Hannay and Hogarth

The superior solvation qualities of supercritical fluids over conventional liquids have been known for more than a century, since 1879 in fact, when Hannay and Hogarth investigated the solubility of different inorganic salts in supercritical ethanol. But it was not until the late 1960s that the extraction potential of supercritical fluids was recognized. 

The enhanced solubility of solids in compressed gases at elevated temperatures and pressures was first noted more than one hundred years ago. Hannay and Hogarth (1) observed that the solubility of salts in compressed ethanol was considerably greater than expected based on the vapor pressure of the salts. Since this early investigation, numerous authors have discussed the phase behavior of solids in dense fluids at elevated temperatures and pressures. 

The ability of a supercritical fluid to dissolve low vapor pressure materials was first reported by Hannay and Hogarth in 1879 (2). 

Industrial applications of supercritical fluids had humble beginnings. The observation of the supercritical phase was first cited in 1822 by Cagniard de la Tour.f In the said work, the disappearance of the gas-liquid boundary by visual inspection of a sealed glass container at elevated temperatures was noted. Following this, in 1879, Hannay and Hogarth reported the ability of an SCF to dissolve low-pressure solid materials. They observed that pressure increases resulted in increased dissolution of metal chlorides in SC ethanol, whereas pressure decreases caused dissolved materials to precipitate as a snow. This increased solubility was later determined to be higher than the solubility predicted by vapor pressure alone. 

The first reported observation of the occurrence of a supercritical phase was made by Baron Cagniard de la Tour in 1822 [3]. He noted visually that the gas/liquid boundary disappeared when heating each of them in a closed glass container increased the temperature of certain materials. From these early experiments, the critical point of a substance was first discovered. The first workers to demonstrate the solvating power of supercritical fluids for solids were Hannay and Hogarth in 1879 [4]. They studied the solubility of cobalt(II) chloride, iron(III) chloride, potassium bromide, and... 

Figure 2.1 Schematic diagram of the experimental apparatus used by Hannay and Hogarth to obtain solid solubilities in supercritical fluids. The glass tubing (a) is first connected to an air manometer and is then immersed in the constant temperature bath (b).

College, Belfast, carried out an extensive investigation in the mid-1800s on the phase behavior of carbon dioxide. In his now quite famous Bakerian Lecture delivered to the Royal Society in 1869 he described his experimental apparatus (which was modified slightly by Hannay and Hogarth) and his observations of the critical properties of carbon dioxide (Andrews, 1875-76). In his lecture he related that... 

This older literature provides very interesting reading. Professor Ramsay, who questioned the results of Hannay and Hogarth, went on to write scores of papers on critical-point phenomena, thermodynamics, and vapor-liquid equilibria, but he was wrong about his hot liquid conclusion. It must be... 

The first reports of solubility phenomena in supercritical fluids emphasized the pressure-dependent dissolution characteristics of high-pressure gases and liquids. But the authors of those early papers point out the potential application of using SCF solvents as media from which to nucleate solid materials. For example, Hannay and Hogarth write in the closing statements of their 1879 publication ... 

The snow and frost described are almost assuredly of different morphology, particle size, and size distribution than the starting material Hannay and Hogarth studied salts such as cobalt chloride and potassium iodide. Incidentally, the reference to the precipitation of the solid is not an Isolated report of nucleation from a supercritical fluid. For example, many other references to snow, fog, fumes, and crystals formed during depressurization of a solution of a solute in a supercritical fluid have been made by researchers studying supercritical fluid solubility phenomena. 

Cagniard de la Tour discovered the critical point in 1822. Hannay and Hogarth reported on the ability of a supercritical fluid to dissolve low vapor pressure solid materials (1). Since then, a spectrum of solids have been studied in a variety of supercritical fluids. Naphthalene is the most extensively studied solute, and carbon dioxide the most popular supercritical fluid. Over the last decade, a large number of books have been published on SFE (2-17). Most of these are proceedings of conferences. McHugh and Krukonis present a good historical review of the research and process applications in this field (8). Bruno and Ely review the theory and practical applications of SFE (3). 

This chapter describes a recent and controversial period of supercritical fluid history, 1977-1987. An outline of the information to be covered in this chapter is given in Table I. The history of supercritical fluid solubility phenomena was summarized in an earlier paper (1). That paper reviewed the first literature report on the subject by Hannay and Hogarth in 1879 (2), the work of many researchers who investigated the phase behavior of various materials dissolved in supercritical fluids (3-5), and some process/product applications of supercritical fluid extraction (6-8). A quite detailed historical development, covering in depth the first score years after 1879, has been published elsewhere (9). 

Thk kind of effect may be called the solvbility of a solid in a gas and it was discovered by Hannay and Hogarth in 1880. In one of their experiments they show that a solution of cobalt chloride could be raked above the critical temperatme, and the dissolved salt was then present in the vapour phase. Its absorption spectrum was the same as in the normal liquid solution. More recently it has been stated that the deposition of silica on turbine blades is due, at least in part, to the solubility of silica in high-pressure steam.f... 

When a gas at high pressure containing a condensable solute expands, the gas is cooled and the solute condenses to form crystalline particles. The production of particles upon decompression of supercritical solutions was first noted over a century ago by Hannay and Hogarth [85]. In recent studies, expansion now typically occurs from a reservoir or flow system through a subsonic or supersonic nozzle. One of the main objectives has been the production of microcrystals with a narrow particle-size distribution. To this end, a number of studies on model systems have been made on the effect of experimental parameters on particle morphology. 

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