Abstract
The permeation properties of Nafion® at 35°C are presented for pure gases H2, N2, O2, CH4, CO2, C2H6 and C3H8, as a function of pressure between 2 and 20atm. The effect of pressure on permeability and selectivity is analyzed to understand two observed phenomena: compression and plasticization. In pure-gas experiments, at increasing feed pressure, compression of the polymer matrix reduced the permeability of low-sorbing penetrants H2, N2, O2, and CH4. In contrast, permeabilities of more soluble penetrants CO2 and C2H6 increased by 18% and 46% respectively, as plasticization effects overcame compression effects. Permeability of C3H8 decreased slightly with increasing pressure up to 4.6atm as a result of compression, then increased by 3-fold at 9atm as a result of plasticization associated with high C3H8 solubility. Binary CO2/CH4 (50:50) mixed-gas experiments at total feed pressures up to 36atm quantified the effect of CO2 plasticization on separation performance. At 10atm CO2 partial pressure, CH4 permeability increased by 23% relative to its pure-gas value of 0.078 Barrer, while CO2 permeability decreased by 28%. Consequently, CO2/CH4 selectivity decreased to 19, i.e., 42% below its pure-gas value of 32.
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•Gas transport in Nafion® revealed two divergent phenomena: compression and plasticization.•Low sorbing gases show decrease in permeability due to chain compaction by compression.•High sorbing gases show increase in permeability due to solubility-induced chain plasticization effect.•Binary mixed-gas CO2/CH4 experiments showed decrease in selectivity induced by CO2 plasticization.