Poly(ethylene-co-methyl acrylate)-solvent-cosolvent phase behaviour at high pressures

Cosolvency effect of SF6 on the solubility of poly(tetrafluoroethylene-co-19 mol % hexafluoropropylene) in supercritical CO2 and CHF3

“…Second, SF 6 decreases the polarity of the mixed solvent because it is nonpolar. Note that the addition of SF 6 to the FEP 19 -CO 2 mixture causes a nonlinear decrease in cloud-point conditions. The cloud-point curve with 47 wt % SF 6 is much closer to the binary FEP 19 -SF 6 curve than to the FEP 19 -CO 2 curve even though on a molar basis the mixed solvent is predominantly CO 2 .…”

“…Figure 3 shows that SF 6 has a dramatic impact on the location of the cloud-point curve. Cloud-point pressures drop from 1500 bar to 1150 bar at 260°C with the addition of 9 wt % (5 mol %) SF 6 . The addition of 51 wt % (35 mol %) SF 6 further lowers the cloud-point pressures to Ϸ800 bar.…”

“…CO 2 is a poor quality solvent for FEP 19 because pressures in the range of 1000 bar are needed to obtain a single phase, as shown in Figure Figure 1 range from Ϸ1500 bar at Mertdogan and coworkers 11 have shown that nonpolar SF 6 is an excellent solvent for FEP 19 . However, Figure 2 reveals that 5 wt % (2 mol %) SF 6 is not enough to prevent CO 2 -CO 2 quadrupolar interactions from dominating favorable FEP 19 -SF 6 interactions at temperatures below 170°C where the cloud-point curve rises rapidly in pressure. With 26 wt % (10 mol %) SF 6 , the cloudpoint curve does not exhibit a sharp rise in pressure but it does intersect an FEP 19 crystallization boundary at Ϸ150°C.…”

“…The parameters are fit to a minimum of five vapor pressure and liquid density data points [22][23][24] to within 50°C of the critical temperature for each solvent. The calculated critical temperatures for these solvents are Ϸ4% too high; the calculated critical pressures are Ϸ13% too high for CHF 3 and Ϸ22% too high for CO 2 and SF 6 ; the calculated liquid densities are typically 20% too low for all of these solvents. An improved fit of the liquid densities could be obtained but it results in a worse fit of the critical temperature and pressure.…”

“…16 Table II lists the three characteristic, pure component parameters, T*, P*, and *, obtained from a fit of the SL equation to the vapor pressure curves and saturated liquid densities of CO 2 , CHF 3 , and SF 6 . The parameters are fit to a minimum of five vapor pressure and liquid density data points [22][23][24] to within 50°C of the critical temperature for each solvent.…”