The performance and cost of an adsorptive separation process frequently is dictated by the properties of the adsorbent. A desirable adsorbent has high capacity for the gas component to be removed (while permitting release of that component under regenerating conditions) and has high selectivity for that component relative to the other components of the gas stream. In addition, the adsorbent must be thermally stable and the adsorption process must be reversible to permit re-use of the adsorbent. Thermal stability is required in the activation and dehydration phases of adsorbent manufacture.
One class of adsorbents, the zeolites, are very effective in gas treatment since they posses very high surface areas and have very desirable selectivity properties. Zeolites are crystalline aluminosilicates composed of alumina
and silica tetrahedra interconnected in a 3D cage-like continuous structure in such a way that a regular array of interconnected channels of micro-dimensions is created. These micro channels of sizes typically less than 1 nanometer exclude large molecules from entering while smaller molecules are readily admitted – the name molecular sieve has therefore been attributed to this class of materials. In addition, cations located within this framework provide energetic sites for selective adsorption of particular molecules. In the past, naturally occurring zeolites were used as well as ion-exchanged forms for different applications. Over the last few decades and in particular in the last 5 years, there has been an explosion in the synthesis of novel molecular sieves. Knowledge of the role of individual
constituents of the synthesis mixture in the structure of the molecular sieve has allowed researchers to nano-engineer microporous materials with a wide variety of channel dimensions and properties. Future advances in our knowledge of engineering these inorganic micro-structures promises to have far-reaching consequences for a range of separation and catalytic applications.
This project is focused on developing improved molecular sieve materials for gas separation by atomic modification of the framework structure accomplished through partial substitution of aluminium with other divalent metals. Zeolites of the faujasite (FAU) group, in particular, zeolite X, have been most effective in the separation of nitrogen from oxygen and oxygen from argon. We have selected the separation of air as the test case for our methodology since we have developed extensive testing and characterization facilities for these zeolite materials over the last 5 years. In addition, the existing class of zeolites for air separation is well characterized and fairly well understood and provides a convenient point of departure for development of new adsorbents for air separation. For more information on this project, contact Dr. Ranjeet Singh or Paul Webley.
