Critical point table

Carbon dioxide and water are the most commonly used SCFs because they are cheap, nontoxic, nonflammable and environmentally benign. Carbon dioxide has a more accessible critical point (Table 6.13) than water and therefore requires less complex technical apparatus. Water is also a suitable solvent at temperatures below its critical temperature (superheated water). Other fluids used frequently under supercritical conditions are propane, ethane and ethylene. 

All Ng,C bonds of cations NgCCNg ( Z ) investigated so far are covalent. This is suggested by the properties of the electron and the energy density evaluated at the bond critical points (Table 14). The density data also reflect the fact that the Ne,C bond is actually weaker than the He,C bond due to 2pn-n electron repulsion absent in the He compound. 

As mentioned above, we shall not describe at this point the method of solving the problem of determinacy for functions of two variables (see Appendix, A2). We shall confine ourselves to providing a list of the simplest potential function, having at x = (0, 0) a regular point, a degenerate critical point, for which the problem of determinacy has been solved. In other words, addition of a perturbation to the functions listed in Table 2.4 must not convert a degenerate critical point into another degenerate critical point. Table 2.4 (functions of two variables) is a counterpart to Table 2.1 (functions of one variable). 

Ritchie and Bachrach have examined the relative acidity of strained and unstrained hydrocarbons. The topological population of hydrogen correlates very well with the deprotonation energy of a series of hydrocarbons, better than the C—H distance or the value of the electron density at the C—H bond critical point (Table 13). 

Vapor pressure, triple point, and critical point. Table S.IO gives the triple-point pressure and temperature of UFj measured by Brickwedde et al. [B6], the critical pressure and temperature reported by CXiver et al. [01], and values of the vapor pressure at temperatures between —200°C and the critical point from the following sources ... 

At low temperatures, using the original function/(T ) could lead to greater error. In Tables 4.11 and 4.12, the results obtained by the Soave method are compared with fitted curves published by the DIPPR for hexane and hexadecane. Note that the differences are less than 5% between the normal boiling point and the critical point but that they are greater at low temperature. The original form of the Soave equation should be used with caution when the vapor pressure of the components is less than 0.1 bar. In these conditions, it leads to underestimating the values for equilibrium coefficients for these components. 

Along the saturation line and the critical isobar (22.1 MPa (3205 psi)), the dielectric constant of water declines with temperature (see Fig. 10). In the last 24°C below the critical point, the dielectric constant drops precipitously from 14.49 to 4.77 in the next 5°C, it further declines to 2.53 and by 400°C it has declined to 1.86. In the region of the critical point, the dielectric constant of water becomes similar to the dielectric constants of typical organic solvents (Table 6). The solubiHty of organic materials increases markedly in the region near the critical point, and the solubiHty of salts tends to decline as the temperature increases toward the critical temperature. 

Some values of physical properties of CO2 appear in Table 1. An excellent pressure—enthalpy diagram (a large Mohier diagram) over 260 to 773 K and 70—20,000 kPa (10—2,900 psi) is available (1). The thermodynamic properties of saturated carbon dioxide vapor and Hquid from 178 to the critical point,... 

Properties of Light and Heavy Hydrogen. Vapor pressures from the triple point to the critical point for hydrogen, deuterium, tritium, and the various diatomic combinations are Hsted in Table 1 (15). Data are presented for the equiUbrium and normal states. The equiUbrium state for these substances is the low temperature ortho—para composition existing at 20.39 K, the normal boiling point of normal hydrogen. The normal state is the high (above 200 K) temperature ortho—para composition, which remains essentially constant. 

Table 1. Vapor Pressures and Triple and Critical Points of Hydrogen Isotopes ...

Condensed and converted from tables of Prydz, NBS Rep. 9276, 1967. c = critical point. 

Values of P and v interpolated and converted from tables in Vargaftik, Handbook of Theimophysical Propeities of Gases and Liquids, Hemisphere, Washington, and McGraw-Hill, New York, 1975. Values of h and s calculated from API tables published by the Thermodynamics Research Center, Texas A M University, College Station, t = triple point c = critical point. 

Interpolated hy P. E. Liley from the Landolt-Bornstein hand IVa, p. 677, 1967 tables hy Steinle/Dienemann. c = critical point. The notation 8.84.—4 signifies 8.84 X 10"h... 

Values converted and mostly rounded off from those of Goodwin, NBSIR 77-860, 1977. t = triple point c = critical point. The notation 3.O.—9 signifies 3.0 X 10 . Later tables for the same temperature range for saturation and for the superheat state from 0.1 to 1000 har, 85.5 to 600 K, were published by Younglove, B. A. and J. F. Ely, J. Fhys. Chem. Ref. Data, 16, 4 (1987) 685-721, but the lower temperature saturation tables contain some errors. 

Values converted from tables of Sbank, Theimodynarmc Propeities of UCON 245 Refiigerant, Union Carbide Corporation, New York, 1966. See also Sbank, ] Chem. Eng. Data, 12, 474 80 (1967). c = critical point. Tbe notation 6.46.—4 signifies 6.46 X 10" ... 

Values interpolated and converted from tables of Kang, McKetta, et al.. Bur. Eng. Res. Repr. 59, University of Texas, Austin, 1961. See also J. Chem. Eng. Data, 6 (1961) 220-227 and Am. Inst. Chem. Eng. ]., 7 (1961) 418. c = critical point. The notation 6.189.—4 signifies 6.189 X 10 . The AIChE publication contains a Mohier diagram to 4500 psia, 480 F, while the reprint contains saturation and superheat tables. 

Various methods are available for estimation of the normal boiling point of organic compounds. Lyman et al. review and give calcula-tional procedures for the methods of Meissner, Miller, and Lydersen/ Forman-Thodos. A more recent method that has been determined to be more accurate is the method of Pailhes, which reqmres one experimental vapor pressure point and Lydersen group contributions for critical temperature and critical pressure (Table 2-385). 

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