(11f) Facilitated Transport Membranes for Hydrogen Purification from Coal-Derived Syngas

Yang Han and W.S. Winston Ho

William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH

In this presentation, three amine-containing facilitated transport membranes were tailored for a single-stage membrane process to decarbonize coal-derived syngas. In these membranes, water-swellable crosslinked polyvinyl alcohol was used as polymer matrix, along with high MW polyvinylamine as fixed-site carrier. For Membrane 1, an amino acid salt of 2-(1-piperazinyl)ethylamine and sarcosine was used as the mobile carrier; sarcosine has a mild degree of steric hindrance. In Membrane 2, the 2-(1-piperazinyl)ethylamine salt of 2-aminoisobutyric acid (PZEA-AIBA) was used as the mobile carrier; AIBA is a sterically hindered amine. Membrane 3 utilized 1-(2-hydroxyethyl)piperazine as the mobile carrier, which contains 2 amino groups and a CO₂-phile hydroxyl group. In addition, poly(ethylene glycol) dimethyl ether was incorporated in Membrane 3 as a CO₂-phile moiety. Nanoporous graphene oxide was dispersed in all three membranes to avoid membrane compaction upon high feed pressure. The membranes were tested at 107 °C and 31.7 bar feed pressure with a CO₂ partial pressure of 12.5 to 0.5 bar, which corresponded to the feed CO₂ partial pressures before and after the bulk CO₂ removal, respectively. The separation performances of Membranes 1 and 2 depended strongly on the CO₂ partial pressure, yielding a CO₂ permeance of 72 – 435 GPU (1 GPU = 10^-6 cm³ (STP)·cm^-2·s^-1·cmHg^-1) with a CO₂/H₂ selectivity of 93 – 558. The CO₂ permeance reduced significantly with increasing CO₂ partial pressure due to the carrier saturation phenomenon. On the other hand, the presence of amino groups and the abundant CO₂-phile moieties in Membrane 3 enhanced the CO₂ solubility at high CO₂ partial pressure, thereby a CO₂ permeance of 206 – 246 GPU and a decent CO₂/H₂ selectivity of 103 – 123 were obtained for a CO₂ partial pressure of 12.5 – 3.5 bar. The different degrees of dependence on the feed CO₂ partial pressure provide a design opportunity for a single-stage membrane process. The more permeable but less selective Membrane 3 can be implemented to the proximity of feed inlet, where the CO₂ partial pressure is high but the H₂ partial pressure is low. Upon CO₂ removal, the feed CO₂ partial pressure sharply reduces whereas the H₂ transmembrane driving force increases. In this case, Membrane 1 or 2 can be used to elevate the CO₂ permeance and CO₂/H₂ selectivity. Initial techno-economic analysis shows that the single-stage membrane process can achieve 90% CO₂ removal with >99% H₂ recovery. A 15.7% increase in cost of electricity is estimated, which is much cost-efficient then Selexol.