初步研究氨基端烷氧基硅烷配体和具有交换阳离子的磺化配体的使用。对于烯烃/石蜡吸附剂，我们将测试银等金属阳离子是否可以与磺化配体一起选择性吸附烯烃。然后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能力。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.