New Amine-Containing Membranes for Hydrogen Purification and CO2 Capture from Coal-Derived Syngas

Amine-containing facilitated transport membranes (FTMs) are of great interest for syngas purification. Herein, a series of α-aminoacids with different alkyl substituents were deprotonated by 2-(1-piperazinyl)ethylamine, resulting in nonvolatile aminoacid salt carriers with different degrees of steric hindrance. The membrane containing the severely hindered carrier (FTM1) showed the highest chemisorption of CO₂, thus a CO₂ permeance of 217 GPU with a CO₂/H₂ selectivity greater than 268 at 1.1 bar CO₂ partial pressure and 107°C. At 13.8 bar of CO₂ partial pressure, however, using alkanolamines as carriers proved to enhance the physisorption of CO₂, and the membrane (FTM2) exhibited less pronounced carrier saturation and gave a high selectivity greater than 125. These two types of FTMs were scaled up by a roll-to-roll continuous coating machine. The 14″ wide scale-up membranes were then rolled into two spiral-wound modules containing 800 and 1600 cm² of the FTM2 and FTM1 membranes, respectively. At 90% CO₂ capture from simulated coal-derived syngas, the FTM2 and FTM1 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 FTM2 membrane treating the syngas near the feed inlet and the FTM1 membrane separating the gas in the proximity of the retentate outlet, the H₂ recovery was improved to 99.3% with 200-h stable operation. Techno-economic analysis shows a hydrogen purification cost of $1.2/kg of H₂ and a carbon capture cost of about $42/tonne of CO₂ vs. $63/tonne for the state-of-the-art technology, Selexol.