Crystallization triple point

Both phosphonitrilic fluorides are solid, colorless, volatile substances at room temperature. They are thermally stable up to 300°C. The trimer boils at 51.8°C and crystallizes in monoclinic prisms. Triple point 27.1°C. It polymerizes to a rubbery form Iqr heating for 15 hours at 350°C. The tetramer boils at 89.7°C and forms triclinic-pinacoidal crystals. Triple point 30.4°C. 

Hence we can jnst deduce from microstructural features what was the composition of the liquid phase. The crystallized triple points were Ta Sij and Ta StjC j with Zr or Hf impnrities. Moreover in the solid solution region, oxygen traces were detected, that means this liquid dragged oxygen-bearing species present on the particles surface. It can therefore be conclnded that a Ta-Si-C-0 based liquid, where Zr, Hf (and Ta) were soluble in, formed dnring densification. 

The crystallized triple points are Ta Sij, Ta SiB and Ta gSijC j with Zr or Hf traces, so we can assume that they are derived from a Ta-Si-B-C-0 based liquid, where the IV group transition metals are soluble. Moreover in the shell region, oxygen traces were also detected, that means this liquid took part in the removal of oxygen-bearing species from powder surfaces. 

At equilibrium, in order to achieve equality of chemical potentials, not only tire colloid but also tire polymer concentrations in tire different phases are different. We focus here on a theory tliat allows for tliis polymer partitioning [99]. Predictions for two polymer/colloid size ratios are shown in figure C2.6.10. A liquid phase is predicted to occur only when tire range of attractions is not too small compared to tire particle size, 5/a > 0.3. Under tliese conditions a phase behaviour is obtained tliat is similar to tliat of simple liquids, such as argon. Because of tire polymer partitioning, however, tliere is a tliree-phase triangle (ratlier tlian a triple point). For smaller polymer (narrower attractions), tire gas-liquid transition becomes metastable witli respect to tire fluid-crystal transition. These predictions were confinned experimentally [100]. The phase boundaries were predicted semi-quantitatively. 

At high pressures, solid II can be converted (slowly) to solid III. Solid III has a body-centered cubic crystal structure. Line bd is the equilibrium line between solid II and solid III, while line be is the melting line for solid III.P A triple point is present between solid II, solid III, and liquid at point b. Two other triple points are present in this system, but they are at too low a pressure to show on the phase diagram. One involves solid II, liquid, and vapor while the other has solid I, solid II, and vapor in equilibrium. 

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... 

White monoclinic crystal sublimes at 317°C melts at 432°C at 33 atm (triple point) critical temperature 452.5°C critical pressure 53.49 atm critical volume 314 cm /mol hydrolyzes in water. 

White tetragonal crystals refractive index 1.973 hardness 1.5 Mohs density 7.16 g/cm3 does not have a normal melting point triple point 525°C sublimes at 383°C insoluble in water, ethanol and ether. 

YeUowish-white tetragonal crystals pungent odor fumes in air dehques-cent density 2.1 g/cm decomposes on heating melts at 166.8°C under the pressure of its own vapor(triple point) sublimes at 160°C critical temperature 373°C hydrolyzes in water soluble in carbon disulfide and carbon tetrachloride. 

White monoclinic crystals density 5.09 g/cm melts at 64°C (triple point) sublimes at 56.6°C critical temperature 232.65°C critical pressure 46 atm critical volume 250 cm /mol reacts with water forming UO2F2 and HF soluble in chloroform, carbon tetrachloride and fluorocarbon solvents soluble in liquid chlorine and bromine dissolves in nitrobenzene to form a dark red solution that fumes in air. 

White monoclinic crystals hygroscopic density 2.80 g/cm sublimes at 331°C triple point 437°C vapor pressure 1 torr at 190°C critical temperature 504.85°C critical pressure 56.95 atm critical volume 319 cm /mol decomposed by water soluble in alcohol, ether, and concentrated hydrochloric acid. 

Stability Limit 1, With the exception of helium and certain apparent exceptions discussed below. Fig. I gives a universal phase diagram liir all pure compounds The triple point of one P and one T is the single point at which all three phases, crystal, liquid, and gas. are in equilibrium. The triple point pressure is normally below atmospheric. Those substances, c.g.. CO . / - 3H85 mm. 7, = -5ft.fi C. for which it lies above, sublime without melting ai atmospheric pressure. 

The CNG process removes sulfurous compounds, trace contaminants, and carbon dioxide from medium to high pressure gas streams containing substantial amounts of carbon dioxide. Process features include 1) absorption of sulfurous compounds and trace contaminants with pure liquid carbon dioxide, 2) regeneration of pure carbon dioxide with simultaneous concentration of hydrogen sulfide and trace contaminants by triple-point crystallization, and 3) absorption of carbon dioxide with a slurry of organic liquid containing solid carbon dioxide. These process features utilize unique properties of carbon dioxide, and enable small driving forces for heat and mass transfer, small absorbent flows, and relatively small process equipment. 

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. 

The triple-point crystallization of carbon dioxide is illustrated in Figure 7, which shows a schematic carbon dioxide phase diagram expanded about the triple-point and a closed-cycle triple-point crystallizer operating with pure carbon dioxide. The operation of this closed-cycle unit is identical to that of a unit in the stripping section of a continous crystallizer cascade, except that in the cascade vapor would pass to the unit above, and liquid would pass to the unit below. 

The adiabatic flash pressure Pf, maintained slightly below the triple-point pressure, causes liquid to spontaneously vaporize and solidify. The ratio of solid to vapor is determined by the heats of fusion and vaporization for carbon dioxide about 1.7 moles of solid are formed for each mole vaporized. The solid, more dense than the liquid, falls through a liquid head and forms a loosely packed crystal bed at the bottom. The liquid head is about 10-12 feet, and increases the hydrostatic pressure on the solid to melter pressure Pm. The crystal bed depth is about two... 

Figure 7. Carton dioxide, triple point crystallization.

Concentration changes observed between mother liquor in the flash zone and liquid product in the melt zone of an experimental triple-point crystallizer have been dramatic. A qualitative concentration profile typical of those observed in the experimental unit is shown in Figure 8. The mother liquor concentration is relatively uniform above the packed bed, but a sharp drop in contaminant concentration occurs within the top several inches of the loosely packed crystal bed. Concentration changes of the order 500 to 5000 have been observed for representative sulfurous compounds and trace contaminants, including hydrogen sulfide, carbonyl sulfide, methyl mercaptan, ethane, and ethylene. Concentration profiles calculated for the packed bed of solid carbon dioxide using a conventional packed bed axial dispersion model agree very well with the observed experimental profiles. 

The process features of carbon dioxide triple-point crystallization and slurry absorption of carbon dioxide have been demonstrated with the first generation bench-scale apparatus. Current efforts are focused on the design and construction of an improved version of the carbon dioxide triple-point crystallizer in cooperation with the U S Department of Energy. Future efforts are planned to design and construct absorption units to study multi-stage slurry absorption of carbon dioxide, and the more conventional gas-liquid absorption of sulfuruous compounds with liquid carbon dioxide. 

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