(278a) Integrated Facilitated Transport Membrane Modules for Highly Selective Syngas Purification and Carbon Capture

Amine-containing facilitated transport membranes (FTMs) are of great interest for syngas purification. Herein, we report a new method 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. 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). 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). These two types of FTMs were successfully scaled up by a roll-to-roll continuous coating machine. The 14″ wide scale-up membranes were then rolled into two prototype spiral-wound modules containing 800 and 1600 cm² of the Type I and Type II membranes, respectively. At 90% CO₂ capture, the Type I and Type II modules achieved a CO₂ purity of ca. 95%, but the H₂ recoveries were only 98.2% and 97.1%, respectively. However, when the two modules were connected in series 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), the H₂ recovery was improved to 99.3%. The integrated membrane array also demonstrated 200-h stability under simulated syngas.