CO₂ Reverse Premeation Behaviors From A Low-pressure Side Toward A High-pressure Side Of Another Gas

A peculiar behavior of gas permeation is discovered by using a variable-volume method to measure CO₂ gas permeation through a cobalt^(â…¡)-neutralized sulfonated ethylene-propene-diene terpolymer ionomer membrane. A short plug of mercury in the capillary at the downstream side is observed to move from outside to inside instead of the usual inside-to-outside direction, i.e. CO₂ permeates spontaneously through the membrane from the downstream side toward the upstream side of N₂ gas or air. The reverse permeation behavior that a gas at the downstream side permeates spontaneously through an especial membrane toward the upstream side is a novel behavior and has not been reported so far.Permeability and selectivity of CO₂, N₂, and CH₄ gases through the ionomer membrane containing Co^(â…¡)are further investigated. The ionomer membrane under the conditions of 20℃ and 0.05 MPa shows better permeaselectivities that the permeability coefficient of CO₂ and CO₂/ N₂ separation factor are 223 Barrer and 65.70, respectively, while CO₂ / CH₄ separation factor is only 14.70. An obvious increase in P_CO2 with decreasing pressure difference exhibits a characteristic of facilitated CO₂ transport, which is not disappear and almost unchange after two months. There is no this behavior for N₂ and CH₄. Hence, P_CO2 and α_CO2/N2 and α_CO2/CH4 can be enhanced simultaneously. The data of the permeation active energies under various pressure differences counted by Arrhenius curves indicate that the lower pressure difference is, the smaller is active energy, the more benefit is it to CO₂ permeation.Some correlative factors which have effect on reverse permeation behavior of CO₂ has been studied further. The reverse permeability coefficients of CO2 is affected by pressure difference and decreases evidently with the increase of the absolute value of pressure difference. The reverse permeation behavior of CO2 can still occur even when the partial pressure of CO₂ is smaller than the atmosphere pressure. The critical volumepercentages of the mixture gases of CO2 / N2 and CO2 / O2 to bring about such reverse permeation behavior are determined and are 40:60 and 50:50, respectively. A blend method that S-EPDM and Co(II)-S-EPDM are chosen as blend matrix materials can be used to regulate cccohni value of the membrane by changing polymeric component ratio and to determine the critical acoiiNi value. Under the conditions of 20°C and 0.40 MPa, the critical cccoiini value to exhibit reverse permeation behavior is confirmed to be 12.38. The reasons for such behavior to occur are discussed. Ionomer membrane containing cobaltous ions, exhibiting CO2 facilitated transport and higher acoi/M value are not ample conditions, but are important factors. The key reasons for the occurring of reverse permeation behavior should be attributed to the polymeric chemical structure and the morphology structure of the membranes as well as other possible unknown factors.