Carbon dioxide pressure/composition diagrams

Figure 4. Pressure-Composition diagrams for poiy(elhyiene giycoi) carbon dioxide systems at 313 K.

In binaiy mixtures of caibon dioxide and the normal hydrocarbons heavier than C7, coexisting liquid-vapour, liquid-liquid, and liquid-liquid-vapour phase splits have been observed above 273.15 K. Pressure-composition diagrams predicted by the PR equation of state for carbon dioxide/decane mixtures at two different temperatures are shown in Figures 5. At 260 K, binaiy mixtures of carbon dioxide and decane separate into a liquid and a vapour phase at low pressures. As the pressure is increasexl, a value is... 

Figure 1.2 Pressure/composition diagrams for carbon dioxide/pentane (a Class A system) at temperatures above and below the critical temperature (31.1°C) of carbon dioxide. (Data from ref. [70].)...

Figure 1.3 Phase behaviour of carbon dioxide/water system at temperatures between the critical hydrate temperature and the upper critical solution temperature, (a) Typical pressure/composi-tion diagram for carbon dioxide/water (a Class B2 system) at temperatures below the critical temperature of carbon dioxide but above the critical hydrate formation temperature. Data for arms B and C are shown in (b) and (c) respectively, (b) Solubility of liquid CO2 in water as a function of temperature and pressure (arm C in (a)), (c) Solubility of water in liquid CO2 as a function of temperature and pressure (arm B in (a)), (d) The three phase pressure curve compared with the vapour pressure curve of carbon dioxide showing the critical locus CsU (i.e. locus of points such as C on (e) where vapour properties merge with those of solvent-rich liquid). (Data reference [75].) (e) Detail of the isothermal pressure/composition diagram at 25°C (on left) and at temperature between Tc and Tu (on right). Subscripts 1 and 2 denote water-rich and C02-rich phase. Critical point C is shown as blocked-in circle. (Data reference for (b) and (c) is [81].)...

Figure 1.6 Pressure/composition diagrams for carbon dioxide/water system at temperatures above 250°C. Critical points are shown as blocked-in circles. Position of minimum M in critical locus estimated from data assembled in ref. [76] (see also ref. [79]).

Figure 1.7 Pressure/composition diagrams for carbon dioxide/squalane system. (Data of Liphard and Schneider (1975) J. Chem. Thermodynam. 1 805.)...

Figure 1.8 Pressure/composition diagrams for carbon dioxide with rape oil or soybean oil at temperatures 40 to 100°C and pressures to 100 bar. (Plotted from data of Klein and Schulz [73], Friedrich [74] and Stahl and Quirin [78].) Critical point at 100°C shown as blocked-in circle. The diagrams for the two oils are very similar in the range shown and no distinction is made in this figure.

Class B1 systems show closed loop vapour/liquid pressure/composition diagrams in the vapour liquid region at all temperatures between the solvent critical temperature and the critical temperature of the heavy component. The system ethane/methanol shows this behaviour. Carbon dioxide/w-hexadecane is probably also of this type (Figure 1.10 and 1.11). 

Figure 1.10 Pressure/composition diagram for carbon dioxide//i-hexadecane (a Class B1 system) at 26.5°C, showing the very restricted range over which liquid CO2 is partially miscible with the -hexadecane. Vapour/liquid equilibria have not been investigated in detail in the immediate vicinity of the vapour pressure for pure CO2 but probably take the form shown in the inset, the mole fraction of CO2 at the point Q being about 0.98. The three phase pressure (P ") is probably about 2 bar less than the CO2 vapour pressure (P°). Subscripts 1 and 2 denote hexadecane-rich and...

Figure 1.11 Pressure/composition diagram for carbon dioxide/n-hexadecane (a Class B1 system)...

As seen in chapter 1 the system carbon dioxide/water is a Class B2 system (Figure 1.6) and this is almost certainly true also of mixtures of carbon dioxide with the natural oils (Figure 1.8). Such systems show low mutual solubilities with the liquid solvent below its critical temperature and form open loop pressure/composition diagrams for a small range of temperatures above the solvent critical temperature. 

In contrast to natural oils and water, some components found in the herbs and spices listed in the appendix to chapter 6 have quite substantial solubilities in liquid carbon dioxide, or are completely miscible with it. Some of these (for example, limonene, cinnamaldehyde, eugenol, hexanol and pinene) were studied by Francis [5], who found that limonene, hexanol and pinene were completely miscible. These are Class A (or possibly Class C) systems. They would thus be anticipated to show closed loop pressure/ composition diagrams at temperatures above the critical temperature of carbon dioxide and to become totally miscible with supercritical carbon dioxide at comparatively low pressures. 

The locations of the tietriangle and biaodal curves ia the phase diagram depead oa the molecular stmctures of the amphiphile and oil, on the concentration of cosurfactant and/or electrolyte if either of these components is added, and on the temperature (and, especially for compressible oils such as propane or carbon dioxide, on the pressure (29,30)). Unfortunately for the laboratory worker, only by measuriag (or correcdy estimatiag) the compositions of T, Af, and B can one be certain whether a certain pair of Hquid layers are a microemulsion and conjugate aqueous phase, a microemulsion and oleic phase, or simply a pair of aqueous and oleic phases. 

The formation of carbonates in the system is limited mainly by the presence of active forms of Si02 and by the concentration of S. On the composite diagram (Fig. 40) the siderite field is represented by a sector of small area in environments with a pH of 5.5 to 6.2 and Eh from +0.05 to — 0.05 V, even at high partial pressure of carbon dioxide (1.0-0.01 bar) with other parameters siderite is replaced by Fe(OH)3 and iron silicates or sulfides. 

The equilibrium phase compositions for PEG - carbon dioxide systems were experimentally measured. The data for PEG(400) - CO2 and PEG(600) - CO2 systems were obtained at 313 K. The PEG(400) > CO2 and PEG(IOOO) - CO2 systems were also studied at 323 K. The pressure versus composition diagrams are presented in Figures 4 and 5. The equilibrium compositions are reported as weight percent of the PEG. 

Figure 4. A (left). Demixing pressures for solutions of poly (dimefhylsiloxane) (Mw = 94,300 and MW/MN = 3) in supercritical carbon dioxide at different concentrations. B (tigh Pressure-composition phase diagram at 350 K.

For a pure substance, the phase diagram is simply a graph of temperature versus pressure. For mixtures, the phase diagram also includes variables that describe the composition of the substance. To illustrate the information contained in a phase diagram, we will examine the phase diagrams of two pure substances water and carbon dioxide. 

Figure 8. Pressure-equilibrium phase composition diagram for isobutane-carbon dioxide system, calculations using Peng-Robin-son equation of state...

Fig. 15.32 Phase composition diagram of water and carbon dioxide [15, 38] and water and nitrogen [39] as a function of pressure...

Supercritical CO2. Union Carbide patented the novel use of supercritical carbon dioxide paint application as a means to effectively lower the VOCs of coatings. In this process, supercritical carbon dioxide, at conditions above critical temperature and pressure in the phase diagram (for CO2 the critical point is 72.8 atm and 31.1°C) acts as a liquid, and is utilized as a solvent enabling a coating to be applied at increased solids and reduced VOCs. Coating composition can remain essentially the same. Advantages of this technology include VOC emission reductions (up to 80% of the solvent can be removed), increased... 

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