Cation-Controlled Gating for Selective Gas Adsorption over Adaptable Zeolites

吸附技术可以净化和分离气流，对许多关键行业至关重要，包括石油和天然气、化工、制造和医疗行业。因此，固体吸附剂每年价值24亿英镑，约占整个工业气体市场的10%。此外，吸附可以为环境应用提供绿色、节能的途径，包括从发电和其他工业来源捕获碳。通常，吸附是通过变压和变温吸附过程实现的，循环时间为几分钟或更长。采用旋转阀、旋转轮吸附剂和新型薄层吸附剂结构的新型动力学吸附技术可以减少设备占地面积，提高这些气体分离过程的效率，例如，纯气体可以在现场产生，而不是集中产生，并降低与之相关的配送成本。沸石，微孔铝硅酸盐，占工业吸附剂价值的30%以上。它们良好的有序和坚固的框架结构赋予了分子筛分和基于热力学的分离的高选择性。虽然已知的沸石结构类型超过200种，但只有极少数被广泛应用于吸附剂，部分原因是它们的合成经济。在我们最近的epsrc资助的研究中，我们已经确定了两种新的机制，通过它们可以实现非常高的吸附选择性。第一种机制是通过化学选择性“活板门”效应，其中占据窗口位置的阳离子只允许与它们强烈相互作用的分子（如二氧化碳）扩散。第二种机制利用一些结构的灵活性来响应其框架外阳离子的组成，因此它们的结构和阳离子组成可以通过“阳离子控制的分子筛分”来调整分子筛分。在这个雄心勃勃的项目中，我们将开发这两种机制的气体分离，沸石不常用作吸附剂，包括我们最近在《自然》杂志上报道的一些二氧化碳吸附剂。新型沸石在动力学分离中的潜在优势（包括对材料的要求少一个数量级）可以承受更高的特定生产成本。因此，潜在的候选吸附沸石的数量增加。为了开发这些新材料并使吸附剂技术的这一步骤改变成为可能，我们组建了一个由材料化学家，计算建模师和化学工程师以及沸石吸附和气体吸附的工业合作伙伴组成的研究团队。材料化学将用于修改和优化所选沸石框架的化学结构，以及它们的结构（粒度、分层孔隙度），用于目标气体分离，化学工程师将对这些新组合物的性能进行测量和宏观建模。多尺度计算模型（通过一系列不同理论水平的技术）将给出机制的详细图像，从而为实验研究提供反馈。这将有助于更好地理解化学结构和动力学与吸附性能的关系。与此同时，在项目会议上与工业项目伙伴进行的持续讨论将使新一代基于沸石的吸附剂的实际开发和利用能够用于工业和环境应用。

Adsorption technology by which gas streams can be purified and separated is essential for many key industries, including those in the oil and gas, chemicals, manufacturing and medical sectors. As a result, solid adsorbents are worth £2.4 billion per year, some 10% of the total industrial gas market. Furthermore, adsorption can offer green, energy-efficient routes to environmental applications, including carbon capture from power generation and other industrial sources. Typically, adsorption is achieved via pressure swing and temperature swing adsorption processes with cycle times of minutes or more. New kinetic-based adsorption technologies, using rotating valves, rotary wheel adsorbers and novel thin layer adsorbent structures can reduce the equipment footprint and increase the efficiency of these processes of gas separation so that, for example, pure gas can be generated on site rather than centrally, with the distribution costs associated with that.Zeolites, microporous aluminosilicates, make up over 30% of industrial adsorbents by value. Their well ordered and robust framework structures impart high selectivity by both molecular sieving and thermodynamics-based separation. Although over 200 zeolitic structure types are known, only a very few find widespread application as adsorbents, in part due to the economics of their synthesis. In our recent EPSRC-funded research, we have indentified two new mechanisms by which very high adsorption selectivity can be achieved. The first mechanism is via a chemoselective 'trapdoor' effect, in which cations occupying window sites only permit diffusion of molecules (such as CO2) that interact strongly with them. The second mechanism makes use of the flexibility of some structures in response to the composition of their extra-framework cations, so that their structure and cation composition can be modified to fine-tune molecular sieving via 'cation-controlled molecular sieving'.In this ambitious project we will develop gas separation by these two mechanism by zeolites not commonly used as adsorbents, including some recently reported by us as CO2 adsorbents in 'Nature'. Their potential advantages of new zeolites in kinetic-based separations (including a requirement for an order of magnitude less material) can enable much higher specific production costs to be tolerated. Consequently, the number of potential zeolite candidates for adsorption is increased. To develop these new materials and make possible this step change in adsorbent technology, we have assembled a research team comprising materials chemists, computational modellers and chemical engineers as well as industrial partners in zeolite adsorption and gas adsorption. Materials chemistry will be used to modify and optimise the chemical structure of chosen zeolite frameworks and also their texture (particle size, hierarchical porosity) for target gas separations, and the performance of these new compositions will be measured and modelled macroscopically by chemical engineers. Multiscale computational modelling (via a range of techniques of different levels of theory) will give a detailed picture of the mechanisms and so provide feedback to inform the experimental studies. This will result in greater understanding of the relationship of chemical structure and dynamics to the adsorption properties. In concert with this, ongoing discussion with industrial project partners at project meetings will enable the practical development and exploitation of a new generation of zeolite-based adsorbents for industrial and environmental applications.