Carbon dioxide isotherm

Carbon dioxide isotherms at —78°C. are also shown in Figure 3. The adsorption of CO2 was relatively slow however, adsorption and desorption points taken at 24-hour intervals seem to represent equilibrium conditions. The pressure scale for CO2 isotherms is given as observed pressure divided by an extrapolated liquid vapor pressure at —78°C. (A plot of the logarithm of vapor pressure of liquid CO2 as a function of reciprocal absolute temperature is linear, and this straight line was the basis of extrapolation. At —78°C. the... 

Fig. 76. Diagrams of mineral equilibria in silicate iron-formations in the absence of carbon dioxide (isothermal sections) / = actual boundaries of stability fields of minerals 2 = boundaries unrealistic under the given conditions S = isobars of fluid pressure (P, = jO + kbar) 4 = isobars of log...

All the nitrogen and argon isotherms could be fitted with the Dubinin-Radushkevich equation between, typically, 10 and p/po 10. At higher pressures capillary condensation causes the isotherm to diverge. At lower pressures the typical deviation described in Fig 1 was observed. The carbon dioxide isotherm showed only a minor deviation from the DR-plot (one point) and was hence excluded from this study. 

Medek J., Possibility of micropore analysis of coal and coke from the carbon dioxide isotherm. Fuel 56 (1977) pp. 131-133... 

Determine the reversible work, in liter-atm., required to expand 1 mole of carbon dioxide isothermally from an initial pressure of 200 atm. to a final pressure of 1 atm. at 50 C, assuming van der Waals behavior. (Instead of solving the cubic equation to obtain the initial and final volumes, they may be obtained more simply by means of the generalized compressibility diagram.) Compare the result mib, that to be expect for an ideal gas. 

Now consider the case depicted in figure 3.20c, an isotherm at the UCEP temperature (see figure 3.19). At the UCEP pressure there is a vapor-liquid critical point in the presence of solid. This requires the solid-liquid equilibrium curve to intersect the liquid-gas envelope precisely at the binary liquid-gas critical point and, hence, exhibit a negative horizontal inflection, i.e., (dPldx)T = 0. Notice that the vapor-liquid envelope has not shrunk to a point, as it did at the naphthalene-ethylene UCEP. The solid curve shown in figure 3.20d is the solubility isotherm obtained if a flow-through apparatus is used and only the solubility in the SCF phase is determined. This solid curve has the characteristics of the 55°C biphenyl-carbon dioxide isotherm shown in figure 3.17. So the 55°C isotherm represents liquid biphenyl solubilities at pressures below 475 bar and solid biphenyl solubilities at pressures above 475 bar. 

Carbon dioxide isotherms at room temperature, and the corresponding surface areas estimated by the Dubinin-Radushkevich equation, are shown in Figures 21 and 22 as a function of reaction time and temperature. CO2 surface areas changed only slightly with CsHe reaction time and ranged between 130 and 170 m /g at 500°C, and 104 to 164 m /g at 700°C. For all samples, no distinct trends are identified on the possible effect of temperature and cracking reaction time on CO2 surface area development. 

Figure 4.4. For a series of activated carbons from PVDC, 0-85 wt% bum-off, the variation of apparent surface area using the BET and DR adsorption equations based on nitrogen (77 K) and carbon dioxide isotherms (195 K) is illustrated. Is there a correct surface area (Marsh and Wynne-Jones, 1964).

The complete isotherm of carbon dioxide a standard isotherm In terms of the characterization of activated carbons, although nitrogen (at 77 K) has been more extensively used than carbon dioxide (at 195 or 273 K) as an adsorbate, it is now appreciated that data from carbon dioxide isotherms are equally informative. In order to understand further the adsorption processes of carbon dioxide (but not specifically to characterize an activated carbon), Guillot and Stoeckli (2001) studied the adsorption of carbon dioxide at 273 K to pressures of 3.2MPa and at 253K to 1.9MPa. 

Informations provided. The nitrogen isotherm provides values of volumes of wider micro-porosity (0.7-2.0nm) and volumes within mesoporosity (2-50 nm). The carbon dioxide isotherm provides values of volumes of narrow microporosity (<0.7 nm). The microcalorimetry describes the chemical composition of the carbon surface by immersion in water (polar) and organic liquids of increasing molecular size (molecular sieving). 

The discussions of Chapter 4 (Section 4.2.5) conclude that the nitrogen (77 K) and carbon dioxide isotherms (273 K) provide micropore volumes in the wider and narrower of the... 

In this work, a series of porous carbon powders is studied using Nitrogen and Carbon Dioxide isotherms at 77 K and 194.5 K, respectively. The pore structure characteristics are deduced and a mechanism of the activation process is proposed. Composite carbon membranes analogues are also studied using both adsorption and permeation techniques. Structural and diffusion characteristics are derived as well as the activation process mechanism of these composite membranes. Finally, the optimum conditions of activation of the membranes are determined. 

FIG. 50 Top Carbon dioxide isotherm measured on Nuxit AL activated carbon at 20°C and its function i/ (P,) middle and bottom The four parts of the isotherms. Measured data (O) calculated data by the Toth equation (-----). 

TABLE 2 Parameters of the Toth Equation Applied to Different Pressure Intervals of the Carbon Dioxide Isotherm... 

In spite of the faets mentioned in points 1, every deviation shown in Table 2 is less than the errors of measuring of an adsorption isotherm ( 2%). This means that every Toth equation with aU of the parameters tabulated in Table 2 can describe the carbon dioxide isotherm with good accuracy. 

Statement 5 is proven in Fig. 50, where the four parts of carbon dioxide isotherm are plotted in middle and bottom parts and die dotted lines represent the calculated isotherms with an average deviation of 1.6%. 

FIG. 51 Deviations between the measured and calculated data as a function of Calculations for the four parts of the carbon dioxide isotherm have been made by the Toth equations. 

Table 6.3 displays the results obtained from the analysis of adsorption isotherms for N2 and CO2 by the Dubinin-Radushkevic (DR) method. The pore volumes measured by the carbon dioxide isotherm are consistently higher than the pore volume... 

The carbon dioxide isotherm at 22 C on y-alumina was found to obey Sips equation [115], which is valid for adsorption, at low pressure, on a non-uniform surface. 

---