Carbon dioxide pressure/temperature diagram

Figure 9.1. Carbon dioxide pressure-temperature phase diagram adapted from McHugh and Krukonis (1994).

Carbon dioxide pressure-temperature phase diagram. 

Available data on the thermodynamic and transport properties of carbon dioxide have been reviewed and tables compiled giving specific volume, enthalpy, and entropy values for carbon dioxide at temperatures from 255 K to 1088 K and at pressures from atmospheric to 27,600 kPa (4,000 psia). Diagrams of compressibiHty factor, specific heat at constant pressure, specific heat at constant volume, specific heat ratio, velocity of sound in carbon dioxide, viscosity, and thermal conductivity have also been prepared (5). 

Fig. 16.1. Phase diagram for carbon dioxide critical temperature 31.3°C critical pressure 72.9 atm.

Blockages of valves and pipes can also occur by gas hydrates. Such adducts can be formed by a number of gases with water. In Fig. 7.1-5 the pressure-temperature diagram of the system propane/water with an excess of propane is presented. The line, (g), shows the vapour-pressure curve of propane. Propane hydrate can be formed at temperatures below 5.3°C. At pressures below the vapor pressure of propane a phase of propane hydrate exists in equilibrium with propane gas (Fig. 7.1-5, area b). At higher pressures above the vapor pressure of propane and low temperatures a propane hydrate- and a liquid propane phase were found (area d). In order to exclude formation of gas hydrates these areas should be avoided handling wet propane and other compounds like ethylene, carbon dioxide [14], etc. 

Figure 5. Pressure-temperature diagram for the naphthalene-CC system. and K are the critical points of pure carbon dioxide ana naphthalene, respectively. The...

Figure 2. Quantitave pressure-temperature diagram for carbon dioxide-water-1-propanol O, exp. ternary critical points, this work O four-phase equilibria, this work x four-phase equilibria, Fleck et al. [5]...

Pressure-temperature diagrams offer a useful way to depict the phase behaviour of multicomponent systems in a very condensed form. Here, they will be used to classify the phase behaviour of systems carbon dioxide-water-polar solvent, when the solvent is completely miscible with water. Unfortunately, pressure-temperature data on ternary critical points of these systems are scarcely published. Efremova and Shvarts [6,7] reported on results for such systems with methanol and ethanol as polar solvent, Wendland et al. [2,3] investigated such systems with acetone and isopropanol and Adrian et al. [4] measured critical points and phase equilibria of carbon dioxide-water-propionic acid. In addition, this work reports on the system with 1-propanol. The results can be classified into two groups. In systems behaving as described by pattern I, no four-phase equilibria are observed, whereas systems showing four-phase equilibria are designated by pattern II (cf. Figure 3). 

Figure 5. Pressure-temperature diagram for carbon dioxide-water-1-propanol — critical lines calculated with Peng-Robinson EOS using the mixing rule of Panagiotopoulos-Reid, parameters fitted to ternary three-phase equilibria at temperatures between 303 and 333 K...

Figure 4 Schematic diagram showing the pressure-temperature behavior for a carbon dioxide / solvent / polymer mixture as a function of carbon dioxide concentration. The diagram shows both the low-temperature (UCST) and the high-temperature (LCST) regions of liquid-liquid immiscibility.

The effect of polymer type and polymer level on the phase boundaries can be shown on a pressure-temperature diagram by keeping the carbon dioxide level and solvent type constant. For low to medium polymer levels, experiments show that the polymer type and polymer level have little effect on the L-LV boundary (bubble-point line) (16). This is illustrated in Figure 6 for four systems having 30% carbon dioxide and tetrahydrofiiran (THF) as the solvent. The following polymers and solvent/polymer ratios were used polybutadiene (PB) at 19/1, 9/1, 5.7/1 as well as with polymethyl methacrylate (PMMA) at 5.7/1. The L-LV boundaries for each system have the same slope and nearly overlap. 

Figure A33 Photos of carbon dioxide during transition through (a) critical and pseudocritical points and (h) corresponding pressure—temperature diagram (Gupta et al., 2013).

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. 

Diagrams of isobaric heat capacity (C and thermal conductivity for carbon dioxide covering pressures from 0 to 13,800 kPa (0—2,000 psi) and 311 to 1088 K have been prepared. Viscosities at pressures of 100—10,000 kPa (1—100 atm) and temperatures from 311 to 1088 K have been plotted (9). 

Use the phase diagram for carbon dioxide (Fig. 8.7) to predict what would happen to a sample of carbon dioxide gas at —50°C and 1 atm if its pressure were suddenly increased to 73 atm at constant temperature. What would be the final physical state of the carbon dioxide ... 

N2 and CO2 have triple points that are well below room temperature. Although both are gases at room temperature and pressure, they behave differently when cooled at P = 1 atm. Molecular nitrogen liquefies at 77.4 K and then solidifies at 63.3 K, whereas carbon dioxide condenses directly to the solid phase at 195 K. This difference in behavior arises because the triple point of CO2, unlike the triple points of H2 O and N2, occurs at a pressure greater than one atmosphere. The phase diagram of CO2 shows that at a pressure of one atmosphere, there is no temperature at which the liquid phase is stable. 

Phase diagrams for molecular nitrogen and carbon dioxide, two substances that are gases at room temperature and pressure. 

Figure 6.4 On the left is a phase diagram for carbon dioxide. Broken lines indicate isotherm crossing at either constant pressure or density. On the right is illustrated the change in solubility of naphthalene as a function of temperature and pressure.

The melting point of carbon dioxide increases with increasing pressure, since the solid-liquid equilibrium line on its phase diagram slopes up and to the right. If the pressure on a sample of liquid carbon dioxide is increased at constant temperature, causing the molecules to get closer together, the liquid will solidify. This indicates that solid carbon dioxide has a higher density than the liquid phase. This is true for most substances. The notable exception is water. 

E) Normal means 1 atm (760 mm Hg) pressure. Boiling occurs at a temperature at which the substance s vapor pressure becomes equal to the pressure above its surface. On this phase diagram, at 1 atm pressure, there is no intercept on a line separating the liquid phase from the gas phase. In other words, carbon dioxide cannot be liquefied at 1 atm pressure. It is in the liquid form only under very high pressures. At 1.0 atm pressure, solid C02 will sublime — that is, go directly to the gas phase. 

The discovery of supercritical fluids occurred in 1879, when Thomas Andrews actually described the supercritical state and used the term critical point. A supercritical fluid is a material above its critical point. It is not a gas, or a liquid, although it is sometimes referred to as a dense gas. It is a separate state of matter defined as all matter by both its temperature and pressure. Designation of common states in liquids, solids and gases, assume standard pressure and temperature conditions, or STP, which is atmospheric pressure and 0°C. Supercritical fluids generally exist at conditions above atmospheric pressure and at an elevated temperature. Figure 16.1 shows the typical phase diagram for carbon dioxide, the most commonly used supercritical fluid [1]. 

Brady et al. [52] have discussed pressure-temperature phase diagrams for carbon dioxide polychlorobiphenyls and examined the rate process of desorption from soils. Supercritical carbon dioxide was used to extract polychlorobiphenyls and DDT and Toxaphene from contaminated soils. 

Each substance has its own phase diagram to display how temperature and pressure determine its properties. Figure 7-4 is the phase diagram for carbon dioxide. 

Look at the phase diagram for carbon dioxide (CO2) in Figure 10-lb. If you put carbon dioxide under a pressure of 4.5 atm at a temperature of 23°C, in what phase of matter would the carbon dioxide be What are the triple point and the critical point of carbon dioxide according to the phase diagram ... 

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