I think this paper is highly cited because in it we describe a
totally new way of recovering solutes from ionic liquid solutions.
Ionic liquids are organic salts that are liquids around room
temperature. Since they are salts, they have no measurable vapor
pressure, so they can't cause air pollution. There is a tremendous
amount of growing interest in ionic 
liquids,
although a significant amount of this activity has been in the
chemistry community. In the paper we show that you can extract all
kinds of things from ionic liquids with supercritical CO2 (which is
generally considered an environmentally benign solvent since CO2 is
used, not produced). This is one of the first papers dealing with
separating things from ionic liquids.
Does
it describe a new discovery or a new methodology that's useful to
others?
We published our very first results on the possibility of using
supercritical CO2 to extract solutes from ionic liquids in Nature
in 1999. That paper has over 100 citations at the moment. This was
an entirely new idea that no one had ever thought of or tried
before.
So I guess it was a "new discovery". In the Nature
paper we showed the general phase behavior and that it worked for
one particular compound. The Ind. Eng. Chem. Res. paper is
the follow-up to the Nature paper. In the Ind. Eng. Chem.
Res. paper we demonstrated the generality of the idea by showing
that it is possible to extract a wide variety of compounds from
ionic liquids with supercritical CO2 without any cross-contamination
(no ionic liquid is in the CO2, just the desired solute). This work
is useful to people in a variety of fields, especially those who are
interested in recovering products from ionic liquids after they've
done a reaction, without having to resort to extraction with
volatile (and, therefore, environmentally unfriendly) organic
solvents. Researchers doing enzymatic reactions in ionic liquids
have shown particular interest because they can separate their
products from the ionic liquid at relatively mild conditions that
don't damage the enzymes.
Could
you summarize the significance of your paper in layman's terms?
This work is significant because it advances the development of
two alternative solvents which could significantly reduce air
pollution (ionic liquids and supercritical CO2) for practical
applications.
How
did you become involved in this research?
I had formerly done research on supercritical fluids. I was at a
DOE/EPA workshop and I heard a lecture by Prof. Ken Seddon (Queen's
University of Belfast) on ionic liquids. I was sitting in the back
of the room with a colleague from the University of Pittsburgh
(Prof. Eric Beckman) and we decided we wanted to do something with
ionic liquids and supercritical CO2 (since we both did research with
supercritical fluids). After a variety of iterations, this very
simple and elegant idea was hatched. And when the student tried it,
it worked on the very first try!
Joan Brennecke
Keating-Crawford Professor
Department of Chemical Engineering
University of Notre Dame
Notre Dame, IN, USA
