Amorphous Teflons AF as organophilic pervaporation materials: Transport of individual components

Permeation and sorption of various organic liquids (chlorinated hydrocarbons, lower alcohols, hydrocarbons, etc.) in amorphous copolymers of 2,2-bis-trifluoromethyl-4,5-difluoro-1,3-dioxole and tetrafluoroethylene (amorphous Teflons AF) were studied in the temperature range 5–95 °C. Based on permeation rate and solubility coefficients, the diffusion coefficients of organic penetrants in AF copolymers AF were estimated. It was shown that the copolymer with a higher content (87%) of the dioxole component (AF2400), as distinguished by a larger free volume, is much more permeable to liquids than the copolymer AF1600 containing 65% of the dioxole comonomer. In contrast, solubility of organic compounds in both copolymers is hardly affected by their composition. The effects of penetrant parameters, such as critical volume (Vc) and critical temperature (Tc) were analyzed. The variation in permeation rates of liquids and gases through these materials are consistent with a mobility (diffusion) controlled mechanism for mass transfer. A trade-off between the Arrhenius parameters for permeability and the van’t Hoff parameters for solubility is demonstrated for pervaporation. On this basis, novel correlations are obtained that enable a determination of the activation energy for permeation EP and the enthalpy of sorption HS from the permeability (P) and solubility (S) coefficients. Long term tests (up to 12 months) showed excellent time stability of the transport parameters, a property unexpected and quite important for a high flux, high free volume pervaporation material.