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 709 degrees C. Membranes prepared by repeating this process two and three times respectively exhibited permeances of approximately 1 x 10(-8) mol . m(-2). s(-1). Pa-1 for C2H4 and 2 x 10(-9) mol . m(-2). s(-1). Pa-1 for C2H6 at 100 degrees C. Permeances to C3H6 and C3H8 at 100 degrees C were 4 x 10(-9) and 1 x 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 degrees 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.