Ethylbenzene solubility, diffusivity, and permeability in poly(dimethylsiloxane)

The pure-gas sorption, diffusion, and permeation properties of ethylbenzene in poly(dimethylsiloxane) (PDMS) are reported at 35, 45, and 55 °C and at pressures ranging from 0 to 4.4 cmHg. Additionally, mixed-gas ethylbenzene/N₂ permeability properties at 35 °C, a total feed pressure of 10 atm, and a permeate pressure of 1 atm are reported. Ethylbenzene solubility increases with increasing penetrant relative pressure and can be described by the Flory-Rehner model with an interaction parameter of 0.24±0.02. At a fixed relative pressure, ethylbenzene solubility decreases with increasing temperature, and the enthalpy of sorption is -41.4±0.3 kJ/mol, which is independent of ethylbenzene concentration and essentially equal to the enthalpy of condensation of pure ethylbenzene. Ethylbenzene diffusion coefficients decrease with increasing concentration at 35 °C. The activation energy of ethylbenzene diffusion in PDMS at infinite dilution is 49±6 kJ/mol. The ethylbenzene activation energies of permeation decrease from near 0 to -34±7 kJ/mol as concentration increases, whereas the activation energy of permeation for pure N₂ is 8±2 kJ/mol. At 35 °C, ethylbenzene and N₂ permeability coefficients determined from pure-gas permeation experiments are similar to those obtained from mixed-gas permeation experiments, and ethylbenzene/N₂ selectivity values as high as 800 were observed.