Cation-Controlled Gating for Selective Gas Adsorption over Adaptable Zeolites

Project: Research council


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 searation 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.
Effective start/end date1/11/1631/10/19