Concentration and temperature dependence on diffusivities of CO 2 and N 2 for poly(dimethyl, methylphenyl siloxane)

Experimental determination of solubility and diffusion coefficients of CO 2 and N 2 in poly(dimethyl, methylphenyl siloxane) (PMPS) for the pressure range 0–150 kPa and the temperature range of −10°C to 45°C is discussed. The absorption isotherms were measured by pressure decay equilibrium. Diffusion coefficients were determined by modeling the transient absorption data by Fickian diffusion. The value of solubility coefficient for CO 2 at 35°C was 1.21 ± 0.02 cm 3 CO 2 (STP)/(cm 3 polymer.atm) and it increased to 2.07 ± 0.01 cm 3 CO 2 (STP)/(cm 3 polymer.atm) at 1°C. The absorption isotherms of CO 2 obtained were linear for the pressure range 0–200 kPa and the enthalpy of sorption value was −10.82 kJ/mole for CO 2 . However, the diffusion coefficients of CO 2 changed with feed pressure. The diffusion coefficient of CO 2 in PMPS at 22°C and 128.6 kPa equilibrium pressure was 7.22 × 10 −6 cm 2 /s and thus the permeability value at these conditions was 1392 Barrers. The diffusion coefficients of CO 2 at 0°C and equilibrium pressures of 125.8 kPa and 10.5 kPa were 5.72 × 10 −6 cm 2 /s and 4.31 × 10 −6 cm 2 /s, respectively. Consequently, the CO 2 permeability in PMPS decreases by about 20% when the pressure is reduced from 125.8 to 10.5 kPa at 0°C. © 2007 American Institute of Chemical Engineers AIChE J, 2008