Supercritical environmental clean-ups
Odd R. Valmot
Chemical research will soon be offering us a new ally in the struggle for a cleaner environment: supercritical technology. Under supercritical conditions, familiar substances such as water and CO2 acquire new properties that can transform them into important allies in the task of improving our environment.
Linda Jenssen of SINTEF Industrial Chemistry in Oslo is trying to turn supercritical extraction into an ally in the struggle for a better environment.
Most of us have heard of the three phaces solid, liquid and gas. However, the fact that substances also take the form of supercritical fluids at high temperatures and pressures is probably less well known.
The supercritical phase is not a recent discovery. It has been recognised since the 19.th century. However during the recent couple of decades that we have begun to exploit supercritical fluids in industry.
This renewal of interest in supercritical fluids is a result of the hunt for more environmentally friendly technologies. Consumers are demanding "pure" products, and new laws are gradually making it extremely complicated and expensive to produce them according to the methods in use today.
"We have great hopes for industrial applications for supercritical extraction" says Linda Jenssen, a scientist at SINTEF Industrial Chemistry. We have been working on this technology for several years and are currently involved in projects for Norwegian companies.
Replaces harmful solvents
The use of harmful organic solvents is a major problem for many companies. But it is difficult to find replacements for substances such as hexane, toluene, CFC gases, etc. because they display properties that we need, even though they may be environmentally harmful, carcinogenic, explosive, harmful to the ozone layer, etc.One of the properties of supercritical fluids is their ability to dissolve other substances. Supercritical CO2 in particular has turned out to be an excellent solvent.
Supercritical CO2 has been used by the food industry since the late 70s. In Germany, for example, most decaffeinated coffee is produced using this method. Not only does this result in a cleaner industrial process, but it also ensures that the final product is purer because it has not come into contact with harmful solvents.
Combustion without flame
Another use for supercritical fluids is to destroy harmful substances from industrial processes.
Water is another substance that displays unique properties in the supercritical state. By adding oxygen and increasing the temperature and pressure until water enters the supercritical phase, we start a combustion process. This may sound strange, but what happens is that the harmful substances burn up, or oxidize, in the supercritical water. Normal combustion in air takes places at temperatures of 1,000 - 1,200oC, and at such temperatures problematic substances may be formed, which may be difficult to remove.
Cleansing of waste water by traditional methods also consumes a great deal of energy. If we combust organic contaminants in a supercritical state the energy of combustion can fuel the process on its own.