Cosolvency Effect of SF_6 on the Solubility of Ply(tetrafluoroethylene-co-19 mol % hexafluoropropylene) in Supercritical CO_2 and CHF_3

摘要

Cloud-point data to 280 deg C and 2800 bar are reported for a binary mixture of poly(tetrafluoroethylene-co-19.3 mol % hexafluoropropylene) (FEP_(19)) in fluoroform (CHF_3) and for ternary mixtures of FEP_(19)-CHF_3-sulfur hexafluoride (SF_6) and FEP_ (19)-CO_2-SF_6.FEP_(19) does not dissolve in CHF_3 at a temperatures less than 235 deg C due to strong dipolar CF_3-CHF_3 interactions relative to FEP_(19)-CHF_3 cross interactions.However,FEP_ (19) dissolves in CO_2 if the temperature is greater than approx= 185 deg C and the pressure is in excess of 1000 bar.When SF_6 is added to either FEP_(19)-CO_2 or EFP_(19)-CHF_3 mixtures,the cloud-point curve is shifted to lower pressures and temperatures due to the increase in favorable dispersion interactions with nonpolar FEP_(19).The magnitude of the shift in cloud-point pressure per amount of SF_6 added to solution decreases in a nonlinear manner wiht increasing amounts of SF_6 .The Sanchez-Lacombe equation of state cna model the binary FEP_(19)-SCF data if the FEP_(19)-CO_2 and FEP_(19)-CHF_3 binary interaction parameters are allowed to vary with temperature.However,a poor representation is obtained for the ternary phase behavior.