Phase behaviour is the oldest topic in supercritical fluid science.
However our group is one of very few that is developing new methods of measuring phase boundaries and the critical points of mixtures relevant to reaction chemistry in SCFs.
Our approach is to devise methods which (i) do not require a window so that the measurement is objective and (ii) if possible, to automate the experiment. Developments have included:
- Time of flight acoustic measurements for locating critical points “How does the Critical Point Change During a Chemical Reaction? A Study of the Hydroformylation of Propene in Supercritical CO2” (J. Ke, B. Han, M. W. George, H. Yan and M. Poliakoff) J. Am. Chem. Soc. (2001) 123, 3661-3670.
- A new experimental approach for locating critical points using a single sensor. “Sensing the Critical Point of High-Pressure Mixtures” (J. Ke, R. M. Oag, P. J. King, M. W. George and M. Poliakoff) Angew. Chem. Intl Ed. Eng. (2004) 43, 5192-5195.
- Use of a single shear-mode sensor to locate those boundaries and even to detect the presence of three phases. “A New Method for Locating of the Vapor-Liquid Critical Point of Multi-Component Fluid Mixtures Using a Shear Mode Piezoelectric Sensor” (J. Ke, P. J. King, M. W. George and M. Poliakoff) Analytical Chem. (2005) 77, 85-92. “The Application of a Shear Mode Piezoelectric Sensor to Monitoring the High Pressure Phase Behavior of Asymmetric Binary Systems” (J. Ke, K. Reid and M. Poliakoff) J. Supercrit. Fluids (2007) 40, 27–39
- Use of a fibre optic reflectometer to measure phase separation, even inside an operating reactor bed, and also to measure the so-called “gas expansion” of organic solvents by scCO2 “The Fibre Optic Reflectometer: a New and Simple Probe for Refractive Index and Phase Separation Measurements in Gases, Liquids and Supercritical Fluids” (M. V. Avdeev, A. N. Konovalov, V. N. Bagratashvili, V. K. Popov, S. I. Tsypina, M. Sokolova, J. Ke and M. Poliakoff) Phys. Chem. Chem. Phys. (2004) 6, 1258 – 1263. “A New Design of Fiber Optic Reflectometer for Determining the Phase Boundary of Multi-Component Fluid Mixtures at High Pressures and High Temperatures” (W. Wu, J. Ke and M. Poliakoff) Rev. Sci. Inst. (2006) 77, 023903.
- Use of a flame ionisation detector (FID), a new synthetic dynamic method for rapid determination of phase boundaries at high pressures and temperatures. "A New Continuous Method for Performing Rapid Phase Equilibrium Measurements on Binary Mixtures Containing CO2 or H2O at High Pressures and Temperatures" (A. A. Novitskiy, E. Perez, W. Wu, J. Ke and M. Poliakoff) J. Chem. Eng. Data, (2009), 54 1580–1584
We have devised an apparatus for demonstrating phase transitions to the general public. “’Supercriticality’; A Dramatic but Safe Demonstration of the Critical Point.” (P. Licence, D. Lichfield, M. P. Dellar and M. Poliakoff) Green Chem., (2004) .6, 352-354.
"Variable-Volume View Cell for the Determination of Phase-Equilibria in High Pressure Systems and Supercritical Fluids.” (P. Licence, M. P. Dellar, R. G. M. Wilson, P. A. Fields, D. Litchfield, M. Poliakoff and S. M. Howdle) Rev. Sci. Inst., (2004) 75, 3233-3236.
We always welcome e- mails to martyn.poliakoff@nottingham.ac.uk from those interested in this area or who would like reprints of papers.