"What is Chemistry Good For?"

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Chemistry is Good for Supplying Gases
Liquid Air, Brrrrr-So Cold

Gases are good for many things. A very simple, readily available gas is nitrogen, which has the simple formula N2. It is very nonreactive, colorless, odorless, tasteless, and has a very low boiling point. The usefulness of nitrogen hinges on its physical properties and lack of chemical properties. Since a nitrogen atmosphere is so unreactive, storing metals or other chemicals in an inert nitrogen atmosphere will prevent them from reacting and decomposing or corroding. Foods that are stored in an inert atmosphere are protected from some forms of spoilage. Since the boiling point of liquid nitrogen is extremely low (-196 degrees Celcius), it is used to generate very low temperatures. This can be used for the rapid freezing of foods like meat patties or prepared dinners and can prevent chemical reactions from happening altogether. Nitrogen react with hydrogen to form ammonia if a catalyst is present. Ammonia is an integral part of the fertilizer production process, without which there is no way that farmers could produce enough food to feed the population of the world. Helium and argon, which are even less reactive than nitrogen, are used for the atmospheres in which arc welding is done. Liquid helium boils at 4K, so a liquid helium bath can provide temperatures that are low enough for many materials to be superconductors. The usefulness of even the least reactive gases is impressive. The reactive gases are used to make important materials and a variety of other chemicals.

An essay that even briefly described the uses of all the known gases would be prohibitively long, so let us just consider the production of the gases that are present in our atmosphere, nitrogen and oxygen. If you wanted to isolate pure oxygen, how would you do it? How much pure oxygen is sold each year? Pure oxygen, in addition to being used as a cryogenic fluid and an oxidant for the hydrogen that fuels the space shuttle, is very important in the medical profession for people who have respiratory problems. One of the leading oxygen-producing companies isolates 5000 tons of oxygen per day. WOW!!

For a very long time, the production of oxygen gas relied on a chemical reaction. One such reaction is the thermal decomposition of potassium chlorate to give potassium chloride and oxygen. Producing 5000 tons of oxygen per day would not be possible using this method. In time, as the technology for better refrigeration processes and better compressors was developed, this made the liquefaction of air possible. At very low temperatures and high pressures, air can be condensed into liquid form and then distilled to isolate the components of air in pure form. Remember that at atmospheric pressure, the boiling point of liquid nitrogen is -196 degrees Celcius. It is no small feat of engineering to produce large quantities of liquid air.

Recently, even other innovative technological processes have been developed that rely either on selectively permeable membranes or gas absorbing beds of chemicals to separate the components of air from each other. The membranes allow certain gases such as water vapor and oxygen to pass through them rapidly, while the nitrogen will make it all the way down the length of the membrane tube and be delivered in very high purity. In 1998, the following four companies controlled over 50% of the 30 billion dollar per year industrial gas business: Air Products and Chemicals (United States), L'Air Liquide (France), The BOC Group (United Kingdom) and Praxair, Inc. (United States).

And here are a few good links to get you started.

1. 2. 3. 4.

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