Book Report

This is a one-page review of a lecture I attended for my Inorganic chemistry lab. Fascinating stuff, yes? -M
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Applications of Molecular Sieves
Seminar Report, Chem 5730
Submitted 22 November 2005

I attended a lecture on molecular sieves presented by Dr. Steve Kuznicki on Friday, 11 November 2005. In this lecture, Dr. Kuznicki discussed both the composition and uses of these remarkable molecules.

Dr. Kuznicki first explained the nature of molecular sieves. They are uniformly porous inorganic structures with charged surfaces. Structurally, they resemble stacked straws, with chains of certain key atoms held together by rings of other atoms. This creates a three-dimensional grid through which molecules of certain sizes can pass. The holes in certain molecular sieves can be made to specific sizes. For example, the holes in titanosilicate sieves such as CTS1 shrink predictably when heated. The size of these holes can be controlled to allow for very precise molecular selectivity.

Dr. Kuznicki also talked about several important applications of sieves. One example was air separation, which has traditionally been done by distillation. Using sieves, however, oxygen and nitrogen can both be separated from air at conditions close to room temperature and normal atmospheric pressure.

A second application of sieves involves separating nitrogen from natural gas. Inert nitrogen gas exists in natural gas in concentrations up to fifteen percent, which makes the natural gas burn less efficiently. With molecular selectivity of as little 0.80 Ångstroms, sieves can be used to trap nitrogen molecules as natural gas flows past. When the sieve is full, the pressure is reversed and nitrogen flows out. Natural gas purity can be increased effectively and inexpensively by this procedure.

One final example involves hydrocarbon cracking. The tar sands of Alberta are thought to contain oil reserves equal to approximately four hundred billion barrels, or about forty percent of the world's known supply. But recovering oil from tar sand is difficult. The density and viscosity of the source material creates problems, and tar sand typically contains about four and a half percent sulphur. Nickel and vanadium contamination are also problems, making the procedure expensive and very hard on catalysts.

Natural molecular sieves may be the solution to these problems. Fossilized zeolite deposits in Arizona could be used to catalyze the recovery of petroleum from tar sand. The structure of these zeolites is such that hydrocarbon cracking can take place on the outside of each zeolite fossil platelet. Impurities such as sulphur and heavy metals would be trapped on the inside of the platelets. This process, if successful, would provide significant financial advantages. The catalyst would be available for pennies per pound, a substantial saving over traditional hydrocarbon cracking catalysts. The waste product—essentially just dirt—could be disposed of equally inexpensively.

Dr. Kuznicki concluded his presentation by providing a look at the structures of specific sieves and talking about other possible uses such as mercury scavenging. His lecture was very informative. Molecular sieves are playing an increasing role in some important industrial processes, and research opportunities in the field are plentiful. Having made many advances in the field himself, Dr. Kuznicki would make an excellent mentor for those wishing to explore chemistry in this emerging discipline.