Olefin/Paraffin Separation through Carbonized Membranes Derived from an Asymmetric Polyimide Hollow Fiber Membrane

Carbonized hollow fiber membranes were prepared by pyrolyzing an asymmetric hollow fiber membrane of a polyimide from 3,3‘,4,4‘-biphenyltetracarboxylic dianhydride and aromatic diamines at temperatures of 500−700 °C under a nitrogen stream. The precursor membrane was treated in air at 400 °C for 0.5 h before the pyrolysis. This pretreatment was effective for improvement of gas permeance of the carbonized membranes. The carbonized membranes had an asymmetric structure with a skin layer of around 200 nm in thickness. They had the characteristics of larger permeance and lower permselectivity for inorganic gas pairs such as O 2 /N 2, but this was rather preferable to the separation of olefin/paraffin. The membranes pyrolyzed at 600−630 °C displayed good stability and excellent performances of propylene/propane and 1,3-butadiene/ n -butane separation based on the molecular sieving.