We’re all familiar with the three states of matter – Liquid, solid and gas.
Let’s look at water.
- Between 32 and 212 degrees F, water is a liquid.
- Below 32 degrees F, water freezes and becomes a solid.
- Above 212 degrees F, water becomes steam and is a gas.
- If we raise the temperature of water to 705 degrees F and raise the pressure to 3191 PSI, it goes supercritical.
Carbon dioxide is the gas most often used to create supercritical fluid.
Carbon dioxide is:
- safe and environmentally friendly
- recyclable
- inexpensive
- readily available
Importantly – by using existing CO2, there is no increase in greenhouse gases
The conditions for supercritical carbon dioxide are very mild. CO2 becomes supercritical around 1073 PSI and 90 degrees F (31 degrees C and 74 bar.) That’s less than body temperature!
So, what is supercritical fluid
It’s not a gas, it’s not a liquid, but it has the properties and advantages of both. It has the density to dissolve but behaves like a gas. It is permeable, has high diffusivity, low viscosity, no surface tension, and it leaves no residue.
Are supercritical fluids only a laboratory phenomenon?
No! For example, supercritical water can be found on the ocean floor around sub-marine volcanoes. At a depth of three kilometers, pressure is over three hundred atmospheres. The water is super-heated to over 375 degrees F. In areas where tectonic plates interface or where sub-marine volcanoes exist, the water in that vicinity may be supercritical.