What Are Zeolites and What Are They Used For?

A zeolite is an oxide structure-an aluminosilicate-having well-defined pores, often between 1 and 20 Ångstroms in size, because of their crystallinity. Stacked tetrahedral structures generate pores of specific sizes so that zeolites can absorb molecules of specific sizes. For that reason, a zeolite can be used in separation procedures. For instance, a particular pore size may be suitable for absorbing a gas such as ammonia out of a stream of gases. Zeolites may occur in nature or be man-made.

Two More Applications

Another application for zeolites is in catalysis reactions to control the positioning of molecules according to shape and size within their pores. This careful positioning is termed a spatial or "steric" influence. This ability is often capitalized upon by the petroleum industry for use in cracking and isomerization reactions. So-called chiral zeolites enable enantiomeric (optically pure) chemical reactions, something not easily achieved.

A third application for zeolites is as ion-exchange agents. So-called "hard" ions such as calcium or magnesium are captured and replaced by soft ions such as sodium or potassium. Thus a very common application is in softening water for industrial and home applications.

Structure Visuals

Structure shapes and pore sizes are determined by a zeolite's chemical structure. Some of these are sketched in a Georgia Tech publication entitled Zeolitic Materials: Ion Exchange and Shape Selective Catalysis. These zeolitic substances are man-made and incorporate other metallic ions such as titanium or germanium and non-metallic ions such as phosphorous within their structure. Thus aluminum bonded to oxygen may be replaced with aluminum bonded to phosphate, etc.

Zeolites Used to Dry Organic Liquids

Sometimes a zeolite can be used to remove on liquid component from another, such as removing water from an alcohol. This depends upon using a zeolite with a very specifically chosen pore design. One component or the other is entrapped in the pores, thus enabling separation. The zeolite used in this instance is termed a molecular sieve. An example of such use is discussed in the article entitled, "Zeolite for Drying of Ethanol-Water and Methanol Water Systems from a Nigerian Clay Resource."¹

In Conclusion

Certain it is that numerous and innovative additional uses will be discovered for the zeolites currently known and ones that are yet to be devised. Shapes and sizes of pores as well as electrical charge are not likely to be the only features that will pave the way for future uses and technologies.

¹Journal of the University of Chemical Technology and Metallurgy, 43, 1, 2008, 109-112, by P.K. Igbokwe, R.O. Okolomike, and S.O. Nwokolo.

Resources and References:

British Zeolite Association - What are Zeolites?

Georgia Tech - Zeolitic Materials: Ion Exchange and Shape Selective Catalysis

University of Tulsa, Professor Geoffrey L. Price - Zeolite Page