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About Zeolites
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Report
Zeolites
- Frequently Asked Questions
What
are zeolites?
Zeolites are three-dimensional, micro porous, crystalline solids
with well-defined structures that contain aluminum, silicon, and
oxygen in their regular framework; cations and water are located
in the pores. The silicon and aluminum atoms are tetrahedrally
coordinated with each other through shared oxygen atoms. Zeolites
are natural minerals that are mined in many parts of the world.
Zeolites have void space (cavities or channels) that can host
cations, water, or other molecules. Because of their known structure,
they behave in a predictable fashion.
When were zeolites discovered?
In 1755, the Swedish mineralogist Axel Fredrick Cronstedt discovered
that stilbite, a natural mineral, visibly lost water when heated,
and he named the class of minerals zeolites from the classical
Greek words meaning 'boiling stones.' Zeolites were considered
an obscure group of minerals with unique properties for almost
200 years, and Cronstedt was remembered primarily for discovering
the element nickel.
What are some major applications for zeolites?
ADSORPTION - Zeolites are used to adsorb a variety of materials.
This includes applications in drying, purification, and separation.
They can remove water to very low partial pressures and are very
effective desiccants, with a capacity of up to more than 25% of
their weight in water. They can remove volatile organic chemicals
from air streams, separate isomers and mixtures of gases.
CATALYSIS
- Zeolites can be shape-selective catalysts either by transition
state selectivity or by exclusion of competing reactants on the
basis of molecular diameter. Zeolites can also be acid catalysts
and can be used as supports for active metals or reagents. They
have also been used as oxidation catalysts.
ION
EXCHANGE - The largest volume use for zeolites is in detergent
formulations where they have replaced phosphates as water-softening
agents. They do this by exchanging the sodium in the zeolite for
the calcium and magnesium present in the water.
Are
zeolites stable?
Many zeolites are thermally stable to over 500 degrees Celsius.
Some are stable in an alkaline environment, and some are stable
in acidic media. They are also stable to ionizing radiation and
can be used to adsorb radioactive cations.
How do zeolites separate molecules?
Zeolites can separate molecules based on size, shape, polarity,
and degree of saturation, among others.
Are zeolites re-usable?
Zeolites should they become saturated with adsorbed water due
to continual levels above equilibrium can be regenerated using
relatively easy methods, such as heating or placing in sunlight
to remove adsorbed water.
What makes zeolites special when compared with other inorganic
oxide materials?
The combination of many properties, among them: the micro porous
character of the uniform pore dimensions, the ion exchange properties,
the ability to develop internal acidity, the high thermal stability,
the high internal surface area. These make zeolite unique among
inorganic oxides.
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