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Research That Gelled
BNH speaks with Andrew Hamilton, Irenee duPont Professor of Chemistry at Yale, who headed the research team that succeeded for the first time in turning supercritical carbon dioxide into gel form
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Business New Haven
12/13/1999
By: Tammy Rachau
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Give us an overview of your current research involving carbon dioxide.
We have discovered a family of very novel molecular structures which are able to turn supercritical carbon dioxide, which is carbon dioxide in the liquid form, into a gel form - basically, to turn it into a Jell-O-like material. That is important for two reasons: First, it allows us to control the viscosity of carbon dioxide as a liquid. That is something that people have been trying to do, unsuccessfully, for a very long time. Secondly, it allows us create a whole new class of materials.
To touch upon the first, supercritical carbon dioxide is a liquid that is of great interest at the present time because many people believe it will be the organic solvent of the next several decades. Currently the chemical industry uses huge amounts of organic solvents to carry out chemical processes. But of course disposal of those organic solvents - such as fluorocarbons and benzenes and alkine - is not only expensive; it also represents quite a serious environmental challenge. So there's a great deal of interest in finding solvents that are environmentally benign, but that can also be quite easily removed, without the same impact on the environment. One possible solvent is supercritical CO2 under high pressure. CO2 is a liquid and has properties that are quite attractive as an organic solvent. One of the less attractive properties of CO2 as an organic solvent is its low viscosity. What we've shown is that we can control that viscosity, making it thicker. We hope that that will lead to some potential application of supercritical CO2 in the chemical industry.
Tell us about the creation of the new materials.
We found - and this is somewhat of a surprise - that once we gelled supercritical CO2 under high pressure, turning it into a solid, Jell-O-like material, that when we released the pressure - and, as a result, released the CO2 as a gas - we were left behind with a material that did not change shape. It was the same shape that it was under the pressure: When the pressure was released, it didn't shrivel, it didn't shrink. If you leave Jell-O out in the open and allow the water to evaporate, it shrivels into a much, much smaller volume. What we found with this special CO2 gel that we had created is that when we allowed it to evaporate we were left behind with a material that had the same shape as it did when the CO2 was present. What we had produced here is something called an aerogel, a solid material that is something like two percent of the density of most liquids or solids. So what we've got now is the beginning of a new batch of materials with an extremely low density - almost foam-like materials. What we can do is control the properties of the foam, the size of the holes in the foam. We think that that will have all kinds of applications in insulation materials, possibly even in the design of novel catalyst and novel separation materials.
What would be some concrete applications of supercritical CO2?
I won't say that there are concrete applications for the new materials - those are things that are on the horizon of potential applications for the new material. In terms of gelling supercritical CO2, there is one very real application: It is in what is called enhanced oil recover. Oil in the ground does not gush out, as you might imagine. In reality, that the oil stays in the ground and has to be pushed out. Usually what is used to push it up is water. But the consequence of that is that the water is then contaminated with oil, and that contaminated water has to be cleaned up. That is an expensive process with the obvious environmental degradation. There's an enormous amount of interest in using supercritical CO2 for the same thing because you're doing it under high pressure, pushing it into the ground to push the oil out and then getting rid of the supercritical CO2 is a simple matter of allowing it to evaporate. So there's a lot of interest in using supercritical CO2 to replace water. One major problem in its use is its very low viscosity, so enhancing the viscosity of the CO2 will lead to its application, we believe, as an enhanced oil-recovery process.
How did you first become interested in this research?
This is a collaboration with the University of Pittsburgh, a group led by professors Eric Beckman and Robert Enick. My interest in this area came from my discussions with those scientists [about] the problems that are currently encountered in CO2 use. [There was] long-standing interest in my laboratory in molecular recognition, the way in which molecules interact with each other. We thought we could design a synthetic molecule that, at very low concentrations, would self-assemble in supercritical CO2 solution and create the gelling properties that we were looking for. So that's where our interest in the research began.
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