Supercritical Water - Gas and Liquid at the Same Time!

The Explanation:

"Supercritical" means, that simple substances such as water or carbon dioxide are made into very effective solvents and reaction media. If they are heated under pressure far beyond their boiling point, the density of their vapour becomes almost as dense as a liquid. In that supercritical state - liquid and gaseous at the same time - these substances show completely new physical characteristics, such as high dissolving powers. Water, for example, is all of a sudden able to dissolve oil and other organic compounds at 374 degrees Celsius and 221 bar. If the pressure or the temperature is lowered, the water loses this increased dissolving power. The solving characteristics of supercritical fluids can be altered within a wide range by pressure or temperature changes. Supercritical fluids can be recovered and therefore they can be used again and again.

Coffee Without Caffeine - Is that Possible?

Nowadays, coffee is decaffeinated by the so-called Bach method, which was invented in 1957. The coffee is put into a high-pressure tank (70-90°C, 100-200 bar) and treated with steam and CO₂. The steam disperses equally and condenses and the CO₂ turns to liquid because of the high pressure. Now the liquid CO₂ reacts with the water and forms carbonic acid. In turn, the carbonic acid dissolves the caffeine from the coffee beans. The aroma, on the other hand, remains in the coffee. At the proper pressure, the carbonic acid is called supercritical, because it shows solvent-like properties. After the extraction, the carbonic acid transports the caffeine to activated charcoal. The activated charcoal absorbs the caffeine and the carbonic acid returns to the coffee. Then the activated charcoal is reactivated by heating it without an oxygen supply. If the oxygen was not kept away from the charcoal, the charcoal would burn to ashes. During the heating process, the caffeine dissolves from the activated charcoal and can be recovered for various means. The remaining activated charcoal is used again. At the end of the whole process, the moist decaffeinated coffee is dried so that it can be roasted like normal raw coffee.

In contrast to other solvents, CO₂ is environmentally friendly and harmless to health, since it is a major part of the air. In addition, it is easy to handle.