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

Abstract

Detecting phase transitions in high-pressure CO 2 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 CO 2 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.

Measurement of the vapour–liquid equilibrium of binary and ternary mixtures of CO2, N2 and H2, systems which are of relevance to CCS technology

“…methods (Weir and de Loos, 2005) or by sensors (Ke et al, 2010). In this work we have chosen a silica-based, single-mode optical fibre sensor as the detection element for monitoring phase transition.…”

“…Among all of the 11 interpolated points from the literature, 5 points are Table 3 Experimental p-T phase boundary of the binary mixtures of CO2 + H2. (Ke et al, 2010). c Data reported graphically in the reference (Ke et al, 2014).…”

“…These results show that even with a small amount of H 2 (5%) in CO 2 , the lower the temperature, the higher pressure is required to keep the CO 2 stream in a single phase for pipeline transport. Furthermore, we have employed the isobaric search method (Ke et al, 2010) to determine the maxcondentherm temperature. The measured T max is 302.7 ± 0.2 K, which is only 1.5 K below the T c of pure CO 2 .…”

Detection of bubble and dew point using optical thin-film interference

“…As described earlier, the phase boundary between liquid and vapor phase of pure CO 2 disappeared when it reached the critical temperature. However, for mixtures, this maximum temperature is formally the maxcondentherm point [32]. The maxcondentherm temperature of impure CO 2 was successfully identified as 26 • C by top and bottom sensors, as indicated by Fig.…”

Desarrollo de una nueva técnica experimental de medida de equilibrio de fases a alta presión basada en una cavidad cilíndrica resonante en microondas con aplicación al biogás

“…Aunque existen numerosas técnicas desarrolladas englobadas dentro de esta clasificación el más frecuente es el que emplea el cambio de pendiente que sucede cuando las isócoras interseccionan con la envolvente de fase. Ke et al (54) destacan las más recientes que se han desarrollado para determinar transiciones de fase de mezclas a alta presión con CO2 supercrítico con aplicación a la química verde.…”