The Frenkel line and supercritical technologies

Abstract

At present, supercritical technologies use fluids (for example, CO2, H2O) at temperatures and pressures close to critical. It is not currently clear how important critical fluctuations are for dissolution processes and chemical reactions in supercritical fluids. At the same time, our recent work has shown that qualitative changes in the system behavior occurred also at temperatures and pressures much higher than critical. This paper briefly summarizes the latest results of the search and study of the parameters P and T of the changes of dynamic types in supercritical fluids. It turned out that this region of parameters corresponded to a narrow band, namely, the “Frenkel line.” Reaching this line with increasing temperature corresponds to the disappearance of shear excitations in the liquid at all frequencies. The Frenkel line can be considered as a boundary between the liquid and the dense gas at extremely high pressures far from the critical point. Recently, a simple and mathematically rigorous method for finding the Frenkel line was proposed based on analysis of the autocorrelation function of particle velocities. We suggest using the data of the Frenkel line parameters for actual fluids to move supercritical technologies into the region of extremely high pressures exceeding critical ones by tens and hundreds of times.