Thursday, July 31, 2014

State funds dry cleaners’ shift to CO2

Wow.  What a great idea.

But... I don't know how they expect something like this to gain wide acceptance.  It's just so much more expensive.

First, the article:
The California Energy Commission’s Public Interest Energy Research Program has produced a dry cleaning machine that uses CO2. The carbon-based cleaning process replaces perchoroethylene chemical-based dry cleaning.

The machine is being tested by the Aramark uniform cleaning corporation in Los Angeles. Colorado-based firm C02Nexus received a $396,200 CEC grant on Dec. 3, 2009 to develop an alternative dry cleaning machine using C02.
Carbon Dioxide is a very powerful solvent.  It's used in the coffee industry to extract caffeine out of the coffee bean, it's that good.

But there is a real problem with this.  CO2 is a great solvent at its super critical point.   The only way to get there is extemely high pressures.

From CO2Nexus' website:
People are more familiar with the practical uses of carbon dioxide (CO2) than they realize. CO2 is the same stuff that puts the fizz in your soda at every restaurant, and dry ice is nothing more than the solid form of carbon dioxide. CO2 can exist as a gas, solid, liquid or supercritical fluid, depending on pressure and temperature.
 The diagram on their website explains where this super critical point is:  31degrees C and 74 bar.

That temperature isn't so bad - this is about 88 deg F. But the PRESSURE is about 1,073 psi!!  I don't know if this is gauge or absolute pressure, but the small difference is inconsequential.

To give you some sort of perspective, a car tire is inflated to 30-35 psi.  A can of hairspray is probably at about 100 psi.

Supercritical CO2 containment is EXPENSIVE.

On the other hand, perchlorethylene, the liquid used in most dry cleaning processes, is used at a much, much lower pressure and require no special containment requirements like supercritical CO2.

I think the answer is to avoid clothes that require dry cleaning.

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