(579f) Upscaling of Facilitated Transport Membranes for Hydrogen Purification from Coal-Derived Syngas

CO₂-selective, amine-containing facilitated transport membranes (FTMs) are of great interest for syngas purification since high-pressure H₂ can be retained upon CO₂ removal. Various FTMs have shown decent chemical and thermal stability at aggressive conditions, but their CO₂/H₂ separation properties are largely limited by the severe carrier saturation at high syngas pressure. Herein, we report a new approach to enhance the CO₂ permeance by manipulating the steric hindrance of the amine carrier. A series of α-aminoacids with different alkyl or hydroxyethyl substituents were deprotonated by 2-(1-piperazinyl)ethylamine, resulting in nonvolatile aminoacid salt carriers with different degrees of steric hindrance. In the presence of moisture, a bulkier alkyl substituent increased the steric hindrance and hence destabilized the carbamate adduct to afford bicarbonate through hydrolysis. Thus, this drastically increased the chemisorption of CO₂. The enhanced CO₂ solubility significantly mitigated the carrier saturation, and an unprecedented CO₂/H₂ selectivity greater than 125 was demonstrated at 107°C and 13.8 bar of CO₂ partial pressure (Type I FTM). As the CO₂ partial pressure reduced to 1.1 bar, a less hindered amine yielded a higher reactive diffusivity of CO₂, resulting in a CO₂ permeance of 217 GPU with a selectivity greater than 268 (Type II FTM). These performances are shown in the following two figures for the Types I and II membranes, respectively. These two types of FTMs were successfully scaled up by a roll-to-roll continuous coating machine. The 14-inch wide scale-up membranes were then rolled into two prototype spiral-wound (SW) modules containing 800 and 1600 cm² of the Type I and Type II membranes, respectively. The two SW modules were connected in series, resulting in a hybrid membrane configuration with the Type I membrane treating the syngas near the feed inlet (i.e., high CO₂ partial pressure) and the Type II membrane separating the gas in the proximity of the retentate outlet (i.e., low CO₂ partial pressure). Initial techno-economic analysis indicates that the hybrid membrane configuration can render a H₂ recovery of 99.4% at 90% CO₂ removal.