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.