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Supercritical Man

In our ongoing love-hate relationship with carbon dioxide it can only come as a pleasant surprise that the ambivalent molecule that brought us both champagne bubbles and global warming has become a fair-haired child of the emerging field of green chemistry. Using waste CO2 and a deep understanding of an exotic state of matter called supercritical fluids, Lalit Chordia, a Pittsburgh chemical entrepreneur, has turned the secret of supercritical fluids into a company that is out to solve the world’s conflicting energy and food crises in a completely green way. Headquartered in RIDC Park, Dr. Chordia’s company is called Thar Technologies and the technology it uses is supercritical fluid extraction with carbon dioxide.

Supercritical fluids (SCF) occur when gases and liquids are placed under extremes of pressure and temperature, resulting in extraordinary changes in their physical states. Hundreds of degrees centigrade and thousands of pounds of pressure are the norm for supercritical fluids. The only place they occur in nature is at the mouths of thermal vents deep in the world’s oceans. Supercritical fluids exhibit an extraordinary set of physical traits. In a supercritical state, substances are neither solid, gaseous nor liquid. These uncommon properties promise to provide an environmentally friendly answer to the problem of dissolving chemical compounds and separating them into their component parts without using dangerous chemical solvents or producing unfriendly byproducts.

The supercritical state is achieved by precisely manipulating the heat and pressure of a gas or liquid to a critical point at which a gas cannot be turned into a liquid no matter how high the pressure. At that point supercritical fluids adopt a new set of materials characteristics unlike those they would exhibit under normal conditions. When viewed through the lens of elementary physics, some of the characteristics of supercritical fluids are mind-boggling. For instance, because there is no liquid/gas interface in a supercritical fluid, it has zero surface tension. This trait combined with densities, viscosities and diffusivities that cross the line between liquids and gases means that SCFs can dissolve materials as though they were liquid and separate them as though they were gaseous.

While the phenomenon of supercriticality has been known for a century and a half, it was not until recently that advanced pumps and computer controls have made supercritical fluids an important tool in the field of chemistry. Thar Technologies designs and manufactures systems for supercritical CO2 separation, both in small-scale modules for pharmaceutical research and industrial-scale systems for food processing.

The beauty of separation by means of supercritical carbon dioxide is multifold. First, the use of harsh chemical solvents, such as acids and caustics, is avoided entirely, because CO2 is not considered harmful to life at low atmospheric concentrations. Second, the process is a closed loop, so all the CO2 is recovered and reused. Third, the CO2 used in the process is imported from manufacturers who generate CO2 as a waste product. Fourth, because the CO2 does not remain in residual products, they may be consumed safely by humans.

Leveraging supercritical fluid technology for all it’s worth, Thar Technologies has developed a method of making fuel and food in the same process by extracting ethanol from soy beans that yields liquid biofuel and a fat-free edible soy flour byproduct.

In a world hungry for environmentally friendly ways to extract materials, such as caffeine from coffee and liquid fuels from solid plants, supercritical fluids provide a verdant path to the promised land of green chemistry.

This story first appeared in Tom Imerito’s TEQ column, Innovation Chronicles.

©Copyright 2007 Thomas P. Imerito/ dba Science Communications

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©2009 Science Communications