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 × 10-9 and 1 × 10-10 mol·m-2·s-1·Pa-1, 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.