Phase equilibria eutectic data

The COt Acceptor Gasification Process is discussed in light of the required properties of the CaO acceptor. Equilibrium data for reactions involving the CO% and sulfur acceptance and for sulfur rejection jit the process requirements. The kinetics of the reactions are also sufficiently rapid. Phase equilibrium data in the binary systems CaO-Ca(OH)t and Ca(OH)jr-CaCOs show the presence of low melting eutectics, which establish operability limits for the process. Data were obtained in a continuous unit which duplicates process conditions which show adequate acceptor life. Physical strength of many acceptors is adequate, and life is limited by chemical deactivation. Contrary to earlier findings both limestones and dolomites are equally usable in the process. Melts in the Ca(OH)2-CaC03 system are used to reactivate spent acceptors. 

As discussed in the chapters above reliable model parameters are most important. While mainly VLE data are used in the chemical industry, it is recommended to use all kinds of reliable data (phase equilibrium data (VLE, azeotropic data, SLE of eutectic systems, etc.), excess enthalpies) for fitting simultaneously -model parameters, which often have to be temperature dependent. To account only far the deviations from Raoult s law, it is recommended to use the pure component vapor pressures measured by the authors for every data set. This can be done by multiplying the vapor pressure with a correction factor, for the Antoine equation, this corresponds to changing the parameter A to A. Sometimes a large number of experimental data are available. 

The low melting eutectics in the CaO-Ca (OH) 2-CaC03 system undoubtedly explain the formation of melts in the gasifier at temperatures of 1500°-1600°F. whenever the steam pressure exceeds the critical value of 13 atm. The equilibrium data above clearly show that Ca(OH)2 cannot exist as a solid phase under these conditions at such low steam pressures. Liquids with melting points below 1600°F. must exist in the above ternary systems where the activity of Ca(OH)2(l) is sufficiently... 

An example of the type of melting point phase diagram that can be obtained for a conglomerate system is shown in Fig. 6, which illustrates one-half of the phase diagram reported for 4,4 -demethyl-8,9,10-trinor-spiro-2,2 -bornane [40]. Below the eutectic temperature of 67°C, the system exists as a mixture of solid o-enantiomer and L-enantiomer. At the exact composition of the racemic mixture X= 0.5), the system will exist entirely in the liquid phase above the eutectic temperature. At mole fractions where the amount of L-enantiomer exceeds that of the o-enantiomer, the system will exist as an equilibrium mixture of racemic liquid and solid L-enantiomer. As required by the phase diagram of a conglomerate, the eutectic temperature is the lowest temperature attainable at which any liquid phase can exist in equilibrium with any solid phase. An excellent fit of the data according to the Schroder-Van Laar equation was obtained, with XH = 5.9 kcal/mol and Tp = 95°C. 

A juxtaposition of the data in Fig. 4.9 with the equilibrium phase diagram of the Pb—Sb system presented in Fig. 4.3 indicates that, at 252 °C and up to 3.5 wt% loading level in the alloy, antimony has the highest solubility in a-Pb dendrites. On cooling, the dendrites get oversaturated with Sb and reorganisation of the structure of the solid phases starts, whereby the content of Sb in the a-Pb dendrites diminishes to 0.1% at room temperature. This improves the mechanical properties of the alloys. At Sb content between 3.0 and 11 wt%, the amount of the eutectic phase in the alloys changes but slightly, which results in minor improvement of their mechanical properties. 

For a simple eutectic and a racemic compound-forming system in Figure 3.30, the measured ternary phase diagrams of the amino acid threonine and the fine chemical mandelic acid, both in water as solvent, are exemplarily shown. The diagrams contain equilibrium data measured in isothermal experiments as described in Section 3.3.5.2. Different temperatures were applied. All solubihties are related to the solid phases given, no solvate was found. Most points measured refer to... 

To produce equilibrium phase data, several cells were loaded, sealed only at the filled end, and stored at room temperature within a 90% RH chamber (prepared from a saturated zinc sulfate solution in equihbrium with crystals and water vapor). After 2 weeks, initiation and DIT studies using these cells displayed none of the above-described behavior. Instead, swelling to form liquid crystal phases occurred at and above the Krafft eutectic temperature. Similar procedures were followed and similar observations made during the dioctadecyldimethylammonium chloride (DOD-MAC)-water DIT study [39]. The difference, in the case of DODMAC, was that much longer equilibration times were required to achieve equilibration (4 months). 

---