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Zeolite refrigerants

February 6, 2006 | A version of this story appeared in Volume 84, Issue 6

Your article "Hot Times Ahead For Refrigerants" deals with a subject with which I have been familiar since I first met Claude Blaizat more than 25 years ago (C&EN, Oct. 3, 2005, page 23). Blaizat is a French inventor who has patented the use of zeolites to transfer heat by evaporating and condensing water under vacuum. The technologies that he has derived from this concept are based upon three well-known thermodynamic properties of water. These are as follows: water evaporating from a substrate cools the substrate, water condensing on a substrate heats the substrate, and absence of air increases the speed of evaporated water transfer.

Zeolites are a type of clay characterized by its very special porous structure. Zeolites can selectively adsorb water evaporated from a substrate at temperatures as low as -40 oC, adsorb water evaporated from a substrate at temperatures as high as 150 oC, and be regenerated at relatively low temperature (200 to 300 oC). Furthermore, while adsorbing water, these zeolites generate twice as much heat as would be generated by condensation. Also, since the pore structure is specific to the water molecule, the zeolite will not adsorb other molecules-particularly those of aromas and flavors.

The following applications have already been demonstrated in the food industry: Quick evaporative cooling of fresh and cooked products; freezing with minimal effect on the texture of the food product; blanching, cooking, and cooling fruits and vegetables without production of wastewater; and drying food at very low temperatures.

The technology has already been successfully lab tested to manufacture refrigerated containers of up to 10,000-gal capacity that do not require energy to maintain their load at low temperature, as long as there is water available and the zeolite load that they carry is not saturated in water. A heat pump that could draw its energy either from a renewable source such as biomass or from the exhaust gas of a cogeneration thermal engine has also been successfully tested.

That this technology has never been industrially developed puzzles me. Maybe the price of oil is still way too low and the greenhouse effect way too unproven? The Department of Energy and the Natural Resources Ecology Lab told me that the matter had been extensively discussed and investigated and that it would never work.

I have seen it work and work well and maintain a 22-foot container between 0 and 3 oC for several days without wires or an onboard generator. Chances are, however, that Blaizat will probably end up paraphrasing a very famous scientist by saying, "And yet it cools."

Jean-Paul Vignal
Argyle, Texas



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