C02 system

Clayton, T. D., Byrne, R. H., Breland, J. A. et al. (1995). The role of pH measurements in modern oceanic C02-system characteristics precision and thermodynamic consistency. Deep-Sea Res. II42,411 30. 

Galivel - Solastiuk F., S. Laugier and D. Richon, "Vapor-Liquid Equilibrium Data for the Propane-MethanoI-C02 System", Fluid Phase Equilibria, 28, 73-85 (1986). 

In the following section we will now briefly describe natural and anthropogenic disturbances of the C02 system which will later be discussed based on the box-diffusion model. 

Several observations could be made from these copolymerizations. High yields ofhigh-molecular-weight copolymer can readily be formed at incorporation levels well in excess of the 2-4 wt% PPVE desired in commercial products. For reactions done in the C02 system, even at high vinyl ether incorporations, melt-... 

Concerning estimation of the activity of CO2 in the fluid phase, besides carbonate equilibria (discussed in some detail in section 8.10), equilibria in the CaO-Si02-C02 system are also important. In the medium-low metamorphism of limestones, the equilibrium... 

Heinen, W. and Lauwers, A. M. (1997). The iron-sulfur world and the origins of life abiotic thiol synthesis from metallic iron, H2S and CO2 a comparison of the thiol generating FeS/HCl(H2S)/C02-system and its Fe /H2S/C02-counterpart. Proc. 

In their test system, the researchers used the ionic liquid l-butyl-3-methylimidazol-ium hexafluorophosphate (bmim)(PF6), which is stable in the presence of oxygen and water, with naphthalene as a low-volatility model solute. Spectroscopic analysis revealed quantitative recovery of the solute in the supercritical CO2 extract with no contamination from the ionic liquid. They found that CO2 is highly soluble in (bmim)(PF6) reaching a mole fraction of 0.6 at 8 MPa, yet the two phases are not completely miscible. The phase behavior of the ionic liquid-C02 system resembles that of a cross-linked polymer-solvent system (Moerkerke et al., 1998), even though... 

Fig 3.4-6. Effect of pressure on the surface tension of the squalene/C02 system from [12] with permission of Steinkopff Verlag... 

This picture fits very well with the tendency of the sorption isotherm curvature (and hence of the site sorption mode) to disappear at T > Tg. On a more quantitative level, the above characterization of the Henry sorption mode is supported by the smooth temperature dependence of K, found in the PET-C02 system 12), which indicates a roughly unchanged enthalpy of sorption AH, above and below Tg. Additional support is provided by the correlation between K, and the Lennard-Jones parameter s/k characteristic of the gaseous penetrant, in accordance with... 

X-Ray diffraction data for simple C02 systems is severely limited but discrete C02 complexes may be divided into three types, which are illustrated diagrammatically in (6a-c). 

Walther et al. improved the Na0Ph/C02 system by tuning the role of the solvent, such that the carboxylation of acetone was carried out selectively by sodium phenoxide with N-methyl-caprolactam under 0.1 MPa C02 to afford 3-ketoglutaric acid in 65% yield [34]. The same authors reported the conversion of acetyl-naphthalene (acetonaphthone) to acetyl-naphthalene carboxylic acid with 84% yield, and of cyclohexanone to cyclohexane-2,6-dicarboxylic acid in 56% yield. 

Jonas and co-workers (68) used Raman spectroscopy to study the naphthalene-C02 system under high pressure. The experimental results (a blue shift of the C-H stretching and C-H out-of-plane bending modes) and model calculations presented indicate that quadrupole-quadrupole coupling is significant in this system. The preferred orientation of the 0=C=0 and naphthalene were determined to be face-to-face. 

Moreover, under a particular set of conditions, the extraction efficiencies for the SC-C02 system were typically found to be very similar to the corresponding values in dodecane. The strong correlation between the SFE and conventional SX results for the two ions suggests that the solvation behavior of SC-C02 is similar to that of dodecane for the TBP system. Substitution of a stronger Lewis base, such as triph-enyl- (TPPO), tributyl- (TBPO), or trioctylphosphine oxide (TOPO) for TBP, generally yielded higher extraction efficiencies for both uranium and thorium. For both TBPO and TOPO, in fact, extraction was nearly quantitative over the entire range of... 

Although not all of the factors that influence homogeneous hydrogenation and hydroboration in sc C02 are fully understood, it is clear that the use of sc C02 can lead to an increase in selectivity for some reactions. Additional work is needed to understand the opportunities for further selectivity enhancements and catalyst separation/recycle strategies. Even sc C02 systems that exhibit similar selectivities to those obtained in organic solvents could offer a practical, environmentally responsible method for the production of many important chiral building blocks. 

The use of sc C02 instead of toluene as a solvent leads to some rate enhancement in these two systems, although it is clear that this activity is still not practical for most nonpolar, nonvolatile substrates. Significant improvements to the biphasic water/supercritical C02 system were accomplished by forming H20/C02 emulsions using newly developed surfactants (Jacobson et al., 1999). Three different surfactants were used that form water in C02 (w/c) or C02 in water (c/w) emulsions (1) anionic surfactant perfluoropolyether ammonium carboxylate, (2) cationic Lodyne 106A, and (3) nonionic poly(butylene oxide)-h-poly(ethylene oxide). The low interfacial tension, y, between water and C02 (17 mNm-1 at pressures above 70 bar), which is significantly lower than water/alkane systems (30-60 mNm-1),... 

The systems selected for evaluation are the PDMS-C02 system studied by Gerhardt et al. (1997, 1998) and PS-gas systems studied by Kwag et al. (1999). Properties for these systems are listed in Table 11.1. The variation in physical properties between these systems provides a very broad basis for evaluating the rheological properties of polymer-gas systems. The PDMS C02 system exhibits a favorable thermodynamic affinity between the polymer and dissolved gas, and provides the opportunity to evaluate the rheology of melts with very high dissolved gas content (up to 21 wt %). Carbon dioxide is much less soluble in polystyrene than in PDMS, so the PS-C02... 

The viscoelastic scaling factor ac is displayed as a function of C02 content for PDMS-C02 systems and PS-C02 systems in Figure 11.7. Clearly, ac varies much more sharply with C02 content for the PS-C02 systems, which are 45-70 °C above Tg of pure PS, than for the PDMS-C02 systems, which are 178-208 °C above Tg of pure PDMS. Moreover, the fine details of the data show that the slope of the ac versus wco, curves decrease with increasing temperature for both the PDMS-C02 and PS-C02 data. Thus, temperature exerts a strong influence on ac. At temperatures within 75 °C of Tg of the pure polymer, a few percent dissolved gas dramatically reduces the viscosity of the melt, reflected by the ac values that are on the order of 10-2 to 10 3. 

Chow (1980), Condo et al. (1994), Wissinger and Paulaitis (1991), and others. Condo et al. (1994) and Wissinger and Paulaitis (1991) and have shown that the Tg of polystyrene can be reduced to values as low as 35 °C by the addition of about 10 wt % C02. Rudimentary calculations employing the Williams-Landel-Ferry (WLF) equation show that the scaling factors presented in Figure 11.7 are consistent with the Tg measurements cited earlier for the PS-C02 system. 

Figure I 1.7. Variation of viscoelastic scaling factors with gas content for PS-C02 and PDMS-C02 systems. Lower scaling factor values for PS-C02 system, compared with PDMS-C02 system, are due to the closer proximity of the experimental temperatures to Tg of the pure polymer. The top curve displaying results for iso-free volume dilution of high-Mw polystyrene by low-Af polystyrene represents the effect on viscosity of volumetric dilution of high-Mw chains. Viscosity reductions for polymer-gas systems are significantly lower than the iso-free volume dilution curve, indicating that viscosity reduction is primarily due to free volume contributed by dissolved gas.

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