(277f) CO2-Selective Facilitated Transport Membranes Containing Sterically Hindered Amines for Hydrogen Purification for Fuel Cells

This presentation covers CO₂-selective facilitated transport membranes containing sterically hindered secondary amines, poly-N-isopropylallylamine, poly-N-isobutylallylamine, and poly-N-tertbutylallylamine. We have synthesized these amines from the unhindered primary amine, polyallylamine, and incorporated them as the improved fixed carriers into polymeric networks for the separation of CO₂ from hydrogen and nitrogen via the facilitated transport mechanism. FTIR spectra revealed that the primary amino groups of polyallylamine were successfully converted into the secondary amino groups through the modification reactions. In side-by-side comparisons, the CO₂ permeability obtained from membranes containing 70 wt.% of sterically hindered amines in polymeric networks was at least three times of that from membranes containing the same amount of polyallylamine. This showed that CO₂ transport capability of the fixed carrier was enhanced significantly by steric hindrance. The sterically hindered amine-containing membranes in crosslinked polyvinylalcohol networks exhibited a high CO₂ permeability of greater than 6500 Barrers (1 Barrer = 10^?10 cm³(STP) ? cm/cm² ? s ? cm Hg) and a high CO₂/H₂ selectivity of more than 250 as well as a CO₂/N₂ selectivity of higher than 2000 at 110°C and a feed pressure of 2 atm. Even higher CO₂ permeability and selectivities versus H₂ and N₂ were reached as water contents in the feed and sweep sides increased. The membrane with sterically hindered amines also showed relatively good stability for 428 hours at 110°C and the feed pressure of 2 atm. These improved membranes are applicable to high-efficiency CO₂ separation in the hydrogen fuel processing for fuel cells.