Triple-point separation

CNG [Consolidated Natural Gas] A process for removing acid gases from natural gas and syngas, using supercritical carbon dioxide. Under development since 1973 by the Consolidated Natural Gas Research Company with assistance from the U.S. Department of Energy and Helipump Corporation. Liquid carbon dioxide is first used to extract the sulfur compounds. Crystallization at the triple point separates these sulfur compounds from the... 

Grain Boundary Sliding and Triple-Point Separation... 

When the sample is a solid, a separation of the analyte and interferent by sublimation may be possible. The sample is heated at a temperature and pressure below its triple point where the solid vaporizes without passing through the liquid state. The vapor is then condensed to recover the purified solid. A good example of the use of sublimation is in the isolation of amino acids from fossil mohusk shells and deep-sea sediments. ... 

Molten Salt Distillation. Hafnium tetrachloride is slightly more volatile than zirconium tetrachloride, but a separation process based on this volatility difference is impractical at atmospheric pressures because only soHd and vapor phases exist. The triple point for these systems is at about 2.7 MPa (400 psia) and 400°C so that separation of the Hquids by distillation would necessarily require a massive pressurized system (13). 

In the phase diagram, panel (a). solid C02 (Dry Ice) is in equilibrium with gaseous C02 at a temperature of —78.7°C and a pressure of 1.00 bar." The solid sublimes without turning into liquid. At any temperature above the triple point at —56.6°C, there is a pressure at which liquid and vapor coexist as separate phases. For example, at 0°C, liquid is in equilibrium with gas at 34.9 bar. Moving up the liquid-gas boundary, we see that two phases always exist until the critical point is reached at 31.3 C... 

Marx and Dole and Miyake have presented descriptive models for the 19° C transition in terms of order-disorder theories. Studies of transitions at high pressure in polytetrafluoroethylene have been reported by Bridgman, Weir (1953), and Beecroft and Swenson. The phase diagram in Fig. 7 shows that in addition to the two crystalline phases which are separated by the 19° transition at atmospheric pressure there is a third modification at high pressures. The triple point has been... 

The CNG acid gas removal process is distinguished from existing AGR processes by three features. The first feature is the use of pure liquid carbon dioxide as absorbent for sulfurous compounds the second feature is the use of triple-point crystallization to separate pure carbon dioxide from sulfurous compounds the third feature is the use of a liquid-solid slurry to absorb carbon dioxide below the triple point temperature of carbon dioxide. Pure liquid carbon dioxide is a uniquely effective absorbent for sulfurous compounds and trace contaminants triple-point crystallization economically produces pure carbon dioxide and concentrated hydrogen sulfide for bulk carbon dioxide absorption the slurry absorbent diminishes absorbent flow and limits the carbon dioxide absorber temperature rise to an acceptable low value. The sequence of gas treatment is shown in Figure 1, an overview of the CNG acid gas removal process. 

Figure 3. (a) The derivative of f with respect to <5i. The lamellar phase cannot exist in the regions where the derivative is positive, (h) The derivative of f with respect to 62. The lamellar phase cannot exist in the regions where the derivative is positive, (c) The contour plot of the derivatives off with respect to hi and 62, respectively. At line 1, df/ddi = 0 and at line 2, 3/7 3 2 = 0 (inside each of the marked domains delimited by lines 1 and 2, an excess phase separates). The intersections of the line 1 and 2 are triple points, where the lamellar phase is in equilibrium with both excess phases. 

It can be seen that the equilibrium coexistence of two different anisotropic phases is also possible for this case. As in Sect. 2 this fact leads to the existence of the critical point in the phase diagram, as well as to the sharp broadening of the phase separation region below the triple point temperature. 

The fact that the temperature, at which the high-temperature expression for (l) matches with the low temperature one, is of the same order of magnitude as the triple point temperature, and the fact that the width of the high-temperature phase separation corridor is constant can be proved in the same way as in Sect. 2. 

Fig. 6. Phase diagram for the solution of semi-flexible macromolecules. I isotropic phase, II anisotropic phase. III phase separation region. Dotted curves - phase diagram for the solution of rigid rods with the same p (see Fig. 2). T3 triple point temperature, 6 the theta temperature...

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