to Supercritical Fluids
Supercritical fluids are highly compressed gases which combine properties
of gases and liquids in an intriguing manner. Fluids such as supercritical
xenon, ethane and carbon dioxide offer a range of unusual chemical possibilities
in both synthetic and analytical chemistry.
We are exploring the use of supercritical CO2 (scCO2)
as an environmentally acceptable alternative to conventional solvents for
reaction chemistry, so called "Clean Technology". In addition, supercritical
fluids can lead to reactions which are difficult or even impossible to
achieve in conventional solvents.
The book by McHugh and Krukonis gives an
excellent introduction to the properties of supercritical fluids. The definition
of a supercritical fluid usually begins with a phase diagram, which defines
the critical temperature and pressure of a substance. (CO2 ;
Tc = 31.1 °C, Pc = 73.8 bar). A recent review
by Poliakoff & Darr gives a comprehensive overview of 'New Directions
in Inorganic and Metal-Organic Coordination Chemistry in Supercritical
Fluids' Chem. Rev. 1999, 99,
Supercritical fluids have solvent power similar to a light hydrocarbon
for most solutes. However, fluorinated compounds are often more soluble
in scCO2 than in hydrocarbons; this increased solubility is
important for polymerisation.
Solublity increases with increasing density (i.e. with increasing pressure).
Rapid expansion of supercritical solutions leads to precipitation of a
finely divided solid. This is a key feature of our flow
The fluids are completely miscible with permanent gases (eg N2
or H2) and this leads to much higher concentrations of dissolved
gases than can be achieved in conventional solvents. This effect has been
exploited in both organometallic
reactions and hydrogenation.
Supercritical Fluid Extraction: Principles & Practice, McHugh, M. A.,
Krukonis, V. J. ; Butterworth-Heinemann, Boston, 1994.
New Directions in Inorganic and Metal-Organic Coordination Chemistry in
Supercritical Fluids, Jawwad A. Darr and Martyn Poliakoff, Chem. Rev.1999,
Supercritical Fluids as Solvents for Chemical and Materials processing,
Eckert, C. A., Knutson, B. L., Debendetti, P. G., Nature, 1996,
Homogeneous Catalytic Hydrogenation of Supercritical Carbon Dioxide, Jessop,
Ph. G., Ikariya, T., Noyori, R., Nature 1994, 368, 231.
Recent Publications from Nottingham
Intermediates in Organometallic and Organic Chemistry: Spectroscopy, Polymers,
Hydrogenation and Supercritical Fluids, Poliakoff M. and George, M. W.
Phys. Organic Chemistry, 1998, 11, 589-96.
A Supercritical Success Story, Poliakoff M., Meehan N. J., and Ross S.
K., Chemistry & Industry 1999, 19, 750-52.
University of Nottingham Welcome
Chemistry Welcome page
The Clean Technology
Research Group Welcome page
Page created by: Simon Poliakoff
Created: July 1997
Last Revised: January 2001