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 C 2 H 4 and 2 × 10 -9 mol·m -2 ·s -1 ·Pa -1 for C 2 H 6 at 100 °C. Permeances to C 3 H 6 and C 3 H 8 at 100 °C were 4 × 10 -9 and 1 × 10 -10 mol·m -2 ·s -1 ·Pa -1, respectively. The selectivities were 4−5 for C 2 H 4 /C 2 H 6 systems and 25−29 for C 3 H 6 /C 3 H 8 systems. When the permeation temperature was decreased to 65 and 35 °C, permeances decreased and selectivities increased to 5−7 for C 2 H 4 /C 2 H 6 systems and 33−56 for C 3 H 6 /C 3 H 8 systems. The permeance and selectivity for an equimolar mixture of C 3 H 6 and C 3 H 8 were nearly the same as those for the single-component gases.