(750a) Facilitated Transport Membranes with Tunable Amine-CO2 Chemistry for Highly Selective CO2/H2 Separation

Authors: 
Han, Y., The Ohio State University
Ho, W. S. W., The Ohio State University
CO2-selective, amine-containing facilitated transport membranes are of great interest for syngas purification since high-pressure H2 can be retained upon CO2 removal. A variety of amine-containing polymers have shown decent chemical and thermal stability at aggressive conditions, but their CO2/H2 separation properties are largely limited by the hydrostatic compaction and severe carrier saturation associated with the high syngas pressure. Herein, we report a new approach to enhance the CO2 permeability by manipulating the steric hindrance of the amine carriers. A series of α-aminoacids with different alkyl or hydroxyethyl substituents are deprotonated by 2-(1-piperazinyl)ethylamine, leading to nonvolatile amine carriers with different degrees of steric hindrance. For hosting the low MW amine carriers, a highly crosslinked poly(vinyl acetal) is synthesized as a water-swellable polymer network. In order to avoid membrane compaction, perforated graphene oxide mono-sheets are dispersed as reinforcement fillers. In the presence of moisture, a bulkier alkyl substituent to the amino site (increasing steric hindrance) destabilizes the carbamate adduct and thus drastically increases the chemisorption of CO2, while the incorporation of ethylene oxide groups provides additional physisorption of CO2. The enhanced CO2 solubility significantly mitigates the carrier saturation behavior, and an unprecedented CO2/H2 selectivity greater than 100 is demonstrated at 107 °C and 12.5 atm of CO2 partial pressure. As the CO2 partial pressure reduces to 0.4 atm, a less hindered amine yields a higher reactive diffusivity of CO2, resulting in a CO2 permeance of 435 GPU with a selectivity greater than 500. These reaction-mediated polymeric membranes are well above the theoretical upper bound, and they are of great interest for designing a highly-selective membrane process for syngas purification.