Carbon dioxide phase diagram, schematic

The triple-point crystallization of carbon dioxide is illustrated in Figure 7, which shows a schematic carbon dioxide phase diagram expanded about the triple-point and a closed-cycle triple-point crystallizer operating with pure carbon dioxide. The operation of this closed-cycle unit is identical to that of a unit in the stripping section of a continous crystallizer cascade, except that in the cascade vapor would pass to the unit above, and liquid would pass to the unit below. 

The phase diagram for carbon dioxide is shown schematically in Fig. 12.7. The solid-liquid line slopes slightly to the right, since > I oiid- Note that liquid CO2 is not stable at pressures below 5 atm. For this reason dry ice is dry under ordinary atmospheric pressure. When carbon dioxide is confined to a cylinder under pressure at 25 °C, the diagram shows that if the pressure reaches 67 atm, liquid CO2 will form. Commercial cylinders of CO2 commonly contain liquid and gas in equilibrium the pressure in the cylinder is about 67 atm at 25 °C. 

Figure 1. Schematic phase diagram of carbon dioxide and views of the transition at the critical point in a window-equipped high-pressure reactor 10 bar = 1 MPa.

Figure 6.3 Schematic of a SFC installation using a HPLC packed column. Carbon dioxide reaches a supercritical state between the pump and the injector. A pressure regulator ( restrictor ), is located after the column and either before or after the detector, depending upon its type. It maintains the mobile phase under supercritical conditions until the outlet of the column A modifier added in small quantity (less than 10 per cent) enables to control the selectivity of the analytes (diagram based upon a document from Vydac).

Fig. 1 Schematic phase diagram and critical data of carbon dioxide.

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