(628e) Crosslinked Polyvinylalcohol/Multi-Walled Carbon Nanotube Mixed Matrix Membranes for CO2/H2 Separation

Hydrogen purification with high efficiency is the key challenge to fuel cell technology.  Carbon dioxide-selective membranes, which can be used in membrane reactor configuration to enhance water gas shift reaction or in the membrane permeation process to purify H₂, provide a new approach to solve this problem.  This presentation covers new crosslinked polyvinylalcohol (PVA)/multi-walled carbon nanotube (MWNT) mixed matrix membranes with significantly enhanced CO₂/H₂ separation and stability for hydrogen purification based on the facilitated transport mechanism.  The membranes were synthesized by the solution casting technique using glutaraldehyde-crosslinked PVA solution containing amines as CO₂ carriers and well-dispersed untreated or acid-treated MWNTs as mechanical reinforcement fillers.  Membranes containing untreated MWNTs of 1 – 8% by weight were prepared and tested at 107°C and different feed pressures using a gas mixture of 20% CO₂, 40% H₂, and 40% N₂.  At the feed pressure of 2 atm, the membrane with 2% untreated MWNTs showed a high CO₂ permeability of 6127 Barrers (1 Barrer = 10^–10 cm³ (STP) • cm/(cm² • s • cm Hg)) along with a high CO₂/H₂ selectivity of 207 and an even higher CO₂/N₂ selectivity of 1743.  Moreover, the membrane stability was dramatically enhanced due to the increased resistance to membrane compaction by MWNTs.  At the feed pressure of 15 atm, the membrane transport properties, i.e., CO₂ permeability, CO₂/H₂ selectivity, and CO₂/N₂ selectivity were stabilized at 1054 Barrers, 43, and 408, respectively, for 20 days.   The MWNTs were functionalized with carboxylic acid groups and hydroxyl groups by strong acid oxidation.  The incorporation of these hydrophilic groups on the MWNT was confirmed by FTIR spectroscopy.  The membrane with a 4% loading of acid-treated MWNTs also showed good stability at the feed pressure of 15 atm.  The MWNT-containing mixed matrix membranes developed in this work demonstrated significant improvement on membrane stability accompanied by high permeability and selectivity for CO₂/H₂ separation.  Therefore, it is not only of a great scientific interest but may also be an important technological advance towards the commercialization of membrane technology for hydrogen fuel processing for fuel cells.