CO₂/N₂ separation by poly(ether block amide) thin film hollow fiber composite membranes

Thin film poly(ether block amide) (PEBA) hollow fiber composite membranes were developed for CO₂/N₂ separation, which is relevant to CO₂ capture from flue gas for greenhouse gas emission control. The membrane was prepared by coating a thin layer of PEBA onto microporous polyetherimide (PEI) hollow fiber substrate membranes. Lab-scale hollow fiber membrane modules were assembled and tested for CO₂/N₂ separation with various flow configurations using a simulated flue gas (15.3% carbon dioxide, balance N₂) as the feed. The shell side feed with counter-current flow was shown to perform better than other configurations over a wide range of stage cuts in terms of product purity, recovery, and productivity. At 23°C and 790 kPa, a permeate stream containing 62 mol % CO₂ was obtained at a CO₂ recovery of 20% in a single-stage operation, whereas 99.4 mol % nitrogen could be produced in the residue with a nitrogen recovery of 36%. It was found that the permeance of CO₂ in the gas mixture was lower than the permeance of pure CO ₂ at the same pressure, while there was little difference in nitrogen permeance between pure gas permeation and gas mixture permeation. The PEBA/PEI thin film hollow fiber composite membrane was not suitable for bore side feed operation because of the potential problems associated with concentration polarization in the microporous substrate and the structural integrity of the membrane when a high pressure was applied in the fiber lumen.