Separation of ethane/ethylene and propane/propylene systems with a carbonized BPDA-pp'ODA polyimide membrane

A BPDA-pp'ODA polyimide film was formed on the outer surface of a porous alumina support tube (outside diameter, 2.4 mm; inside diameter, 1.8 mm; void fraction, 0.48; and average pore size, 140 nm) and was then carbonized at an optimized temperature of 700 ̊C. Membranes prepared by repeating this process two and three times respectively exhibited permeances of approximately 1 × 10^-8 mol·m^-2·s^-1·Pa^-1 for C₂H₄ and 2 × 10^-9 mol·m^-2·s^-1·Pa^-1 for C₂H₆ at 100 °C. Permeances to C₃H₆ and C₃H₈ at 100 °C were 4 × 4 × 10^-9 and 1 × 10^-10 mol·m^-2·s^-1·Pa1, respectively. The selectivities were 4-5 for C₂H₄/C₂H₆ systems and 25-29 for C₃H₆/C₃H₈ systems. When the permeation temperature was decreased to 65 and 35 °C, permeances decreased and selectivities increased to 5-7 for C₂H₄/C₂H₆ systems and 33-56 for C₃H₆/C₃H₈ systems. The permeance and selectivity for an equimolar mixture of C₃H₆ and C₃H₈ were nearly the same as those for the single-component gases.