The cell is fitted with Sapphire windows in each end, which allow for viewing of all phases and any phenomena appearing during experiments. The temperature, measured by platinum resistance thermometers, is monitored and recorded over time through a computer.
Detailed description
The main part of the equipment is the high-pressure equilibrium cell, specially designed for this application. The equilibrium cell is situated in a liquid bath (water or glycol dependent on temperature range), where the temperature is regulated by external liquid circulation thermostat, enabling temperature to be held constant within 0.5 K
The cell is in stainless steel, which is fitted with sapphire windows in each end. The inner diameter of the cell is 25mm. The sapphire windows have a thickness of 30mm and it was dimensioned according to the properties of the material provided by the supplier, to cope with pressures of 30MPa for extended periods of time.
The synthetic sapphire single crystal (Al2O3, 99.9%) was acquired from Encole LLC, USA, with a polishing better than 0.1 micrometer Ra (the average radius of the irregularities or cavities in the surface is inferior 0.1 micron).
An important part of the equilibrium cell, is the possibility of proper stirring of the mixture. The stirring should be powerful enough, so that all phases (vapor–liquid–liquid) get mixed properly and equilibrium is achieved. The stirring is done using powerful magnets from Supermagnete, Germany.
A winged axis is placed within the cell, situated in a small sapphire bearing in the center of each sapphire window. The axis is powered by a magnetic belt, which is fitted on the outside of the cell, similar fitted with high powered magnets.
The principal idea is that the magnetic belt turns the axis within the cell, without any direct contact, since the magnets are powerful enough, to work through the thick stainless steel cell.
The equilibrium cell is fitted with two automatic electromagnetic capillary ROLSITM samplers a product developed by the CENERG-TEP laboratory of the ENSMP (École Nationale Supérieure des Mines de Paris), with patents registered to Armines (PCT patent 2004/090508, PCT patent 2000/011462, EPO patent EP 1105722) and commercialized by Transvalor, France.
Gas chromatograph used for the experimental set-up is a PR2100 GC System (Alpha Mos, France). The GC is equipped with a RTX1 capillary column (This can be changed to Packed column Shincarbon ST 80/100 or Column RTX-WAX, dependent on the experimental needs).
Publications
Michael Frost, Nicolas von Solms, Dominique Richon, Georgios M. Kontogeorgis, “Measurement of vapor–liquid–liquid phase equilibrium—Equipment and results,” Fluid Phase Equilibria 405 (2015) 88–95