Detecting phase transitions in supercritical mixtures: an enabling tool for greener chemical reactions

Detecting phase transitions in high-pressure CO2 and supercritical fluids was first attempted in the nineteenth century. By contrast, Green Chemistry, the design and implementation of cleaner methods of manufacturing and processing chemicals, is barely 20 years old. Now, the use of CO2 as an environmentally more acceptable replacement for traditional solvents for greener chemical reactions is creating the need for new, more rapid methods for elucidating high-pressure phase behaviour. This paper describes the advantages and limitations of a number of approaches, developed in Nottingham, to meet this need, including acoustic measurements, shear-mode quartz sensors, the fibre-optic reflectometer, the use of holey fibres, attenuated total reflectance infrared spectroscopy and pressure drop measurements.